Abstract
Early auditory deprivation has serious neurodevelopmental and cognitive repercussions largely derived from impoverished and delayed language acquisition. These conditions may be associated with early changes in brain connectivity. Vibrotactile stimulation is a sensory substitution method that allows perception and discrimination of sound, and even speech. To clarify the efficacy of this approach, a vibrotactile oddball task with 700 and 900 Hz pure-tones as stimuli [counterbalanced as target (T: 20% of the total) and non-target (NT: 80%)] with simultaneous EEG recording was performed by 14 profoundly deaf and 14 normal-hearing (NH) subjects, before and after a short training period (five 1-h sessions; in 2.5–3 weeks). A small device worn on the right index finger delivered sound-wave stimuli. The training included discrimination of pure tone frequency and duration, and more complex natural sounds. A significant P300 amplitude increase and behavioral improvement was observed in both deaf and normal subjects, with no between group differences. However, a P3 with larger scalp distribution over parietal cortical areas and lateralized to the right was observed in the profoundly deaf. A graph theory analysis showed that brief training significantly increased fronto-central brain connectivity in deaf subjects, but not in NH subjects. Together, ERP tools and graph methods depicted the different functional brain dynamic in deaf and NH individuals, underlying the temporary engagement of the cognitive resources demanded by the task. Our findings showed that the index-fingertip somatosensory mechanoreceptors can discriminate sounds. Further studies are necessary to clarify brain connectivity dynamics associated with the performance of vibrotactile language-related discrimination tasks and the effect of lengthier training programs.
Highlights
The rationale that auditory deprivation could benefit sensory modalities that remain intact (Mayberry, 2002; Auer et al, 2007) underlies the exploration of vibrotactile stimulation as an alternative sound perception method for the population with profound bilateral deafness by enabling discrimination of sound and even spoken language
Significant changes were found in pre- and post-training performance, but no such changes were demonstrated across training conditions between groups. Both groups increased the number of correct responses [F(1,22) = 6.604, p < 0.05, η = 0.231; mean standard error (MSE) = 1.59] and decreased the number of incorrect responses [F(1,22) = 22.232, p < 0.001, η = 0.503; MSE = 1.48]
The maximum P3 and P4 voltages were identified in each individual mean event-related potentials (ERPs) in both groups and conditions to comparatively evaluate the ERP waveforms while performing the vibrotactile discrimination task. The results of these analyses indicate a significant increase of the P300 amplitude due to training [F(1,22) = 6.078, p < 0.05, η = 0.216]
Summary
The rationale that auditory deprivation could benefit sensory modalities that remain intact (Mayberry, 2002; Auer et al, 2007) underlies the exploration of vibrotactile stimulation as an alternative sound perception method for the population with profound bilateral deafness by enabling discrimination of sound and even spoken language. The effects of early auditory deprivation on brain organization due to neuroplasticity in developmental stages have been explored, primarily in the sensory cortices (Huttenlocher, 2002) and language-related areas (Huttenlocher and Dabholkar, 1997; Neville and Bavelier, 1998). The recruitment of auditory cortices for processing sign language (Chlubnová et al, 2005), visual tasks (Finney et al, 2003), and vibrotactile stimulation (Levänen et al, 1998; Auer et al, 2007), are cross-modal changes related to profound deafness (Merabet and Pascual-Leone, 2010)
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