The rare, genetically based disorder, Williams syndrome (WMS), produces a constellation of distinctive cognitive, neuroanatomical, and electrophysiological features which we explore through the series of studies reported here. In this paper, we focus primarily on the cognitive characteristics of WMS and begin to forge links among these characteristics, the brain, and the genetic basis of the disorder. The distinctive cognitive profile of individuals with WMS includes relative strengths in language and facial processing and profound impairment in spatial cognition. The cognitive profile of abilities, including what is ‘typical’ for individuals with WMS is discussed, but we also highlight areas of variability across the group of individuals with WMS that we have studied. Although the overall cognitive abilities (IQs) of individuals with WMS are typically in the mild-to-moderate range of mental retardation, the peaks and valleys within different cognitive domains make this syndrome especially intriguing to study across levels. Understanding the brain basis (and ultimately the genetic basis) for higher cognitive functioning is the goal we have begun to undertake with this line of interdisciplinary research.

Williams Syndrome (WMS) is a genetically based disorder characterized by pronounced variability in performance across different domains of cognitive functioning. This study examined brain activity linked to face-processing abilities, which are typically spared in individuals with WMS. Subjects watched photographic pairs of upright or inverted faces and indicated if the second face matched or did not match the first face. Results from a previous study with normal adults showed dramatic differences in the timing and distribution of ERP effects linked to recognition of upright and inverted faces. In normal adults, upright faces elicited ERP differences to matched vs. mismatched faces at approximately 320 msec (N320) after the onset of the second stimulus. This “N320” effect was largest over anterior regions of the right hemisphere. In contrast, the mismatch/match effect for inverted faces consisted of a large positive component between 400 and 1000 msec (P500) that was largest over parietal regions and was symmetrical. In contrast to normal adults, WMS subjects showed an N320-mismatch effect for both upright and inverted faces. Additionally, the WMS subjects did not display the N320 right-hemisphere asymmetry observed in the normal adults. WMS subjects also displayed an abnormally small negativity at 100 msec (N100) and an abnormally large negativity at 200 msec (N200) to both upright and inverted faces. This ERP pattern was observed in all subjects with WMS but was not observed in the normal controls. These results may be linked to increased attention to faces in subjects with WMS and might be specific to the disorder. These results were consistent with our ERP studies of language processing in WMS, which suggested abnormal cerebral specialization for spared cognitive functions in individuals with WMS.

Readers routinely draw inferences with remarkable efficiency and seemingly little cognitive effort. The present study was designed to explore different types of inferences during the course of reading, and the potential effects of differing levels of working memory capacity on the likelihood that inferences would be made. The electroencephalogram (EEG) was recorded from five scalp sites while participants read 90 paragraphs, composed of 60 experimental paragraphs and 30 filler paragraphs. Each experimental paragraph was four sentences long, and the final sentence stated explicitly the inference that readers did or did not make. There were four types of experimental paragraphs: (1) Bridging inference, (2) Elaborative inference, (3) Word-Based Priming control, and (4) No Inference control. Participants were tested using the Daneman and Carpenter (1980) Reading Span Task and categorized as having low or high working memory capacity. The average peaks of the N400 component of the event-related brain potential (EM) were used as a measure of semantic priming and integration, such that the lower the N400 was in response to the explicitly stated inference concept, the more likely it was that the reader made the inference. Results indicate that readers with high working memory capacity made both bridging (necessary) and elaborative (optional) inferences during reading, whereas readers with low working memory capacity made only bridging inferences during reading. We interpret the findings within the framework of the Capacity Constrained Comprehension model of Just and Carpenter (1992).

Previous research on the N400 component of the event-related brain potential (ERP) has dealt primarily with measuring the degree of expectancy on the part of the reader as a result of the context within a sentence. Research has shown that when the final word in a sentence is unexpected or incoherent, a greater N400 amplitude is elicited than if the final word is expected or coherent within the context of the sentence. The present study investigated whether the N400 component is sensitive to global, as well as local, semantic expectancy. Global coherence refers to the ease with which subjects can relate the current proposition they are reading with theme-related ideas. In the present study, the effect of global coherence on event-related brain potentials was tested using four titled and untitled paragraphs (Bransford & Johnson, 1972; Dooling & Lachman, 1971), presented one word at a time. These paragraphs are noncoherent, and are made coherent only with the presentation of a title. The EEG was recorded in response to every word in all four paragraphs. We found an increase in N400 amplitude in response to the words in the Untitled paragraphs relative to the Titled paragraphs, indicating that global coherence does affect the N400. In addition, subjects in the Titled group showed an enhanced P1-N1 component relative to the Untitled group suggesting that the presence of global coherence allows greater attention to be allocated to early visual processing of words.