The interface between morphology and action planning: a comparison of two species of New World monkeys

Recent research with several species of nonhuman primates suggests sophisticated motor-planning abilities observed in human adults may be ubiquitous among primates. However, there is considerable variability in the extent to which these abilities are expressed across primate species. In the present experiment, we explore whether the variability in the expression of anticipatory motor-planning abilities may be attributed to cognitive differences (such as tool use abilities) or whether they may be due to the consequences of morphological differences (such as being able to deploy a precision grasp). We compared two species of New World monkeys that differ in their tool use abilities and manual dexterity: squirrel monkeys, Saimiri sciureus (less dexterous with little evidence for tool use) and tufted capuchins, Sapajus apella (more dexterous and known tool users). The monkeys were presented with baited cups in an untrained food extraction task. Consistent with the morphological constraint hypothesis, squirrel monkeys frequently showed second-order motor planning by inverting their grasp when picking up an inverted cup, while capuchins frequently deployed canonical upright grasping postures. Findings suggest that the lack of ability for precision grasping may elicit more consistent second-order motor planning, as the squirrel monkeys (and other species that have shown a high rate of second-order planning) have fewer means of compensating for inefficient initial postures. Thus, the interface between morphology and motor planning likely represents an important factor for understanding both the ontogenetic and phylogenetic origins of sophisticated motor-planning abilities.

Change in First-Year Women's Body Dissatisfaction in Relation to Drive for Thinness and Social Body Comparison

Drive for thinness (DT) and social body comparison (SBC) have been highly correlated with body dissatisfaction, a robust risk factor for eating disorders; however, there is little understanding of how these two variables relate to increases in body dissatisfaction over time. In the present study, I investigated how high initial levels of DT and SBC correlate with changes in body dissatisfaction and ideal body by surveying 110 first-year women at the beginning and end of their first semester. There was no significant relationship between high initial DT and SBC and changes in either body dissatisfaction or ideal body. However, high initial SBC was almost significantly correlated with change in ideal body due to women with low SBC choosing larger bodies at follow-up. In addition, women with high initial DT and SBC had higher body dissatisfaction than women with low initial levels of both variables. Women with high initial SBC chose thinner ideal bodies than women with low initial SBC. Lastly, change in body dissatisfaction was negatively correlated with change in ideal body. If replicated, I would hope these findings could contribute to a better understanding of how women’s perception of their bodies changes over the course of their first semester in college and inform interventions to address this potential risk factor for disordered eating.