Fluctuating maskers produce masking release that Fletcher’s power spectrum model cannot explain.

Evidence

In contrast to the results of Fletcher, Hall et al. found that increasing the bandwidth of the modulated noise first increased thresholds but then thresholds decreased as the bandwidth was further increased, as shown by the unfilled circles in Figure 3–16. … We see from Figure 3–16 that the decrease in threshold provided by the fluctuating masker did not begin until the masker bandwidth was greater than the critical band, or around 60 to 100 Hz. The difference in threshold between the steady masker and the fluctuating masker is the fluctuating masker benefit. The size of the benefit increased as the bandwidth of the masker increased, with a benefit of over 10 dB for the 1000-Hz wide masker. When the fluctuations across frequency were synchronous, a release from masking occurred. Data such as these point to problems with Fletcher’s power spectrum model of masking, which would have predicted the same thresholds regardless of stimulus fluctuations. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 548

Categorization

• XREF: The masking-release results connect to later ch. 7 material on cochlear amplitude compression and how compression enables dip listening — a core mechanism that will come back when discussing hearing loss.
• DEFINE: Defines the ‘fluctuating masker benefit’ as the threshold difference between steady and fluctuating maskers.