Visual detail about the body modulates tactile localisation biases

Abstract

1The localisation of tactile stimuli requires the integration of visual and somatosensory inputs within 2 an internal representation of the body surface, and is prone to consistent bias. Joints may play a role 3 in segmenting such internal body representations, and may therefore influence tactile localisation 4 biases, although the nature of this influence remains unclear. Here, we investigate the relationship 5 between conceptual knowledge of joint locations and tactile localisation biases on the hand. In one 6 task, participants localised tactile stimuli applied to the dorsum of their hand. A distal localisation 7 bias was observed in all participants, consistent with previous results. We also manipulated the 8 availability of visual information during this task, to determine whether the absence of this 9 information could account for the distal bias observed here and by Mancini and colleagues (2011). 10The observed distal bias increased in magnitude when visual information was restricted, without a 11 corresponding decrease in precision. In a separate task, the same participants indicated, from 12 memory, knuckle locations on a silhouette image of their hand. Analogous distal biases were also 13 seen in the knuckle localisation task. The accuracy of conceptual joint knowledge was not 14 correlated with tactile localisation bias magnitude, although a similarity in observed bias direction 15 suggests that both tasks may rely on a common, higher-order body representation. These results also 16 suggest that distortions of conceptual body representation may be more common in healthy 17 individuals than previously thought. 18 19

Implicit body representations and tactile spatial remapping

“…Consistent with our previous results (Mancini et al, 2011;Margolis & Longo, 2015), there were clear constant errors in tactile localisation in the Skin Localisation Task1 (see Figures 9-10). There was a highly significant distal bias (.434 Bookstein units), t(11) = 9.90, p < .0001, as well as a radial bias (i.e., towards the thumb; .132 Bookstein units), t(11) = 5.61, p < .0005.…”

“…In previous studies (Mancini et al, 2011;Margolis & Longo, 2015), we found stereotyped biases (i.e., constant errors) in the localisation of tactile stimuli on the hand dorsum. If these biases also influence tactile spatial remapping, they should appear in the present experiment when participants judge the spatial location of touch (which requires tactile localisation on the skin), but not when participants localise verbally-given landmarks (which does not require tactile localisation).…”

“…We used a two-point registration procedure (Bookstein coordinates) to assess localisation biases (as in Azañón et al, 2010;Mancini et al, 2011;Margolis & Longo, 2015). In this procedure, two landmarks are designated as points (0,0) and (1,0), thus defining a twodimensional coordinate system centred on and scaled to the two landmarks (Bookstein, 1991).…”

Distorted Body Representations in Healthy Cognition

“…Moreover, the same effect was found when participants judged the locations of the experimenter's knuckles, suggesting that it does not reflect something about people's representations of their own hands specifically, but rather something about their conceptual understanding of hands in general. Margolis and Longo (2015) found a similar distal bias when participants were asked to locate their knuckles on a silhouette image of their hand.…”

Expansion of Perceptual Body Maps Near – But Not Across – The Wrist

“…We have recently reported large misunderstandings about the location of other joints in the hand – the knuckles – which people appear to believe are substantially farther forward in the hand than they actually are (Longo, 2015b; Margolis and Longo, 2015). Indeed, we found that the magnitude of this bias was correlated across participants with the extent of underestimation of finger length in the hand mapping task (Longo et al, 2015c).…”