As predicted by the cbDDM, for trials in which subjects took more time to make a decision, the response in OFC generally increased with a shallower slope and commenced later in the trial. There was both a main effect of time (p =

0.024) and a condition-by-time interaction (p = 0.027), demonstrating faster rates of increase for shorter trials. Similar OFC time series profiles were observed when the analysis was restricted either to mixtures of the same difficulty level (Figure S4) or to correct trials only (Figure S5), supporting the rationale behind combining trials of different stimulus difficulty and further confirming DDM predictions. The current results suggest that humans integrate olfactory perceptual evidence in order to enhance perceptual decision-making. These findings were supported across two independent psychophysical experiments. First, in a fixed-sniff paradigm, choice accuracy improved NVP-BKM120 datasheet when subjects were given an opportunity to make more sniffs, especially

for difficult odor mixtures (Figure 1C). This behavioral profile accords with temporal integration. Second, in an open-sniff paradigm, a drift-diffusion model of integration accounted for the resulting RT distributions significantly better than did a nonintegrative (stochastic) model (Figure 3D). This effect was particularly A-1210477 supplier true when the simulation model incorporated decision bounds that collapsed over time (Figure 4). The use of two complementary paradigms was necessary to establish that information accumulates in the human olfactory system. In the open-sniff paradigm, subjects only make a choice once a decision bound is reached, effectively clamping performance accuracy. This has the benefit of generating RT distributions that can be compared to model-derived RT distributions, such as the DDM, to provide evidence for or against integration. However, the open-sniff task is unable to demonstrate the type of choice-accuracy profiles that would be in keeping with integration. On the other hand, in the fixed-sniff

paradigm, subjects make a response at a specified time, effectively disengaging their choices from a decision criterion. This has the potential benefit of eliciting behavioral accuracy profiles reflective of integration over time, although the resulting RT distributions (arising from imposed trial first lengths) cannot be used to model integrative processing mechanisms. Together these two paradigms provide converging evidence that the human olfactory system, like other sensory systems, can integrate perceptual information. Brain imaging data highlighted a corresponding fMRI signature of temporal integration in the OFC. Using a regionally unbiased approach, we found that odor-evoked activity in both right and left medial OFC conformed closely to integration profiles as predicted from the DDM (Figure 5). Specifically, time series increased at slower rates for longer trials, peaked at the time of decision, and had lower peaks for longer trials.