Differential Pitch Threshold Shift Associated with Moderately High-Level Background Noise

Abstract

Normal ears are known to exhibit a distortion of the normal loudness growth function (pseudo-recruitment) in the presence of threshold shifting levels of thermal noise. A deterioration of the pitch discrimination function has often been associated with loudness recruitment in abnormal ears. This study involves the determination of differential pitch thresholds (DPT) for normals in the presence of 50- to 70-db threshold shifting levels of thermal noise for comparison with determinations in quiet. Testing for DPT was done with an automated instrument using a modified method of constant stimuli. Frequencies tested were 500, 1000, 2000, and 4000 cps at 50-db SL. Levels in the noise situation were equated to the quiet SL using a loudness balancing method. Maximum shifts in the DPT were found at the highest frequency though most subjects showed noticeable shifts at the other frequencies, also. As might be expected, some increase in variability is also evident in the data obtained in noise. (This work supported in part by a Public Health Service grant.)