The Impact of Target Depth on Pointing Performance

An important visual cue for the distance to a target is its binocular depth, the disparity between the left and right eyes. We examined mid-air pointing on a large screen, varying the physical distances (depths) to targets. Welford's two-part formulation provided a better model than the one-part Fitts's Law formulation to predict movement time from movement amplitude and target width. Angular measures suggested by Kopper et al. did not improve the model. Consistent variations of Shoemaker et al.'s k-factor suggest target depth plays a role similar to gain for mid-air pointing. We compared both physical and virtual targets to determine if artificial binocular depth cues induce the same performance as purely physical binocular depth cues. Variation of the k-factor was different when virtual depth and physical depth were not identical. This has implications for calibrating 3-D virtual environments and for the design of interactive 3-D pointing techniques for those environments.