A CNV rebound effect.

Fifty normal volunteers were tested in two conditions: (1) a constant-foreperiod reaction time situation consisting of a flash-tone-key press sequence (control trials); (2) a '50%-letters' condition, in which two types of trials occurred randomly--no letters trials, which were identical to control trials, and letters trials, which were similar to control trials but also involved the presentation of four auditory letters within the flash-tone interval as part of a short-term memory task. Compared to control trials, CNV amplitude showed a pattern of reduction in letters trials accompanied by slower reaction times to tone (CNV distraction effect). Compared to control trials, CNV amplitude showed an unexpected supranormal increase in no-letters trials. The CNV rebound effect observed in no-letters trials was interpreted as reflecting a switching of attention from the divided attention set intrinsic to letters trials (listening for letters and preparing for response to tone) to an undivided attention set in no-letters trials (simply preparing for response to tone). The CNV rebound effect, which is diminished in aging individuals and absent in psychosurgery patients, appears to represent a non-invasive technique of possible value in assessing pathophysiology of human brain functioning.