ARTICLE Original Article Estimating Occult Timing of Surprise Gunshot Sounds in Silent Film via Observed Start of Human Voluntary Reactions of Concern Brian Roselle1 & Kenneth Scearce2 1Fairfield, OH, USA 2San Francisco, CA, USA ABSTRACT ARTICLE INFORMATION Voluntary human reactions, and associated perception times when reaction movements commence, are iden- Received: 2 March 2019 tified to estimate gunshot sound arrival time to subjects in a shooting scenario recorded on silent film. Com- Revised: 23 January 2020 mon involuntary reactions (startle) and voluntary reactions are reviewed to help identify proper reaction Accepted: 29 January 2020 types being observed and apply in back-calculating gunshot timing. With a focus on voluntary reactions, Published: 8 August 2020 values for perception time as a function of stimulus expectancy, specifically in the case of a surprise stimulus, Citation: Roselle B, Scearce K. Estimat- are determined by reapplication of brake perception-reaction time (brake PRT) modeling of extensive driver ing Occult Timing of Surprise Gunshot Sounds in Silent Film via Observed reaction time studies in traffic flow theory. Using a modified model in conjunction with sampling human Start of Human Voluntary Reactions reactions observed on film allows back-calculating surprise gunshot sound timing. To detail use of this of Concern. J Assoc Crime Scene approach, a well-known example of a silent film, the Abraham Zapruder film of the Kennedy shooting, is Reconstr. 2020;24:1-22. considered to help identify the first shot timing in that case. Author contact: Keywords: chronology, gunshot timing, perception-reaction time, perception time, surprise voluntary [email protected] reaction, startle reaction, Zapruder film, shooting reconstruction, crime scene reconstruction, forensic science [email protected] Introduction An integral part of overall crime scene throughout the scene and are often critical to reconstruction is determining the chronological the overall analysis”. timing of events. When investigating crime A parameter that can be useful in the timing scenes involving gunshots, understanding analysis of crimes, and a particular focus in this overall event timing is necessary and report, is that of human reaction time. “reconstruction is most effective when a Human reaction time studies which have comprehensive approach is taken including helped advance perspective on many timing consideration of events before, during, and related questions date back to the beginnings after the shooting incident” Chisum & Turvey of human study as a science. In 1862 the [1]. Further Gardner & Bevel [2] state that eminent Swiss scientist Adolph Hirsch used “to ignore aspects of chronology (timing and a chronoscope to show that human reaction sequencing aspects) in crime scene analysis is to times varied slightly between auditory, tactile, ignore what is often half of the data available to and visual stimulation as well as varying us. Timing and sequencing relationships exist between individuals. They were also dependent J Assoc Crime Scene Reconstr. 2020:24 1 WWW.ACSR.ORG on stimulus expectedness. Hirsch’s insights the impending stimulus, a particular challenge helped to explain and understand the variability in forensically evaluating reaction time to in, and between, astronomers’ reactions in loud stimuli like a gunshot on silent film is to measuring the exact transit time of stars viewed determine the subject’s level of expectedness to in telescopes [3]. Later F.C. Donders (1868) and it. Expectedness can range from very highly then Wilhelm Wundt (1879) further explored expected to totally unexpected (i.e., a complete measuring the time from an auditory stimulus surprise), and levels in between those extremes. to a voluntary reaction in response, in what was In many cases it is possible, from the context of called mental chronometry [4,5]. silent film, to be fairly confident that reactions The purpose of our report is to apply are surprise reactions, in that there is no the science related to human reaction time, anticipation or pre-knowledge of the stimulus, specifically based on brake perception- but in other situations stimuli may not be a reaction time (brake PRT), to crime scene surprise, making it difficult to estimate or assign reconstruction and forensic analysis. This a mid- or intermediate-level of expectedness or is achieved by applying a modification of a awareness to the ensuing stimulus. The approach modern brake perception-reaction time model described here is therefore limited to cases where (taken from automobile driver reaction time reactions observed can be readily classified as studies in traffic flow theory) to evaluations voluntary reactions to a surprise stimulus. As of silent film which include surprise voluntary surprise reactions can be involuntary startle reactions. The approach is developed as a way or voluntary in nature, distinctions between to improve estimates of stimulus (primarily these types of reactions are briefly reviewed as gunshot) arrival time to human subjects, from reference. film and video which lacks audio but