Patterns and trajectories in Williams Syndrome: The case of visual orientation discrimination

Williams Syndrome (WS) is a developmental disorder typified by deficits in visuospatial cognition. To understand the nature of this deficit, we characterized how people with WS perceive visual orientation, a fundamental ability related to object identification. We compared WS participants to typically developing children (3–6 years of age) and typical adults in an orientation discrimination task with four stimulus types (small circular, large circular, collinear elongated and parallel elongated gratings). We measured orientation discrimination thresholds and the proportion of orthogonal errors (i.e., mirror-image reversal errors). We evaluated how these metrics (1) are modulated by stimulus condition, and (2) vary with chronological or mental age. We found that orientation perception in WS is comparable to that of typically developing children. Orientation discrimination thresholds were better for elongated gratings than circular gratings across all participant groups. For large circular gratings, the proportion of orthogonal errors was disproportionately greater in WS participants and typically developing 3–6 year old children than in typical adults. Moreover, we found that the ability to judge orientation in WS improves with increasing mental age, but not chronological age. These results suggest that orientation discrimination in WS is developmentally arrested, as opposed to abnormal or delayed.

Research highlights
► The ability to judge orientation as a function of stimulus size and elongation was evaluated in Williams Syndrome, and was compared to that of typically developing children and typical adults.
► The orientation discrimination thresholds and the prevalence of orthogonal errors for WS participants were similar to that of typically developing.
► Increasing size of circular gratings reliably increased the proportion of orthogonal errors in WS participants and typically developing children.
► Orientation discrimination in WS improved with increasing mental age rather than chronological age.