Semantic Context Can Mask Intelligibility Declines at Above-Conversational Speech Levels in Normal-Hearing Listeners.

Abstract

While speech audibility generally improves with increasing level, declines in intelligibility are inconsistently observed at above-conversational levels, even in listeners with normal audiograms (NAs). The inconsistent findings could be due to different types of speech materials, ranging from monosyllabic words to everyday sentences, used across studies. Here, we hypothesized that semantic context can "mask" intelligibility declines at high levels by constraining plausible response options. Intelligibility was assessed in speech-shaped noise with monosyllabic words, sentences without semantic context, and sentences with semantic context. Two presentation levels were used: 80 and 95 dB SPL broadband. Bandpass filtering was applied to minimize upward spread of masking. Twenty-two young adults with NAs were tested. Poorer performance at the higher level was found with the monosyllabic words and context-free sentences but not with the context-rich sentences. The scores obtained at the higher level with the two context-free materials were strongly correlated. The correlation was independent of the lower-level scores, suggesting that the high-level performance declines reflect "normal" auditory functioning. Young adults with NAs show intelligibility decreases at above-conversational levels when tested with speech materials without semantic context. Top-down processing as facilitated by context information can mask such declines.