Pairs of the above elemental models

Pairs of the above elemental models were combined by the program either by adding the two HDDs from IP (a one-dimensional interaction, 1D) or by taking the square root of the sum of the squares of the values for HDDs from IP (two orthogonal dimensions, 2D), in accord with Pythagoras’s Theorem. It should be noted that 1D models are in Euclidean space, just like the 2D models, not on a city-block metric as stated by Booth and Conner (1990); this approach is psychophysical (relating responses to stimuli), not psychometric (modeling responses without incorporating data on stimuli; Booth, 1995). 。