Behavioral and Brain Sciences

Open Peer Commentary
Pessoa et al.: Perceptual completion

The level of filling-in and when it is cognitive

Richard L. Gregory a1
a1 Department of Experimental Psychology, University of Bristol, Bristol BS8 1TN United Kingdom


This informative and conceptually stimulating target article is very useful. I merely query whether the term “illusory contours” is appropriate for gap filling; “illusory surfaces” seems better – and “fictional surfaces” better still. These seem to be rule based rather than knowledge based, suggesting indeed the importance of distinguishing rules (analogous to syntax in language) from knowledge (equivalent to semantics) for classifying perceptual phenomena.