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Abstract:
Finding a target among uniformly oriented non-targets is typically faster when this target is perpendic-
ular, rather than parallel, to the non-targets. The V1 Saliency Hypothesis (V1SH), that neurons in primary
visual cortex (V1) signal saliency for exogenous attentional attraction, predicts exactly the opposite in a spe-
cial case: Each target or non-target comprises two equally sized disks displaced from each other by 1.2 disk
diameters center-to-center along a line defining its orientation. A target has two white or two black disks.
Each non-target has one white disk and one black disk, and thus, unlike the target, activates V1 neurons
less when its orientation is parallel rather than perpendicular to the neurons’ preferred orientations. When
the target is parallel, rather than perpendicular, to the uniformly oriented non-targets, the target’s evoked
V1 response escapes V1’s iso-orientation surround suppression, making the target more salient. I present
behavioral observations confirming this prediction.
