Judgments of perceptual groups: Reliability and sensitivity to stimulus transformation

The reliability of subjects' judgments of the groups present in dot pattern s and the sensitivity of those judgments to stimulus transformation were as sessed. The subjects indicated the groups that they saw within random dot p atterns, and each judgment was compared with those of other subjects and wi th their own judgments for related presentations. Within subjects, each pat tern appeared in an initial presentation, an identical repetition, and a tr ansformed state (a rotation or a change in scale), Within-subjects judgment s were more reliable than between-subjects judgments, An interpretation of within-subjects results was made in relation to predictions made by a forma l algorithm of grouping by proximity (the CODE algorithm), which assumes th at grouping by proximity is invariant over transformations such as rotation s or changes in scale. A slight cost to transforming the patterns was found . The implications for CODE and for using grouping judgments as data are di scussed.