Analogies and Abstracted Grammars : Comments on Reber ( 1989 ) and Mathews et al . ( 1989 )

Analogies and Abstracted Grammars: Comments on Reber (1989) and Mathews et al. (1989) Lee R. Brooks McMaster University Hamilton, Ontario, Canada John R. Vokey University of Lethbridge Lethbridge, Alberta, Canada Reber (1969, 1989a) and Mathews et al. (1989), in experiments on learning artificial grammars, reported good transfer to letter strings consisting of letters not used in the training stimuli, provided that the same grammar generated both training and transfer strings. They concluded from this that the transfer predominantly relies on abstract knowledge. An experiment is reported that shows much of the transfer to "changed letter-set" strings is due to abstract similarity between test strings and specific training stimuli (i.e., a string such as MXWVM could be seen as similar to BDCCCB without implying that regularities common to a large number of training items had been abstracted). The conclusion of this article is that reliance on an abstract (relational) analogy to an individual item must be distinguished from reliance on knowledge of the structure of the grammar abstracted across many training items. In a number of recent articles, artificial grammars have been used to study the way in which people learn complex regularities (e.g., Mathews et al., 1989; Reber, 1989a, reviewing the extensive work in his laboratory). In these studies, letter strings generated from an artificial grammar, such as those shown in Figure 1 and Table 1, are presented to learners. The extent to which the learners become sensitive to the regularities in the generating grammar is tested by asking them to sort new items generated by the grammar from similar strings that violate the grammar. Much of the interest in these materials has come from the claim that the learner more or less automatically acquires an abstract representation of the structure of the experienced material, which becomes the major basis of grammaticality judgments. Reber argued strongly for a separate, sophisticated, and tacit system that accomplished this abstraction for complex domains. Recent controversy has centered on Reber's claims that the abstracted knowledge is unconscious (Brody, 1989; Dulaney, Carlson, & Dewey, 1984, 1985; and with respect to the sophistication of the unconscious system, Lewicki & Hill, 1989; Mathews, 1991;Perruchet&Pacteau, 1990,1991; Reber, 1989a, 1989b, 1990; Reber, Allen, & Regan, 1985). However, the focus of the present comment is on a particular line of evidence used to support the assertion that grammaticality judgments are predominantly based on abstract knowledge. Both Reber (1969) and Mathews et al. (1989) have demonstrated very good transfer when subjects were trained on a set of strings generated using one set of letters Preparation of this article was supported in part by operating grants to Lee R. Brooks and John R. Vokey from the Natural Sciences and Engineering Research Council of Canada. We thank Lorna Moore for her invaluable assistance in collecting the data and Kris Woeppel and Mathew Davidson for their contributions to earlier phases of the project. Correspondence concerning this article should be addressed to Lee R. Brooks, Department of Psychology, McMaster University, Hamilton, Ontario, Canada L8S 4K1. Electronic mail may be sent to brookslr@sscvax.mcmaster. ca. and tested on a set of items written in a different set of letters, provided the same grammar was used to generate both sets of items. For example, the grammar shown in Figure 1 will produce all of the items listed in Table 1 as "same-letter training items" (first column) as well as the items listed as "grammatical transfer items" (second column). If the training items were in fact the items listed as "same-letter training items," then the training and the transfer set would be generated from the same letter set and by the same grammar, a condition referred to as same letter-set transfer. To produce "changed letter-set" stimuli similar to those used by Reber and by Mathews et al., each of the letters in the grammar would be systematically replaced by a different letter wherever it occurred. So for example, in all occurrences an M could be replaced by a Q, V by Z, X by J, T by F, and R by L. This would produce the correspondences shown between the "grammatical transfer items" and the training items for Subject 1 in Table 1: the same grammar but a changed letter set. In both studies, the transfer performance on the changed letter sets was not statistically distinguishable from the transfer performance on the same letter sets. Reber and Mathews et al. concluded that the excellent transfer with the changed letter sets was strong evidence that transfer was based on abstract knowledge, rather than on similarity to prior items. It is this claim that we wish to dispute. There is no doubt that good transfer to items written in a different letter set entails abstraction in some sense. But it is possible that performance is based on similarity between the transfer string being tested and an individual training string. For example, a string such as MXWVM could be seen as similar to BDCCCB in that they both start and end with the same letter and have a repeated letter triplet next to the end. We will refer to this possible similarity as an abstract analogy, or relational analogy, in contrast with literal similarity. For example, perceived similarity between MXWVM and MTVWM could be because of overlap of letters-in-position, because of the similar relations among letters, or both; this degree of similarity is an example of literal similarity. Perceived similarity between MXWVM and BDCCCB could