Asymmetrical Body Perception
Running head: ASYMMETRICAL BODY PERCEPTION
Asymmetrical Body Perception: A Possible Role for Neural Body Representations
Sally A. Linkenauger*1, Jessica K. Witt2, Jonathan Z. Bakdash1, Jeanine K. Stefanucci3, &
Dennis R. Proffitt1
1
University of Virginia
2
3
Word Count: 3,897
Purdue University
The College of William and Mary
1
Asymmetrical Body Perception
Abstract
Perception of our body is not only related to the physical appearance of the body but also to the
neural representation of the body in somatosensory cortex. In right-handed people, the area of
the somatosensory cortex devoted for the right hand is larger than the left hand, but for lefthanded people there is symmetry. Taking advantage of these naturally occurring neural
differences, we examined perceived arm length in right-handed and left-handed participants.
When looking at each arm and hand individually, right-handed participants perceived their right
arms and hands to be longer than their left arms and hand, while left-handed participants
perceived both arms accurately. These experiments reveal a possible relationship between
implicit body maps in the brain and conscious perception of the body.
2
Asymmetrical Body Perception
3
Asymmetrical Body Perception: Neural Representations Relate to Body Perception
When we look at our body, what we see is likely influenced by the neural representation
of the body in the cortex and is not solely due to the way the body appears physically. In righthanded individuals, the neural representations of the body are asymmetric, in that there is
typically more cortical area and higher neural activation associated with the right side of the
body than the left; whereas left-handed individuals usually have symmetrical cortical body
representations (ref, ref, ref). Extending this finding, the current studies assessed whether
asymmetries in cortical representation would also be related to the perceived size of the
associated body part. Obtaining variability in the size of cortical areas was achieved by taking
advantage of naturally occurring individual differences due to handedness. If the amount of
neural representation influences the perceived size of the body, then right-handed people should
perceive their right arm longer than their left arm, and left-handed people should perceive both
arms as the same. For right-handed participants, we found these anticipated asymmetries in
perceived arm length and hand size as well as in anticipated reachability and graspability. In
contrast, perceived arm length and anticipated reachability were symmetrical for left-handed
participants, paralleling the symmetries in their cortical representations. These findings provide
compelling evidence for the hypothesis that neural bodily representations are reflected in how we
visually perceive our body.
Neuroimaging studies have uncovered hemispheric asymmetries in cortical areas
associated with body representation in right-handed people but not in left-handed people. Righthanded individuals have a greater cortical surface area in their left sensory cortex and higher
activation their left primary motor and sensory cortices for contralateral movements, while lefthanded individuals appear to have a near symmetrical surface area and activation (Amunts et al.,
Asymmetrical Body Perception
1996; Zilles et al., 1997; Kawashima, et al. 1997; Kim et al., 1993).
4
Electroencephalography
(EEG) studies have reported that right-handers show greater neural activation and a larger hand
area in the left somatosensory cortex than in the right when engaging in a motor task (Jung et al.,
2003, Buchner, Ludwig, Waberski, Wilmes, & Ferbert, 1995). Hemispheric asymmetries have
also been revealed in areas of the parietal lobe associated with visuomotor processing. The left
(but not right) inferior parietal lobule has been implicated in the updating of the body
representation in right-handed individuals (Devlin et al., 2002). Right-handed patients with optic
ataxia due to damage to the left parietal lobe show deficits in reaching to stimuli in the right
visual field and deficits in reaching with the right hand, whereas similar damage to the right
hemisphere results in only a deficit in reaching to the left visual field, suggesting an asymmetry
in the body representation between the two hemispheres (Perenin & Vighetto, 1988).
Paralleling the neuroimaging data, right-handed people tend to be much more reliant on
their dominant hand than left-handed people. For example, when performing a grasping task,
right-handed people use their right hand for 90% of the grasps, while left-handed people used
both hands equally (Gonzalez, Whitwell, Morrissey, Ganel, & Goodale, 2007). In addition,
right-handed people evaluate that their ability to reach and grasp a hand tool as more impaired
than left handed people if the tool’s handle is oriented towards the non-dominant hand
(Linkenauger, Witt, Stefanucci, Bakdash & Proffitt, in press). In general, hand preference
surveys indicate that left-handed people are typically less “left-handed” than right-handed are
right-handed (Tan, 1998).
