1. ALL INDIA INSTITUTE OF SPEECH AND HEARING,MYSORE-6
National Symposium on Acoustics : Mysore 2014
NEURAL REPRESENTATION OF DIFFERENT SPEECH STIMULI AT CORTEX IN INDIVIDUALS WITH NORMAL HEARING  
Presenter
Himanshu Kumar Sanju
ALL INDIA INSTITUTE OF SPEECH AND HEARING,MYSORE-6

2. CAEPs reflect maturation of the human brain through
Cortical auditory evoked potentials (CAEPs) are
- non-invasive measures
- reflects cortical maturation.
CAEPs reflect maturation of the human brain through
- changes in their latency
- amplitude
- morphology
(Eggermont,1989;Sharma,Dorman & Spahr, 2002;Pang & Taylor, 2000)

3. CAEPs can also be elicited -using speech stimuli
Maturation is likely to have impact on speech and oral language skills, which are primarily acquired through auditory modality.
CAEPs can also be elicited
-using speech stimuli
- help in quantifying the central auditory system
Kraus, McGee, Micco,Sharma,Carrell, & Nicol(1993).
CAEPs are sensitive tool for evaluating the
- audibility of speech sounds in children with hearing impairment Golding, Purdy,Sharma,Dillon(2006); Sharma, Dorman & Spahr,
(2002);Carter,Dillon, Seymour, Seeto,Van(2013).

4. Need for the study There is a dearth of information
- to explore speech evoked CAEPs with different speech stimuli in children and adults with normal hearing.
- change in neural representation of different speech stimuli

5. Aim of the study
To find out neural representation of different speech stimuli (/m/,/g/ & /t/) in children and adults with normal hearing.

6. Method

7. 20 Subjects
10 Children
(5-7 Years)
10 Adults
(17-24 years)

8. Participants Selection Criteria
Hearing sensitivity within normal limits
(≤ 15 dB HL) in both ears.
Normal middle ear function as indicated by Immittance evaluation.
Not having any history of otologic, neurologic problems and illness on the day of testing.

9. 250 to 8000 Hz for air conduction 250 to 4000 Hz for bone conduction
Procedure
250 to 8000 Hz for air conduction
Pure Tone Audiometry
250 to 4000 Hz for bone conduction

10. Immittance Evaluation
Tympanometry with 226Hz
Immittance Evaluation
Reflexomatry
Ipsilateral and contralateral acoustic reflex thresholds was measured at 500Hz, 1000Hz, 2000Hz and 4000 Hz.

11. To verify normal hearing sensitivity of the participants &
Click evoked ABR
To verify normal hearing sensitivity of the participants &
to rule out RCP

12. Speech evoked cortical potential recording
HEARlab (version 1.0) evoked potential system

13. Speech evoked cortical potential
Parameters
Speech evoked cortical potential
Stimulus
/m/ (30 ms ) , /g/ (30ms)
/t/ (30 ms)
Electrode Placement
Reference: M1/M2
Active: Cz
Ground: Fz
Intensity
65 dB SPL
Transducer
Loudspeaker
Transducer Position
0 degree azimuth
Ear
Binaural
Polarity
Alternating
Filter setting
1-30 Hz
Repetition rate
1.1/sec
Total no. of sweeps
200
Impedance
< 5 kΩ
No. of Channels
One
Analysis Time
500 ms

14. Explore speech evoked CAEPs with speech stimuli (/m/, /g/, and /t/) which have a spectral emphasis in LF, MF and HF respectively.

15. Figure: 3rd octave power spectra for speech sounds /m/, /g/ and /t/ with overall levels normalized at 65 dB SPL

16. /m/
/g/
/t/
A sample waveform of cortical potentials for speech stimuli (/m/, /g/ & /t/) in children with normal hearing (Red color- /m/; Green color- /g/; Blue color- /t/ speech stimuli).

17. A sample waveform of cortical potentials for speech stimuli (/m/, /g/ & /t/) adults with normal hearing (Red color- /m/; Green color- /g/; Blue color- /t/ speech stimuli).

18. Result &
Discussion

19. Descriptive Statistics
Mann Whitney U test
Non-parametric Test
Kruskal Wallis test

20. P1 Latency
N1 Latency
Error bar for latency measures of wave P1 and N1 in children and adults.

21. P1 Amplitude
N1 Amplitude
Error bar for amplitude measures of wave P1 and N1 in children and adults.

22. Mann-Whitney U test : Between group comparison (children and adults)
Latency
Significant differences between children and adult
for wave P1 (Z = , p <0.05) and wave N1 (Z = , p<0.05)
Amplitude
Significant difference between children and adult
for wave P1 (Z = , p<0.05) and wave N1 (Z = , p<0.05).

