Influence of Alignment Strategies and Consonant Acoustic Features on Laterality Index in Dichotic Testing in Indian...

The right ear advantage (REA) observed for dichotic CV (DCV) testing in Indian languages is seen to be smaller compared with the observations in several studies in English and other languages.

The present study aims to explore whether the differences in the temporal alignment of consonant-vowel (CV) stimuli used for the dichotic task is a contributing factor that can explain the smaller REAs observed in Indian languages.

The study compared the laterality index (LI) values between DCV test results obtained using CV stimuli that were temporally aligned at the acoustic onset versus the burst onset, with 0 milliseconds lag between the right and left ears.

A total of 50 right-handed individuals (native speakers of Kannada language) in the age range of 17 to 30 years with normal hearing sensitivity participated in the study.

The participants' responses to the two sets of DCV stimuli were recorded and compared. LI was calculated for the overall scores as well as for specific voiced and unvoiced segment combinations. To test the reliability of the findings, 10 of the participants were re-tested using the same stimuli and the data were checked for reliability.

The overall LI was 15.1% for the stimuli temporally aligned at the burst onset, whereas it was 5.7% for the stimuli temporally aligned at the acoustic onset. The difference in LI was not significant between the alignment conditions for unvoiced-unvoiced and voiced-voiced CV combinations, but this difference was significant for the unvoiced-voiced and voiced-unvoiced CV combinations. Comparing test and re-test scores showed good reliability.

The results support our hypothesis that smaller REA observed in DCV task in Indian languages was due to the temporal alignment of CV stimuli. In the acoustic-onset-aligned condition, presenting pairs contrasting in the voicing feature tends to cancel out a relative ear advantage.