RESUMEN
An oddball paradigm was used to elicit event-related potentials from 10 normal-hearing young adult subjects. The frequent signal (90% probability) was a 1000 Hz tone burst at 75 dB nHL and the oddball signal (10% probability) was a similar tone burst at 60 dB nHL. A mock or control condition in which both frequent and oddball signals were 60 dB nHL also was run. The subjects were given no instructions other than to lie quietly on a cot in a test booth. They were awake throughout the test session. The identical procedure was repeated in a second session at least 24 hr after the first. Subtraction of the frequent (60 dB nHL) from the oddball (60 dB nHL) averaged evoked potential (AEP) in the mock condition yielded virtually a straight line. However, subtraction of the frequent (75 dB nHL) AEP from the oddball (60 dB nHL) AEP revealed a negative difference that peaked at about 175 ms. Subtraction of either the frequent or the oddball AEP obtained in the mock condition from the 60 dB nHL oddball of the experimental condition also produced a negative peak at about 175 ms and, in addition, a smaller negative difference that peaked at about 75 ms. Observations were consistent across sessions.