What happens in your brain when you see a dinosaur in this stenographic image? You might have come across stereographic Images like the one shown below (found here):




What happens in your brain when you observe the dinosaur? (as you put your face on the image by touching your nose and then slowly withdrawing from the image.)
Is this perception a particular trick that my eye performs or is it processing the visual data in an alternative way?
Is the effect of this percept measurable by an EEG?
The source I have quoted below gives an example of the following stenographic image:-



Is this perception a particular trick that my eye performs or is it processing the visual data in an alternative way?


  Stereograms can be viewed as three-dimensional images by providing two
  side-by-side views of a three-dimensional scene, rendered from
  slightly different viewpoints. Stereoscopes facilitate focusing of the
  eyes depths other than the surface of a two-dimensional stereogram
  image, allowing the two separate images to overlap in the center of
  the field of vision (Kimmel, 2002). Once the correct depth is
  achieved, it may seem to the viewer as if the two images are different
  due to the horizontal retinal disparities. Then the two images can
  fuse into a coherent three- dimensional percept where horizontal
  disparities in the images provide important depth cues.




Is the effect of this percept measurable by an EEG?


  Autostereograms have been used in recent research to investigate
  three-dimensional depth perception. These efforts have improved
  understanding of the various visual cues involved in forming
  three-dimensional percepts, perceiving motion in depth, attention-
  switching in the depth of field, and the neural correlates of forming
  and maintaining a unified three-dimensional structure in awareness.
  
  Revonsuo and colleagues (Revonsuo, et al., 1997) used neural
  synchronization to investigate the neural correlates of
  three-dimensional percept formations. They confirmed that
  autostereoscopic perception is primarily mediated by right
  parieto-temporal activity. Their research indicated a region of
  synchrony spanning portions of the right temporal, parietal and
  occipital lobes, with maximum power in the gamma (36-44Hz) frequency
  range. Also employing electroencephalogram (EEG) recording, Burgess,
  Rehman, and Williams (2003) located particular brain regions,
  including the left frontal (F7) and the right and midline occipital
  (Oz, O2) clusters, exhibiting functional clustering during
  autostereoscopic perception. Overall, neural complexity was highest
  with the most functional clustering of responses during observer
  awareness of the three-dimensional object. Additional clustering
  analyses revealed functional clusters of scalp recordings in the
  aforementioned areas that correlated with both phases of
  three-dimensional perception (search to three-dimensional and
  three-dimensional maintenance).




Sources


Autostereograms and Autostereoscopic Perception 
Authors: Leslie Blaha, Christopher Honey, and Eric Nichols 
Date: October 31, 2005
Burgess, A.P., Rehman, J., &amp; Williams, J.D. (2003). Changes in neural complexity during the perception of three-dimensional images using random dot stereograms. International Journal of Psychophysiology, 48, 35-42.
Kimmel, R. (2002). Three-dimensional shape reconstruction from autostereograms and stereo. Journal of Visual Communication and Image Representation, 13, 324-333.