Rett syndrome: an eye-tracking study of attention and recognition memory

Aim The aim of this study was to examine attention and recognition memory for faces and patterns in Rett syndrome, a severely disabling neurodevelopmental disorder caused by mutations in the X-linked MECP2 gene. Method Because Rett syndrome impairs speech and hand use, precluding most neuropsychological testing, the visual paired-comparison paradigm (VPC) was used, together with eye tracking. In the VPC, two identical stimuli are presented for familiarization. On test, the familiar stimulus and a new one are paired, and recognition inferred from preferential looking to the novel target. Attention is measured by looking time, gaze dispersion, and number/length of fixations. Twenty-seven female patients with Rett syndrome (mean age 10y 6mo; SD 6y 8mo, age range 222y) from the Rett clinic at a children's hospital were assessed in this study, along with 30 age- and sex-matched typically developing participants (outpatients from the same hospital). Results Although patients with Rett syndrome showed recognition of both faces and patterns, with novelty scores greater than chance (50%), their performance was significantly poorer than that of the typically developing comparison group. Their attention to both was less mature and marked by a more narrowly focused gaze, with fewer and longer fixations. When inspecting faces, attention to the eyes was similar in both groups; however, patients with Rett syndrome tended to ignore the nose and mouth. Interpretation This is one of the first studies to characterize attention and memory in individuals with Rett syndrome. Visually based techniques, such as the VPC, open a new avenue for quantifying the cognitive phenotype associated with this syndrome.