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Models of visual scanning for homogeneous displays: A test of two underlying assumptions

Thomas Allen Ranney, University of Massachusetts Amherst


Searchers typically adopt random-appearing scan patterns when inspecting homogeneous surfaces, presumably because the absence of critical features (pattern irregularities and edges) precludes development of systematic and efficient scanning strategies. The present research attempted to determine whether available modeling tools were appropriate for developing optimal scanning aids for homogeneous displays. Three experiments were conducted to test two critical assumptions that underlie existing models of visual scanning. The first experiment tested the assumption that a static visual lobe, obtained in a task in which the eyes remained fixated at a single location, was the same as a dynamic visual lobe, obtained in a task in which the eyes moved before and after the display presentation. The dynamic lobe was slightly smaller, but no different in shape than the static lobe. The second experiment tested the Independence Model, according to which information acquired in a given fixation cannot be combined with information acquired in a subsequent fixation. Each trial consisted of two tachisoscopic presentations of overlapping portions of the same homogeneous field, controlling target presence on each fixation. Detection performance was compared between conditions on which the target was present on one or two display presentations. The results were consistent with Independence Model. In the third experiment, the Independence Model was tested in a multiple-fixation continuous dynamic scanning task. The subjects' unexpected inability to fixate accurately at specified locations precluded a direct test of the Independence Model, however a Static Independence Model was constructed using a single-fixation continuous lobe model to predict target-detection at each fixation within the dynamic scanning task. Dynamic scanning performance differed systematically from predictions of the Static Independence Model, reflecting an apparent shift in allocation of attentional resources to the center and away from the top and bottom of the display. The attentional shift was embodied in a Dynamic Independence Model which better predicted dynamic scanning performance. Although there was considerable individual variation, the results suggest the requirement to fixate at specified locations may have interfered with target-detection performance at certain target locations. Implications for the development of optimal scanning aids for homogeneous display were discussed.

Subject Area

Industrial engineering|Occupational psychology

Recommended Citation

Ranney, Thomas Allen, "Models of visual scanning for homogeneous displays: A test of two underlying assumptions" (1998). Doctoral Dissertations Available from Proquest. AAI9909207.