(Disparity-Driven) Accommodation Response Contributes to Perceived Depth

Abstract

When looking at objects at various distances in the physical space, the accommodation and vergence systems adjust their parameters to provide a single and clear vision of the world. Subtended muscle activity provides oculomotor cues that can contribute to the perception of depth and distance. While several studies have outlined the role of vergence in distance perception, little is known about the contribution of its concommitant accommodation component. It is possible to unravel the role of each of these physiological systems by placing observers in a situation where there is a conflict between accommodation and vergence distances. We thus sought to determine the contribution of each response system to perceived depth by simultaneously measuring vergence and accommodation while participants judged the depth of 3D stimuli. The distance conflict decreased depth constancy for stimulus displayed with negative disparity steps (divergence). Although vergence was unaffected by the stimulus distance, accommodation responses were significantly reduced when the stimulus was displayed with negative disparities. Our results show that biases in perceived depth follow undershoots in the disparity-driven accommodation response. These findings suggest that accommodation responses (i.e., from oculomotor information) can contribute to perceived depth.

Keywords: accommodation; oculomotor cues; perceived depth; sensory conflict; stereoscopic displays; vergence.

Figure 1

A typical trial. Before initiation, the fixation cross was located on the screen plane at a given distance (57, 80, and 133 cm). Following initiation by the participant, the fixation cross jumped in depth or remained in the same plane, and then stayed on the display for 2 s. The apex of the angle was then placed at one of three possible distances (57, 80, and 133 cm), while the screen plane was set at one of these three possible distances. After adjusting the hinge angle, the cross returned back to the screen plane. Drawing is not to scale.

Figure 2

Left: scaling distances as a function of vergence distance for the three accommodation distances (red: 57 cm, blue: 80 cm, and black: 133 cm). Middle: variable error as a function of vergence distance for the same conditions. Right: slopes of depth constancy as a function of accommodation distances. The gray bar represents the condition where accommodation distance equals vergence distance. Vertical error bars show 95% Cousineau-Morey confidence intervals for within-subjects designs (Cousineau, ; Morey, 2008).

Figure 3

Averaged accommodation (Top) and vergence (Bottom) responses to a ± 1 Diopter depth step of a representative observer. The left column shows near-to-far depth steps (i.e., disaccommodation and divergence) and the right column shows far-to-near depth steps (i.e., accommodation and convergence). D stands for Diopters and MA for Meter Angles. Central curves depict the averaged response over ten trials. Thin curves indicate the 95% bootstrap confidence interval of the mean response.

Figure 4

Left: accommodation response as a function of vergence distance, accommodation distance (red: 0.57 m, blue: 0.8 m and black: 1.33 m, circle: no conflict) and distance conflict (square: ± 0.5 D, triangle: ± 1 D). Middle: vergence response as a function of vergence distance, accommodation distance, and distance conflict (same legend). Negative responses indicate disaccommodation or divergence response functions whereas positive responses indicate accommodation or convergence response steps. Right: accommodation and vergence response amplitude as a function of distance conflict. Accommodation is depicted in dark orange and vergence in dark blue. Vertical error bars show 95% Cousineau-Morey confidence intervals for within-subjects designs (Cousineau, ; Morey, 2008).

Figure 5

Accommodation and vergence response amplitude as a function of perceived depth difference (dark orange: accommodation, dark blue: vergence). Lines represent linear regression fit. Note that negative values refer to divergence or disaccommodation, while positive values refer to convergence or accommodation.

Figure A1

Accommodation responses as a function of participant's age (sorted in ascending order) for each accommodation distances (royal blue: 0.57 m, cadet blue: 0.80 m, and medium green: 1.33 m; conflict is represented by circles: 0 D, squares: ± 0.5 D, and triangles: ± 1 D). Lines represent linear regression fit for each set of distances. Negative values refer to disaccommodation, while positive values refer to accommodation.