An Action Field Theory of Peripersonal Space.

The neuroscience of body memory: From the self through the space to the others.

To respond to a touch, it is often necessary to localize it in space, and not just on the skin. The computation of this external spatial location involves the integration of somatosensation with visual and proprioceptive information about current body posture. In the past years, the study of touch localization has received substantial attention and has become a central topic in the research field of multisensory integration. In this review, we will explore important findings from this research, zooming in on one specific experimental paradigm, the temporal order judgment (TOJ) task, which has proven particularly fruitful for the investigation of tactile spatial processing. In a typical TOJ task participants perform non-speeded judgments about the order of two tactile stimuli presented in rapid succession to different skin sites. This task could be solved without relying on external spatial coordinates. However, postural manipulations affect TOJ performance, indicating that external coordinates are in fact computed automatically. We show that this makes the TOJ task a reliable indicator of spatial remapping, and provide an overview over the versatile analysis options for TOJ. We introduce current theories of TOJ and touch localization, and then relate TOJ to behavioral and electrophysiological evidence from other paradigms, probing the benefit of TOJ for the study of spatial processing as well as related topics such as multisensory plasticity, body processing, and pain.

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Using time to investigate space: a review of tactile temporal order judgments as a window onto spatial processing in touch

The rubber hand universe: On the impact of methodological differences in the rubber hand illusion.

Body ownership refers to the perceptual experience of a body or body part as one's own. Integration of signals from different sensory modalities is considered to play a central role in the emergence of this fundamental experience. This chapter reviews behavioral and neuroimaging studies that have investigated the multisensory processes and neural mechanisms involved in body ownership. First, we will discuss behavioral studies that have used different versions of the rubber hand illusion to identify the spatial, temporal, and other multisensory congruence rules that determine ownership of a limb. Thereafter, we will review neuroimaging studies that have linked changes in limb ownership to changes in neural activity in specific multisensory areas in the frontal and parietal association cortices. Finally, we will discuss studies that have used full-body ownership illusions to examine how the sense of ownership of an entire body arises and that have clarified the role of multisensory processes in this perceptual phenomenon. Collectively, the available data suggest an important role for multisensory integration in body ownership; the data also provide substantial support for the hypothesis that body ownership can be seen as multisensory perception of one's own limbs and one's entire body.

Multisensory processes in body ownership

The region surrounding our body (i.e. peripersonal space) is coded in a multimodal representation by fronto-parietal bimodal neurons integrating tactile stimuli on the body with nearby visual stimuli. This has often been suggested to serve a defensive purpose, which we propose could be mediated through visuotactile predictions. An approaching threat would then be of particular interest to peripersonal space processing. To investigate this, we asked participants to respond as fast as possible to a tactile stimulus on the hand, while looking at an animation of an approaching or receding spider or butterfly. Tactile stimulation was applied at one of 25 possible time points during the animation. Tactile reaction times were faster when an approaching stimulus was closer to the hand at the time of tactile presentation. Critically, this effect of distance on reaction times was larger when participants saw an approaching spider compared to an approaching butterfly, but only for participants who were afraid of spiders. This finding demonstrates that the perceived threat of an approaching stimulus modulates visuotactile interactions in peripersonal space and is consistent with the idea that visuotactile predictions are important for defensive purposes and maintaining bodily integrity.

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Approaching threat modulates visuotactile interactions in peripersonal space

No consistent cooling of the real hand in the rubber hand illusion.

Mental imagery is considered to be important for normal conscious experience. It is most frequently investigated in the visual, auditory and motor domain (imagination of movement), while the studies on tactile imagery (imagination of touch) are scarce. The current study investigated the effect of tactile and auditory imagery on the left/right discriminations of tactile and auditory stimuli. In line with our hypothesis, we observed that after tactile imagery, tactile stimuli were responded to faster as compared to auditory stimuli and vice versa. On average, tactile stimuli were responded to faster as compared to auditory stimuli, and stimuli in the imagery condition were on average responded to slower as compared to baseline performance (left/right discrimination without imagery assignment). The former is probably due to the spatial and somatotopic proximity of the fingers receiving the taps and the thumbs performing the response (button press), the latter to a dual task cost. Together, these results provide the first evidence of a behavioural effect of a tactile imagery assignment on the perception of real tactile stimuli.

/pdf/thinking-about-touch-facilitates-tactile-but-not-auditory-1umkk9k4vj.pdf

Thinking about touch facilitates tactile but not auditory processing.

Processing of tactile stimuli requires both localising the stimuli on the body surface and combining this information with a representation of the current posture. When tactile stimuli are applied to crossed hands, the system first assumes a prototypical (e.g. uncrossed) positioning of the limbs. Remapping to include the crossed posture occurs within about 300 ms. Since fingers have been suggested to be represented in a mainly somatotopic reference frame we were interested in how the processing of tactile stimuli applied to the fingers would be affected by an unusual posture of the fingers. We asked participants to report the direction of movement of two tactile stimuli, applied successively to the crossed or uncrossed index and middle fingers of one hand at different inter-stimulus intervals (15 to 700 ms). Participants almost consistently reported perceiving the stimulus direction as opposite to what it was in the fingers crossed condition, even with SOAs of 700 ms, suggesting that on average they did not incorporate the unusual relative finger positions. Therefore our results are in agreement with the idea that, by default, the processing of tactile stimuli assumes a prototypical positioning of body parts. However, in contrast to what is generally found with tactile perception with crossed hands, performance did not improve with SOAs as long as 700 ms. This suggests that the localization of stimuli in a somatotopic reference and the integration of this representation with postural information are two separate processes that apply differently to the hands and fingers.

/pdf/fingers-crossed-an-investigation-of-somatotopic-1dncnfvlaz.pdf

Fingers crossed! An investigation of somatotopic representations using spatial directional judgements.

The aim of this study is to investigate whether the fingers are represented separately from the palm. An exogenous spatial orientation paradigm was used where participants had to detect a tactile stimulus that could appear on the palm, the middle finger or the ring finger of the left hand. The tactile target was preceded by a non-predictive cue using different stimulus-onset asynchronies (SOA). We observed a Facilitation Effect in the palm and Inhibition of Return (IOR) for fingers using a short cue-target SOA, whereas the IOR was found in fingers and palm in long cue-target SOA. Also we observed a ‘Cue above Target’ effect (facilitation effect when the Cue had appeared distal to the target location in a vertical line) at the long SOA. Together, we suggest that the general pattern of results supports the proposed hypothesis about the different mental representation of fingers and palms, but with a considerable and hierarchical interrelation between them.

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Alyanne M. de Haan

Papers

Approaching threat modulates visuotactile interactions in peripersonal space

No consistent cooling of the real hand in the rubber hand illusion.

Thinking about touch facilitates tactile but not auditory processing.

Fingers crossed! An investigation of somatotopic representations using spatial directional judgements.

An attentional approach to study mental representations of different parts of the hand.