WHAT IS A COCHLEAR IMPLANT?
Cochlear implant (CI) is a surgically implanted electronic device that
provides a sense of sound to a person who is profoundly deaf or severely
hard of hearing.
1
The implant is surgically placed under the skin behind the ear.
The basic parts of the device include:
External:
¾ a microphone which picks up sound from the environment
¾ a speech processor which selectively filters sound to prioritize
audible speech and sends the electrical sound signals through a thin
cable to the transmitter,
¾ a transmitter, which is a coil held in position by a magnet placed
behind the external ear, and transmits the processed sound signals to
the internal device by electromagnetic induction,
2
Internal:
¾ a receiver and stimulator secured in bone beneath the skin, which
converts the signals into electric impulses and sends them through an
internal cable to electrodes
¾ an array of up to 22 electrodes wound through the cochlea, which
send the impulses to the nerves in the scala tympani and then directly
to the brain through the auditory nerve system.
3
LANGUAGE DEVELOPMENT IN EARLY IMPLANTED CI CHILDREN.
AN EXPERIMENTAL INVESTIGATION
Participants
33 prelinguistically deaf CI children ranging in age from 50 to 82 months
(mean age=63.9).
They were all born to hearing parents and were diagnosed as being deaf
in a period that varied between 2 months and 51 months of life (mean
age=14).
They received their CI at the Ospedale di Circolo di Varese between 12
and 56 months (mean age=21.7) and have been carrying it for a period
varying between 23 and 60 months (mean=42,7).
4
All children, but one, were born deaf. This single child had meningitis at 11
months. Eight of these children had a monoaural CI, 5 a binaural
sequential CI and the other 20 a binaural simultaneous.
All children followed the same rehabilitation procedure at the Ospedale di
Circolo di Varese before and after surgery and were learning Italian as
their primary language. No child was reported as having any mental deficit,
as assessed by a neuropsychological evaluation.
33 normal-hearing children (NH) recruited from the local community in the
Milano area and matched in chronological age to CI children (±3 months,
only in one case -5 months) served as control subjects (however, see
below on the issue of the identification of a proper control group).
5
Material
Three standardized language tests:
(i) the Peabody Picture Vocabulary Test (PPVT, Stella et al. 2000).
(ii) grammatical comprehension [Test di comprensione grammaticale per
bambini (TCGB, Chilosi et al., 1995)
(iii) pseudo-word repetition (PRCR-2, Cornoldi et al. 1995),
Two non standardized tasks:
(iv) Production of clitic pronouns
(v) Conversational Violation Test (Surian et al,1996).
and..
(vi) the Frog story test (Mayer, 1969).
6
Peabody Picture Vocabulary Test (PPVT)
7
The test is given verbally. No reading is required by the individual. For its
administration, the examiner presents a series of pictures to each person.
There are four pictures to a page, and each is numbered. The examiner
states a word describing one of the pictures and asks the individual to
point to or say the number of the picture that the word describes.
8
TCGB (Test di Comprensione Grammaticale per Bambini)
Età per la quale esistono misure standardizzate: dai 3 anni e mezzo
agli 8 anni.
Descrizione del test: è costituito da 76 frasi stimolo, rappresentate
graficamente, che illustrano i seguenti otto tipi principali di strutture
grammaticali:
¾
¾
¾
¾
¾
¾
¾
¾
frasi dative
passive-negative
attive-negative
locative
flessionali
attive-affermative
passive affermative
relative
9
Ogni pagina del test è costituita da quattro immagini, di cui una sola
corrispondente alla frase stimolo e le altre tre con funzione di distrattori,
poiché rappresentano contenuti simili.
Somministrazione: l’esaminatore pronuncia la frase stimolo e chiede al
bambino di indicarla; perciò al bambino non viene richiesta una risposta
verbale (quindi si tratta unicamente di un test di comprensione, la
produzione non gioca un ruolo). In presenza di risposta errata l’item deve
essere proposto una seconda volta.
Valutazione: si trascrivono nell’apposito protocollo le risposte fornite alla
prima o alla seconda presentazione. Vengono assegnati 0 punti se la
risposta è corretta, 0,5 punti se è errata solo alla prima somministrazione e
1,5 punti se è errata a entrambe le somministrazioni.
