Evidence for independent processing of shape by vision and touch

Although visual object recognition is well-studied and relatively well understood, much less is understood about how shapes are recognized by touch and how such haptic stimuli might be compared to visual shapes. One might expect that the processes of visual and haptic object recognition engage identical brain structures given the similarity of the problem and the advantages of avoiding redundant brain circuitry, but it has not yet been established the extent to which this is true. We recruited human participants to perform a one-back same-different visual and haptic shape comparison task both within (i.e., comparing two visual shapes or two haptic shapes) and across (i.e., comparing visual with haptic shapes) modalities. Participants saw or felt a shape and responded according to whether they thought the shape was the same or different from the previously felt or seen shape. We then used various shape metrics to predict performance based on the shape, orientation, and modality of the two stimuli which were being compared on each trial. We found that the fixed orientation of the shape stimuli was an important factor for predicting within-modal behavior, but the orientation of shapes compared across modality did not depend on knowing the presented orientation. We also found that the metrics which best predict shape comparison behavior heavily depended on the modality of the two shapes. We take these results as evidence that object recognition is not necessarily performed in a single, modality-agnostic region.