The child directed speech of 20 English-speaking mothers was analysed for Mean Length of Utterance (MLU) and the frequency distribution of morphemes during play based interactions with their children who use cochlear implants

1. Analysis of maternal morphemes:
Input provided to children using cochlear implants
Shani Dettman1,2, Melina Ramp1, Colleen Holt1, Richard Dowell1,2,3, Denise Courtenay3
The University of Melbourne, Department of Otolaryngology, 2 The HEARing Cooperative Research Centre, 3Royal Victorian Eye and Ear Hospital
Aims of the Study. Very few studies have attempted to document the full range of linguistic expressions and constructions that children with normal hearing and
children with significant hearing loss have exposure to in their daily lives. This study investigated the length of input that parents used when talking to their children with
significant hearing loss, which enabled comparisons to be made with existing data for hearing children. It was hypothesized that the length of MLU would be fine-tuned to
the child’s chronological age. Secondly, this study provided a detailed description of the types and prevalence of morphemes that were embedded in the parental
language directed to the child.
The nature and prevalence of linguistic forms provided by the
mother is of considerable interest to clinicians working with children who have significant hearing loss.
Clinicians currently guide and coach parents to provide the best possible language input and language
models to the child, but understanding whether parents should be encouraged to use single words, whole
phrases, or more enriched discourse input is unproven at this time.
…to understand the nature of the relationship
between maternal input ‘IN’ and the child’s language
acquisition and ‘OUTPUT’
MLU Results
The average maternal MLUm and MLUw was 3.51 and 3.02 respectively, and
ranged from 1.26 to 8.74 for morphemes and 1.24 to 6.94 for words. Overall, parents did increase the
length of their MLUm (red triangles) and MLUw (black squares) in line with the child’s age (Figure 2).
There was a significant correlation between MLUm and age at sample (r=0.501, p<0.001) and duration
post CI (r=0.664, p<0.001) and a significant correlation between MLUw and age at sample (r=0.509,
p<0.001) and duration post CI (r=0.544, p<0.001).
9
Maternal MLU
Background to this study
For young hearing children who are learning language, the literature suggests that parents use modified
linguistic input such as shorter utterances (Phillips, 1973; Snow, 1972), fewer broken or run on
sentences, less complex but well formed grammatically correct sentences, and approximately 50% of
utterances are single words or short declaratives (Owens, 1992, p. 233). These simplifications in the
parent’s input appear to support vocabulary development and the acquisition of receptive and expressive
language. Cross (1977) did not find that parental input was always fine-tuned to the child’s linguistic
abilities and demonstrated low correlations between some variables under study. Overall, however,
results suggested a relationship between parental discourse, referential and syntactic features with the
child’s receptive skills, ability to get the message across, age, vocabulary (type-token ratio), and
measures of utterance length (longest utterance and mean). Thus, the parents of the infants with normal
hearing in Cross’ (1977) study appeared to be altering many facets of their input at different times.
Parental MLU appears to be a good match to the child’s linguistic abilities and varies according to the
language used and the age of the listener. The MLU results from a range of studies investigating input to
children with normal hearing and normal language are charted against the child participants’
chronological age in Figure 1. Results suggest a longer maternal input length during the neonatal period
(Penman et al., 1983; Phillips, 1973) while the child has the opportunity to listen to his/her native
language. Subsequent to this, we see a low or falling maternal MLU in the child’s first year of life prior to
the emergence of the child’s first words (Murray, Johnson & Peters, 1990), followed by a gradual increase
in MLU with each child chronological year (Cramblit & Siegel, 1977; Cross, 1977; Kaye, 1980; Lasky &
Klopp, 1982; Lord, 1975, cited in Owens, 1992; Newport, Gleitman & Gleitman, 1977; Seewald &
Brackett, 1984).
6
MLU
3
0
1
2
3
4
5
6
7
8
Chronological Age (years)
Figure 2. Parental MLU in morphemes (red triangles) and MLU in words (black squares)
N=20 children with significant hearing loss using cochlear implants.
There was a wide variation in maternal MLUm and MLUw to children with significant hearing loss
(Figure 2) in comparison to the averages for parental input to children with normal hearing (Figure 1).
Some mothers persisted with shorter MLU to their 3 and 4 year olds, as if they were speaking to toddlers.
Importantly, there was an absence of longer maternal input early in the child’s development. Some
parents reduced input to single words in a ‘teaching’ style of interaction. The authors suggest that parents
were unaware of the importance of exposing the child to the full rich character of the language or were
confused whether to fine-tune their MLU to the child’s hearing age, chronological age or linguistic ability.
