Asymmetric interaural generalization of learning gains in a speech-in-noise identification task

The pattern of generalization of learning gains to untrained conditions in adult human perceptual skill learning has been used as an effective behavioral probe for studying the functional organization of the learning system. Learning gains were previously reported to generalize symmetrically between the ears for tonal stimuli. However, given the open question concerning the specialization of the hemispheres in the processing of speech sounds, it is not clear whether symmetrical interaural generalization will follow training on such stimuli. Here the effect of monaural single-session training on the identification of consonant-vowel stimuli in noise was examined. Participants showed similar robust gains in performance at 24 h post-training in both trained ears. There was, however, an asymmetrical generalization of the learning gains from the trained to the untrained ear, with more transfer from the right-trained to the left-untrained ear than vice versa. Training and transfer gains were retained for both ears over an interval of several months, although for the untrained ear a brief exposure was necessary to relearn the task. These results provide first-time evidence for an asymmetry in interaural generalization for speech sounds following training and provide further support to the lateralization of speech sounds along the auditory system.