The discovery of natural classes by non-native listeners

John Kingston and Elliott Moreton

Using natural disyllabic stimuli, English speakers were trained to
sort one, two, or three pairs of German nonlow rounded vowels into two
categories.  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 fo 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.]

[Abstract in Journal of the Acoustical Society of America 103(5, Part
2):2986 (1998).]