Second, at each point in time, the prior probability, p(sx,t+1)p(sx,t+1), is updated from the posterior probability at the previous point in time, p(s|νx,t)p(s|νx,t), smoothed by a Gaussian function, h(x) (see Experimental Procedures), representing the diffusion of an object or edge due to the random walk movement of fixational drift eye movements. The integral of h(x) was less than

1, reflecting the occasional possibility of saccadic eye movements that redirect gaze to a different image location. When presented with a brief strong stimulus—35% contrast—on a background of weak input—5% contrast—this optimal model maintained a spatiotemporal BVD-523 solubility dmso bias, predicting an increased probability that a signal was present outside of the spatial range of the object, even after the object was no longer detectable (Figure 6C). This optimal behavior was qualitatively similar to the sensitizing field we observed in Off cells (Figure 1). We compared how

the changes in the response function during sensitization corresponded to the changes expected from this framework of ideal signal detection. The effect of a changing prior value, p  (s  ), on the posterior probability, p(s|ν)p(s|ν), depends upon the buy MLN8237 shapes of p(ν|s)p(ν|s) and p(ν|η)p(ν|η). For the case where p(ν|s)p(ν|s) and p(ν|η)p(ν|η) are both Gaussian with

a different width, when p(s) decreases, the slope decreases, the threshold decreases, and the baseline increases, Calpain reflecting the increased bias toward the presence of the signal ( Figure 6B). After a transition to low contrast, sensitization, by definition, consists of a decrease in threshold (Kastner and Baccus, 2011). By intracellularly recording from sensitizing ganglion cells, we found that an increased baseline of the nonlinearity accompanied the decreased threshold during L  early ( Figure S3B). This depolarization was 35% ± 18% of the membrane potential SD during L  late (n = 3). Finally, even though sensitization decreases the threshold during L  early, it also decreased the slope in the spiking nonlinearity, as measured from extracellular recordings ( Figure S3C). This indicates that sensitization differs from changes in sensitivity due to adaptation, where the slope increases when the threshold decreases ( Baccus and Meister, 2002). In the model, the decrease in slope occurs because of the bias conferred by an increased p  (s  ). When a signal is more likely, a greater influence on p(s|ν)p(s|ν) comes from the prior probability, p(s), and a smaller influence comes from the new input, ν.