Orienting attention in time. Modulation of brain potentials.

With the aim of casting light on the neural mechanisms that support our ability to modulate visual attention over time, we recorded event-related potentials (ERPs) while normal human subjects performed a target detection task with temporal contingencies between cue and target stimuli. The task used two central cues, which predicted (80% validity) when a subsequent target would occur (either 600 or 1400 ms after cue onset). Unlike previous tasks of attentional orienting, there was no spatial information provided and all stimuli were presented foveally. Reaction times and ERPs linked to targets presented at the shorter interval showed significant effects linked to attentional orienting. Reaction times were faster when the cues correctly predicted the cue-target interval, suggesting the ability of the brain to use information about time to deploy attentional resources. ERPs differed according to the predicted time interval. In particular, the P300 amplitude and latency were enhanced when the cue predicted the cue-target interval accurately. The ERPs elicited by the cues also differed according to the time interval that they predicted. Differences were observed in potentials linked to motor preparation and expectancies. The results reveal dynamic neural activity involved in orienting attention to time intervals, as well as the consequent modulation of target-related neural activity resulting from differing temporal expectations.