Effects of regular or irregular event schedules on cerebral hemovelocity during a sustained attention task

Transcranial Doppler sonography was used to measure bilateral cerebral blood flow velocity during sustained attention task performance where the background event schedule occurred in a synchronous (temporally regular) or asynchronous (temporally irregular) manner. Perceptual sensitivity was greater in the synchronous case and declined over time in both conditions. Blood flow velocity was greater in the more difficult asynchronous condition and declined over time in both conditions in the right hemisphere, but the decline in blood flow velocity was limited to the asynchronous condition in the left hemisphere. The results are interpreted in terms of a resource model of sustained attention.