Methods used by FonoFix
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
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.
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