Measuring premorbid IQ in aphasia using indirect lexical access

Estimating premorbid IQ is an important facet to neuropsychological or language evaluations, as it can provide valuable information when determining if performance represents a decline or impairment. In aphasia, assessment of premorbid abilities is difficult due to expressive and receptive language deficits. Past research has demonstrated that despite impairments in several cognitive domains, aphasic patients may retain some aspects of premorbid intelligence. In fact, performance on tests of intelligence has been shown to be unrelated to the severity or degree of language impairment. Previous research has also indicated that aphasic patients can access lexical items under indirect, or implicit conditions. For example, several studies have shown that despite an inability to overtly pronounce or understand words, aphasic patients demonstrate intact semantic priming, indicating successful retrieval of lexical-semantic information (Milberg & Blumstein, 1981). There is also evidence to suggest that patients with aphasia can differentiate orthographically regular from irregular words, indicating potential preservation of lexical-orthographic knowledge. In the current study, we evaluated a new test that indexes preserved lexical information to estimate premorbid intelligence in language-disordered individuals. We developed the lexical-orthographic familiarity test (LOFT), a lexical-familiarity measure containing words from a standardized test of word reading (Wechsler Test of Adult Reading; WTAR) paired with antiquated but real English words. Antiquated English words were selected from a previous study (Barnhardt, Glisky, Polster, & Elam, 1996) and were chosen to represent words that would be unfamiliar due to their low frequency and rare usage in current English language but were nevertheless pronounceable, and morphologically similar to more familiar English words. The test was modeled after the Spot-A-word test, a lexical-decision task proven to be highly correlated with verbal intelligence (Baddeley, Emslie, & Nimmo-Smith, 1993). Successful LOFT performance does not require correct pronunciation, and as a result, can provide information regarding word knowledge in patients who may have difficulty reading. Task instructions were to identify the word in each pair that is ‘most familiar’ and correct responses required selection of the word taken from the WTAR