MISMATCH NEGATIVITY IN DICHOTIC-LISTENING - EVIDENCE FOR INTERHEMISPHERIC DIFFERENCES AND MULTIPLE GENERATORS

The characteristics of mismatch negativity (MMN) elicited by dichotic stimulation were examined using frequency-deviant stimuli presented to the right, to the left, or to both sides. The experiment was run twic e, once using earphones and once using loudspeakers in free field. Wit h both modes of stimulation, deviants presented in the left, right, or both ears, or tones that were switched between ears, elicited compara ble MMNs, with a peak latency of about 180 ms. With earphones, the amp litude of the MMN was bigger at the frontal-lateral right hemisphere s ites than at the homologous left-hemisphere sites for all deviance con ditions. Scalp current density analysis revealed that deviance in the right side elicited bilaterally equivalent frontal current sinks and a trend towards stronger contralateral current sources at the mastoid s ites. In contrast, left side deviance elicited frontal sinks and tempo ral current sources stronger over the right hemiscalp. These results a re compatible with the multiple-generator model of MMN. The attention- related role of the MMN is discussed, suggesting comparable attention mechanisms for vision and audition.