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Arnold School of Public Health


Acoustic Contributions to Speech Intelligibility

We have been interested in identifying how listeners use general acoustic properties for the perception of speech in quiet and during interruption. Acoustic signals can be divided into two different domains: the frequency domain and the temporal domain. The frequency domain can be divided into multiple regions or bands, such as low, middle, and high frequencies. Each of these frequency bands contain different speech information, and therefore may contribute differently to speech intelligibility. The temporal domain can also be subdivided into different rates. Slow rates correspond to how the amplitude of the speech signal changes over time. These amplitude modulations are called the speech envelope (E). Faster rates correspond to how frequency changes over time, and are called the temporal fine structure (TFS). Each frequency band contains these two different temporal properties.

We have investigated how listeners perceptually weight these different types of acoustic information. The figure shown here depicts the relative weight obtained for the E and TFS in each of these frequency bands for uninterrupted, meaningful sentences. Results demonstrated that listeners weighted mid frequencies, containing the predominant cues of the second formant frequency (F2). In addition, envelope cues were weighted more highly than the fine structure.

Additional experiments have explored how listeners' perceptual weights are influenced when cues from only one channel are predominantly available as well as when all channels are available during an interrupting context. These results are important for the design of assistive listening devices, as listeners may obtain maximal benefit if these devices preserve and enhance the cues that listeners weight the most. In addition, it appears that the processing of these devices may need to be adaptive, as listener weighting strategies are altered in different listening environments.

Representative Publications:
Fogerty, D. (2011). Perceptual weighting of individual and concurrent cues for sentence intelligibility: Frequency, envelope, and fine structure. Journal of the Acoustical Society of America, 129, 977-988. [pdf] [online]

Fogerty, D. (2011). Perceptual weighting of the envelope and fine structure across frequency for sentence intelligibility: Effect of interruption at the syllabic-rate and periodic-rate of speech. Journal of the Acoustical Society of America, 130, 489-500. [pdf] [online]