The effect of voice-onset-time on dichotic listening with consonant-vowel syllables.

Dichotic listening (DL) is the most frequently used method to study language lateralization. The current study investigated the effect of voice-onset-time (VOT) in dichotic listening with consonant-vowel (CV) syllables. Eighty-nine subjects with normal hearing and overall right-ear-advantage (REA) were tested with a PC version of the DL test. Voiced and unvoiced stop-consonants were used in combination with the vowel /a/. This produced three syllables with short VOT /ba, da, ga/ and three syllables with long VOT /pa, ta, ka/. There were, therefore, four possible combinations of VOTs when the syllables were presented as dichotic pairs. These were short-long (SL), i.e. syllable-pairs with a short VOT in the left ear and a syllable with a long VOT in the right ear; and similarly long-short (LS), short-short (SS), and long-long (LL). The results showed that syllable pairs with long VOT presented in the right ear and short VOT simultaneously presented in the left ear, produced the largest REA. This was followed by the LL and SS conditions. The LS condition produced a significant left-ear-advantage (LEA). These results demonstrate that VOT significantly affects ear-advantage as observed in the DL test and suggest that VOT may be a more powerful determinant of DL performance than the classic REA effect. The findings are discussed within the framework of different hypotheses about speech laterality.