La somma del punteggi viene confrontata con la tabella di distribuzione in
percentili dei punteggi totali, in relazione all’età del bambino.
10
PSEUDO-WORD REPETITION (PRCR-2, CORNOLDI ET AL. 1995)
La prova misura la capacità di discriminazione fonemica e la memoria
immediata di fonemi e parole prive di senso. La prova é strutturata in
cinque serie di non parole: una serie di 5 monosillabi di crescente
complessità, una serie di 5 bisillabi di cinque lettere, una serie di 5 bisillabi
di sei lettere, una serie di 5 trisillabi ed una serie di 5 quadrisillabi.
-
Somministrazione. Al soggetto viene richiesto di ripetere, ad una
ad una, le sillabe e le parole senza senso presentategli subito prima
dall'esaminatore.
-
Punteggio. E' calcolato in base al numero di sillabe correttamente
ripetute (1 punto per ogni sillaba), fino ad un massimo di 60 punti. Ad
ogni errore di accento viene tolto 1 punto.
11
PRODUCTION OF CLITICS PRONOUNS
The clitic task was meant to elicit the production of direct object clitic
pronouns:
La rana mangia la mosca
La rana la mangia
Clitic pronouns are a hard object in the acquisition of Italian by a variety of
learners, possibly because their mastery requires the coordination of
phonological, morphosyntatic, syntactic and pragmatic competence.
Typically developing children start to use them around the age of 2;6-3;0
but full mastery is achieved at around 4/5 years, with children often
omitting them. Specifically language impaired children omit clitic pronouns
more often than typically developing children and for a longer period. Adult
learners of Italian as a second language find the use of clitic pronouns
hard.
12
The child was invited to tell what was happening in the picture to a puppet
manipulated by a research assistant. First, a picture was displayed to the
child and a voice described what was happening in the picture. For
example for the sentence in (2) the voice said: “In questo disegno ci sono
un bambino e una farfalla ”. Then, a second picture showing the boy
holding the butterfly in his net was presented and the voice said: “Qui il
bambino ha preso la farfalla. Puoi dire al pupazzo cosa ha fatto il bambino
alla farfalla?” An appropriate answer to this question would be: "l'ha presa”.
(1) Cosa ha fatto il bambino alla farfalla?
(2) (Il bambino) l’ha presa
Stimuli consisted of 16 situations introduced by a question like the one in
(1), each meant to elicit a sentence like the one in (2).
13
Half of the trials had the verb in the question in the present and half in the
present perfect, so as to elicit sentences with the verb either in the present
or in the present perfect. Of the 8 sentences with the present perfect, 4
required a feminine pronoun. In this case, the past participle had to display
feminine agreement with the clitic as shown in (2).
Verbs for the sentences to be elicited are very common in children’s
vocabulary and included:
asciugare pettinare lavare coprire svestire bere leggere spaventare
mangiare prendere legare aggiustare rompere sporcare svegliare
tagliare
14
COSA FA IL GATTO CON LA COCA COLA? LA BEVE
15
CONVERSATIONAL VIOLATION TEST (CVT)
This test examines pragmatic competence and is aimed at establishing
whether a maxim of conversation in the Gricean framework has been
violated. The maxim of quantity (be as informative as required by the
current situation), quality (say only what you believe is true), relation (be
relevant) and manner (be polite) were tested.
There were 10 items for the quantity maxim and 5 for each of the other
maxims for a total of 25 items.
16
This test was presented by means of a portable computer. One male
puppet appeared, who explained to the child that he was going to ask
questions to two female friends. Each of these would give an answer and
the child was asked to say which one said something silly or strange.
For example, one question was “What did you get for your birthday?” One
female puppet answered “a present” and the other “a bicycle”. The first
answer is strange, as it does not add any information that was not already
present in the question, while the second answer is informative. The child
was expected to say that the first answer was the strange one.
Another example: the puppet asks his friends what they bought in the
animal shop. One friend answers that she bought an animal, while the
other answers that she bought a cat. The first answer may be true, but it is
not informative and violates the maxim of quantity. The child should say
that it is strange.
