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Kalanit Grill-Spector is an Associate Professor in Psychology and the Stanford Neurosciences Institute. Her research examines how the brain processes visual information and perceives it. She uses functional imaging techniques to visualize the living brain in action and understand how it functions to recognize people, objects and places. Additionally, she investigates how the anatomical and functional properties of the brain change from childhood through adolescences to adulthood, and how this development is related to improved recognition abilities. She received her PhD from the Weizmann Institute of Science in Israel and was a postdoctoral fellow in Brain and Cognitive Sciences at MIT before joining Stanford University. She has received several awards and honors including the Human Sciences Frontier Fellowship, the Sloan Fellowship and the Klingenstein Fellowship in Neuroscience. She has served as an Editor for the Journal of Vision and Neuropsychologia, is a board member of the Center for Cognitive and Neurobiological Imaging at Stanford University, is on the Scientific Advisory Board for the Organization for Human Brain Mapping, and has an active and diverse laboratory in the Psychology department at Stanford University.
Academic Appointments
Professor, Psychology
Member, Bio-X
Member, Stanford Neurosciences Institute
Boards, Advisory Committees, Professional Organizations
Editor, Neuropsychologia (2016 - Present)
Editor, Journal of Vision (2008 - 2012)
Editorial Board, NeuroImage (2005 - 2008)
Additional Info
Current Research and Scholarly Interests
For humans, recognition is a natural, effortless skill that occurs within a few hundreds of milliseconds, yet it is one of the least understood aspects of visual perception. Our research utilizes functional imaging (fMRI),diffusion weighted imaging (DWI), computational techniques, and behavioral methods to investigate the neural mechanisms underlying visual recognition in humans. We also examine the development of these mechanisms from childhood to adulthood as well as between populations.
2017-18 Courses
- Computational Neuroimaging: Methods & Analyses
PSYCH 204B (Spr)
- Cortical Plasticity: Perception and Memory
PSYCH 206 (Win)
- Introduction to Perception
PSYCH 30 (Aut)
Independent Studies (7)
- Directed Reading in Neurosciences
NEPR 299 (Aut, Win, Spr, Sum)
- Graduate Research
NEPR 399 (Aut, Win, Spr, Sum)
- Graduate Research
PSYCH 275 (Aut, Win, Spr, Sum)
- Practicum in Teaching
PSYCH 281 (Aut, Win, Spr)
- Reading and Special Work
PSYCH 194 (Aut, Win, Spr, Sum)
- Senior Honors Tutorial
SYMSYS 190 (Win, Spr)
- Special Laboratory Projects
PSYCH 195 (Aut, Win, Spr, Sum)
- Directed Reading in Neurosciences
Prior Year Courses
2016-17 Courses
- High-level Vision: From Neurons to Deep Neural Networks
PSYCH 250 (Spr)
- High-level Vision: From Neurons to Deep Neural Networks
PSYCH 250A (Spr)
- Human Neuroimaging Methods
PSYCH 204B (Spr)
- Introduction to Perception
PSYCH 30 (Aut)
2015-16 Courses
- Computational Neuroimaging: Analysis Methods
PSYCH 204B (Spr)
- Cortical Plasticity: Perception and Memory
PSYCH 206 (Win)
- Introduction to Perception
PSYCH 30 (Aut)
2014-15 Courses
- Computational Neuroimaging: Analysis Methods
PSYCH 204B (Win)
- From Classic Experiments to Cutting Edge Neuroimaging: The Functional Neuroanatomy of Visual Cortex
PSYCH 222 (Spr)
- Introduction to Perception
PSYCH 30 (Aut)
- High-level Vision: From Neurons to Deep Neural Networks
Stanford Advisees
Doctoral Dissertation Reader (AC)
Rosemary Le
Postdoctoral Faculty Sponsor
Mareike Grotheer
Doctoral Dissertation Advisor (AC)
Lior Bugatus, Jesse Gomez, Anthony Stigliani
Doctoral (Program)
Lior Bugatus, Rebecca Finzi, Mona Rosenke, Anthony Stigliani
Graduate and Fellowship Programs
All Publications
Development of Neural Sensitivity to Face Identity Correlates with Perceptual Discriminability.
journal of neuroscience
2016; 36 (42): 10893-10907
Face perception is subserved by a series of face-selective regions in the human ventral stream, which undergo prolonged development from childhood to adulthood. However, it is unknown how neural development of these regions relates to the development of face-perception abilities. Here, we used functional magnetic resonance imaging (fMRI) to measure brain responses of ventral occipitotemporal regions in children (ages, 5-12 years) and adults (ages, 19-34 years) when they viewed faces that parametrically varied in dissimilarity. Since similar faces generate lower responses than dissimilar faces due to fMRI adaptation, this design objectively evaluates neural sensitivity to face identity across development. Additionally, a subset of subjects participated in a behavioral experiment to assess perceptual discriminability of face identity. Our data reveal three main findings: (1) neural sensitivity to face identity increases with age in face-selective but not object-selective regions; (2) the amplitude of responses to faces increases with age in both face-selective and object-selective regions; and (3) perceptual discriminability of face identity is correlated with the neural sensitivity to face identity of face-selective regions. In contrast, perceptual discriminability is not correlated with the amplitude of response in face-selective regions or of responses of object-selective regions. These data suggest that developmental increases in neural sensitivity to face identity in face-selective regions improve perceptual discriminability of faces. Our findings significantly advance the understanding of the neural mechanisms of development of face perception and open new avenues for using fMRI adaptation to study the neural development of high-level visual and cognitive functions more broadly.Face perception, which is critical for daily social interactions, develops from childhood to adulthood. However, it is unknown what developmental changes in the brain lead to improved performance. Using fMRI in children and adults, we find that from childhood to adulthood, neural sensitivity to changes in face identity increases in face-selective regions. Critically, subjects' perceptual discriminability among faces is linked to neural sensitivity: participants with higher neural sensitivity in face-selective regions demonstrate higher perceptual discriminability. Thus, our results suggest that developmental increases in face-selective regions' sensitivity to face identity improve perceptual discrimination of faces. These findings significantly advance understanding of the neural mechanisms underlying the development of face perception and have important implications for assessing both typical and atypical development.
View details for PubMedID 27798143
View details for PubMedCentralID PMC5083016
The Face-Processing Network Is Resilient to Focal Resection of Human Visual Cortex.
journal of neuroscience
2016; 36 (32): 8425-8440
Human face perception requires a network of brain regions distributed throughout the occipital and temporal lobes with a right hemisphere advantage. Present theories consider this network as either a processing hierarchy beginning with the inferior occipital gyrus (occipital face area; IOG-faces/OFA) or a multiple-route network with nonhierarchical components. The former predicts that removing IOG-faces/OFA will detrimentally affect downstream stages, whereas the latter does not. We tested this prediction in a human patient (Patient S.P.) requiring removal of the right inferior occipital cortex, including IOG-faces/OFA. We acquired multiple fMRI measurements in Patient S.P. before and after a preplanned surgery and multiple measurements in typical controls, enabling both within-subject/across-session comparisons (Patient S.P. before resection vs Patient S.P. after resection) and between-subject/across-session comparisons (Patient S.P. vs controls). We found that the spatial topology and selectivity of downstream ipsilateral face-selective regions were stable 1 and 8 month(s) after surgery. Additionally, the reliability of distributed patterns of face selectivity in Patient S.P. before versus after resection was not different from across-session reliability in controls. Nevertheless, postoperatively, representations of visual space were typical in dorsal face-selective regions but atypical in ventral face-selective regions and V1 of the resected hemisphere. Diffusion weighted imaging in Patient S.P. and controls identifies white matter tracts connecting retinotopic areas to downstream face-selective regions, which may contribute to the stable and plastic features of the face network in Patient S.P. after surgery. Together, our results support a multiple-route network of face processing with nonhierarchical components and shed light on stable and plastic features of high-level visual cortex following focal brain damage.Brain networks consist of interconnected functional regions commonly organized in processing hierarchies. Prevailing theories predict that damage to the input of the hierarchy will detrimentally affect later stages. We tested this prediction with multiple brain measurements in a rare human patient requiring surgical removal of the putative input to a network processing faces. Surprisingly, the spatial topology and selectivity of downstream face-selective regions are stable after surgery. Nevertheless, representations of visual space were typical in dorsal face-selective regions but atypical in ventral face-selective regions and V1. White matter connections from outside the face network may support these stable and plastic features. As processing hierarchies are ubiquitous in biological and nonbiological systems, our results have pervasive implications for understanding the construction of resilient networks.
