Cross-Sectional and Longitudinal Analyses of the Receptive Vocabulary Ability of Individuals with Williams Syndrome Reb

1. Cross-Sectional and Longitudinal Analyses of the Receptive Vocabulary Ability of Individuals with Williams Syndrome Rebecca L. Johnson and Carolyn B. Mervis Department of Psychological and Brain Sciences, University of Louisville • RESULTS • QUESTION 1 • To address Question 1, we first calculated descriptive statistics for the standard scores of the cross-sectional sample. • Mean: 78.98 • SD: 13.36 • Range: 40 to 117 • We then made a histogram (Figure 1) to examine the distribution of PPVT-III standard scores. • As indicated in Figure 1, PPVT-III standard scores are normally distributed for individuals with Williams syndrome. • The mean standard score of the sample (78.98) is 1.40 SD below the mean standard score of the general population. • Figure 1. Histogram of PPVT-III standard scores for 124 individuals with Williams syndrome. • QUESTION 2 • To address Question 2, we plotted the PPVT-III raw scores of all cross-sectional participants as a function of chronological age (Figure 2). • As indicated in Figure 2, the receptive vocabulary size of individuals with Williams syndrome continues to increase across the lifespan. • r (cubic) = .89 df = 120 • Vocabulary acquisition rate increases rapidly during childhood. • In adulthood, rate of vocabulary acquisition decreases. • Although the mean receptive vocabulary size of individuals with Williams syndrome is consistently below that expected for their CA, the developmental pattern of vocabulary acquisition closely matches that of the general population. • Figure 2. PPVT-III raw scores as a function of CA for 124 individuals with Williams syndrome (blue line = cubic trend line). • QUESTION 3 • To address Question 3, we plotted the PPVT-III standard scores of the cross-sectional participants as a function of their chronological age (Figure 3). • r = .01 • df = 122 • This very low correlation indicates that, on average, receptive vocabulary ability of individuals with Williams syndrome relative to CA-matched individuals in the general population does not vary as a function of CA. • That is, on average, individuals with Williams syndrome hold a consistent position relative to the general population across the entire range of CA tested (4 - 49 years). • Figure 3. PPVT-III standard scores as a function of CA for 124 • individuals with Williams syndrome. • To further address Question 3, we compared the performance of the longitudinal participants on their first and second assessments (Figure 4, Table 1). • Figure 4. PPVT-III standard scores of 21 individuals with Williams • syndrome who were assessed longitudinally. • Table 1. PPVT-III standard scores for 21 individuals with Williams syndrome who were assessed longitudinally. • INTRODUCTION • Williams syndrome is a genetic disorder caused by a microdeletion of the long arm of chromosome 7 (7q11.23). Affecting 1/20,000 live births, Williams syndrome is characterized by dysmorphic facial features, mild to moderate mental retardation (~75%) or learning disabilities (~25%), a unique gregarious personality, and a distinctive cognitive profile. Individuals with William syndrome evidence relative strength in the areas of auditory rote memory and language and have most difficulty with tasks that require visual-spatial construction skills. • The purpose of this study was to explore the receptive vocabulary abilities of individuals with Williams syndrome across a wide age range. • RESEARCH QUESTIONS • QUESTION 1 • What are the receptive vocabulary capabilities of individuals with Williams syndrome relative to those of the general population? • QUESTION 2 • Do the receptive vocabularies of individuals with Williams syndrome continue to increase across the lifespan? • QUESTION 3 • Is the receptive vocabulary level of individuals with Williams syndrome relative to their CA-matched normally developing peers maintained across the lifespan? • METHOD • PARTICIPANTS • Cross-sectional Analysis • 124 individuals with Williams syndrome • 58 males, 66 females • Age: • Mean: 176.36 months (14 years, 8 months) • SD: 130.93 months (10 years, 10 months) • Range: 49 months to 594 months (4 years, 1 month to 49 years, 6 months) • Longitudinal Analysis • 21 individuals (also included in cross-sectional analysis) • 7 males, 14 females • Each participant was tested twice • Age: • MEASURE • Peabody Picture Vocabulary Test - Third Edition (PPVT-III) • The PPVT-III is designed to measure an individual’s receptive vocabulary by testing his/her knowledge of nouns, verbs, and descriptors. Participants are shown a page with four pictures and are then asked to identify the picture that best fits the meaning of the word spoken by the researcher. Standard scores on the PPVT-III have a mean of 100 and a standard deviation of 15. • PROCEDURE • The PPVT-III was administered and scored according to standard procedures. • QUESTION 3 (continued) • As indicated in Table 1, standard scores, on average, showed no change when individuals were tested over time. • The standard deviation of the Williams syndrome group is similar to that of the general population. • A matched pairs t-test confirmed that receptive vocabulary ability relative to the general population is consistent over the time interval included in this study. • t (20) = -.02 • p = .98 • DISCUSSION • The receptive vocabulary capabilities of individuals with Williams syndrome are significantly below that expected for CA-matched peers in the general population. • Average performance is in the borderline normal range. • Nevertheless, the shape of the distribution of standard scores is similar to that of the general population. • Standard scores are normally distributed. • The standard deviation is similar to that of the general population, indicating a similar amount of variability but a lower mean level of performance. • The developmental pattern of receptive vocabulary acquisition of individuals with Williams syndrome is similar to that of the general population. • Rate of acquisition is rapid in childhood. • Rate of acquisition slows considerably during adulthood. • Individuals with Williams syndrome maintain their ability to learn new words across the lifespan, continuing to increase their absolute receptive vocabulary size. • On average, receptive vocabulary ability of individuals with Williams syndrome relative to normally developing CA-matched peers is constant over the lifespan. • ACKNOWLEDGEMENT • This research was supported by grant # HD29957 from the National Institute of Child Health and Human Development and by grant # NS35102 from the National Institute of Neurological Disorders and Stroke to Carolyn Mervis. Rebecca Johnson’s participation in this project was supported by the Summer Research Opportunity Program, University of Louisville. We thank the individuals with Williams syndrome for their enthusiastic participation in this research project.