Effect of Transcranial Direct Current Stimulation (tDCS) on Speech Perception in Noise

Speech perception in competing noise (SIN) is an essential auditory function that deteriorates with age and hearing impairment, and can be challenging even for adults with normal sensory hearing and cognitive abilities. While tDCS has proven effective in enhancing learning and cognitive abilities, its effect on SIN perception remains understudied. This study examined the impact of anodal tDCS applied over the left posterior Superior Temporal Gyrus (STG) on SIN performance. Twenty-five healthy young students (13 females, aged 20-34) participated in a double-blind study, completing both True and Sham experiments in randomized order, one week apart. Participants were assessed using the Quick SIN test-English version before and immediately after twenty minutes of anodal tDCS (TP7 and FP2 areas), combined with a Hebrew training task presented with competing background babble noise. The sample included six Hebrew native speakers and nineteen Arabic native speakers proficient in Hebrew. Contrary to our hypothesis, no significant effect of stimulation type was found in the general analysis. However, subgroup analysis revealed that 83.3% of Hebrew native speakers showed significant improvement following True stimulation compared to only 36.8% of Arabic native speakers. This finding suggests that the native Hebrew speakers were more likely to benefit from tDCS in improving their speech perception in competing noise performance, possibly due to the language of the training task (Hebrew) during stimulation. These results indicate that for non-native language tasks, the stimulated area may not have been optimal for Arabic native speakers, suggesting different neural mechanisms might underlie non-native speech perception in noise. Future research should consider native language when determining stimulation areas, potentially using fMRI during SIN tests for more precise targeting.

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