ISCA Workshop on Plasticity in Speech Perception (PSP2005)
Senate House, London, UK
One of the main advantages of using a dichotic listening task to investigate hemispheric lateralisation to auditory stimuli is that since there is ipsilateral suppression of the auditory pathways (Bryden, 1988), any lateralised response is more pronounced. Dichotic listening tasks using speech sounds have often shown a right-ear advantage, indicating left-hemisphere dominance (Schwartz and Tallal, 1980). An objective measure of brain laterality can be obtained by measuring auditory evoked potentials and obtaining a measure of the mismatch negativity (MMN); a cortical brain response elicited by a deviant sound presented occasionally in a sequence of standard sounds. The aim of this study was to investigate the extent of left and right hemisphere contribution to MMN strength, for both meaningful words and meaningless pseudowords, using a dichotic presentation. The task was a dichotic version of a paradigm devised by Shtyrov and Pulvermuller (2002). The meaningful word and meaningless pseudoword stimuli were bisyllables with identical first syllables and different second syllables. 10 normal-hearing, right-handed subjects were presented with a repeating standard (meaningless pseudoword) to both right and left ears at a probability of 0.8, with a deviant (a meaningful word, OR meaningless pseudoword) presented at a probability of 0.1 in the left OR right ear. The MMN was calculated by subtracting the response of the standard stimulus from that of the deviant stimulus after the onset of the second syllable. Results indicate that left hemispheric activity is greater for a meaningful word (baby or lady) than for a meaningless pseudoword (bady, bagy or laby, lagy). Furthermore, a left-right hemispheric difference was seen only when the second syllable created a meaningful word.
Bibliographic reference. Yasin, Ifat / Bishop, Dorothy (2005): "An objective measure of hemispheric differences in processing dichotic meaningful words and meaningless pseudowords as indexed by mismatch negativity", In PSP2005, 63 (abstract).