Dissociating neural correlates of meaningful emblems from meaningless gestures in deaf signers and hearing non-signers

Abstract

Emblems are meaningful, culturally-specific hand gestures that are analogous to words. In this fMRI study, we contrasted the processing of emblematic gestures with meaningless gestures by pre-lingually Deaf and hearing participants. Deaf participants, who used American Sign Language, activated bilateral auditory processing and associative areas in the temporal cortex to a greater extent than the hearing participants while processing both types of gestures relative to rest. The hearing non-signers activated a diverse set of regions, including those implicated in the mirror neuron system, such as premotor cortex (BA 6) and inferior parietal lobule (BA 40) for the same contrast. Further, when contrasting the processing of meaningful to meaningless gestures (both relative to rest), the Deaf participants, but not the hearing, showed greater response in the left angular and supramarginal gyri, regions that play important roles in linguistic processing. These results suggest that whereas the signers interpreted emblems to be comparable to words, the non-signers treated emblems as similar to pictorial descriptions of the world and engaged the mirror neuron system.

Figure 1

Pictures of the two types of stimuli: (a) meaningful emblematic and (b) meaningless gestures.

Figure 2

Timeline of a trial and a scanning session.

Figure 3

Behavioral results, accuracy and (b) reaction times of correct trials. D: Deaf, H: Hearing. Asterisks denote significant results of paired t-tests for the IDN and CAT tasks.

Figure 4

Statistical parametric maps computed using two-way ANOVA (with stimulus and group as factors) rendered on surface of a template brain. (a) Effect of group. Results from (1) Deaf>Hearing contrast and (2) Hearing > Deaf contrast. (b) Effect of stimulus types. Results from the MEANINGFUL>MEANINGLESS contrast. The reverse contrast (MEANINGLESS>MEANINGFUL) resulted in 0 suprathreshold voxels and is not shown here. The results were corrected for cluster-wise multiple comparisons (p<0.05 FWE).

Figure 4

Statistical parametric maps computed using two-way ANOVA (with stimulus and group as factors) rendered on surface of a template brain. (a) Effect of group. Results from (1) Deaf>Hearing contrast and (2) Hearing > Deaf contrast. (b) Effect of stimulus types. Results from the MEANINGFUL>MEANINGLESS contrast. The reverse contrast (MEANINGLESS>MEANINGFUL) resulted in 0 suprathreshold voxels and is not shown here. The results were corrected for cluster-wise multiple comparisons (p<0.05 FWE).

Figure 5

Results of two-sample t-tests for the groups for a particular stimulus condition: (a) Meaningful stimuli: Deaf>Hearing, (b) Meaningful stimuli: Hearing> Deaf, and (c) Meaningless stimuli: Deaf>Hearing contrasts.

Figure 6

Statistical parametric maps computed using two-way ANOVA (with stimulus and task as factors) rendered on surface of a template brain: (a) Effect of stimulus type, (b) Effect of task. The results were corrected for cluster-wise multiple comparisons (p<0.05 FWE). In sub-figure (a), the effect of the stimulus condition is depicted by the contrast MEANINGLESS>MEANINGFUL for the hearing group (top), and the effect of the stimulus condition depicted by the contrast MEANINGFUL>MEANINGLESS for the Deaf group (bottom). No suprathreshold voxels remained for the opposite contrasts in either case, MEANINGFUL>MEANINGLESS for the hearing group and the MEANINGLESS>MEANINGFUL for the Deaf group. In sub-figure (b), the effect of the contrast IDN>CAT is shown for the hearing group (top) and the Deaf group (bottom). No suprathreshold voxels remained for the contrast CAT>IDN for either group.

Figure 6

Statistical parametric maps computed using two-way ANOVA (with stimulus and task as factors) rendered on surface of a template brain: (a) Effect of stimulus type, (b) Effect of task. The results were corrected for cluster-wise multiple comparisons (p<0.05 FWE). In sub-figure (a), the effect of the stimulus condition is depicted by the contrast MEANINGLESS>MEANINGFUL for the hearing group (top), and the effect of the stimulus condition depicted by the contrast MEANINGFUL>MEANINGLESS for the Deaf group (bottom). No suprathreshold voxels remained for the opposite contrasts in either case, MEANINGFUL>MEANINGLESS for the hearing group and the MEANINGLESS>MEANINGFUL for the Deaf group. In sub-figure (b), the effect of the contrast IDN>CAT is shown for the hearing group (top) and the Deaf group (bottom). No suprathreshold voxels remained for the contrast CAT>IDN for either group.