Table 1. Estimates of various factors to account for activations.

Factors in the hierarchical tree structures	Factor	Simple	Linear	Quad	Match
	DoM	1	2	3	0
	No. of nodes	6	5	9	5
		Simple – Match	Linear – Match	Quad – Match	Linear – Simple
	DoM	1	2	3	1
	No. of nodes	1	0	4	−1

We defined the estimate of a factor as the largest value that the factor can take for each condition: e.g., “1, 2, 3, and 0” for the DoM in the hierarchical tree structures. For each factor, its unit load should be invariable among all conditions, making an independent subtraction between estimates of the same factor possible. We assumed that positive and negative values of the subtracted estimates corresponded to activations and deactivations, respectively. Under all tested conditions, “number of operations” was equal to “number of Merge,” which was the total number of binary branches in the tree structures (Figure 2). Null or negative subtracted estimates were denoted in bold.