View details for DOI 10.1523/JNEUROSCI.4509-15.2016
View details for PubMedID 27511014
View details for PubMedCentralID PMC4978802
Learning the 3-D structure of objects from 2-D views depends on shape, not format
2016; 16 (7)
Humans can learn to recognize new objects just from observing example views. However, it is unknown what structural information enables this learning. To address this question, we manipulated the amount of structural information given to subjects during unsupervised learning by varying the format of the trained views. We then tested how format affected participants' ability to discriminate similar objects across views that were rotated 90° apart. We found that, after training, participants' performance increased and generalized to new views in the same format. Surprisingly, the improvement was similar across line drawings, shape from shading, and shape from shading + stereo even though the latter two formats provide richer depth information compared to line drawings. In contrast, participants' improvement was significantly lower when training used silhouettes, suggesting that silhouettes do not have enough information to generate a robust 3-D structure. To test whether the learned object representations were format-specific or format-invariant, we examined if learning novel objects from example views transfers across formats. We found that learning objects from example line drawings transferred to shape from shading and vice versa. These results have important implications for theories of object recognition because they suggest that (a) learning the 3-D structure of objects does not require rich structural cues during training as long as shape information of internal and external features is provided and (b) learning generates shape-based object representations independent of the training format.
View details for DOI 10.1167/16.7.7
View details for Web of Science ID 000377938400007
View details for PubMedID 27153196
Corresponding ECoG and fMRI category-selective signals in human ventral temporal cortex.
2016; 83: 14-28
Functional magnetic resonance imaging (fMRI) and electrocorticography (ECoG) research have been influential in revealing the functional characteristics of category-selective responses in human ventral temporal cortex (VTC). One important, but unanswered, question is how these two types of measurements might be related with respect to the VTC. Here we examined which components of the ECoG signal correspond to the fMRI response, by using a rare opportunity to measure both fMRI and ECoG responses from the same individuals to images of exemplars of various categories including faces, limbs, cars and houses. Our data reveal three key findings. First, we discovered that the coupling between fMRI and ECoG responses is frequency and time dependent. The strongest and most sustained correlation is observed between fMRI and high frequency broadband (HFB) ECoG responses (30-160hz). In contrast, the correlation between fMRI and ECoG signals in lower frequency bands is temporally transient, where the correlation is initially positive, but then tapers off or becomes negative. Second, we find that the strong and positive correlation between fMRI and ECoG signals in all frequency bands emerges rapidly around 100ms after stimulus onset, together with the onset of the first stimulus-driven neural signals in VTC. Third, we find that the spatial topology and representational structure of category-selectivity in VTC reflected in ECoG HFB responses mirrors the topology and structure observed with fMRI. These findings of a strong and rapid coupling between fMRI and HFB responses validate fMRI measurements of functional selectivity with recordings of direct neural activity and suggest that fMRI category-selective signals in VTC are associated with feed-forward neural processing.
View details for DOI 10.1016/j.neuropsychologia.2015.07.024
View details for PubMedID 26212070
Two New Cytoarchitectonic Areas on the Human Mid-Fusiform Gyrus.
Cerebral cortex
Areas of the fusiform gyrus (FG) within human ventral temporal cortex (VTC) process high-level visual information associated with faces, limbs, words, and places. Since classical cytoarchitectonic maps do not adequately reflect the functional and structural heterogeneity of the VTC, we studied the cytoarchitectonic segregation in a region, which is rostral to the recently identified cytoarchitectonic areas FG1 and FG2. Using an observer-independent and statistically testable parcellation method, we identify 2 new areas, FG3 and FG4, in 10 human postmortem brains on the mid-FG. The mid-fusiform sulcus reliably identifies the cytoarchitectonic transition between FG3 and FG4. We registered these cytoarchitectonic areas to the common reference space of the single-subject Montreal Neurological Institute (MNI) template and generated probability maps, which reflect the intersubject variability of both areas. Future studies can relate in vivo neuroimaging data with these microscopically defined cortical areas to functional parcellations. We discuss these results in the context of both large-scale functional maps and fine-scale functional clusters that have been identified within the human VTC. We propose that our observer-independent cytoarchitectonic parcellation of the FG better explains the functional heterogeneity of the FG compared with the homogeneity of classic cytoarchitectonic maps.
View details for PubMedID 26464475
Temporal Processing Capacity in High-Level Visual Cortex Is Domain Specific.
journal of neuroscience
2015; 35 (36): 12412-12424
Prevailing hierarchical models propose that temporal processing capacity-the amount of information that a brain region processes in a unit time-decreases at higher stages in the ventral stream regardless of domain. However, it is unknown if temporal processing capacities are domain general or domain specific in human high-level visual cortex. Using a novel fMRI paradigm, we measured temporal capacities of functional regions in high-level visual cortex. Contrary to hierarchical models, our data reveal domain-specific processing capacities as follows: (1) regions processing information from different domains have differential temporal capacities within each stage of the visual hierarchy and (2) domain-specific regions display the same temporal capacity regardless of their position in the processing hierarchy. In general, character-selective regions have the lowest capacity, face- and place-selective regions have an intermediate capacity, and body-selective regions have the highest capacity. Notably, domain-specific temporal processing capacities are not apparent in V1 and have perceptual implications. Behavioral testing revealed that the encoding capacity of body images is higher than that of characters, faces, and places, and there is a correspondence between peak encoding rates and cortical capacities for characters and bodies. The present evidence supports a model in which the natural statistics of temporal information in the visual world may affect domain-specific temporal processing and encoding capacities. These findings suggest that the functional organization of high-level visual cortex may be constrained by temporal characteristics of stimuli in the natural world, and this temporal capacity is a characteristic of domain-specific networks in high-level visual cortex.Visual stimuli bombard us at different rates every day. For example, words and scenes are typically stationary and vary at slow rates. In contrast, bodies are dynamic and typically change at faster rates. Using a novel fMRI paradigm, we measured temporal processing capacities of functional regions in human high-level visual cortex. Contrary to prevailing theories, we find that different regions have different processing capacities, which have behavioral implications. In general, character-selective regions have the lowest capacity, face- and place-selective regions have an intermediate capacity, and body-selective regions have the highest capacity. These results suggest that temporal processing capacity is a characteristic of domain-specific networks in high-level visual cortex and contributes to the segregation of cortical regions.
View details for DOI 10.1523/JNEUROSCI.4822-14.2015
View details for PubMedID 26354910
The evolution of face processing networks.
Trends in cognitive sciences
2015; 19 (5): 240-241
Recent studies in marmosets, macaques, and humans have begun to show commonalities and differences in the evolution of face processing networks. Despite differences in brain size and gyrification across species, myelination and motion may be key anatomical and functional features contributing to the surprising similarity of face networks across species.
View details for DOI 10.1016/j.tics.2015.03.010
View details for PubMedID 25840651
Attention reduces spatial uncertainty in human ventral temporal cortex.
Current biology
2015; 25 (5): 595-600
Ventral temporal cortex (VTC) is the latest stage of the ventral "what" visual pathway, which is thought to code the identity of a stimulus regardless of its position or size [1, 2]. Surprisingly, recent studies show that position information can be decoded from VTC [3-5]. However, the computational mechanisms by which spatial information is encoded in VTC are unknown. Furthermore, how attention influences spatial representations in human VTC is also unknown because the effect of attention on spatial representations has only been examined in the dorsal "where" visual pathway [6-10]. Here, we fill these significant gaps in knowledge using an approach that combines functional magnetic resonance imaging and sophisticated computational methods. We first develop a population receptive field (pRF) model [11, 12] of spatial responses in human VTC. Consisting of spatial summation followed by a compressive nonlinearity, this model accurately predicts responses of individual voxels to stimuli at any position and size, explains how spatial information is encoded, and reveals a functional hierarchy in VTC. We then manipulate attention and use our model to decipher the effects of attention. We find that attention to the stimulus systematically and selectively modulates responses in VTC, but not early visual areas. Locally, attention increases eccentricity, size, and gain of individual pRFs, thereby increasing position tolerance. However, globally, these effects reduce uncertainty regarding stimulus location and actually increase position sensitivity of distributed responses across VTC. These results demonstrate that attention actively shapes and enhances spatial representations in the ventral visual pathway.
View details for DOI 10.1016/j.cub.2014.12.050
View details for PubMedID 25702580
Feature saliency and feedback information interactively impact visual category learning
2015; 6
Visual category learning (VCL) involves detecting which features are most relevant for categorization. VCL relies on attentional learning, which enables effectively redirecting attention to object's features most relevant for categorization, while 'filtering out' irrelevant features. When features relevant for categorization are not salient, VCL relies also on perceptual learning, which enables becoming more sensitive to subtle yet important differences between objects. Little is known about how attentional learning and perceptual learning interact when VCL relies on both processes at the same time. Here we tested this interaction. Participants performed VCL tasks in which they learned to categorize novel stimuli by detecting the feature dimension relevant for categorization. Tasks varied both in feature saliency (low-saliency tasks that required perceptual learning vs. high-saliency tasks), and in feedback information (tasks with mid-information, moderately ambiguous feedback that increased attentional load, vs. tasks with high-information non-ambiguous feedback). We found that mid-information and high-information feedback were similarly effective for VCL in high-saliency tasks. This suggests that an increased attentional load, associated with the processing of moderately ambiguous feedback, has little effect on VCL when features are salient. In low-saliency tasks, VCL relied on slower perceptual learning; but when the feedback was highly informative participants were able to ultimately attain the same performance as during the high-saliency VCL tasks. However, VCL was significantly compromised in the low-saliency mid-information feedback task. We suggest that such low-saliency mid-information learning scenarios are characterized by a 'cognitive loop paradox' where two interdependent learning processes have to take place simultaneously.
