How Auditory Experience Differentially Influences the Function of Left and Right Superior Temporal Cortices

Abstract

To investigate how hearing status, sign language experience, and task demands influence functional responses in the human superior temporal cortices (STC) we collected fMRI data from deaf and hearing participants (male and female), who either acquired sign language early or late in life. Our stimuli in all tasks were pictures of objects. We varied the linguistic and visuospatial processing demands in three different tasks that involved decisions about (1) the sublexical (phonological) structure of the British Sign Language (BSL) signs for the objects, (2) the semantic category of the objects, and (3) the physical features of the objects.Neuroimaging data revealed that in participants who were deaf from birth, STC showed increased activation during visual processing tasks. Importantly, this differed across hemispheres. Right STC was consistently activated regardless of the task whereas left STC was sensitive to task demands. Significant activation was detected in the left STC only for the BSL phonological task. This task, we argue, placed greater demands on visuospatial processing than the other two tasks. In hearing signers, enhanced activation was absent in both left and right STC during all three tasks. Lateralization analyses demonstrated that the effect of deafness was more task-dependent in the left than the right STC whereas it was more task-independent in the right than the left STC. These findings indicate how the absence of auditory input from birth leads to dissociable and altered functions of left and right STC in deaf participants.SIGNIFICANCE STATEMENT Those born deaf can offer unique insights into neuroplasticity, in particular in regions of superior temporal cortex (STC) that primarily respond to auditory input in hearing people. Here we demonstrate that in those deaf from birth the left and the right STC have altered and dissociable functions. The right STC was activated regardless of demands on visual processing. In contrast, the left STC was sensitive to the demands of visuospatial processing. Furthermore, hearing signers, with the same sign language experience as the deaf participants, did not activate the STCs. Our data advance current understanding of neural plasticity by determining the differential effects that hearing status and task demands can have on left and right STC function.

Keywords: deaf; language; plasticity; sign language; superior temporal cortex; visuo-spatial working memory.

Figure 1.

Stimulus examples. Top, BSL phonological task “Same handshape?” Middle, Semantic task “Same category?” Bottom, Visual task “Same picture?”

Figure 2.

Behavioral results. Left, Response sensitivity (d′). Right, RTs (ms). Both show a main effect of task, and a significant task by age of acquisition interaction on the RTs only. PHON, BSL phonological task; SEM, semantic task; VIS, visual task.

Figure 3.

The main effect of deafness and the interaction of deafness and task at p < 0.05 FWE-corrected (red to yellow). At the FWE-corrected level, these effects in STC were task-independent on the right (top) and task-dependent on the left (bottom). The bar plots of parameter estimates at these peaks are also shown. Error bars indicate SE. PHON, Phonological task; SEM, semantic task; VIS, visual task.

Figure 4.

LI values for top (deaf > hearing), middle (deaf > hearing by the BSL phonological task > the semantic task), and bottom (deaf > hearing by the BSL phonological task > the visual task) within temporal cortices.