Under certain conditions, the perception of a given sound stimulus in one ear may be altered when a different sound is presented to the opposite ear. For instance, changing an observer's perception of the loudness of a sound presented by an earphone to one ear by introducing a dissimilar sound in the opposite ear has been reported in the literature. Egan (1948), using two subjects, found that the loudness of speech delivered to one ear only was nearly 7 db louder than when a 70 to 80 db sensation level thermal noise was introduced into the opposite ear. A possible explanation of the increase in loudness, according to Egan, may be that there is a sort of summation because of the similarity between the temporal and frequency characteristics of thermal noise and speech. In seeming contrast, Bekesy and Rosenblith (1951) have stated that a loud high frequency pure tone delivered to one ear will reduce the loudness of a low frequency tone in the opposite ear between five and ten db. According to these writers this reduction in loudness can be attributed to the acoustic reflex.
Proceedings of the Iowa Academy of Science
Shapley, James L.
"Reduction in the Loudness of a 250-Cycle Tone in One Ear Following the Introduction of a Thermal Noise in the Opposite Ear,"
Proceedings of the Iowa Academy of Science, 61(1), 417-422.
Available at: https://scholarworks.uni.edu/pias/vol61/iss1/55