Left-handed Male Subjects Research Articles

Inverse relationship between nonverbal intelligence and the parameters of pattern reversal visual evoked potentials in left-handed male subjects: importance of right brain and testosterone.

The relationships between latencies of visual evoked potentials (VEPs) and nonverbal intelligence test scores (IQs from Cattell's Culture Fair Intelligence Test) and correlations between serum testosterone level and VEP latencies were studied to examine the neural speed hypothesis of intelligence and its hormonal mechanisms in left-handed male subjects (Geschwind Scores). In accordance with the speed theory of intelligence, N1 and P1 latencies (and amplitudes) were found to be inversely related to IQ. However, this was true only for the right brain; the left brain did not contribute to this relationship. There was an inverse relationship between serum testosterone level and P1 latency; left minus right N1 latency, depending on N1 latency from right brain, linearly increased with testosterone. It was concluded that nonverbal intelligence largely depends on speed of information processing only by the right brain, not by the left brain in left-handed male subjects. This may have been created by testosterone in these subjects. Inconsistencies in the IQ literature concerning the speed hypothesis of intelligence may be explained by differences in cerebral lateralization.

Relationships among nonverbal intelligence, hand speed, and serum testosterone level in left-handed male subjects.

The relationships among nonverbal intelligence, hand speed, and serum testosterone level were studied in male left-handers ranging in age from 17 to 19 years. Hand speed was measured by a peg moving task. To assess the differences between nonverbal IQs. Cattell's Culture Fair Intelligence Test was used. There was a direct correlation between IQ and testosterone. IQ increased linearly with right-hand speed, which was directly related to testosterone. There was no significant correlation between IQ and left-hand speed, which was not significantly correlated with testosterone. IQ decreased with left- minus right-hand speed, which also decreased with testosterone. It was suggested that nonverbal spatial reasoning ability may be directly associated with the efficiency of left brain, which is favored by testosterone in male left-handers. It was also concluded that the left to right asymmetry in hand speed may depend on efficiency of the right brain in left-handed males.

The left brain determines the degree of left-handedness

The contribution of right- and left-hand skills to left-handedness was studied in 42 left-handed male subjects. Hand preference was assessed by the Edinburgh Handedness Inventory. Hand skill was assessed by a peg-moving task; 10 trials were given to each hand. Peg-moving times decreased linearly with each trial (visuomotor learning). Both hands exhibited equal learning capacities. The learning curves were the same for the left-hands of left-handers with and without familial sinistrality (FS). The right-hand of left-handers with FS was found to be slower than that without FS. The right- and left-hand skills and their learning curves were about the same in left-handers with right-hand writing, exhibiting no difference from the left-hand skill and learning curve of left-handers with left-hand writing. Right-hand skill decreased linearly as left-hand preference increased from -40 to -100; left-hand skill was not related to hand preference. Right-minus left (R-L) time for peg moving increased linearly with hand preference from -40 to -100. R-L time for peg moving linearly decreased as the right-hand skill increased; the left-hand skill was not associated with R-L time for peg moving. It was concluded that the right hand (left brain) determines left-handedness; the neural structures only on the left side exhibit pronounced plastic changes to genetic and environmental influences in left-handers.