A tale of two agnosias: Distinctions between form and integrative agnosia

Abstract

The performance of two patients with visual agnosia was compared across a number of tests examining visual processing. The patients were distinguished by having dorsal and medial ventral extrastriate lesions. While inanimate objects were disadvantaged for the patient with a dorsal extrastriate lesion, animate items are disadvantaged for the patient with the medial ventral extrastriate lesion. The patients also showed contrasting patterns of performance on the Navon Test: The patient with a dorsal extrastriate lesion demonstrated a local bias while the patient with a medial ventral extrastriate lesion had a global bias. We propose that the dorsal and medial ventral visual pathways may be characterized at an extrastriate level by differences in local relative to more global visual processing and that this can link to visually based category-specific deficits in processing.

Keywords:

• Apperceptive agnosia
• Form agnosia
• Local/global processing
• Extrastriate lesions

We are extremely grateful for the kind participation of H.J.A., S.A., and K.A. in these studies. The work was supported by grants from the Medical Research Council (MRC) and the Stroke Association, UK.

Notes

¹This term was originally coined by Freud (1891).

²However, we note that S.A. was at the low end of the control range on the position of the gap task.

³H.J.A. performed the nonhierarchical conditions twice, a total of 80 trials each.