Tactile picture recognition: errors are in shape acquistion or object matching?

Numerous studies have demonstrated that sighted and blind individuals find it difficult to recognize tactile pictures of common objects. However, it is still not clear what makes recognition of tactile pictures so difficult. One possibility is that observers have difficulty acquiring the global shape of the image when feeling it. Alternatively, observers may have an accurate understanding of the shape but are unable to link it to a particular object representation. We, therefore, conducted two experiments to determine where tactile picture recognition goes awry. In Experiment 1, we found that recognition of tactile pictures by blindfolded sighted observers correlated with image characteristics that affect shape acquisition (symmetry and complexity). In Experiment 2, we asked drawing experts to draw what they perceived after feeling the images. We found that the experts produced three types of drawings when they could not recognize the tactile pictures: (1) drawings that did not look like objects (incoherent), (2) drawings that looked like incorrect objects (coherent but inaccurate) and (3) drawings that looked like the correct objects ( coherent and accurate). The majority of errors seemed to result from inaccurate perception of the global shape of the image (error types 1 and 2). Our results suggest that recognition of simplistic tactile pictures of objects is largely inhibited by low-level tactile shape processing rather than high-level object recognition mechanisms.