Brian Roselle & Kenneth Scearce
Abstract: Voluntary human reactions, and associated perception times when reaction movements commence, are identified to estimate gunshot sound arrival time to subjects in a shooting scenario recorded on silent film. Common involuntary reactions (startle) and voluntary reactions are reviewed to help identify proper reaction types being observed and apply in back-calculating gunshot timing. With a focus on voluntary reactions, values for perception time as a function of stimulus expectancy, specifically in the case of a surprise stimulus, are determined by reapplication of brake perception-reaction time (brake PRT) modeling of extensive driver reaction time studies in traffic flow theory. Using a modified model in conjunction with sampling human reactions observed on film allows back-calculating surprise gunshot sound timing. To detail use of this approach, a well-known example of a silent film, the Abraham Zapruder film of the Kennedy shooting, is considered to help identify the first shot timing in that case.