Introduction

This chapter focuses on spatial cross-modal integration between visual and tactile stimuli, which is often thought to arise primarily in the peripersonal space near the body or hands within which objects can be touched and manipulated (see, e.g., Duhamel, Colby, & Goldberg, 1998; Fogassi et al., 1996; Gentilucci et al., 1988; Graziano & Gross, 1995; Rizzolatti, Scandolara, Matelli, & Gentilucci, 1981). We examine how such integration can be extended into more distant space, either when a person wields a tool that brings distant visual stimuli within touchable or manipulable reach or when the hands are seen in a mirror, so that their distant visual reflections can relate to touch at the hands' true location. Data from studies in normal and brain-damaged adult humans are tentatively related to the growing body of neurophysiological data on multisensory representations of space near the body at the single-cell level (see, e.g., Colby, Duhamel, & Goldberg, 1993; Gentilucci et al., 1988; Graziano & Gross, 1995; Graziano, Yap, & Gross, 1994; Leinonen, Hyvärinen, Nyman, & Linnankoski, 1979; Rizzolatti et al., 1981). The work reviewed shows how classical notions of the “body schema” (Head & Holmes, 1911; see also Ishibashi, Obayashi, & Iriki, Chap. 28, this volume, for a detailed discussion of this construct) may now be subjected to psychological and neuroscientific scrutiny (cf. Aglioti, Smania, Manfredi, & Berlucchi, 1996; Berlucchi & Aglioti, 1997; Frederiks, 1985), leading to more mechanistic formulations of how the space near our body parts may be represented and how these spatial representations can be dynamically altered by wielding tools or viewing mirror reflections.

In the first section of the chapter, we discuss recent evidence that visual-tactile spatial integration can be modulated by the use of long tools. Wielding long tools not only extends reaching abilities into far space but also may modulate the integration between distant visual stimuli at the end of the tool (which become reachable by it) and tactile stimuli on the hands wielding the tool. Far visual events that can be reached by the tool start to influence tactile stimulation in a similar fashion to visual stimuli that are located nearer to the stimulated hand. In effect, the distant visual stimuli become “peripersonal” when a tool allows them to be reached.

In the second part of the chapter, we consider situations in which the hands are seen reflected in a mirror, so that their distant visual images reflect information that is actually located near (or at) the hands in external space. Intriguingly, in this situation, visual input from the mirror is seen as far away (“through the looking glass”), projecting the same optical images as those that would be produced by distant sources. We show that distant visual stimuli (now reflections in the mirror) can interfere with tactile stimuli in an analogous manner to visual stimuli that are directly seen as close to the hand, provided the mirror reflections are represented as having a peripersonal source, as when the true location of the source of the mirror image can be encoded. These results can be seen as analogous to the effects of tool use in some respects, with mirrors serving as a more abstract kind of tool that can also allow distant visual information to be related to touch on the body or hands. Finally, we discuss the possible roles of learning, or of top-down knowledge, in producing these various extensions of tactile-visual interactions into distant visual space.