Brain and Language 81, 66–78 (2002) doi:10.1006/brln.2001.2507, available online at http://www.idealibrary.com on The Probability of the Least Likely Non-Length- Controlled Bigram Affects Lexical Decision Reaction Times Chris Westbury* and Lori Buchanan² *University of Alberta, Edmonton, Alberta, Canada; and ²University of Windsor, Windsor, Ontario, Canada Published online January 28, 2002 The frequency effect, by which high frequency words are recognized with more ease than low frequency words, is one of the most robust effects in cognitive psychology. Frequency interacts with many word-level variables, to the extent that most effects reported in word recognition literature have an impact only on low frequency words. This has been taken as evidence that high frequency words are accessed in a special way, via either an addressed pathway as in the dual-route model or an assembled pathway as in a PDP model. Under either model, sublexical effects should have no bearing on the ease with which representations for high frequency words are accessed. In this article, however, we describe a series of studies that examine a sublexical effect (namely nonlength controlled minimal bigram frequency) that is only found for high frequency words, suggesting that sublexical processing must play a role in the recognition of even high frequency words.  2002 Elsevier Science (USA) Orthographic neighborhood size (ON) or Coltheart’s N (Coltheart, Davelaar, Jonasson, & Besner, 1977) is defined as the number of different words that can be created by changing one letter of a word while maintaining letter position. Numer- ous experiments investigating ON effects in English lexical decision have found a frequency-modulated facilitatory neighborhood size effect. Low frequency words with large neighborhoods are recognized more rapidly than low frequency words with small neighborhoods (see Andrews, 1997, for a review), but this effect is either not found or is greatly reduced in magnitude for high frequency words (Andrews, 1992; Sears, Hino, & Lupker, 1995; Peereman & Content, 1995). This ON effect is consistent with a more general tendency of high frequency words to be relatively impervious to the disparate influences that can systematically affect reading of low frequency words, such as regularity (Andrews, 1982; Jared & Seidenberg, 1990) and pronunciation consistency (Glushko, 1979; Jared, McRae, & Seidenberg, 1990; but see also Jared, 1997). The apparent imperviousness of high frequency words to factors affecting reaction time (RT) supports the idea that high frequency words are accessed so quickly in the lexical pathway (of the dual-route model; cf. Coltheart et al., 1993) that any effects of sublexical processing are masked. The identification of sublexical variables This work was supported by grants from the Alberta Foundation for Medical Research and NSERC. We thank two anonymous reviewers for helpful feedback on an earlier version of this article. Address correspondence and reprint requests to Lori Buchanan, Department of Psychology, Uni- versity of Windsor, Windsor, Ontario N9B3P4, Canada. Fax: 519-973-7021. E-mail: lori.buchanan@ uwindsor.ca. 66 0093-934X/02 $35.00  2002 Elsevier Science (USA) All rights reserved.