Estimation of premorbid intelligence and executive cognitive functions with lexical reading tasks

Introduction: Estimation of premorbid function is essential to accurate assessment of cognitive impairments in clinical neuropsychology and behavioral neurology, and has numerous research applications. However, current methods are rudimentary and imperfect. We explored how lexical tasks can be best used to accurately and precisely estimate intelligence and executive functions.Methods: We studied lexical word pronunciation, lexical decision, and stem-completion naming in the estimation of cognitive ability, in samples of healthy adults (n = 143), and patients with cognitive impairment due to neurological illness (n =15). Cognitive assessments included intelligence (WAIS-IV), episodic memory, and eight tests of executive functioning, including Theory of Mind.Results: When examined at the group level, single word pronunciation was particularly robust in the presence of cognitive impairment in patients with dementia. However, as a case series, patients showed idiosyncratic patterns of preservation of lexical skills including on tests of pronunciation, lexical decision and stem-completion naming. All of these tasks were highly correlated with IQ scores in a non-clinical sample, suggesting that they could be used as estimators of premorbid intelligence. Simulated impairments in non-clinical controls suggested that the median score from the three different tasks had the highest correlation with, and provided the most accurate and precise estimates of, intelligence, and was also the least sensitive to impairment. Finally, we show that these methods also predict executive functions, in particular, strong correlations were found for proverb interpretation, phonemic/semantic alternating verbal fluency, and working memory span performance. Conclusions: Several lexical tasks are potentially useful in predication of pre-illness cognitive ability in patients with neurological or psychiatric illness. However, due to the heterogeneity of impairments between patients, estimation of premorbid levels could be improved by the use of the median estimated values from multiple tests. This could potentially improve diagnostic accuracy and quantification of neuropsychological impairments.

Sleep-dependent consolidation in children with comprehension and vocabulary weaknesses: It’ll be alright on the night?

Background: Vocabulary is crucial for an array of life outcomes and is frequently impaired in developmental disorders. Notably, ‘poor comprehenders’ (children with comprehension deficits but intact word-reading) often have vocabulary deficits, but underlying mechanisms remain unclear. Prior research suggests intact encoding but difficulties consolidating new word knowledge. We test the hypothesis that poor comprehenders’ sleep-associated vocabulary consolidation is compromised by their impoverished lexical-semantic knowledge.Methods: Memory for new words was tracked across wake and sleep to isolate processes of encoding and consolidation in 8-to-12-year-old good and poor comprehenders. Each child participated in two sets of sessions in which they were taught 12 new words either at the start (AM-encoding) or end (PM-encoding) of the day, alongside training on a nonverbal declarative task. Memory was assessed immediately, 12-, and 24- hours later via stem-completion, picture-naming, and definition tasks to probe different aspects of new word knowledge. Long-term retention was assessed 1-2 months later. Results: Recall of word-forms improved over sleep and post-sleep wake, as measured in both stem-completion and picture-naming tasks. Counter to hypotheses, deficits for poor comprehenders were not observed in consolidation but instead were seen across measures and throughout testing, suggesting an encoding deficit. Variability in vocabulary knowledge across the whole sample predicted sleep-associated consolidation, but only when words were learned early in the day and not when sleep followed soon after learning.Conclusions: Poor comprehenders showed weaker encoding of new word knowledge than good comprehenders, but sleep-associated consolidation benefits were comparable between groups. Sleeping soon after learning had long-lasting benefits for memory, and may be especially beneficial for children with weaker vocabulary. These results provide new insights into the breadth of poor comprehenders’ vocabulary weaknesses, and ways in which learning might be better timed to remediate vocabulary difficulties.