Haptic Object Recognition: How Important are Depth Cues and Plane Orientation?

Abstract

Raised-line drawings of familiar objects are very difficult to identify with active touch only. In contrast, haptically explored real 3-D objects are usually recognised efficiently, albeit slower and less accurately than with vision. Real 3-D objects have more depth information than outline drawings, but also extra information about identity (eg texture, hardness, temperature). Previous studies have not manipulated the availability of depth information in haptic object recognition whilst controlling for other information sources, so the importance of depth cues has not been assessed. In the present experiments, people named plastic small-scale models of familiar objects. Five versions of bilaterally symmetrical objects were produced. Versions varied only in the amount of depth information: minimal for cookie-cutter and filled-in outlines, partial for squashed and half objects, and full for 3-D models. Recognition was faster and much more accurate when more depth information was available, whether exploration was with both hands or just one finger. Novices found it almost impossible to recognise objects explored with two hand-held probes whereas experts succeeded using probes regardless of the amount of depth information. Surprisingly, plane misorientation did not impair recognition. Unlike with vision, depth information, but not object orientation, is extremely important for haptic object recognition.