THE AUDITORY TRANSIENT 40-HZ RESPONSE IS INSENSITIVE TO CHANGES IN STIMULUS FEATURES

TEN subjects were presented with tone pips occasionally interspersed w ith deviant tone pips of a higher frequency. The transient 40-Hz respo nse was insensitive to change in qualitative stimulus features. In con trast, stimulus changes elicited a later and slower event-related pote ntial, the mismatch negativity (MMN). As a response to changes in stim ulus features implies the existence of a memory system, and because ch anges in qualitative stimulus aspects do not activate the generator me chanisms underlying the 40-Hz response, the 40-Hz response can be diss ociated from memory mechanisms. Furthermore, the analysis of phase-loc ked (synchronous) and non-phase-locked (asynchronous) responses reveal ed that the 40-Hz response might be caused by the synchronization of a lready active oscillators.