Gender differences in a dichotic listening and movement task: lateralization or strategy?

Although the dichotic listening procedure has been used as a non-invasive neuropsychological technique for assessing laterality of speech perception, it has tended to underestimate the proportion of the right-handed population that is left-hemisphere lateralized for speech perception [Segalowitz SJ, Bryden MP. Individual differences in hemispheric representation of language. In: Segalowitz SJ (Ed.), Language Functions and Brain Organization. Toronto: Academic Press, 1983, pp. 341-72]. These underestimations may be due to traditional dichotic procedures being susceptible to attentional biases, order of report effects, and/or memory effects that obscure functional differences between the cerebral hemispheres. In the present study, we used an adaptation of the dichotic listening procedure that was designed to be less sensitive to these confounding effects. Participants were required to move as quickly as possible to one of the two color-coded targets following verbal cues presented via headphones. Conditions of cue-word presentation were monaural, (e.g. 'blue' in one ear and a blank track in the other), dichotic-same (e.g. 'blue' in both ears), and dichotic-different (e.g. 'green' in one ear and 'blue' in the other). Ninety-three percent (26 of 28) of the participants demonstrated a right ear advantage (REA) for correct responses. There was also a REA for reaction time, movement time, and the total response time. The pattern of reaction time and movement errors, however, suggest that gender differences found utilizing this dichotic procedure may be due to differences in strategic approach to the task rather than to differences in cerebral laterality. Overall, results suggest that this new adaptation of the dichotic listening procedure is very sensitive to lateralization for speech perception.