Electrical responses reveal the temporal dynamics of brain events during involuntary attention switching.

Surviving in the natural environment requires the rapid switching of attention among potentially relevant stimuli. We studied electrophysiologically the involuntary switching time in humans performing a task designed to study brain mechanisms of involuntary attention and distraction (C. Escera et al., 1998, J. Cogn. Neurosci., 10, 590-604). Ten subjects were instructed to discriminate visual stimuli preceded by a task-irrelevant sound, this being either a repetitive tone (P = 0.8) or a distracting sound, i.e. a slightly higher deviant tone (P = 0.1) or an environmental novel sound (P = 0.1). In different conditions, the sounds preceded the visual stimuli by 245 or 355 ms. Deviant tones and novel sounds prolonged reaction times significantly to subsequent visual stimuli by 7.4 (P < 0.02) and 15.2 ms (P < 0.003), respectively. In addition to a mismatch negativity (MMN) and a positive-polarity, 320-ms latency, P3a event-related potential associated, respectively, with detection of the distracting sound and the subsequent orienting of attention to it, a late frontal negative deflection was observed in distracting trials. The peak latency of this brain response from sound onset was 580 ms in the 245-ms condition and 115 ms longer in the 355-ms condition (P < 0.001), peaking consequently at 340 ms from visual stimulus onset, irrespective of the onset of the distracting sound. We suggest that this late frontal negative response may signal over the scalp the process of reallocating attention back to the original task after momentary distraction, and therefore that recovering from distraction may take a similar shifting time as orienting attention involuntarily towards unexpected novelty.