When time is up: CNV time course differentiates the roles of the hemispheres in the discrimination of short tone durations.

Numerous studies have suggested that the CNV (contingent negative variation), a negative slow wave developing between a warning and an imperative stimulus, reflects, among other things, temporal processing of the interval between these two stimuli. One aim of the present work was to specify the relationship between CNV activity and the perceived duration. A second aim was to establish if this relationship is the same over the left and right hemispheres. Event-related potentials (ERPs) were recorded for 12 subjects performing a matching-to-sample task in which they had to determine if the duration of a tone (490 ms, 595 ms, 700 ms, 805 ms, and 910 ms) matched that of a previously presented standard (700 ms). CNV activity measured at the FCZ electrode was shown to increase until the standard duration had elapsed. By contrast, right frontal activity increased until the end of the current test duration, even when the standard duration had elapsed. Moreover, for long test durations (805 ms and 910 ms), correlations were observed between CNV peak latency and subjective standard, over left and medial frontal sites. We propose that left and medial frontal activity reflects an accumulation of temporal information that stops once the memorized standard duration is over, while right frontal activity subserves anticipatory attention near the end of the stimulus.