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.