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Constance S. Royden, Erin M. Connors; The effect of eccentricity on detection of a moving object by a moving observer. Journal of Vision 2006;6(6):585. doi: 10.1167/6.6.585.
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© ARVO (1962-2015); The Authors (2016-present)
To detect an object moving with respect to stationary items in a scene, an observer moving in a straight line must identify the object whose image motion differs from the radial motion pattern of the images of stationary items. We tested whether the ability to detect a moving object varies with its distance from the center of the radial pattern (the focus of expansion, or FOE). In each trial, observers viewed a scene consisting of 25 white circles moving in a radial pattern on a black background. In half the trials the target circle moved with some angular deviation from the radial pattern. Observers pressed a key to indicate whether or not this target circle was present in a trial. We measured the percentage of correct responses for angular deviations ranging from 8 to 40 deg and target positions of 2.5, 5.0 or 10.0 deg from the FOE. For 6 observers, the average angular deviation threshold for detection was 25.7, 14.9 and 12.3 deg for the 2.5, 5.0 and 10.0 deg eccentricities, respectively. The thresholds for the 2.5 and 5.0 deg eccentricities were consistent with an error in localizing the FOE of about 1.3 deg, similar to the accuracy with which humans judge the location of the FOE. This suggests that error in locating the FOE may be one factor limiting the ability to identify moving objects for small eccentricities. It is likely that speed also plays a role, because images move faster at larger distances from the FOE.
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