Face context interferes with local part processing in a prosopagnosic patient

We investigated the role of local and global information on perceptual encoding of faces in patient HJA, who shows prosopagnosia and visual agnosia following occipito-temporal damage. HJA and an age-matched control were tested in a simultaneous matching task which focused on detection of local changes in faces: the inversion of central parts (eyes and mouth) relative to their context (as in the Thatcher illusion). Same-different judgements were made to normal, “thatcherised” and mixed type face pairs. Whole faces (Experiment 1), or face parts (Experiment 2), were presented in upright and inverted orientations. Compared to the control, HJA was severely impaired at matching whole faces, but he improved dramatically when face parts were presented in isolation. This suggests an inhibitory influence of face context on HJAs processing of local parts and a relatively intact ability to process part-based information from a face (when context cannot interfere). Face inversion did not affect HJAs performance. A control experiment (Experiment 3) with non-face stimuli (houses) suggested that the inhibitory influence of context on HJAs performance was restricted to faces. These results indicate that contextual information in a face can have an adverse influence on the processing of local part-based information in prosopagnosia.