Subjects: The children were recruited from primary and secondary schools in the Freiburg area. Adults were recruited from students and other volunteers. Altogether, the data from 437 subjects were collected, 243 of them were females and 194 were males. None of them had any diseases or reported problems in acquiring reading or spelling skills.
Tasks: The instrument provided 5 different tasks as described
below. All subjects were tested in 5 sessions, one for each task, in a
fixed order. Each session consisted of a sequence of trials with
stepwise increasing difficulty (lowering the difference between the two
tones). In each trial two sounds were presented one after the other.
Both sounds were slightly different in one certain aspect depending on
the task. The subjects had to press one of two keys (two alternative
forced choice task). The temporal order of the two sounds was
Intensity discrimination: Two white-noise sounds were presented binaurally with different intensity. The subjects had to press the up-key when they perceived the second sound with higher intensity (louder), or the down key when they perceived the second with lower intensity. The reference intensity was 55.0 dB(A), the starting intensity difference was 8.1 dB(A) as measured at the earphones.
Frequency discrimination: Two tones were presented binaurally with different frequencies. The subjects had to press the up key when the second tone was higher, or the down key when the second tone was lower in frequency. The reference frequency was 1000 Hz, the starting frequency difference was 100 Hz.
Gap detection: Two white noise sounds were presented to the right ear one after the other. In the middle of one of the two sounds was a short gap. The subject had to press the right key when the gap was in the second sound, or the left key when it was in the first sound. The starting gap duration was 40 ms.
Time order: Two very short tones of different frequency were presented to the right ear with varying time between them. One had a frequency of 1000 Hz and the other a frequency of 1120 Hz. The subject had to press the up key when the higher tone was second, or the down key when the lower tone was second. The starting pause duration was 300 ms.
Side order: A short white-noise click was given, one to the right and one to the left ear with a short temporal gap between them. The subject had to press the right key when the order of the tones was left-right, or the left key when the order was right-left. The starting pause duration was 300 ms.
Algorithm: The instrument increased the level of difficulty in steps after each trial. A session was terminated when the series of correct responses turned into a 50% random sequence. The difficulty of the last correct response preceding the first error in a sequence of 7 trials was used as "just noticeable difference".
Procedure: The subjects were given a verbal instruction before each task. They had the opportunity to practice each task at the easiest level until they produced 5 correct responses in a row. No feedback was given during the test session.
Data analysis: The values of threshold determined at the end of each session were pooled for each age group. Median values were calculated and plotted against age for each task and each group.