The thresholds of hearing in normal individuals were measured in microbars, and the following results were obtained.
1.The normal hearing threshold showed a variation of 10 to 20 db.in the individuals tested with lapse of time.
2.The types of variation in respect to time lapse were classified into the following 4 groups.
a) Adaptative Variation Gradual lowering or threshold with lapse of time (20-60 minutes).
b) Flat Variation Threshold subjected to changes within a range of 10 db.
c) Sudden Variation Abrupt change in threshold of over 10 db.after a short time lapse (5 min.)
d) Increasing Variation Elevation of threshold with lapse of time (5-60 minutes).