displays In this report a subject’s stimulus arrival time individual reactions which can be classified will be a reference film frame number or film as surprise voluntary reactions. A goal is to time that the stimulus arrives at the subject. For improve gunshot timing estimates based on example, when a sound arrives at them or image observed film reactions and further inform and appears to them. In this case a gunshot sound correct some previous misconceptions along arrival time may be slightly after the shot was these lines. fired as the gunshot sound takes a little time to In situations where silent film or video reach the subjects depending on the subject-to- recorded during a crime is forensically evaluated gun distance. for evidence, it is common to assess the human In principle, an estimate of gunshot sound reactions visible to gain insight into the events arrival time to subjects for a surprise gunshot on that occurred. Identification of the type of silent film, as determined by observed voluntary reactions being displayed is important to help reactions, is obtained by subtracting a best put the scene in proper context and if timing of estimate of the general population’s median the stimuli causing reactions is to be estimated perception time after encountering a surprise for crime scene reconstruction purposes then stimulus from the median value of the sampled utilization of proper estimates on human onset times of surprise voluntary reactions reaction time is essential. observed for the subjects on film. The onset There have been examples in media over the time of these voluntary reactions indicates the past few years where the scope and interpretation end of a perception phase or perception time. of reactions and reaction time have not been A need for further promoting awareness presented clearly and in some cases have even on the subtleties of reaction time for use in been in error. In this study we re-emphasize analysis like this was recently highlighted while that voluntary reaction time is not just a fixed viewing documentary specials summarizing number, but in addition to the normal person- the assassination of the U.S. President John to-person variability in the population it can Fitzgerald Kennedy (JFK). Some forensic differ as a function of a number of factors assumptions in that case for individual and perhaps most commonly varies with the reactions and reaction times used to determine expectancy of the impending stimulus. the first shot timing in the shooting sequence Even though it has been known since Hirsch (a shot that missed), based on reviewing the that reaction time varies with the expectancy of Zapruder film, contained errors that continue WWW.ACSR.ORG 2 J Assoc Crime Scene Reconstr. 2020:24 to be referenced. These errors have resulted in any case when using a film or video format in a general consensus about the duration of is to get an accurate real-time full frame rate the shooting sequence and timing of the first, value which is necessary for detailed timing missed shot that is incorrect. calculations. The prevailing but incorrect timing estimate of the first shot in the Kennedy assassination Reactions and Reaction Time based off the Zapruder film is an understandable Material consequence of attempting to determine The material related to reactions and reaction the timing based on misclassified human time consists primarily of human factors reactions. Close inspection of and familiarity studies on involuntary (startle) and voluntary with reaction types are needed when reviewing reactions. human reactions in motion pictures where The following descriptions of flexion and interpretation can be challenging especially rotation will be useful herein for describing if the motion picture is low in visual quality, body movements related to joint articulations or silent, so that other contextual evidence is occurring in these reactions. limited or absent. The Zapruder film presents an Flexion: Bending the joint resulting in a excellent example to demonstrate how correct decrease of angle; e.g., moving the head forward application of reaction type and reaction time at the joint just below the skull. science can provide improved forensic estimates Rotation: Rotary movement around the on the chronology of surprise gunshot timing longitudinal axis of the bone; e.g., turning the occurring in silent films. head to the side (right or left) at a joint below Interpretation of reactions observed when the skull. analyzing silent film where gunshots occurred is likely to be increasingly useful in the future Characteristics of involuntary as video surveillance, police body cams, reactions of the startle reflex dash cams, and security cameras continue to Strauss [6] with Landis and Hunt in “The Startle proliferate (perhaps quasi-exponentially). Pattern” (1929) discusses using a revolver shot as a stimulus to isolate a definite startle behavior Materials pattern. It was a general flexion response, Material used to complete this research was symmetrical, and relatively uninfluenced by sourced extensively from published literature postural changes.