• The effects of postural threat on sample entropy

      Fischer, Olivia; Applied Health Sciences Program
      The objectives of this thesis were to 1) explore the effects of postural threat on sample entropy, a measure interpreted to reflect the attentional investment in postural control, and to 2) examine the relationships between threat-related changes in physiological arousal, perceived anxiety, attention focus, conventional postural control measures, and sample entropy. A secondary data analysis was conducted on a combined data set derived from two published studies; each study used the postural perturbation threat model which allowed for a comparison between No Threat and Threat conditions. Young adults (N = 105) stood without (No Threat) and with (Threat) the expectation of receiving a temporally and directionally unpredictable support surface translation in the forward or backward direction. Mean electrodermal activity and anterior-posterior centre of pressure mean position, root mean square, mean power frequency, power within low (0–0.05 Hz), medium (0.5–1.8 Hz), and high frequency (1.8–5 Hz) components, and sample entropy were calculated for each trial. Anxiety and attention focus to movement processes, task objectives, threat-related stimuli, self-regulatory strategies, and task-irrelevant information were rated after each trial. The results of the thesis showed that postural threat had a significant effect on sample entropy; higher values were reported in the Threat compared to No Threat condition. However, threat-related changes in physiological arousal, perceived anxiety, and attention focus were not significantly related to changes in sample entropy. Threat-related changes in sample entropy were related to changes in sway amplitude and frequency. The results of this thesis suggest a shift to a more automatic control of posture when threatened despite evidence of increased attention to postural control.