Taken together, there is compelling evidence for structural and functional cortical
symmetry differences between right- and left-handed people. In the current experiments, we
Asymmetrical Body Perception
5
assessed whether these differences would be reflected in the visually perceived size of arms and
hands.
Experiment 1: Handedness and Arm Length Perception
If the cortical representations of the arm affect perceived arm length, then right-handed
people should perceive their left and right arms to be different lengths, because right-handed
people have a larger representation of their right arm than their left. However, because lefthanded people have a near equal sized cortical representation their left and right arms, the extents
of their right and left arms should appear similar. To test this notion, right- and left-handed
participants indicated the perceived length of both their left and right arms.
Method
Participants. Fifteen right-handed (7 female) and 15 left-handed (7 female) University of
Virginia students participated. Handedness was assessed through self-report, which was
consistent with the hand that signed the consent form. All participants had normal or correctedto-normal vision.
Design and Procedure. Participants were instructed to stand and extend their right or left
arm to be perpendicular to their body and to place the fingers of their non-extended hand on the
protrusion of their shoulder defined by the intersection of the clavicle and the humerus. Then,
participants made estimates of the lengths of their arms as defined by the distance from the
protrusions on their shoulders to the end of their finger tips on their extended hands. Participants
estimated arm length by instructing a researcher standing perpendicular to the extended arm to
adjust a blank measuring tape horizontally so that the extent on the tape matched the perceived
Asymmetrical Body Perception
6
length of the participant’s arm. Participants could refer to the extent of their arms continuously
while making the estimate (see Figure 1). Next, participants’ grip strength was assessed for each
hand using a dynamometer. Then, participants estimated the length of their other arm; arm order
was counterbalanced. Lastly, the actual extents of the participants’ arms were measured.
Results. Arm length estimates were assessed by calculating a ratio of perceived arm
length divided by actual arm length. A repeated-measures analysis of variance (ANOVA) with
arm as a within-participants factor was used to compare the arm length ratios between right- and
left-handed participants. No main effect of arm was found, F(1, 28) = 1.37, prep = .67; however,
as predicted, an significant interaction was found between arm and handedness, F(1, 28) = 4.74,
prep = .90, ηp2 = .15. Separate paired-samples t-tests for right- and left-handed participants
revealed that right-handed participants underestimated the length of their left arm more than the
length of their right arm, t(14) = 2.12, prep = .91, always one-tailed. However, we did not find
this difference for left-handed individuals, t(14) = -.82, prep = .70 (see Figure 2A). One-sample ttests were used to compare the ratios to 1 (perfect accuracy) and revealed that right-handed
participants were accurate in their perception of their right arm, t(14) = -.85, prep= .50, but
underestimated their left arm, t(1,14) = -2.38, prep= .94, ηp2 = .29. Left-handed participants were
accurate in estimating both their right and left arms, prep = .75, prep = .50; respectively.
Variability in the difference between the left and right arm estimates did not differ by
handedness, prep = .52, suggesting that these differences are not due to increases in variability of
the spectrum of left-handedness.
Given that sensory feedback is generally greater for body parts that engage in more
activity (Pantev, Engelien, Candia, & Elbert, 2001; Hamilton & Pascual-Leone, 1998), requiring
a larger somatosensory area, we hypothesized that perceived arm length would be related to the
Asymmetrical Body Perception
arm’s strength. Relative strength ratios were created by dividing participants’ grip strength
measurements of the right hand by that of the left hand1. Ratio scores greater than 1 indicate
increased strength with the right-hand compared to the left-hand, and ratio scores less than 1
indicate higher relative strength with left-hand. Relative hand strength significantly correlated
with relative arm length (perceived length of right arm/perceived length of left arm), r = .44,
prep= .91 (see Figure 2B). Asymmetries in hand strength were positively related to asymmetries
in perceived arm length.
Experiment 2: Handedness and Perceived Reachability
With perceptual differences often come behavioral consequences. Given that righthanded people perceive their right arms as being longer than their left arms, they should also
anticipate that they can reach farther with their right arm than their left. In this experiment,
right- and left-handed participants estimated how far they could reach with their left and right
arms.
