(Editor: Maureen McCarthy)
Are there asymmetries in the functions of the two cerebral hemispheres?
A great deal of evidence has accumulated in recent years suggesting that
the left brain and the right brain are not identical in their capabilities
(Gazzaniga, Bogen, & Sperry, 1967;Gazzaniga, 1970; Nass, & Gazzaniga, 1987;
Springer & Deutsch, 1989). This study is designed to demonstrate that
for right-handed people, who comprise over 90% of the population, the right
hemisphere performs visual spatial tasks better than the left hemisphere.
For most right-handers, whereas the left hemisphere excels in verbal and
analytical tasks, the right hemisphere specializes in emotional, nonverbal,
and visual-spatial tasks.
The mirror-image tracing study requires that the participant use
the mouse to trace the star as shown in Figure 1, first with one hand,
and then with the other hand. Because mirror image tracing is primarily
a visual-spatial task, and each half of the brain controls the contralateral
side of the body, it is expected that right-handed participants will take
longer to complete the task with their right hand (controlled by the left hemisphere)
compared to their left hand ( controlled by the right hemisphere).
Please note that this prediction may not necessarily hold for left-handed participants,
because their brains are more bilateral.
This study uses one independent variable in a within subjects design.
There are two levels to the independent variable: the left vs. the right hand.
The dependent variable is the time it takes the participant to complete the tracing.
Data is downloadable in three formats (XML, Excel spreadsheet format,
and comma delimited for statistical software packages like SPSS).
We are providing definitional information for each of the labeled columns as shown in
The first column provides the participant ID number.
The second column provides the class ID for which a participant's data is affiliated.
Gender and age are self-explanatory and are located in columns three and four.
Hand preference is located in column five. The date of participation is located
in column six. Column seven contains the amount of time for completion of the
task using the left hand. Column eight contains the time for completion of
the task using the right hand.
A paired t-test can be conducted to determine if the completion times
of the two conditions (the left-hand condition vs. the right-hand condition)
are significantly different.
The mirror tracing task has historically been used to study learning and the effects of distributive practice (Snoddy, 1920; Adams, 1987). The task has also been used as a classic experimental activity designed to illustrate the effects of learning in many undergraduate laboratories for decades. More recently Goldstein, Hopkins and Strube (1994) used the task to demonstrate observer bias. Although this activity is designed to provide students with an experience that will allow for comparison of the left and right hand, this activity may also be used to illustrate the effects of distributive practice effects and observer bias.
Adams, J. A. (1987). Historical review and appraisal of research on the learning,
retention, and transfer of human motor skills. Psychological Bulletin, 101, 41-74.
Gazzaniga, M. S. (1970). The bisected brain. New York: Appleton-Century-Crofts.
Gazzaniga, M. S., Bogen, J. E., & Sperry, R. W. (1967). Dyspraxia following division
of the cerebral commissures. Archives of Neurology, 16, 606-612.
Goldstein, M. D., Hopkins, J. R.,& Strube, M. J. (1994). "The eye of the beholder":
A classroom demonstration of observer bias. Teaching of Psychology, 21, 154-156.
Nass, R. D., & Gazzaniga, M. S. (1987). Lateralization and specialization in human
central nervous system. In F. Plum (Ed.), Handbook of physiology: The nervous
system: Vol. 5. Higher functions of the brain (pp. 701-761). Bethesda, MD: The
American Physiological Society.
Snoddy, G. S. (1920). The experimental analysis of a case of trial and error learning
in the human subject. Psychological Monographs, 28(2), 1-79.