Response time distributional evidence for distinct varieties of number attraction.

Speakers are known to make subject-verb agreement errors both when a number-mismatching noun intervenes between the head of the subject phrase and the verb (e.g., *The key to the cabinets are on the table) and in configurations in which there is a number-mismatching noun that does not intervene (e.g., *The cabinets that the key open are on the second floor). Using a two-choice response time (RT) paradigm, Staub (2009) found that correct agreement decisions were also slowed in both cases. The present article reports a new experiment designed to explore whether these two RT effects are qualitatively similar or different. Fitting of the ex-Gaussian distribution (Ratcliff, 1979) to individual subjects' RT data, in each condition, demonstrated that the effect of an intervening number attractor on correct RT is due to both a shifting of the distribution to the right and to increased skewing, while the effect of a non-intervening attractor is almost entirely a skewing effect. A non-parametric vincentizing procedure supported these conclusions. These findings are taken to support the view that these two types of number attraction involve distinct processing mechanisms. Copyright 2009 Elsevier B.V. All rights reserved.