Research into Phonological Mean Length of Utterance (pMLU)

Specific language impairment (SLI) is a disorder defined by exclusion. Children with SLI exhibit language difficulties in the absence of other factors, such as hearing loss, mental impairment, physical impairment, emotional disturbance, or environmental deprivation (Bishop, 1992a, 1992b; Lubert, 1981). Children with SLI have difficulty acquiring one or more of the components of language, i.e. form (phonology, morphology, and syntax), content (semantics), and use (pragmatics). The field of phonological acquisition has made extensive efforts to measure its development through normative studies (Templin, 1957; Olmstead, 1971) and articulation tests (Hodsen& Paden, 1991). Earlier, the research focus was on correctness of consonants as well as the analysis of segments in general. Recently the whole word complexity has been stressed (Masterson &Kamhi, 1992, Ingram, 2002). One such measure is the Phonological mean length of utterance (pMLU). It is a whole word measure for measuring phonological proficiency (Ingram,2002). It measures the length of a child’s words and the number of correct consonants. The pMLU for a speech sample is calculated by: (1) counting the number of segments (consonants and vowels) in each word as produced by the child; (2) counting the number of consonants produced in each word that the child produced accurately; (3) summing these two numbers; (4) totaling these sums; and (5) dividing this total by the total number of words in the sample. pMLU quantifies development of phonology and focuses on the children’s whole-word productions instead of specific segments. Ingram demonstrates the value of the pMLU measure by applying it wide range of contexts.

NEED FOR THE STUDY

Although pMLU has been addressed in normal as well as phonological disorders and cochlear implanted children, the same is not focussed on children with SLI. Since PMLU is a whole word measure, problems in phonology and morphosyntax are expected to reduce the score. Hence PMLU can be used to investigate the difficulties if any in phonology and morphosyntax of children with SLI. Hence the present study was planned.

AIM OF THE STUDY: To compare the pMLU of children with SLI in comparison with typically developing Kannada speaking children.

METHOD: This study followed a case control design. Participants were divided into 2 groups. Clinical group comprised of six individuals (5 males & 1 female) with SLI in the age range of 4 to 6 years. The diagnosis of SLI was done on the basis of Leonards exclusionary criteria and the informal assessment of morpho-syntax by the primary investigator. The control group comprised of age matched 30 children out of which 15 were males and 15 females. Exclusion criteria considered were speech, language, hearing and neurological problems. A minimum of 50 spontaneous speech utterances were elicited from each child for a duration of 30 to 40 minutes which was audio recorded using SONY recorder.

The children’s utterances were narrow transcribed and pMLU was calculated for each word produced by the child. The sum of each word in all the utterances were totalled and divided by the number of words produced by the child to obtain the pMLU scores. pMLU was calculated for all the children in both the groups. Mann Whitney U test was administered to find out the significant differences between the means of both the groups.

RESULTS: The results of the Mann Whitney U Test revealed a statistically significant difference between the means of pMLU scores across the group at p< 0.05 indicating that children with SLI obtained poorer scores in pMLU than the age matched peers.

DISCUSSION: pMLU is a whole-word measure for phonological development. The results of the present study revealed that the pMLU scores for the children with SLI were lower in comparison to children with normal language development. This could be attributed to the increased number of incorrect consonants in the speech of clinical group when compared to the control group.

The decrease in pMLU scores in the clinical group could also be due to the deficit in the use of morphosyntax as these children were having morphosyntactic errors. This in turn suggests that children with SLI are inferior in the acquisition of segments and in their whole-word phonological proficiency to typically developing children. As this pMLU measure includes the number of segments in a word, pMLU can be used to indicate morphosyntactic abnormalities in children with SLI. This tool can also serve as an aid for monitoring the progress of a child when assessed pre and post therapeutically.

CONCLUSION: The present study investigated pMLU in children with SLI in the age range of 4-6 years. The results revealed that children with SLI are inferior in the acquisition of segments including morphemes as well as in their whole-word phonological proficiency than the typically developing children. Hence, pMLU measure could be regarded as a yardstick for phonological and morphosyntactic development in children with SLI.

INTRODUCTION:

SLI is a disorder defined by exclusion. Children with SLI exhibit language difficulties in the absence of other factors, such as hearing loss, mental impairment, physical impairment, emotional disturbance, or environmental deprivation (Bishop, 1992a, 1992b; Lubert, 1981). Specific language impairment (SLI) has been estimated to affect approximately 7 percent of children (Leonard, 1998; Tomblin et al., 1997) and to persist into adolescence (Aram et al., 1984; Beitchman et al., 1996; Stothard et al., 1998;Johnson et al., 1999). Children with SLI have difficulty acquiring one or more of the components of language, i.e. form (phonology, morphology, and syntax), content (semantics), and use (pragmatics).

However, as a group they show disproportionate difficulty with some areas, performing worse than typically developing children matched on vocabulary level or mean length of utterance. Several authors (eg, Leonard et al.,1992; Rice et al., 1995; Rice and Wexler, 1996; Oetting and Horohov, 1997; van der Lely and Ullman, 2001) observe that this is particularly the case in the area of verb morphology and it has also been reported in some areas of syntax, including the comprehension of passive sentences (Bishop, 1979; van der Lely and Harris, 1990; van der Lely, 1996) and formation of wh-questions (Leonard 1995; van der Lely and Battell, 2003).

