Laterality Differences in Native Arabic Speakers and English Speakers - Article Example

 Laterality Differences in Native Arabic Speakers and English Speakers Summary of Results and Discussion Tabular Summary of Results English language test (ELT) Arabic language test (ALT) Comparison between both English (ELT) and Arabic (ALT) tests LEP REP LEP REP LEP REP 1a. Arabic language speakers No significant difference between LEP and REP Average scores for REP is significantly greater than average scores for LEP No significant difference ALT average score is significantly greater than ELT average score 1b. English language speakers Average score for REP is significantly greater than average score for LEP No significant difference between LEP and REP ALT average score is significantly greater than ELT average score No significant difference 2. Handedness No significant difference between LHP and RHP No significant difference between LHP and RHP No significant difference between LHP and RHP Average score for LHP is significantly greater than average score for RHP - - 3. Sex category Average score for males is significantly higher than average score for females No significant difference between males and females No significant difference between males and females No significant difference between males and females - - 4. Native language of participants No significant difference between ASP and ESP No significant difference between ASP and ESP No significant difference between ASP and ESP Average score for ASP is significantly greater than average score for ESP - - Note: All findings are at the 5% level of significance and all significant differences are italicized. Abbreviations: ALT: Arabic language test, ELT: English language test LEP: Left-ear perception, REP: Right-ear perception LHP: Left-handed participants, RHP: Right-handed participants ASP: Arabic speaking participants, ESP: English speaking participants Summary and Main Findings This research sought to investigate the right and left ear preferences on the lateralized perception of speech stimuli. The four objectives provided the context to observe differences for each ear (left/right) and language (Arabic/English) based on factors that were believed to influence the ear preference in hearing the sounds of both languages. The main idea being that ear preference (lateralized perception) is affected by the language used, handedness and gender. These contexts were thus, the language used by the participants, being right or left handed (handedness), being male or female (sex category), and the native language of the participants. This first for example, tests whether an English speaker is able to give right ear preference in hearing Arabic sounds and vice versa. This was then extended to include the other categories. Although the majority of tests showed no significant differences for left or right ear perception i.e. showed no suggestion of lateralized perception, at least one from each of the 4 categories of objectives did show evidence of a significant difference at the 5% level of significance. In the first set of tests in which all participants were exposed to both native and non-native sounds to observe any lateralized perception, it was found that each group of speakers had lateralized perception for their own native language but not for the non-native language. That is, lateralized perception was evident amongst Arabic speakers during the Arabic language test, and amongst English speakers during the English language test, but not during the language test that was in a foreign language for each group. The significant finding was that in these cases, the average scores for right-ear perception was greater than the average scores for left-ear perception. Furthermore, in a comparison between the two tests, the average score on the Arabic language test was significantly greater than the average score on the English language test for right-ear perception in the case of Arabic language speakers, and left-ear perception in the case of English language speakers. Whereas the above was as expected, when the three factors of handedness, gender and native language were studied, the results were more interesting, and lateralization was evident in one of the 4 instances for each factor. In the English language test, gender was the only significant factor whereas, in the Arabic language test, the other two factors rather than gender were significant. In the English language test, left-ear perception was found to be more prevalent in males than females. In the Arabic language test, right-ear perception was found to be more prevalent amongst left-handed participants, and amongst Arabic speaking participants. Relation of Results to Existing Literature The evidence for lateralized perception demonstrated by right-ear preference during the language test in the language that was native for the participants, is in accordance with the general evidence for the greater superiority of the left hemisphere in processing meaningful linguistic stimuli such as Price et al (2005) and fMRI studies. In particular, the studies such as Best et al (1988) who noted that this phenomenon is true for listeners exposed to their own native language sounds (especially the consonants) is supported by this study. As Naatanen et al (1997) and Breier et al (1999) observed and mentioned earlier, native speakers have natural biological responses to linguistic stimuli, which are primarily processed and controlled by the left hemisphere. Tallal et al (1993) and Fitch et al (1997) were more specific in relating this to consonants whose sounds change rapidly but again that is precisely what this study involved. The certainty in the connection between the ear preference and the associated hemisphere is of course due to the dichotic test as used in this study. Studies have also been conducted previously taking handedness and gender into account. For example, Knecht et al (2000) who studied the association between handedness and hemispherical language dominance, found that “left-handedness increases the likelihood of right-hemisphere language dominance… [and that] the degree of handedness is linearly and highly significantly related to the side of language dominance” (p.2517). This study considered both left and right-handedness, but only found a significant difference for right-ear perception during the Arabic language test. In this case, the average score for left-handed participants was greater than that for right-handed participants. These results are contrary to the findings in the aforementioned study because they indicate lateralization in the left hemisphere rather than the right hemisphere for left-handed participants. Moreover, the fact that no significant differences for left or right ear perception were found between left and right handed participants in the English language test casts doubt on the universality of this supposed phenomenon. Similarly, Kulynych et al (1994) studied the factor of gender on lateralization. They observed gender differences in the normal lateralization of the supratemporal cortex using MRI surface-rendering morphometry of Heschl’s Gyrus (HG) and the Planum Temporale (PT). With only a slighter larger sample size than this study, they found “a significant interaction between gender and hemisphere for the PT, with males having significantly larger left-versus right PTs” (p.107) but not so for females. Overall however, they found no effect of gender for the total PT or HG. The only anomaly, which suggests therefore that there is “reduced asymmetry among females in the lateralization of language functions attributable to the supratemporal cortex” is mentioned as consistent with other evidence from other studies. However, this study only found significant gender differences in the English language test (not in the Arabic language test) but that too showed a left-ear preference for males suggesting lateralization in the right hemisphere. Again this specific finding is in contradiction with the aforementioned study for males, but overall it is consistent with there being no effect of gender generally. Methodological Issues and Significance of the Study The 4 stop sounds used in the study in the Arabic test, and the six plosive syllables in the English test were appropriate in testing for left or right ear preference as used by others as mentioned above. Moreover, the selections covered all likely arrangements though the pairing task and designing the final Arabic dichotic was very time consuming. Participants were also permitted to categorise some sounds as missing in case they were confused about a particular sound. The number of participants was also reasonable, although testing for handedness and gender factors could have been better served with a greater sample size given that finding related to these factors are not consistent with findings from previous studies. That said, the range of factors considered was probably unprecedented. This study clearly supported the established understanding that there is left hemisphere lateralization (right-ear preference) as far as one’s native language is concerned but could not further these findings in the context of specific factors. A number of suggestions can therefore be made so that future research on the same topic at this institution can be more expansive and show revealing and certain results with greater confidence to further research in linguistics concerning lateralization. The single biggest constraint was time. Research work of this nature should be given ample time for a careful study and using a larger sampling size too. Access to the speech laboratory was also restricted which required heavy equipment to be relocated for the study. Such difficulties encountered and obstacles would need to be removed to allow serious research to take place. In addition, the incident in which one participant’s results were asked to be removed highlights that even this project was not immune from ethical requirements, which must therefore be carefully considered beforehand prior to starting the research. References Knecht, S. et al. 2000. Handedness and hemispheric language dominance in healthy humans. Brain, 123, 2512-2518. Kulynych et al. 1994. Gender Differences in the Normal Lateralization of the Supratemporal Cortex: MRI Surface-rendering Morphometry of Heschl’s Gyrus and the Planum Temporale. Cerebral Cortex, Mar/Apr 1994; 4: 107-118. Read More