Static & Dynamic Global Integration in Typically Developing Children & in Williams Syndrome
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Williams Syndrome (WS) is a genetic disorder occurring in 1 out of every 7,500 live births that results in visual perception deficits (Stromme, Bjornstad, & Ramstad, 2002). People with WS have strong language skills, but they are weak in visual and spatial abilities. The specific vision weaknesses in WS are believed to be caused by the potential damage of brain networks that control dorsal visual functions, which facilitate motion processing, as opposed to ventral visual functions, which facilitates form recognition (Reiss, Hoffman, & Landau, 2005). A previous study (Atkinson, et al., 2003) involving WS participants reported the identification of similar oriented lines in a random array of lines as better than identification of similar moving dots within an array of random moving dots. This suggests a damage vulnerability to dorsal visual functions compared to ventral visual functions in WS. This idea is formally termed the dorsal-stream vulnerability hypothesis (Atkinson, et al., 2003). We conducted a similar study, using only presentations of dots, to further investigate dorsal and ventral visual functions in WS participants.
During July 2012, we attended the Williams Syndrome Association National Convention to evaluate aspects of the dorsal-stream vulnerability hypothesis. We had participants look at pairs of images containing different patterns of dots to see if they could tell which showed an overall circular pattern. The slides were presented on a computer screen and were made of circular or random assortments of dots in still and moving conditions. The still or “static” condition was designed to test form perception (ventral visual functions), while the moving or “dynamic” condition was designed to test form and motion perception (ventral and dorsal visual functions together).The overall circular pattern of dots was hidden within random dots on the screen. The number of random dots was increased and decreased to measure the lowest proportion of random dots needed to correctly identify the circular pattern 82% of the time. If the dorsal-stream vulnerability hypothesis is true for WS participants, then those participants would show atypical processing of the dynamic condition compared to the other participant groups.
In all, we recruited 77 participants: 12 typical adults (19-27 years), 48 typically developing children (4-15 years), and 17 individuals with WS (8-35 years). The lowest proportion identification scores for WS participants were matched according to age and IQ with the scores of typically developing children and adults. Overall, the dynamic condition was more easily identified. The lowest proportion identification scores were higher for typical children (4-6 years) and WS individuals relative to the other age groups (7 years, 8-9 years, 10-15 years, and adults[JMP1] ). This suggests that the ability to identify form is immature in WS, rather than atypical. These data offer additional information to the dorsal-stream vulnerability hypothesis, in that perception of visual dot form is different from perception of visual dot form and motion together. This information can be used to develop future experiments that examine how form and motion perception changes during development and whether or not those changes are reflected in WS.