Table 2.

Mean parameter values across participants from the one-choice and two-choice diffusion models.

Task-version	Age	a	z	T er	η	sz	st	po	χ2	N(<${\chi }_c^2$¿
One-choice Clear	Young	0.220		0.352	0.200		0.205		12.2	29/30
	Older	0.200		0.339	0.200		0.238		8.6	27/29
Two-choice Clear	Young	0.137	0.071	0.701	0.167	0.041	0.368	0.002	33.4	28/30
	Older	0.145	0.070	0.714	0.149	0.044	0.479	0.002	43.3	19/29
Two-choice City	Young	0.129	0.068	0.804	0.170	0.035	0.309	0.005	31.6	29/30
	Older	0.122	0.058	0.845	0.135	0.057	0.410	0.001	41.9	19/29

Note: a represents the decision boundary separation; z represents the starting point; T_er represents nondecision time; η represents standard deviation in drift rate across trials; s_z represents range of the distribution of starting points (z); s_t represents range of the distribution of nondecision times; p_o represents proportion of contaminants; χ² represents the average goodness-of-fit (group level); and N(< ${\chi }_c^2$]¿ represents the number of participants with χ² value below the critical value (out of N=30 for young adults and N=29 for older adults). The critical χ² values were 23.7 with 14 degrees of freedom for the one-choice model and 47.4 with 33 degrees of freedom for the two-choice model.