An evolutionary perspective of the effects of emotion on the post-auricular reflex
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] The post-auricular reflex (PAR), contrary to other components of the startle reflex, is potentiated by positive emotions and inhibited by negative emotions. We investigated this "paradoxical" modulation, testing two hypotheses. In the Nursing hypothesis, infant mammals instinctively retract their pinnae while nursing; hence, appetitive emotions will prime the ear retraction musculature. In the Grimace hypothesis, the act of "smiling" in our simian ancestors reflected an unpleasant, defensive state with ear-retraction linked to teeth-baring circuits. Human smiles during appetitive states still prime the defensive, pinna-flexion pathways. We acoustically startled 47 young adult volunteers who made lip-pursing or grimacing maneuvers while they simultaneously viewed neutral, intimidating, or appetitive slides. Results: An interaction between facial maneuver and image was identified with larger PAR amplitudes for appetitive than neutral images ([rho] [less than] .05), but only during the pursed-lips maneuver. Our results support the Nursing hypothesis that appetitive emotions will prime the ear-retraction musculature.
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