Atypical Language Development in Williams and Down Syndromes

Modularity Hypothesis (Fodor 1983): Proposes that language development is independent of other nonlinguistic cognitive functions. Early findings in Williams Syndrome (WS) supported this by showing 'spared' language despite cognitive deficits.
Piagetian View: Language emerges from a general symbolic representation system.
Neuroconstructivism (Karmiloff-Smith): Suggests that performance in the normal range may be achieved through atypical processes and that cognitive modules are not necessarily 'intact' or 'spared' in developmental disorders.

Mean and SD: Population mean IQ is $100$ with a standard deviation (SD) of $15$ .
Mild: IQ of $55$ to $69$ ( $85\%$ of those with ID); may live independently with minimal support.
Moderate: IQ of $40$ to $54$ ( $10\%$ ); often live in group homes.
Severe: IQ of $20$ to $39$ ( $3.5\%$ ); require daily assistance and supervision.
Profound: IQ less than $20$ ( $1.5\%$ ); require $24$ -hour care.

Genetics: A rare disorder ( $1 \text{ in } 7,500$ to $1 \text{ in } 20,000$ ) involving a genetic deletion on chromosome $7$ detectable via the fluorescent in situ hybridisation (FISH) test.
Physical and Personality Traits: Characteristics include facial dysmorphia, cardiac/kidney problems, hypersensitivity to sound, and ADHD. Personalities are described as gregarious, overfriendly, and high in empathy, yet prone to anxiety and phobias.
Cognitive Profile: Marked by a mean IQ of approximately $55$ (range $26$ - $82$ ). Key deficits exist in visuo-spatial construction (e.g., copying patterns) and configural face processing, though facial recognition (Benton task) is a relative strength.
Language Profile: Relative strength in concrete vocabulary (Peabody Picture Vocabulary Test/PPVT) and phonological memory. Weaknesses include conceptual vocabulary (spatial/temporal terms like "above" or "after") and complex grammar (marking past tense or third-person singular).

Genetics: Most common cause of intellectual disability ( $1 \text{ in } 700$ to $1,000$ live births). $94\%$ of cases are caused by Trisomy 21.
Physical Traits: Physical markers include a wide, flat face, poor muscle tone, and heart disease risks. Notable hearing and speech-motor difficulties are common.
Cognitive Profile: IQs usually range from $25$ to $70$ . Non-verbal ability is often less impaired than verbal ability. Significant deficits exist in verbal short-term memory and executive-loaded working memory.
Language Profile: Characterized by an underspecified phonological system ( $67\%$ inconsistency in verbal repetition) and delayed expressive vocabulary. Syntax is a major weakness, with shorter Mean Length of Utterance (MLU) compared to matches.
Pragmatics: A relative strength; individuals often stay on topic and follow social rules better than language-matched peers.

WS vs. DS: WS typically shows better verbal than non-verbal skills, whereas DS shows the opposite.
Implications: The contrasting profiles indicate that general cognitive ability is not a reliable predictor of all language functions.
Research Limitations: Studies often suffer from small sample sizes, assumptions of group homogeneity, and a lack of developmental perspective in older subjects.

Williams Syndrome (WMS): "He will go right up to a stranger, get eye contact, and say 'hi' again and again until that person says 'hi' back."
Down Syndrome (DNS): "Shy, averts eyes, avoids person, physically withdrawn unless person can communicate with him."
Autistic: "All people are treated the same — avoid whenever possible… ignores people but prefers to be alone."

Williams Subject (Age $17$ , IQ $50$ ): Provided a descriptive, dramatic narrative: "Once upon a time when it was dark at night, the boy had a frog… Then suddenly when he opened his eyes, he looked at the jar and then suddenly the frog was not there."
Down Subject (Age $18$ , IQ $55$ ): Provided a minimal, literal description: "The frog is in the jar. The jar is on the floor… That's it. The stool is broke."