, 2011). Together, these observations learn more make a strong case for the representation of the integral of the sensory signal plus noise, beginning ∼200 ms after onset of motion. This is

a long time compared to visual responses of neurons in MT and LIP, but remember, this is not a visual response. The RDM is not in the response field of the LIP neuron. The brain must establish a flow of information such that motion in one part of the visual field bears on the salience of a choice target in another location (Figure 3A). Below, we refer to this operation as “circuit configuration.” It is one of the mysteries we hope to understand in the next decade. It is unlikely to be achieved by direct connections from MT to LIP. It requires too much flexibility. Indeed, a cue at the beginning of a trial can change the configuration of what evidence supports what possible action. This is why we believe that even this simple task involves a level Selleck GDC-0449 of function that is more similar to the flexible operations underlying cognition than it is to the specialized

processes that support sensory processing. Recall that the behavioral data—choice and RT—support the idea that each decision terminates when the DV reaches a threshold or bound. A neural correlate of this event can be seen in the traces in Figure 3D, which shows the responses leading up to a decision in favor of the target in the response field (Tin). The responses achieve a stereotyped level of firing rate 70–100 ms before the eye movement. So the bound or threshold inferred from the behavior has its neural correlate in a level of firing rate in LIP. This holds for Sitaxentan the Tin choices, but not when the monkey makes the other choice. The idea is that this is when the firing rate of another population of LIP neurons—the ones with the other choice target in their response fields—reach a threshold. One implication

is that the bounded evidence accumulation is better displayed as a race between two DVs, one supporting right and the other supporting left, as mentioned earlier (Figure 2B). This is convenient because it allows the mechanism to extend to decisions among more than two options (Bollimunta et al., 2012, Churchland et al., 2008, Ditterich, 2010 and Usher and McClelland, 2001). It is just a matter of expanding the number of races. With a large number of accumulators the system can even approximate direction estimation (Beck et al., 2008, Furman and Wang, 2008 and Jazayeri and Movshon, 2006). A race architecture also introduces some flexibility into the way the bound height is implemented in the brain. In behavior, when a subject works in a slow but more accurate regime, we infer that the bound is further away from the starting point. Envisioned as a race, the change in excursion can be achieved by a higher bound or by a lower starting point. It appears that the latter is more consistent with physiology (Churchland et al., 2008).