FREE ESSAY ON GENDER DIFFERENCES IN VISUAL AND TACTILE LINE BISECTION

GENDER DIFFERENCES IN VISUAL AND TACTILE LINE BISECTION

Running Head: ATTENTIONAL BIAS IN NORMAL SUBJECTS
Gender Differences in Visual and Tactile Line Bisection: Attentional Bias
in Normal Subjects
Abstract
Attentional bias in line bisections may be influenced by the position of the stimulus,
the type of stimulus, and the gender of the bisector. Past research has found that below
eye level bisection stimuli is biased away from the body in the visual mode, and towards
the body in the tactile mode. Above eye level bisections have not been significantly
biased in either direction due to a cancellation of the object centered bias by the body
centered bias. Research has also concluded that no gender differences are statistically
significant in attentional bias studies, using line bisection tasks. This report suggests
that gender differences are statistically significant in favor of male subjects, when
using above eye level stimuli, and when using tactile stimuli. Overall, however, these
differences become statistically insignificant, when combined with below eye level tasks
and visual tasks. Current findings also point to a trend towards supporting past research
findings which state that in below eye level bisections both males and females are biased
away from the body in the visual mode, and towards the body in the tactile mode. 
Gender Differences in Visual and Tactile Line Bisections: Attentional Bias 
in Normal Subjects
The act of survival requires humans to pay attention to their surroundings. In order to
pay attention to surroundings, one must allocate resources of attention to the space
around one's body. Taking a common sense approach, the sense of vision and the sense of
touch would be the candidates for "most important senses in terms of survival". For
example, imagine a primitive hunter trying to catch prey, using only his sense of smell;
or imagine someone trying to build a hut, without the use of sensitive fingers to wield
tools. Vision is generally used as a means to detect and interpret objects at a distance,
whereas, touch is used to detect and interpret objects which are relatively close to the
body. Historically, visual and tactile attention have been studied along a left-right
horizontal axis (Shelton, Bowers, & Heilman, 1990 as cited in Geldmacher & Heilman,
1994); however, there has been a recent expansion of this research, into the vertical and
radial axes. The current study will attempt to confirm the findings of Geldmacher and
Heilman (1994), Jeerakathil and Kirk (1994), and Drain and Reuter-Lorenz (1996) that
below eye level bisection stimuli will be biased away from the body (far peripersonal
space) in the visual mode, and towards the body (near peripersonal space) in the tactile
mode. Above eye level bisections should not be significantly biased, however, due to a
cancellation of biases -i.e., the object centered bias nullifies body centered bias. 
Drain and Reuter-Lorenz (1996) are one of the only research teams to have considered
gender as a factor in the results of such studies. They concluded that although gender
does contribute to real sex differences, it is not a significant factor in assessing
attentional bias in normal subjects on line bisection tasks, due to the minuteness of
these differences. However, given the common perception that males are superior to
females in tasks of visuo-spatial dexterity (Maccoby & Jacklin, 1974, Caplan, MacPherson,
& Tobin, 1985, Newcombe & Dubas, 1992, all as cited in Dworetzky, 1996), it should be a
natural to examine the results of men vis-a-vis women. Thus, in the spirit of gender
equality and the pursuit of confirming such a hypothesis, the current study will include
gender as a factor of analysis.
In 1994, Geldmacher and Heilman studied 10 normal subjects in radial line bisection
tasks. That is, they had participants determine where the middles of lines were, when the
lines ran outward from the subjects' bodies, on a horizontal plane. They found that
significant near peripersonal misbisections occurred in the above eye level tasks.
Whereas, far peripersonal misbisections were replicated in the below eye level tasks.
Further, Jeerakathil and Kirk (1994) found similar results. Their study showed
significant bisection biases towards the TOP (they used labels at each end of stimulus
lines: TOP, BOTTOM) of both horizontal and vertical lines, as well as in the below eye
level radial condition. Again, the bias towards far peripersonal space in the below eye
level condition was nullified when the stimuli were presented above eye level. Kageyama,
Imagase, Okubo and Takayama (1994), looked at vertical and radial neglect in unilateral
brain damaged patients. They concluded that neither vertical nor radial neglect can be
explained by visual field defect, because some of the participants in this study did not
have visual field defect, but they consistently displayed far or near peripersonal bias
in radial line bisections and superior vertical neglect. Thus, the results tend to
support the attentional bias theory of line bisection.
