The role of inhibition in older and younger adults’ lexical competition

Résumé

With age, uncertainty becomes more pronounced in speech perception; it becomes harder to recognize words in noise (Helfer & Freyman, 2014) and to inhibit similar sounding high-frequency lexical competitors (Revill & Spieler, 2012). Similar to McMurray, Munson, and Tomblin (2014), we contrast lexical competition and speech perception, but in older and younger adults, because older adults have weaker encoding of some phonetic contrasts (Anderson, Parbery-Clark, White-Schwoch, & Kraus, 2012; Bidelman, Villafuerte, Moreno, & Alain, 2014) and greater lexical effects than younger adults (Mattys & Scharenborg, 2014; Revill & Spieler, 2012). The lexical bias found in older adults (Mattys & Scharenborg, 2014) could be indicative of decreased lexical inhibition, which would result in increased activation among lexical competitors. Indeed, Sommers and Danielson (1999) found that older adults had greater difficulty than younger adults recognizing words with many semantic neighbours, suggesting that older adults exhibit difficulty inhibiting competitors. Using the visual world paradigm, we investigated the role of inhibition, lexical competition and phonetic sensitivity for word recognition in younger (n=28) and older adults (n=27). We manipulated voice onset time and included a phonological competitor to the target to contrast the effects of lexical competition and phonetic sensitivity. To measure domain-general inhibition, participants completed a Simon task. Results from a mixed-effects linear regression on discrimination score (difference between looks to the target image and to the competitor) suggest that all listeners have better discrimination for less ambiguous stimuli, but individuals with poorer inhibition were more affected by stimulus ambiguity (Continuum step x Inhibition: Beta=0.12, t(54)=2.4, p=0.02). Additionally, younger adults with poorer inhibition are less distracted by weak competitors, but more distracted by strong competitors than those with better inhibitory abilities (Continuum step x Inhibition x Age Group: Beta=0.28, t(54)=2.77, p=0.008). These results suggest that older and younger adults perform similarly when distinguishing between competitors, and that individual ability to inhibit competitors informs word recognition behaviour as speech ambiguity increases. This provides evidence that older and younger adults employ different strategies when resolving lexical competition, as inhibitory ability plays a different role across the two age groups. [Full references included in supplementary material]