Method
Participants. Fifteen right-handed (11 female) and 15 left-handed (8 female) University
of Virginia students participated. Handedness was assessed through self-report and by the
Edinburgh Handedness survey (Oldfield, 1971), right-handed participants (M = 91.3, SD =
12.11); left-handed participants (M = -70.7, SD = 28.22). All participants had normal or
corrected-to-normal vision.
Stimuli and Apparatus. Participants were seated on a chair at a uniformly colored table
that measured 91.5 cm by 91.5 cm and was 74.5 cm tall. Participants’ shirt backs were clamped
to the back of the chair using binder clips to prevent forward lean. Participant sat at a close but
comfortable distance to the table.
7
Asymmetrical Body Perception
8
Design and Procedure. Participants estimated their reach with their right and left arms.
From the opposite side of the table from the participant, the experimenter moved a white plastic
chip toward the participants. The participants informed the experimenter when they thought the
chip was close enough that they could just grasp the chip with a specific arm without moving
their shoulders from the back of the chair. The binder clips served as a constant reminder of this
constraint. Participants were encouraged to instruct the experimenter to make adjusts to the
position of the chip. Participants made 3 estimates of reachability with a specific arm that were
contralateral (starting 30º from center moving towards center, away from the reaching arm),
ipsilateral (30º from center, towards the reaching arm), and central, and then made the 3 same
estimates of reachability using the other arm. This order was counterbalanced. Between right
and left arm reachability estimates, participants performed the grip strength task as described in
Experiment 1. At no time during the reachability estimates were participants allowed to reach
over the table. At the end of the estimates, participants’ actual reaching abilities were assessed
for each arm in each direction.
Results
Accuracy of reachability was determined by dividing perceived reachability by actual
reachability. As in other reaching studies (Rochat & Wraga, 1996), participants overestimated
their reaching ability. To compare reachability for right- and left-handed participants, a 2 (left
vs. right hand) by 3 (direction: contralateral, ipsilateral, and center) by 2 (right vs. lefthandedness) repeated measures ANOVA was performed. Hand and direction were both
specified as within-participants factors, whereas handedness was a between-participants factor.
The most interesting finding was a hand by handedness interaction, F(1, 28) = 14.14, prep > .99,
ηp2 = 0.34 (see Figure 3). No other main effects were significant, except for direction, F(2,27) =
Asymmetrical Body Perception
9
27.72, prep >.99, which revealed that participants overestimated their contralateral (M =1.22, SD
=.19) and center (M = 1.19, SD = .16) reaches more than their ipsilateral reach (M =1.09, SD
=.13).
Separate 2 (arm) by 3 (reaching direction) repeated-measures ANOVAs for right- and
left-handed participants showed that for right-handers, main effects were found for arm, F(1, 14)
= 21.53, prep = .99, ηp2 = 0.59. Right-handed participants overestimated their reach more with
their right arm (M = 1.17, SD = 0.15) than with their left (M = 1.08, SD = 0.14). For left-handed
participants, no main effect of arm was found, F(1, 14) = 1.86, prep = 0.72. For both groups,
there was a main effect for direction, Fs (2, 28) > 10.71, preps = .99, ηps2 > 0.43, with similar
patterns as was found in the 3-way ANOVA. These results show that in addition to perceiving
their right arm as longer, right-handers also thought they could reach farther with their right arm;
whereas, left-handed people did not perceive any difference between their arms.2
Experiment 3: Right-handedness, Hand Size and Graspability
Because the hand area in the somatosensory cortex is asymmetrical in right-handed
individuals, we also expected a difference in the perceived size of the right and left hands. We
had right-handed participants estimate the size of their right and left hands as well as indicate
their maximum grasping abilities with their right and left hands.
Method
Participants. Fifteen right-handed (6 female) University of Virginia students participated
to fulfill a research requirement for course credit. Handedness was assessed through self-report
Asymmetrical Body Perception
10
and the Edinburgh Handedness survey (Oldfield, 1971) (M = 87.35, SD = 22.87). All
participants had normal or corrected-to-normal vision.
