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Sensation and Perception Sensation and Perception: Psych 115s

Puzzle #2: Drawing the Retinotopic Representation

Look at the simple stimulus at left with your right eye, fixating at the center of the crosshairs. Applying what you know about retinotopy and the representation of the visual world in primary visual cortex, draw the "neural image"-- the spatial pattern of activity evoked by flashing on this pattern-- as it would appear in your right primary visual cortex. (Note that the large circle and crosshairs denote the shape and location of the visual field, and are not part of the stimulus). Hint: Remember that the neural image is distorted.

Answer: There were three important components to drawing the retinotopic representation of the stimulus in visual cortex:
  1. Visual field separation: with fixation at the center of the cross-hairs, the left half of the stimulus would fall in the left visual field; right V1 would therefore only represent this half of the stimulus.
  2. Flip: the 'neural image' in V1, just like the retinal image, is flipped relative to the world. So, the left half of the stimulus should have been drawn upside-down (note that the characters themselves should be upside-down, not just the relative positions).
  3. Cortical magnification: remember that the cortical representation of the fovea-- the central few degrees of vision-- is disproportionately large relative to the periphery. So, the more central characters-- the '4' and the 'y'-- should have been draw relatively larger than the more peripheral characters (1,2,3,w,x,z).
Email: psych115s@psych.stanford.edu