Clocking perceptual processing speed

Abstract:

In situations that require a fast action in response to a sensory event, success depends on the interplay between perceptual and motor neural processes, both of which contribute to the total amount of time that a subject needs to respond. Although in most choice paradigms one can only measure this combined quantity, the reaction time, the perceptual and motor components can be accurately dissociated under certain conditions; the key is to present the relevant sensory information after the instruction to make a response. I will discuss tasks with this particular feature, in which psychophysical performance can be understood as the result of an ongoing motor program that is modified by the outcome of a perceptual process. This interaction is described quantitatively by simple phenomenological models in which saccade planning is conceived as a gradual build-up of oculomotor activity toward a threshold value, but such that the rising neural activity can be accelerated after the relevant sensory cue appears. This framework achieves three things: (1) it replicates and reconciles behavioral results in numerous experiments, (2) it shows that the detection and discrimination of high-visibility stimuli are extremely fast, requiring on the order of 25 ms of effective viewing time, and (3) it makes specific predictions about the neuronal activity that should be observed across a variety of experimental conditions.