Central auditory processing disorder [(C)APD] refers to a deficit in auditory stimuli processing in nervous system that is not due to higher-order language or cognitive factors. One of the problems in children with (C)APD is spatial difficulties which have been overlooked despite their significance. Localization is an auditory ability to detect sound sources in space and can help to differentiate between the desired speech from other simultaneous sound sources. Aim of this research was investigating effects of an auditory lateralization training on speech perception in presence of noise/competing signals in children suspected to (C)APD.
In this analytical interventional study, 60 children suspected to (C)APD were selected based on multiple auditory processing assessment subtests. They were randomly divided into two groups: control (mean age 9.07) and training groups (mean age 9.00). Training program consisted of detection and pointing to sound sources delivered with interaural time differences under headphones for 12 formal sessions (6 weeks). Spatial word recognition score (WRS) and monaural selective auditory attention test (mSAAT) were used to follow the auditory lateralization training effects.
This study showed that in the training group, mSAAT score and spatial WRS in noise (
We used auditory lateralization training for 6 weeks and showed that auditory lateralization can improve speech understanding in noise significantly. The generalization of this results needs further researches.
Sound localization is one of the most important functions of auditory system in humans and other animals and is mainly achievable by using binaural cues including interaural time difference (ITD)/phase difference and interaural level difference (ILD)/intensity difference. Accurate sound localization in animals is crucial for survival (escaping from a predator, hunting a prey and finding a mate) [
Central auditory processing disorder [(C)APD] is a deficit in auditory neural processing that is not caused by higher-order language, cognitive or related factors [
It is supposed that auditory localization/lateralization training may change children' ability to use spatial clues for segregating target speech from competing signals/noise and improve their speech perception in everyday listening situations. So aim of the present research was investigating effects of an auditory lateralization training on speech perception in presence of competing signals/noise in children suspected to (C) APD. As it is difficult to diagnose children with pure (C)APD, term "suspected to (C)APD" seems more appropriate [
In this analytical interventional study, 60 children suspected to (C)APD (40 boys and 20 girls) were selected based on inclusion criteria. All inclusion criteria were same for training and control group and children who met inclusion criteria were randomly divided into two groups: 30 children in the control group (mean age 9.07±1.25 years; 10 females and 20 males) and 30 children in the training group (mean age 9.00±1.28; 10 females and 20 males). Both groups were matched in terms of sex and age. As there is not a gold standard test for (C)APD diagnosis, we selected dichotic digit test (DDT) [
Inclusion criteria for children suspected to (C)APD were as follows: normal PTA (auditory threshold less than 20 dB HL in 500 to 4,000 Hz frequency range) in both ears; symmetric hearing (PTA difference less than 5 dBHL between two ears); normal middle ear function (A type tympanogram); 85 or higher Wechsler IQ score, monolingualism (Persian language); no history of ADHD, seizures, behavioral or developmental disorders; not being on any central nervous system medications; poor academic performance; abnormal results in DDT, PPS and mSAAT. If a child had scores less than 2 standard deviations from established norms in these three tests, he/she was suspected to (C)APD.
DDT is composed of naturally spoken digits from 1 to 10 (except for number 4 in Persian language). It requires that 2 number pairs be presented simultaneously to each ear of listeners, and subjects are asked to repeat all 4 numbers regardless of order (free recall). Forty patterns are presented in total. Outcome measure is the percentage of correct responses [
PPS test reflects temporal component of auditory pattern recognition. Each item is a set of three pure tones with two different pitches, with a low-frequency tone at 880 Hz and a high-frequency tone at 1,122 Hz. The duration of every tone is 200 ms with 10-ms rise and fall time. These tones are separated by 150-ms intervals and the silence epoch between every set is 6 s. Totally 30 patterns are presented monaurally to each ear. Stimuli were presented at 55 dB SL (re: 1,000 Hz threshold). Outcome of this test is percentage of correct responses [
To evaluate speech understanding in presence of competing signals, the Persian version of mSAAT was used. This test is one of the monaural low redundancy tests and it can assess auditory figure-ground skill [
To evaluate spatial processing, auditory lateralization of monosyllabic words in white noise with zero dB SNR was used. Words were presented randomly through headphones at -90, -60, -30, zero, +30, +60, +90° azimuth (5 words were presented for each location). Test was made by Sound Forge software v8. Word recognition score (WRS) and number of auditory lateralization errors were examined for each spatial location.
