Visual processing in infants with fragile X syndrome

Abstract

Many studies have reported that deficits in visual motion processing exist in groups with developmental disorders such as autism, Williams syndrome, and Dyslexia. More recently, evidence has shown that a selective motion processing deficit is present in adults with fragile X syndrome (FXS), the most common cause of inherited mental delay. Using a direction discrimination task, adults with FXS were found to have increased thresholds for motion but no difference on form perception compared to controls (Kogan et al., 2004). Here we examined low-level visual processing in infants with FXS to explore the developmental trajectory of this putative deficit. Using a forced-choice preferential looking paradigm, we measured detection thresholds for first-order (luminance defined) and second-order (contrast defined) moving and static stimuli. Detection thresholds for static first- and second-order stimuli were consistent for typical infants and those with FXS, which would be expected based on previous work. More interestingly, there was no difference in motion detection thresholds for the two groups, even for contrast defined second-order motion. The results indicate that infants with FXS have detection thresholds comparable to mental age-matched controls, and are important because they rule out a low-level motion processing deficit in infants with FXS. Evidently, any visual deficits manifested in FXS syndrome must arise at a later stage of development or at a higher stage of visual processing.