Abstract
Studies of compensatory plasticity in early deaf (ED) individuals have mainly focused on unisensory processing, and on spatial rather than temporal coding. However, precise discrimination of the temporal relationship between stimuli is imperative for successful perception of and interaction with the complex, multimodal environment. Although the properties of cross-modal temporal processing have been extensively studied in neurotypical populations, remarkably little is known about how the loss of one sense impacts the integrity of temporal interactions among the remaining senses. To understand how auditory deprivation affects multisensory temporal interactions, ED and age-matched normal hearing (NH) controls performed a visual-tactile temporal order judgment task in which visual and tactile stimuli were separated by varying stimulus onset asynchronies (SOAs) and subjects had to discern the leading stimulus. Participants performed the task while EEG data were recorded. Group averaged event-related potential waveforms were compared between groups in occipital and fronto-central electrodes. Despite similar temporal order sensitivities and performance accuracy, ED had larger visual P100 amplitudes for all SOA levels and larger tactile N140 amplitudes for the shortest asynchronous (± 30 ms) and synchronous SOA levels. The enhanced signal strength reflected in these components from ED adults are discussed in terms of compensatory recruitment of cortical areas for visual-tactile processing. In addition, ED adults had similar tactile P200 amplitudes as NH but longer P200 latencies suggesting reduced efficiency in later processing of tactile information. Overall, these results suggest that greater responses by ED for early processing of visual and tactile signals are likely critical for maintained performance in visual-tactile temporal order discrimination.
Highlights
Natural timing discrepancies between multiple sensory signals inherently relay the source(s) and degree of congruency between those signals
early deaf (ED) and normal hearing (NH) groups did not perform differently overall [F(1,22) = 3.03, p = 0.10], there was a significant interaction between group and stimulus onset asynchronies (SOAs) [F(5,110) = 3.85, p < 0.01, np2 = 0.15]
Follow up t-tests that compared group accuracy performance at each SOA level using a corrected p value of 0.0083 showed that ED did not perform significantly different from NH at any SOA
Summary
Natural timing discrepancies between multiple sensory signals inherently relay the source(s) and degree of congruency between those signals. Throughout development, with normal exposure to multisensory events, the brain develops an intrinsic strategy to compensate for the inherent differences in propagation and processing speeds of multimodal information allowing for coherent percepts (for review see Murray et al, 2016) This integrative mechanism is largely driven by Altered Visual-Tactile Processing in Deaf sensitivities to the temporal and serial nature of the particular sensory cues. Due to the fact that visual information typically precedes auditory information, individuals are more sensitive to temporal asynchronies for auditory-leading compared to visual-leading information (Conrey and Pisoni, 2006; van Eijk et al, 2008; Cecere et al, 2016) This is reflected in the asymmetry of the temporal binding windows (Conrey and Pisoni, 2006; van Wassenhove et al, 2007; Powers et al, 2009; Hillock et al, 2011; Stevenson et al, 2012), the period of time within which multiple stimuli are likely to be perceptually integrated, indicating that exposure to patterns of natural temporal delays within multimodal signals is a major driver in fine-tuning this sensitive process. Early deaf adults demonstrated reduced sensitivity for sensory-motor timing and deficits in sensorymotor temporal recalibration for visual stimuli in the central visual field suggesting impairments in perception of sensorimotor causality (Vercillo and Jiang, 2017)
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