Intelligibility of chimeric locally time-reversed speech: Relative contribution of four frequency bands

Release from same-talker speech-in-speech masking: Effects of masker intelligibility and other contributing factorsa)

Human speech perception declines in the presence of masking speech, particularly when the masker is intelligible and acoustically similar to the target. A prior investigation demonstrated a substantial reduction in masking when the intelligibility of competing speech was reduced by corrupting voiced segments with noise [Huo, Sun, Fogerty, and Tang (2023), "Quantifying informational masking due to masker intelligibility in same-talker speech-in-speech perception," in Interspeech 2023, pp. 1783-1787]. As this processing also reduced the prominence of voiced segments, it was unclear whether the unmasking was due to reduced linguistic content, acoustic similarity, or both. The current study compared the masking of original competing speech (high intelligibility) to competing speech with time reversal of voiced segments (VS-reversed, low intelligibility) at various target-to-masker ratios. Modeling results demonstrated similar energetic masking between the two maskers. However, intelligibility of the target speech was considerably better with the VS-reversed masker compared to the original masker, likely due to the reduced linguistic content. Further corrupting the masker's voiced segments resulted in additional release from masking. Acoustic analyses showed that the portion of target voiced segments overlapping with masker voiced segments and the similarity between target and masker overlapped voiced segments impacted listeners' speech recognition. Evidence also suggested modulation masking in the spectro-temporal domain interferes with listeners' ability to glimpse the target.

Auditory grouping is necessary to understand interrupted mosaic speech stimuli

The intelligibility of interrupted speech stimuli has been known to be almost perfect when segment duration is shorter than 80 ms, which means that the interrupted segments are perceptually organized into a coherent stream under this condition. However, why listeners can successfully group the interrupted segments into a coherent stream has been largely unknown. Here, we show that the intelligibility for mosaic speech in which original speech was segmented in frequency and time and noise-vocoded with the average power in each unit was largely reduced by periodical interruption. At the same time, the intelligibility could be recovered by promoting auditory grouping of the interrupted segments by stretching the segments up to 40 ms and reducing the gaps, provided that the number of frequency bands was enough ( ≥ 4) and the original segment duration was equal to or less than 40 ms. The interruption was devastating for mosaic speech stimuli, very likely because the deprivation of periodicity and temporal fine structure with mosaicking prevented successful auditory grouping for the interrupted segments.

The common limitations in auditory temporal processing for Mandarin Chinese and Japanese

The present investigation focused on how temporal degradation affected intelligibility in two types of languages, i.e., a tonal language (Mandarin Chinese) and a non-tonal language (Japanese). The temporal resolution of common daily-life sentences spoken by native speakers was systematically degraded with mosaicking (mosaicising), in which the power of original speech in each of regularly spaced time-frequency unit was averaged and temporal fine structure was removed. The results showed very similar patterns of variations in intelligibility for these two languages over a wide range of temporal resolution, implying that temporal degradation crucially affected speech cues other than tonal cues in degraded speech without temporal fine structure. Specifically, the intelligibility of both languages maintained a ceiling up to about the 40-ms segment duration, then the performance gradually declined with increasing segment duration, and reached a floor at about the 150-ms segment duration or longer. The same limitations for the ceiling performance up to 40 ms appeared for the other method of degradation, i.e., local time-reversal, implying that a common temporal processing mechanism was related to the limitations. The general tendency fitted to a dual time-window model of speech processing, in which a short (~ 20-30 ms) and a long (~ 200 ms) time-window run in parallel.

Checkerboard speech vs interrupted speech: Effects of spectrotemporal segmentation on intelligibility

The intelligibility of interrupted speech (interrupted over time) and checkerboard speech (interrupted over time-by-frequency), both of which retained a half of the original speech, was examined. The intelligibility of interrupted speech stimuli decreased as segment duration increased. 20-band checkerboard speech stimuli brought nearly 100% intelligibility irrespective of segment duration, whereas, with 2 and 4 frequency bands, a trough of 35%-40% appeared at the 160-ms segment duration. Mosaic speech stimuli (power was averaged over a time-frequency unit) yielded generally poor intelligibility ( ⩽10%). The results revealed the limitations of underlying auditory organization for speech cues scattered in a time-frequency domain.