The Time Course of Lexical Competition in Young and Older Adults

The Time Course of Lexical Competition in Young and Older Adults Kathleen Pirog Revill (kate.pirog@psych.gatech.edu) & Daniel H. Spieler (spieler@gatech.edu) School of Psychology, Georgia Institute of Technology 654 Cherry Street, Atlanta, GA 30332 USA presbycusis, an age-related reduction in auditory sensitivity starting at high frequencies and progressing into the lower frequencies with age (Humes et al., 1994). However, cognitive changes also affect older adult performance above and beyond what is predicted by auditory thresholds. In the visual word processing literature, the lexical frequency of the target word itself has been shown to have a larger influence on older compared to younger adults (Spieler & Balota, 2000). In spoken word recognition, factors like neighborhood density and neighborhood frequency (the average lexical frequency of all of the words in the neighborhood) affect word identification in both young and older adults (Sommers, 1996; Sommers & Danielson, 1999). Like young adults, older adults have more difficulty identifying ‘difficult’ words (words from high density, high frequency neighborhoods) than ‘easy’ words (words from low density, low frequency neighborhoods). However, the disadvantage for difficult words is increased for older adults even after equating for acuity. While neighborhood structure and density affect the time course of lexical competition in young adults (Magnuson et al., 2007), little is known about age differences in the time course of competition. Some evidence is available from gating paradigms. Here, listeners hear increasing fragments of a word and are asked to identify the word. Older listeners needed to hear slightly more of a word than younger listeners (57% versus 52% respectively) before correct identification (Wingfield, Aberdeen, & Stein, 1991). Because participants make responses long after the offset of the word fragment, this evidence is only a very indirect measure of the time course of recognition. If older adults need to hear more of a word before identification occurs, then lexical activation may simply build more slowly in older compared to younger listeners. This slowed time course of activation need not influence the overall pattern of competition between target words and phonologically related “cohort” competitors. However, older adults’ increased difficulty with identification of words in hard neighborhoods and the observation of larger effects of lexical frequency in visual word identification studies suggest that age differences may result from increased competition from high frequency competitors instead of an overall delay in lexical activation. More direct information about the time course of lexical activation and competition is needed to distinguish these alternatives. If the age difference is due to differences in the resolution of competition, then we would expect differences in the patterns of activation primarily when competitors compete strongly with the target word, for example, when the target is a low frequency word and the competitor is high in Abstract Although hearing loss accounts for much of the difficulty older adults have comprehending spoken language, cognitive factors also play a role. There is evidence that, relative to younger listeners, older listeners have more difficulty recognizing a word when it has many lexical competitors, but little is known about the time course of lexical competition in older adults. We monitored the eye movements of sixteen young adults (18-30 years) and sixteen older adults (60-80 years) as they followed spoken instructions to click on objects displayed on a computer screen. We manipulated the lexical frequencies of the target word and the phonologically similar competitor. Older listeners were more likely than younger listeners to fixate competitors during comprehension only when the competitor was high frequency. Simulations using a model of spoken word recognition suggest that these age differences may arise from a combination of differences in the effect of frequency and competitor inhibition. Keywords: cognitive aging; spoken word recognition; visual world paradigm. Introduction Theories in cognitive aging have long focused on the seeming difficulty that older adults have in selecting between competing representations during processing (Hasher & Zacks, 1988). Indeed, older adults are disadvantaged in situations when multiple mental representations compete for selection. While this can be seen most clearly in areas such as attentional control (e.g., Spieler, Balota, & Faust 1996), selection during language processing is also adversely influenced. For example, during language production, older adults have particular difficulty in lexical selection (LaGrone & Spieler, 2006). Here, we focus on another aspect of selection, namely the need to select the correct word from a set of competing lexical candidates during spoken language comprehension. Because spoken language input arrives incrementally, competition occurs between similar word representations during moments of temporary ambiguity. In most current models of spoken word recognition (SWR), the acoustic input activates multiple lexical candidates that compete for eventual recognition (though see Norris & McQueen, 2008 for a Bayesian perspective on activation and competition). Spoken Word Recognition and Aging Although language abilities are frequently cited as being relatively preserved in old age, older adults do have difficulty with spoken language comprehension under a variety of circumstances. Most of this difficulty (up to 80% of the variance in some studies) can be attributed to