, 2011). Consistent with this interpretation, increasing accuracy was accompanied by decreasing response time to the go signal. In addition, it is critical to note that maximal performance in go-signal tasks never exceeded performance in the equivalent RT paradigm. Thus, go signals can reduce accuracy when it is not fully anticipated, but cannot increase accuracy. Finally, when plotting accuracy conditioned on odor sampling duration, we observed no relationship between time to peak and difficulty
for individual animals ( Figure S5), as might be expected from integration. In sum, the effects of go-signal delay on performance accuracy and RT are parsimoniously explained as effects of go-signal anticipation but are not easily explained as effects of integration time. Temporal expectation can be considered an orientation or allocation of “attention in time” (Griffin et al., 2001; Nobre, 2001; Correa et al., 2006). Most studies of attention Y-27632 datasheet in time involve anticipation of a brief stimulus cue at a random time interval.
Such temporal attention has been shown to modulate activity in neocortical neurons (Ghose and Maunsell, 2002; Janssen and Shadlen, 2005; Jaramillo and Zador, 2011). Our protocol differed from such studies in using a constant stimulus presentation in conjunction with a temporally randomized response signal. Therefore go-signal anticipation effects might act at the stage of motor preparation and execution as opposed to sensory processing (McDonald et al., 2000; Correa MEK inhibition et al., 2006). These data have some potential implications with respect to possible sensory integration processes operating during olfactory categorization decisions. First, it is important to note that an odor sampling duration
of 300 ms does not imply 300 ms of integration. RTs also include “nondecision time” representing delays from sensory and motor processes that do not contribute to integration. It is typical in RT models Carnitine dehydrogenase to include delays of 200–300 ms or more (Luce, 1986; Mazurek et al., 2003). Although the length of nondecision times are not easy to estimate independently, molecular manipulations of olfactory bulb circuitry can lead to increases or decreases in sensory neural responses on the order of 100 ms (Abraham et al., 2010). Assuming 100–150 ms motor delays, only 50–100 ms would remain for integration processes within the 300 ms OSD. A measurement more directly related to integration time is the change in RT from the easiest to most difficult stimulus. The small difference we observed, 30 ms, is consistent with the conclusion that nondecision delays make up the bulk of a 300 ms RT and that the incoming signal strength is high relative to the “bound” or threshold of evidence so that a decision is reached relatively quickly. As discussed above, part of this 30 ms difference might also result from motivational differences between easy and difficult stimuli.