Research

The Sensomotoric Centre in Mjölby, Sweden has used reflex- and visual stimulation programs since 1987 and specific auditory stimulation (Johansen IAS ) programs since 1990, with a total of some 800 students (Sohlman, 2000, pg. 16).

The auditory stimulation in this (and in the other three reported programs) is based on assessment procedures comprising hearing tests (hearing thresholds, auditory laterality and some form of dichotic listening). The students are tested prior to and following intervention.

The students listen to specially composed and recorded music CDs for 10-15 minutes daily over a period of 3-18 months. Volume is manipulated (lowered or boosted) through an equalizer in 1/3 octave bands to compensate in part for the variation between the measured hearing thresholds and the optimum curve as suggested by Gulick (1971) and by Tomatis (1991). The sounds entering the right ear are boosted more than those entering the left ear for all right handed and the majority of left handed students. The students’ hearing is retested at regular intervals, following which a new CD based on the follow-up assessment is recorded.

(The music has been specially made for this purpose by the Danish composer Bent-Peder Holbech and covers the frequency range 100 Hz to 16000 Hz).

The sample

Fourteen files (m: 13; f: 1) were randomly drawn from 127 cases who completed the programme between January 1997 and April 2000. The small sample was chosen due to expected large effect size based on earlier pilot studies. All the individuals were right handed with a mean age of 10yr 10m (9;1-13:7). One student did not complete the stimulation program. All students had normal hearing according to standard hearing tests (20 dB screenings). All students were referred by their school or by their parents following tests for language impairment, delayed reading and/or spelling. The mean stimulation period for the reported study was 29 weeks (10 – 65 weeks). The students listened at home and were supervised by their parents.

Controls

An age-matched control group (N=24) mean age 10yr 10m (8;3-12;9) of good readers (above the mean on teachers’ assessments) were tested on dichotic listening (Hughdahl DLCV-108 NF).

Results

1) The total variation (sum) in dB at eleven frequencies between the measured hearing thresholds for both ears and the optimum hearing curve was calculated for each individual and correlated with the number of errors on dichotic listening in the non-forced condition (Hughdal DLCV-108 NF). The correlation was moderately negative (-.49).

This may indicate that initially a slight to moderate variation between the actual hearing and the optimum hearing in some individuals is more damaging to auditory acuity than a more profound variation approaching a small hearing loss or hypersensitivity.

2) Files from six of the thirteen students had enough data to deal with questions 2, 3 and 4. These six students were all right-handed males with a mean age of 10yrs 01m (9;10-10;04).

The mean variation from the optimum curve for the six hearing curves (R + L) before stimulation was 205.00 (SD=54.16). After stimulation the mean variation from the optimum curve was found to be 122.50 (SD=39.44); d  (effect size) > .80.  (According to Cohen (1988) a d above .80 is a large effect size).

The mean error rate for these six students as measured by DL-NF was 33.33 (SD=13.05) prior to the stimulation period. Following the stimulation period the mean error rate was 14.00 (SD= 9.24)); d >.80.

The mean error rate as measured by DL-NF for the 24 age matched controls (good readers) was 13.50 (SD=6.13). Thus the difference in mean error rate between the controls and the research sample after intervention was not significant.

For the thirteen students who completed the stimulation period the mean variation from the optimum curve was reduced from 220.38 (SD=75.77) to 143.46 (SD=77.12); d >.80.

After 19 weeks of stimulation one of these students showed no alteration in the hearing curve of his right ear (variation from the optimum curve before and after was 230, which appeared to be the largest variation in the sample). Variation in his left ear improved from 210 to 155 (reduction in variation between curves.)

In several other clinical trials the left ear has shown the most rapid improvements in sensitivity, followed later by improvements of sensitivity in the right ear. This may be related to the known better myelination of the neuronal fibres in the right hemisphere and to the known earlier maturation of the right hemisphere (Korpilahti 1996).

The remaining twelve students had a mean variation from the optimum curve (right ear only) of 87.92 (SD=15.61) before the stimulation period and of 57.08 (SD=18.31) after stimulation; d >.80.

Thus 92.3 per cent showed positive effects as a result of stimulation of their hearing during the training period with a large effect size.  t test for dependent means (repeated measures design): t(11)= –12.210; p<.01, one tailed.

It can therefore be concluded that specific auditory stimulation has an effect on hearing sensitivity. (Generally sensitivity is reduced in the low frequency range (< 1000 Hz) and increased in the high frequency range (> 1000 Hz)).

3) For the six students the reduction in total variation (R + L) between the actual hearing curves and the optimum hearing curve correlated with reduction in errors by DL-NF at r =.19. This is a minor correlation, but contrary to the suggestion that the variation between the actual hearing curves and the optimum curve is negatively correlated with errors at DL-NF and thus with hearing sensitivity.

Looking at the right ears only in these six students it was found that the mean variation between the actual and the optimum hearing curve was reduced from 88.33 (SD=15.72) to 57.50 (SD=20.56).  d >.80.

The correlation between the reduction in variation between the actual hearing curves for the right ears only and the optimum curve and the reduction in errors by DL-NF was found to be .68.

Therefore it can be concluded that reduction in variation between the actual hearing curve and the optimum hearing curve for the right ear alone (altered sensitivity) after specific auditory stimulation (Johansen IAS) can lead to improved auditory acuity.

4) For the six students with a complete set of filed data the stimulation periods varied from 21 weeks to 65 weeks. The reduction in error rate by DL-NF correlated with the length of stimulation period (r = .86) – fig.

In this study it was shown that the reduction in errors in different individuals happens at a very similar rate during the stimulation period (apx. .5 pct/week). However, due to the small number of students this must be interpreted with caution.Audiograms from two students who had the longest stimulation periods students before and after auditory stimulation show that . These and the largest reduction in error rates by DL-NF.

Student AB: The variation between the actual hearing curve for the right ear and the optimum curve decreased from 65 to 35. Reduction in error rate by DL-NF: From 58% to 31%.

Student CD: The variation between the actual hearing curve for the right ear and the optimum curve decreased from 80 to 30. Reduction in error rate by DL-NF: From 42% to 11%.