, 1998), V4 (Mazer and Gallant, 2003), and FEF (Serences and Yantis, 2007 and Thompson and Bichot, 2005). However, neural activities in all these areas are also involved in top-down attentional direction. It is therefore unclear whether the observed neural correlates of saliency are relayed

from brain regions upstream along the visual pathway, and whether they are the cause or the consequence of selection. In particular, because salient visual inputs typically enter awareness, it is difficult to determine whether the observed neural activities represent saliency as such, as opposed to being caused by the consequent perception of the selected stimuli. A dominant view of the saliency map (Itti and Koch, 2001, Koch and Ullman, 1985 and Wolfe, 1994) presumes that saliency selleck chemical results from pooling different visual features, being independent of whether the feature distinction making a location salient is in color, orientation, or other features. Hence, previous attempts to find the saliency map have typically concentrated in higher cortical areas, particularly the parietal cortex, whose neurons, unlike those in primary visual cortex (V1), are less selective to specific visual features. By contrast,

buy PD98059 Li, 1999 and Li, 2002 proposed that V1 (which, notably, projects directly and indirectly to all the previously proposed brain regions for the saliency map [Shipp, 2004]) creates a saliency map via intracortical interactions that are manifest in contextual influences (Allman et al., 1985). According to this theory, the saliency of a location is monotonically related to the highest neural response among all the V1 cells that cover that location

with their spatial receptive fields (relative to the V1 responses to the other locations), regardless of of the preferred feature of the most responsive neuron. Many psychophysical predictions arising from this proposal have been confirmed (Koene and Zhaoping, 2007 and Zhaoping and May, 2007). One particularly interesting confirmation is that an eye of origin singleton, e.g., a bar presented to the left eye among many other bars presented to the right eye, can distract attention away from a very salient visual search target (e.g., a uniquely oriented bar presented to the right eye), even when observers cannot distinguish this eye of origin singleton from other items (Zhaoping, 2008). This supports the V1 theory, because the reason that observers cannot distinguish this singleton is that the eye of origin feature is not represented in any cortical area except V1. Indeed, Wolfe and Franzel (1988) reported that observers found it impossible to find a visual search target defined by its unique eye of origin.