Peer Review Version
The different impact of attention, movement and sensory 
information on body metric representation
Journal: Quarterly Journal of Experimental Psychology
Manuscript ID QJE-STD-22-414.R1
Manuscript Type: Standard Article
Date Submitted by the 
Author: 15-May-2023
Complete List of Authors: Caggiano, Pietro; University of Hertfordshire, 
Cocchini, Gianna; Goldsmiths University of London Department of 
Psychology, 
De Stefano, Danila; Goldsmiths University of London
Romano, Daniele; University of Milan at Bicocca
Keywords: body representation, body schema, body image, body metric, arm bisection task
 
Quarterly Journal of Experimental Psychology
DOI: 10.1177/17470218231187385
Author Accepted Manuscript
Peer Review Version
The different impact of attention, movement and sensory information on body metric 
representation
Pietro Caggiano1#, Gianna Cocchini2, Danila De Stefano2, Daniele Romano3
1 School of Life & Medical Sciences, University of Hetfordshire, Hatfield, UK
2 Psychology Department, Goldsmiths University of London, New Cross, London, UK
3 Psychology Department, University of Milano Bicocca, Milan, Italy 
#Corresponding author: Pietro Caggiano
https://orcid.org/0000-0001-5560-4870
University of Hertfordshire
Hatfield AL10 9AB
UK
p.caggiano@herts.ac.uk
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The different impact of attention, movement and sensory information on body metric 
representation
Abstract 
A growing body of research investigating the relationship between body representation and 
tool-use has shown that body representation is highly malleable. The nature of the body 
representation does not consist only of sensory attributes but also of motor action-oriented 
qualities, which may modulate the subjective experience of our own body. However, how these 
multisensory factors and integrations may specifically guide and constrain body reorientation’s 
plasticity has been under-investigated. In the present study, we used a forearm bisection task 
to selectively investigate the contribution of motor, sensory and attentional aspects in guiding 
body representation malleability. Results show that the perceived forearm midpoint deviates 
from the real one. This shift is further modulated by a motor task but not by a sensory task, 
whereas the attentional task generates more uncertain results. Our findings provide novel 
insight into the individual role of movement, somatosensation and attention in modulating body 
metric representation.
Keywords: body representation, body schema, body image, body metric, arm bisection task. 
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Introduction 
How we represent our own body is crucial for everyday actions and for successful interactions 
with the external environment (Maravita et al., 2003). Although it may appear a fairly simple 
concept to grasp, the understanding of the underlying cognitive processes and the interaction 
of various factors is complex and convoluted. Traditionally, the terms body schema and body 
image have been extensively used to conceptualise one’s own body representation  (Gallagher, 
1986; 2005); however, different representations have emerged at different times throughout the 
literature and, despit  numerous studies have been dedicated to investigating body 
representations, a clear-cut theory or model providing a full explanation of the relationships 
between the different bodily representations remains difficult to delineate (e.g., de Vignemont, 
2010; Longo, 2022). Although the notion of body representation is in itself yet to be 
unanimously characterised, current literature does offer a critical and reliable body of evidence 
indicating that body representation is highly plastic and malleable (e.g., Martel et al., 2016, 
2021; Medina & Coslett, 2010; Caggiano et al., 2021). and can be affected by pathological 
conditions, such as acquired brain damage (e.g. Bassolino et. al, 2022; Caggiano et al., 2020; 
Tosi et al., 2018; Garbarini et al., 2015; Mora et al., 2023) and limb amputation (e.g Rognini 
et al., 2019; Sato et al., 2017; Canzoneri et al., 2013).
