Paper Type

Master's Thesis


College of Arts and Sciences

Degree Name

Master of Science in Psychological Science (MSPS)



NACO controlled Corporate Body

University of North Florida. Department of Psychology

First Advisor

Dr. Lori Lange

Second Advisor

Dr. Gregory Kohn

Department Chair

Dr. Lori Lange

College Dean

Kaveri Subrahmanyam


Fight-or-flight is a commonly known response to threatening situations, but the freeze response is another defensive mechanism that might arise in such situations. There is also evidence that exposure to trauma can impact physiological reactions when defensive mechanisms are not required, such as freezing in response to non-threatening situations. The current study aimed to replicate and expand upon a limited number of previous studies on the human freeze response by implementing measurements of postural sway, heart rate, and infrared thermography while valenced images were shown to participants. Ninety-two participants were recruited from the University of North Florida and participants were split into groups of low/no, moderate, or high trauma post-traumatic stress disorder (PTSD) symptomology. Results of this study provided some evidence of the freeze response with bradycardia occurring during exposure to unpleasant images versus neutral or positively valenced images. There was a pattern of reduced body sway during the negative imagery, but this was not statistically significant, and thermal imaging results were inconclusive. Also, PTSD severity groups interacted significantly with image condition on mean heart rate, with the moderate PTSD group showing bradycardia during negative images compared to other image types. Further research on the freeze response and trauma is required to better understand the mechanisms involved in the defense cascade.