Jun 26, 2015

Lefties and Digits

Kangaroos prefer to use one of their hands over the other for everyday tasks in much the same way that humans do, with one notable difference, generally kangaroos are lefties. A study found that wild kangaroos show a natural preference for their left hands when performing particular actions, such as grooming the nose, picking a leaf, or bending a tree branch.

Psychologist Eliza L. Nelson observed several monkeys using individual fingers to grab food. The spider monkeys also were able to insert one or two fingers into a tube to grab a serving of peanut butter. It is the first time this type of independent digit control has been reported for this species.

The unexpected observation occurred during Nelson's research study evaluating measures of handedness in nonhuman primates, the tendency to use one hand more naturally than the other. Spider monkeys' hands have four fingers and no thumb. "We collected a large number of data points on each measure to allow for analyses. The team analyzed reach and coordination, both of which are difficult for spider monkeys given their unique hand structure. Comparing results of both tasks is critical for understanding the evolution of hand-use preferences in primates.

Contrary to predictions and previous findings, Nelson's research shows multiple measures are needed to fully characterize the concept of handedness as a single handedness test cannot effectively predict hand preference in nonhuman primates. The findings were recently published in the journal Animal Cognition.

Infants who exhibit a consistent right hand preference are more likely to develop advanced language skills by age two, according to another study by Nelson. The findings were recently published in the Journal of Developmental Psychology.

In the study, Nelson measured handedness in different ways according to the age-appropriate motor level. She looked at how infants used their hands to pick up toys and compared it to how they used their hands in combination to manipulate toys as toddlers. The study results suggest there may be an advantage to having consistent hand preference as an infant. Results showed children who had clear early hand preference performed better on language skills tests than those who did not develop handedness until toddlerhood. Those who were inconsistent in their hand use as infants, but developed a preference for the left or right hand as toddlers, had language scores in the typical range for their age. We should give her a hand for these interesting studies.