View details for DOI 10.3389/fpsyg.2015.00074
View details for Web of Science ID 000349595900001
View details for PubMedID 25745404
Functionally defined white matter reveals segregated pathways in human ventral temporal cortex associated with category-specific processing.
2015; 85 (1): 216-227
It is unknown if the white-matter properties associated with specific visual networks selectively affect category-specific processing. In a novel protocol we combined measurements of white-matter structure, functional selectivity, and behavior in the same subjects. We find two parallel white-matter pathways along the ventral temporal lobe connecting to either face-selective or place-selective regions. Diffusion properties of portions of these tracts adjacent to face- and place-selective regions of ventral temporal cortex correlate with behavioral performance for face or place processing, respectively. Strikingly, adults with developmental prosopagnosia (face blindness) express an atypical structure-behavior relationship near face-selective cortex, suggesting that white-matter atypicalities in this region may have behavioral consequences. These data suggest that examining the interplay between cortical function, anatomical connectivity, and visual behavior is integral to understanding functional networks and their role in producing visual abilities and deficits.
View details for DOI 10.1016/j.neuron.2014.12.027
View details for PubMedID 25569351
View details for PubMedCentralID PMC4287959
Spatiotemporal information during unsupervised learning enhances viewpoint invariant object recognition
2015; 15 (6)
Recognizing objects is difficult because it requires both linking views of an object that can be different and distinguishing objects with similar appearance. Interestingly, people can learn to recognize objects across views in an unsupervised way, without feedback, just from the natural viewing statistics. However, there is intense debate regarding what information during unsupervised learning is used to link among object views. Specifically, researchers argue whether temporal proximity, motion, or spatiotemporal continuity among object views during unsupervised learning is beneficial. Here, we untangled the role of each of these factors in unsupervised learning of novel three-dimensional (3-D) objects. We found that after unsupervised training with 24 object views spanning a 180° view space, participants showed significant improvement in their ability to recognize 3-D objects across rotation. Surprisingly, there was no advantage to unsupervised learning with spatiotemporal continuity or motion information than training with temporal proximity. However, we discovered that when participants were trained with just a third of the views spanning the same view space, unsupervised learning via spatiotemporal continuity yielded significantly better recognition performance on novel views than learning via temporal proximity. These results suggest that while it is possible to obtain view-invariant recognition just from observing many views of an object presented in temporal proximity, spatiotemporal information enhances performance by producing representations with broader view tuning than learning via temporal association. Our findings have important implications for theories of object recognition and for the development of computational algorithms that learn from examples.
View details for DOI 10.1167/15.6.7
View details for Web of Science ID 000357858600007
View details for PubMedID 26024454
Electrical Stimulation of the Left and Right Human Fusiform Gyrus Causes Different Effects in Conscious Face Perception
2014; 34 (38): 12828-12836
View details for DOI 10.1523/JNEUROSCI.0527-14.2014
View details for Web of Science ID 000341767800019
Where Is Human V4? Predicting the Location of hV4 and VO1 from Cortical Folding.
Cerebral cortex
2014; 24 (9): 2401-2408
A strong relationship between cortical folding and the location of primary sensory areas in the human brain is well established. However, it is unknown if coupling between functional responses and gross anatomy is found at higher stages of sensory processing. We examined the relationship between cortical folding and the location of the retinotopic maps hV4 and VO1, which are intermediate stages in the human ventral visual processing stream. Our data show a consistent arrangement of the eccentricity maps within hV4 and VO1 with respect to anatomy, with the consequence that the hV4/VO1 boundary is found consistently in the posterior transverse collateral sulcus (ptCoS) despite individual variability in map size and cortical folding. Understanding this relationship allowed us to predict the location of visual areas hV4 and VO1 in a separate set of individuals, using only their anatomies, with >85% accuracy. These findings have important implications for understanding the relation between cortical folding and functional maps as well as for defining visual areas from anatomical landmarks alone.
View details for DOI 10.1093/cercor/bht092
View details for PubMedID 23592823
The functional architecture of the ventral temporal cortex and its role in categorization.
Nature reviews. Neuroscience
2014; 15 (8): 536-548
Visual categorization is thought to occur in the human ventral temporal cortex (VTC), but how this categorization is achieved is still largely unknown. In this Review, we consider the computations and representations that are necessary for categorization and examine how the microanatomical and macroanatomical layout of the VTC might optimize them to achieve rapid and flexible visual categorization. We propose that efficient categorization is achieved by organizing representations in a nested spatial hierarchy in the VTC. This spatial hierarchy serves as a neural infrastructure for the representational hierarchy of visual information in the VTC and thereby enables flexible access to category information at several levels of abstraction.
View details for DOI 10.1038/nrn3747
View details for PubMedID 24962370
The mid-fusiform sulcus: A landmark identifying both cytoarchitectonic and functional divisions of human ventral temporal cortex
2014; 84: 453-465
Human ventral temporal cortex (VTC) plays a pivotal role in high-level vision. An under-studied macroanatomical feature of VTC is the mid-fusiform sulcus (MFS), a shallow longitudinal sulcus separating the lateral and medial fusiform gyrus (FG). Here, we quantified the morphological features of the MFS in 69 subjects (ages 7-40), and investigated its relationship to both cytoarchitectonic and functional divisions of VTC with four main findings. First, despite being a minor sulcus, we found that the MFS is a stable macroanatomical structure present in all 138 hemispheres with morphological characteristics developed by age 7. Second, the MFS is the locus of a lateral-medial cytoarchitectonic transition within the posterior FG serving as the boundary between cytoarchitectonic regions FG1 and FG2. Third, the MFS predicts a lateral-medial functional transition in eccentricity bias representations in children, adolescents, and adults. Fourth, the anterior tip of the MFS predicts the location of a face-selective region, mFus-faces/FFA-2. These findings are the first to illustrate that a macroanatomical landmark identifies both cytoarchitectonic and functional divisions of high-level sensory cortex in humans and have important implications for understanding functional and structural organization in the human brain.
View details for DOI 10.1016/j.neuroimage.2013.08.068
View details for Web of Science ID 000328868600042
View details for PubMedID 24021838
Global Similarity and Pattern Separation in the Human Medial Temporal Lobe Predict Subsequent Memory
2013; 33 (13): 5466-5474
Intense debate surrounds the role of medial temporal lobe (MTL) structures in recognition memory. Using high-resolution fMRI and analyses of pattern similarity in humans, we examined the encoding computations subserved by MTL subregions. Specifically, we tested the theory that MTL cortex supports memory by encoding overlapping representations, whereas hippocampus supports memory by encoding pattern-separated representations. Consistent with this view, the relationship between encoding pattern similarity and subsequent memory dissociated MTL cortex and hippocampus: later memory was predicted by greater across-item pattern similarity in perirhinal cortex and in parahippocampal cortex, but greater pattern distinctiveness in hippocampus. Additionally, by comparing neural patterns elicited by individual stimuli regardless of subsequent memory, we found that perirhinal cortex and parahippocampal cortex exhibited differential content sensitivity for multiple stimulus categories, whereas hippocampus failed to demonstrate content sensitivity. These data provide novel evidence that complementary MTL encoding computations subserve declarative memory.
View details for DOI 10.1523/JNEUROSCI.4293-12.2013
View details for Web of Science ID 000316948600005
View details for PubMedID 23536062
Neural representations of faces and limbs neighbor in human high-level visual cortex: evidence for a new organization principle
2013; 77 (1): 74-97
Neurophysiology and optical imaging studies in monkeys and functional magnetic resonance imaging (fMRI) studies in both monkeys and humans have localized clustered neural responses in inferotemporal cortex selective for images of biologically relevant categories, such as faces and limbs. Using higher resolution (1.5 mm voxels) fMRI scanning methods than past studies (3-5 mm voxels), we recently reported a network of multiple face- and limb-selective regions that neighbor one another in human ventral temporal cortex (Weiner and Grill-Spector, Neuroimage, 52(4):1559-1573, 2010) and lateral occipitotemporal cortex (Weiner and Grill-Spector, Neuroimage, 56(4):2183-2199, 2011). Here, we expand on three basic organization principles of high-level visual cortex revealed by these findings: (1) consistency in the anatomical location of functional regions, (2) preserved spatial relationship among functional regions, and (3) a topographic organization of face- and limb-selective regions in adjacent and alternating clusters. We highlight the implications of this structure in comparing functional brain organization between typical and atypical populations. We conclude with a new model of high-level visual cortex consisting of ventral, lateral, and dorsal components, where multimodal processing related to vision, action, haptics, and language converges in the lateral pathway.
