Sign language experience has little effect on face and biomotion perception in bimodal bilinguals

Abstract

Sensory and language experience can affect brain organization and domain-general abilities. For example, D/deaf individuals show superior visual perception compared to hearing controls in several domains, including the perception of faces and peripheral motion. While these enhancements may result from sensory loss and subsequent neural plasticity, they may also reflect experience using a visual-manual language, like American Sign Language (ASL), where signers must process moving hand signs and facial cues simultaneously. In an effort to disentangle these concurrent sensory experiences, we examined how learning sign language influences visual abilities by comparing bimodal bilinguals (i.e., sign language users with typical hearing) and hearing non-signers. Bimodal bilinguals and hearing non-signers completed online psychophysical measures of face matching and biological motion discrimination. No significant group differences were observed across these two tasks, suggesting that sign language experience is insufficient to induce perceptual advantages in typical-hearing adults. However, ASL proficiency (but not years of experience or age of acquisition) was found to predict performance on the motion perception task among bimodal bilinguals. Overall, the results presented here highlight a need for more nuanced study of how linguistic environments, sensory experience, and cognitive functions impact broad perceptual processes and underlying neural correlates.

Figure 1

Face identification by group. Performance did not vary as a function of group in this task. Black squares represent the mean for each group in each stimulus condition. Dots show individual participant data. Dotted line shows chance level performance. Bimodal bilinguals who acquired ASL at 13-years-old or earlier are highlighted as solid triangles. Error bars show ± 2SD.

Figure 2

Face identification collapsed across groups. Performance was superior for upright (light) versus inverted faces (dark), and for centrally-presented (left) versus peripherally-presented faces (right). Black squares represent the mean for each group in each stimulus condition. Dots show individual participant data. Dotted line represents chance level performance. Bimodal bilinguals who acquired ASL at 13-years-old or earlier are highlighted as solid triangles. Error bars show ± 2SD.

Figure 3

Peripheral face identification by hemifield. Bimodal bilinguals showed superior face identification for stimuli presented in the right versus the left visual hemifield. Across groups, performance was worse for inverted faces presented in the left hemifield than any other hemifield × orientation combination. Black squares represent the mean for each group in each stimulus condition. Colored dots show individual participant data. Dotted line represents chance level performance. Bimodal bilinguals who acquired ASL at 13-years-old or earlier are highlighted as solid triangles. Error bars show ± 2SD.

Figure 4

Biomotion direction discrimination by group. Performance did not differ by group across the range of orientations, locations, and durations tested. Error bars show ±SE. Dotted lines show chance level performance.

Figure 5

Effects of ASL proficiency on biomotion performance. Lines of best fit to the relationship between age of ASL acquisition and biomotion direction discrimination performance are shown for each location and duration combination. Early ASL acquisition predicted improved performance for brief centrally-presented walkers and for longer duration stimuli presented in the visual periphery. Dotted lines show chance level performance.

Figure 6

Biomotion direction discrimination reaction times by group. Reaction times did not differ by group. However, at longer durations, bimodal bilinguals (blue) were quicker to respond that hearing non-signers (red) to central stimuli, but took longer to respond to those in the visual periphery. Error bars show ±SE.

Figure 7

Distribution of age of ASL acquisition. Age of ASL acquisition for bimodal bilinguals in the current study ranged from 0 to 54 years of age. Median age of acquisition was 21 years.

Figure 8

Face identification task illustration. Participants were briefly presented with a target face either at the centre of the screen or in the periphery that was followed by a visual mask. Participants were then asked to select a face from an array of four images that matched the identity of the target face. Stimuli were inverted on 50% of trials (not shown).

Figure 9

Biomotion direction discrimination task illustration. Participants saw a point light walker either at the centre of the screen or in the periphery and were asked to indicate whether the walker was moving toward the left- or right-hand side of the screen. Stimuli were inverted on 50% of trials (not show).