The field of phonological acquisition has made extensive efforts to measure its development through normative studies (Templin, 1957; Olmstead, 1971) and articulation tests (Hodsen & Paden, 1991). Earlier studies have focused on correctness of consonants as well as the analysis of segments in general. Recent studies have focused on the whole word complexity (Masterson &Kamhi, 1992, Ingram, 2002). One such measure is the Phonological mean length of utterance (PMLU). It is a whole word measure for measuring phonological proficiency (Ingram, 2002). It measures the length of a child’s words and the number of correct consonants. The PMLU for a speech sample is calculated by: (1) counting the number of segments (consonants and vowels) in each word as produced by the child; (2) counting the number of consonants produced in each word that the child produced accurately; (3) summing these two numbers; (4) totaling these sums; and (5) dividing this total by the total number of words in the sample. PMLU quantifies development of phonology and focuses on the children’s whole-word productions instead of specific segments. Ingram demonstrates the value of the PMLU measure by applying it in a wide range of contexts. These include a comparison of monolingual children, a comparison across languages, and the diagnosis of impairment or delay. Very few studies have addressed the PMLU in different languages. One such study is by Ingram (2002) who proposed preliminary PMLU stages, reflecting the possible level of development in English speaking children which are as follows.

Helin, Makkonen & Kunnari (2006) reported that PMLU was much higher in Finnish speaking children than those reported for children acquiring English. Balasubramanium & bhat (2009) reported the same in kannada speaking typically developing children. Other studies have focused PMLU on the disordered population. Schauwers, Taelman, Gillis & Govierts (2005) reported lower PMLU scores in children with cochlear implant than age matched typically developing peers and they also concluded that the earlier implanted children were more proficient than the later implanted children. Prasad, Hossabetu, Balasubramanium & Bhat (2010) studied phonological mean length of utterance in children with phonological disorder and they reported, children with phonological disorder are inferior in the acquisition of segments as well as in their whole-word phonological proficiency than the typically developing children.

NEED FOR THE STUDY:

Although pMLU has been addressed in normal as well as phonological disorders and cochlear implanted children, the same is not focussed on children with SLI. Since PMLU is a whole word measure, problems in phonology and morphosyntax are expected to reduce the score. Hence PMLU was used to investigate the difficulties if any in phonology and morphosyntax of children with SLI. Hence the present study was attempted in this direction.

AIM OF THE STUDY: To compare the pMLU of children with SLI in comparison with typically developing Kannada speaking children.

METHOD

Participants

The study followed a case control design. Participants were divided into 2 groups i-e the control group and clinical group. Clinical group comprised of six individuals (5 males & 1female) with specific language impairment in the age range of 3 to 6 years. The control group comprised of age matched 30 children out of which 15 were males and 15 females. The diagnosis of specific language impairment was done on the basis of Leonard’s exclusionary criteria and the informal assessment of morpho-syntax by the primary investigator. The exclusion criteria for the controls were the history of speech, language, neurological and hearing problems.

Procedure

In order to assess the phonological mean length of utterance, spontaneous speech utterances were elicited from each child for duration of 30 to 40 minutes. Samples consisted of minimum of 50 utterances. The experimenter served as a conversational partner and introduced the child to age appropriate toys and questions. The samples were obtained in an informal setting within the school premises for the control group and in the therapy premises for the clinical group. Audio recording was done using a portable Sony Recorder in a relatively quiet environment. The words were accepted for analysis according to the rules suggested by Ingram and Ingram which are mentioned in the table mentioned in appendix. The children’s production of utterances was narrow transcribed and PMLU was calculated for each child. For each word, the number of segments (consonants and vowels) as produced by the child was counted and summed with the number of correct consonants in a word. The sum of each word in all the utterances of a single subject were totaled and divided by the number of words produced by the child to obtain the PMLU scores. Mann Whitney U test was administered to find out the significant differences between the means of both the groups.

RESULTS: The results of the Mann Whitney U Test revealed a statistically significant difference between the means of pMLU scores across the group at p< 0.05 indicating that children with SLI obtained poorer scores in pMLU than the age matched peers.

Group Statistics

DISCUSSION:

pMLU is a whole-word measure for phonological development and is used to investigate the difficulties if any in phonology and morphosyntax. The present study compared the pMLU of children with SLI in comparison with typically developing Kannada speaking children. The results of the study revealed that the pMLU scores for the children with SLI were lower in comparison to children with normal language development. This could be attributed to the increased number of incorrect consonants in the speech of clinical group when compared to the control group as these children were neutralizing the sound contrasts and also exhibiting syllable reduction strategies. Whether it is syllable structure reduction or sound contrast neutralization, it reduces the overall pMLU score. As children with SLI are inferior in the acquisition of segments as well as in their whole-word phonological proficiency than the typically developing children, phonological errors are reflected in the pMLU scores. Hence it can be concluded that pMLU reflects on the phonological errors.

The results of the present study are in consonance with findings that the developments of phonology in children with SLI are much later in comparison to typically developing children (Balasbramanium & Bhat, 2009) and also that children with phonological disorder are inferior in the acquisition of segments as well as in their whole-word phonological proficiency than the typically developing children (Prasad, Hossabetu, Balasubramanium & Bhat 2010). Hence, pMLU can be used as an assessment tool for children with SLI as this provides an objective assessment tool in the evaluation process.

The decrease in pMLU scores in the clinical group could also be due to the deficit in the use of morphosyntax as these children were having morphosyntactic errors. This in turn suggests that children with SLI are inferior in the acquisition of morphemic segments when compared to typically developing children. As this pMLU measure includes the number of segments in a word, pMLU can be used to indicate morphosyntactic abnormalities in children with SLI. This tool can also serve as an aid for monitoring the progress of a child when assessed pre and post therapeutically.

CONCLUSION:

The present study investigated pMLU in children with SLI in the age range of 4-6 years. The results revealed that children with SLI are inferior in the acquisition of segments including morphemes as well as in their whole-word phonological proficiency than the typically developing children. Hence, pMLU measure could be regarded as a yardstick for phonological and morphosyntactic development in children with SLI.

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