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Impaired spatial coding within objects but not between objects in prosopagnosia

From the Departments of Neurology (Dr. Barton, M.V. Cherkasova) and Ophthalmology (Dr. Barton), Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA; and Departments of Neurology, Ophthalmology, and Visual Sciences (Dr. Barton), University of British Columbia, Vancouver, Canada.

Address correspondence and reprint requests to DrS. Barton, Neuro-ophthalmology Section D, VGH Eye Care Center, 2550 Willow St., Vancouver, BC, Canada V5Z 3N9; e-mail: jasonbarton{at}shaw.ca

Background: Patients with prosopagnosia from occipitotemporal lesions have impaired perception of the configuration of facial features. This may be an example of impaired "within-object" spatial coding, which others propose to be distinct from "between-object" spatial coding.

Objective: To determine whether the prosopagnosic deficit in perceiving spatial configuration was specific to within-face and not between-face spatial coding and whether the deficit was face-selective or extended to objects other than faces.

Methods: Six prosopagnosic patients were tested using an oddity paradigm in which they detected which of three simultaneously seen stimuli was an altered target. In the "within-face" task, the target face had altered interocular distance or mouth position. In the "between-face" task, the target face was located farther away from the other two. In the "within-object" task, the stimulus was a two-dot pattern, and the target pattern had altered interdot distance.

Results: Spatial judgments were impaired within faces for all six patients and within the two-dot pattern for five of six patients. However, all six had normal between-face spatial perception.

Conclusions: Impaired perception of spatial relations in prosopagnosia is selective to the spatial structure within individual objects and spares the perception of spatial location of objects. It is not specific to faces. It reveals a process involved in analyzing object structure, consistent with the patients’ deficits in recognizing facial identity, and illustrates a different type of "visuospatial" defect.

J.J.S.B. was supported by National Institute of Mental Health grant 1R01 MH069898, a Canada Research Chair, and a Michael Smith Foundation for Health Research Senior Scholarship.

Portions of these data were presented at the meetings of the Eastern Psychology Association, Boston, MA, 2002, and the American Academy of Neurology, Denver, CO, 2002 (Neurology 58(suppl 3):A244).

Note: numbering convention of patients follows that in Barton and Cherkasova (Neurology 2003;61:220–225). This is also similar to the numbering in Barton et al. (Neurology 2001;57:1161–1167), with the exception that Subject 007 is Patient 4 and Subject 004 is Patient 7 in that report. In Barton et al. (Neurology 2002;58:71–78), Patient 2 is Subject 004, Patient 3 is Subject 007, and Patient 4 is Subject 005.

Received September 23, 2004. Accepted in final form April 11, 2005.