Stimuli and Apparatus. Participants were seated on a chair at the table described in
Experiment 2. Block size estimates were made on a Dell laptop computer whose screen
measures 33.5 cm diagonal. Sixteen square blocks of different sizes (ranging from 4 cm to 24
cm) were constructed from foam board that was 1.5 cm thick. Each block had two parallel black
lines (3 cm in length) marked on two opposing sides of the block to indicate where the
participants should anticipate placing their fingers when grasping.
Design and Procedure. Participants sat at the table and were told that they were going to
estimate whether they thought they could grasp the block in front of them. Participants were told
that the grasp that they had to anticipate entailed placing their thumb on one of the black lines on
the edge of the block and then extending their hand across the entire block to place any one of
their other fingers on the black line on the other side of the block. A successful grasp was
defined as being able to lift the block completely off the table. When participants indicated that
they understood the instructions, they were asked to close their eyes as the experimenter placed
one of the 16 blocks in the center of the table in front of the participant with the black lines on
the block perpendicular to the participant. The participant opened their eyes and indicated
whether they thought they could successfully grasp the block with a specific hand. Then
participants estimated the width of the block by using the arrow keys on the laptop to move two
circular white dots (.30cm in diameter) on a black background to be the same distance away
from each other as the distance between the two black lines on the blocks (the width of the
block). The laptop computer was placed on a stool beside the participant’s hand that was not
being used for grasp estimates. Participants estimated their grasping ability with all 16 blocks
Asymmetrical Body Perception
11
with one hand and then all 16 blocks with the other hand for a total of 32 trials. Blocks were
presented in random order and hand order was counterbalanced.
After making grasping ability judgments, participants were told to estimate the length and
width of their hand. Hand length was defined as the extent between the crease at the bottom of
their palm and the longest fingertip. Hand width was defined as the extent between the
intersection of the pinky and palm to the intersection of the index finger and palm. The
experimenter stood in front of participants while participants looked at the palm of their hand,
and the experimenter extended a blank tape measure perpendicularly to the extent they were
estimating (horizontally for length and vertically for width; as prevention from using a landmark
matching heuristic). Participants indicated to the experimenter when they thought that the extent
on the tape measure matched the length (or width) of their hand. Participants were encouraged
to make fine adjustments. After participants estimated the length and width of one hand, their
grip strength for both hands was assessed. Participants then estimated the length and width of
their other hand. Hand order was counterbalanced. After making the estimates, the actual length
and width of each hand was measured as well as actual maximum graspability for each hand.
Results and Discussion
Graspability accuracy was determined for each participant’s left and right hand by
dividing perceived graspability by actual graspability. Right and left hand graspability
accuracies were compared using a paired-samples t-test which indicated that participants
overestimated their grasping ability more with their right hand (M = 1.12, SD =.13) than with
their left (M = 1.07, SD = .15), t(14) = 2.14, prep = .93, ηp2 = .25. Similar to reachability,
participants overestimated their graspability with both their right and left hands, t(1, 14) = 3.60,
prep = .98, ηp2 = .48; t(14) = 1.85, prep =.89, ηp2 = .20, respectively (see Figure 4A).
Asymmetrical Body Perception
12
In order to determine hand size accuracy values, perceived hand area was determined by
multiplying the perceived width and length for each hand. The perceived area was then divided
by the actual area to arrive at a measure of accuracy. One participant’s data was removed from
the analysis due to his admission of misunderstanding the instructions. Participants
underestimated the size of their left hand (M = .91, SD = .19) more than the right hand (M = .99,
SD = .18), t(1,13) = 3.03, prep =.97, ηp2 = .41. As found with arm length perception, participants
were accurate in perceiving the size of their right hand (M = .99, SD = .18), prep = .29, while
participants underestimated the size of their left (M = .91, SD = .19), t(13) = 1.82; prep = .89, ηp2
=.20 (see Figure 4B).
Strength ratios were constructed as in previous experiments. Hand size ratios were
calculated by dividing the perceived right hand area by the perceived left hand area. Graspability
ratios were calculated by dividing perceived graspability with the right hand by perceived
graspability with the left hand. Although graspability ratios were not significantly related to the
strength ratios, r = .22, prep= .71, hand size symmetry ratios were positively related to strength
ratios, r = .54, prep = .93 (see Figure 4). This finding suggests that the stronger the right hand is
in comparison to the left, the larger the right hand is perceived relative to the left. As found with
reaching and arm length perception, the right hand is perceived to be larger and more capable of
grasping than the left.
