A new experimental method for evaluating the effectiveness of auditory signals under realistic background noise...

This study introduces a new experimental method for analyzing auditory signals in the presence of background noise and identifying sounds that are consistently easy for humans to notice in daily environments. Attention to a signal was inferred from a physiological orienting response, measured as the change in heart rate (HR) before and after the presentation of a test sound in an experimental environment designed to simulate daily life. The test sounds consisted of eight musical sounds each composed of two piano notes at different pitches, and eight complex sounds, each composed of two pure tones. Each sound interval-C + E or C + G#-was recorded at four different octaves, covering the frequency range of 130.8 Hz to 1661.4 Hz. The change in HR was calculated as the difference in the mean RR interval (RRI) over five beats before and after the test sound. The strength of the orienting response (OR) was quantified as the RRI difference normalized by the standard deviation of RRI. An absolute value greater than 2 was considered to indicate the presence of an orienting response. Twenty-two healthy young male participants participated in the experiment during a three-day, two-night stay, which was repeated after a washout period of at least one week. The results showed that OR values were reproducible for 11 of the 16 test sounds. Based on the corresponding OR values, C3 + E3 (musical sound) was identified as a suitable pre-signal due to its calming response (negative OR), whereas C6 + G#6 (complex sound) was identified as a suitable alarm signal due to its tension-inducing response (positive OR). These findings suggest that the OR metric for assessing physiological responses, provides a novel and effective approach for objectively evaluating human reactions to unexpected auditory stimuli, when combined with an experimental protocol that simulates daily life and background noise.