SPEECHREADING IN THE AKINETOPSIC PATIENT, L.M

Patient L.M. has a well-documented, long-standing and profound deficit in the perception of visual movement, following bilateral lesions of area V5 (visual movement cortex). Speechreading was explored in this p atient in order to clarify the extent to which the extraction of dynam ic information from facial actions is necessary for speechreading. Sin ce L.M. is able to identify biological motion from point-light display s of whole-body forms and has some limited visual motion capabilities, we expected that some speechreading effaces in action would be possib le in this patient. LM.'s reading of natural speech was severely impai red, despite unimpaired ability to recognize speech-patterns from face photographs and reasonable identification of monosyllables produced i n isolation. She was unable to track multisyllabic utterances reliably and was insensitive to vision when incongruent audiovisual speech syl lables were shown. Point-light displays of speech were as poorly read as whole face displays. Rate of presentation was critical to her perfo rmance. With speech, as with other visual events, including tracking t he direction of gaze and of hand-movement sequences, she could report actions that unfolded slowly (similar to one event per 2 s). In line w ith this, she was poor at reporting whether seen speech rate was norma l, fast (double-speed) or slow (half-speed). LM.'s debility is the con verse of that reported for a patient with lesions primarily to V4 (H.J .A.), who is unable to speechread photographs of faces but can speechr ead moving faces. The visual analysis of both form and motion is requi red for speechreading; the neural systems that support these analyses are discussed.