Holmes NP (2005) Of tools, mirrors, & bodies: Multisensory interactions in peripersonal space. PhD Thesis, Wolfson College, University of Oxford, 302pp.
This thesis reports 22 experiments involving 508 healthy human participants, involving behavioural, functional magnetic resonance imaging (fMRI), and repetitive transcranial magnetic stimulation (rTMS) techniques. The experiments reported in Chapter 2 and Chapter 3 were designed to address the question: Does tool-use extend peripersonal space? Recent single-cell neurophysiological, neuropsychological, and behavioural evidence suggests that tool-use can lead to an extension of the visual receptive fields of neurons representing multisensory peripersonal space, or of an extension of that representation of space in general. The evidence for this hypothesis is critically discussed in Chapter 1, and several key predictions of this hypothesis are tested in Chapter 2 and Chapter 3, using crossmodal congruency behavioural tasks and fMRI to distinguish between competing theoretical accounts of the reported multisensory effects of tool-use. The results of these experiments suggest that tools affect multisensory integration by acting as salient visual and motor cues to attend to different regions of space, or to different responses, rather than acting as extensions of hand-centred peripersonal space. Chapter 4 addresses the representation of peripersonal space from the perspective of the multisensory representation of hand position prior to reaching and pointing movements. The experiments reported in Chapter 4 used a ‘mirror-illusion’ in order to induce conflicts between the visually- and proprioceptively-specified position of participants’ hands. The effect of different manipulations of that conflict on the generation and control of reaching movements was studied. Finally, the role of the superior parietal lobule in integrating visual and proprioceptive signals in the control and generation of reaching movements was investigated with rTMS. The discussion in Chapter 5 examines the sensory and motor aspects of the representation of peripersonal space. The thesis concludes by outlining several possible solutions to address empirical differences between the neurophysiological literature, which emphasizes the representation and sensory guidance of movement, and the psychological literature, which emphasizes the representation of sensory and perceptual space. While peripersonal space in the monkey may be intimately involved in the sensory guidance of reflexive or automated hand and mouth movements, the role of such a representation in humans is not yet clear, but, if it exists, offers a fascinating and empirically challenging area for future study