Illusory Conjunctions of Color and Motion With Shape Following Bilateral Parietal Lesions

The primate visual system responds to shapes, colors, and various other features more strongly in some brain areas than others. However, it remains unclear how these features are bound together so that an object with all its attributes is perceived. A patient (R.M.) with bilateral parietal-occipital lesions has been shown previously to miscombine the shape and color of items, making errors known as illusory conjunctions (ICs). In this study, we examined the effects of a third feature (motion) on this patient's IC rates. R.M. was presented with two letters that moved in different ways. He often reported seeing the shape of one of the letters with the other letter's motion. His performance on the same task with three features shows that correctly combining two features did not necessarily lead to correctly binding the third. These data support modularity of feature representations in the human brain and provide supporting evidence that spatial representations associated with the parietal lobe are necessary for normal feature integration.