The limits of top-down control in visual selection.

Jan Theeuwes

Vrije Universiteit, Amsterdam

Even though it is undisputed that prior information regarding the location of a target affects
visual selection in a top-down way, the issue whether information regarding non-spatial features such
as color and shape has similar effects has been a matter of debate since the early 1980's. In this talk I
will show that visual selection is affected by a top-down set for spatial information but not by top-down
set for non-spatial information. So knowing where the target is affects perceptual selectivity; knowing
what it is does not help selectivity.

Furthermore, perceptual sensitivity can be enhanced by non-spatial features but only through a
process related to bottom-up priming. On the basis of these experiments we conclude that top-down
control for non-spatial information cannot modulate the initial sweep of information through the brain.
This suggests the first feedforward sweep is bottom-up and not biased by top-down information. We
assume that the modifications of the initial bottom-up saliency map through recurrent processing is the
way top-down control is implemented in the brain.