In healthy population, the plasticity and reorganisation of metric body representation has been 
investigated in the context of ageing (Sorrentino et al., 2021 ; Garbarini et al., 2015) gestures 
(Mora et al., 2021), passive and active actions (Bruno et al., 2019), bodily illusions (Tosi et al., 
2022), response modality (Tosi et al., 2020) and tool-use where the morphology and functional 
aspects of a tool appear to modulate the subjective experience of our own body metrics (e.g., 
Maravita & Romano, 2018; Galigani et al., 2020; Romano et al., 2019). Manipulation of tools 
re-shapes the body representation during and after use (Martel et al., 2016) as observed in cases 
of tool embodiment (e.g., Iriki et al., 1996; Maravita et al., 2002; Farnè et al., 2007; Maravita 
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& Iriki, 2004; Cardinali et al., 2009; Sposito et al., 2012; Cardinali et al., 2016).  It seems, 
therefore, that the continuous reshaping of our perception of body parts is determined by 
various factors.
Somatosensory attributes are clearly crucial components in the context of body plasticity, as 
indicated by a number of studies on tool embodiment. For example, in a recent study Martel 
and colleagues (2019) have shown that somatosensory signals evoked by tool use alone are 
sufficient to alter kinematic profiles of reach-to-grasp movements. Similarly, previous studies 
with brain-damaged patients with unilateral spatial attentional disorders demonstrated that tool-
use could lead to crossmodal tactile extinction when a visual stimulus was presented at the 
extremity of a used (embodied) tool (Farnè et al., 2005, 2007; Farnè & Làdavas, 2000; Maravita 
et al., 2001), suggesting a predominance of sensory-motor information in determining 
embodiment and body representation plasticity. A hypothesis that has been recently challenged 
(Maravita & Romano, 2018). For example, in a recent study (Romano et al., 2019), we 
observed that active training, requiring movements either of the shoulders (proximal actions) 
or of the wrist (distal actions), induced a different shift of the perceived forearm’s midpoint. 
Crucially, the findings suggested that the type of action required while using a tool significantly 
contributes to modulating the representation of the body part involved. The tool-use-dependent 
change of body representation would not be a mere morphological change. A further crucial 
factor that tends to conflate with the motor aspect is attention, as the focus of attention tends to 
be directed to the part of the body that needs to be moved. It seems, therefore, that also shift of 
attentional resources can conflate with motor and sensory information (Holmes et al., 2007a; 
Homes et al., 2007b). 
Therefore, the representation of one’s own body part does not depend on one unitary 
mechanism but on a combination of factors. The aim of the current study is to investigate the 
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selective impact of motor and sensory aspects and focus of attention on body metric 
representation by means of a forearm bisection task.
Materials and methods 
Participants
A group of 24 right-handed healthy female adults took part in the study. Their average age was 
25.7 years (SD = 3.73) and their average formal education was 17.1 years (SD = 2.9; range: 8-
22). The study was approved by the Goldsmiths Departmental Ethics Committee in accordance 
with the standards of the 1964 Declaration of Helsinki (BMJ 1991; 302: 1194). All participants 
gave written informed consent before taking part in the study.
Procedure
Participants were blindfolded for the entire experiment and comfortably sat at a table in a 
floodlit and sound-attenuated room. Their right forearm rested, palm down, on the table in a 
comfortable position. Participants were asked to perform the Forearm Bisection Task, an 
experimental procedure frequently used in the context of body-metric representation studies 
(Garbarini et al., 2015; Romano et al., 2019; Sposito et al., 2010; 2012; Tosi et al., 2018; 
D’Angelo et al., 2018). In this task, participants are asked to indicate, with their left index 
finger, the midpoint of a body segment that goes from the tip of the middle finger to the right 
olecranon (elbow). Ballistic movements of the left-hand index finger indicated the subjective 
midpoint; corrections were not allowed. Each trial started with the left index finger placed at 
about 30 cm distance from the participant’s midsagittal plane in a standard point. To avoid 
tactile feedback by touching the right forearm during the bisection task, a custom-made plastic 
table ruler was placed a few millimetres above the forearm to be bisected. Once the left finger 
touched the plastic table ruler, it remained in place for a few seconds, allowing the experimenter 
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to record the position (subjective midpoint). Then the left finger was positioned back at the 
starting point for the new trial. 
