Table 2.

Order-Dependency of Ketamine Effects on Wisconsin Card Sorting Test Performance

Outcome Measure	Order	Ketaminea	Placeboa	First vs. Second Dayd	Drug by Order Effecte
Category criteria met	Ketamine firstb	1.5 ± .7f	4.8 ± .6	t9 = 5.7, p = .0003	p = .003
	Placebo firstc	4.5 ± .7	5.1 ± .4	ns
Percent perseverative errors	Ketamine first	69.2 ± 5.5g	53.1 ± 3.6	t9 = 3.3, p = .009	p = .03
	Placebo first	49.2 ± 3.6	46.0 ± 3.6	ns
Perseverative errors	Ketamine first	53.4 ± 8.6h	21.8 ± 5.9	t9 = 4.2, p = .002	p = .004
	Placebo first	19.3 ± 3.8	13.8 ± 3.9	ns
Total errors	Ketamine first	74.0 ± 8.1f	37.8 ± 7.4	t9 = 5.4, p = .0004	p = .005
	Placebo first	42.8 ± 8.4	27.7 ± 6.5	ns
Number of items	Ketamine first	124.6 ± 3.4h	110.0 ± 4.8	t9 = 3.3, p = .009	p = .04
	Placebo first	112.4 ± 5.5	101.0 ± 7.9	ns
Trials to first criterion	Ketamine first	21.9 ± 10.4	20.8 ± 3.3	ns	ns
	Placebo first	14.3 ± 3.2	23.4 ± 5.7	ns
Loss of set	Ketamine first	1.2 ± .5	1.3 ± .6	ns	ns
	Placebo first	.9 ± .3	1.5 ± .6	ns

^aData are presented as mean ± SEM.

^bKetamine first subjects received ketamine on the first test day and placebo on the second test day (n = 10).

^cPlacebo first subjects received placebo on the first test day and ketamine on the second test day (n = 12).

^dTwo-tailed post hoc paired t tests comparing subjects on their first and second test days. All post hoc tests underwent Bonferroni adjustments.

^eSignificance of the drug by time interaction effect in the repeated measures ANOVA, see text for other analyses. Two-tailed post hoc Student’s t tests comparing groups of subjects on the same test day:

^fp ≤ .005;

^gp ≤ .05;

^hp ≤ .01.