Combining depth cues: effects upon accuracy and speed of performance in a depth-ordering task

Two experiments investigated how the number of available depth cues affected the speed and accuracy of depth-ordering judgements. A series of textured tiles was presented on a computer monitor, with relative depths defined by combinations of contrast, blur and interposition. Subjects were required to move a mouse pointer inside each tile in turn, starting with the tile that appeared nearest, clicking on each. Accuracy of depth-ordering was much higher than chance in all conditions, though performance using the interposition cue alone was worse than in all other conditions. The only difference in reaction time in different cue conditions was in the time elapsed before the first-click. Subjects responded substantially faster when three depth cues were present (0.84 s) than when only one depth cue was present (1.41 s). The improvement in reaction time with cue numerosity is consistent with probability summation between cues extracted by independent processes.