Individual’s forearm length (i.e., distance from the elbow to the middle fingertip) was measured 
at the beginning of the study to calculate the objective forearm midpoint. The zero was set at 
the most proximal landmark (i.e., elbow). For each participant, the subjective midpoint was 
calculated by averaging each pointing position across trials (details on the number of trials and 
conditions are reported in the following sections below).  We than calculated the subjective 
midpoint deviation as the difference between the perceived and objective midpoint, as a 
percentage of the participant’s actual forearm length:
𝑆𝑢𝑏𝑗𝑒𝑐𝑡𝑖𝑣𝑒 𝑀𝑖𝑑𝑝𝑜𝑖𝑛𝑡 𝐷𝑒𝑣𝑖𝑎𝑡𝑖𝑜𝑛 = (𝑆𝑢𝑏𝑗𝑒𝑐𝑡𝑖𝑣𝑒 𝑚𝑖𝑑𝑝𝑜𝑖𝑛𝑡 ― 𝑂𝑏𝑗𝑒𝑐𝑡𝑖𝑣𝑒 𝑚𝑖𝑑𝑝𝑜𝑖𝑛𝑡𝐹𝑜𝑟𝑒𝑎𝑟𝑚 𝑙𝑒𝑛𝑡ℎ ) ×  100
According to this formula, a negative value indicates a proximal subjective deviation (i.e. a 
shift of the subjective midpoint toward the elbow), a positive value indicates a distal subjective 
deviation (i.e. a shift of the subjective midpoint toward the wrist) and a value equal to 0% 
indicates no deviation (i.e. subjective and objective midpoints are identical). Each participant 
performed the bisections under three different tasks respectively named: Motor, Sensory, and 
Attention (described below). The order of the tasks was counterbalanced across participants. 
Motor Task
Participants were asked to perform the Forearm Bisection Task immediately after a movement 
of their right middle finger (Distal movement) or their right elbow (Proximal movement). 
Movements consisted of three relatively rapid taps of the finger or the elbow, maintaining the 
rest of the forearm as stationary as possible. Each movement condition consists of a block of 
12 trials with no movement (baseline) followed by 12 trials with movement (either distal or 
proximal). Each participant performed both movement conditions for a total of 48 trials:  24 
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for the two baselines and 24 for the two movement conditions. The order of movement 
conditions was counterbalanced across participants.
Sensory task
Participants were asked to perform the Forearm Bisection Task immediately after a 
somatosensory stimulation of either their right middle finger (Distal stimulation) or their right 
elbow (Proximal Stimulation) or both locations as an additional control condition (Distal-
Proximal Stimulation). Double stimulation was introduced to distinguish the sensory effect 
from the possible attentional effect. Supra-threshold somatosensory stimulation (Francis et al., 
2000) was induced by means of a vibration stimulator. Two vibration pads (10mm 
approximately) were placed on both the elbow and the middle finger. Three keys were used to 
deliver single stimulation either to the elbow or the middle finger, and double stimulation to 
both sites (i.e. the elbow and the finger) simultaneously. Vibration frequencies of 50Hz were 
delivered by the examiner for approximately 1 second and consisted of a block of 12 trials with 
no stimulation (baseline) followed by 12 trials of stimulation (either distal, proximal, or 
double). Each participant performed all the stimulation conditions (order counterbalanced 
across participants) for a total of 72 trials (i.e. 36 for the three baselines and 36 for three 
stimulation conditions). 
It should be noted that vibrotactile stimulation at the level of the elbow has been reported to 
induce illusions of limb movement. However, the frequency (50 Hz) and duration of 
stimulation (∼1 second) delivered in the current study did not induce any illusory movement 
as typically higher frequencies (above 90 Hz) and longer stimulation (above 100 seconds) are 
needed for vibration-induced illusions to occur (e.g. Purcell et al., 2020; Burrack & Brugger, 
2005; de Vignemont et al., 2005; Lackner, 1988).
 
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Attention task
Participants were asked to perform the Forearm Bisection Task (as described above) 
immediately after focusing their attention on their hand (Distal attention) or on their elbow 
(Proximal attention). Location of attention was manipulated by asking participants to detect 
‘very light’ somatosensory stimulation (i.e., vibrations) under the tip of their middle finger or 
under their elbow. The same equipment described above was used to deliver the vibrations. 