View details for DOI 10.1007/s00426-011-0392-x
View details for Web of Science ID 000313053700008
View details for PubMedID 22139022
Electrical Stimulation of Human Fusiform Face-Selective Regions Distorts Face Perception
2012; 32 (43): 14915-14920
Face-selective neural responses in the human fusiform gyrus have been widely examined. However, their causal role in human face perception is largely unknown. Here, we used a multimodal approach of electrocorticography (ECoG), high-resolution functional magnetic resonance imaging (fMRI), and electrical brain stimulation (EBS) to directly investigate the causal role of face-selective neural responses of the fusiform gyrus (FG) in face perception in a patient implanted with subdural electrodes in the right inferior temporal lobe. High-resolution fMRI identified two distinct FG face-selective regions [mFus-faces and pFus-faces (mid and posterior fusiform, respectively)]. ECoG revealed a striking anatomical and functional correspondence with fMRI data where a pair of face-selective electrodes, positioned 1 cm apart, overlapped mFus-faces and pFus-faces, respectively. Moreover, electrical charge delivered to this pair of electrodes induced a profound face-specific perceptual distortion during viewing of real faces. Specifically, the subject reported a "metamorphosed" appearance of faces of people in the room. Several controls illustrate the specificity of the effect to the perception of faces. EBS of mFus-faces and pFus-faces neither produced a significant deficit in naming pictures of famous faces on the computer, nor did it affect the appearance of nonface objects. Further, the appearance of faces remained unaffected during both sham stimulation and stimulation of a pair of nearby electrodes that were not face-selective. Overall, our findings reveal a striking convergence of fMRI, ECoG, and EBS, which together offer a rare causal link between functional subsets of the human FG network and face perception.
View details for DOI 10.1523/JNEUROSCI.2609-12.2012
View details for Web of Science ID 000310523900008
View details for PubMedID 23100414
Face-likeness and image variability drive responses in human face-selective ventral regions
2012; 33 (10): 2334-2349
The human ventral visual stream contains regions that respond selectively to faces over objects. However, it is unknown whether responses in these regions correlate with how face-like stimuli appear. Here, we use parameterized face silhouettes to manipulate the perceived face-likeness of stimuli and measure responses in face- and object-selective ventral regions with high-resolution fMRI. We first use "concentric hyper-sphere" (CH) sampling to define face silhouettes at different distances from the prototype face. Observers rate the stimuli as progressively more face-like the closer they are to the prototype face. Paradoxically, responses in both face- and object-selective regions decrease as face-likeness ratings increase. Because CH sampling produces blocks of stimuli whose variability is negatively correlated with face-likeness, this effect may be driven by more adaptation during high face-likeness (low-variability) blocks than during low face-likeness (high-variability) blocks. We tested this hypothesis by measuring responses to matched-variability (MV) blocks of stimuli with similar face-likeness ratings as with CH sampling. Critically, under MV sampling, we find a face-specific effect: responses in face-selective regions gradually increase with perceived face-likeness, but responses in object-selective regions are unchanged. Our studies provide novel evidence that face-selective responses correlate with the perceived face-likeness of stimuli, but this effect is revealed only when image variability is controlled across conditions. Finally, our data show that variability is a powerful factor that drives responses across the ventral stream. This indicates that controlling variability across conditions should be a critical tool in future neuroimaging studies of face and object representation.
View details for DOI 10.1002/hbm.21367
View details for Web of Science ID 000308589400007
View details for PubMedID 21823208
White matter microstructure on diffusion tensor imaging is associated with conventional magnetic resonance imaging findings and cognitive function in adolescents born preterm
2012; 54 (9): 809-814
Diffusion tensor imaging (DTI) was used to evaluate white matter architecture after preterm birth. The goals were (1) to compare white matter microstructure in two cohorts of preterm- and term-born children; and (2) within preterm groups, to determine if sex, gestational age, birthweight, white matter injury score from conventional magnetic resonance imaging (MRI), or IQ was associated with DTI measures.Participants (n=121; 66 females, 55 males) were aged 9 to 16 years. They comprised 58 preterm children (site 1, n=25; and site 2, n=33) born at less than 36 weeks' gestation (mean 29.4 wks; birthweight 1289g) and 63 term children (site 1, n=40; site 2, n=23) born at more than 37 weeks' gestation. DTI was analyzed using tract-based spatial statistics. Diffusion measures were fractional anisotropy, axial, radial, and mean diffusivity.In no region of the white matter skeleton was fractional anisotropy lower in the preterm group at either site. Within the preterm groups, fractional anisotropy was significantly associated with white matter injury score, but not sex, gestational age, or birthweight. At site 1, fractional anisotropy was associated with IQ.DTI contributes to understanding individual differences after preterm birth but may not differentiate a relatively high-functioning group of preterm children from a matched group of term-born children.
View details for DOI 10.1111/j.1469-8749.2012.04378.x
View details for Web of Science ID 000307468700011
View details for PubMedID 22803787
View details for PubMedCentralID PMC3683593
The improbable simplicity of the fusiform face area
2012; 16 (5): 251-254
The fusiform face area (FFA) is described as an easily identifiable module on the fusiform gyrus. However, the organization of face-selective regions in ventral temporal cortex (VTC) is more complex than this prevailing view. We highlight methodological factors contributing to these complexities and the extensive variability in how the FFA is identified. We suggest a series of constraints to aid researchers when defining any functionally specialized region with a pleasing realization: anatomy matters.
View details for DOI 10.1016/j.tics.2012.03.003
View details for Web of Science ID 000304026200001
View details for PubMedID 22481071
Not one extrastriate body area: Using anatomical landmarks, hMT+, and visual field maps to parcellate limb-selective activations in human lateral occipitotemporal cortex
2011; 56 (4): 2183-2199
The prevailing view of human lateral occipitotemporal cortex (LOTC) organization suggests a single area selective for images of the human body (extrastriate body area, EBA) that highly overlaps with the human motion-selective complex (hMT+). Using functional magnetic resonance imaging with higher resolution (1.5mm voxels) than past studies (3-4mm voxels), we examined the fine-scale spatial organization of these activations relative to each other, as well as to visual field maps in LOTC. Rather than one contiguous EBA highly overlapping hMT+, results indicate three limb-selective activations organized in a crescent surrounding hMT+: (1) an activation posterior to hMT+ on the lateral occipital sulcus/middle occipital gyrus (LOS/MOG) overlapping the lower vertical meridian shared between visual field maps LO-2 and TO-1, (2) an activation anterior to hMT+ on the middle temporal gyrus (MTG) consistently overlapping the lower vertical meridian of TO-2 and extending outside presently defined visual field maps, and (3) an activation inferior to hMT+ on the inferotemporal gyrus (ITG) overlapping the parafoveal representation of the TO cluster. This crescent organization of limb-selective activations surrounding hMT+ is reproducible over a span of three years and is consistent across different image types used for localization. Further, these regions exhibit differential position properties: preference for contralateral image presentation decreases and preference for foveal presentation increases from the limb-selective LOS to the MTG. Finally, the relationship between limb-selective activations and visual field maps extends to the dorsal stream where a posterior IPS activation overlaps V7. Overall, our measurements demonstrate a series of LOTC limb-selective activations that 1) have separate anatomical and functional boundaries, 2) overlap distinct visual field maps, and 3) illustrate differential position properties. These findings indicate that category selectivity alone is an insufficient organization principle for defining brain areas. Instead, multiple properties are necessary in order to parcellate and understand the functional organization of high-level visual cortex.
View details for DOI 10.1016/j.neuroimage.2011.03.041
View details for Web of Science ID 000291457500029
View details for PubMedID 21439386
Sparsely-distributed organization of face and limb activations in human ventral temporal cortex
2010; 52 (4): 1559-1573
Functional magnetic resonance imaging (fMRI) has identified face- and body part-selective regions, as well as distributed activation patterns for object categories across human ventral temporal cortex (VTC), eliciting a debate regarding functional organization in VTC and neural coding of object categories. Using high-resolution fMRI, we illustrate that face- and limb-selective activations alternate in a series of largely nonoverlapping clusters in lateral VTC along the inferior occipital gyrus (IOG), fusiform gyrus (FG), and occipito-temporal sulcus (OTS). Both general linear model (GLM) and multivoxel pattern (MVP) analyses show that face- and limb-selective activations minimally overlap and that this organization is consistent across experiments and days. We provide a reliable method to separate two face-selective clusters on the middle and posterior FG (mFus and pFus), and another on the IOG using their spatial relation to limb-selective activations and retinotopic areas hV4, VO-1/2, and hMT+. Furthermore, these activations show a gradient of increasing face selectivity and decreasing limb selectivity from the IOG to the mFus. Finally, MVP analyses indicate that there is differential information for faces in lateral VTC (containing weakly- and highly-selective voxels) relative to non-selective voxels in medial VTC. These findings suggest a sparsely-distributed organization where sparseness refers to the presence of several face- and limb-selective clusters in VTC, and distributed refers to the presence of different amounts of information in highly-, weakly-, and non-selective voxels. Consequently, theories of object recognition should consider the functional and spatial constraints of neural coding across a series of minimally overlapping category-selective clusters that are themselves distributed.
