Do curved reaching movements emerge from competing perceptions? A reply to van der Wel et al. (2009)

Spivey, Grosjean, and Knoblich (2005) reported smoothly curved reaching movements, via computer-mouse tracking, which suggested a continuously evolving flow of distributed lexical activation patterns into motor movement during a phonological competitor task. For example, when instructed to click the "candy," participants' mouse-cursor trajectories curved conspicuously toward a picture of a candle before landing on the picture of the candy. In their commentary on this work, van der Wel, Eder, Mitchel, Walsh, and Rosenbaum (2009) describe a quantitative simulation of reaching movements that stands as an existence proof that a discrete-processing speech perception system can feed into a continuous-processing motor movement system to produce reach trajectories similar to that observed by Spivey et al. In this reply, we describe eye-tracking evidence, new mouse-tracking evidence, and a dynamic version of van der Wel et al's simulation, all of which suggest that competing perceptual representations may instigate the preparation of multiple movement plans that are merged in a dynamically weighted average, thus producing a single smoothly curved movement. Like van der Wel et al., we are optimistic that an emphasis on the computational linking hypothesis between hypothesized perceptual representations and recorded motor movements will elucidate the discrete versus continuous aspects of perceptual, cognitive, and motor processing.