Emotion Induced by Acoustic and Odor Stimulation Measured with Startle Probe Paradigm

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The purpose of this reserch was to investigate the magnitude of startle eyeblink reflex would reflect the subjective feeling of pleasantness provoked by natural sound and odor stimulations.In the first experiment, subjects were 18 volunteers whose mean age was 21.0 ranged from 18-23. Subjects received the startle noise pulse during natural sound stimulation. The exposure duration of natural sound was 10-sec and its maximum intensity was less than 70dB.Three categories of sound, Pleasant, Unpleasant, or Neutral, were selected among 50 standardized sound samples. Startle pulse was presented 4-, 6-, or 8-sec after the natural sound presentation via headphones. The intensity of the startle noise was set at 110dB(A) at the headphones. The noise durations was 50-ms and its rise/fall times were less than 0.1-ms. Integrated EMG of Orbicularis Oculi, 20ms after the onset of startle stimulus, was assessed for statistical analysis. Results showed that the magnitude of EMG activity during pleasant … More sound condition significantly lower than neutral condition. On the other hand, EMG maguitude during unpleasant condition higher than the neutral condition, but not significant.In the second experiment, 18 university students, 9 males and 9 females, were served as subjects. Pleasant odor (chocolate and banana) and unpleasant odor (pork acid and cod roe) were presented for 5 sec with an intervals of 40-60s. A pulse of white noise (105 dB, 50ms, Oms r/f time) was presented 0.5s, 1.5s, or 3s after the onset of odor stimulation. Reflex magnitude was assessed as an integrated EMG (in A/D unit) of Orbicularis-Oculi within a window of 20-120ms after a pulse onset. Results showed that the mean magnitude of the eyeblink reflex was smaller in pleasant odor condition than that in unpleasant odor condition. The difference between pleasant and unpleasant odor condition was significant only in 1.5s lead interval. It is recommended that startle eyeblink reflex would be used as an objective tool for evaluation of odor with an lead interval of 1.5s.As these results were compatible to the experiments using visual stimuli, it is suggested that startle eyeblink reflex would be a good index of subjective feeling of pleasantness. Less