General Discussion
Although functional and structural differences have been documented between cortical
hemispheres, this is the first demonstration that these differences may have perceptual
consequences. Conscious perception of the dimension of arms and hands appear to be consistent
the size of their neural bodily representations. Currently, we cannot determine whether these
Asymmetrical Body Perception
13
perceptual effects are the result, the cause, or just coincidental with the neurological
discrepancies between right- and left-handers. Neuroimaging research has shown that training in
complex actions with a specific body part can increase the size of the representation of that body
part in the motor and somatosensory cortices (Elbert, Pantev, Wienbruch, Rockstroh, & Taub,
1995; Hamilton & Pascual-Leone, 1998; Nelles, Jentzen, Jueptner, Muller, & Diener, 2001).
Similarly, increasing the use of a certain effector over an extended period may also affect the
perception of the effector in addition to the size of its area on the somatosensory cortex.
However, because many neural and perceptual differences accompany handedness that cannot be
attributed to experience (McManus, 2002), it is possible that these perceptual effects are the
result of innate differences between right- and left-handed people rather than a byproduct of
experience. In addition, these affects could arise from a reciprocal relationship between
experience-driven and innate differences.
Just as handedness is considered to have an adaptive function (Wilson, 1998), we believe
that these perceptual effects are adaptive as well. Right-handers perceive their right, and more
functional arm, as being longer than their left arm. An exaggerated perception of one arm, which
coincides with the anticipation of greater reaching capabilities with that arm, may suggest a
mechanism for why right-handers tend to use their right arm more often, even when reaching
awkwardly to the left side (Gonzalez et al., 2007).
The current findings are nicely situated in the context of other research that demonstrates
effects of functionality on perceived distance. For instance, targets just beyond reach look closer
when a participant intends to reach to them with a tool compared to when no tool is held (Witt,
Proffitt, & Epstein, 2005). Tools placed in an orientation that make them easier to grasp appear
closer than when their orientation makes them more difficult to grasp (Linkenauger et al., in
Asymmetrical Body Perception
14
press). Golf holes and softballs look bigger to athletes who are playing well (Witt, Linkenauger,
Bakdash, & Proffitt, 2008; Witt & Proffitt, 2005). Here, we demonstrated differences in the
perceived length of the effector itself. Thus, the perceptual differences documented here could
reflect the functionality of the arm as well as the neurological representation of the arm.
Future studies could look at whether neurological and functional differences affect the
perception of other body parts. For instance, perhaps soccer players who favor their right leg
perceive it to be longer than their left. These results can also be explored within training and
developmental paradigms. If perceptual differences are present early in life or in training, then
perhaps special care to engage the opposite hand will help those developing new skills to reduce
their right biases, especially in situations where ambidexterity is advantageous.
In summary, right-handed people perceived their right arm to be longer and their right
hand to be larger than their left counterparts. This perceptual bias extended into their perceived
action capabilities such that right-handed people judged that they could reach farther with their
right arm and grasp larger objects with their right hand compared with their left arms and hands.
In contrast, left-handed people perceived their arms to be equally long and to be able to reach
equally far. Similarly for left-handers, there is no difference between perceived hand size and
the maximum size of objects that can be grasped with each hand. These results suggest that the
body representation in the somatosensory cortex may extend beyond tactile sensations and bodily
awareness and may influence visual perception of the body as well.
Asymmetrical Body Perception
15
References
Amunts, K., Schlaug, G., Schleicher, A., Steinmetz, H., Dabringhaus, A., Roland, P., Zilles, K. (1996).
Asymmetry in the human motor cortex and handedness. Neuroimage, 4, 216-222.
Berlucchi, G., & Aglioti, S. (1997). The body in the brain: neural bases of corporeal awareness, Trends
in Neurosciences, 12, 560-564.
Buchner, H., Ludwig, I., Waberski, T., Wilmes, K., & Ferbert, A. (1995). Hemispheric asymmetries of
early cortical somatosensory evoked potentials revealed by topographic analysis.
