Monaural ear differences for reaction times to speech with a many-to-one mapping paradigm

On each trial, subjects were presented monaurally with single synthetic speech syllables. In Experiment I, when /ba/ and /ta/ specified one response, and /da/ and /ka/ another response, a right-ear advantage in reaction time was observed; when/ba/ specified one response and all the other stimuli specified the other response, no ear effect was observed. Unsuccessful attempts to obtain a monaural right-ear advantage for consonants in some reaction-time tasks might be due to some kind of prephonetic matching between a representation of the stimulus attended to and the presented stimulus, the output of this match providing sufficient information for response. In Experiment II, /bi/ and /b ? / specified one response and /b?/ and/bu/ the other response, but no ear effect was observed. It was concluded that the right-ear advantage displayed for consonants in the corresponding condition of Experiment I was not the pure effect of a particular stimulus-response mapping, but depended also on the phonetic properties of consonants.