Cognitive abilities were assessed using four tests. Verbal ability was assessed using the Mill Hill Vocabulary Scale, junior and senior synonyms (Raven 1965). Immediate and delayed scores from the recall section of one story of the Wechsler Logical Memory test were summed to provide a measure of verbal declarative memory (Wechsler 1998). The Wechsler Digit Symbol Coding test was used to measure processing speed (Wechsler 1998). Executive function was measured using the letter‐based phonemic verbal fluency test (letters C, F and L for 1 minute each) (Lezak 1995).
