Motor speed does not impact the drift rate: a computational HDDM approach to differentiate cognitive and motor speed

Cognitive Research: Principles and Implications

Table 4 Correlations between symbol digit modalities test (SDMT), nine-hole peg test (NHPT) and HDDM parameter estimates for drift rate (v), boundary separation (a) and non-decision time (Ter)

	SDMT Oral	SDMT Written	NHPT	SS 3 v	SS 5 v	SS 3 Stiff a	SS 5 Stiff a	SS 3 Soft a	SS 5 Soft a	SS 3 Stiff Ter	SS 5 Stiff Ter	SS 3 Soft Ter
SDMT Oral
SDMT Written	0.40**
NHPT	− 0.13	− 0.17
SS 3 v	0.35**	0.21*	− 0.11
SS 5 v	0.32**	0.23*	− 0.05	0.84**
SS 3 Stiff a	− 0.05	0.04	0.20	− 0.03	0.12
SS 5 Stiff a	− 0.05	0.04	0.12	− 0.20	0.12	0.65**
SS 3 Soft a	− 0.19	0.04	0.13	− 0.28**	0.00	0.71**	0.72**
SS 5 Soft a	− 0.11	0.07	0.10	− 0.30**	0.06	0.55**	0.91**	0.74**
SS 3 Stiff Ter	− 0.16	− 0.12	0.06	− 0.47**	− 0.38**	− 0.03	0.40**	0.14	0.37**
SS 5 Stiff Ter	− 0.17	− 0.13	0.06	− 0.47**	− 0.42**	0.05	0.31**	0.12	0.29**	0.94**
SS 3 Soft Ter	− 0.18	− 0.14	− 0.03	− 0.57**	− 0.45**	− 0.08	0.37**	0.12	0.40**	0.93**	0.87**
SS 5 Soft Ter	− 0.21*	− 0.20*	− 0.05	− 0.57**	− 0.49**	− 0.06	0.30**	0.18	0.29**	0.89**	0.87**	0.93**

Parameter estimates are derived from a hierarchical structure which may in some cases inaccurately estimate correlation strength. These values should be interpreted with a degree of caution
Italics values emphasize primary correlations of interest described in main text. N = 1 participant missing SDMT Oral and N = 1 participant missing NHPT not included in correlational analysis. Given model 4 was the preferred model from experiment 1 and similar BPIC values for models 4 and 5 from experiment 2, correlations are computed using model 4 parameter estimates combined across experiments 1 and 2
SS set size