Personality traits and individual differences predict changes in postural control under conditions of height-induced postural threat

This thesis explored whether individual characteristics could predict changes in postural control in young adults under conditions of height-induced postural threat. Eighty-two young adults completed questionnaires to assess trait anxiety, trait movement reinvestment, physical risk-taking, and previous experience with height-related activities. Tests of static (quiet standing) and anticipatory (rise to toes) postural control were completed under conditions of low and high postural threat manipulated through changes in surface height. Individual characteristics were able to significantly predict changes in static, but not anticipatory postural control. Trait movement reinvestment and physical risk-taking were the most influential predictors. Evidence was provided that changes in fear and physiological arousal mediated the relationship between physical risk-taking and changes in static postural control. These results suggest that individual characteristics shape the postural strategy employed under threatening conditions and may be important for clinicians to consider during balance assessment and treatment protocols.

The Role of Experience in the Organization and Refinement of Face Space

Adults code faces in reference to category-specific norms that represent the different face categories encountered in the environment (e.g., race, age). Reliance on such norm-based coding appears to aid recognition, but few studies have examined the development of separable prototypes and the way in which experience influences the refinement of the coding dimensions associated with different face categories. The present dissertation was thus designed to investigate the organization and refinement of face space and the role of experience in shaping sensitivity to its underlying dimensions. In Study 1, I demonstrated that face space is organized with regard to norms that reflect face categories that are both visually and socially distinct. These results provide an indication of the types of category-specific prototypes that can conceivably exist in face space. Study 2 was designed to investigate whether children rely on category-specific prototypes and the extent to which experience facilitates the development of separable norms. I demonstrated that unlike adults and older children, 5-year-olds rely on a relatively undifferentiated face space, even for categories with which they receive ample experience. These results suggest that the dimensions of face space undergo significant refinement throughout childhood; 5 years of experience with a face category is not sufficient to facilitate the development of separable norms. In Studies 3 through 5, I examined how early and continuous exposure to young adult faces may optimize the face processing system for the dimensions of young relative to older adult faces. In Study 3, I found evidence for a young adult bias in attentional allocation among young and older adults. However, whereas young adults showed an own-age recognition advantage, older adults exhibited comparable recognition for young and older faces. These results suggest that despite the significant experience that older adults have with older faces, the early and continuous exposure they received with young faces continues to influence their recognition, perhaps because face space is optimized for young faces. In Studies 4 and 5, I examined whether sensitivity to deviations from the norm is superior for young relative to older adult faces. I used normality/attractiveness judgments as a measure of this sensitivity; to examine whether biases were specific to norm-based coding, I asked participants to discriminate between the same faces. Both young and older adults were more accurate when tested with young relative to older faces—but only when judging normality. Like adults, 3- and 7-year-olds were more accurate in judging the attractiveness of young faces; however, unlike adults, this bias extended to the discrimination task. Thus by 3 years of age children are more sensitive to differences among young relative to older faces, suggesting that young children's perceptual system is more finely tuned for young than older adult faces. Collectively, the results of this dissertation help elucidate the development of category-specific norms and clarify the role of experience in shaping sensitivity to the dimensions of face space.

The influence of cognitive resources on compensatory arm responses

The purpose of this study was to determine the influence of an ongoing cognitive task on an individual’s ability to generate a compensatory arm response. Twenty young and 16 older adults recovered their balance from a support surface translation while completing a cognitive (counting) task of varying difficulty. Surface electromyographic (EMG) recordings from the shoulders and kinematics of the right arm were collected to quantify the compensatory arm response. Results indicated that the counting task, regardless of its difficulty as well as the age of the individual, had minimal influence on the onset or magnitude of arm muscle activity that occurred following a loss of balance. In contrast to previous research, this study’s findings suggest that the cortical or cognitive resources utilized by the cognitive task are not relied upon for the generation of compensatory arm responses and that older adults are not disproportionately affected by dual-tasking than young adults.

Photograph - Group Standing together with a small dog

A group of young adults standing together in front of a stone house. There are three young men and two young women and a small dog posing together.