Of Hissing Snakes and Angry Voices: The Processing of Evolutionary Fear-Relevant Sounds in Infancy

Nicole Erlich (2010). Of Hissing Snakes and Angry Voices: The Processing of Evolutionary Fear-Relevant Sounds in Infancy PhD Thesis, School of Psychology, The University of Queensland.

       
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Author Nicole Erlich
Thesis Title Of Hissing Snakes and Angry Voices: The Processing of Evolutionary Fear-Relevant Sounds in Infancy
School, Centre or Institute School of Psychology
Institution The University of Queensland
Publication date 2010-06
Thesis type PhD Thesis
Supervisor Virginia Slaughter
Ottmar Lipp
Total pages 220
Total colour pages 8
Total black and white pages 212
Subjects 17 Psychology and Cognitive Sciences
Abstract/Summary Humans demonstrate preferential processing toward stimuli that would have been threatening throughout our evolutionary history. For instance, adults show differential responding to snakes and spiders compared to modern threatening stimuli (e.g., damaged electrical outlets, guns or rifles), or non-threatening stimuli (e.g., mushrooms, flowers and household objects). These findings have lead Öhman and Mineka (2001) to posit the existence of an evolved “fear module”. More recent studies indicate that human infants demonstrate differential attention to evolutionary threatening stimuli, providing increased support for the notion of an inbuilt fear module. Researchers have found that 5-month old infants show increased attention to a normally configured spider compared to a reconfigured or scrambled spider (Rakison & Derringer, 2008), and by 7-18 months of age, there is evidence for preferential looking to snakes as opposed to non-threatening animals when these are paired with a fearful vocalisation (DeLoache & LoBue, 2009). These results strongly suggest that young infants demonstrate a predisposition to attend to, and learn to fear, evolutionary fear-relevant threats. The present research sought to demonstrate differential processing of evolutionary fear-relevant stimuli in infancy using a combination of behavioural and physiological measures and carefully chosen stimuli. Previous research using infants has neglected to compare evolutionary and modern threats, making it impossible to ascertain whether differential responding has been due to the evolutionary nature of the stimuli, or due to the stimuli being generally threatening. Furthermore, responses to evolutionary threats have only been tested using stimuli in the visual modality. As the auditory modality is critical in early detection of threat, and infants demonstrate dominance in this modality, the use of sound rather than visual stimuli is a more ecologically valid method of measuring whether infants treat evolutionary fearful stimuli differently. Experiments 1 and 2 were carried out with the aim of selecting stimulus categories and controlling properties of the stimuli as stringently as possible, so differences between threat categories could be confidently attributed to the phylogenetic (evolutionary) or ontogenetic (modern) nature of the sounds. In Experiment 1a and 1b, an initial selection of sounds was chosen to cover a wide range of evolutionary relevant stimuli (e.g., predators and prey, natural sounds, emotive human vocalisations), as well as a range of sounds from a standardized database. These sounds were rated by adults to determine their perceived levels of arousal and valence (Experiment 1a), and modified according to a second experiment (Experiment 1b) in which the sound peak intensity levels were identified that would not systematically enhance the magnitude of the participants’ eye blinks and overshadow differences due to the inherent fear-relevant properties of the sounds. In Experiment 2 more extensive matching was undertaken, whereby adult participants were presented with the sound stimuli while physiological indices of arousal (heart rate and skin conductance) and of pleasantness (zygomaticus major and corrugator supercilii facial muscles, and startle-eye blink modulation) were measured, as well as subjective self-report ratings. Based on the results of these experiments, evolutionary and modern threatening sound categories were constructed that did not differ in physiological arousal or valence. A further category of pleasant sounds was constructed to control for the possibility that differences in threat categories were driven by the animate sounds in the evolutionary sound category. In Experiment 3 sounds from each of these categories were presented to 61 nine-month-old infants. During sound presentation, infants had their startle eye-blink and heart rate measured, as well as their referencing behaviour to both their caregiver and the sound source. Results indicated that while listening to the evolutionary threatening sounds, infants demonstrated three statistically significant physiological and behavioural effects compared to the modern or pleasant sounds: decreased heart-rate, larger eye-blink, and increased referencing behaviour. Caregiver ratings on a familiarity questionnaire ruled out the possibility that these differences were due to the evolutionary sounds being either more novel or more familiar than the other sound categories. These studies demonstrate that infants show a constellation of converging responses to evolutionary threats at both physiological and behavioural levels that are strongly suggestive of preferential processing of such stimuli. These responses cannot be attributed to such factors as the relative novelty of the stimulus categories, differential animacy between categories, or emotive or physical characteristics such as the arousal, pleasantness, peak intensity or duration of the sounds. These results support the notion of an evolved fear module and also illustrate the importance of using auditory as well as visual stimuli to test evolutionary hypotheses.
Keyword development
evolution
fear relevance
heart rate
infant
sounds
startle
Additional Notes Colour pages (pdf numbers): 100,130,133,134,135,165,170,220.

 
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Created: Mon, 18 Oct 2010, 22:22:19 EST by Ms Nicole Erlich on behalf of Library - Information Access Service