Intelligibility and detectability of speech measured diotically and dichotically in groups of listeners with, at most, "slight" hearing loss.

The purpose of this investigation was to determine if a group of listeners having thresholds at 4 kHz exceeding 7.5 dB HL, and no more than "slight" hearing loss, would exhibit degradations in performance when "target" stimuli were masked tokens of speech. Intelligibility thresholds and detection thresholds were measured separately for speech masked by flat-spectrum noise or speech-shaped noise. Both NoSo and NoSπ configurations were employed. Consistent with findings of earlier investigations, when maskers and speech tokens were broadband, NoSo and NoSπ detection thresholds were substantially lower than intelligibility thresholds. More importantly, for the small cohorts tested, mean thresholds obtained from the ≤7.5 dB and >7.5 dB groups were equivalent. When maskers and speech targets were high-pass filtered at 500 Hz and above, the mean intelligibility thresholds obtained from the >7.5 dB group were about 4 dB higher than those obtained from the ≤7.5 dB group, independent of masker type and interaural configuration of the stimuli. In real-world listening situations, such deficits may manifest themselves as substantially reduced speech intelligibility and, perhaps, increased "listening effort" for listeners whose thresholds at 4 kHz exceed 7.5 dB HL and who have no more than "slight" hearing loss.