Akaysha Tang, Barak Pearlmutter, Tim Hely, Michael Zibulevsky, Michael Weisend
Human reaction times during sensory-motor tasks vary consider(cid:173) ably. To begin to understand how this variability arises, we exam(cid:173) ined neuronal populational response time variability at early versus late visual processing stages. The conventional view is that pre(cid:173) cise temporal information is gradually lost as information is passed through a layered network of mean-rate "units." We tested in hu(cid:173) mans whether neuronal populations at different processing stages behave like mean-rate "units". A blind source separation algorithm was applied to MEG signals from sensory-motor integration tasks. Response time latency and variability for multiple visual sources were estimated by detecting single-trial stimulus-locked events for each source. In two subjects tested on four visual reaction time tasks, we reliably identified sources belonging to early and late vi(cid:173) sual processing stages. The standard deviation of response latency was smaller for early rather than late processing stages. This sup(cid:173) ports the hypothesis that human populational response time vari(cid:173) ability increases from early to late visual processing stages.