Abstract
BackgroundIndividuals with Williams syndrome (WS) exhibit an atypical social phenotype termed hypersociability. One theory accounting for hypersociability presumes an atypical function of the amygdala, which processes fear-related information. However, evidence is lacking regarding the detection mechanisms of fearful faces for individuals with WS. Here, we introduce a visual search paradigm to elucidate the mechanisms for detecting fearful faces by evaluating the search asymmetry; the reaction time when both the target and distractors were swapped was asymmetrical.MethodsEye movements reflect subtle atypical attentional properties, whereas, manual responses are unable to capture atypical attentional profiles toward faces in individuals with WS. Therefore, we measured both eye movements and manual responses of individuals with WS and typically developed children and adults in visual searching for a fearful face among neutral faces or a neutral face among fearful faces. Two task measures, namely reaction time and performance accuracy, were analyzed for each stimulus as well as gaze behavior and the initial fixation onset latency.ResultsOverall, reaction times in the WS group and the mentally age-matched control group were significantly longer than those in the chronologically age-matched group. We observed a search asymmetry effect in all groups: when a neutral target facial expression was presented among fearful faces, the reaction times were significantly prolonged in comparison with when a fearful target facial expression was displayed among neutral distractor faces. Furthermore, the first fixation onset latency of eye movement toward a target facial expression showed a similar tendency for manual responses.ConclusionsAlthough overall responses in detecting fearful faces for individuals with WS are slower than those for control groups, search asymmetry was observed. Therefore, cognitive mechanisms underlying the detection of fearful faces seem to be typical in individuals with WS. This finding is discussed with reference to the amygdala account explaining hypersociability in individuals with WS.
Highlights
Individuals with Williams syndrome (WS) exhibit an atypical social phenotype termed hypersociability
Overall, we did not find group differences in terms of visual search asymmetry; there were prolonged reaction times (RTs) for searching for a neutral face among fearful faces, but these were not obtained for searching for a fearful face among neutral faces
We found significant main effects for group [p < 0.01; faster RTs for the chronologically agematched (CA) group than those for the mentally agematched (MA) and WS groups but not significant between the MA and CA groups (WS 2899.7 ms, MA 2967.7 ms, and CA 1996.5 ms)] and target facial expression [p < 0.01; faster RTs for fearful face target than those for neutral face target]
Summary
Individuals with Williams syndrome (WS) exhibit an atypical social phenotype termed hypersociability. Recent neuroimaging studies have revealed that individuals with WS show atypical increases in gray matter volumes in the frontal lobes [12]. Another finding showed difficulties in executive functions similar to those seen in individuals with attention deficit and hyperactivity disorders (ADHD) [13]. Further evidence such as a study employing a rating system for approachability implies that the atypical social approachability of individuals with WS is not due to difficulties in the recognition of emotion but due to the problem of inhibition [7, 8]. Other neuroimaging evidence has suggested that the dorsolateral frontal cortex and dorsal anterior cingulate cortices in the WS group were significantly reduced in neural activity compared with typical controls during a Go/No-go inhibition task [14]
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