This study will be based on previous works by Heilman and other research teams, in the
area of visual and tactile line bisection and the pursuit of attentional biases. 
It is expected that the results will show a difference in mean line bisection error (LBE)
in favor of the male participants, thus confirming the common perception of male
superiority in visual spatial tasks, versus women.
Method
Participants 
Four men and eight women participated in this study. They are students at Simon Fraser
University, in a Psychology 303 course. All are participating as part of their class
participation mark, as well as a reciprocal subject cooperative. The researcher should
have confirmed that all subjects have normal vision (corrected if necessary), no
neurological deficits, and no history of brain injury or trauma, however, due to time
constraints, these possible confounds were not accounted for.
Materials
Single, 3mm wide, black lines drawn in the center of 8.5 x 11 in. white paper were used
as the visual stimuli (see Appendices A, B, C). Increasing in increments of 5 cm, three
lengths were used, ranging from 10cm-20cm. According to Kageyama et al. (1994), multiple
line lengths will minimize the possibility of motor set effects from repeated identical
length stimuli. These sheets were taped to a table in the below eye level condition (30cm
from the body), and were held at a predetermined distance (30cm) from the body by the
researcher, in the above eye level condition. 
The tactile stimuli consisted of nylon string (approx. width=3mm; approx. height=3mm)
glued to 8.5 x 11 in white paper (see Appendix D). This paper was then attached to larger
cardboard to provide rigidity in the above eye level condition. The tactile stimuli
ranged from 10cm - 20cm with 5cm increments, identical to the visual stimuli.
In all, four test conditions occurred, visual above eye level (VA), visual below eye
level (VB), tactile above eye level (TA), and tactile below eye level (TB). In each
condition, all three lengths were tested in a random order. 
Design and Procedure
The current study is a mixed design, due to the calculation of results within subjects on
different conditions (VA, VB, TA, TB), as well as between subjects (mean line bisection
error and gender differences). The independent variables are thus, position and type of
stimulus (VA, VB, TA, TB), and gender (male, female). The dependent variable is mean line
bisection error.
Each subject bisected 12 radial lines presented along the midsagittal plane. The visual
and tactile above and below eye level stimuli were presented 30cm from the participants
(following most other studies in this area, Geldmacher et al., 1994, Jeerakathil et al.,
1994, Kageyama et al., 1994). The tactile stimuli were presented with the subject's eyes
closed. Each task was preluded by the researcher asking the subject to bisect the line in
front of them either visually or tactually. As with the above studies, no corrections
were allowed, however, in the tactile condition, subjects could pass their finger over
the stimuli as many times as needed to make a decision for bisection. 
Bisections occurred en bloc, in a single session. Individual conditions were presented
all at once, but in a pseudo-random order chosen by the researcher. Testing occurred in a
windowless room with ceiling lamp illumination.
Line bisection errors were measured to the nearest 1mm, and were recorded as distance
from the true midpoint. Bisections proximal to midpoint were arbitrarily given negative
values, whereas, bisections distal to the midpoint were given positive values.
Participants were debriefed by way of verbal explanation and written information (see
Appendix E). The researcher also gave subjects the opportunity to ask any questions they
may have had at the time, they were also advised to contact the researcher at any later
point in time, should further questions arise.
Results
Line bisection errors (LBE) were measured to the nearest millimeter from the true
midpoint. Demarcations away from the body, or with far peripersonal bias from center,
were arbitrarily assigned a positive value. Demarcations towards the body, or with near
peripersonal bias, were assigned a negative value. In each condition, data for each
subject was pooled and given a mean LBE. An overall mean LBE was calculated per subject
and per gender, as was the mean LBE per trial (above eye level, below eye level) per
subject, and per gender. Further, the mean LBE per modality (visual, tactile) was
calculated per subject, and per gender. The standard deviation for each mean LBE was also
calculated. All raw data and calculations were tabulated in Table 1. 
