, 2009). This suggests that inefficiencies

in sensory pooling and decision making play a large role in explaining the difference in performance accuracy for focal and distributed cue trials. We propose a particular example of a model that exhibits such inefficiencies, which we call the “selection model.” The selection model pools sensory responses across the four stimulus locations according to a max-pooling rule (it weighs Cyclopamine ic50 the largest response the most). This ensures that decisions on focal cue trials are based primarily on responses to the target stimuli (which are larger than responses to nontargets because the baseline responses are larger for attended stimuli), leading to good behavioral performance. On distributed cue trials, one of the nontarget stimuli evokes the largest responses (noting that in our experimental protocol one of the nontargets typically had a higher contrast than the target). Max pooling thereby causes decisions to be based primarily on irrelevant sensory signals corresponding to incorrect locations, leading to correspondingly poor behavioral performance. We begin by considering attentional selection via max pooling in a focal cue trial. Epigenetic inhibitor Figure 7A shows simulation results, idealized sensory response distributions for the two intervals in the task at each of the four

target locations. Each location Phosphoprotein phosphatase elicited some response as measured by the contrast-response function for target and nontarget stimuli. Only the target location had an actual difference in mean response between the two intervals (because there was a contrast increment added only at this location). For these simulations, the means of the sensory response distributions in Figure 7 were set to be the mean fMRI

response amplitudes (from V1) for the target and nontarget locations, and the standard deviation of the sensory response distributions was set to the best-fit value from the sensitivity model fit (see above, Testing Sensory Noise Reduction) for the focal cue condition. To readout the responses, the max-pooling operation weighted responses differently depending on their relative amplitude (Figure 7B): equation(1) Rp=14∑i=14rikk,where ri was the response at each of the four stimulus locations, Rp was the pooled readout of the responses, and k was a model parameter that changed the pooling operation from averaging (k = 1) to maximizing (k = ∞). With a large k, the largest amplitude response dominated the readout distribution from which the decision was made. For focal cue trials, attention served to boost the target response above the nontarget responses, and therefore, the readout distribution was dominated by the response to the target (i.e.