Amplitude and phase-shift effects on dichotic listening performance.

OBJECTIVE: Previous dichotic listening (DL) studies have shown that interaural amplitude or phase shifts have powerful effects on dichotic ear advantage. However, it is not known how these two factors interact. The present study aims to explore this interaction when amplitude (intensity) and phase (time) shifts occur simultaneously.

DESIGN: Participants listened to dichotically presented pairs of consonant-vowel syllables (216 trials) under nine different experimental conditions, systematically varying amplitude (+9 dB) and phase (+35 ms) shifts. Participants reported which syllable they perceived on each trial.

STUDY SAMPLE: Thirty-two healthy adults.

RESULTS: The results showed an expected right ear advantage (REA) in the baseline (nosound manipulation) condition. While amplitude shifts favoring the right ear were found to have a greater effect on REA than phase shifts, phase shifts favoring the left ear were found to have a greater effect on left ear advantage (LEA) than amplitude shifts. Furthermore, phase shifts favoring the left ear had a greater effect on LEA than phase shifts favoring the right ear on REA.

CONCLUSIONS: Present results may have consequences for the training of individuals with auditory and phonetic difficulties, e.g. auditory processing deficits or dyslexia, by aiding the design of optimal combinations of acoustic and phonetic training tools.