Changing grasp position on a wielded object provides self-training for the perception of length

Calibration of perception to environmental properties typically requires experiences in addition to the perceptual task, such as feedback about performance. Recently, it has been shown that such experiences need not come from an external source or from a different perceptual modality. Rather, in some cases, a given perceptual modality can train itself. In this study, we sought to expand on the range of experiences in which this can occur for perception of the length of a wielded occluded object. Specifically, in two experiments, we investigated whether the act of perceiving the length of a wielded object from a given grasp position could recalibrate the perception of length from a different grasp position. In both experiments, three groups of participants perceived the lengths of wielded rods in a pretest, practice, and a posttest. The practice included either (a) experimenter feedback, (b) changing the grasp position on the object (and again attempting to perceive length), or (c) no additional experiences. In Experiment 1, participants changed their grasp position from the middle to the end of each rod, and in Experiment 2, they did so from the end to the middle of each rod. In both experiments, the results showed that perceiving length from a different grasp position can recalibrate (i.e., provide self-training for) the perception of length.