Intensities Difference in Dichotic Listening Tasks

Résumé

A wealth of previous studies have continuously demonstrated that when consonant-vowel (CV) nonsense syllables are simultaneously presented to normal hearing subjects in a dichotic listening task, a significant hemispheric asymmetry will be reflected from reported scores. That is when speech is used as a dichotic stimuli, a right ear advantage (REA) results. While functional hemispheric asymmetry has received supporting evidence from electrophysiological animal study as well as anatomical and physiological evidence in man, the actual size of the right ear advantage has varied from study to study. One parameter of dichotic listening tasks which have produced inconsistent differences between right and left ear scores as well as overall performance, may be attributed to changes in the intensity presentation level. Depending on the intensity level used, a wide variance in ear score differences have been observed. To date, presentation intensities have been based on absolute sound pressure levels (SPL). As an alternative to this procedure, the use of the most comfortable loudness levels (MCL) have been suggested. Recently, data have provided results which indicated that MCL is clinically feasible, statistically reliable and provides the intensity presentation level that would produce maximum speech discrimination. To date, incorporation of MCL as a presentation level in dichotic listening studies has not been explored. Due to the variance in ear scores derived under different levels of stimulus presentation, it was the purpose of this study to determine if the use of MCL as a presentation intensity could be demonstrated to be a viable alternative to absolute intensity levels in dichotic listening tasks.