Listeners may be judging speech intelligibility rather than raw signal-to-noise ratio

Evidence

We reasoned that by changing the stimuli to ones with a far steeper psychometric function (MacPherson and Akeroyd 2014 ), namely triple digits, the JND in the appropriate domain would be constant, but the JND in the other domain would change. On testing this hypothesis, we found that the mean SNR JND for digits was 2.5 dB (σ= 0.8 dB) and the mean Intelligibility JND estimate for digits was 17.5 % (σ= 7.2 %). … That both differences were non-zero was unexpected; it indicates that one cannot be certain whether the 3 dB SNR JND is indeed the JND for SNR or instead the JND for Intelligibility. — Dijk, Pim van, Physiology, Psychoacoustics and…, 5673

Categorization

• DEEPTHINKING: The subtle methodological logic — changing psychometric-function slope as the probe to identify which perceptual domain dominates — is itself a neat experimental design, and the ambiguous result genuinely undermines a basic assumption about what ‘detectable benefit’ means.
• XREF: Connects to the reader’s interest in cognition of hearing: apparently the listener converts the available cues into whatever domain is most accessible, not necessarily the one the experimenter intends.