Participants were told that, in this task, the vibrations could be ‘extremely’ light and possibly 
under the individual threshold. They were also told that intensity increased across 6 trials until 
they could feel it. In reality, during the first five trials, the examiner pretended to deliver the 
stimulation, but no vibration was given. Under this condition, the participants would have 
focused their attention on the ‘stimulated’ extremity of their upper limb without interference 
from sensory information. A supra-threshold stimulation was delivered only on trial 6 to 
facilitate participants’ engagement on the task, and data from these trials were not considered 
in the final analysis. After each trial, they were asked to perform the arm bisection and asked 
whether they detected the vibration. Each attention condition (Distal or Proximal) consisted of 
two blocks of 12 trials without stimulation (baseline) followed by four blocks of 6 trials with 
distal or proximal stimulations. In total, each participant performed a total of 72 trials: 24 trials 
for the two baselines, 48 trials for proximal and distal attention stimulations; of these last trials, 
only those with ‘simulated stimulations’ (n=40) were entered in the final analysis.
Statistical analysis
Inferential statistics were performed through linear mixed models (LMM) by means of lme4 
package implemented in the statistical software R (R Core Team 2016). 
Subjective Midpoint Deviation (SDM) was used as the dependent variable (i.e. the discrepancy 
between the perceived and actual midpoint between the elbow and the tip of the middle finger 
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calculated as indicated in the Procedure section), including subjects as the random intercept 
variable. The fixed effect models tested always included a within-subject factor Time with two 
levels (baseline/post manipulation) and another within-subjects factor, Body Part. The latter 
has two levels for the motor and attention tasks (distal/proximal), and three levels for the 
sensory task (distal/proximal/both). 
Significant interactions have been explored by the inspection of confidence intervals of the 
different conditions for which we reported mean values and 95% Confidence Intervals (CI) 
(Cohen, 1990, 1994; Masson & Loftus, 2003). 
Results
Motor Task
LMM analysis revealed a significant main effect of Time (F(1,1020)=17.719, p<.001) and 
Body Part (F(1,1020)=11.972, p<.001). The interaction was not significant (F(1,1020)=0.074, 
p=.786). 
The inspection of CI (Figure 1) shows that moving a body part induces a proximal shift 
(baseline: -4.25% [-7.34,-1.16]; post-action: -5.32% [-8.42,-2.23]). Moreover, the block 
involving the elbow shows a more proximal deviation than those involving the index finger 
(proximal: -5.23% [-8.32,-2.14]; distal: -4.35% [-7.44,-1.25]).
--- Insert Figure 1 about here ---
Sensory Task
LMM showed that nor the main effect of Time (F(1,1546)=3.166, p=.075) or Body Part 
(F(1,1546)=0.736, p=.48), neither the interaction was significant (F(1,1546)=2.019, p=.133). 
For the sake of transparency Figure 2 reports all the condition averages and the related CIs.
--- Insert Figure 2 about here ---
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Attention Task
LMM identified a significant main effect of Body Part (F(1,1020)=20.354, p<.001). The 
interaction between Body Part and Time fall in the grey area of a p-value that approaches the 
significant level without crossing it (F(1,1020)=3.354, p=.067). The main effect Time was not 
significant (F(1,1020=0.038, p=.846).
The inspection of CI (Figure 3) shows that the blocks involving the elbow have a more proximal 
deviation than those involving the index finger (proximal: -7.48% [-11.11,-3.86]; distal: -
6.38% [-10.00,-2.76]). Crucially, when considering Time, we observed that attention to the 
proximal end tends to induce a more proximal shift (baseline proximal: -7.24% [-10.86,-3.61]; 
post-attention proximal: -7.73% [-11.36,-4.11]) than moving the attention to the distal end 
finger (baseline distal: -6.58% [-10.21,-2.96]; post-attention distal: -6.18% [-9.80,-2.56]) that 
instead reduce the proximal shift; however, it is important to consider these latter results 
cautiously considering the level of evidence.
