Recruitment can explain why loudness summation is absent in noise-induced hearing loss

Evidence

In these low-level regions, loudness summation does not take place in normally hearing subjects because of the steepness of the curve relating specific loudness to excitation level. If the exponent is 1 instead of 0.25, such as at medium and high levels, then intensity and loudness grow in the same way, i.e. no loudness summation takes place. Therefore, the effect “f recruitment may also be the reason that loudness summation does not occur in listeners with noise-induced hearing loss. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1960

Sensorineural hearing loss (SNHL) has a robust and profound effect on loudness, with a primary effect being abnormally rapid growth of loudness. Fowler (1928) was the first to report that listeners with SNHL experienced a similar range of loudness (from very soft to uncomfortably loud) but over a smaller range of decibel levels due to reduced audibility. He dubbed this phenomenon loudness recruitment. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 838

At a centre frequency of 500 Hz, the results of hearing-impaired subjects are also in close agreement with the calculated data. At 4-kHz centre frequency, however, subjects with noise-induced hearing loss produce not only higher thresholds, near 50 dB in this case, but they also do not show any reasonable loudness summation. Predicted data, and those of normally hearing subjeds, show a loudness summation corresponding to values of up to 13 dB. Normally hearing subjects reach such values already 40 to 45 dB above threshold in quiet, whereas listeners with noise-induced hearing loss show an increment of only 1 to 2 dB at 40 dB above threshold in quiet, which is actually near 90 dB SPL. This means that in the frequency region of elevated threshold in quiet, loudness summation is almost negligible for listeners with noise-induced hearing loss. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1957

Categorization

• DEFINE: Introduces and names loudness recruitment, a core term for the reader’s stated interest in hearing perception.
• corroborated: 4 independent passages support this claim — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1960; Jennifer Lentz, Psychoacoustics- Perception of Normal…, 838; Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1957
• XREF: connects to: Hearing-impaired listeners experience a steeper loudness-growth function known as recruitment; Loudness recruitment shrinks dynamic range while preserving overall loudness; Hearing-impaired patients with loudness recruitment could disentangle intensity and loudness encoding. (+9 more)

Broader Connections

• Loudness recruitment shrinks dynamic range while preserving overall loudness #qualifies (0.80)
• Cochlear hearing loss spares envelope processing but amplifies perceived fluctuation via recruitment #complicates (0.80)
• Sensorineural hearing loss compresses the full loudness range into fewer decibels #expands (0.80) — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 838
• Hearing-impaired patients with loudness recruitment could disentangle intensity and loudness encoding. #expands (0.75)
• Absence of loudness recruitment signals retrocochlear rather than cochlear pathology #contradicts (0.75)
• Loudness perception involves central mechanisms beyond cochlear vibration #expands (0.75)
• Loudness recruitment in hearing loss could be probed via Heschl’s gyrus fMRI #expands (0.72) — Dijk, Pim van, Physiology, Psychoacoustics and…, 2645
• Recruitment patients could disambiguate loudness from intensity encoding in fMRI #expands (0.72)