Previous studies have shown bilingually and monolingually developing children to differ in their sensitivity to referential pragmatic deixis in challenging tasks, with bilinguals exhibiting a higher sensitivity. The learning of adjectives is particularly challenging, but has rarely been investigated in bilingual children. In the present study we presented a pragmatic cue supporting the learning of novel adjectives to 32 Spanish-German bilingual and 28 German monolingual 5-year-olds. The children's responses to a descriptive hand gesture highlighting an object's property were measured behaviorally using a forced choice task and neurophysiologically through functional Near-Infrared Spectroscopy (fNIRS). While no group differences emerged on the behavioral level, fNIRS revealed a higher activation in bilingual than monolingual children in the vicinity of the posterior part of the right superior temporal sulcus (STS). This result supports the prominent role of the STS inprocessing pragmatic gestures and suggests heightened pragmatic sensitivity for bilingual children.
Perceptual learning requires the generalization of categorical perceptual sensitivity from trained to untrained items. For degraded speech, perceptual learning modulates activation in a left-lateralized network, including inferior frontal gyrus (IFG) and inferior parietal cortex (IPC). Here we demonstrate that facilitatory anodal transcranial direct current stimulation (tDCS anodal ) can induce perceptual learning in healthy humans. In a sham-controlled, parallel design study, 36 volunteers were allocated to the three following intervention groups: tDCS anodal over left IFG, IPC, or sham. Participants decided on the match between an acoustically degraded and an undegraded written word by forced same-different choice. Acoustic degradation varied in four noise-vocoding levels (2, 3, 4, and 6 bands). Participants were trained to discriminate between minimal (/Tisch/-FISCH) and identical word pairs (/Tisch/-TISCH) over a period of 3 d, and tDCS anodal was applied during the first 20 min of training. Perceptual sensitivity (dЈ) for trained word pairs, and an equal number of untrained word pairs, was tested before and after training. Increases in dЈ indicate perceptual learning for untrained word pairs, and a combination of item-specific and perceptual learning for trained word pairs. Most notably for the lowest intelligibility level, perceptual learning occurred only when tDCS anodal was applied over left IFG. For trained pairs, improved dЈ was seen on all intelligibility levels regardless of tDCS intervention. Over left IPC, tDCS anodal did not modulate learning but instead introduced a response bias during training. Volunteers were more likely to respond "same," potentially indicating enhanced perceptual fusion of degraded auditory with undegraded written input. Our results supply first evidence that neural facilitation of higher-order language areas can induce perceptual learning of severely degraded speech.
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