Schizotypal traits are not related to multisensory integration or audiovisual speech perception

Multisensory integration, the process by which sensory information from different sensory modalities are bound together, is hypothesized to contribute to perceptual symptomatology in schizophrenia, including hallucinations and aberrant speech perception. Differences in multisensory integration and temporal processing, an important component of multisensory integration, have been consistently found among individuals with schizophrenia. Evidence is emerging that these differences extend across the schizophrenia spectrum, including individuals in the general population with higher levels of schizotypal traits. In the current study, we measured (1) multisensory integration using an audiovisual speech-in-noise task, and the McGurk task. Using the speech-in-noise task, we assessed (2) susceptibility to distracting auditory speech to test the hypothesis that increased perception of distracting speech that is subsequently bound with mismatching visual speech contributes to hallucination-like experiences. As a measure of (3) temporal processing, we used the ternary synchrony judgment task. We measured schizotypal traits using the Schizotypal Personality Questionnaire (SPQ), hypothesizing that higher levels of schizotypal traits, specifically Unusual Perceptual Experiences and Odd Speech subscales, would be associated with (1) decreased multisensory integration, (2) increased susceptibility to distracting auditory speech, and (3) less precise temporal processing. Surprisingly, neither subscales were associated with any of the measures. These results suggest that these perceptual differences may not be present across the schizophrenia spectrum.

Neural timing signal for precise tactile timing judgments

The brain can precisely encode the temporal relationship between tactile inputs. While behavioural studies have demonstrated precise interfinger temporal judgments, the underlying neural mechanism remains unknown. Computationally, two kinds of neural responses can act as the information source. One is the phase-locked response to the phase of relatively slow inputs, and the other is the response to the amplitude change of relatively fast inputs. To isolate the contributions of these components, we measured performance of a synchrony judgment task for sine wave and amplitude-modulation (AM) wave stimuli. The sine wave stimulus was a low-frequency sinusoid, with the phase shifted in the asynchronous stimulus. The AM wave stimulus was a low-frequency sinusoidal AM of a 250-Hz carrier, with only the envelope shifted in the asynchronous stimulus. In the experiment, three stimulus pairs, two synchronous ones and one asynchronous one, were sequentially presented to neighboring fingers, and participants were asked to report which one was the asynchronous pair. We found that the asynchrony of AM waves could be detected as precisely as single impulse pair, with the threshold asynchrony being ∼20 ms. On the other hand, the asynchrony of sine waves could not be detected at all in the range from 5 to 30 Hz. Our results suggest that the timing signal for tactile judgments is provided not by the stimulus phase information but by the envelope of the response of the high-frequency-sensitive Pacini channel (PC), although they do not exclude a possible contribution of the envelope of non-PCs.

Accuracy of Synchrony Judgment and its Relation to the Auditory Brainstem Response: the Difference Between Pianists and Non-Pianists

Synchrony judgment is one of the most important abilities for musicians. Only a few milliseconds of onset asynchrony result in a significant difference in musical expression. Using behavioural responses and Auditory Brainstem Responses (ABR), this study investigates whether synchrony judgment accuracy improves with training and, if so, whether physiological responses are also changed through training. Psychoacoustic experiments showed that accuracy of synchrony judgment of pianists was higher than that of non-pianists, implying that pianists’ ability to perceive tones increased through training. ABRmeasurements also showed differences between pianists and non-pianists. However, cochlear delay, an asymmetric aspect of temporal processing in the human auditory system, did not change with training. It is possible that training improved ability related to temporal tone perception and that training may increase synchrony in auditory nerve firing.