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Journal Article•DOI•

A common representation of fingers and toes

Kelda Manser-Smith1, Luigi Tamè1, Matthew R. Longo1•
Birkbeck, University of London1
01 Aug 2019-Acta Psychologica (Elsevier)-Vol. 199, pp 102900
TL;DR: This work obtained confusion matrices showing the pattern of mislocalisation on the hairy skin surfaces of both the fingers and toes, which suggest that there is a common representation of the hands and toes.
About: This article is published in Acta Psychologica.The article was published on 2019-08-01 and is currently open access. It has received 8 citations till now.

Summary (2 min read)

Jump to: [1. Introduction] – [2.1. Participants] – [2.3. Task] – [2.4. Analysis] – [3.1. Directional bias for localisation of the toes] – [3.2. Directional bias for localisation of the fingers] – [3.3. Shared individual differences between the fingers and the toes] and [4. Discussion]

1. Introduction

  • These similarities in tactile mislocalisation of the digits indicate that there may be commonalities in mental representations of the hands and feet, despite their divergent physical and functional properties.
  • Moreover, the authors used a form a representational similarity analysis (RSA; Kriegeskorte, Mur, & Bandettini, 2008) to investigate whether individual differences between participants are shared across the glabrous and hairy skin surfaces of each limb.
  • Together these results suggest that mislocalisations arise at the level of complete digits, not of individual skin surfaces, consistent with their arising from higher-level body representations.

2.1. Participants

  • In their previous study (Manser-Smith et al., 2018), the individual differences found between the two surfaces of the fingers and toes using their decoding approach showed Cohen’s d’s of 1.76 and 1.04, respectively.
  • As the authors reduced the number of trials completed by each participant in the present experiment (due to time constraints during testing), and they expected a weaker effect than in their previous study because they were comparing two different body parts, they conducted a power analysis using an effect size of half the smaller value found in their previous study.
  • The authors based their calculations on a one-tailed t-test, as they have a clear directional prediction that classification accuracy should be greater than chance levels, rather than lower than chance.

2.3. Task

  • The testing procedure closely resembled that used in their previous study (Manser-Smith et al., 2018).
  • This posture was kept consistent regardless of whether the hand or foot was being tested, and they were instructed to remain as still as possible throughout each experimental block.
  • Touch was only applied to the hairy skin, and not the glabrous skin.
  • Vision was prevented throughout the experiment using a blindfold.
  • The order of digit stimulation was pseudo-randomised within each block of trials, so that there was an approximately equal number of each type of preceding trial.

2.4. Analysis

  • The analyses carried out closely resembled those of their previous study, and were exactly as described in the pre-registration document.
  • The authors regressed the 20 off-diagonal cells (i.e., the localisation errors) of each participant’s confusion matrix (Ci) on the grand average confusion matrix for the other 39 participants (CGA), as in Equation 2.
  • These residuals were calculated separately for the confusion matrices on the fingers and the toes, resulting in two sets of residuals per participant.
  • Classification accuracy was calculated for each participant as the percentage of those 78 between-participant correlations which were smaller than the within-participant cross-correlation.
  • The authors preregistered analysis plan specified a one-sample t-test to assess whether classification accuracy was significantly greater than chance (i.e. 50%).

3.1. Directional bias for localisation of the toes

  • Figure 2 (left panel) shows the confusion matrix for tactile toe localisation on the hairy skin of the toes.
  • As in their previous study, the majority of mislocalisations were made onto neighbouring toes.
  • These results provide a direct replication of the results of their previous study and of Cicmil et al. (2016), corroborating the presence of directional biases for tactile toe localisation in response to stimulation of the hairy skin of the toes.

3.2. Directional bias for localisation of the fingers

  • Figure 2 (right panel) shows the confusion matrix for tactile finger localisation on the hairy skin of the fingers.
  • Once again, these results provide a direct replication of the results of their previous study, that there are consistent directional biases for tactile finger localisation in response to stimulation of the hairy skin of the fingers.

3.3. Shared individual differences between the fingers and the toes

  • The key question was whether person-to-person differences in the pattern of mislocations is shared between the fingers and toes.
  • A Bayesian onesample t-test provided moderate evidence in support of the alternative hypothesis against the null hypothesis, BF10 = 3.56.
  • This result provides evidence for shared individual differences between the fingers and toes in how people mislocalise touch on the digits.