Electromyography and Clinical Neurophysiology 35, 207-215.
Elbert, T., Pantev, C., Wienbruch, C., Rockstroh, B., & Taub, E. (1995). Increased cortical
representation of the fingers of the left hand in string players, Science, 270, 305-307.
Gonzalez, C., Whitwell, R., Morrissey, B., Ganel, T., & Goodale, M. (2007). Left handedness does not
extend to visually guided precision grasping. Experimental Brain Research, 182, 275-279.
Grüsser, S., Winter, C., Mühlnickel, W., Denke, C., Karl, A., Villringer, K., & Flor, H. (2001). The
relationship of perceptual phenomena and cortical reorganization in upper extremity amputees,
Neuroscience, 102, 263-272.
Hamilton, R., & Pascual-Leone, A. (1998). Cortical plasticity associated with Braille learning. Trends in
Cognitive Sciences, 2, 168-174.
Jung, P., Baumgärtner, U., Bauermann, T., Magerl, W., Gawehn, J., Stoeter, P., & Treede, R. (2003).
Asymmetry in the human primary somatosensory cortex and handedness. Neuroimage, 19, 913923.
Karl, A., Birbaumer, N., Lutzenberger, W., Cohen, L., & Flor, H. (2001). Reorganization of motor and
somatosensory cortex in upper extremity amputees with phantom limb pain. Journal of
Neuroscience, 21, 3609-3618.
Asymmetrical Body Perception
16
Linkenauger, S., Witt, J. K., Stefanucci, J. K., Bakdash, J. Z., & Proffitt, D. R. (in press). Effects of
handedness and reachability on perceived distance. Journal of Experimental Psychology: Human
Perception & Performance.
McManus, C. (2002). Right Hand Left Hand: The Origins of Asymmetry in Brains, Bodies, Atoms, and
Cultures, Cambridge, MA: Harvard University Press.
Merzenich, M. (1998). Long-term change of mind. Science, 282, 1062-1063.
Nelles, G., Jentzen, W., Jueptner, M., Müller, S., & Diener, H. (2001). Arm training induced brain
plasticity in stroke studied with serial positron emission tomography. Neuroimage, 13, 11461154.
Pantev, C., Engelien, A., Candia, V., & Elbert, T. (2001). Representational cortex in musicians. Plastic
alterations in response to musical practice. Ann. N.Y. Acad. Sci. 930, 300-314.
Perenin, M., & Vighetto, A. (1988). Optic ataxia: Specific disruption in visuomotor mechanisms. Brain,
111, 643-674.
Ramachandran, V., & Hirstein, W. (1998). The perception of phantom limbs. The D. O. Hebb lecture,
Brain, 121, 1603-1630.
Sörös, P., Knecht, S., Imai, T., Gürtler, S., Lütkenhöner, B., Ringelstein, E., & Henningsen, H. (1999).
Cortical asymmetries of the human somatosensory hand representation in right- and left-handers.
Neuroscience Letters, 271, 89-92.
Wilson, F. (1998). The Hand, How its Use Shapes the Brain, Language, and Human Culture. New
York: Random House.
Witt, J. K., Linkenauger, S. A., Bakdash, J. Z., & Proffitt, D. R. (2008). Putting to a bigger hole: Golf
performance relates to perceived size. Psychonomic Bulletin and Review, 15, 581-585.
Asymmetrical Body Perception
17
Witt, J.K., & Proffitt, D.R. (2005). See the ball, hit the ball: Apparent ball size is correlated with batting
average. Psychological Science, 16, 937-938.
Witt, J.K., Proffitt, D.R., & Epstein, W. (2005). Tool use affects perceived distance but only when you
intend to use it. Journal of Experimental Psychology: Human Perception and Performance, 31,
880-888.
Zilles, K., Schleicher, A., Langemann, C., Amunts, K., Morosan, P., Palomero-Gallagher, N.,
Schormann, T., Mohlberg, H., Bürgel, U., Steinmetz, H., Schlaug, G., & Roland, P. (1997).
Quantitative analysis of sulci in the human cerebral cortex: Development, regional heterogeneity,
gender difference, asymmetry, intersubject variability and cortical architecture. Human Brain
Mapping, 5, 218-221.
