Differences in Physiological Responses to Exposure of Disturbing Auditory Versus Audiovisual Stimuli

Fear plays a significant role in the lives of many people, from crippling fear that prevents people from performing everyday activities, to that which is intentionally experienced from video game or horror movies. The physiological responses to fear-inducing stimuli may vary between individuals, but some common reactions include increased heart rate, respiration rate and muscle tension, collectively referred to in this study as the “fear response”. These common reactions are a result of the sympathetic nervous system reacting when presented with a threat, a.k.a: a scary scene in a horror movie. The hypothalamic-pituitary adrenal axis regulates the body’s behavior, including the autonomic responses that are being measured in this experiment. The purpose of this study is to analyze the fear response to either audio or audiovisual stimuli, and compare the severity of the physiological changes induced by both stimuli against each other. The 29 participants were randomly assigned to one of two groups: 15 Audio (Group A) and 14 Audiovisual (Group AV). Group A was instructed to listen only to the audio track of a stimulating horror movie trailer broken up into 4 segments, and Group AV was subjected to the same trailer but also experienced the visual aspects of the stimulus. It was hypothesized that the fear response to an auditory stimulus would be larger than the response to the audiovisual stimulus. Of the two groups, those who received the audiovisual stimulus elicited a stronger physiological response than the audio group in heart rate and respiration frequency, but there were no statistically significant difference between the two groups when measuring muscle tension and respiration frequency. However, the audio stimulus induced a biological response of greater magnitude in muscle tension compared to the audiovisual stimulus. The reason for heart rates showing the only significant difference in physiological measurements between Group A and Group AV may be because heart rate is an involuntary physiological response. In contrast, the measurements for EMG and respiration could be voluntarily altered by participants during the experiment. Overall, although our results did not all show statistical significance, differences between the two treatments groups were observed for each variable and therefore show a degree of biological significance. Introduction In our society, people watch horror movies despite the disturbing emotions and images that they present. Whether it is in groups or alone, scary movies are used for entertainment, for study, etc. According to Dr. Glenn Walters, people are lured into watching horror films because of their unrealism (Griffiths, 2015). The unrealistic qualities incorporated in scary films, allow viewers to place themselves at a distance from the horror they are viewing and instead enjoy it as entertainment (Griffiths, 2015). In addition, gender, age and personality are important underlying factors that contribute to one’s motivation for watching a scary movie (Johnston, 1995). Fear has evolved as a necessary tool to help a person increase their likelihood of survival. When watching horror movies, fear is often experienced because of the mystery, shock, terror and gore being shown (Griffiths, 2015). To deal with this emotion, the neurological, endocrine, cardiovascular, and other organ systems become activated (Palmer, 2008). The physiological reactions elicited when people subject themselves to this genre affect their experience and emotions both during the film. Scary movies’ use of audio and visual cues have been shown to change heart rate, respiration rate, and muscle tension in response to the fear they create. As Palmer stated, “[e]veryone has seen the person frightened so badly at the movie theater that he is perspiring... [or] felt your heart rate increase during an intense scene right before the movie’s killer strikes” (2008). In one study, physiological reactions were examined in people viewing a video that involved threat versus a film that involved surgery (Palomba et al., 2000). The violent threat film resulted in a reaction consistent with sympathetic nervous system activation. The participants exhibited significant cardiac acceleration. The threat film group also presented the largest increase in heart rate during the first minute of the film, followed by smaller increase as the film proceeded (Palomba, 2000). This all suggests that the fear stimulus significantly induced a fightor-flight reaction (Palomba et al., 2000). In another study, participants sat in a room viewing the Texas Chainsaw Massacre film and other participants sat in the room watching a neutral video. Data showed significant increases in heart rate and blood pressure in response to viewing the Texas Chainsaw Massacre film compared to those not watching the film’s stressful scenes (Main et al., 2002). A third study, measured heart rate, respiration, and skin conductance while watching a horror movie (Fukumoto & Tsukino 2015). The participants then reported how scared they were and when they were scared during the film watching period. The experimental data showed a change in all three physiological variables, with greater changes being observed at points when the participant admitted to being scared. Respiration intensity was increased and respiration cycle decreased during the film watching period for all ten male subjects (Fukumoto & Tsukino 2015). This data again shows sympathetic activation. But what this study shows is that fear is a subjective response and one’s physiological response to fear can be altered by their perception. Most of the existing data significantly correlates horror scenes to fear and fear to sympathetic nervous system responses, however, a majority of these results are found from studies with experimental stimuli which include both visual and auditory cues. While the essence of horror movies elicit the fear emotion and sympathetic physiological responses, hearing and seeing said horror movies may have very different effects. It has been argued that the key to making a horror movie scary is the sound (Hanson, 2013). If the sound is sudden or utilizes frightful tones, our brains interpret the scene as scary. Many scare sounds are produced from animal distress calls and are used to invoke terror because of humans’ evolutionary adaptation of survival when faced with animal danger (Hanson, 2013) . Frightful tones come with rapid frequency jumps, nonstandard harmonies, and noises pushed beyond their normal range. These sounds innately trigger our brains to stimulate a danger signal that results in fear (Haggin, 2012). Therefore, scary movies could evoke less fear if it weren’t for their audio component. In addition, physiological responses may be different due to the amount of sensory stimuli one is experiencing. Because of the greater amount of sensory information produced from the audiovisual stimuli, the brain has more to process and has the potential to trigger greater compounded physiological reactions (Collingnon et al., 2008). However, in the auditory group, despite there being only one sensory stimuli, there may be fear of the unknown that comes with the absence of visual cues. An unknown outcome can trigger the sensation of suspense which then triggers an increased magnitude of physiological responses (Miko, 1996). Because of our evolutionary instincts to avoid potential threats, regardless of there being an imminent threat or not, humans have evolved to outrun predators even before their visual presence (Lima, 1990). The auditory stimulus alone may elicit greater fear response than the same auditory stimulus accompanied visually because the visual stimulus might constrain the imagination. Can it be argued then that hearing a scary movie could generate a stronger physiological response, than both seeing and hearing the same stimulus? Or does the combination of sensory intake create a more realistic and compound experience, ultimately causing an even greater physiological experience of fear? We hypothesize that if presented with a disturbing stimulus via auditory or audio-visual means, then the fear response to an auditory stimulus will be larger than the physiological response to an audiovisual stimulus.