Touch perception reveals the dominance of spatial over digital representation of numbers

Institut National de la Santé et de la Recherche Médicale, Unité Mixte de Recherche-S 864 "Espace et Action," F-69500 Bron, France.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 05/2008; 105(14):5644-8. DOI: 10.1073/pnas.0708414105
Source: OAI


We learn counting on our fingers, and the digital representation of numbers we develop is still present in adulthood [Andres M, et al. (2007) J Cognit Neurosci 19:563-576]. Such an anatomy-magnitude association establishes tight functional correspondences between fingers and numbers [Di Luca S, et al. (2006) Q J Exp Psychol 59:1648-1663]. However, it has long been known that small-to-large magnitude information is arranged left-to-right along a mental number line [Dehaene S, et al. (1993) J Exp Psychol Genet 122:371-396]. Here, we investigated touch perception to disambiguate whether number representation is embodied on the hand ("1" = thumb; "5" = little finger) or disembodied in the extrapersonal space ("1" = left; "5" = right). We directly contrasted these number representations in two experiments using a single centrally located effector (the foot) and a simple postural manipulation of the hand (palm-up vs. palm-down). We show that visual presentation of a number ("1" or "5") shifts attention cross-modally, modulating the detection of tactile stimuli delivered on the little finger or thumb. With the hand resting palm-down, subjects perform better when reporting tactile stimuli delivered to the little finger after presentation of number "5" than number "1." Crucially, this pattern reverses (better performance after number "1" than "5") when the hand is in a palm-up posture, in which the position of the fingers in external space, but not their relative anatomical position, is reversed. The human brain can thus use either space- or body-based representation of numbers, but in case of competition, the former dominates the latter, showing the stronger role played by the mental number line organization.

