Zvi Shapiro¹ (), Alexander Weigard², Daniel Dilks¹; ¹Emory University, ²University of Michigan

Williams syndrome (WS) – a genetic disorder – is often characterized by a dorsal stream deficit. However, beyond impairment on many dorsal stream tasks, yet sparing on many ventral stream tasks, what does "dorsal stream deficit" mean? What is the mechanism driving this impairment? A recent computational modeling study found excessive noise explained the impairment on one dorsal stream task (a visually-guided navigation task) relative to one ventral stream task (a scene categorization task) in adults with WS. This finding leads to the intriguing hypothesis that excessive noise explains impairment on all dorsal stream tasks in WS. To directly test this hypothesis, we modeled the performance of adults with WS and mental-age (MA) matched controls on 3 pairs of dorsal/ventral tasks: i) intuitive physics/intuitive psychology, ii) configural/featural face processing, iii) configural/featural scene processing. Using each group of participants’ response times and accuracy for each task, we fit a hierarchical Linear Ballistic Accumulator model, an evidence accumulation model of decision-making. and operationalized the rate of information accumulation to the correct response (i.e., correct drift rate) as “signal,” the rate of information accumulation to the incorrect response (error drift rate) as “noise,” and the amount of information needed before making a decision (boundary) as “threshold.” Consistent with our hypothesis, we found disproportionately more noise in each of the three dorsal tasks in WS adults compared to MA controls, relative to the three ventral tasks. No such difference between groups was found for signal or threshold. Taken together, our results reveal excessive noise explains the deficit across dorsal stream tasks in WS, and suggests a reformulation of WS from simply being characterized by a dorsal stream deficit to being characterized by excessive noise in the dorsal stream.

Acknowledgements: NIH NEI R01 EY297242DDD