Focused and divided attention in stereoscopic depth

Abstract

Two experiments are described which examine the effect of distance in the depth plane, as defined operationally by binocular disparity, on focused and divided attention. In both experiments, disparity was manipulated with a Tektronix stereoscopic 3D display system. In Experiment 1 (focused attention), 10 subjects classified letter stimuli presented at zero disparity. The targets were surrounded, either vertically or horizontally, by two irrelevant stimuli. The distractors were presented at 7 different depth planes relative to the target (i.e., 3 in front, 3 behind, and 1 at the same depth). The distractors showed evidence of being processed when at the same depth plane as the central relevant stimulus, but diminished processing when presented at different depth planes. This pattern of data provides evidence for a fairly narrow attentional bandwidth in depth, for focused attention. In Experiment 2 (divided attention), 8 subjects performed a one-axis pursuit tracking task at 0 disparity, while concurrently responding to stimuli presented immediately below, and at 5different depth planes (1 at the same disparity as the tracking task, 2 in front of, and 2 behind the tracking display). While there was considerable interference between the two tasks, there was no evidence that this interference was modulated by similarity of depth when the depth plane of stimulus presentation was known in advance (i.e., was blocked). These results suggest that in divided attention, where stimulus location is known in advance, the attentional bandwidth in depth is sufficiently broad to accommodate the same range of depth planes over which filtering had been observed in focused attention. When however the depth plane was randomized and unpredictable, evidence for a depth gradient of divided attention was found. The results are discussed in terms of attentional theory and the usefulness of stereoscopic displays.