Development and normative data for the Flemish/Dutch Matrix test
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Development And Normative
Development and normative data for the Flemish/Dutch Matrix test December 2014
Luts H.1, Jansen S. 1, Dreschler W. 2, & Wouters J. 1
1 ExpORL, Dept. Neurosciences, KU Leuven, Belgium
2 Clinical and Experimental Audiology, Academic Medical Center Amsterdam, The Netherlands
Methods
...
Development and normative data for the Flemish/Dutch Matrix test December 2014
Luts H.1, Jansen S. 1, Dreschler W. 2, & Wouters J. 1
1
ExpORL, Dept. Neurosciences, KU Leuven, Belgium
2
Clinical and Experimental Audiology, Academic Medical Center Amsterdam, The Netherlands
Methods
Speech material
The Flemish/Dutch Matrix consists of 10 names, 10 verbs, 10 numerals, 10 colors and 10 objects (see
Table 1). Within a column, all words have the same number of syllables. The verbs are all in the
present tense, and the adjectives are all colors. The occurrence of phonemes in the base matrix
closely resembles the reference distribution of phonemes in the Dutch language (Luyckx et al., 2007,
Figure 1). A professional Belgian female speaker was selected. The speech material was recorded in a
soundproof booth at the KU Leuven, Dept. Of Neurosciences, ExpORL, with an Edirol R-4 PRO
recorder and a Sennheiser HS2 headset microphone, at a 44.1 kHz sampling rate and 24 bits
resolution. A set of one hundred different sentences was recorded several times. In this set, each
word occurred 10 times, always with the coarticulation to another adjacent word. The best recording
of each sentence was selected, and these 100 sentences were equalized in rms (based on the
average root-mean-square of a complete sentence, with silence parts included). The sentences were
cut into words, preserving the coarticulation to the next word. This resulted in 500 different *.wav-
files (each containing a word with the coarticulation to the following word). Subsequently, 50 lists of
10 sentences were generated with Matlab. Each list contained all words of the base matrix and was
thus phonetically balanced. In this set of 500 sentences, each combination of a word with the
coarticulation to the following word occurred exactly 5 times. All 500 sentences were included in the
optimization measurements.
Table 1. The closed set of 50 words of the Flemish/Dutch Matrix
Name Verb Numeral Color Object
1 Jeroen heeft twee witte fietsen
2 Thomas kiest drie gele manden
3 Lucas koopt vier bruine doeken
4 Jacob zoekt vijf rode dozen
5 Sofie draagt zes blauwe kousen
6 Ellen maakt acht groene bedden
7 Johan wint tien grijze jassen
8 Sara krijgt elf zwarte pennen
9 Emma ziet twaalf paarse ringen
10 David leent veel beige boten
Noise material
To generate the stationary speech-weighted noise the long-term average speech spectrum (LTASS) of
the 500 sentences was determined. For each sentence, silence parts were removed (frames of 20 ms
with RMS < 0.001) and the spectrum was calculated with a 4096-points fast Fourier transform using a
rectangular window and without overlap. These spectra were then averaged, applying a weight
according to the length of each sentence. For this LTASS, a 2048-taps finite impulse response filter
was generated and applied on an 11 seconds long white noise. Transients at the start and the end of
the speech-shaped noise were removed to allow looping of the noise without any clicks. The average
RMS level of the noise was -27.0 dB FS.
1
, Figure 1. Phonetic distribution of the Flemish/Dutch Matrix (open triangles), compared to the mean phonetic
distribution of spoken Dutch (Luyckx et al, 2007, filled diamonds)
Subjects
For the development of the Flemish/Dutch Matrix test, 98 normal-hearing Flemish subjects were
tested. Hearing thresholds for the test ear were equal to or better than 20 dBHL for all octave
frequencies between 250 and 8000 Hz. They were all native Dutch speakers from Belgium. Fifty-two
normal-hearing adults (15 men) aged between 18 and 54 years (median age 22 years) participated in
the optimization measures. Twenty-six normal-hearing adults (4 men) between 18 and 34 years old
(mean age 21 years) participated in the selection phase. Twenty normal-hearing adults (7 men)
between 18 and 25 years old (mean age 21 years) participated in the evaluation measurements.
Test set-up
All perceptual measurements were performed using a PC running Apex 3 software (Francart et al,
2008), a high-quality 24-bit RME sound card, and Sennheiser HDA200 headphones. The speech and
noise were always presented monaurally to the subject’s best ear. The setup was calibrated with a
B&K sound level meter 2250 and a B&K artificial ear 4153. The noise started 500 ms before and
ended 500 ms after each sentence, and was a randomly selected segment from the noise file. The
noise level was always 65 dBSPL. The subjects received the base matrix on paper and were instructed
to repeat the sentences as accurate and complete as possible. They were not obliged to guess if they
were not sure. A word scoring procedure was used.
Optimization procedure
In order to reach the steepest possible slope at the SRT of the final reference psychometric curve, the
speech material of the Flemish/Dutch Matrix was further optimized according to the procedure
described by Wagener et al (2003) and Jansen et al (2012). Each subject listened to all 500 sentences
(20 lists of 25 sentences) in two separate test sessions that started with one additional training list.
The sentences were presented at 13 fixed SNRs (ranging from -20 to +4 dB in steps of 2 dB) and a
noise level of 65 dBSPL. The SRT (speech reception threshold) of each of the 500 single words was
then determined by applying a logistic regression fit to the data of all listeners together. To improve
the homogeneity of the words with regard to their intelligibility, the level of each word was now
adjusted towards the mean SRT. The level of the individual words was adjusted by maximally 6 dB.
2
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