4. Discussion

  • These results provide evidence for a common representation of fingers and toes.
  • A shared high-level mental representation of the hands and feet may have developed to be beneficial to their primate ancestors, and would still beneficial to primates that retain similar structure and functional use of the hands and feet, to facilitate co-ordinated use.
  • In their previous study the authors found strong idiosyncratic differences in the tactile localisation task comparing performance on the two skin surfaces of the hand or foot, providing strong evidence that there is a shared mental representation of the two skin surfaces of the hands and feet (such as a volumetric 3-D model of the body part).

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Citations
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Journal Article•DOI•
Evolution of the Human Foot

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Richard Hope
18 Apr 1942-BMJ

58 citations

Journal Article•DOI•
Four meta-analyses across 164 studies on atypical footedness prevalence and its relation to handedness.

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Julian Packheiser1, Judith Schmitz2, Gessa Berretz1, David P. Carey3, Silvia Paracchini2, Marietta Papadatou-Pastou4, Sebastian Ocklenburg1, Sebastian Ocklenburg5 •
Ruhr University Bochum1, University of St Andrews2, Bangor University3, National and Kapodistrian University of Athens4, University of Duisburg-Essen5
02 Sep 2020-Scientific Reports
TL;DR: It was showed that the prevalence of atypical footedness ranges between 12.10% using the most conservative criterion of left-footedness to 23.7% including all left- and mixed-footers as a single non-right category, and that footing is a valuable phenotype for the study of lateral motor biases, its underlying genetics and neurodevelopment.
Abstract: Human lateral preferences, such as handedness and footedness, have interested researchers for decades due to their pronounced asymmetries at the population level. While there are good estimates on the prevalence of handedness in the population, there is no large-scale estimation on the prevalence of footedness. Furthermore, the relationship between footedness and handedness still remains elusive. Here, we conducted meta-analyses with four different classification systems for footedness on 145,135 individuals across 164 studies including new data from the ALSPAC cohort. The study aimed to determine a reliable point estimate of footedness, to study the association between footedness and handedness, and to investigate moderating factors influencing footedness. We showed that the prevalence of atypical footedness ranges between 12.10% using the most conservative criterion of left-footedness to 23.7% including all left- and mixed-footers as a single non-right category. As many as 60.1% of left-handers were left-footed whereas only 3.2% of right-handers were left-footed. Males were 4.1% more often non-right-footed compared to females. Individuals with psychiatric and neurodevelopmental disorders exhibited a higher prevalence of non-right-footedness. Furthermore, the presence of mixed-footedness was higher in children compared to adults and left-footedness was increased in athletes compared to the general population. Finally, we showed that footedness is only marginally influenced by cultural and social factors, which play a crucial role in the determination of handedness. Overall, this study provides new and useful reference data for laterality research. Furthermore, the data suggest that footedness is a valuable phenotype for the study of lateral motor biases, its underlying genetics and neurodevelopment.

33 citations

Journal Article•DOI•
Tactile distance anisotropy on the feet.

[...]

Kelda Manser-Smith1, Luigi Tamè2, Luigi Tamè1, Matthew R. Longo1•
Birkbeck, University of London1, University of Kent2
08 Jul 2021-Attention Perception & Psychophysics
TL;DR: In this paper, the authors investigated tactile distance anisotropy on the foot, a body part structurally and embryologically similar to the hand, but with very different patterns of functional usage in humans.
Abstract: Perception of distance between two touches varies with orientation on the hand, with distances aligned with hand width perceived as larger than those aligned with hand length. Similar anisotropies are found on other body parts (e.g., the face), suggesting they may reflect a general feature of tactile organization, but appear absent on other body parts (e.g., the belly). Here, we investigated tactile-distance anisotropy on the foot, a body part structurally and embryologically similar to the hand, but with very different patterns of functional usage in humans. In three experiments, we compared the perceived distance between pairs of touches aligned with the medio-lateral and proximal-distal foot axes. On the hairy skin of the foot dorsum, anisotropy was consistently found, with distances aligned with the medio-lateral foot axis perceived as larger than those in the proximo-distal axis. In contrast, on the glabrous skin of the sole, inconsistent results were found across experiments, with no overall evidence for anisotropy. This shows a pattern of anisotropy on the foot broadly similar to that on the hand, adding to the list of body parts showing tactile-distance anisotropy, and providing further evidence that such biases are a general aspect of tactile spatial organization across the body. Significance: The perception of tactile distance has been widely used to understand the spatial structure of touch. On the hand, anisotropy of tactile distance perception is well established, with distances oriented across hand width perceived larger than those oriented along hand length. We investigated tactile-distance anisotropy on the feet, a body part structurally, genetically, and developmentally homologous to the hands, but with strikingly different patterns of functional usage. We report highly similar patterns of anisotropy on the hairy skin of the hand dorsum and foot dorsum. This suggests that anisotropy arises from the general organization of touch across the body.

