What characterizes changing-state speech in affecting short-term memory? An EEG study on the irrelevant sound effect.

The irrelevant sound effect (ISE) describes reduced verbal short-term memory during irrelevant changing-state sounds which consist of different and distinct auditory tokens. Steady-state sounds lack such changing-state features and do not impair performance. An EEG experiment (N=16) explored the distinguishing neurophysiological aspects of detrimental changing-state speech (3-token sequence) compared to ineffective steady-state speech (1-token sequence) on serial recall performance. We analyzed evoked and induced activity related to the memory items as well as spectral activity during the retention phase. The main finding is that the behavioral sound effect was exclusively reflected by attenuated token-induced gamma activation most pronounced between 50-60 Hz and 50-100 ms post-stimulus onset. Changing-state speech seems to disrupt a behaviorally relevant ongoing process during target presentation (e.g., the serial binding of the items).