Stimulus pairs
| Medium pairs | Texture pairs |
|---|---|
| Sawdust vs sand | Yellow fuzzy vs reversed yellow fuzzy |
| Gravel vs plastic beads | Waxed paper vs fine sandpaper |
| Ribbon vs crinkled paper strips | Velvet vs reversed velvet |
The exemplars within a dimension (medium or texture) were always used in pairs. No two rats within a group received the same combinations, but groups of virgin and mother rats were matched.