Lateralization of Categorical and Coordinate Spatial Functions: A Study of Unilateral Stroke Patients

Abstract

Sixty patients with unilateral stroke (half with left hemisphere damage and half with right hemisphere damage) and a control group (N = 15) matched for age and educational level were tested in two experiments. In one experiment they were first shown, on each trial, a sample drawing depicting one or more objects. Following a short delay, they were asked to identify the drawing when it was paired with a drawing in which the same object(s) was transformed in categorical or coordinate spatial relations. In the other experiment, the same subjects first were shown, on each trial, a sample drawing. They then judged which of two variants (each in one type of spatial relation) looked more similar to the sample drawing. Typically, patients with left-sided stroke mistakenly identified the categorical transformation for the sample drawing in the first task; in the second task, they judged the categorical transformation as more similar to the sample drawing. Patients with right-sided stroke mistakenly identified the coordinate transformations for the sample drawing in the first task, and, in the second task, typically judged the drawings transformed along coordinate spatial relations as more similar to the sample drawing. These findings provide evidence for complementary lateralization of the two types of spatial perception. It can therefore be inferred that separate functional subsystems process the two types of spatial relations.

Categorical and coordinate spatial representations within object-location memory

“…Although impaired memory for coordinate position information due to damage to the right hemisphere has been found previously (Kessels et al, 2002(Kessels et al, , 2004, a deficit for pure categorical position memory after damage to the left hemisphere has not yet been demonstrated within this object-location paradigm. The results are in line with the idea that categorical spatial representations are processed by the left hemisphere and coordinate spatial representations are processed by the right hemisphere (Kosslyn et al, 1989;Laeng, 1994;Laeng and Peters, 1995). Importantly, this lateralization effect for categorical and coordinate spatial information was not found when position information had to be integrated with object information.…”

“…Kosslyn et al (1989) showed that healthy participants could evaluate categorical representations better when they were initially presented to the left hemisphere, whereas coordinate representations were evaluated better when information was initially presented to the right hemisphere (Kosslyn et al, 1989). Similar effects were found when examining the processing of categorical and coordinate position information in patients with focal lesions in either the left or right hemisphere (Laeng, 1994). The ''identity task'' was used in which a drawing of one or more objects was shown during a short period of time.…”

“…This computerized version of the Identity test used by Laeng (1994) included the same 20 stimulus pairs as the original experiments with cards. Black-and-white drawings of animals (e.g., rabbit) and objects (e.g., football) were shown on a 15-inch computer-screen during 5 sec.…”

“…Since patients might be impaired in their ability to perform the precise motor movements that this condition requires, the visuo-spatial construction condition was used as a covariate. Finally, the identity task was included as well, because of its potential to demonstrate the hypothesized function lateralization (Laeng, 1994). In general, we hypothesized that encoding coordinate spatial positions would relate to the right hemisphere, whereas encoding categorical spatial positions were impaired by damage to the left hemisphere.…”

“…Twenty-five patients who had suffered from a stroke and 36 healthy controls were tested with different tests assessing categorical and coordinate position memory, and categorical and coordinate object-to-position memory. The identity task that was used by (Laeng, 1994) was included as well as a control task for measuring lateralization effect for categorical and coordinate information. Moreover, object-recognition and visuo-spatial perception were assessed.…”