Pointing the Way to New Constraints on the Dynamical Claims of Computational Models

The reach-to-touch paradigm has become an increasingly popular tool in the study of human cognition. It is widely held that reaching responses are able to reveal the moment-by-moment unfolding of decision processes by virtue of an assumed continuity between reaching trajectories and the underlying "cognitive trajectory." Yet the standard analysis of reaching trajectories aggregates the trajectories across stimulus viewing times, which yields ambiguous results. Here we introduce a new version of the reach-to-touch paradigm that incorporates the response-signal procedure to elicit reaching movements across a wide range of stimulus viewing times. We then analyze the direction of the initial movement by stimulus viewing time, which produces a sigmoidal growth pattern. Of note, we show how this sigmoidal relationship between stimulus viewing time and initial direction can be used to test and constrain the dynamical claims of computational models of basic cognitive processes. We introduce our new version of the reach-to-touch paradigm and analyses in the context of a lexical decision task and we compare our results with the dynamical claims of the dual-route cascaded model of reading.