Samuel McDougle¹, Dawei Bai¹, Brian Scholl¹, Zekun Sun; ¹Yale University

Visuomotor adaptation is thought to be driven by sensory prediction errors – the difference between predicted and observed visual feedback given an outgoing motor command. In typical tasks in this domain, visual feedback is given in the form of objects such as a white cursor moving on a black background. As a result, the ensuing adaptation could be driven either by the persisting lower-level visual feature (a white patch moving across a black background), or by the resulting object representation itself. To find out requires a stimulus that at first blush may sound impossible: a persisting object without any persisting features. That is what we explored in the present project, exploiting “featureless objects.” In Experiment 1, subjects moved their cursor in a workspace tiled with blue squares of varying brightness. As they moved, each square their hand entered changed from one random shade to another. These brief transients supported the perception of a persistent, trackable object, even though no surface feature was preserved across frames and no static frame allowed for object identification. Feedback was then rotated relative to the angle of subjects’ hand movements, and adaptation was measured via implicit aftereffects (i.e., automatic compensatory adjustments to the induced errors). Subjects adapted robustly, and aftereffects were larger under featureless object feedback versus conventional cursor feedback. In Experiment 2, we extended this finding to another form of featureless object feedback: random pixel shuffling within a static background. We again observed adaptation, and observed a canonical cosine-shaped generalization function when aftereffects were measured at nearby reaching directions not experienced during training. In Experiment 3, we discovered that different forms of featureless object feedback could be tied to the same visuomotor memory, observing complete transfer of adaptation between the two feedback contexts. We conclude that implicit visuomotor adaptation is fundamentally an object-based process.

Acknowledgements: NIH R01 NS134754 (S.D.M.)