Auditory lateralization training including 12 formal sessions (2 sessions in each week) was started in the training group. Each session lasted 45 minutes. A high pass and a low pass noise with 2 kHz cutoff point, with 250 milliseconds duration and 20 milliseconds rise and fall times were used. Stimuli were presented through headphones with 880, 660, 220, zero, -220, -660, -880 microseconds ITDs at 50 dB HL, and the children had to point to the perceived location of sound source [
In the training group, mSAAT and lateralization test were performed again after 12 sessions of lateralization training. For comparison and determining training effects, in the control group, mSAAT and lateralization test were also repeated after 2 months from the first evaluation.
SPSS v21 (IBM, Armonk, NY, USA) was used for statistical data analysis. In addition to descriptive analysis, covariance and Wilcoxon tests were used to show training effects and within group comparisons respectively.
Written consent was received from the parents for evaluation and auditory lateralization sessions. All tests were noninvasive. The control group also received auditory lateralization training after research. Patients' information were kept private.
750 normal children (8 to 12 years old; mean age 10.00±1.41 year) including 250 males and 500 females were selected and used for establishing normative data. The means and standard deviations (SDs) of mSAAT-Persian version, Persian version of DDT and PPS test are shown in
Covariance test showed that in the training group, the mSAAT score in right and left ear, spatial WRS in noise at -90, -60, -30, zero, +30, +60, +90° improved significantly (
Kolmogorov-Smirnov test showed that mSAAT, spatial WRS in noise and number of auditory lateralization errors at -90, -60, -30, zero, +30, +60, +90° azimuth had non-normal distribution in both training and control groups (
Children suspected to (C)APD were selected and based on our hypothesis about importance of spatial abilities in understanding speech in noise/competing signal, they were trained by using an auditory lateralization practice and finally changes in spatial WRS in noise and mSAAT score were tracked. There are few studies about spatial hearing and its relation to speech understanding in noise in children with (C)APD. Studies with similar concepts will be used for discussion.
In this study spatial WRS in noise and mSAAT score in children with (C)APD was more than 2 SDs below normal children and number of lateralization errors were more than 2 SDs higher than normal children before training. These tests can recognize the most common complaint of children with (C)APD which is understanding speech in background noise and in presence of competing signals [
After lateralization training, number of auditory lateralization errors fell down significantly in only training group. Many human and animal studies have shown that appropriate localization/lateralization training can reduce spatial errors in time. Localization/lateralization training has been used in many animal researches, blind humans, and even normal-hearing adults in virtual auditory field researches and in almost all of these researches, spatial training has been found effective [
After auditory lateralization training mSAAT and spatial WRS score showed significant improvement in only training group. The control group did not show any significant changes. Since we only used auditory lateralization training, these improvements can be attributed to lateralization training. Cameron and Dillon developed and used LiSN & Learn software (NAL, New South Wales, Australia) for remediating spatial processing disorder in children suspected to (C) APD. This software can be used at home and it is a training game. A pair of headphones is used for delivering stimuli. Child has to perceive a target word nested within a sentence that is delivered from zero degree and ignore other competing sentences that are sent from ±90° azimuth. After 120 game sessions, children with SPDs showed 10.9 dB improvements for speech reception thresholds and responses from parents, teachers, and self-reported questionnaires showed positive outcomes [
Finally it should be noted that we used auditory lateralization training for a time period of 6 weeks and showed that auditory lateralization can improve speech understanding in noise significantly. The generalization of this results needs further researches. The authors recommend other studies with higher sample size and auditory lateralization training for more extended time period. Furthermore we recommend follow up evaluations several months after completion of auditory training to see if these results are long term.
We thank our colleague Dr. Saeedeh Mehrkian who provided insight and expertise that greatly assisted the research.