Individual mean LBE overall were higher for women than men (see Figure 1). The mean LBE
for women was 0.70cm, whereas the mean LBE for men was -0.10cm. The standard deviation
for women was 1.13cm and 0.77cm for men. Using a calculation of difference between mean
LBEs over the largest standard deviation, these differences do not seem to be
statistically significant.
Figure 1. Overall mean line bisection error (LBE) per participant. The diamond shapes
represent female subject mean LBE, and the squares represent male subject mean LBE. 
Mean LBE per trial revealed that women (m=1.10cm) scored much higher than the men
(m=-0.18cm) in the above eye level condition, with standard deviations of 0.14cm and
0.25cm respectively. This seems to be a statistically significant result. The below eye
level condition yielded a mean LBE of -0.13cm for the women and -0.43 for the men. The
respective standard deviations are 0.04cm and 0.67cm. These do not seem to be
statistically significant differences.
By calculating the mean LBE per modality, this study got results of 0.04cm for the women
and 0.06cm for the men, using vision to bisect the lines. The standard deviations were
0.48cm for females and 0.05cm for males. Again, these differences do not seem
statistically significant. In the tactual modality, mean LBE for females was 0.95cm and
-0.19cm for males, with respective standard deviations of 0.78cm and 0.34cm. These
differences do seem statistically significant.
Discussion
Although the results point towards a difference in mean LBE overall, in favor of the male
participants, these differences were not found to be statistically significant.
Therefore, one can say that the current study found similar findings to the study by
Drain and Reuters-Lorenz (1996). There seem to be real gender differences in
visuo-spatial tasks, however, the magnitude of these differences is negligible. If one
breaks down the overall mean LBE scores, it becomes clear that gender differences may be
statistically significant in terms of favoring males, with tasks involving above eye
level stimuli, and tactile stimuli. Further research may shed more light onto these
intriguing findings. Past research which found far peripersonal biases in the below eye
level visual modes (Jeerkathil et al., 1994, and Kageyama et al., 1994) was not supported
by the current study. Nor were the research findings of Geldmacher et al. (1994)
supported by the current study. They found that below eye level tactile stimuli received
a near peripersonal attentional bias. Although there were apparent trends in the
directions of the above findings, none were calculated to be statistically significant.
Some of the plethora of possible reasons for these findings include: no determination of
normal vision (corrected if necessary), no determination of neurological deficits, no
account of brain injury or trauma history by the researcher. Further, since the sample
size was so small, perhaps there was not enough data to display the true distribution of
results expected from a study of this sort. In order to get a fuller picture of the
present data, the researcher could have implemented a calculation of the mean LBE per
subject per modal trial. That is, I should have calculated the mean LBEs per subject in
the visual above trials, the visual below trials, the tactile above trials, and the
tactile below trials. This would allow a more precise comparison of the data sets in
question. 
Regardless the outcomes or possible trends in the current study, the debate as to whether
men are actually superior to women in visuo-spatial dexterity, will continue to raise
questions and spur contemporary research. The findings of yesteryear are beginning to
fade and lose their lustrous influence on society. More and more, women are taking their
place in a world once dominated by men. Perhaps the slim differences between the sexes
are shrug issues, useful only as interesting topics of debate, but of little tangible
value in the 21st century?
References
Drain, M., and Reuter-Lorenz, P. (1996). Vertical orienting control: Evidence for
attentional bias and neglect in the intact brain. Journal of experimental psychology:
general, 125, 139-158.
Dwaretzky, J. (1996). Introduction to child development (6th ed.). New York: West
Publishing Company.
Geldmacher, D., and Heilman, K. (1994). Visual field influence on radial line bisection.
Brain and Cognition, 26, 65-72.
Jeerakathil, T., and Kirk, A. (1994). A representational vertical bias. Neurology, 44,
703-706.
Kageyama, S., Imagase, M., Okubo, M., Takayama,Y. (1994). Neglect in three dimensions.
American Journal of Occupational Therapy, 48, 206-210.