View details for DOI 10.1016/j.neuroimage.2010.04.262
View details for Web of Science ID 000280695200044
View details for PubMedID 20457261
fMRI-Adaptation and Category Selectivity in Human Ventral Temporal Cortex: Regional Differences Across Time Scales
2010; 103 (6): 3349-3365
Repeating object images produces stimulus-specific repetition suppression referred to as functional magnetic resonance imaging-adaptation (fMRI-A) in ventral temporal cortex (VTC). However, the effects of stimulus repetition on functional selectivity are largely unknown. We investigated the effects of short-lagged (SL, immediate) and long-lagged (LL, many intervening stimuli) repetitions on category selectivity in VTC using high-resolution fMRI. We asked whether repetition produces scaling or sharpening of fMRI responses both within category-selective regions as well as in the distributed response pattern across VTC. Results illustrate that repetition effects across time scales vary quantitatively along an anterior-posterior axis and qualitatively along a lateral-medial axis. In lateral VTC, both SL and LL repetitions produce proportional fMRI-A with no change in either selectivity or distributed responses as predicted by a scaling model. Further, there is larger fMRI-A in anterior subregions irrespective of category selectivity. Medial VTC exhibits similar scaling effects during SL repetitions. However, for LL repetitions, both the selectivity and distributed pattern of responses vary with category in medial VTC as predicted by a sharpening model. Specifically, there is larger fMRI-A for nonpreferred categories compared with the preferred category, and category selectivity does not predict fMRI-A across the pattern of distributed response. Finally, simulations indicate that different neural mechanisms likely underlie fMRI-A in medial compared to lateral VTC. These results have important implications for future fMRI-A experiments because they suggest that fMRI-A does not reflect a universal neural mechanism and that results of fMRI-A experiments will likely be paradigm independent in lateral VTC but paradigm dependent in medial VTC.
View details for DOI 10.1152/jn.01108.2009
View details for Web of Science ID 000278493900035
View details for PubMedID 20375251
The Fusiform Face Area is Enlarged in Williams Syndrome
2010; 30 (19): 6700-6712
Williams syndrome (WS) is a genetic condition characterized by atypical brain structure, cognitive deficits, and a life-long fascination with faces. Face recognition is relatively spared in WS, despite abnormalities in aspects of face processing and structural alterations in the fusiform gyrus, part of the ventral visual stream. Thus, face recognition in WS may be subserved by abnormal neural substrates in the ventral stream. To test this hypothesis, we used functional magnetic resonance imaging and examined the fusiform face area (FFA), which is implicated in face recognition in typically developed (TD) individuals, but its role in WS is not well understood. We found that the FFA was approximately two times larger among WS than TD participants (both absolutely and relative to the fusiform gyrus), despite apparently normal levels of face recognition performance on a Benton face recognition test. Thus, a larger FFA may play a role in face recognition proficiency among WS.
View details for DOI 10.1523/JNEUROSCI.4268-09.2010
View details for Web of Science ID 000277653600023
View details for PubMedID 20463232
Controlling stimulus variability reveals stronger face-selective responses near the average face
17th Annual Meeting on Object Perception, Attention and Memory
View details for Web of Science ID 000274036200010
Differential development of the ventral visual cortex extends through adolescence.
Frontiers in human neuroscience
2010; 3: 80-?
The ventral temporal cortex (VTC) in humans includes functionally defined regions that preferentially respond to objects, faces, and places. Recent developmental studies suggest that the face selective region in the fusiform gyrus ('fusiform face area', FFA) undergoes a prolonged development involving substantial increases in its volume after 7 years of age. However, the endpoint of this development is not known. Here we used functional magnetic resonance imaging (fMRI) to examine the development of face-, object- and place selective regions in the VTC of adolescents (12-16 year olds) and adults (18-40 year olds). We found that the volume of face selective activations in the right fusiform gyrus was substantially larger in adults than in adolescents, and was positively correlated with age. This development was associated with higher response amplitudes and selectivity for faces in face selective regions of VTC and increased differentiation of the distributed response patterns to faces versus non-face stimuli across the entire VTC. Furthermore, right FFA size was positively correlated with face recognition memory performance, but not with recognition memory of objects or places. In contrast, the volume of object- and place selective cortical regions or their response amplitudes did not change across these age groups. Thus, we found a striking and prolonged development of face selectivity across the VTC during adolescence that was specifically associated with proficiency in face recognition memory. These findings have important implications for theories of development and functional specialization in VTC.
View details for DOI 10.3389/neuro.09.080.2009
View details for PubMedID 20204140
The representation of object viewpoint in human visual cortex
2009; 45 (2): 522-536
Understanding the nature of object representations in the human brain is critical for understanding the neural basis of invariant object recognition. However, the degree to which object representations are sensitive to object viewpoint is unknown. Using fMRI we employed a parametric approach to examine the sensitivity to object view as a function of rotation (0 degrees-180 degrees ), category (animal/vehicle) and fMRI-adaptation paradigm (short or long-lagged). For both categories and fMRI-adaptation paradigms, object-selective regions recovered from adaptation when a rotated view of an object was shown after adaptation to a specific view of that object, suggesting that representations are sensitive to object rotation. However, we found evidence for differential representations across categories and ventral stream regions. Rotation cross-adaptation was larger for animals than vehicles, suggesting higher sensitivity to vehicle than animal rotation, and was largest in the left fusiform/occipito-temporal sulcus (pFUS/OTS), suggesting that this region has low sensitivity to rotation. Moreover, right pFUS/OTS and FFA responded more strongly to front than back views of animals (without adaptation) and rotation cross-adaptation depended both on the level of rotation and the adapting view. This result suggests a prevalence of neurons that prefer frontal views of animals in fusiform regions. Using a computational model of view-tuned neurons, we demonstrate that differential neural view tuning widths and relative distributions of neural-tuned populations in fMRI voxels can explain the fMRI results. Overall, our findings underscore the utility of parametric approaches for studying the neural basis of object invariance and suggest that there is no complete invariance to object view in the human ventral stream.
View details for DOI 10.1016/j.neuroimage.2008.11.009
View details for Web of Science ID 000263863000031
View details for PubMedID 19100844
Fine-Scale Spatial Organization of Face and Object Selectivity in the Temporal Lobe: Do Functional Magnetic Resonance Imaging, Optical Imaging, and Electrophysiology Agree?
2008; 28 (46): 11796-11801
The spatial organization of the brain's object and face representations in the temporal lobe is critical for understanding high-level vision and cognition but is poorly understood. Recently, exciting progress has been made using advanced imaging and physiology methods in humans and nonhuman primates, and the combination of such methods may be particularly powerful. Studies applying these methods help us to understand how neuronal activity, optical imaging, and functional magnetic resonance imaging signals are related within the temporal lobe, and to uncover the fine-grained and large-scale spatial organization of object and face representations in the primate brain.
View details for DOI 10.1523/JNEUROSCI.3799-08.2008
View details for Web of Science ID 000260827600009
View details for PubMedID 19005042
Relating retinotopic and object-selective responses in human lateral occipital cortex
2008; 100 (1): 249-267
What is the relationship between retinotopy and object selectivity in human lateral occipital (LO) cortex? We used functional magnetic resonance imaging (fMRI) to examine sensitivity to retinal position and category in LO, an object-selective region positioned posterior to MT along the lateral cortical surface. Six subjects participated in phase-encoded retinotopic mapping experiments as well as block-design experiments in which objects from six different categories were presented at six distinct positions in the visual field. We found substantial position modulation in LO using standard nonobject retinotopic mapping stimuli; this modulation extended beyond the boundaries of visual field maps LO-1 and LO-2. Further, LO showed a pronounced lower visual field bias: more LO voxels represented the lower contralateral visual field, and the mean LO response was higher to objects presented below fixation than above fixation. However, eccentricity effects produced by retinotopic mapping stimuli and objects differed. Whereas LO voxels preferred a range of eccentricities lying mostly outside the fovea in the retinotopic mapping experiment, LO responses were strongest to foveally presented objects. Finally, we found a stronger effect of position than category on both the mean LO response, as well as the distributed response across voxels. Overall these results demonstrate that retinal position exhibits strong effects on neural response in LO and indicates that these position effects may be explained by retinotopic organization.
