ABSTRACT
A unique vertical bar among horizontal bars is salient and pops out perceptually regardless of the observer’s goals. Physiological data have suggested that mechanisms in the primary visual cortex (V1) contribute to the high saliency of such a unique basic feature, but the data fail to indicate whether V1 plays an essential or peripheral role in input-driven or bottomup saliency. Meanwhile a biologically based V1 model has suggested that V1 mechanisms can also explain bottom-up saliencies beyond the pop out of basic features (Li, 1999a, 2002). For instance, the low saliency of a unique conjunction feature like a red-vertical bar among red-horizontal and greenvertical bars is explained under the hypothesis that the bottom-up saliency at any location is signaled by the activity of the most active cell responding to it, regardless of the cell’s preferred features such as color and orientation. While some recent experimental data have provided support for this V1 saliency hypothesis, higher visual areas such as V2 and V4 also contain neurons tuned to similar basic features that can pop out in the bottomup manner. Furthermore, previous saliency models can capture much of the visual selection behavior using generic rather than V1-specific neural mechanisms. It is therefore important to ascertain V1’s role in saliency by identifying visual selection behavior that shows specific identifying characteristics – that is, fingerprints – of V1 or other cortical areas. In this chapter, we present our recent findings on bottom-up saliency-based behavior of visual search and segmentation that directly implicate V1 mechanisms. The three specific fingerprints are: (1) an ocular singleton captures attention despite being elusive to awareness, (2) V1’s collinear facilitation is manifested in texture segmentation, and (3) there is a match between the redundancy gains in double-feature singleton search and V1’s conjunctive cells.
