Impaired geometric reorientation caused by genetic defect

Abstract

The capacity to reorient in one's environment is a fundamental part of the spatial cognitive systems of both humans and nonhuman species. Abundant literature has shown that human adults and toddlers, rats, chicks, and fish accomplish reorientation through the construction and use of geometric representations of surrounding layouts, including the lengths of surfaces and their intersection. Does the development of this reorientation system rely on specific genes and their action in brain development? We tested reorientation in individuals who have Williams syndrome (WS), a genetic disorder that results in abnormalities of hippocampal and parietal areas of the brain known to be involved in reorientation. We found that in a rectangular chamber devoid of surface feature information, WS individuals do not use the geometry of the chamber to reorient, failing to find a hidden object. The failure among people with WS cannot be explained by more general deficits in visual-spatial working memory, as the same individuals performed at ceiling in a similar task in which they were not disoriented. We also found that performance among people with WS improves in a rectangular chamber with one blue wall, suggesting that some individuals with WS can use the blue wall feature to locate the hidden object. These results show that the geometric system used for reorientation in humans can be selectively damaged by specific genetic and neural abnormalities in humans.

Fig. 1.

Illustration of the testing environment for the current experiments. A, B, C, and D denote each of the four walls. In the black wall condition, all walls were black. In the blue wall condition, wall A was blue. C, R, N, and F illustrate the four corners in which the toy was hidden (with hiding location counterbalanced across participants). C, correct corner (i.e., corner where the toy was hidden); R, rotationally equivalent corner (i.e., the corner that is rotationally equivalent to the correct corner); N, near corner (i.e., the corner that is closest to the correct corner); F, far corner (i.e., the nonrotationally equivalent corner that is farthest from the correct corner). In previous studies using similar testing environments (see text), nonhuman species and human toddlers show characteristic breakdown patterns in their search for a hidden object, even when a feature, such as a colored wall, fully species the object's location. This characteristic breakdown pattern is to search at the correct corner (C) as well as the rotationally equivalent corner (R), suggesting that reorientation is based upon the geometry of the layout.

Fig. 2.

Average proportion of search (and SEs) at each corner (correct, rotationally equivalent, near, and far) for the WS participants in experiment 1 (A, four black walls; B, one blue wall) and experiment 2 (C, four black walls, no disorientation)