View details for DOI 10.1152/jn.01383.2007
View details for Web of Science ID 000257635400023
View details for PubMedID 18463186
Developmental neuroimaging of the human ventral visual cortex
2008; 12 (4): 152-162
Here, we review recent results that investigate the development of the human ventral stream from childhood, through adolescence and into adulthood. Converging evidence suggests a differential developmental trajectory across ventral stream regions, in which face-selective regions show a particularly long developmental time course, taking more than a decade to become adult-like. We discuss the implications of these recent findings, how they relate to age-dependent improvements in recognition memory performance and propose possible neural mechanisms that might underlie this development. These results have important implications regarding the role of experience in shaping the ventral stream and the nature of the underlying representations.
View details for Web of Science ID 000255469200008
View details for PubMedID 18359267
Object recognition: Insights from advances in fMRI methods
2008; 17 (2): 73-79
View details for Web of Science ID 000254807700004
Representation of shapes, edges, and surfaces across multiple cues in the human visual cortex
2008; 99 (3): 1380-1393
The lateral occipital complex (LOC) responds preferentially to objects compared with random stimuli or textures independent of the visual cue. However, it is unknown whether the LOC (or other cortical regions) are involved in the processing of edges or global surfaces without shape information. Here, we examined processing of 1) global shape, 2) disconnected edges without a global shape, and 3) global surfaces without edges versus random stimuli across motion and stereo cues. The LOC responded more strongly to global shapes than to edges, surfaces, or random stimuli, for both motion and stereo cues. However, its responses to local edges or global surfaces were not different from random stimuli. This suggests that the LOC processes shapes, not edges or surfaces. LOC also responded more strongly to objects than to holes with the same shape, suggesting sensitivity to border ownership. V7 responded more strongly to edges than to surfaces or random stimuli for both motion and stereo cues, whereas V3a and V4 preferred motion edges. Finally, a region in the caudal intraparietal sulcus (cIPS) responded more strongly to both stereo versus motion and to stereo surfaces versus random stereo (but not to motion surfaces vs. random motion). Thus we found evidence for cue-specific responses to surfaces in the cIPS, both cue-specific and cue-independent responses to edges in intermediate visual areas, and shape-selective responses across multiple cues in the LOC. Overall, these data suggest that integration of visual information across multiple cues is mainly achieved at the level of shape and underscore LOC's role in shape computations.
View details for DOI 10.1152/jn.01223.2007
View details for Web of Science ID 000253969300030
View details for PubMedID 18171705
Differential development of high-level visual cortex correlates with category-specific recognition memory
2007; 10 (4): 512-522
High-level visual cortex in humans includes functionally defined regions that preferentially respond to objects, faces and places. It is unknown how these regions develop and whether their development relates to recognition memory. We used functional magnetic resonance imaging to examine the development of several functionally defined regions including object (lateral occipital complex, LOC)-, face ('fusiform face area', FFA; superior temporal sulcus, STS)- and place ('parahippocampal place area', PPA)-selective cortices in children (ages 7-11), adolescents (12-16) and adults. Right FFA and left PPA volumes were substantially larger in adults than in children. This development occurred by expansion of FFA and PPA into surrounding cortex and was correlated with improved recognition memory for faces and places, respectively. In contrast, LOC and STS volumes and object-recognition memory remained constant across ages. Thus, the ventral stream undergoes a prolonged maturation that varies temporally across functional regions, is determined by brain region rather than stimulus category, and is correlated with the development of category-specific recognition memory.
View details for DOI 10.1038/nn1865
View details for Web of Science ID 000245228600023
View details for PubMedID 17351637
Autism and the development of face processing.
Clinical neuroscience research
2006; 6 (3): 145-160
Autism is a pervasive developmental condition, characterized by impairments in non-verbal communication, social relationships and stereotypical patterns of behavior. A large body of evidence suggests that several aspects of face processing are impaired in autism, including anomalies in gaze processing, memory for facial identity and recognition of facial expressions of emotion. In search of neural markers of anomalous face processing in autism, much interest has focused on a network of brain regions that are implicated in social cognition and face processing. In this review, we will focus on three such regions, namely the STS for its role in processing gaze and facial movements, the FFA in face detection and identification and the amygdala in processing facial expressions of emotion. Much evidence suggests that a better understanding of the normal development of these specialized regions is essential for discovering the neural bases of face processing anomalies in autism. Thus, we will also examine the available literature on the normal development of face processing. Key unknowns in this research area are the neuro-developmental processes, the role of experience and the interactions among components of the face processing system in shaping each of the specialized regions for processing faces during normal development and in autism.
View details for PubMedID 18176635
Autism and the development of face processing
85th Annual Conference of the Association-for-Reseach-in-Nervous-and-Mental-Disease
View details for DOI 10.1016/j.cnr.2006.08.001
View details for Web of Science ID 000242486200006
High-resolution imaging reveals highly selective nonface clusters in the fusiform face area
2006; 9 (9): 1177-1185
A region in ventral human cortex (fusiform face area, FFA) thought to be important for face perception responds strongly to faces and less strongly to nonface objects. This pattern of response may reflect a uniform face-selective neural population or activity averaged across populations with heterogeneous selectivity. Using high-resolution functional magnetic resonance imaging (MRI), we found that the FFA has a reliable heterogeneous structure: localized subregions within the FFA highly selective to faces are spatially interdigitated with localized subregions highly selective to different object categories. We found a preponderance of face-selective responses in the FFA, but no difference in selectivity to faces compared to nonfaces. Thus, standard fMRI of the FFA reflects averaging of heterogeneous highly selective neural populations of differing sizes, rather than higher selectivity to faces. These results suggest that visual processing in this region is not exclusive to faces. Overall, our approach provides a framework for understanding the fine-scale structure of neural representations in the human brain.
View details for DOI 10.1038/nn1745
View details for Web of Science ID 000240080800020
View details for PubMedID 16892057
Object-selective cortex exhibits performance-independent repetition suppression
2006; 95 (2): 995-1007
Object-selective cortical regions exhibit a decreased response when an object stimulus is repeated [repetition suppression (RS)]. RS is often associated with priming: reduced response times and increased accuracy for repeated stimuli. It is unknown whether RS reflects stimulus-specific repetition, the associated changes in response time, or the combination of the two. To address this question, we performed a rapid event-related functional MRI (fMRI) study in which we measured BOLD signal in object-selective cortex, as well as object recognition performance, while we manipulated stimulus repetition. Our design allowed us to examine separately the roles of response time and repetition in explaining RS. We found that repetition played a robust role in explaining RS: repeated trials produced weaker BOLD responses than nonrepeated trials, even when comparing trials with matched response times. In contrast, response time played a weak role in explaining RS when repetition was controlled for: it explained BOLD responses only for one region of interest (ROI) and one experimental condition. Thus repetition suppression seems to be mostly driven by repetition rather than performance changes. We further examined whether RS reflects processes occurring at the same time as recognition or after recognition by manipulating stimulus presentation duration. In one experiment, durations were longer than required for recognition (2 s), whereas in a second experiment, durations were close to the minimum time required for recognition (85-101 ms). We found significant RS for brief presentations (albeit with a reduced magnitude), which again persisted when controlling for performance. This suggests a substantial amount of RS occurs during recognition.
View details for DOI 10.1152/jn.00500.2005
View details for Web of Science ID 000234759600040
View details for PubMedID 16236787
Selectivity of adaptation in single units: Implications for fMRI experiments
2006; 49 (2): 170-171
Understanding the neural basis of adaptation (repetition suppression) is critical for interpreting fMRI-adaptation experiments. Sawamura and colleagues provide a critical stepping-stone by elucidating the relation between neural adaptation and response selectivity. They find some cross-adaptation by two different stimuli that activate the same neuron.
View details for DOI 10.1016/j.neuron.2006.01.004
View details for Web of Science ID 000234979900003
View details for PubMedID 16423690
Repetition and the brain: neural models of stimulus-specific effects
2006; 10 (1): 14-23
One of the most robust experience-related cortical dynamics is reduced neural activity when stimuli are repeated. This reduction has been linked to performance improvements due to repetition and also used to probe functional characteristics of neural populations. However, the underlying neural mechanisms are as yet unknown. Here, we consider three models that have been proposed to account for repetition-related reductions in neural activity, and evaluate them in terms of their ability to account for the main properties of this phenomenon as measured with single-cell recordings and neuroimaging techniques. We also discuss future directions for distinguishing between these models, which will be important for understanding the neural consequences of repetition and for interpreting repetition-related effects in neuroimaging data.
