Abstract
Previous work (Heath et al., 2011) has shown that grip aperture variability (i.e., just-noticeable-differences: JNDs) elicits a time-dependent early, but not late, adherence to Weber's law. The present study examined whether such a time-dependent effect is related to the explicit visual properties of a to-be-grasped target object or the proportional relation between the forces involved in grip aperture specification and aperture variability. Participants (N=15) grasped differently sized target objects in movement time criteria of 400 and 800 ms. If the time-dependent adherence to Weber's law is associated with a dynamic use of visual codes, a parallel scaling of JNDs to object size should be observed between conditions. Alternatively, if adherence to Weber's law is a derivative of aperture kinetics, then JND values should elicit larger scaling in the 400 ms condition. As expected, grip aperture velocities for the 400 ms condition were greater during early and late aperture shaping. Notably, however, the increased velocities did not differentially influence the previously reported temporal adherence of JNDs to object size. As such, the present results indicate that the time-dependent adherence to Weber's law is not tied to the inherent variability in forces associated with grip aperture shaping; rather, results suggest a respective early and late use of relative and absolute visual codes.Acknowledgments: Supported by NSERC