Fig 1.
Optical and non-optical consequences of a movement executed within the plane of a stationary object.
The egocentric distance can be expressed as a function of directional parameters (α, θ) and linear parameters about head movements (v).
Fig 2.
(A) Set up. The participant’s head position and orientation were sampled and used in real time to drive the display of a HMD so as to depict a stationary virtual target. (B) Experimental conditions (see text for details). (C) Screen capture. The virtual target was the only visible element on the HMD screen.
Fig 3.
(A) Global regression curves (lines) and means (symbols) for both groups of participants in Movement (blue), Stationary (violet) and Playback conditions (green). The percentage of positive responses is plotted as a function of target distance (expressed in proportion of the actual maximum reachable distance, MRA). (B) Perceived maximum reachable distance MRP for each group (Near and Far, respectively dark and light blue dots) in the Movement condition. The vertical grey bars mark the median of the set of tested distances for each group of participant (the range of tested distances is indicated by the grey brackets and dotted lines). The vertical orange bar represents MRA for both groups. In each group, MRP is biased toward the median (black arrows) but simultaneously attracted toward MRA, as expected (brown arrows).
Fig 4.
Mean confidence ratings expressed as a function of target distance.
The rating scale ranged from 1 (lowest) to 5 (highest). (A) Near Group. (B) Far Group. Distance on abscissa axis is expressed in proportion of the actual maximum reachable distance, MRA. Dotted lines represent second order polynomial regressions (see text and S2 Table for details).
Fig 5.
Frequency plot of principal directions of movement for all trials and participants in Movement condition.
The principal direction corresponded to the eigenvector associated with the largest eigenvalue of the trial orientation matrix. A principal direction was computed for each trial, but only those for which the eigenvalue exceeded. 5 and the ratio of second and largest eigenvalues was less than. 8 were included in the plot (1147 out of the 1190 trials). The red and orange dots represent the two directions usually tested in the literature: toward the target (AP) and laterally (ML), respectively.
Fig 6.
Amplitude, instantaneous speed, and acceleration of head movements in the Movement condition.
Mean values with standard errors are plotted as a function of initial target distance, expressed in proportion of the actual maximum reachable distance, MRA. (A) Mean range along principal axis. (B) Mean norm of instantaneous velocity. (C) Mean norm of instantaneous acceleration.
Fig 7.
Distance information created through movement during one representative trial in the Movement condition.
Data from participant Near 2, trial 33. (A) Head trajectory (bird’s eye view). The scale is in meters. The green cylinder indicates the location and size of the virtual target. (B) Evolution over time of the actual distance of the target and of the distance specified by Eqs 10, 1 and 13. The curve for the actual distance is not visible on the plot because of the perfect overlap with the distance specified by Eq 10. (C) Evolution over time of the optic and inertial components of Ii as formalized in Eq 10.