Number of cases | mSAAT |
DDT | PPS | ||
---|---|---|---|---|---|
Right ear | Left ear | ||||
Normative data | 750 | 91.86 (±5.47) | 90.19 (±5.89) | 82.21 (±7.20) | 91.47 (±4.05) |
(C)APD data | 60 | 64.16 (±2.15) | 64.10 (±2.12) | 63.33 (±7.92) | 64.00 (±3.29) |
SD: standard deviation, mSAAT: monaural selective auditory attention test, DDT: dichotic digit test, PPS: pitch pattern sequence test, (C)APD: central auditory processing disorder
Number of cases | At -90˚ | At -60˚ | At -30˚ | At 0˚ | At +30˚ | At +60˚ | At +90˚ | |
---|---|---|---|---|---|---|---|---|
Number of errors | ||||||||
Normative data | 750 | 0.10 (±0.31) | 0.08 (±0.28) | 0.03 (±0.16) | 0.02 (±0.13) | 0.03 (±0.16) | 0.09 (±0.31) | 0.10 (±0.33) |
(C)APD data | 60 | 2.95 (±0.62) | 2.88 (±0.61) | 1.35 (±0.48) | 1.46 (±0.50) | 1.30 (±0.46) | 2.88 (±0.61) | 2.95 (±0.62) |
WRS in noise | ||||||||
Normative data | 750 | 99.41 (±3.37) | 99.40 (±3.25) | 99.65 (±2.61) | 100 (±0.00) | 99.47 (±3.22) | 99.36 (±3.52) | 99.25 (±3.79) |
(C)APD data | 60 | 33.00 (±9.61) | 37.33 (±6.85) | 56.00 (±9.60) | 53.33 (±10.84) | 56.00 (±8.86) | 36.66 (±8.36) | 35.00 (±8.73) |
SD: standard deviation, WRS: word recognition score, (C)APD: central auditory processing disorder
mSAAT right ear | mSAAT left ear | WRS in noise at -90˚ | WRS in noise at -60˚ | WRS in noise at -30˚ | WRS in noise at zeroº | WRS in noise at +30˚ | WRS in noise at +60˚ | WRS in noise at +90˚ | |
---|---|---|---|---|---|---|---|---|---|
Control | |||||||||
Before | 64.2 (±2.31) | 64.33 (±2.23) | 34 (±9.32) | 37.33 (±6.91) | 56 (±9.68) | 54 (±10.69) | 58 (±8.05) | 35.33 (±10.08) | 36.66 (±7.58) |
After | 64.66 (±2.18) | 63.26 (±1.99) | 33.33 (±9.58) | 35.33 (±8.60) | 53.33 (±9.58) | 55.33 (±8.60) | 34.66 (±8.99) | 51.33 (±11.36) | 34.66 (±8.99) |
Training | |||||||||
Before | 64.13 (±2.02) | 63.86 (±2.02) | 32 (±9.96) | 37.33 (±6.91) | 56 (±9.68) | 52.66 (±11.12) | 54 (±9.32) | 38 (±6.10) | 33.33 (±9.58) |
After | 81.2 (±3.66) | 81.2 (±4.15) | 45.33 (±10.41) | 44 (±9.68) | 64 (±8.13) | 67.33 (±9.80) | 66 (±9.32) | 52 (±9.96) | 46.66 (±9.58) |
SD: standard deviation, WRS: word recognition score, mSAAT: monaural selective auditory attention test
Error number at -90˚ | Error number at -60˚ | Error number -30˚ | Error number at zero˚ | Error number at +30˚ | Error number +60˚ | Error number at +90˚ | |
---|---|---|---|---|---|---|---|
Control | |||||||
Before | 3.03 (±0.55) | 2.96 (±0.61) | 1.36 (±0.49) | 1.40 (±0.49) | 1.30 (±0.46) | 3.00 (±0.58) | 3.00 (±0.52) |
After | 3.16 (±0.59) | 3.03 (±0.66) | 1.53 (±0.68) | 1.63 (±0.71) | 1.53 (±0.73) | 3.06 (±0.66) | 3.06 (±0.56) |
Training | |||||||
Before | 2.86 (±0.68) | 2.80 (±0.66) | 1.33 (±0.47) | 1.53 (±0.50) | 1.30 (±0.46) | 2.76 (±0.62) | 2.90 (±0.71) |
After | 2.46 (±0.50) | 1.76 (±0.50) | 0.53 (±0.50) | 0.46 (±0.50) | 0.63 (±0.49) | 1.76 (±0.50) | 2.40 (±0.49) |
SD: standard deviation
mSAAT right ear | mSAAT left ear | |
---|---|---|
Control | ||
Before | 64.20 (±2.31) | 64.33 (±2.23) |
After | 64.66 (±2.18) | 63.26 (±1.99) |
Training | ||
Before | 64.13 (±2.02) | 63.86 (±2.01) |
After | 81.20 (±3.66) | 81.21 (±4.15) |
SD: standard deviation, mSAAT: monaural selective auditory attention test