View details for DOI 10.1016/j.tics.2005.11.006
View details for Web of Science ID 000234910400007
View details for PubMedID 16321563
Visual recognition - As soon as you know it is there, you know what it is
2005; 16 (2): 152-160
What is the sequence of processing steps involved in visual object recognition? We varied the exposure duration of natural images and measured subjects' performance on three different tasks, each designed to tap a different candidate component process of object recognition. For each exposure duration, accuracy was lower and reaction time longer on a within-category identification task (e.g., distinguishing pigeons from other birds) than on a perceptual categorization task (e.g., birds vs. cars). However, strikingly, at each exposure duration, subjects performed just as quickly and accurately on the categorization task as they did on a task requiring only object detection: By the time subjects knew an image contained an object at all, they already knew its category. These findings place powerful constraints on theories of object recognition.
View details for Web of Science ID 000226656000011
View details for PubMedID 15686582
The fusiform face area subserves face perception, not generic within-category identification
2004; 7 (5): 555-562
The function of the fusiform face area (FFA), a face-selective region in human extrastriate cortex, is a matter of active debate. Here we measured the correlation between FFA activity measured by functional magnetic resonance imaging (fMRI) and behavioral outcomes in perceptual tasks to determine the role of the FFA in the detection and within-category identification of faces and objects. Our data show that FFA activation is correlated on a trial-by-trial basis with both detecting the presence of faces and identifying specific faces. However, for most non-face objects (including cars seen by car experts), within-category identification performance was correlated with activation in other regions of the ventral occipitotemporal cortex, not the FFA. These results indicate that the FFA is involved in both detection and identification of faces, but that it has little involvement in within-category identification of non-face objects (including objects of expertise).
View details for DOI 10.1038/nn1224
View details for Web of Science ID 000221101300034
View details for PubMedID 15077112
The human visual cortex
2004; 27: 649-677
The discovery and analysis of cortical visual areas is a major accomplishment of visual neuroscience. In the past decade the use of noninvasive functional imaging, particularly functional magnetic resonance imaging (fMRI), has dramatically increased our detailed knowledge of the functional organization of the human visual cortex and its relation to visual perception. The fMRI method offers a major advantage over other techniques applied in neuroscience by providing a large-scale neuroanatomical perspective that stems from its ability to image the entire brain essentially at once. This bird's eye view has the potential to reveal large-scale principles within the very complex plethora of visual areas. Thus, it could arrange the entire constellation of human visual areas in a unified functional organizational framework. Here we review recent findings and methods employed to uncover the functional properties of the human visual cortex focusing on two themes: functional specialization and hierarchical processing.
View details for DOI 10.1146/annurev.neuro.27.070203.144220
View details for Web of Science ID 000223246300023
View details for PubMedID 15217346
The neural basis of object perception
2003; 13 (2): 159-166
Humans can recognize an object within a fraction of a second, even if there are no clues about what kind of object it might be. Recent findings have identified functional properties of extrastriate regions in the ventral visual pathway that are involved in the representation and perception of objects and faces. The functional properties of these regions, and the correlation between the activation of these regions and visual recognition, indicate that the lateral and ventral occipito-temporal areas are important in perceiving and recognizing objects and faces.
View details for DOI 10.1016/S0959-4388(03)00040-0
View details for Web of Science ID 000183092700004
View details for PubMedID 12744968


text:
|Publication number
|Publication type
|Application number
|Publication date
|Feb 25, 1997
|Filing date
|Nov 9, 1994
|Priority date
|Jul 16, 1991
|Fee status
|Also published as
|Publication number
|Raymond J. Hasler, Oliver P. Leisten
|Original Assignee
|Symmetricom, Inc.
|Export Citation
|BiBTeX, EndNote, RefMan
|Patent Citations (14), Non-Patent Citations (2), Referenced by (71), Classifications (20), Legal Events (6)
|External Links: USPTO, USPTO Assignment, Espacenet
Δf.sub.L01 +Δf.sub.L02 =Δf
This application is a continuation of application Ser. No. 07/913,291, filed Jul. 14, 1992, now abandoned.
This invention relates to a radio receiver, and in particular to a receiver for satellite navigation and position-fixing.
The American GPS (Global Positioning System) and the Russian GLONASS system are both satellite-based position-fixing systems using a number of earth orbiting satellites. Although each is capable of providing a high level of position-fixing accuracy neither is capable of a grade of certainty and coverage to satisfy the needs of the most demanding of applications, such as those of the civil aviation business, in which satellite navigation receivers are used only as "secondary navigation aids". However, use of both systems together gives a much higher grade of certainty since one system can be used to check the other.
The GPS civil position-fixing service makes use of signals transmitted by a number of satellites on a common carrier frequency (LI) of 1575.42 MHz. Since each GPS satellite transmits a unique modulation code it is possible for a single receiver, tuned to the common carrier frequency, to extract data separately from the transmissions of each satellite. In contrast, the GLONASS service has satellites transmitting signals on different frequencies with a common code modulation scheme. Currently, the L1 group of channels comprises 24 channels in the range 1602.5625 MHz to 1615.5000 MHz.
Naturally, it is possible to equip users each with one GPS receiver and one GLONASS receiver, or to build a receiver with largely separate frequency synthesizer and intermediate frequency stages for GPS and GLONASS, but both approaches are costly in comparison with the provision of a single GPS receiver, for example.
It is an object of the present invention to produce a receiver which is capable of receiving signals from different transmission systems having substantially unrelated frequency characteristics and which uses common components for receiving the signals from the different systems to reduce cost.
According to this invention, there is provided a heterodyne radio receiver having at least two successive frequency down-converters arranged to be fed by respective local oscillator signal sources, wherein, for tuning the receiver to different frequencies, the frequencies of the said sources are variable and related by the expression fL01 =X.fL02, where fL01 and fL02 are the frequencies of a first and a second of the said sources respectively, and X is a fixed integer in at least one mode of the receiver.
The local oscillator signal sources may be provided by a single frequency synthesizer, the second source being formed by the output of a digital frequency divider which has an input associated with the first source. The frequency divider may be a fixed division ratio part of a variable divider chain linking an electrically controlled oscillator and a phase or frequency comparator for comparing the output of the divider chain with a signal the frequency of which is governed by a reference oscillator operable at a reference oscillator frequency. The receiver frequency is variable in a series of regular frequency increments corresponding to the predetermined frequency spacing of a series of transmission channels, with the frequency fL02 of the second source varying in a series of corresponding increments ΔfL02 each equal to a factor (preferably, the highest factor) common to the frequency spacing and the reference oscillator frequency.
In the case of a receiver operable at UHF frequencies or higher, such as a satellite navigation receiver for receiving satellite signals in L-band, the divider determining the ratio (X) between the frequencies of the first and second local oscillator signal sources is advantageously a binary divider. In the particular dual conversion embodiments of the invention to be described below the ratio (X) is 8 in at least one mode of the receiver. This figure is chosen because, firstly, a convenient reference frequency for satellite navigation receivers is 10 MHz (or a multiple thereof), and the highest common factor of 10 MHz and the GLONASS channel spacing (for the L1 channels) of 0.5625 MHz is 62.5 KHz, and secondly, the ratio X is determined by the relationships:
Δf.sub.L01 +Δf.sub.L02 =Δf
Δf.sub.L01 =Δf.X/(X+1)
where ΔfL01 and ΔfL02 are the frequency increments of the variable local oscillator frequencies and Δf is the frequency increment of the input frequency of the receiver (i.e. the channel spacing), so that, putting ΔfL02 =62.5 KHz and Δf=0.5625 MHz, it is seen that X=8.
In the drawing:
FIG. 1 is a block diagram of a first radio receiver in accordance with the invention;
FIG. 2 is a block diagram of part of a second radio receiver in accordance with the invention; and
FIG. 3 is a block diagram of part of a third radio receiver in accordance with the invention.
It has been stated above that a satellite navigation receiver for GLONASS signals can be produced using a reference oscillator of 10 MHz or a multiple of 10 MHz by employing a double-conversion superhet signal chain in which the two down-converters are fed with local oscillator signals the frequencies of which are in the ratio of 8 to 1. Referring to FIG. 1, such a receiver may comprise an antenna 10, an input filtering and amplifying stage 12, a first mixer 14, a first intermediate frequency (i.f) filtering and amplifying stage 16, a second mixer 18, a second i.f filtering and amplifying stage 20, and signal detection and processing circuitry 22. First and second local oscillator signals are fed to the first and second mixers 14, 18 respectively on lines 24 and 26, the source of the first local oscillator signal being a voltage controlled oscillator (VCO) 28 forming part of a frequency synthesizer loop 30. Control of the VCO frequency is established in conventional manner by means of a digital frequency divider chain 32, 34 feeding a phase comparator 36 which also receives a reference signal derived from a reference frequency source 38. The output of the phase comparator 36 is integrated in a low-pass filter stage 40 and applied to the control voltage input of the VCO 28.
In the present case the divider chain includes, firstly, a fixed divider 32 which acts as a prescaler for dividing the VCO frequency by a constant integer X and, secondly, a variable divider 34 for further division by a variable number n according to settings signalled via control input 34A. Coupled to the output of the fixed divider 32 is the local oscillator input of the second mixer 18 so that the second local oscillator frequency fL02 is equal to fL01 divided by X, X being 8 in this example.
