The Development of Sensitivity to Amplitude and Frequency Modulation Follow Distinct Time Courses Karen Banai, Andrew T. Sabin, Nina Kraus & Beverly A. Wright

928

Northwestern University, Evanston, IL, USA

FM Detection

Group analyses

Group Analyses

While average AM sensitivity continued to develop beyond 12 years of age, performance consistency was already adult like by 8 years of age.

For FM detection, no significant development beyond 8 years of age was observed on either average performance or performance consistency.

30

20

20

10

10

10

0

0

0

Consistency (SD,%)

50

11-12

50

ns

17+

8-10

50

ns

40

40

40

30

30

30

20

20

20

10

10

0 11-12

17+

11-12

ns

0 8-10

11-12

8-10

17+

11-12

ns 1.5

9

1

6

0.5

0.5

3

0

0

8-10

2

11-12

2

ns

1.5

1 0.5

11-12

17+

0

Performance measures •The data set for each listener consisted of all reversal values obtained on all runs (excluding the first 3-4 reversals per run). •Each reversal value was the modulation depth expressed as a percentage.

•Average performance: within subject mean of reversals

m

64 Hz

125 Hz

2 Hz

r = -0.51**

ns

60 50

40

40 30 20 10 0

20 10

ns

30

30

ns

30

25

20

10 0

10

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30

ns

30 25

25

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20 20

15

15 15

10 5 0

10

p<.1; * p<.05; ** p<.01

20

10 30 0

10 10

20

17+

8-10

11-12

17+

• Large variability across children and poor average performance within a child are not always signs of individual inconsistency.

30

5 0

Age (adjusted for SD/Average)

10

20

30

• Average performance and performance consistency may be governed by separate neural mechanisms.

Consistency Develops During Adolescence

r = -0.59**

30

11-12

The individual analyses on the FM data supported the group level analysis. Neither average performance nor performance consistency improved significantly beyond 8 years of age.

8 Hz

20

• Average performance and performance consistency are independent and therefore should both be assessed when development is studied.

2

8-10

Age

r = -0.35m

10

2. For AM detection, average performance and performance consistency develop at different rates. Interestingly, a similar dissociation was found for a number of other tasks (see table below) suggesting that:

Individual Listener Analyses

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10 0

• The dissociation of development on AM and FM tasks suggests that during maturation they may be processed at least partially through distinct neural mechanisms.

17+

ns

8

0

0 8-10

Average Performance (%, adjusted for SD)

Average Performance (%, adjusted for SD) Performance Consistency (SD %, adjusted for average)

Stimuli •AM: 0.5-s white-noise modulated at 8, 64, 125 Hz •FM: 1-s 1-kHz tone modulated at 2, 20, 240 Hz

10

11-12

4

Partial correlations between average performance and age were significant, but those between performance consistency and age were not.

20

8-10

6

1 0.5

17+

The same conclusions regarding the AM data were reached when the relationship between average performance and performance consistency was taken into account at the individual level.

30

17+

ns

Age

50

11-12

1.5

Individual Listener Analyses

40

• The developmental difference between AM and FM detection can not be attributed to the assessment procedure which was shared between the two.

0

8-10

17+

• Development of AM sensitivity is an outcome of improved average performance, but not of improved consistency.

ns

1

17+

10

0 8-10

Task •Modulation detection •3-AFC oddball task administered using CAPE4 •Modulation depth adapted in a 3 down/1 up staircase •ISI = 0.5 s •3 runs of 40 trials administered for each modulation rate

•Performance consistency: within subject standard deviation (SD) of reversals

8-10

17+

240 Hz 12

ns

1.5

Performance Consistency (SD %, adjusted for average)

Participants •29 listeners with normal hearing •Adults (n = 9, age 17-27 yrs) •Children (n=20, age 8-12 yrs)

11-12

20 Hz 2

2

• Average performance on AM still develops beyond 12 years of age.

0.7

20 Hz

1.5

0.6

ns

ns

1 0.5

0.4 10 20 30 ns

0.4

1.5

1

0.5

0

240 Hz

0 0 1.5

10 20 30 ns

0.5 0 1.5

1

1

0.5

0.5

0.1 0

ns

0 10 20 30 0

Age (adjusted for SD/Average)

No •AM •Simultaneous masking (0ms)5

•Forward masking

•FM

•Simultaneous masking (200ms)5

•Intensity •Frequency

References • • • • •

0 10 20 30 0

•Backward masking5

10 20 30

0.3 0.2

Yes Yes

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20

2 Hz

p = .005

40

30

Here we investigated the development of AM and FM detection thresholds between 8 years of age and adulthood, evaluating both within-listener average performance and within-listener consistency.

Method

125 Hz 50

p = .001

40

• FM performance is mature by 8 years of age.

No

40

8-10

Furthermore, these and other developmental investigations of auditory skills have focused on a single measure of performance -- average ability -- ignoring another informative measure -performance consistency. Thus, it is not known whether the development of average performance and performance consistency follow the same time course either within a skill or across skills.

64 Hz 50

p = .001

Summary and Conclusions 1. AM detection has a longer developmental time course than FM detection.

Average Develops During Adolescence

Average (%)

8 Hz 50

Average (%)

Despite the crucial role of AM and FM cues in complex sound perception, the normal development of the ability to detect these two types of modulation has only been examined in a few investigations. From these it appears that AM detection is mature by 10 years of age1,2 whereas FM detection is mature by 8 years of age3. However, the AM studies relied on only a few (≤ 4) children per age group. In addition, for any given age group, AM and FM detection have not been, to our knowledge, studied within the same individuals.

AM Detection

Consistency (SD,%)

Introduction The ability to adequately follow modulations in amplitude (AM) and frequency (FM) is important for normal speech and language skills, and impairments in this capacity have been associated with language disorders in both children and adults.

Hall J, Grose J (1994). J. Acoust. Soc. Am., 96(1):150-4. Lorenzi C, Dumont A, Fullgrabe C (2000). J. Speech Lang. Hear. Res., 43(6), 1367-79. Sutcliffe P, Bishop D (2005). J. Exp. Child. Psychol. 91:249-70. Cowan J, Hind S, Smith P, Ferguson M, Riley A, Folkard T, Moore D (2005). Presented at the 28th ARO MWM (A). Huyck J, Wright BA (2006). J. Acoust. Soc. Am., 119:3331 (A).

Acknowledgements 10 20 30

We thank David Moore from the MRC Institute of Hearing Research for the use of CAPE, and J. Huyck and Y. Zhang S. Trosman, P. Chintamaneni, M. Mehta and M. Baese for their helpful comments. This study was supported by NIH/NIDCD.