Table 2.

Parameter Values and Standard Errors From Fits of the Diffusion Model

Condition	Subjects	as	aa	Ter	η	sz	v1	v2	v3	v4	po	st
Subjects	Old	0.107	0.168	0.413	0.276	0.034	0.043	0.112	0.214	0.305	0.006	0.136
M data	Old	0.103	0.162	0.407	0.231	0.010	0.039	0.094	0.183	0.266	0.000	0.143
Subjects	Young	0.084	0.122	0.343	0.239	0.053	0.140	0.317	0.427	0.491	0.007	0.112
M data	Young	0.079	0.121	0.353	0.246	0.055	0.141	0.313	0.423	0.487	0.005	0.126
SDs over subjects	Old	0.034	0.039	0.048	0.092	0.032	0.044	0.070	0.089	0.105	0.016	0.053
SDs over Subjects	Young	0.016	0.032	0.032	0.094	0.019	0.089	0.126	0.154	0.159	0.012	0.045

Note. a_s = boundary separation for speed condition; a_a = boundary separation for accuracy condition; T_er = nondecision component of response time; η = standard deviation in drift across trials; s_z = range of the distribution of starting point (z); v = drift rates; p_o = proportion of contaminants; s_t = range of the distribution of the nondecision component of processing. In the subjects condition, the model was fit to each individual subject and the parameter values averaged over the subjects’ values. The SDs were standard deviations over the parameter values for the fits for the individual subjects. In the M data condition, the model was fit to the data averaged over subjects.