--- Insert Figure 3 about here ---
Discussion
Our findings showed that, at baseline, participants tended to perceive their forearm as shorter 
than its real length, as indicated by the proximal shift of the subjective midpoint. This pattern 
of data is in line with the studies in the literature showing that the representation of upper body 
parts is usually underestimated (e.g. for hands, see Longo, 2022; for arms, see Romano et al., 
2019; Bolognini et al., 2012; Tosi et al., 2018; for face, see Mora et al., 2018). Although some 
exceptions have also been reported (Fuentes et al., 2013; Sadibolova et al., 2019 Linkenauger 
et al., 2015), especially when different aspects of body representation were explored or the use 
of a tool was required (e.g., Garbarini et al., 2015, Sposito et al., 2012). It has been suggested 
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that the pattern of under-over-estimation of body parts may be linked to the specific use of 
these body parts in everyday life (Ferretti, 2016; Caggiano & Cocchini, 2020; Caggiano et al., 
2021), and distortions may be crucial for more efficient and adaptive motor control (Longo, 
2022; Bassolino & Becchio, 2023). In our study, the same trend of underestimation was also 
observed after all three types of manipulation, suggesting a relatively stable underestimation 
of the representation of one’s own upper limb. However, the impact of each manipulation was 
different. In detail, the subjective midpoint deviation scores were significantly modulated by 
the Motor task but not by the Sensory one, whereas in the Attentional task, a close-to-
significance interaction between Body Part and Time was observed. These results shed 
interesting light on the differential contribution of movement and attention in shaping 
subjective body metric changes.
The Motor task induced an increment, compared to the baseline, of the proximal shift 
regardless of which body part was moved. At first glance, this seems to contradict evidence 
from one of our recent studies, which showed proximal shift when active motor training 
involved shoulder movements and distal shift when active training involved the use of the wrist 
and fingers (Romano et al., 2019). Critically, the effect observed in our previous study was 
interpreted as result of the crucial role of motor patterns in determining the direction of the 
perceived changes in body metric therefore, a possible explanation of the current findings, is 
that movement per se, when not goal-directed to any external target in the environment, tends 
to induce a shift toward the body (proximal); possibly because of the preponderant weight of 
proprioceptive information in non-goal-directed motor actions. The crucial aspect of goal-
direction of purposeful actions was elegantly demonstrated in a study by D’Angelo et al. 
(2018). The authors showed how the agency of goal-directed movements could induce 
enlargement or contraction of body representation depending on the location of the target of 
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the action and agency. The lack of a purposeful goal toward an external target may have 
allowed the isolation of the impact of movement on the representation of one’s own body part.
Focusing attention on a specific body part (i.e. hand or elbow) also seems to potentially 
moderate body representation even if the results suggest different implications from the Motor 
task. Although the effect has to be taken cautiously, in the Attention task, we observed a 
possible interaction effect which seems to suggest that the allocation of attention to the elbow 
is likely to lead to a further proximal shift, whereas the allocation of attention to the hand is 
likely to lead to a reduction of the proximal shift. It might be argued that the trend observed in 
this condition could be the effects of the ‘stimulation trials’ which intermingled with the 
‘neutral trials’ (i.e., no stimulation). However, considering the absence of any effect in the 
Sensory task (where stimulations were delivered consistently across trials), we believe it is 
unlikely that a single supra-threshold stimulation drives the potential effect observed in the 
Attention task.
