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document
Global contour saliency and local colinear interactions . Our visual system can link components of contours and segregate contours from complex backgrounds based on geometric grouping rules . This is an important intermediate step in object recognition . The substrate for contour integration may be based on contextual interactions and intrinsic horizontal connections seen in primary visual cortex ( V1 ) . We examined the perceptual rules governing contour saliency to determine whether the spatial extents of contextual interactions and horizontal connections match those mediating saliency . To quantify these rules , we used stimuli composed of randomly oriented nonoverlapping line segments . Salient contours within this complex background were formed by colinear alignment of nearby segments . Contour detectability was measured using a 2-interval-forced-choice design . Contour detectability deteriorated with increasing spacing between contour elements and improved as the number of colinear line elements was increased . At short contour spacing , the detectability reached a plateau with alignment of a few line segments that together formed a contour subtending several visual degrees . At intermediate spacing , saliency built up progressively with a greater number of colinear lines , extending up to 30 degrees . When contour spacing was beyond a critical range ( about 2 degrees ) , however , the detectability dropped to chance levels , regardless of the number of colinear lines . Contour detectability was found to be a function not only of the relative spacing of contour elements with respect to the noise elements but also of the average density of the overall pattern . Furthermore , training significantly improved contour detection , increasing the critical spacing of line elements beyond which contours were no longer detectable . Our data suggest that global contour integration is based on mechanisms of limited spatial extent , comparable to the interactions observed in V1 . These interactions can cascade over larger distances provided the spacing of stimulus elements is kept within a limited range .
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Intervention_Physical
stimuli composed of randomly oriented nonoverlapping line segments
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Intervention_Physical
2-interval-forced-choice design
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Outcome_Physical
object recognition .
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Outcome_Physical
Contour detectability
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Outcome_Other
Contour detectability
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Outcome_Physical
spacing
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Outcome_Mental
saliency
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Outcome_Other
detectability
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Outcome_Other
Contour detectability
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Outcome_Mental
contour detection
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Outcome_Mental
critical spacing
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Outcome_Other
global contour integration