Vertical displacement threshold sensitivity along the horizontal meridian as a function of stimulus rate, duration, and length
Haines, R.F.; Kiefel, S.M.
Aviation Space and Environmental Medicine 59(4): 321-329
1988
ISSN/ISBN: 0095-6562 PMID: 3370040 Document Number: 318105
Vertical displacement thresholds (DT) were quantified in 24 observers at the fovea and each of 8 retinal positions out to 80.degree. along the horizontal meridian during inocular viewing. Stimulus length was increased with eccentricity angle in accordance with the cortical magnification factor (21); a 1.degree. arc long stimulus served as a control at each position. Three movement durations (from 0.25 to 4 s) and three angular rates (from 0.04 to 0.42.degree. arc.cntdot. s-1) were also quantified at each position to determine whether peripheral DT is mediated predominantly by an image displacement- or rate-sensitive mechanism. It was found that 1) DT is mediated predominately by a constant rate-sensitive mechanism at each position when stimulus length is increased in proportion to the cortical magnification factor; 2) mean percent correct displacement judgments decrease significantly into the periphery for both stimulus lengths, however, increasing stimulus length yields signiinficantly higher accuracy; and 3) at 10 and 30.degree. eccentricity, increasing rate and duration significantly improve displacement judgment accuracy, but beyond 40.degree. only lengthening the stimulus improves accuracy. The findings are related to the design optimization of dynamic attitude displays and symbology for aircraft.