17
FROG STORY
The frog story consists of a series of 24 pictures illustrating the story of a
child and a frog. Initially, the child is keeping his frog into a can, but while
he was sleeping the frog runs away. Then, when the child wakes up, he
looks around to search for the frog. He looks outside and with his dog he
goes into the wood. He calls her, he looks in several places, his dog
breaks a hive and all the bees chase the dog. Then, the child encounters
several animals and has some adventures. In the end he finds a free trunk
and behind it several frogs included his own. He takes it with him and say
hello to the other frogs.
18
The pictures of the Frog Story were presented one at a time to the
participants who were asked to tell what is happening from one picture to
the other. When the child did not say anything, the researcher assistant
asked questions like: what is happening here? and tried to stimulate the
child to speak.
19
20
RESULTS
21
A PRELIMINARY QUESTION
A preliminary question is which type of control is more appropriate for CI
children. NH children of the same chronological age may not be an optimal
control since they have been exposed to language for a longer time.
Another control group might be NH children of the same chronological age
as the length of CI use of IC children. This control group may be less than
optimal for a different reason, since CI children cannot be assimilated to
younger children, as they are chronologically older and cognitively more
skilled.
Since both control groups have advantages and disadvantages, when
possible, comparison was made with both, when possible.
22
CI CHILDREN COMPARED WITH CHILDREN OF THE SAME
CHRONOLOGICAL AGE
CI children obtained lower scores than NH on all standardized tests (TCGB
PPVT and non-word repetition) but the difference between the two groups
is less marked in the non-word repetition task.
In order to have an approximate measure of the delay in the TCGB and
PPVT, we determined the age at which the raw scores obtained by the CI
children corresponded to the mean then we subtracted that age from the
chronological age. On average, CI were 15 months behind their
chronological age on the TCGB and 11 months on the PPVT.
23
2
1
0
SCORE AT TCGB
-1
-2
-3
-4
-5
-6
-7
-8
IC
CC
Median value
25%-75%
Interv. Non-Outlier
Outlier
GROUP
24
2
1
0
SCORES AT PEABODY
-1
-2
-3
-4
-5
-6
-7
-8
-9
IC
CC
Median value
25%-75%
Interv. Non-Outlier
Outlier
GROUPS
25
CI CHILDREN COMPARED WITH CHILDREN OF THE SAME
CHRONOLOGICAL AGE AS THE LENGTH OF CI USE
Next, we examined the outcomes in the PPVT and in the TCGB taking into
account the age of the implant, that is, we assigned standard scores at the
PPVT and TCGB considering the length of CI use as their age.
For the Peadoby, this was possible for 12 children. Of these, 5 were below
the 25° percentile, 5 were between the 25° and 50° percentile and 2 were
above the 50°.
For the TCGB, this analysis was possible for 17 children. For this subset,
we found that 5 children were between the 25° and the 50° percentile and
12 were above the 50°.
In other words, with few exception at the PPVT, their performance was well
within normal range when their age of CI use was considered.
26
CORRELATION AMONG THE THREE STANDARDIZED TESTS
The TCGB and PPVT scores were positively correlated in CI children even
when chronological age was partialled out.
TCGB and PPVT did not correlate in NH children, if chronological age was
partialled out.
In CI children, but not in NH children, scores at TCGB and Nonword
repetition were also correlated.
27
COMMENT ON THE CORRELATION
The correlation between TCGB and PPVT replicated previous finding and
may reflect the fact that for comprehending grammatical structures one
needs to know the words. At the same time, to discover the meaning of
unknown words, one needs to be acquainted with the syntactic structures
in which these words are inserted.
In the present study, this correlation was not found in NH children, possibly
because this correlation is typical in the first years of the linguistic
development and our NH were already older.
28
RESULTS, CLITICS
There was an effect of group indicating that NH children tend to produce
more clitics than CI.
29
30
RESULTS, CLITICS
A survey of the literature on clitic production in Italian showed that CI
children produce more or less the same proportion of clitic produced by 3
year olds, that is, of children two years younger.
Next, only for CI children we examined whether there was a correlation
between the use of clitics, on the one hand, and age of implantation,
duration of CI use and chronological age, on the other. Only age at
implantation significantly predicts the accuracy in clitics production.
