Abstract
Effects of stimulus length on reaction times (RTs) in the lexical decision task are the topic of extensive research. While slower RTs are consistently found for longer pseudo-words, a finding coined the word length effect (WLE), some studies found no effects for words, and yet others reported faster RTs for longer words. Moreover, the WLE depends on the orthographic transparency of a language, with larger effects in more transparent orthographies. Here we investigate processes underlying the WLE in lexical decision in German-English bilinguals using a diffusion model (DM) analysis, which we compared to a linear regression approach. In the DM analysis, RT-accuracy distributions are characterized using parameters that reflect latent sub-processes, in particular evidence accumulation and decision-independent perceptual encoding, instead of typical parameters such as mean RT and accuracy. The regression approach showed a decrease in RTs with length for pseudo-words, but no length effect for words. However, DM analysis revealed that the null effect for words resulted from opposing effects of length on perceptual encoding and rate of evidence accumulation. Perceptual encoding times increased with length for words and pseudo-words, whereas the rate of evidence accumulation increased with length for real words but decreased for pseudo-words. A comparison between DM parameters in German and English suggested that orthographic transparency affects perceptual encoding, whereas effects of length on evidence accumulation are likely to reflect contextual information and the increase in available perceptual evidence with length. These opposing effects may account for the inconsistent findings on WLEs.
Highlights
The cognitive processes underlying visual word processing have been the target of intensive psycholinguistic research for many decades (Jacobs and Grainger, 1994; Norris, 2013)
On the lexical route letter representations are mapped directly to lexical word-form representations, whereas on the sublexical route orthographic signs are mapped to sublexical phonology by means of Diffusion Modeling of Word Length Effects grapheme-to-phoneme associations (Coltheart et al, 2001; Perry et al, 2007)
In contrast to the overall null effect of length on word response times (RTs), we found that while perceptual encoding became slower with length, evidence accumulation accelerated for words of both languages, as evident by increased non-decision times as well as faster drift rates with length
Summary
The cognitive processes underlying visual word processing have been the target of intensive psycholinguistic research for many decades (Jacobs and Grainger, 1994; Norris, 2013). The increase in response times (RTs) with stimulus length, coined the word length effect (WLE), is thought to arise during sublexical processing (Barton et al, 2014) It is commonly interpreted as reflecting serial mapping in the sublexical route, requiring more time as an input contains more graphemes. There have been different proposals as to the exact locus of the length effect within the sublexical route, in particular early visual encoding (Nazir et al, 1991; O’Regan and Jacobs, 1992; Jacobs et al, 2008), letter-to-grapheme mapping in the CDP+ model (Perry et al, 2007), or grapheme-to-phoneme mapping in the dual-route model (Coltheart et al, 2001), all models converge on the necessary activation of phonological representations in this task as the source for length effects (Hudson and Bergman, 1985; Ziegler et al, 2001b; Ferrand et al, 2011)
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