PREDICTING THE EXTENSION OF EQUIVALENCE CLASSES FROM PRIMARY GENERALIZATION GRADIENTS - THE MERGER OF EQUIVALENCE CLASSES AND PERCEPTUAL CLASSES

In Experiment 1, 6 college students were given generalization tests us ing 25 line lengths as samples with a long line, a short line, and a ' 'neither'' option as comparisons. The neither option was to be used if a sample did not go with the other comparisons. Then, four-member equ ivalence classes were formed. Class 1 included three nonsense words an d the short line. Class 2 included three other nonsense words and the long line. After repeating the generalization test for line length, ad ditional tests were conducted using members of the equivalence classes (i.e., nonsense words and lines) as comparisons and intermediate-leng th. lines as samples. All Class 2 comparisons were selected in the pre sence of the test lines that also evoked the selection of the long lin e in the generalization test that had been given before equivalence cl ass formation. Class 1 yielded complementary findings. Thus, the precl ass primary generalization gradient predicted which test lines acted a s members of each equivalence class. Regardless of using comparisons t hat were nonsense words or Lines, the post-class-formation gradients o verlapped, showing the substitutability of class members. Experiment 2 assessed the discriminability of the intermediate-length test lines f rom the Class I (shortest) and Class 2 (longest) lines. The test lines that functioned as members of an equivalence class were discriminable from the line that was a member of the same class by training. Thus, these test lines also acted as members of a dimensionally defined clas s of ''long'' or ''short'' lines. Extension of an equivalence class, t hen, involved its merger with a dimensionally defined class, which con verted a close-ended class to an open-ended class. These data suggest a means of predicting class membership in naturally occurring categori es.