Implitict object recognition in visual integrative agnosia: Patient SE

Abstract

The present study investigates implicit object recognition in a patient with visual integrative agnosia. Consequent to a bilateral infarct due to CVA of the posterior cerebral arteries, patient SE exhibited severe object and face recognition impairments. Although he was unable to identify hierarchical stimuli at the global level, SE's performance on the local components of these figures suggested implicit processing of global identity, however. The goal of the present study was to investigate whether objects that SE fails to identify explicitly were identified implicitly. In Experiment 1, a target word (the probe) was preceded by a drawing of an object or animal (the prime). SE performed a word categorization task (animate/inanimate) on the probe. Picture primes represented either the same exemplar as that of the probe (e.g. a picture of a dog followed by the word probe “DOG”), or a different exemplar from the same category (e.g. a picture of a camel followed by the probe “DOG”) or an unrelated noun from a different category (e.g. a picture of a chair followed by the probe “DOG”). In Experiment 2, the prime was a word and the probe was a picture. The task was to determine whether the picture represented a possible or an impossible object or animal. Pictures in the impossible condition were created by seamlessly combining the parts of different objects or animals. For possible pictures the word primes denoted either the same exemplar or a different exemplar from the same category. A third condition presented a noun followed by a picture of an impossible object. In both experiments the response to the probe was facilitated in the same condition compared to the different condition, providing clear evidence for bi-directional semantic mediation (from words to pictures, and from picture to words) without explicit identification of the pictures. These findings will be discussed in the context of theories of perceptual organization of visual input and visual awareness.