Listeners only rate a speech-quality change as meaningful when it exceeds detectability thresholds

Evidence

The simplest, most direct rating of preference is a better/worse scaling procedure. Thirty six participants (median age: 62 years; range: 31–74) of varying hearing ability (median BE4FA: 21 dB HL; range 3–85 dB HL) heard two intervals of IEEE sentences in same-spectrum noise, one at 0 dB SNR, and the other at 0 dB plus a ΔSNR of 1, 2, 4, 6 or 8 dB. The overall level of each interval was 63 dB A (73 for those with more severe losses); unlike the JND experiments, the level was not roved across intervals. Participants were asked how much better/worse the second interval was on a discrete, signed 11-point scale with ‑5 marked “much worse” and + 5 marked “much better.” Each of the ten conditions (5 ΔSNRs × 2 orders) was repeated 12 times in randomized order, resulting in 120 trials completed in three blocks of 40. … This asymmetry was most likely due to an order effect; the second iteration of a sentence has been shown to be more intelligible (e.g., Thwing 1956 ), hence second-interval deficits would be deflated, and second-interval benefits inflated. Regarding the JMD, the ratings significantly increased only at 4 dB, regardless of order, lending support to the notion of detectability being a requisite for meaningfulness. — Dijk, Pim van, Physiology, Psychoacoustics and…, 5687

Categorization

• DEFINE: Introduces the better/worse scaling procedure and the JMD (just-meaningful-difference) concept.