Rett syndrome: recognition of facial expression and its relation to scanning patterns

Rett syndrome is a severely disabling neurodevelopmental disorder caused by mutations in the X-linked MECP2 gene. Very little is known about its cognitive phenotype and nothing about recognition of emotional expression, a key factor for social interaction and communication. Using eye tracking technology, a technique uniquely suited for studying cognition in this disorder, we examined this ability here.

Rett syndrome female patients (n = 37; 2-31 years) and a typically developing age- and gender-matched comparison group (n =34; 2-30 years) were assessed on recognition of three basic emotions (happy, sad, and fear) using six visual paired-comparison problems. Each problem consisted of a 10-second familiarization, in which two identical faces posing one emotion were presented, followed by a 10-second test, in which the familiar emotion was paired with a novel one posed by the same model. Recognition was inferred from preferential looking to the novel target on test. During familiarization, attention was measured by total looking time, number and/or length of fixations, and gaze dispersion across three key facial features (eyes, nose, and mouth).

Individuals with Rett syndrome had difficulty recognizing most emotional expressions, unlike the typically developing comparison group. Also, their scanpaths were atypical-less looking, fewer and/or longer fixations, and less time devoted to all facial features (48% versus 72%), particularly the mouth. Significant correlations between looking to critical features and recognition underscored the importance of scanning.

Our results suggest that individuals with Rett syndrome have difficulty reading emotional expressions and that these problems are linked to atypicalities in scanning.