STIMULUS-DURATION AND THE SENSORY MEMORY TRACE - AN EVENT-RELATED POTENTIAL STUDY

The mismatch negativity (MMN) of the auditory event-related potential is elicited when a stimulus deviates from that represented by the neural memory trace developed by preceding stimuli. The effect of stimulus duration on this trace was studied by presenting sequences of 1000 Hz, 80 dB stimuli to subjects engaged in silent reading. Stimuli were, in different blocks, either of 4, 10, 30, 100 or 300 ms in duration. 5% of the stimuli were deviants which were either higher in frequency (1050 Hz) or lower in intensity (70 dB) than the standards. The ''silent'' period between two successive stimuli was constant at 300 ms. The minimum stimulus duration with which a distinct MMN was elicited by frequency deviants was 30 ms, but the MMN amplitude was not increased when stimulus duration was further prolonged. In contrast, the intensity MMN was elicited even with stimulus duration of 10 ms and its amplitude increased as a function of stimulus duration. Reaction times and hit percentages in response to these deviant stimuli in a separate discrimination task displayed analogous patterns of results.