## A retrospective study project in Mjölby
The Sensomotoric Centre in Mjölby, Sweden has
since 1987 used reflex- and visual stimulation programs and since 1990 also
specific auditory stimulation (ADT) programs with a total of some eight hundred
students (Sohlman, 2000, pg. 16). The auditory stimulation in this (and in the
other three reported programs) are based on assessment procedures comprising
hearing tests (hearing thresholds, auditory laterality and some form of
dichotic listening). The students were tested prior to and post intervention. Over a period of 3-18 months the students
listen daily for 10-15 minutes to
specially composed and recorded music tapes, where the volumes via equalizer in
1/3 octave bands are manipulated (lowered or boosted) to partly compensate for
the variation between the measured hearing thresholds and the optimum curve as
suggested by Gulick (1971) and by Tomatis (1991). In all right handed and in
the majority of left handed students, the sounds to the right ear are boosted
the most. (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 students’ hearings are controlled at
regular intervals, and new tapes based on the follow-up assessments are
recorded and handed out. ## The sample
From a file with 127 cases completed during
Jan. 1997 - April 2000 fourteen files (m: 13; f: 1) were randomly drawn. The
small sample was chosen due to expected large effect size based on earlier
pilot studies. All were right handed with a mean age of 10yr10m (9;1-13:7). One
student had dropped out before finishing the stimulation program. All students
had normal hearing according to standard hearing tests (20 dB screenings). All
students were referred from school or from parents based on tests for language
impairments, delayed reading and/or spelling. The mean stimulation period for
the reported study was 29 weeks (10 - 65). The students had been listening at
home and were supervised by their parents. ## Controls
An
age-matched control group (N=24) mean
age 10yr10m (8;3-12;9) of good readers (above the mean on teachers assessments)
were tested on dichotic listening (Hughdahl DLCV-108 NF).
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 by dichotic listening in the non-forced condition (Hughdal
DLCV-108 NF). The correlation was moderately negative (- 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 mean age of 10yrs01m (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); The mean error rate by DL-NF before the
stimulation period was for these six students 33.33 (SD=13.05). After the
stimulation period the mean error rate was 14.00 (SD= 9.24)); The mean error rate 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 (fig. 1). 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); After 19 weeks of stimulation one of these
students had no alterations in hearing curve at the 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.) It may be essential to note that in several
other clinical trials also the left ear has shown the most rapid improvements
in sensitivity later followed by improvements of sensitivity in the right ear. It
may be related to the known better myelination of the neuronal fibers 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; Thus 92.3 per cent had positive effects from
stimulation of hearing during the training period with a large effect size. Therefore it can 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= 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).
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 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
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 length of stimulation period
(r= Surprisingly enough fig. 1 shows that reduction
in errors by different individuals happens at a very similar rate during the
stimulation period (apx. Fig. 3 shows 2 x 2 audiograms from students
before and after auditory stimulation. These two students had the longest
stimulation periods 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%.
CAPD is generally not assessed by simple means
such as audiometry, binaural audiometry and dichotic listening. The reported results from the clinical work in
Mjölby indicate that assessment procedures utilizing these simple tools can
provide valuable information about a language impaired child’s auditory
difficulties and at the same time provide the necessary information for a
remedial technique where listening to specially composed and specially recorded
(manipulated) music is an essential part. |