Laterality Effects in the Recall of Steady-State and Transient Speech Sounds

Abstract

The cues for discriminating fricatives are known to lie both in the spectrum of the friction itself and in the formant transitions into adjacent vowels. Although both these cues can vary acoustically with context, only the formant-transition cue is lateralized in dichotic listening. Steady-state fricatives, whether isolated or followed abruptly by a vowel were recalled equally well from either ear; however, when the appropriate transition was added there was an improvement in recall from the right ear, but no improvement from the left. This advantage for the right ear remained when the friction was removed but the transition left intact to give a stoplike sound. The right-ear advantage for recall of dichotically presented initial stops has been confirmed and a similar advantage found for both released and unreleased final stops. This latter effect is influenced by the relative onset times of the preceding vowels within a dichotic pair. By contrast, no preference for either ear could be found for isolated vowels of the same duration as the stop transitions (40 msec). These results indicate that speech sounds only give an advantage for the right ear in a dichotic listening task when they contain formant transitions.