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Abstract:
Extensive studies have shown that the stimulus-evoked neuronal activity in area MT is causally related to motion perception. Yet little is known about how ongoing (pre- and inter-stimulus) activity in area MT influences the subjects ability to perceive and respond to stimuli. Here we ask whether the activity level of area MT preceding stimulus onset has an influence on the subjects psychophysical performance during physically identical, but perceptually ambiguous visual stimulation. Two rhesus monkeys were well trained to indicate the perceived direction of rotation of bistable structure-from-motion (SFM) stimuli by pulling one of two levers. During this task, multi-channel multi-unit activity (MUA) and local field potentials (LFP) were recorded from area MT while monitoring the animal‘s psychophysical performance and response times.
We investigated the effect of trial-to-trial differences in prestimulus activity (MUA and LFP) on the variability of psychophysical performance. We found that the level of prestimulus alpha and gamma power as well as MUA are significantly correlated with response times. This correlation between response times and the level of ongoing neuronal activity was found to be positive. In other words, the lower the power of the MUA and alpha and gamma LFP, the shorter it took the animal to report the perceived rotation of the ambiguous stimulus. These findings suggest that the state of area MT before stimulus onset can predict to some extent the subjects psychophysical performance in a perceptual task.