6 citations

Journal Article•DOI•
Fingers hold spatial information that toes do not.

[...]

Kelda Manser-Smith1, Daniele Romano2, Daniele Romano1, Luigi Tamè1, Luigi Tamè3, Matthew R. Longo1 •
Birkbeck, University of London1, University of Milan2, University of Kent3
01 Jan 2021-Quarterly Journal of Experimental Psychology
TL;DR: Spatial information held by the fingers is stronger and more reliable than for the toes, so is not a general characteristic of limbs, but possibly related to hand use.
Abstract: Fingers have preferential associations with relative spatial locations. Tactile localisation is faster when the fingers are in these locations, such as when the index finger is in a relatively higher spatial position, and the thumb in a relatively lower position. However, it is unclear whether these associations are related to hands specifically, or are a more general characteristic of limbs. The present study therefore investigated whether toes have similar spatial associations. If these associations reflect the statistics of natural limb usage, very different patterns of association would be expected for the fingers and toes, given their different functional roles in daily behaviour. We measured reaction time (RT) and error rates of responses to tactile stimuli applied to the middle finger/toe or thumb/big toe, when they were positioned in a relative upper or lower location. We replicated the finding that fingers have preferential associations that facilitates localisation – RT and error rate were lower when the index finger was in the top position, and the thumb in the bottom position. We found that toes do not hold the same spatial information, though it remains unclear whether toes hold different spatial information or none at all. These results demonstrate spatial information held by the fingers is stronger and more reliable than for the toes, so is not a general characteristic of limbs, but possibly related to hand use.

3 citations

Journal Article•DOI•
Body structural representation in schizotypy.

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Francesca Fotia1, Loes van Dam2, Loes van Dam1, John Sykes, Ettore Ambrosini3, Marcello Costantini4, Francesca Ferri4 •
University of Essex1, Technische Universität Darmstadt2, University of Padua3, University of Chieti-Pescara4
01 Jan 2022-Schizophrenia Research
TL;DR: This article found that individuals with high schizotypal traits in the general population may be characterized by a progressive sense of detachment from one's lived body, which may represent a potential marker for schizophrenia proneness.

2 citations

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"A common representation of fingers ..." refers background in this paper

  • ...…monkeys such as chimpanzees, the hands and feet share many functions such as grasping and propulsion during locomotion (Rolian, 2009; Schmitt, Zeininger, & Granatosky, 2016; Szalay & Dagosto, 1988), although there is evidence for divergent use occurring during reaching tasks (Hunt, 1994)....

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"A common representation of fingers ..." refers background in this paper

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Journal Article•DOI•
Whole-body mapping of spatial acuity for pain and touch.

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Flavia Mancini1, Armando Bauleo1, Armando Bauleo2, Jonathan Cole3, Fausta Lui2, Carlo Adolfo Porro2, Patrick Haggard1, Gian Domenico Iannetti1 •
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TL;DR: This work provides the first systematic whole‐body mapping of spatial acuity for pain in the body, more than a century after the initial description of tactile acuity across the body.
Abstract: Tactile spatial acuity is routinely tested in neurology to assess the state of the dorsal column system. In contrast, spatial acuity for pain is not assessed, having never been systematically characterised. More than a century after the initial description of tactile acuity across the body, we provide the first systematic whole-body mapping of spatial acuity for pain. We evaluated the two-point discrimination thresholds for both nociceptive-selective and tactile stimuli across several skin regions. Thresholds were estimated using pairs of simultaneous stimuli, and also using successive stimuli. These two approaches produced convergent results. The fingertip was the area of highest spatial acuity, for both pain and touch. On the glabrous skin of the hand, the gradient of spatial acuity for pain followed that observed for touch. On the hairy skin of the upper limb, spatial acuity for pain and touch followed opposite proximal-distal gradients, consistent with the known innervation density of this body territory. Finally, by testing spatial acuity for pain in a rare participant completely lacking Aβ fibers, we demonstrate that spatial acuity for pain does not rely on a functioning system of tactile primary afferents. ANN NEUROL 2014. © 2014 American Neurological Association.

