By Vishakha Rawool,
West Virginia University, Morgantown, WV, USA.
One of the tests included in an auditory processing disorder (APD) test battery is a dichotic test. Dichotic listening refers to the ability to repeat different stimuli that are presented to right and left ears at the same time. For example, in the dichotic digits test (Musiek, 1983) the patient may hear “two, four” in one ear and at the same time hear “five, one” in the other ear. The Staggered Spondaic Words (SSW) (Katz, 1998) and the competing words (CW) test within the SCAN-C test battery (Keith, 2000) are two of the other dichotic tests that allow us to evaluate dichotic listening skills. The purpose of this case-study is to compare the results obtained from the CW and the SSW tests in a child diagnosed with a combined type of attention deficit hyperactivity disorder (ADHD).
Differences between the SSW and CW Tests
A critical difference between the CW and the SSW tests is that for the CW (directed recall version) test the patient is instructed to say the words in one ear first and then in the other ear (e.g., Say the two words you hear but say the word you hear in the right ear first). Thus, the patient is expected to exercise executive control in attending to and remembering which stimuli are to be repeated first.
Such executive control is not required during the SSW test. Instead, the patient’s attention is pulled to the right or left ear alternately by presenting a non-competing word to the right or left ear before presenting the dichotic stimuli. For example, the word “day” is presented only to the right ear and is followed by simultaneous presentations of the words “light” to the right ear and “lunch” to the left ear, which is followed by presentation of the word “time” only to the left ear. Thus, in this case for the dichotic listening conditions, the patient is more likely to repeat the word in the right ear first and then the word in the left ear, although reversals can occur. Another difference between the two tests is that in the SSW test, the patient is expected to repeat four words or two spondees after the presentation of each item whereas in the CW test the patient is expected to repeat only two words. Thus the demands on short-term memory may be greater during the SSW test compared to the CW test.
Patient Information and the APD Test Battery
The patient is a 7-year-old boy diagnosed with a combined type of ADHD. He was referred by his pediatrician to rule out an auditory processing deficit. A complete auditory processing test battery was administered to the child. The test battery included all tests in the SCAN-C test battery, the SSW test, the Spondaic Words for Masking Level Difference (MLD) Test, and the Random Gap Detection test.
The boy was attentive and cooperative throughout the session. Children with ADHD often function well in structured environments (NIMH, 2008), such as the sound-treated booth used during testing.
Tests Yielding Normal Results
Results were within the normal range for MLD, auditory figure ground (speech in noise), and filtered words tests, suggesting no adverse effects of ADHD on test performance and good binaural interaction, speech perception in noise, and spectral auditory closure skills.
Inconclusive Test Results
Results of the Random Gap Detection test suggested that the client may not have understood the task, so a temporal resolution deficit could not be ruled out.
Dichotic Test Results
SSW test results. Conventional analyses showed significant number of errors in all four test conditions, including the right non-competing, right competing, left competing, and left non-competing conditions (Table 1). In addition there was a significant ear effect with more errors in the left ear and significant order effect with more errors on the second spondee compared to the first spondee.
CW test results. The raw score for the CW test was 27/60 and the standard score was 7, suggesting performance within normal limits with a percentile rank of 16. A significant right ear advantage was apparent in the right ear first condition with a prevalence of only 5% in his age-group (Right ear 80%, left ear 13.33%) and a significant left ear advantage in the left ear (left ear 46.67%; right ear 40%) first condition with a prevalence of 15% (Table 2).
Procedure for comparing SSW and CW test results. To allow easier comparisons between the two tests, separate calculations were performed as discussed below:
- SSW is usually scored in % error while the competing words test is scored in % correct. Therefore, the SSW % error scores were converted to % correct scores.
- The norms for SSW are provided for four (Table 1) conditions: Right non-competing, right competing, left non-competing, and left competing. For this comparison, scores in only the competing conditions were considered. In addition, right ear and left ear scores were computed in both the right ear and left ear first conditions as shown in Table 2.
- For the CW test norms are provided for the total score and not separately for the right ear first versus left ear first conditions for each ear. For the current comparison right ear and left ear scores are computed separately for the right ear first and left ear first conditions for each of the tests as shown in Table 3.
Performance during the Left Ear First Tasks
Figure 1 adapted from Rawool (2014) shows performance in the left ear first condition on the two tests. As noted previously, there is a slight but significant left ear advantage on the CW with a15% prevalence in the age-matched peers.
