Abstract
In human movement coordination 0° and 180° mean relative phase (MRP) are the only spontaneously stable states, with 0° more stable than 180°. Our research focuses on the role of perceptual information in producing this pattern, specifically perceived phase. With both visual (e.g. Zaal, Bingham & Schmidt, 2000) and haptic (Wilson, Bingham & Craig, submitted) phase information, 180° was judged as intrinsically more variable than 0°, and at other MRPs, added variability was not discriminated. This motivated a new model of rhythmic movement coordination (Bingham, 2001; Bingham & Collins, submitted) in which (non-linear autonomous) oscillators are driven and coupled by perceived phases. The current research separates the contributions of visually and haptically perceived phase in a movement coordination task. Participants moved a joystick to maintain a visual MRP of 0° between 2 dots on a screen, joystick and computer controlled respectively. The mapping between the joystick and its dot was manipulated to be either 0° (labeled 0/0) or 180° (0/180). We hypothesized that participants would be able to discriminate small variations from the intended visual MRP of 0° and use this to drive stable performance. In both cases participants maintained visual MRP close to 0° (−14.9° for 0/0, −17.4° for 0/180). Stable visual perception of 0° did indeed stabilize the movement. However, 0/180 (mean vector length (MVL) = 0.45) was more variable than 0/0 (MVL=0.58, where a larger MVL denotes less variable data). Additionally, a control case in which participants moved at 180 to produce 180 visually (180/180), demonstrated that participants could not do this as stably as 0/180 (MRP = 149.5°, MVL = 0.36). The haptic MRP was still having an effect consistent with the movement stability pattern. Results are discussed in terms of the relative contributions of visually and haptically perceived phase to the performance of coordinated movement.