Auditory brainstem responses in adults with autism spectrum disorder.

OBJECTIVE: To investigate possible differences in the auditory peripheral and brainstem functions between adults with autism spectrum disorder (ASD) and neurotypical (NT) adults. METHODS: Click-evoked auditory brainstem responses (ABRs) were obtained from 17 high-functioning ASD adults (aged 21-38 years) and 20 NT adults (aged 22-36 years). A relatively large number of stimulus presentations (6000) were adopted, and ABRs by horizontal and vertical electrode montages were evaluated, in order to allow precise evaluations of early ABR components. RESULTS: Waves I, II, III, and V were identified in the vertical electrode montage, and wave I and the summating potential (SP) in electrocochleograms were identified in the horizontal electrode montage. There were no significant group differences in the wave I, II, III, and V latencies or the interpeak latencies (IPLs) in the vertical electrode montage. In the horizontal montage, the ASD adults exhibited significantly shortened SP latencies compared with the NT adults, whereas there was no significant group difference in the wave I latency. CONCLUSION: The ASD adults may have the abnormalities of processing more in the peripheral auditory system than in the brainstem. SIGNIFICANCE: The current study suggests that the peripheral abnormality is associated with ASD.

Disorder in sequential speech perception: a case study on pure word deafness.

We described disorders of a patient which were uniquely restricted to speech perception of syllable sequences after brain damage. The results of series of experiments using syllable sequences showed "negative recency effect," in which the subject's repetition performance at the latter syllable position was remarkably poor. Experimental analyses suggested that the "negative recency effect" could be due to dual factors: the lower rate of processing of speech sounds and the memory load of holding processes of preceding syllables imposed on the succeeding phonological processing. The results also suggested that the holding processes which imposed the memory load on the succeeding auditory phonological coding processing were modality nonspecific.

Adaptation in the processing of interaural time differences revealed by the auditory localization aftereffect.

Two experiments were conducted involving the auditory localization aftereffect, in which the perceptual lateralization of a test sound having an interaural time difference (ITD) shifts away from that of a prior adapting sound having a different ITD. First, the frequency selectivity of the aftereffect was examined for sinusoids presented through headphones, with various combinations of adapter and test frequencies below 800 Hz, using the method of constant stimuli. The magnitude of the aftereffect was found to be largest when the frequencies of the two tones were similar, and virtually disappeared at a frequency difference of one-half octave. Second, the ITD selectivity of the aftereffect was examined for 400-Hz sinusoids. Subjects' judgments of lateralization were measured directly in terms of the perceived azimuth of the test tone for various combinations of adapter and test ITDs in the range of +/- 625 microseconds. The magnitude of the aftereffect was found to be largest when adapter and test ITDs differed by approximately 250 microseconds. These results were successfully simulated by an interaural cross-correlation model having gain control. The results are consistent with the idea that the gain of ITD-selective units, located after binaural interaction but before across-frequency integration, is changed by recent input.

Binaural release from temporal induction.

This study examined the effects of interaural phase difference (IPhD) relations in temporal induction (TI)-that is, the perceived continuity of a fainter sound (inducee) through an interrupting higher amplitude sound (inducer). The extent of TI was measured both directly as the upper amplitude level for continuity and indirectly as the loudness reduction of the inducer. It was found that TI was inhibited when the IPhD of the inducer and the IPhD of the inducee differed. It was also found that the extent of induction was positively related to the masking potential of the inducer as measured by the binaural masking level difference procedure. These results suggest that TI involves processes that are affected by interaural phase differences and that the masking potential rule, shown by previous studies to apply in the frequency domain, applies also in the IPhD domain. The present findings are consistent with the hypothesis that TI results from allocation of a portion of the neural excitation produced by the inducer over to the inducee if the inducer has the appropriate masking potential. As a consequence, obliterated signals can be selectively restored on the basis of both frequency-specific monaural cues and azimuth-related binaural cues, abilities that can enhance detection of signals under the noisy conditions of everyday life.