Figure 3.

Description of the different spatial models (egocentric and allocentric) tested in this study. A, Physical variables in one trial. The projections of initial gaze (magenta dot), initial head (green cross), final gaze (black dot), and final head (green dot) orientations on the screen are depicted. Note: final gaze often lands between the target (T, red dot) and shifted target (T’, light red dot). B, While head-unrestrained, these positions can be encoded in relation to three egocentric frames of reference: eye (e), head (h), and space/body (s). Since the target was sufficiently far from the head to minimize translation effects, and because our model-fitting method is insensitive to these biases, we centered these frames to be aligned as shown in C. C, Different canonical models derived after plotting the physical parameters in fundamental egocentric frames. dG: gaze displacement referring to final gaze position with respect to the home fixation point (not the eye); dH: displacement of head in space coordinates; dE (data not shown): the displacement of eye in the head accompanying the gaze shift. Target and final gaze, eye, and head positions can be represented in any one of the three initial reference frames. See text for details of all egocentric models. D, Allocentric models that were compared with the most relevant egocentric models (Te, Ge). The broken black cross represents the location of initial landmark (L) and the solid black cross stands for the shifted (indicated by orange arrow) landmark (L’). The red, the black, and the light red solid circles correspond to the target (T), the gaze endpoint (G), and the virtual target (T’) locations, respectively. Tested allocentric models: Ls, landmark relative to space; Le, landmark relative to eye; TL, target relative to landmark; L’s, shifted landmark relative to space; L’e, shifted landmark relative to eye, TL’, target relative to shifted landmark, T’e, shifted target relative to eye; T’s, shifted target relative to space.