Table 1.

Stimulus exemplars used in the attentional set-shifting task

Dimension	Exemplar pairs
Outer texture
Set A	Smooth plastic	Smooth cardboard	Aluminum foil	Coarse sandpaper	Regular paper
Set B	Bubble wrap	Ridged cardboard	Pink cloth	Fine sandpaper	Waxed paper
Digging medium
Set 1	Aspen bedding a	Moss	Repti Bark	CareFresh	Crystalit
Set 2	Aquarium gravel	Kay-Kob	Alpha-dri	Ultra White CareFresh	PaperChip
Odor
Set ■	Sage	Pepper	Cumin	Thyme	Nutmeg
Set ○	Coriander	Cinnamon	Ginger	Oregano	Cloves

Compound discriminations were based on fixed combinations of pairs of exemplars. The exemplar pairs from different dimensions were presented in random combination, but each sequence performed by a control mouse was matched by that of a COMT-Val-tg littermate. Neutral stimuli for the different dimensions were: no outer texture; sawdust bedding (Harlan Teklad); digging medium; and no odor. The digging medium was changed often so the mice would not use odor cues to locate the bowls baited with food pellets. For 500 ml of each medium, 10 ml of crushed food pellets (about 6 g) were mixed with the medium to mask the smell of the hidden food pellet. For scented mixtures, an odor (0.7g) was mixed with 500 ml of the medium and crushed pellets.

^aAspen bedding, Aquarium gravel, Moss, Kay-Kob, Repti Bark (PetSmart); Alpha-dri (Shepherd Specialty Papers); CareFresh, Ultra White CareFresh (International Absorbents); Crystalit (Pharmacal Research Laboratories); PaperChip (Shepherd Specialty Papers).