Performance during the Right Ear First Tasks
Figure 2 adapted from Rawool (2014) shows performance in the right ear first condition on the two tests. A significant right ear advantage is apparent on the CW test with a 5% prevalence in the age-matched peers. A similar advantage is apparent for the SSW test. This figure also shows performance on the competing sentence (CS) task of the SCAN-C test battery which is a binaural separation task. During the CS test, sentences are presented simultaneously to each ear and the individual is expected to ignore the sentences in one ear and repeat only the sentences in the other ear. As shown in Figure 2, score for the attend the right ear condition (ignore left ear) is 80% and the score for attend the left ear condition (ignore the right ear) is 30%. Using Bellis (2003) norms, the right ear performance is within normal limits but the left ear performance is below the normal cutoff of 35% for 7 years old children, confirming a left ear deficit or right ear advantage.
Summary of Comparison of the dichotic test results:
In this case, simple analyses of the SSW and CW tests suggested contrary results. The conventional analysis of SSW suggests significant errors in all conditions and no right ear advantage while a simple analysis of CW test suggested results within normal limits. However, a detailed analysis (Figure 2) of the results suggests that the patient has a binaural integration deficit along with a weaker left ear. This is confirmed by an atypical right ear advantage (5% prevalence in age-matched peers) on the CW test and the significantly poor performance in the left ear in the competing sentences binaural separation task. The ‘attend the left ear and ignore the right ear condition’ during the binaural separation task appears to require inhibitory control (Hugdahl et al., 2009) to counteract the natural right ear advantage due to left hemisphere dominance (Kimura, 1961).
Note that the type of analyses performed here would be difficult if the patient showed several reversals. In the right ear first condition the patient may actually say the words in the left ear first indicating a reversal. Similarly in the left ear first conditions the patient may say the words in the right ear first.
Left Ear Advantage in the Left Ear First Condition
An atypical left ear advantage (15% prevalence in age matched peers) was apparent in the left ear first condition on the CW test. A similar slight left ear advantage in the left ear first condition was also apparent on the SSW test (Figure 1). This advantage may be a result of poor working memory. In the left ear first condition the child is trying to recall the words in the left ear first which can interfere with the later recall of the words in the right ear. This fading memory deficit is supported by significantly more errors on the second spondee compared to the first spondee on the SSW test. In addition, the child’s percentile rank was 13th on the working memory index of the Wechsler Intelligence Scale for children (4th edition) (Wechsler, 2003). The poor working memory can also exaggerate the existing left ear weakness in the right ear first task. Thus, in this case it is helpful to have confirmation of the left ear weakness during a task such as the competing sentences task which requires the child to repeat the stimuli presented to only one ear. Auditory processing deficits can lead to poor working memory as detailed in Rawool (2014).
Poor Performance in Both Ears during the Left Ear First Condition
As is apparent in Figure 3, the performance in both ears is relatively poor during the left ear first condition leading to the conclusion of significantly higher number of errors in all conditions in the SSW task. During the left ear first condition, the child has to counteract the natural right ear advantage and focus attention to the left ear. Since the natural advantage is in the right ear, pushing attention to the left ear yields a poor score in the left and the right ear. Figure 3 also shows that the average performance during each condition remains similar (around 50%) and thus normative data averaged across left and right ears in each condition are unlikely to reveal any abnormal patterns.
Recommendations for the Patient
Recommendations for this patient included further testing to assess temporal resolution and temporal patterning skills, dichotic interaural intensity difference (DIID) training to strengthen the left ear, and use of a personal FM device in the classroom to improve attention and to deliver the teacher’s speech clearly without background competition to the child’s ear (Schafer et al., 2013). The child will also benefit from training designed to improve working memory (Rapport, Orban, Kofler, & Friedman, 2013). Additional recommendations might be necessary if further testing reveals additional deficits in the temporal domain.
Overall, the results also suggest that normative data without and with reversals in percent correct scores for each ear in each of the right ear first and left ear first conditions for right handed and left handed individuals, may make it easier to compare the results of CW and SSW tests and to reveal abnormal processing patterns.
Vishakha Rawool obtained her PhD from Purdue University and completed a post-doctoral fellowship at Johns Hopkins University. She is currently a Professor in the Department of Communication Sciences & Disorders at West Virginia University and teaches several courses, including courses related to hearing conservation and auditory processing disorders. She has several publications to her credit including the textbooks Hearing Conservation in Occupational, Recreational, Educational, and Home Settings (2012, Thieme) and Auditory Processing Deficits: Assessment and Intervention (2014, Thieme, in press). She has extensive clinical experience in providing comprehensive audiological services to all populations, including infants and older adults.
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