Face perception after brain injury. Selective impairments affecting identity and expression.

Current theoretical models of face perception postulate separate routes for processing information needed in the recognition of a familiar face, for matching photographs of unfamiliar faces and for the analysis of facial expressions. The present study investigated this claim in a group of ex-servicemen who had sustained unilateral brain injuries affecting posterior areas of the left or right cerebral hemisphere. Care was taken to confirm the nature of impairment by using two different tasks to assess each of the three theoretically defined abilities (leading to a total of six tasks). We adopted a stringent application of the double dissociation methodology to investigate the pattern of performance across tasks of individual ex-servicemen. A selective impairment was defined as a significantly impoverished performance on both tests of a specific ability, while all other tasks were performed within normal limits. In addition, we used both accuracy and response latency measures to substantiate evidence for spared or defective abilities. The results showed selective impairments of all three abilities on accuracy scores. Response latency data confirmed the finding of a selective deficit in the processing of facial expressions, but produced evidence suggesting that impairments affecting familiar face recognition and unfamiliar face matching were not completely independent from each other in this group of ex-servicemen.