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

Abstract

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.

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

“…To calculate the JND, the proportion of right hand first responses across all SOAs was fitted to a logistic regression model for each participant and posture separately (using a generalized linear model fit function, glmfit in Matlab), as when plotted, performance resembled a typical psychophysical, S-shaped curve (see Heed & Azañón, 2014). The point of each curve at which the proportion of right-first responses was 25 and 75%, respectively, were projected onto the SOA axis.…”

“…In this posture, a touch on the right hand (in skin-based coordinates), is located in left space, creating an incongruence between reference frames in the right-left dimension (Shore et al, 2002;Yamamoto & Kitazawa, 2001; for a review see Heed, Buchholz, Engel, & Röder, 2015). A well-known consequence of this conflicting information is the impairment in the ability to report the order of two stimuli, one applied to each hand, when hands are crossed (Heed & Azañón, 2014;Shore et al, 2002;Yamamoto & Kitazawa, 2001). In such instances, the order of two stimuli might be correctly computed, but it is inaccurately reported because of the incorrect localization of the stimuli in space (Badde, Heed, & Röder, 2016;Overvliet, Azañón, & Soto-Faraco, 2011;Roberts & Humphreys, 2008).…”

Integration of anatomical and external response mappings explains crossing effects in tactile localization: A probabilistic modeling approach

“…Yet, to plan actions toward the object, its location must be transformed into another, posture-dependent reference frame (Pouget et al, 2002;Sober & Sabes, 2005). Any perceived tactile stimulus seems to be transformed into an external-spatial reference frame (Driver & Spence, 1998;Yamamoto & Kitazawa, 2001a;Shore et al, 2002;Spence et al, 2004;Soto-Faraco et al, 2004;Röder et al, 2004;Schicke & Röder, 2006;Heed & Azañón, 2014;Heed et al, 2015), even when such recoding is currently not required (Kitazawa, 2002;Azañón et al, 2010a). This process of coordinate transformation is addressed as tactile remapping (Driver & Spence, 1998) and has been associated with regions of the intraparietal sulcus in posterior parietal cortex (Azañón et al, 2010b;Bolognini & Maravita, 2007;Renzi et al, 2013).…”

“…A well-known consequence of hand crossing is that participants' ability to judge which of two successive tactile stimuli, one applied to each hand, occurred first is markedly impaired compared to an uncrossed hands condition (Yamamoto & Kitazawa, 2001a;Shore et al, 2002). These so-called crossing effects in temporal order judgments (TOJ) are thought to arise from conflicting leftright mappings in the different spatial reference frames (Yamamoto & Kitazawa, 2001a;2001b;Shore et al, 2002;Röder et al, 2004;Schicke & Röder, 2006;Heed et al, 2012;Heed & Azañón, 2014;Azañón et al, 2015). However, it is unclear whether this conflict bears on the remapping process, impairing the establishment of the external response mapping (Yamamoto & Kitazawa, 2001a;Röder et al, 2004;Kóbor et al, 2006;Azañón & Soto-Faraco, 2007;Kitazawa et al, 2008), or whether it unfolds its effect at the stage of information integration once remapping is complete (Shore et al, 2002;Badde et al, 2013;Badde et al, 2015).…”

“…The resulting probit values were linearly regressed onto their corresponding SOA. The regression slope was used as a measure of TOJ performance with steeper probit slopes indicating better performance (Shore et al, 2002;Heed & Azañón, 2014). STL performance was quantified by mean accuracy only, as this task involved just one touch.…”