CI children produce past participle agreement less that NH children, when
this is required.
CI children provide agreement on the past participle in the 69% of the
cases, while NH children in 89%.
31
RESULTS, CONVERSATIONAL VIOLATION TEST
As two CI children did not complete the CVT, they were not included in this
analysis, which is therefore based on the responses of 31 CI and 31
matched NH children.
32
33
In the CVT, CI children overall obtained slightly lower scores than NH
children, but both groups were similar in responding less accurately to the
quantity maxim than to the other maxims.
The analysis of these data revealed that neither age at implantation nor
duration of implant use nor chronological age significantly predicted the
accuracy in the CVT.
34
RESULTS, FROG STORY
Discourse level: total number of words and total number of utterances
were analysed. We found a significant effect of group for total number of
words with CI children using less words than NH children.
No effect was found for total number of utterances. As total number of
words is taken to be an index of productivity, this means that CI children
are less productive than NH children.
35
Vocabulary: We found an effect of group for the number of different words,
for number of different nouns, different verbs, but not for number of
different function words. When there was a difference, the number of
different items was higher in the transcripts of NH than of CI children.
Sentence level. Mean length of utterances (MLU) did not differ between
the two groups and is correlated with chronological age in CI children and
in NH children.
36
COMMENT ON AGE OF IMPLANTATION
We did not find any effect of age of implantation on most of the tasks when
chronological age and length of implant use were partialled out.
Based on what we know from the literature on CI, this may not be
surprising. Age effects have been generally reported in studies with wider
age range of implantation. For example, children implanted before 5-6
years of age are reported to have better performance than children
implanted after this age. It has also been reported that children implanted
under age 3 perform better than children implanted between 3 and 5.
It has been found that for speech perception the optimal age of
implantation cut-off was 4;4 and for more complex tasks, such as those of
spoken word recognition the optimal split was even 8;4.
37
Thus, the general picture that seems to emerge is that children who benefit
from a CI under 3 years outperform those receiving their CI over 6 years.
Given these findings, the lack of an age of implantation effect in our
standardized tests is expected, as the mean age of implantation of our
children was 1;9 and only 3 children of our sample were implanted after 3
years.
38
EFFECTS OF AGE OF IMPLANTATION IN THE PRODUCTION OF
CLITICS
However, we did find an effect of age of implantation in the production of
clitics, with performance on this task improved with an earlier age of
implantation.
This result is in line with the finding in the second language literature that
there are multiple sensitive periods.
These results complement the tentative findings that CI are about one year
behind NH children in performance on the TCGB and PPVT, but two years
on clitic production.
The finding that there are multiple-sensitive periods is important. For
clinical purposes and rehabilitation, this finding informs us about areas that
require sustained intervention, as a function of the age of implantation.
39
TENTATIVE CONCLUSIONS ON A COMPLEX ISSUE
The issue of cochlear implantation of children is very complex and
scientific research can only contribute evidence to better inform the people
involved in the decision.
However, same tentative conclusions can be drawn:
40
¾ First, for most children IC is a useful tool, since their linguistic
behaviour in the spoken language is delayed with respect to NH
children but not dramatically so.
¾ Second, IC children are still hearing-impaired and cannot be
assimilated to NH children.
¾ Third, this study (and all the others that compare IC and NH
children) should be complemented with studies that compare IC
children with deaf children with no IC but have a similar speech-therapy
path, in order to disentangle IC effects and speech-therapy effects.
41
¾ Last but not least, there are some outliers who do not seem to
benefit much from IC. This is shown for example by the TCGB
performance:
2
1
0
SCORE AT TCGB
-1
-2
-3
-4
-5
-6
-7
-8
IC
CC
Median value
25%-75%
Interv. Non-Outlier
Outlier
GROUP
42
The children who are outliers risk to remain without sufficiently developed
language skills and, since they did not have any mental deficit, this
potential damage is to be attributed to the choice of not expose them to
sign language.
If these children had access to sign language in addition to IC, they would
be saved from this dangerous situation.
43
So, IC is an important tool and it is very useful in many cases. But it does
not cancel deafness and in a few cases it fails. For this reason, it seems
unwise to consider it as an alternative to sign language exposure.
44