Ingram (1959) classified the causes of child language disorders into “mental retardation”, “impaired hearing” ,“environmental causes”, “structural, neurological or neuromuscular abnormalities affecting the speech apparatus”, and “autism”. Mental retardation not only affects the general cognitive abilities but also delays (or
holdbacks) the development of language in PWS (Munson-Davis, 1988). Besides, in light of Åkefeldt, Åkefeldt and Gillberg‟s (1997), mental retardation was regarded as an underlying factor for certain patterns of language disorder in PWS. The speech and language skills are widely disparate in the severity and type of deficits among PWS patients, ranging from being nonverbal to being those who acquire normal speech and language skills by adulthood. Despite the great variability in the speech and language skills, several common speech or language characteristics have been noted, which include poor/retarded speech-sound development, hampered oral motor skills, and language deficits. PWS individuals‟ speech is often associated with articulatory imprecision (i.e. some sounds are specifically difficult for PWS individuals to pronounce/articulate correctly or precisely; some of the sounds are reported to have been distorted or altered unintentionally while uttered), hypernasality or hyponasality (i.e. improperly or abnormally converting oral sounds to nasals or in an inverse manner: too much or not enough nasal sounds in speech), flat/changeless intonation patterns, an abnormal pitch, and a harsh voice quality. Prosody, or the melody of speech, may also be malfunctioned. Speech that is very slow and sometimes
15
unconfident, typical of a “flaccid dysarthria” (i.e. faulty speech production characterized by imprecise consonants and irregular articulation, due to motor difficulties resulting from hypotonic muscle tone), may also be reported (Lewis, 2006). Zellweger (1979) presented that articulation disturbances are prevalent among most children with PWS, and dysarthria triggers the incomplete intelligibility of their speech. Developmental apraxia of speech has also been observed with some children with PWS (Branson, 1981; Munson-Davis, 1988). Dysfluency is another problem that PWS patients may have. Kleppe, Katayama, Shipley and Foushee (1990) found that many of the 18 subjects in their study were dysfluent, with the percentage of fluency ranging from 66% to 99%, with a median of 91%, and that the primary types of dysfluencies were involved with interjections and revisions.
In addition to these speech difficulties, individuals with PWS may have other language problems. Language problems include inadequacies in vocabulary, grammar, morphology, discourse (e.g. narrative abilities), and pragmatics (Lewis, 2006). In terms of speech perception and production, poor receptive and expressive abilities are frequently identified, as evidenced by age normative data with 90.5% presenting receptive language delays and 91.7% presenting expressive language delays (Lewis, Freebairn, Heeger & Cassidy, 2002). Expressive language skills are usually more hampered than receptive skills (Branson,1981; Kleppe, Katayama, Shipley & Foushee, 1990; Munson-Davis, 1988). Å kefeldt, Å kefeldt and Gillberg (1997) launched a comprehensive investigation on the speech and language skills in 11 PWS subjects and controls (matched with sex, age, BMI and IQ) and found that the differences in speech and language skills (e.g. phonology, grammar, and language comprehension) were marginally significant, but the voice quality, pitch level, resonance, and oral motor function were significantly more impaired in PWS than those in the control, which is in accordance with what the previous studies suggested.
16
As to language acquisition, a weak cry and early feeding difficulties are presented mostly because of hypotonia in infancy. Reduced babbling and early language delay are often noticed. Children with PWS are 18 months of age before they begin to verbally evidence a vocabulary, combine words, and develop early syntax while typically developing children have acquired at least two words in addition to “dada” and “mama” by 12 months of age. A substantial number of
affected children are much later in acquiring speech; some may be as late as 6 years of age (Lewis 2006). According to Hall and Smith (1972), some children with PWS may begin uttering short sentences at approximately 42 months of age, while other studies suggested that some children may begin talking as early as 24 months (Hall & Smith 1972; Prader-Willi Syndrome Association, 1980b).
As to word usage specifically, Branson (1981) reported that the word-recall difficulties create the repetitions, additions, and circumlocutions in the spontaneous speech of the subjects with PWS, which is one of the decisive factors in the presence of dysfluent behavior. With regard to content words and function words, content words were used more than function words from each subject‟s language sample, with content words ranging from 51% to 69% (M=58%), and function words from 31% to 49% (M=42%) (Kleppe, Katayama, Shipley & Foushee, 1990). The lopsided tendency towards content-word use can be accounted for by the deficiency of the “higher-order cognitive processing” in PWS (Whitman &Thompson, 2006). Defloor, Van Borsel and Curfs (2000) investigated speech fluency in 15 individuals with PWS (CA from 9;9 to 20;0 and total IQ from 40 to 94) and found that dysfluent speech behavior is a common symptom in PWS, with whole-word repetitions being seen more often on function words while part-word repetitions being observed more on lexical (content) words. Additionally, dysfluencies often affected monosyllabic words, with
whole-word repetitions and prolongations occurring preeminently on monosyllabic
17
words. Defloor et al. (2000) also presented that the dysfluent speech behaviors associated with PWS do not conform completely to developmental stuttering despite some of the shared features observed between these two.
PWS patients have been found to have great difficulty with narrative or story telling/retelling tasks (Lewis, Freebairn, Sieg & Cassidy, 2000), which may be due to specific deficits in “auditory short-term memory (Dykens, Hodapp, Walsh, and Nash, 1992)”, “linear or temporal order processing”, and “auditory verbal processing skills (Curfs, Wiegers, Sommers, Borghgraef & Fryns, 1991). Besides, poor pragmatic or social skills are often observed in individuals with PWS. For instance, Munson-Davis (1988) demonstrated that deficits of pragmatics and unawareness of social norms or etiquette in communicational interactions can be a problem in older children and adolescents. Disabilities of higher-order cognitive processing mentioned previously also trigger the ignorance of implicature (implied meaning) in conversations.
Individuals with PWS thus cannot or hardly seize the connotation, infer the extra meanings, follow the speech acts, and read between the lines when they have
conversational interactions with other people (Whitman & Thompson, 2006). Besides, the socio-pragmatic features, such as temper tantrums, stubbornness, difficulties in detecting social cues and poor social relationships also prevent PWS individuals from abiding by the Cooperative Principle in the conversation.