Cross-modal transfer effects on visual discrimination depends on lesion location in the rat visual system

Transfer of auditory perceptual learning with spectrally reduced speech to speech and nonspeech tasks: implications for cochlear implants

OBJECTIVE

The objective of this study was to assess whether training on speech processed with an eight-channel noise vocoder to simulate the output of a cochlear implant would produce transfer of auditory perceptual learning to the recognition of nonspeech environmental sounds, the identification of speaker gender, and the discrimination of talkers by voice.

DESIGN

Twenty-four normal-hearing subjects were trained to transcribe meaningful English sentences processed with a noise vocoder simulation of a cochlear implant. An additional 24 subjects served as an untrained control group and transcribed the same sentences in their unprocessed form. All subjects completed pre- and post-test sessions in which they transcribed vocoded sentences to provide an assessment of training efficacy. Transfer of perceptual learning was assessed using a series of closed set, nonlinguistic tasks: subjects identified talker gender, discriminated the identity of pairs of talkers, and identified ecologically significant environmental sounds from a closed set of alternatives.

RESULTS

Although both groups of subjects showed significant pre- to post-test improvements, subjects who transcribed vocoded sentences during training performed significantly better at post-test than those in the control group. Both groups performed equally well on gender identification and talker discrimination. Subjects who received explicit training on the vocoded sentences, however, performed significantly better on environmental sound identification than the untrained subjects. Moreover, across both groups, pre-test speech performance and, to a higher degree, post-test speech performance, were significantly correlated with environmental sound identification. For both groups, environmental sounds that were characterized as having more salient temporal information were identified more often than environmental sounds that were characterized as having more salient spectral information.

CONCLUSIONS

Listeners trained to identify noise-vocoded sentences showed evidence of transfer of perceptual learning to the identification of environmental sounds. In addition, the correlation between environmental sound identification and sentence transcription indicates that subjects who were better able to use the degraded acoustic information to identify the environmental sounds were also better able to transcribe the linguistic content of novel sentences. Both trained and untrained groups performed equally well ( approximately 75% correct) on the gender-identification task, indicating that training did not have an effect on the ability to identify the gender of talkers. Although better than chance, performance on the talker discrimination task was poor overall ( approximately 55%), suggesting that either explicit training is required to discriminate talkers' voices reliably or that additional information (perhaps spectral in nature) not present in the vocoded speech is required to excel in such tasks. Taken together, the results suggest that although transfer of auditory perceptual learning with spectrally degraded speech does occur, explicit task-specific training may be necessary for tasks that cannot rely on temporal information alone.

Postoperative haptic training facilitates the retrieval of visual-based memories after visual cortex lesions in rats

Two experiments examined the effects of postoperative haptic discrimination training on the relearning of a maze visual discrimination in rats with visual cortex lesions. In the first experiment, rats learned a visual intensity discrimination prior to ablation of the lateral Oc2L cortex. Lesion rats were exposed to either a rough/smooth haptic discrimination training condition, a random training condition, or a no-training condition prior to relearning the visual task. Lesion rats relearned the visual task faster after haptic training than after other postoperative experiences. The second experiment replicated these procedures but with rats in which most of the visual cortex was removed. The lesion-induced relearning deficits in the second experiment were similar to the deficits seen for the smaller Oc2L lesions in the first experiment, supporting the hypothesis that the lateral visual cortex is critical for intensity discrimination. Haptic training also reduced these deficits, but the magnitude of this effect was related to the characteristics of the haptic cue. Postoperative training with haptic cues can produce specific and nonspecific information transfer from the intact somatosensory system to the damaged visual system that can facilitate the visual relearning. Possible implications for neuropsychological rehabilitation are also discussed.