Spatial remapping of touch: Confusion of perceived stimulus order across hand and foot

Abstract

The ''body schema,'' a spatial representation of the body in its environment, has been suggested to be an emergent property of a widespread network of effector-specific frontal and parietal areas, many of which integrate sensory input from the different modalities. On a behavioral level, such multimodality has been shown with temporal order judgment tasks, in which participants decide which of the two hands received a tactile stimulus first. The accuracy of these judgments is influenced by body posture, indicating that tactile stimuli are not simply represented in an anatomical reference frame, but are transformed into external spatial coordinates. So far, these studies have only investigated the hands. It is therefore unclear whether a default remapping of touch into external space is a special feature of visual-manual control or whether all body parts are represented in a common nonanatomically anchored reference frame. In the present study, blindfolded participants made temporal order judgments of stimuli presented to both hands, both feet, or one hand and one foot. The stimulated limbs were held in either a parallel or a crossed posture. Judgments were equally impaired by limb crossing in all limb combinations (hands only, feet only, hand and foot). These results suggest a remapping of tactile location of all body parts into a nonanatomically anchored and, importantly, common reference frame rather than a specific remapping for eye-hand coordination only.body schema ͉ feet ͉ tactile ͉ temporal order judgment ͉ visual-manual control

A three-dimensional spatial characterization of the crossed-hands deficit

“…Intriguingly, this contrasts with previous research that has shown that the addition of non-spatial information, such as when the stimuli differ in the identity of the stimulated body part, has little if any effect on the deficit (Schicke & Roder, 2006;Shore et al, 2002). For instance, TOJ crossing effects are comparable when same or different fingers of each hand are stimulated (Shore et al, 2002), or even when stimuli are applied to one hand and to one foot, while they are crossed with each other (Schicke & Roder, 2006). Moreover, the effect of crossing the arms when stimuli differs in frequency or duration is comparable to any standard crossing effect (see Figures 2 and 6 in Roberts & Humphreys, 2008; though see Badde, Röder, et al, 2015, where TOJ crossing effects are reduced when location, but also non-spatial characteristics of the stimuli, are reported in a dual task).…”

“…Intriguingly, this contrasts with previous research that has shown that the addition of non-spatial information, such as when the stimuli differ in the identity of the stimulated body part, has little if any effect on the deficit (Schicke & Roder, 2006;Shore et al, 2002). For instance, TOJ crossing effects are comparable when same or different fingers of each hand are stimulated (Shore et al, 2002), or even when stimuli are applied to one hand and to one foot, while they are crossed with each other (Schicke & Roder, 2006).…”

Peripersonal space boundaries around the lower limbs

“…In one study, van Elk et al (2013) showed that the foot PPS (as measured by a visuotactile crossmodal congruency task) is mostly unaffected by factors such as limb posture and the congruency of a fake limb placed nearby, whereas the hand PPS is sensitive to these factors. In addition, other studies suggest that the lower limbs are slower (when compared to the hands) at remapping tactile information (e.g., Schicke and Röder 2006). So it might not be surprising that the lower limb PPS size differs from the upper limb PPS size.…”

“…Further, some neurophysiological evidence in monkeys suggests that the dorsal areas of the ventral premotor cortex (Muakkassa and Strick 1979;Kurata et al 1985;Kurata 1989) and medial regions of area 7 (Hyvärinen 1981) might be responsible for a 'foot-centered' PPS network, though an investigation using dynamic sensory stimuli was never formally reported. Thus, behavioural studies have uncovered the presence of PPS around the legs and feet (Schicke and Röder 2006;Schicke et al 2009;Van Elk et al 2013;Pozeg et al 2015;Scandola et al 2016;Stettler and Thomas 2016), but no study, to the best of our knowledge, has specifically examined how far PPS extends for the lower body.…”

“…Yet, as only static visual stimuli were used, and tactile detection was not assessed, it was not specified at what point in space multisensory integration (i.e., the boundaries of PPS) might occur around the feet. Certainly, some investigations have focused on the integration of visual and tactile information within PPS around the feet (Schicke and Röder 2006;Schicke et al 2009;Van Elk et al 2013;Scandola et al 2016). For example, Schicke et al (2009) were one of the first groups to show (behaviourally) that a PPS representation around the feet exists using a crossmodal congruency task.…”