Seewald and Bracket (1991) suggested that parents of children with hearing loss may believe the
common and naïve view of language learning; that it occurs in a ‘bottom-up’ rather than ‘top down’
fashion. Parents who perceive themselves in this teaching role may reflect this in their style of
interacting, and may provide far more language at the word level rather than the phrase level. We
observed (Figure 3, below) that children only had the opportunity to hear numerous examples of bound
morphemes (20 or more bound morphemes in a 50 utterance sample) once the parental MLUm
exceeded 3 or 4.
Bound Morpheme Types
The
morphemes found in the present study that were
also described by Brown (1973) are on the left of
Figure 4, below (e.g. -ing, plural -s, irregular
past tense, possessive –‘s, regular past tense
-ed). Other bound morphemes, not described by
Brown, continue from left to right in no particular
order. The following were frequently heard by
the children;
• contracted copula BE e.g. that’s, he’s
• contracted modal auxiliary will, e.g. she’ll
• regular plural -s e.g. cats,
• present progressive Ving form e.g. jumping
In contrast, there were infrequent opportunities
for the children to hear;
• irregular plurals e.g. mouse/mice
• comparatives e.g. big-bigger
• superlatives e.g. biggest
100
80
60
40
20
0
0
2
3
4
6
8
10
Maternal MLU morphemes
Figure 3. Raw score difference between
bound morpheme and word total.
child first
words
0
25
8
20
Chronological Age (years)
dettmans@unimelb.edu.au
www.hearingcrc.org
creating sound value
unanalysed
diminutive
other prefix/suffix
quantifier
catenative
intensifier
preposition (compound)
suffix - superlative - est, st
-er - comparative -er, r
-er - person's name/job
adverb -ly
negative - contracted
contracted us
0
adjective -y, ly
5
irregular plural
Twenty children who received a cochlear implant before 4 years of
age, were recorded in play for over 10 minutes with their mothers pre- and post-implant (mean age at
sample 2.74 yrs, range 1.04 to 7.70, SD 1.10). All maternal input was orthographically transcribed and
analysed. Previous literature had used Browns (1973) 14 morphemes which is a simplified list of just
some of the morphemes used in everyday speech. In order to complete this analysis, the authors
developed two tools; a definition of the types of morphemes in Australian English and an alphabetical
glossary to aid coding. The mean length of utterance in morphemes (MLUm) and words (MLUw) from
50 consecutive utterances, from 175 samples was calculated. Individual bound morphemes were
defined and totalled for each sample. The raw score total of each bound morpheme type was expressed
as a percentage of all bound morphemes to derive the prevalence.
10
yours , his, hers, theirs, ours
Methods and Materials
15
-en
Figure 1. Parental MLU to children with normal hearing. Each black box represents mean MLU results.
%
irregular 3rd person
7
contracted aux
6
contracted copula
5
regular past -ed
4
regular 3rd person -s
3
irregular past
2
possessive -s
1
-ing
0
regular plural -s
Speaker's MLU
9
6
0
R a w S c o r e - d iffe r e n c e
b e tw e e n w o r d a n d b o u n d
m o rp h e m e s c o re s
One measure of linguistic complexity is the mean length of utterances in ‘morphemes’ (MLUm). As the
child learns language, he/she comes to understand that some words are made up of smaller functional
parts. These smaller units of meaning are called morphemes and include: unbound morphemes (we
refer to as words) consisting of sole morphemes (simple content words) such as ball, walk, car, function
and social words such as no, a, to, you, and bound morphemes such as inflectional and derivational
bound morphemes e.g. prefixes/suffixes or grammatical markers such as im-, dis-, possessive –s, and
past tense –ed. Brown (1973) suggested that a child acquires these meaningful units in a typical order
and there is some debate in the literature whether their order of acquisition is related to the parental input
frequency, parental ‘rough-’ or ‘fine-’ tuning or due to other factors.
Deafness Foundation
compound word
1
Figure 4. Prevalence of each bound morpheme type expressed as a percentage of all bound morphemes,
across 175 samples from N=20 children.
Conclusions A social interactionist account of language acquisition would suggest that maternal language input has important facilitatory effects on child language
development. This study has determined that for some cases, maternal MLU to children with significant hearing loss may be shorter than MLU in speech directed to hearing
children. Although mothers in this study did increase MLU over time in line with the child’s chronological development, important exposure to particular morphemes appeared to
be lacking. Infrequently heard bound morphemes are the same morphemes for which children with significant hearing loss typically demonstrate poor understanding and
expression, suggesting that specific training is required.
Acknowledgements to the patients, speech pathologists, audiologists , surgeons and administrative staff at the Cochlear Implant Clinic, RVEEH, Melbourne, Australia.