Influence of Encoding and Acoustic Similarity on the Ear Advantage and Lag Effect in Dichotic Listening

Abstract

Experiments with simultaneous and time lag dichotic listening conditions were used to test two hypotheses concerning the right ear advantage and lag effect in dichotic listening. One hypothesis is based on the similarity of acoustic spectra, and the other is based on a categorization of speech sounds as being either encoded or not encoded. Natural vowels and consonant-vowel syllables were used to obtain seven different types of speech stimuli: stop vowel syllables, fricative vowel syllables, stop burst noise, fricative noise, stop vowel transitions, fricative vowel transitions, and steady state vowels. The presentation conditions were monaural, simultaneous dichotic, and dichotic with interaural time delays of 15, 30, 60, and 90 msec. With monaural presentation, all stimuli were identifiable above chance levels. For the simultaneous dichotic condition, significant right ear advantages occurred for stop vowel syllables, fricative vowel syllables, stop burst noise, and steady state vowels. For the time lag conditions, stop vowel syllables, stop bursts, and fricative noise produced consistent lag effects, but steady state vowels produced consistent lead effects. In general, the results gave stronger support to the hypothesis of acoustic similarity than to the encoding hypothesis in that stop burst noise produced both a right ear advantage and a lag effect whereas consonant-vowel transitions produced neither a right ear advantage nor a lag effect.