Definition and Clinical Implication of Temporal Fine Structure / 대한이비인후과학회지

Perception of sound is associated with the use of multiple acoustic cues in the human auditory system. These acoustic cues can be classified by their temporal and spectral properties. Temporal information can be considered as a slowly varying envelope (ENV) superimposed on a more rapid temporal fine structure (TFS). Various sound-processing techniques have been developed to assess the role of acoustic information carried by temporal ENV and TFS information. Previous studies demonstrated that ENV cues are associated with speech recognition in quiet, while TFS cues have a role to melody/pitch perception and listening to speech in a competing background noise. Besides, a number of studies have shown that the relative insensitivity of hearing-impaired subjects to TFS information. Although current technologies used in cochlear implants are not efficient in delivering the TFS cues, new speech processing strategies have been proposed to deliver TFS information. We herein review the cutting edge of TFS related studies and discuss the clinical implication of TFS.

The Effect of Temporal Information in Cochlear Implant Analog Sounds on the Tone Recognition of Normal Hearing Young People / 听力学及言语疾病杂志

Objective By comparing the tone recognition rates for different cochlear implant (CI) analog sounds ,the effects of the temporal coding strategy on tone recognition were investigated .Methods The professional announcer read 6 vowel (/a/,/o/,/e/,/i/,/u/,/ü/) of 4 different tones at a normal speed .After adjusting the am-plitude envelope and increasing the fine structure ,the audios with different sampling accuracy below 500 Hz(125 ,250? ?1500 pps) were obtained ,including 288 audio amplitude envelope adjusted and 288 not adjusted .Thirty young participants of normal hearing had tone recognition tests .The results and the tone recognition rates under two dif-ferent temporal properties were compared .Results When the temporal fine structures were combined in considera-tion ,the amplitude envelope as adjusted to match the fundamental frequency (F0) had a significant effect on the tone recognition .The tone recognition rate after amplitude envelope adjusted (80 .22％ ± 16 .32％ ) was higher than before (74 .83％ ± 20 .24％ ) [F(1 ,9)=16 .91 ,P=0 .002] .When the amplitude envelopes were combined in consider-ation ,changing the fine structure of the frequency below 500 Hz had a significant effect on the tone recognition [F (11 ,99)=38 .86 ,P<0 .001] .When the sampling precision was <375 pps ,the tone recognition had improved re-markably with the improvement of sampling precision (P<0 .004) .When the sampling precision was ≥375 pps , the effect on the tone recognition was not significant (P>0 .004) .The interaction between changing amplitude en-velopes and increasing the fine structure had a significant effect on the tone recognition [ F(11 ,99 )= 3 .78 , P<0 .001] .When the fine structure ≤375 pps ,adjustment on the amplitude envelope to increase the information of F0 had a significant impact on the tone recognition (P<0 .05) .When the fine structure was >375 pps ,the difference of the tone recognition before and after the adjustment tended to 0 (P>0 .05) .Conclusion In the CI coding strate-gy ,adjusting the amplitude envelope to get more F0 information improves tone recognition .To a certain degree ,the tone recognition improves when the sampling precision of frequency below 500 Hz is improved .Adjusting the ampli-tude envelope to F0 and increasing the temporal fine structure below 500 Hz can be combined in the same speech coding strategy to optimize the tone recognition .

What Is Temporal Fine Structure and Why Is It Important?

Complex sound like speech can be characterized as the sum of number of amplitude-modulated signals representing the outputs of an array of narrow frequency bands. Temporal information at the output of each band can be separated into temporal fine structure (TFS), the rapid oscillations close to the center frequency and temporal envelope (ENV), slower amplitude modulations superimposed on the TFS. TFS information can be carried in the pattern of phase locking to the stimulus waveform, while ENV by the changes in firing rate over time. The relative importance of temporal ENV and TFS information in understanding speech has been studied using various sound-processing techniques. A number of studies demonstrated that ENV cues are associated with speech recognition in quiet, while TFS cues are possibly linked to melody/pitch perception and listening to speech in a competing background. However, there are evidences that recovered ENV from TFS as well as TFS itself may be partially responsible for speech recognition. Current technologies used in cochlear implants (CI) are not efficient in delivering the TFS cues, and new attempts have been made to deliver TFS information into sound-processing strategy in CI. We herein discuss the current updated findings of TFS with a literature review.