23. Kruskal Wallis test: To compare differences across different speech stimuli in children as well as adults
Children
No significant differences across stimuli (/m/, /g/ and /t/)
Latency measures of wave P1 (ᵡ2= 0.485, df=2, p>0.05) and wave N1 (ᵡ2= 2.56, df=2, p>0.05).
Amplitude measures of wave P1 (ᵡ2= 0.589, df = 2, p>0.05) and wave N1 (ᵡ2= 0.143, df=2, p>0.05).
Adults
No significant difference across stimuli for
Latency measures of wave P1 (ᵡ2= 0.356, df=2, p>0.05) and wave N1 (ᵡ2= 5.145, df=2, p>0.05).
Amplitude measures of wave P1 (ᵡ2= 0.218, df=2, p>0.05) and wave N1 (ᵡ2= 1.577, df=2, p>0.05).

24. The present study shows robust wave P1 and N1 responses from both children and adults with normal hearing.
In adults though later peaks (wave P2 & N2) were notice it was not mentioned due to lack of occurrences of later peaks in children.

25. Statistically significant differences between children and adults for latency and amplitude measures of wave P1 and N1 at 0.05 levels.
Because CAEPs reflect maturational changes of the human brain in terms of the changes in their latency, amplitude and morphology (Eggermont, 1989; Gilley et al., 2005; Fox et al., 2010).

26. Another major finding of the present study was no statistically significant difference across different speech stimuli in both children as well as in adults.
The above finding is in agreement with other reported literature (Dun, Carter & Dillon, 2012; Munro, Purdy, Ahmed, Begum & Dillon, 2011s

27. A study done by Munro et al
A study done by Munro et al. (2011) on adult listener reported that the there is no differences in latency and amplitude measures across different speech stimuli.
A study done by Garinis and Cone (2007) also reported no significant difference in CAEP waveform for latency and amplitude measures using /sa/ and /da/ as speech stimuli.
However, the above finding is in contrast with Golding et al (2006) study, they reported /t/ speech stimuli evoked significantly larger in amplitude and earlier in latency than for the other two speech stimuli (/m/ & /g/).

28. To conclude, differentiation of CAEP responses between speech stimuli, was not being observed while measuring cortical potential as synthesized short duration speech stimuli was used and there was greater spread in amplitude and latency in individuals with normal hearing
As far field recording of CAEP causes blurred spatial distribution compared with potential at the source which reduces the temporal and spectral difference between stimuli.
However, present study finding should be considered with caution and requires validation on large sample size.

29. Conclusion
The present study clearly shows that due to maturational changes there are differences between children and adults cortical potential responses in terms of latency and amplitude measures.
Further, the neural representations of different speech stimuli are shown to be alike in children and adults with normal hearing.
There is need for alternative objective electrophysiological measure of speech discrimination in individuals.
Probably present study outcomes can help researchers to consider as a reference while performing cortical potential measures in clinical populations like individual with hearing impairment.

30. Reference
Carter, L., Dillon, H., Seymour, J., Seeto, M., Van, B. (2013). Cortical auditory-evoked potentials
(CAEPs) in adults in response to filtered speech stimuli. Journal of the American Academy
of Audiology. 24(9),
Cone, B., & Whitaker, R. (2013). Dynamics of infant cortical auditory evoked potentials for tone
and speech tokens. International Journal of Pediatric Otolaryngology, 77(7),
Dun, B., Carter, L., & Dillon, H. (2012). Sensitivity of cortical auditory evoked potential
detection for hearing-impaired infants in responses to short speech sounds. Audiology
Research, 13(2),
Eggermont, J.J., (1989). The onset and development of auditory function: contributions of
evoked potential studies. Journal of Speech Language Pathology and Audiology, 13(1),
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Fox, A., M., Anderson, M., Reid, C., Smith, T., & Bishop, D., V. (2010). Maturation of auditory
temporal integration and inhibition assessed with event related potential (ERPs). BMC
Neuroscience, 16; 11:49.
Garinis, A., C., & Cone, B., K. (2007). Effect of stimulus level on cortical auditory event-
realated potentials evoked by speech. Journal of the American Academy of Audiology,
18(2),

31. Gilly, P. , Sharma, A. , Dorman, M. , & Martin, K. (2005)
Gilly, P., Sharma, A., Dorman, M., & Martin, K. (2005). Development changes in refractoriness
of the cortical auditory evoked potential. Clinical Neurophysiology, 116(3),
Golding, M., Purdy, S., Sharma, M., Dillon, H. (2006). The effect of stimulus duration and inter
stimulus interval on cortical responses in infants. The Australian and New Zealand
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32. Acknowledgement Director of AIISH, Mysore Organizers of NSA 2014
Participants of our study

33. Discussion