Taking these findings together, they suggest that subjective elongation of the arm observed 
during tool-use might be the result of an embodiment of the motor characteristics of tool-use 
guided by an attention shift, towards the body part actively used during the use of the tool, that 
may trigger the incorporation of the tool (Romano & Maravita, 2021). It has been consistently 
shown that the modulation of body representation for action and perceived reachable space 
occurs when individuals use a tool that functionally increases action capabilities (Bourgeois et 
al. 2014; Patané et al. 2016, 2017). However, the modulation of our subjective body 
representation is also possible, though diminished, without the tool manipulation (e.g. Romano 
et al., 2019; Caggiano et al., 2021; Bassolino et al., 2015) suggesting that the presence of the 
tool is not, strictly speaking, necessary to induce a detectable bisection shift towards the body 
part manipulated. In light of these considerations, we need to reconsider the aforementioned 
point about the purpose of a movement. In virtually all studies investigating the malleability of 
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body schema, participants are asked to perform a movement in order to accomplish a task and, 
crucially, the internal focus of attention is directed not only to the specific body part but also 
to the goal-oriented motor patterns required to accomplish the task (Bruno et al., 2019). Indeed, 
rapid processes of internal concentration and automatic attentional shift on the tool (or the body 
part) have been shown to guide other sensory integrations in the perception of body 
representation and the direction of perceived body representation changes (Holmes, Calvert, et 
al., 2007; Holmes, Sanabria, et al., 2007; Reed & Park, 2021). Therefore, a shift in attention 
seems to be an important modulator of the body metrics change. However, the weak effect that 
we observed after the manipulation of attention seems to indicate that attention needs to be 
coupled with motor signals to induce a significant effect (Longo et al., 2010; Medina & Coslett, 
2016; Romano et al., 2019).  
The lack of any effect of the Sensory task/manipulation on body representation is a bit 
surprising, but we cannot exclude a lack of sensitivity of our paradigm for this specific factor 
considering that the lack of evidence should not be confounded with the evidence of lack of 
effect in the frequentist inferential framework. 
Although, to our knowledge, gender has not been typically reported to be a significant factor 
modulating body metrics in similar experimental paradigms on healthy individuals (e.g Fuentes 
et al., 2013; Stone et al., 2018; D’Angelo et al., 2018, Bassolino et al., 2015), further studies 
may want to replicate these findings with the inclusion of male participants. Our findings are 
not conclusive, but they contribute to filling an important gap in the current literature and call 
for some reconceptualization of the empirical investigation of body representation. It has often 
been pointed out that body representation is susceptible to experimental task demand; hence, 
different experimental conditions may lead to different results (de Vignemont, 2010). Because 
the body representation is multimodal and extremely complex in its nature, this observation is 
not entirely surprising but poses a significant question in regard to how to overcome this 
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potential limitation. Often researchers have tackled the topic of body representation by devising 
studies that address a specific question with a specific experimental paradigm without 
necessarily considering the different contributions of cognitive and sensorimotor components 
that may have in the observed results. 
In the present study, we adopted a ‘comparative’ approach to isolate and disentangle the role 
of movement, somatosensation and attention directed towards the body on the modulation of 
perceived body metrics by isolating these factors from others. Such comparisons have 
highlighted that within the same experimental paradigm (i.e. the forearm bisection task), 
different manipulations produce different outcomes raising the question of what these 
differences tell us about the nature of body representation.
Overall, the above considerations and the present results suggest that changes in body 
representation are not simply shaped by motor patterns or attentional factors. These two are not 
mutually exclusive, and their interaction might be crucial. Future studies should attempt to 
further elucidate the individual weight of these factors and how they may interact and drive 
body representation’s plasticity with and without the use of a tool. 
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, 
and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of 
this article.
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Data availability
Readers seeking access to the datasets generated and/or analysed during the current study 
should contact the corresponding author. Access will be granted to named individuals. There 
are no further conditions. No part of the study procedures and analyses were pre-registered 
prior to the research being conducted.
Authors’ contribution
GC & DR formulation of hypotheses and paradigm, DR data analysis, DDS data collection and 
feedback on drafts; PC, GC, DR interpretation of findings and writing the manuscript. All 
authors provided relevant contributions to the study.
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Figure Captions
Figure 1. Results from the Motor task
Bars indicate 95% confidence interval
Figure 2. Results from the Sensory task
Bars indicate 95% confidence interval
Figure 3. Results from the Attention task
Bars indicate 95% confidence interval
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