Asymmetrical Body Perception
18
Author Note
Sally A. Linkenauger, Jonathan Z. Bakdash, Dennis R. Proffitt; Department of
Psychology; University of Virginia. Jessica K. Witt; Department of Psychological Sciences,
Purdue University. Jeanine K. Stefanucci; Department of Psychology; The College of William
and Mary.
We wish to thank William Epstein, Judy Deloache, and Daniel Willingham for their
comments and revisions on earlier versions of the manuscript. This research has been supported
by NIH Grant RO1MH075781to the fourth and fifth authors.
Address correspondence to Sally Linkenauger, 102 Gilmer Hall, Charlottesville, VA
22904; email: sal3g@virginia.edu.
Asymmetrical Body Perception
19
Footnotes
1
Due to a coding error, grip symmetry scores for 3 right-handers and 3 left-handed were
unavailable and hence, not included in the correlation.
2
Due to a coding area, a substantial portion of the grip strength data was not recorded,
and as a result, we have not reported the results associated with it.
Asymmetrical Body Perception
20
Figure Captions
Figure 1. Photograph of example participant estimating the length of her right arm. The
participant instructed the experimenter to increase or decrease the length of the visible portion of
the backside of a tape measure until she perceived this length to be the same length as that of her
arm.
Figure 2. (A) Perceived arm length as a function of handedness. Ratios were computed
of perceived arm length divided by actual arm length for each arm. Data are plotted by arm and
handedness. Error bars represent 1 standard error of the mean. (B) Correlation between grip
strength symmetry and symmetry in perceived arm length. Grip strength symmetry scores were
computed as grip strength in right hand divided by grip strength in left hand. Symmetry in arm
length was computed as perceived length of right arm divided by perceived length of left arm.
Line represents linear regression of the data.
Figure 3. (A) Perceived maximum reach distance divided by actual maximum reach
distance as a function of arm and reaching direction for right-handed participants. Error bars
represent 95% within-subjects confidence intervals. (B) Perceived maximum reach distance
divided by actual maximum reach distance as a function of arm and reaching direction for lefthanded participants. Error bars represent 95% within-subjects confidence intervals.
Figure 4. (A) Ratio scores of perceived hand size divided by actual hand size for the each
hand for right-handed participants. Error bars represent 95% within-subjects confidence
intervals. (B) Ratio scores of perceived maximum grasp size divided by actual maximum grasp
size for the each hand for right-handed participants. Error bars represent 95% within-subjects
confidence intervals. (C) The relationship between grip strength symmetry and perceived hand
size. Line represents linear regression of the data. (D) The relationship between grip strength
symmetry and perceived maximum grasp size symmetry. Line represents linear regression of the
data.
Asymmetrical Body Perception
Figure 1.
21
Asymmetrical Body Perception
22
Figure 2
A
B
Right arm
1.05
1.2
Right / left
perceived arm length
Perceived / actual arm length .
Left arm
1
0.95
0.9
1.1
1
0.9
0.8
0.85
1
Right-handed
Left-handed
0.7
0.9
1.1
1.3
Right / left grip strength
1.5
Asymmetrical Body Perception
Figure 3
A
Perceived / actual
maximum reach distance
Right-handed participants
Left hand
Right hand
1.4
1.3
1.2
1.1
1.0
0.9
Contralateral
Center
Ipsilateral
B
Perceived / actual
maximum reach distance
Left-handed participants
Left hand
1.5
Right hand
1.4
1.3
1.2
1.1
1.0
0.9
Contralateral
Center
Ipsilateral
23
Asymmetrical Body Perception
Figure 4
B
1.2
1.2
Perceived / actual
maximum grasp size
Perceived / actual hand size .
A
1.1
1.0
0.9
1.1
1.0
0.9
0.8
0.8
Left
hand
Left
hand
Right
hand
C
Right
hand
D
1.3
Right / left perceived
maximum grasp size
Right / left
perceived hand size
1.3
1.2
1.1
1
0.9
0.8
0.7
1.2
1.1
1
0.9
0.8
0.7
0.9
1.1
1.3
Right / left grip strength
1.5
0.7
0.9
1.1
1.3
Right / left grip strength
1.5
24