![]() However, few studies have compared the auditory functions of both hemispheres or evaluated interhemispheric transfer and binaural integration in blind individuals ( Hugdahl et al., 2004). The visual cortices of blind subjects have been shown to be recruited following auditory signals ( Weeks et al., 2000 Voss et al., 2008 Gougoux et al., 2009). ![]() Abundant neuroimaging evidence supports the theory that the cerebral cortex experiences compensatory plasticity after visual deprivation. The difference in auditory performance in early-blind subjects compared to sighted subjects is presumed to be due to plastic changes in the central auditory system. However, a recent study showed enhanced spatial hearing abilities in early-blind subjects and claimed that vision is not a prerequisite for developing an auditory sense of space ( Battal et al., 2020). Some studies found impaired sound localization abilities in early-blind subjects, especially in the sound localization task in the vertical plane ( Zwiers et al., 2001 Lewald, 2002) or the performance of more complex tasks requiring a metric representation of the auditory space ( Gori et al., 2010, 2014 Finocchietti et al., 2015 Vercillo et al., 2016). Several studies have reported the better performance of early-blind subjects over sighted subjects in speech memory ( Amedi et al., 2003), pitch discrimination in pure tone ( Gougoux et al., 2004 Shim et al., 2019), temporal resolution ( Stevens and Weaver, 2005 Shim et al., 2019), ultrafast speech comprehension ( Hertrich et al., 2013), and dichotic listening ( Hugdahl et al., 2004). These advantages may be attributable to the enhanced activity of the central auditory nervous system, especially the right hemisphere function, and the transfer of auditory information between the two hemispheres.īecause congenitally blind or early-blind individuals depend exclusively upon auditory sensory cues, without visual cues when communicating, their auditory processing can develop differently from that of sighted subjects. The results of this study revealed early-blind subjects exhibited some advantages in dichotic listening, and temporal sequencing ability compared to those shown in sighted subjects. Acoustic change complex responses to/ba/in babble noise, recorded with electroencephalography, showed a greater N1 peak amplitude at only FC5 electrode under a signal-to-noise ratio of –8 and –4 dB in the early-blind subjects than in the sighted subjects ( p = 0.004 and p = 0.003, respectively, Bonferroni’s corrected α = 0.05/5 = 0.01). Monosyllable perception in noise tended to be better in early-blind subjects than in sighted subjects at a signal-to-noise ratio of –8 ( p = 0.054), the results at signal-to-noise ratios of –4, 0, +4, and +8 did not differ. In the frequency patterning test (five tones), the early-blind subjects performed better (both ears in the humming response, but the left ear only in the labeling response) than the sighted subjects ( p < 0.008, Bonferroni’s corrected α = 0.05/6 = 0.008). In the dichotic listening test (three-digit pair), the early-blind subjects achieved higher scores than the sighted subjects in the left ear ( p = 0.003, Bonferroni’s corrected α = 0.05/6 = 0.008), but not in the right ear, indicating a right ear advantage in sighted subjects ( p < 0.001) but not in early-blind subjects. The study included 23 early-blind subjects and 22 age-matched sighted subjects. Therefore, we evaluated whether there are differences in dichotic listening, auditory temporal sequencing ability, or speech perception in noise (all of which have been used to diagnose central auditory processing disorder) between early-blind subjects and sighted subjects. However, few studies have compared the auditory functions of both hemispheres or evaluated interhemispheric transfer and binaural integration in blind individuals. Several studies have reported the better auditory performance of early-blind subjects over sighted subjects. 2Division of Speech Pathology and Audiology, Research Institute of Audiology and Speech Pathology, Hallym University, Chuncheon, South Korea. ![]()
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