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Thomas Lunner

Research Area Manager / Adj. Professor

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mail@eriksholm.com

Investigations into the benefits of TFS information in speech have revealed greater benefits for open-set sentences (difficult) than for closed-set sentences (easy) for normal-hearing listeners. The assumption is that TFS information reduces informational masking in difficult situations by aiding perceptual segregation of the target and background.

Testing TFS benefit in easy and difficult listening situations

The purpose of this study was to investigate the influence of the type of speech material on the benefit obtained from TFS information for young normal-hearing (YNH) participants, and older hearing-impaired (OHI) participants.

The design was based on the work of Hopkins et al. (2008), who measured speech reception thresholds (SRT) for a target talker in a background, as a function of the frequency range over which TFS information was available. The signal was split into 32, 1-ERBN-wide channels. Above a cut-off channel (CO), these channels were vocoded, containing only temporal envelope information. Channels up to and including CO were not processed.

Hopkins et al. found that increases in CO resulted in more decreases in SRTs for normal-hearing participants than for participants with cochlear hearing loss. This suggests that the latter were less able to utilise TFS information. Following the same design, we chose to compare results when the target speech materials were open-set sentences (difficult; HINT or ASL sentences) as used by Hopkins et al., and when they were more predictable sentences (easy) with a closed-word set (Danish Dantale 2).

Sound examples

Hopkins et al made ASL-sentences the target, and spectrally-matched IEEE sentences the background. The target-to-background-ratio in the examples was 0 dB. The unprocessed example (CO=32) gave the impression of two different male speakers, whereas the perceptual difference between the two male speakers was reduced in the fully vocoded example (CO=0).

tfs-benefit

Results

With the open-set material, YNH listeners benefited more from TFS information than OHI listeners, replicating Hopkins et al. (2008). For the YNH participants, the benefit of adding TFS was greater for the open-set material than for the closed-set material, while no difference in TFS benefit across speech materials was found for the OHI participants.

The choice of speech material is important when assessing the benefit of TFS. Several factors may facilitate recognition in the absence of TFS cues - including small set size, predictable temporal structure of the target speech, and contextual effects. We assume that TFS information is useful for reducing informational masking, by providing cues for the perceptual segregation of the target and background. When the target speech is highly predictable (easy), informational masking may be minimal, rendering TFS cues unnecessary.


Further reading

Hopkins K, Moore BCJ, Stone MA (2008) Effects of moderate cochlear hearing loss on the ability to benefit from temporal fine structure information in speech. Journal of the Acoustical Society of America, 123(2), p. 1140-1153.

Hopkins K, Moore BCJ (2011). The effects of age and cochlear hearing loss on temporal fine structure sensitivity, frequency selectivity, and speech reception in noise. Journal of the Acoustical Society of America, 130(1), pp. 334-349.

Lunner T, Hietkamp RK, Andersen MR, Hopkins K, Moore BCJ (in press). Effect of Speech Material on the Benefit of Temporal Fine Structure Information in Speech for Normal-Hearing and Hearing-Impaired Participants. Ear and Hearing.

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    Poster

    Replication of TFS experiments

  • learnmore-poster

    Poster

    Effect of speech material on the benefit of temporal fine structure