Neural and behavioral sensitivity to boundary cues across typical and atypical development

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Date
2015-07-16
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Johns Hopkins University
Abstract
Boundaries are fundamental features that define a scene and contribute to its geometric shape. For example, four-year-olds reorient in accord with the geometry of a layout defined by a curb that is 2 cm high, but fail to do so when the curb is replaced by a flat mat on the floor (Lee & Spelke, 2011). Our previous research using fMRI showed a similar distinct sensitivity to boundaries in scene representation by the healthy adult brain (Ferrara & Park, 2014). In the present research, I aim to determine whether this finely tuned sensitivity to boundaries may be impaired by genetic deficit. Behavioral (Experiment 1) and neuroimaging (Experiment 2) methods are used to study individuals with Williams syndrome (WS), a developmental disorder characterized by a profile of severe impairment in a range of spatial functions. In Experiment 1, individuals with WS and typically developing (TD) age-matched controls were disoriented and then recovered a hidden target in three different types of arrays that varied in terms of boundary cue: a Mat, a Curb and full Walls. Unlike TD controls, who reoriented geometrically in all three arrays, people with WS only reliably used geometry in the Wall condition. In Experiment 2, we measured fMRI activity in scene-selective regions of the same WS and TD participants. Scene stimuli were used that mirrored the physical boundary arrays of Experiment 1: a Mat, a Curb, and a Wall. In TD controls, the parahippocampal place area (PPA) showed increases in activity from the Mat, to Curb, to Wall. In WS participants however, PPA activity did not distinguish between the Mat and Curb. Multivoxel pattern analyses using a linear classifier confirmed this difference between the two participant groups. Taken together, these results reveal one of the crucial aspects of scene representation that is manifested behaviorally as fine-grained sensitivity to slight boundary cues in reorientation. Using WS as a test case, we find that atypical patterns of reorientation correspond with less fine-grained distinction at the neural level. By coupling behavioral and neuroimaging methods, this research sheds light on the connection between scene representation in the brain and fluid navigation in behavior.
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Keywords
Navigation, Vision, Geometric reorientation, Development, Spatial perception, Williams syndrome
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