Visual mismatch negativity elicited by facial expressions under non-attentional condition.

A modified "cross-modal delayed response" paradigm was used to investigate putative processing of face expression in the absence of focused attention to the face. Neutral, happy and sad faces were presented during intervals occurring between a tone and a response imperative signal (a faint click), while subjects were instructed to discriminate the location of the tone as quickly and accurately as possible and to ignore the faces. A neutral face was presented in 80% of the trials whereas the happy and sad faces were presented in the remaining trials - 10%, respectively. Expression mismatch negativity (EMMN) was obtained by subtracting the ERP elicited by neutral faces from that elicited by sad faces or happy faces. The EMMN started from around 120 ms (sad) and 110 ms (happy) lasting up to 430 ms (sad) and 360 ms (happy) post-stimulus. The EMMN elicited by sad faces was more negative than that elicited by happy faces. Both EMMNs distributed over posterior areas and covered larger areas in the right than in the left hemisphere sites (especially for happy EMMN).