Experiment 1: dependence of vergence linked to horizontal gaze shifts on compression (data for three subjects). A. Mean vergence gain; filled symbols, horizontal compression; open symbols, vertical compression; error bars, 1 SE; each datum point is an average of at least 118 (subject BMS), 143 (subject FAM), and 65 (subject NPB) individual responses. B. Mean VH Ratios (vergence gain with vertical compression expressed as a percentage of the vergence gain with horizontal compression). Straight gray lines are regression lines whose defining coefficients are shown together with the coefficients of determination (R2). Symbols denote subjects: diamonds, BMS; squares, FAM; circles, NPB.