[Development of sound lateralization]

Perceptual sound lateralization is determined from differences in time and loudness of signals arriving separately at bilateral ears, with the time difference being the more important one. The author examined the development of sound lateralization using a self-recording device developed by Sato T, which measures the sensitivity of sound lateralization on the basis of time and loudness differences separately. Subjects were 59 children aged 2 to 18 years and 12 adults who were audiologically and neurologically normal. Sound stimulus was 500 Hz continuous band noise. (1) The testable rate was increased in children older than the age of 4, and all children over 7 years of age could be tested. (2) Children over 4 years of age could lateralize sound on the basis of time difference. Sensitivity to time differences improved rapidly, showing a steep curve, in children from the ages of 4 to 6, and then increased slowly until adulthood. (3) Sensitivity to loudness differences increased and the normal range distribution decreased with age. There is a possibility that children aged 4 can discriminate loudness difference almost as well as adults.