The GLONASS satellite navigation system currently transmits signals on 24 channels between 1602.5625 MHz and 1615.5000 MHz separated by increments of 0.5625 MHz. These are often referred to as the GLONASS "L1" channels, 24 out of 32 channel allocations actually being used at present. Conventionally, in a single loop frequency synthesizer for a receiver receiving such signals, a comparison frequency (at the phase comparator) of 0.5625 MHz might be chosen to allow switching between channels by altering the division ratio of the variable divider in increments of 1, and to give adequate synthesizer response speed and noise performance. However, such a comparison frequency cannot be obtained by direct division from a reference crystal oscillator running at 10 MHz, 20 MHz or, perhaps, 40 MHz. These frequencies are convenient for use in GPS satellite navigation receivers due to the speed requirements of the processing circuitry and the ease with which a calendar time reference can be generated for predictive acquisition of satellite signals. Indeed, stages such as frequency multipliers or non-linear mixers are required, together with filters for blocking unwanted frequency components, which are expensive in relation to dividers and, in the case of filters particularly, are difficult to incorporate in integrated circuit devices.
Instead, the receiver of FIG. 1 uses a comparison frequency of 62.5 KHz, which is the highest common factor of 10 MHz and the channel spacing 0.5625 MHz. By selecting a division ratio of 8 for the fixed divider 32 and taking the output of that fixed divider as the local oscillator input for the second mixer, it will be seen that the receiver can be tuned to the 24 GLONASS channels by altering the division ratio n of the variable divider 34 in steps of 1, and by dividing the reference frequency 10 MHz in a reference divider (not shown in FIG. 1) by 160, i.e. without frequency multipliers or other complex components.
In terms of precise frequencies and division ratios, the frequency synthesizer may be arranged to produce first and second local oscillator frequencies of 1402.0 MHz and 175.25 MHz respectively to receive channel 1 (1602.5625 MHz), yielding a first i.f of 200.5625 MHz and a second i.f of 25.3125 MHz. The division ratio n is 2804. Changing the division ratio n to 2827 produces first and second local oscillator frequencies of 1413.5 MHz and 176.6875 MHz for receiving channel 24 (1615.5000 MHz). The second i.f remains constant at 25.3125 MHz. It will be noted now that the first i.f has changed to 202.0000 MHz. In fact, as the receiver is tuned from channel to channel, the first i.f frequency changes in steps of 62.5 KHz together with the second local oscillator frequency. A change of first i.f frequency of this order is acceptable and can be accommodated within the first i.f filter bandwidth. It will also be noted that the first local oscillator frequency is incremented in steps of 0.5 MHz, i.e 8 times the increments of the second local oscillator frequency and one 20th of a reference oscillator frequency of 10 MHz.
The above example uses local oscillator signals having frequencies which are lower than the input and first i.f frequencies respectively. Arrangements of one higher and one lower or two higher frequencies are also possible, still using the same division ratio between the two local oscillator frequencies. In other words, the relationship X=(Δf/ΔfL02)-1 holds true in each case.
It is possible, within the scope of the invention to choose common factors of the channel spacing and the reference oscillator frequency which are not the highest common factor. Thus, for example, the second local oscillator frequency may be incremented in steps of 31.25 KHz or 20.8333 KHz, with X equal to 17 or 26 respectively. However, these result in lower comparison frequencies, which has disadvantages as will become clear below.
By appropriate selection of a fixed value for the variable division ratio n, by switching in a different first i.f filter, by alteration of the comparison frequency, if required, and by changing the division ratio of the reference divider in the reference frequency source 38, the receiver of FIG. 1 can be used to receive GPS signals on the GPS L1 frequency of 1575.42 MHz.
The receiver described above with reference to FIG. 1 does have the disadvantage that the comparison frequency may not be sufficiently high to avoid limiting synthesizer switching speed undesirably. A higher comparison frequency is also preferable for reducing noise in the synthesizer loop, since loop noise is related to the ratio of the VCO frequency (the first local oscillator frequency) and the comparison frequency.
However, it is possible to trade the bandwidth of the variable divider for frequency changing agility and synthesizer loop noise. Referring to FIG. 2, this is achieved by reducing the overall division ratio in the loop 30 by, for example, taking the input for the variable divider 34 from a point further "upstream" than in the loop of the previous example (shown in FIG. 1). Thus, the input to the variable divider 34 may be coupled to a "tap-off" point between the two fixed ratio dividers 42, 44 which together, perform the same function and have the same overall division ratio X as the single divider 32 in the previous example.
To take, again, the example of X=8, dividers 42 and 44 are binary dividers with division ratios 2p and 2y respectively, where p+y=3. It will be seen that if p=1, and the variable divider 34 is unchanged compared with the first example, the comparison frequency is raised from 62.5 KHz to 250 KHz. Indeed, it is possible to make p=0 and eliminate the divider 42 altogether so that the comparison frequency becomes 500 KHz.
However, whether the variable divider 34 takes its input from the end output of the fixed divider section, or from a "tap-off" point, or directly from the output of the VCO 28, the division ratio between the inputs 24, 26 of the mixers 14, 18 remains the same.
The example of FIG. 2 is particularly susceptible for use in a combined GPS/GLONASS receiver, because with p=0 and a comparison frequency of 0.5 MHz in the GLONASS mode, a 10 MHz reference frequency may be used with a simple reference divider 46 having a division ration m equal to 20. Interposing a switch 48 in the reference circuitry as shown to allow bypassing of the reference divider 46 enables the comparator 36 to be operated at 10 MHz in the GPS mode, the variable divider 34 being operated with a fixed division ratio of 128. Both the switch 48 and the divider 34 are controlled via control inputs 50 when switching between modes. This particular example produces a first i.f of 295.42 MHz in GPS mode and, therefore, needs different i.f filtering in the two modes. In some circumstances, frequencies and division ratios may be selected to avoid the need to change the first i.f filtering between modes.
Further possibilities can be realised by altering the division ratio of the divider feeding the second mixer 18 when switching to GPS mode, as shown in FIG. 3. Referring to FIG. 3, this divider is split into three parts 52, 54 and 56, each a simple binary divider dividing by 2. The input 26 to the second mixer 18 is taken from the output of divider 56 or from the output of divider 54 according to the position of a second electronic switch 58. In GLONASS mode, the switch 58 is operated to connect the mixer 18 to the output of divider 56 to give the required ratio of 8 between the first and second local oscillator signals. In GPS mode, the mixer is instead switched to the output of the divider 54 so that the ratio between the local oscillator signals is now 4. At the same time, as in the FIG. 2 embodiment, the reference divider 46 is bypassed to alter the comparison frequency, except that in this case the reference frequency and the division ratio m of the reference divider 46 are 40 MHz and 160 respectively. In GPS mode, the division ratio of the variable divider 34 is held at 16.
To minimise cost the receivers described above have been designed, as far as possible, to allow the majority of their components to be embodied in an integrated circuit or circuits. To take the example of FIG. 3, the dotted line 60 indicates some of the components that may be integrated on a chip. In practice, much of the reference source circuitry can also be "on chip" as well as some of the amplifier circuitry in the radio frequency and subsequent stages. The variable divider 34 can be "off-chip" if required, an option which is of particular interest if the chip is to be used as the basis of an integrated circuit which can be incorporated in the radio frequency stages of either a GPS receiver, or a GLONASS receiver, or a combined GPS/GLONASS receiver, since the GPS only receiver does not require the variable divider and a fixed ratio divider can be substituted.
The invention includes such an integrated circuit receiver or synthesizer chip as another aspect of the inventive concept, the chip including at least divider means operable to divide a first local oscillator signal by a fixed integer, preferably the integer 8, to produce a second local oscillator signal. The chip may include one or more of the other elements as shown in FIG. 3.
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|U.S. Classification
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|International Classification
|Cooperative Classification
|European Classification
|Oct 22, 1996
Owner name: SYMETRICOM, INC., CALIFORNIA
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|Maintenance fee reminder mailed
|Feb 25, 2005
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|Apr 26, 2005
|Expired due to failure to pay maintenance fee
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subset: commoncrawl


text:
Normally, those giant displays are just graphics on a loop, fooling only the smallest of children and the nerdiest of nerds (who secretly hope the giant tablet will actually let them swipe).
But the Best Buy store in San Carlos (the City of Good Living) has mounted a 42-inch Android Nexus S that actually works like a phone -- including the camera.
Intrepid TechCrunch reporter Jason Kincaid traversed the Bay to get there this morning for fresh video.
The phone is supported by a real Nexus S that is equipped with a special media-out function.
Now, which aisle has those 72-inch holiday stockings??
Published at 11:38 AM PST on Dec 23, 2010 | Updated at 11:45 AM PST on Dec 23, 2010