Tinnitus selectively disrupts phoneme level speech perception.

Chronic subjective tinnitus has been linked to impaired speech-in-noise perception, yet its impact on phoneme level processing remains unclear. We assessed phoneme discrimination in 49 normal hearing participants (26 with chronic subjective tinnitus and 23 matched controls), with matched audiometric thresholds and supra-threshold processing, and found no statistically significant differences between groups on the assessed cognitive measures, using a two-alternative forced-choice identification task with fricatives (/s, ʃ/) and plosives (/ph, t/) presented in quiet and individualized noise conditions. Performance on the tested fricative contrast was preserved in the tinnitus group (observed noise accuracy: 0.69 vs 0.73 in controls; model based group contrast, p=0.778). In contrast, plosive processing showed a selective alteration: tinnitus participants were significantly slower than controls in noise (model estimate +89 ms, p=0.002) despite comparable observed accuracy (0.47 vs 0.49; model-based group contrast, p=0.212). Controls exhibited a clear speed-accuracy trade-off (p<0.001), which was absent in tinnitus. These findings suggest a dissociation between preserved spectral processing and impaired temporal processing in tinnitus.