Study of the relationship between degree of handedness and cerebral
lateralization for language using the Dichotic Speech Test

Sowmya M¹, Kanchana Bobby²
Department of Physiology, ¹Karpagam Faculty of Medical Sciences and Research, Othakkalmandapam,Coimbatore, ²Coimbatore Medical College, Coimbatore, Affiliated to the Tamil Nadu Dr. MGR Medical
University, Chennai, Tamil Nadu, India

  • Background: Dichotic listening is a procedure in which both ears are stimulated simultaneously with different speech sounds and the listener is required to report what was heard. An Ear Advantage (EA) score is then calculated based on the responses. This test is used as a method of assessment of hemispheric lateralization for language. Language and handedness are closely related. Handedness is quantitatively assessed by Laterality Quotient (LQ) calculated using Edinburgh Handedness Inventory (EHI).
  • Aim: The aim of this study was to examine the relationship between LQ and the magnitude of the EA scores for dichotic listening in right handed individuals.
  • Materials and Methods: After outliers and anomalous results were removed, the total sample size was 150 right-handed subjects (79 males and 71 females aged between 18 to 35 years). Handedness was confirmed and quantified using the EHI which is a validated questionnaire consisting of 20 questions related to hand preference for certain uni-manual tasks. Handedness Consonant-Vowel (CV) syllables (Ba, Da, Ga, Ka, Pa, Ta), recorded in a uniform male voice and digitally mixed in pairs using the software Audacity®, were delivered in random order. The EA score was calculated. Statistical analysis was done using SPSS 20.
  • Results: There was a significant positive correlation between LQ and EA (Pearson’s R=0.568, p<0.05), with males having a stronger correlation.
  • Conclusion: Our study revealed a positive correlation between LQ and EA implying that the stronger and more consistent the handedness, greater was the cerebral lateralization for language with this effect being higher in males.

Keywords: dichotic listening, dominance, handedness, lateralisation