Abstract
Much of the work on fixation patterns in complex scenes has been performed with 2D images. However, in natural behaviour fixation patterns are highly task dependent. 2D images differ from the natural world in several ways, including the nature of the task demands and the dimensionality of the display. To investigate the role of these factors in gaze patterns, we monitored eye movements in both normal and schizophrenic participants. Schizophrenic patients have previously been shown to exhibit prolonged fixations and reduced spatial exploration in free viewing of 2D images. Participants started with two free viewing tasks. They were asked to (1) look at a scene on a computer screen (2D passive exploration) and (2) look at a real scene on a table (3D passive exploration). Then, participants performed two other ""active viewing"" tasks: (1) picturing themselves making a sandwich in front of a computer screen (2D active exploration) and (2) making a sandwich (3D active exploration). The scenes contained both task- relevant and irrelevant objects. Temporal and spatial characteristics of gaze were compared for each task. The primary factor in determining gaze location and duration was the task demands. Fixation durations were longer for the active than the passive task for both 2D and 3D images. Normal participants did not show any difference between 2D and 3D images in passive viewing condition, although 2D and 3D active viewing conditions differed. Moreover, allocation of gaze between relevant and irrelevant objects differed in active viewing but not in passive viewing. Participants looked more at relevant objects during the real task. For patients with schizophrenia, the introduction of a task essentially eliminated differences from normal controls that are observed in passive viewing. Thus real versus 2D images had little effect on viewing patterns, but the task constraints were critical.