Dynamic Manipulation Generates Touch Information That Can Modify Vision

>> This report constitutes a critical expansion of a recent study on tool use (Carlson, Alvarez, Wu, & Verstraten, 2010), published in this journal. Carlson et al. explored the classic question of how, during manipulation, an external object may seem to become an extension of one’s body. They demonstrated that objects manipulated with the hand can become one with the body, but objects manipulated with a tool cannot. They interpreted this as evidence that such integration is limited to first-order extensions. However, close inspection of the experimental conditions reveals that Carlson et al. overlooked how dynamic manipulation of an object affects the prehensile system. They used just one tool: a pair of grippers fixed to, and supported by, a table. In this arrangement, the table absorbs most of the forces associated with object manipulation. By contrast, when a freely maneuverable handheld tool is used, the forces are transmitted through the tool and interact with the arm and body, much as they do during direct manual manipulation. The notion that, without vision, object properties such as the length of a handheld rod can be perceived during dynamic manipulation has been well established. This system of touch perception is known as dynamic touch— perception based on information from effort-related muscle and tendon deformations (Carello & Turvey, 2000; Gibson, 1966; Turvey, 1996; Turvey & Carello, 2011). However, little is known about the perception of a target object when it is manipulated with a handheld tool. We concluded that the approach used by Carlson et al. would be a useful way to test such perception empirically, and we extended their conditions to include one with a freely maneuverable tool. Moreover, we predicted that the target object would be perceived with and without a tool, but only when the prehensile limb was maneuvering freely.