The effects of postural threat on postural control among younger and older adults were examined. Fifteen younger (YA;8 females and 7 males; mean age 22.00 + 2.17 years) and fifteen older (OA; 10 females and 5 males; mean age 69.98 + 5.35 years) adults performed quiet standing and forward reaching under four conditions of postural threat. Postural threat was achieved by the manipulation of height (low(0.43m) and high (1.4m)) and stepping constraint (unconstrained (0.91m from the anterior edge of an elevating platform) or constrained (0m from the anterior edge of an elevating platform). Younger and older adults demonstrated conservative modifications to postural control that may reduce the likelihood of a fall in tenuous conditions. Interestingly, age-related differences emerged in the mechanism of achieving these accomodations to postural threat. Our findings indicate that older adults may adopt more proximal postural strategies under condtion of postural threat. The shift toward a more proximal postural strategies under conditions of postural threat. The shift toward a more proximal control of balance may reflect the age-related declines in the ability to control the movement of the trunk. Although these adaptations appear benefical to older adults, the possibility exists for detrimental consequences to postural recovery following a balance disturbance. / xi, 173 leaves : ill. ; 29 cm.

A diagrammatic method of recording static human postures was developed. Criteria established for the recording method were speed of completion, accuracy, reliability, ease of use, and universal applicability. Design of the recording method was based on cognitive, perceptual, and anthropometric considerations related to these criteria, and a review of existing posture recording methods. A validation study was carried out to assess the recording method against the established criteria. The study entailed having several subjects use the recording method to record various postures and a comparison of their results. The recording method proved to be moderately accurate for the postures studied. The recording method should prove useful in providing a record of the general posture being recorded. However, time required to complete the posture recordings was extensive. Recommendations are given for improving the posture recording method. Among these is a recommendation for more extensive training and practice than was afforded the subjects in this study. Other recommendations have been incorporated into a modified set of recording diagrams. Whether these modifications will improve the recording method remains to be determined. / Master of Science

The purpose of this thesis was to investigate the influence of postural anxiety on the capacity for Flexible Resource Allocation (FRA) among younger (YA) and older adults (OA). Two experiments were conducted to explore (a) the influence of heightened postural anxiety on the flexible allocation of attention among OA and (b) the influence of concurrent postural challenge and postural anxiety on FRA among YA. Participants performed a postural task concurrently to a cognitive task according to three instructional sets directing task priority. Experiment one revealed that FRA was compromised among OA during circumstances of heightened anxiety. This capacity however, remained available among YA. Therefore, for the second experiment I varied the support surface to explore whether the capacity for FRA could be sustained when posture was challenged beyond static stance. Results indicated that YA altered cognitive task performance according to instructional set without compromising postural stability. These findings suggest that even when posture is challenged during heightened postural anxiety, YA maintain the capacity to automatically allocate attention to a postural task while performing a secondary task. Conversely, it seems that heightened postural anxiety strengthens the attentional bias to posture and subsequently compromises FRA among OA. Overall, results from this thesis suggest that the capacity for FRA is age and situation dependent. / xi, 107 leaves : ill. ; 29 cm