Readiness to respond in a target detection task: pre- and post-stimulus event-related potentials in normal subjects.
Brain potentials were recorded from 12 normal subjects engaged in an auditory target detection task (target stimulus probability of 0.2, stimulus rate of 1 every 2 sec) when instructions were (1) to press a response button with the thumb of the dominant hand to each target or (2) to keep a mental count of each target. A pre-stimulus slow negative potential was identified before every stimulus except non-targets immediately after targets. The amplitude of the pre-stimulus negativity was significantly affected by task instructions and was up to 4 times larger during the button press than the mental count condition. In contrast, the amplitudes and latencies of the event-related components (N100, P200, N200 and P300), when slow potentials were removed by filtering, were not different as a function of press or count instructions. The immediately preceding stimulus sequence affected both the amplitude and onset latency of the pre-stimulus negativity; both measures increased as the number of preceding non-targets increased. The amplitude of the pre-stimulus negative shift to targets also increased significantly as RT speed decreased. The major portion of the pre-stimulus negative potential is considered a readiness potential (RP) reflecting preparations to make a motor response. The amplitude of the RP during the target detection task did not significantly lateralize in contrast to the RP accompanying self-paced movements.
Starr
A
A
Department of Neurology, University of California, Irvine 92717.
Sandroni
P
P
Michalewski
H J
HJ
D000328:Adult; D003265:Contingent Negative Variation / Q000502:physiology*; D004576:Electromyography; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011597:Psychomotor Performance / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D012016:Reference Values; D013647:Task Performance and Analysis