The discovery of natural classes by non-native listeners

Abstract

Using natural disyllabic stimuli, English speakers were trained to sort one, two, or three pairs of German nonlow rounded vowels into two cat-egories, then a new pair was added and their ability to sort it into the same categories was tested. Each pair contrasted in [high], [tense], and [back]. Category membership was determined by only one of these features. Three-pair training provided enough information to tell which one; two-pair narrowed it down to two possibilities; one-pair left it open. Listeners in three experiments using different pairs of test vowels sorted the test vowels significantly better as the number of training pairs increased. This suggests they were inducing feature-based natural classes. The rival exemplar model of Nosofsky [J. Exp. Psych.: Gen. 115, 39–57 (1986)] would say that while more pairs bring more phonetic variety, they also exemplify more robustly the dimensions along which the categories differ phonetically, and thereby shift attentional weight to those dimensions. Similar experiments will pit these two hypotheses against one another with training pairs which contrast only in the feature that defines the sort categories. If listeners are using feature-based natural classes, their performance should not improve with more training pairs; if they are using exemplars, it should. [Work supported by NIH.]