Master of Science (MSc)
Faculty of Science
Pamela J Bryden
The ratio of the difference between the 2nd and 4th digits of the hand (2D:4D ratio) has been demonstrated to be an indirect indicator of prenatal testosterone levels. Prenatal testosterone has been found to play a role in brain development in utero, and thus may influence lateral asymmetries, such as handedness. Consequently, one of the aims of the current study was to examine relationships between the 2D:4D ratio, hand preference, and hand performance with the factors of sex (males and females), handedness (right handers and left handers), and age considered. A total of 104 participants were tested, 90 right handers and 14 left handers (age range = 5-to-90, mean age = 31.93, SD = 20.18, females = 58). Participants completed the Waterloo Handedness Questionnaire (WHQ) as an indicator of hand preference and the Tapley- Bryden Dot Marking (TBDM) task to evaluate hand performance. Right and left 2D:4D ratios were measured for all participants using Vernier calipers, measured to the nearest 0.01mm. Regardless of age and sex, left handers had significantly reduced hand preference strength and trended in having reduced hand performance differences between the hands. Furthermore, although only significant in the 50+ years age group, it appeared as though males tended to have decreased handedness compared to females. No significant relationships nor main effects were found with regards to the 2D:4D ratios measured, though.
Additional testing was conducted including participants with ASD, who have been illustrated to have lower than average 2D:4D ratios, as well as increased hand ambiguity. Relationships were examined between the 2D:4D ratio, hand preference, and hand performance and comparisons were analyzed between neurotypical participants and participants with ASD. A total of 5 participants with ASD were tested, 4 right handers and 1 left hander (age range = 6-to- 36, 5 males). With the small sample size, all relationships were found to be insignificant and were not generalizable. Comparisons did display significant differences in hand performance, where individuals with ASD illustrated greater hand ambiguity.
Overall, the study has demonstrated that sex, handedness, and age influence hand preference and hand performance. However, no relationships were found between handedness and the 2D:4D ratios. Moreover, continuing research on hand ambiguity in individuals with ASD could better the understanding of brain lateralization.
Protopapas, Helen A M Ms., "THE 2D:4D RATIO, HANDEDNESS, AND SEX ACROSS THE AGE SPAN" (2016). Theses and Dissertations (Comprehensive). 1873.