218 citations

Journal Article•DOI•
A pure case of Gerstmann syndrome with a subangular lesion.

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Eugène Mayer, Marie-Dominique Martory, Alan J. Pegna, Theodor Landis, Jacqueline Delavelle, Jean-Marie Annoni 
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Abstract: Summary The four symptoms composing Gerstmann's syndrome were postulated to result from a common cognitive denominator (Grundstorung) by Gerstmann himself. He suggested that it is a disorder of the body schema restricted to the hand and fingers. The existence of a Grundstorung has since been contested. Here we suggest that a common psychoneurological factor does exist, but should be related to transformations of mental images rather than to the body schema. A patient (H.P.) was studied, who presented the four symptoms of Gerstmann's syndrome in the absence of any other neuropsychological disorders. MRI showed a focal ischaemic lesion, situated subcortically in the inferior part of the left angular gyrus and reaching the superior posterior region of T1. The cortical layers were spared and the lesion was seen to extend to the

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Journal Article•DOI•
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Matthew W. Tocheri1, Caley M. Orr2, Marc C. Jacofsky2, Mary W. Marzke2•
National Museum of Natural History1, Arizona State University2
01 Apr 2008-Journal of Anatomy
TL;DR: A majority of primitive features most likely present in the Pan‐Homo last common ancestor are retained in the hands of Australopithecus, Paranthropus/early Homo, and Homo floresiensis, which suggests that further derived changes to thehands of other hominins such as modern humans and Neandertals did not evolve until after 2.5 Ma, which is currently the earliest evidence of Acheulian technology.
Abstract: Molecular evidence indicates that the last common ancestor of the genus Pan and the hominin clade existed between 8 and 4 million years ago (Ma). The current fossil record indicates the Pan-Homo last common ancestor existed at least 5 Ma and most likely between 6 and 7 Ma. Together, the molecular and fossil evidence has important consequences for interpreting the evolutionary history of the hand within the tribe Hominini (hominins). Firstly, parsimony supports the hypothesis that the hand of the last common ancestor most likely resembled that of an extant great ape overall (Pan, Gorilla, and Pongo), and that of an African ape in particular. Second, it provides a context for interpreting the derived changes to the hand that have evolved in various hominins. For example, the Australopithecus afarensis hand is likely derived in comparison with that of the Pan-Homo last common ancestor in having shorter fingers relative to thumb length and more proximo-distally oriented joints between its capitate, second metacarpal, and trapezium. This evidence suggests that these derived features evolved prior to the intensification of stone tool-related hominin behaviors beginning around 2.5 Ma. However, a majority of primitive features most likely present in the Pan-Homo last common ancestor are retained in the hands of Australopithecus, Paranthropus/early Homo, and Homo floresiensis. This evidence suggests that further derived changes to the hands of other hominins such as modern humans and Neandertals did not evolve until after 2.5 Ma and possibly even later than 1.5 Ma, which is currently the earliest evidence of Acheulian technology. The derived hands of modern humans and Neandertals may indicate a morphological commitment to tool-related manipulative behaviors beyond that observed in other hominins, including those (e.g. H. floresiensis) which may be descended from earlier tool-making species.

202 citations

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Frequently Asked Questions (2)
Q1. What contributions have the authors mentioned in the paper "A common representation of fingers and toes" ?

Manser-Smith et al. this paper found that the human hands and feet are serially homologous structures that have co-evolved, resulting in numerous similarities between the two body parts. 

To attempt to disentangle how the body representation itself and the body ’ s position in external space contribute to localisation biases, future experiments may focus on manipulating posture of the fingers and toes relative to one another, or relative to the gaze-direction, for example. From the results of this experiment and others the authors have suggested that patterns of tactile confusions may arise from high-level body representations, which likely originate in the posterior parietal cortex. Cortical somatotopy suggests manual dexterity is primitive and evolved independently of bipedalism.