Role of subvocal motor activity in dichotic speech perception and selective attention

Twenty right-handed male and female subjects were asked for ear-by-ear recall of dichotically presented consonant--vowel syllables. Stimuli within each dichotic pair were contrasted on the features on voicing and/or place, or were differentiated by manner of production. While listening to the stimuli, the subjects were required to concurrently reduce the electromyographic subvocal activity recorded from the lips and throat or from a control site, the frontalis muscle. A right-ear advantage was observed during the control condition, the largest advantage occurring when the pairs were contrasted on both voicing and place. In contrast, a left-ear advantage was observed when subvocal articulatory activity was voluntarily reduced. These results suggest that subvocal articulatory activity contributes to the observed right-ear advantage for speech by affecting attentional bias and not phonetic processing. Possible underlying mechanisms for this effect are discussed.