Many researches in split-brain patients have performed to show that the left hemisphere is more responsible for language and phonological functioning, while the right one is responsible for emotion and creativity (Pinel, 1997). Myers and Sperry (1953, as cited in Pinel) conducted an experiment in cats whose corpus callosum was cut. The cats were trained to perform a simple visual discrimination and learn which symbol they had to press in order to get a food reward. They tested one hemisphere at time by putting a patch on the eye depending on the hemisphere they wanted to test. The optic chiasm was cut as well. The results showed that the two hemispheres work as two different brains.
Another method of studying language lateralization is to assess the asymmetry not only of the speech but the movements that accompany the language as well. Kimura (1973, as cited in Pinel, 1997) found that the hand gestures which accompany speech are made by the contralateral hand of the left hemisphere. Studies in epileptic humans have conducted to show the same results (Pinel, 1997).
This research examines two hypotheses. The first one suggests that the phonological processing, as measured by a rhyme/nonrhyme task, is faster in the left hemisphere than in the right and the second hypothesis proposes that the degree of the left/right functional cerebral asymmetry is more marked in men than in women.
Methodology
Participants: The participants of this study are 15 right handed women and 15 right handed men, whose first language is English.
Material: The experiment was based on the divided visual field paradigm and a phonological rhyme/nonrhyme task developed by Mead & Hampson (1996). Computer screens were also used for the experiment.
Design: The study began with a set of 20 practice trials and after a brief rest period two blocks of 40 experimental trials followed. Each trial began after the press of a button with the appearance of a central fixation point (+), which lasted for 1 to 2 seconds. After these seconds the point was replaced by a cue word which lasted for 1 second. After a pause period of 40 ms, two word appeared on the screen one to each side of a central arrow, which either pointed to the left or right. The arrow always indicated the target word for 200ms and the other one was supposed to be ignored.
Procedure: At the beginning of the test the participants were asked their sex, if they were right handed and if their first language was English. Then they were instructed to look at the central point and keep their eyes at a distance of 30 cm of the computer screen, which ensures the presentation of the word only in one visual field and the contralateral hemisphere transmission. When the participants were feeling ready they had to press a button in order to start each of the trials. When the cue word and the target words appeared they had to decide whether or not they rhyme. If they rhymed they had to press the “K” key and if they didn’t rhyme they had to press the “A” key.
Results
Table 1 shows the mean and standard deviation of correct answers of the left hemispheres from all the participants.
Table 2 reveals the mean and standard deviation of correct answers of the right hemisphere from all participants.
Table 3 shows the descriptive statistics of correct answers, separately from men and women, given from the right hemisphere.
Table 4 shows the descriptive statistics of correct answers, separately from men and women, given by the left hemisphere.
Discussion
This research has conducted in order to study and test two hypotheses. The first hypothesis is that phonological processing is faster in the left hemisphere than in the right. By measuring the correct answers in the rhyme/nonrhyme tasks we tried to support this hypothesis. According to the results showed in Table 1 and Table 2 we observe that that the correct answers given by the left hemisphere are more, which results to the conclusion that the phonological processing in the left hemisphere is faster. We notice though that the difference between the correct answers of the left hemisphere and the right one is small as the mean of the correct answers for the left hemisphere is 68,17 and for the right one is 63,30. So we can say that indeed the phonological process is faster in the left hemisphere but the phonological process in the right one is very important as well. This proposition is supported by brain-imagining studies that revealed a greater activation in the left hemispheres during language-related tasks, but activation in the right hemisphere as well (see Roland, 1993, as cited in Pinel, 1997). Also some Z-lens studies of split-brain patients have shown that the right hemisphere understand many spoken words and even simple sentences ( see Zaidel, 1983, 1987, as cited in Pinel, 1997).
The second hypothesis tested in this research is that the degree of left and right functional asymmetry is more marked in men than in women. According to the results of Table 3 we observe that female participants scored almost the same in the tasks testing the left and the right hemisphere but in Table 4 we notice that men scored higher in the tasks testing the left hemisphere than in the right. So our hypothesis is very possible to be correct. Earlier studies of McGlone (1977, 1980 as cited in Pinel, 1997) in unilateral stroke victims showed that males brains are more lateralized than the brains of females. Kold and Whishaw (1990 as cited in Pinel, 1997) suggested that the differences between males and females in brain lateralization are showed in the strategies they use in order to solve problems.
It is clear that our results need to be tested more with a Mann Whitney U Test, which will show the percentage of validity and reliability of our results, concerning the sex differences in brain lateralization.
References
Pinel, P., John. (1997). Lateralization, language and the split brain. Biopsychology. 3rd edition.
