Abstract
The ability to accurately integrate or bind stimuli from more than one sensory modality is highly dependent on the features of the stimuli, such as their intensity and relative timing. Previous studies have demonstrated that the ability to perceptually bind stimuli is impaired in various clinical conditions such as autism, dyslexia, schizophrenia, as well as aging. However, it remains unknown if adult-onset hearing loss, separate from aging, influences audiovisual temporal acuity. In the present study, rats were trained using appetitive operant conditioning to perform an audiovisual temporal order judgment (TOJ) task or synchrony judgment (SJ) task in order to investigate the nature and extent that audiovisual temporal acuity is affected by adult-onset hearing loss, with a specific focus on the time-course of perceptual changes following loud noise exposure. In our first series of experiments, we found that audiovisual temporal acuity in normal-hearing rats was influenced by sound intensity, such that when a quieter sound was presented, the rats were biased to perceive the audiovisual stimuli as asynchronous (SJ task), or as though the visual stimulus was presented first (TOJ task). Psychophysical testing demonstrated that noise-induced hearing loss did not alter the rats’ temporal sensitivity 2–3 weeks post-noise exposure, despite rats showing an initial difficulty in differentiating the temporal order of audiovisual stimuli. Furthermore, consistent with normal-hearing rats, the timing at which the stimuli were perceived as simultaneous (i.e., the point of subjective simultaneity, PSS) remained sensitive to sound intensity following hearing loss. Contrary to the TOJ task, hearing loss resulted in persistent impairments in asynchrony detection during the SJ task, such that a greater proportion of trials were now perceived as synchronous. Moreover, psychophysical testing found that noise-exposed rats had altered audiovisual synchrony perception, consistent with impaired audiovisual perceptual binding (e.g., an increase in the temporal window of integration on the right side of simultaneity; right temporal binding window (TBW)). Ultimately, our collective results show for the first time that adult-onset hearing loss leads to behavioral plasticity of audiovisual perception, characterized by a rapid recalibration of temporal sensitivity but a persistent impairment in the perceptual binding of audiovisual stimuli.
Highlights
In order to create an unified percept of objects or events within our external environment, our brain must be able to accurately integrate or bind stimuli from more than one sensory modality
The effect of sound intensity on audiovisual temporal order perception was examined during the temporal order judgment (TOJ) task using three testing conditions which differed in the intensity of the auditory stimulus presented (i.e., 60, 75 and 90 dB sound pressure level (SPL))
Rats were trained and tested on either a TOJ task in which they reported the relative timing of audiovisual stimuli presented at various stimulus onset asynchronies (SOAs), or an synchrony judgment (SJ) task in which they reported whether audiovisual stimuli were presented at the same moment in time or at different times
Summary
In order to create an unified percept of objects or events within our external environment, our brain must be able to accurately integrate or bind stimuli from more than one sensory modality (e.g., hearing and vision). Decades of research in numerous species has confirmed that the successful integration of multisensory information is highly dependent upon the features of the unimodal stimuli presented, most notably their intensity and spatiotemporal alignment (King and Palmer, 1985; Meredith and Stein, 1986, 1996; Meredith et al, 1987; Stein and Meredith, 1993; Perrault et al, 2005; Stanford et al, 2005; Rowland and Stein, 2008; Miller et al, 2015) In such cases when an auditory and visual stimulus occur within ∼100 ms of each other, the stimuli can be perceived by the observer as having occurred at the same moment in time even though the stimuli were physically asynchronous. The TBW provides insight into the degree of temporal tolerance in which asynchronous audiovisual stimuli are likely to be integrated and perceptually bound (Krueger Fister et al, 2016)
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