Interarticulator co-ordination in deaf signers with Parkinson's disease.

Motor control deficits in signers with Parkinson's disease (PD) were examined through analysis of their production of American Sign Language (ASL) fingerspelling, which is sequential and rapid motor behavior that has theoretical models of its underlying structure. Free conversation of two Deaf signers with PD and two Deaf control signers was analysed. In addition, scripted productions of one control signer were also analysed and directly compared to the same productions by the signers with PD. A featural analysis of ASL fingerspelling and a frame-by-frame analysis of multiple articulator movements were used to examine the fingerspelled productions. On the basis of the featural analysis, the signers with PD showed a variety of error patterns, all of which reflected attempts to reduce the motoric demands of coarticulation and thereby facilitate ease of articulation. Signers with PD either held individual segments in a fingerspelling sequence for a long time (segmentation), blended adjacent segments into a single segment (sequential blending), or broke handshapes down sequentially into their component features (featural unraveling). The results of both the featural analysis and the frame-by-frame analysis show that the PD signers have difficulty co-ordinating the movements of independent articulators in complex sequences. For example, the movements of independent articulators for fingerspelling (the thumb, fingers, and wrist) were markedly farther apart in time and more variable for the signers with PD. In addition, the signers with PD used fewer wrist movements while fingerspelling. Such deficits are consistent with claims that patients with PD are impaired in their ability to use ongoing sensorimotor information to program multi-articulator movements.