Abstract: he effects of category mixing and prior target category knowledge on preview search were investigated in the present study. The categorical stimuli were Chinese and Arabian numbers in magnitudes from two to nine. Subjects’ task was to detect a target number (three or seven in two kinds of numbers). The experimental method was a preview search paradigm. In some conditions, subjects were told the target’s category; in others, they were not. The results showed that: a) Foreknowledge of the target’s category produced large improvement in search (Experiment 1); b) The magnitude of this anticipatory effect was reduced if the target shared its category with a single categorical set of previewed numbers (Experiment 2); c) The magnitude of this effect was greatly increased when the target didn’t share its category with a single categorical set of previewed numbers (Experiment 3). The implications of these results for current theories on visual selection were discussed

Key words: visual selective attention, preview effect, categorical representation, activation, inhibition