Stimulus-dependent ear asymmetry in a dichotic monitoring task

Auditory lateralization was investigated in 26 right-handed and 26 left-handed, normal subjects using two dichotic monitoring tasks in each proband [dichotic consonant-vowel (CV) syllable monitoring once with the syllable /ta/ and once with the syllable /da/ as target]. Subjects were instructed to monitor for the presence of a target CV which could occur in either ear. They responded by depressing a response button; reaction time (RT) and hit rates were recorded. In right-handers the syllable /ta/ presented to the right ear was detected more frequently, on the average, than presented to the left ear. Also, RT was shorter for detection of /ta/ in the right ear than for detection in the left ear for both right- and left-handers. The detection of /da/ showed no ear advantage in hit rate and RT either for right-handers or for left-handers. These results demonstrate the existence of a right-ear advantage in dichotic monitoring of the target syllable /ta/ but not for the target syllable /da/. This difference in evoking a right-ear advantage is attributed to a difference in the difficulty of detection of both targets. It is argued that the detection of /da/ is too difficult to evoke phonetic processing, leading to a right-ear advantage.