Impaired Visual Search in Children with Rett Syndrome

Aim
This study aims to investigate selective attention in Rett syndrome, a severely disabling neurodevelopmental disorder caused by mutations in the X-linked MECP2 gene.
Method
The sample included 28 females with Rett syndrome (RTT) and 32 age-matched typically developing controls. We used a classic search task, in conjunction with eye-tracking technology. Each trial included the target and several distractors. The distractors varied in number and differed from targets in either a ‘single feature’ (color or shape), creating a pop-out effect, or in a ‘conjunction of features’ (color and shape), requiring serial search. Children searched for the target in arrays containing 5 or 9 objects; trials ended when the target was fixated (or 4000 ms elapsed).
Results
Children with Rett syndrome had more difficulty finding the target than typically developing children in both conditions (success rates <50% vs 80%) and their success rates were little influenced by display size or age. Even when successful, children with RTT took significantly longer to respond (392--574 ms), although saccadic latency differences were observed only in the single feature condition. Both groups showed the expected slowing of saccadic reaction times for larger arrays in the conjunction feature condition. Search failures in RTT were not related to symptom severity.
Conclusion
Our findings provide the first evidence that selective attention, the ability to focus on or select a particular element or object in the environment, is compromised by Rett syndrome. They reinforce the notion that gaze-based tasks hold promise for quantifying the cognitive phenotype of RTT.