Table 4.

Multiple regressions for the discovery sample. Each model quantifies the contribution of mean activation and trial-by-trial activation variability to WJ-III Letter Word Identification raw scores

Region	Regressor	Print							Speech
		β	SE	ΔAIC	ΔBIC	ΔR2adj	F	p	β	SE	ΔAIC	ΔBIC	ΔR2adj	F	p
Left IFGop	Mean activation	−0.072	0.146	1.73	3.52	−0.015	0.246	0.623	−0.043	0.158	1.92	3.71	−0.021	0.075	0.786
	Activation variability	0.177	0.146	0.405	2.19	0.009	1.48	0.231	0.208	0.179	0.536	2.32	0.008	1.35	0.252
Left IFGtr	Mean activation	0.042	0.130	1.88	3.67	−0.015	0.106	0.746	−0.043	0.150	1.91	3.69	−0.021	0.083	0.775
	Activation variability	0.329	0.129	−4.66	−2.87	0.095	6.53	0.014	0.150	0.150	0.904	2.69	<0.001	1.01	0.321
Left SPL	Mean activation	−0.006	0.136	2.00	3.78	−0.019	0.002	0.964	−0.011	0.150	1.99	3.78	−0.023	0.006	0.939
	Activation variability	0.221	0.141	−0.644	1.14	0.028	2.48	0.123	0.086	0.166	1.71	3.49	−0.017	0.267	0.608
Left MTG	Mean activation	0.046	0.137	1.88	3.66	−0.017	0.111	0.741	0.057	0.153	1.85	3.63	−0.020	0.138	0.712
	Activation variability	0.211	0.137	−0.537	1.25	0.026	2.37	0.131	0.107	0.153	1.47	3.25	−0.012	0.490	0.488
Left ITG	Mean activation	−0.093	0.138	1.51	3.29	−0.011	0.449	0.507	0.103	0.171	1.61	3.40	−0.015	0.364	0.549
	Activation variability	0.102	0.141	1.42	3.21	−0.009	0.527	0.472	−0.187	0.171	0.739	2.52	0.005	1.19	0.281
Left STG	Mean activation	−0.039	0.140	1.92	3.70	−0.018	0.077	0.782	0.224	0.179	0.353	2.14	0.013	1.56	0.218
	Activation variability	0.102	0.141	1.42	3.21	−0.009	0.530	0.471	−0.399	0.179	−3.01	−1.23	0.088	4.95	0.032
Left thalamus	Mean activation	0.413	0.119	−9.52	−7.74	0.160	12.0	0.001	0.304	0.147	−2.39	−0.604	0.072	4.30	0.044
	Activation variability	0.160	0.120	0.095	1.88	0.011	1.77	0.191	−0.156	0.147	0.802	2.59	0.003	1.13	0.294

In all models, removal of the activation variability term did not affect the significance of the mean activation term.