Lexical access and frequency sensitivity: Frequency saturation and open/closed class equivalence

Whether closed-class words use the same lexical access route(s) as open-class words has been intensely debated recently. Differences in frequency sensitivity have been suggested as one manifestation of separable access routes. However, all the lexical decision studies have been limited by floor effects at the higher frequency ranges which could mask theoretically important differences in the behavior of the two classes. We studied lexical decisions to high- and very-high frequency words of both classes using stimulus masking and speeded responses, in order to minimize floor effects, to try to reveal potential differences between the behavior of the two classes, and to contrast theories of lexical access. We did not find evidence to support the view that closed-class words have a different or special access route. Neither word class showed any appreciable frequency effect for Kućera-Francis frequencies of 400/million or greater, on either reaction time or error analyses. We did find open-class words to have somewhat faster responses than comparable closed-class words, but this may contradict some explanations of the reported word class effect (Bradley et al., 1980). Moreover, our data also show what may be word-specific influences on lexical decision times-effects which may be impossible to factor out of the word class effect in English. In order to accommodate the frequency insensitivity that we found, logogen-based models of lexical access have to be amended to include a floor on threshold settings. Resonance models (Gordon, 1983), already predict this frequency insensitivity. It should be possible to distinguish between these two accounts by comparing masked and routine lexical decisions, but the unexpected word-specific effects prevented us from doing so.