Sequential ordering of morphed faces and facial expressions following temporal lobe damage.

A card ordering task was developed to evaluate the role of the temporal lobe in perceiving subtle featural displacements of faces that contribute to judgments of facial expression and identity. Individuals with varying degrees of temporal lobe damage and healthy controls were required to manually sort cards depicting morphs of facial expressions or facial identities so that the cards were sequentially ordered from one morph endpoint to another. Four morph progressions were used--three emotion morphs (neutral-to-anger, neutral-to-fear, and fear-to-anger) and an identity morph. Five exemplars were given per morph type. Debriefing verified that participants were using feature-level cues to sort the cards. A patient with bilateral amygdala damage due to epilepsy did not differ in her sorting abilities from unilateral temporal lobectomy patients or controls. In contrast, a post-encephalitic patient with widespread left temporal lobe damage showed impairments that were most marked on the fear-to-anger and identity sorts. These results show that amygdala-damaged individuals can use information contained in facial expressions to solve tasks that rely on feature-level analysis, which recruits processing in other temporal lobe regions involved in making fine featural distinctions.