PERCEPTION AND CONFUSION
OF SPEECH SOUNDS BY
CHILDREN AND ADULTS WITH A
COCHLEAR IMPLANT
Arne K. Rødvik
Rikshospitalet University Hospital
Norway
Aim
A Norwegian non-word test, will be used to identify
typical confusions of consonants and vowels by
children and adults with a cochlear implant. We
expect that this study will be beneficial both for the
fitting process of the cochlear implants, and for the
work of the speech therapists post operatively.
Moreover, it may be useful for the improvement of
the speech processing algorithms of the cochlear
implants.
1
Description of the speech
perception test
• Developed at the University of Iowa in USA
and adapted to Norwegian at Rikshospitalet
• Contains two consonant confusion tests
and one vowel confusion test
• The words in the test are being read by a
25 years old woman
Description of the speech perception
test (cont.)
/! C! /
/! C! /
/bVb/
/! ! ! ! !
/! ! ! ! !
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
/! ! ! ! /
2
Method
The informants will be asked to listen to the
recorded nonwords aCa, iCi and bVb, and asked
to repeat what they hear. Their repetitions will be
recorded and transcribed phonetically. The
collected data will be arranged in confusion
matrices to find the most common and the most
uncommon speech sound confusions. The
matrices will be analyzed by counting the correct
repetitions, as well as by phonetic analysis. An
acoustic analysis of the recordings will also be
performed, in order to look at characteristic
features of the voice quality of the cochlear
implanted informants.
Test equipment and setup
• Pioneer DVD player and Sony APM-X5A loudspeakers.
• The distance between the informant and the middle point
between the loudspeakers is ca 2 meters.
• The average loudness in listening position is 65 dB (SPL).
• The words stored on the DVD are represented by bar
codes, and are played one by one by means of a bar code
reader connected to the DVD player.
• The utterances of the informants are recorded to a Sony
NZ-707 MiniDisc-player and a Sony ECM-MS907 stereo
microphone.
• The distance between the microphone and the mouth of
the informant is 50 cm.
• The testing is performed in an anechoic chamber.
3
Inclusion criteria of the informants
• Post lingually profoundly deaf adults with a
cochlear implant (CI)
• Speech understanding on IOWAsentences10 above 50%.
• Speech understanding on a test with
monosyllabic words above 50 %
• Ability to repeat nonsens words.
• Ability to pronounce all of the Norwegian
phonemes11
Briefing of the informants
Before we run the test, the informant are told that:
• The words are nonsens words
• Whether s/he is to listen for consonants or vowels
• Which sound comes before and after the
significant sound
• S/he should make a guess if unsecure of which
sound is presented
• A response must be given to all of the presented
words
4
Confusion matrices
Pilot study
A pilot study with 5 informants has been conducted9, and the
results showed that
• Manner of articulation is rarely confused
• Place of articulation is often confused
Manner of
articulation
Plosives
Frikatives
Nasals
Liquids
Place of articulation
Bilabial
Labio dental
/p/, /b/
/f/, /V/
/m/
Dental/alveolar/ Palatal
postalveolar
/t/, /d/
/s/, /S/
/ç/, /Æ/
/n/
Velar
/k/, /g/
/N/(ng-lyd)
/r/, /l/
5
Pilot study (cont.)
• There was a tendency that consonants
were more often confused in the /iCi/
combination than in the /ACA/ combination.
• Voiced and unvoiced sounds were rarely
confused
• Nasal and not nasal sounds were rarely
confused, except /l/ and /n/
• Words which resemble meaningful words
were more easily recognised than nonsens
words
Changes of the protocol from the pilot
study
• More detailed phonetic transcription
• Randomization of the informants’ responses
before transcription
• Larger number of informants
• Inclusion of children
6
Hypotheses
Based on the results of the pilot study, the following hypotheses will be
investigated further:
• The confusion of speech sounds with the same place of articulation and
different manner of articulation is more common than the confusion of speech
sounds with the same manner and different place of articulation.
• Consonants are more often confused in the iCi context than in the aCa
context.
• Nasal and oral speech sounds are seldomly confused, except /l/ and /n/.
• Nonwords which resemble real words are more easily recognized than
nonwords which do not resemble real words.
• Postlingually and prelingually deaf confuse speech sounds differently.
• The voice quality of the cochlear implanted is proportional to the ability to
discriminate between speech sounds.
• Factors that make a significant influence on the ability to recognize nonwords
are time period of using the CI, time of deafness prior to the implantation,
amount and quality of speech and listening training post operatively, type of
implant and speech processing strategy of the implant.
References
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Thanks for your attention!
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