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    • "This result, as well as other studies reporting a SNARC effect in the context of a parity task performed using two fingers of the same hand (Priftis, Zorzi, Meneghello, Marenzi, & Umiltà, 2006), suggest that a finger-based reference frame can be relevant for eliciting a SNARC effect. However, in a tactile detection paradigm where short pulses were applied to the fingers of the right hand, the presentation of a small number facilitated the detection of a tactile stimulus delivered to the leftmost finger, and the presentation of a large number facilitated the detection of the stimulus delivered to the rightmost finger, independent of the position of the hand (Brozzoli et al., 2008). This result suggests a stronger involvement of a left–right-oriented (allocentric or egocentric) reference frame over a finger-based reference frame in the SNARC effect. "
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    ABSTRACT: Abstract The SNARC effect refers to faster reaction times for larger numbers with right-sided responses, and for smaller numbers with left-sided responses (Dehaene et al., 1993), even when numerical magnitude is irrelevant. Although the SNARC is generally thought to reflect a mapping between numbers and space, the question of which spatial reference frame(s) are critical for the effect has not been systematically explored. We propose a dynamic hierarchical organization of the reference frames (from a global left-right frame to body- and object-related frames), where the influence of each frame can be modulated by experimental context. We conducted two experiments based on predictions derived from this organizational system. Experiment 1 compared instructions that differed only in focusing participants' attention on either the response buttons or the hands. Instructions focusing on a hand-based reference frame eliminated the SNARC. Experiment 2 provided the opportunity for an object-centered reference frame to manifest itself in the SNARC. Although we did not observe an effect of an object-centered reference frame, we observed the influence of other reference frames in a context where an object-centered reference frame was emphasized. Altogether, these results support the proposed organization of the reference frames.
    Quarterly journal of experimental psychology (2006) 02/2014; 67(8). DOI:10.1080/17470218.2014.897358 · 2.13 Impact Factor
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    • "A few other studies had previously introduced postural manipulations in simple numerical tasks (e.g., Leuthard et al., 2005; Di Luca et al., 2006; Brozzoli et al., 2008). Brozzoli et al. (2008), for example, had their participants perform a tactile detection task by foot pedal responses. The tactile stimulus could be delivered either on their right thumb or on their right little finger following the appearance of a digit on a computer display. "
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    ABSTRACT: A structural representation of the hand embedding information about the identity and relative position of fingers is necessary to counting routines. It may also support associations between numbers and allocentric spatial codes that predictably interact with other known numerical spatial representations, such as the mental number line. In this study, 48 Western participants whose typical counting routine proceeded from thumb-to-little on both hands performed magnitude and parity binary judgments. Response keys were pressed either with the right index and middle fingers or with the left index and middle fingers in separate blocks. 24 participants responded with either hands in prone posture (i.e. palm down) and 24 participants responded with either hands in supine (i.e. palm up) posture. When hands were in prone posture, the counting direction of the left hand conflicted with the direction of the left-right mental number line, whereas the counting direction of the right hand was consistent with it. When hands were in supine posture, the opposite was true. If systematic associations existed between relative number magnitude and an allocentric spatial representation of the finger series within each hand, as predicted on the basis of counting habits, interactions would be expected between hand posture and a unimanual version of the Spatial-Numerical Association of Response Codes (SNARC) effect. Data revealed that with hands in prone posture a unimanual SNARC effect was present for the right hand, and with hands in supine posture a unimanual SNARC effect was present for the left hand. We propose that a posture-invariant body structural representation of the finger series provides a relevant frame of reference, a within-hand directional vector, that is associated to simple number processing. Such frame of reference can significantly interact with stimulus-response correspondence effects that have been attributed to the mapping of numbers on a mental number line.
    Frontiers in Psychology 12/2011; 2:372. DOI:10.3389/fpsyg.2011.00372 · 2.80 Impact Factor
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    • "Recent findings in children included the following: that finger gnosis was a better predictor than was global development for calculation skills 1 year later but not for reading (Noël, 2005); that a pure finger gnosis training improved some numerical skills (Gracia-Bafalluy and Noël, 2008); and that finger-related split-five-errors occurred in a high percentage of primary school children, especially when they were starting to retrieve the results of simple addition and subtraction as arithmetical facts from long-term memory (Domahs et al., 2008). In adults, it has been shown that directional finger counting habits have an effect on individual cognitive spatial–numerical associations (Di Luca et al., 2006; Fischer, 2008; Sato and Lalain, 2008; but see Brozzoli et al., 2008, for contrasting results) and that even in adults, finger counting-related sub-base-5 representations have an impact in Arabic number magnitude comparisons (Domahs et al., 2010). "
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    ABSTRACT: A possible functional role of finger representations for the development of early numerical cognition has been the subject of recent debate; however, until now, only behavioral studies have directly supported this view. Working from recent models of number processing, we focused on the neural networks involved in numerical tasks and their relationship to the areas underlying finger representations and saccades in children aged 6-12 years. We were able to differentiate three parietal circuits that were related to distinct aspects of number processing. Abstract magnitude processing was subserved by an association area also activated by saccades and visually guided finger movements. Addition processes led to activation in an area only engaged during saccade encoding, whereas counting processes resulted in the activation of an area only activated during visually guided finger movements, namely in the anterior intraparietal sulcus. Apart from this area, a large network of specifically finger-related brain areas including the ventral precentral sulcus, supplementary motor area, dorso-lateral prefrontal cortex, insula, thalamus, midbrain, and cerebellum was activated during (particularly non-symbolic) exact addition but not during magnitude comparison. Moreover, a finger-related activation cluster in the right ventral precentral sulcus was only present during non-symbolic addition and magnitude comparison, but not during symbolic number processing tasks. We conclude that finger counting may critically mediate the step from non-symbolic to symbolic and exact number processing via somatosensory integration processes and therefore represents an important example of embodied cognition.
    Frontiers in Psychology 12/2011; 2:373. DOI:10.3389/fpsyg.2011.00373 · 2.80 Impact Factor
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