Burkhart Fischer and Klaus Hartnegg
Brain Research Group
University of
Freiburg
email: bfischer@uni-freiburg.de
web: www.brain.uni-freiburg.de/fischer
Introduction:
Auditory information is processed at several sub cortical structures before language
comprehension takes place. Developmental deficits in language processing as well
as in reading and spelling have been attributed to auditory deficits. It seems
suitable to know more about nonlinguistic auditory processing at low levels to
see the age development and to possibly form the basis for quantitative testing
of subjects with learning problems.
Methods:
The data of 478 normal subjects aged 7 to 35 years have been collected. They performed
5 tasks challenging low level auditory discrimination in 5 domains: intensity,
frequency, gap detection, time order (monaural), and side order. The stimuli were
presented by ear phones. A small instrument controlled the tasks and collected
the data. The stimuli were white noise and sinus tones (55 dB, 1 kHz).
In each trial 2 different stimuli were presented in random sequence. The task
was to tell which was first (2-alternative forced choiced with increasing difficulty).
From trial to trial the difference was decreased in steps. The threshold was defined
by the last correct response in the first sequence of 7 trials containing 4 errors.
Other details are found in
www.brain.uni-freiburg.de/fischer/fono/method.html
Results:
The 5 variables show no correlations indicating that the tasks probe independent
sub functions of auditory processing. A considerable number of younger subjects
were unable to do the tasks even at the easiest level (low performance). Especially
the frequency discrimination and the time order tasks were difficult. However,
none of the subjects failed in all 5 tasks. The percentage of low performance
subjects decreased systematically with age. Subjects were grouped into 7 age groups
and the medians were calculated.
Fig.
1 shows the age curves indicating a development lasting up to the age of 15-20
years independently in all 5 tasks. Note the difference between time and side
order.
Discussion:
This study shows that low level auditory discrimination is still not fully developed
at the beginning of school age. A proportion of young subjects appear to be unable
to perform one or other task even at its easiest level. The development can last
up to the age of 20 years. The data of several hundred dyslexic children indicate
systematic deficits in the auditory domains tested in this study. The tasks can
be used as routine diagnostic tests and as a basis for designing tasks for daily
practice to improve those components in low level auditory processing that showed
developmental deficits.
December
2001
Prof.
Dr. Burkhart Fischer
is a neurobiophysicist at the Medical Faculty
of the University of Freiburg. His main research fields are: vision and eye movements
- development - deficits in dyslexica, ADHD, and in children with unclassified
developmental deficits. He has published more than 160 papers in international
journals. He discovered the optomotor reflex (Express Saccade) in 1983/84. He
also developed a new eye tracker "ExpressEye" for clinical application and tests
of dynamic vision "FixTest", and the low level auditory discrimination "FonoTest"
as well as the corresponding instruments for daily practice "FixTrain" and "FonoTrain".
His website is www.optom.de.
Klaus
Hartnegg
is a physicist and software specialist and member of the
Optomotor Brain Research Group of the Medical Faculty of the University of Freiburg.
He developed software for data acquisition and analysis used in this research
group and the software for controls of the test and training devices.