Objects can be recognized using any of our sensory modalities. For instance, a bumblebee can be recognized by seeing its characteristic yellow and black colors, by hearing its distinctive buzzing sound, by feeling the fuzzy surface of its body as it walks across our hand, by experiencing the pain as it stings our finger, or by any combination of these cues. But, it is only by using vision and touch that the complex three-dimensional (3-D) geometric properties of particular objects can be recognized. Of these two senses, vision is the one we use most often to identify objects-although the tactile system (or haptics) is also useful, particularly in situations where the objects cannot be seen. Haptics can also provide information about the weight, compliance, and temperature of an object-as well as information about its surface features, such
as how sticky or slippery it is-information that is not readily available by merely looking at the object. But, by the same token, vision can provide information about an object’s color and surface patterns-features that cannot be detected by haptics. Moreover, even though both haptics and vision provide information about an object’s volumetric shape, there are clear differences in the way in which that information is garnered by the two systems. The haptic system can operate only on objects that are located within personal space, that is, on objects that are within arm’s reach. The visual system, however, can analyze not only objects that reside within personal space but also those that are at some distance from the observer. Of course, when objects are at a distance, only the surfaces and parts of an object that face the observer can be processed visually (although it is possible, in some cases, for the observer to walk around the object and take in information from multiple viewpoints). When objects are within reach, however, they can be manipulated, thus revealing the structure and features of the previously unseen surfaces and parts to both the visual and the haptic system.