Colour, form, and movement are not perceived simultaneously

Behavioural, neuro-anatomical and clinical evidence suggests that different aspects of the visual scene are processed separately, but the extent to wh ich the processing is carried out along segregated and independent parallel pathways is still debated. Moreover. it is also unclear whether these aspe cts are processed at the same rate. and their neural correlates reach consc iousness at the same time. An experiment investigated this issue in the cas e of three attributes of 2D displays: colour, form, and movement. There wer e three conditions. one for each possible pairing of these attributes. Stim uli were combinations of two values for each attribute (red/green, circle/s quare. fixed/moving). In each condition the Stimuli changed twice in close temporal succession, each attribute switching asynchronously between the tw o possible values. The observer's task was to report which change had occur red first. Response probabilities were computed for 13 values of the asynch rony, and transformed into estimates of perception time with the help of a psychophysical model. The results showed that colour and form are processed almost simultaneously. By contrast, movement perception is delayed by abou t 50 ms. The implications of these findings vis vis the so-called perceptua l binding problem are discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.