Authors:

SHTYROV, Y., Kujala, T. & PULVERMULLER, F.

Reference:

Year of publication:

2007

CBU number:

6624

Abstract:

The mismatch negativity (MMN) reflects activation of neural memory traces for spoken words. Memory trace activation leads to an enhanced MMN response to meaningful words as opposed to senseless matched pseudowords. This lexical MMN enhancement was found in passive oddball designs and was therefore suggested to be automatic and attention-independent. To test this, we systematically varied the level of attention by using a stimulus detection task and recorded MMN responses to a set of phonologically and acoustically balanced words and pseudowords using a multi-deviant paradigm. Under non-attend conditions, the word-elicited MMN (peaking at ~120 ms after the words could be uniquely recognized) was significantly larger than that to pseudowords, confirming early activation of lexical memory traces. However, when attention was directed towards the stimuli, such word-pseudoword difference in the MMN was not any longer present, even with a trend to pseudoword advantage at ~190ms. Whereas MMNs to words seemed unchanged by attentional variation, the first phase of the pseudoword response was significantly enhanced by attention. At later times, attention significantly modulated a positive deflection at ~230ms and a second negative wave at ~370ms for all stimuli. The data indicate that the early word processing is not affected by attentional demands and may thus indeed be automatic with attention effects on lexical processing accumulating at latencies above ~200ms. Lexical enhancement of the MMN seems specific to conditions where the subjects’ attention is directed away from the stimuli. These effects may be explained in terms of the strength of cortical feedback control.