Purchase this article with an account.
R. Dirk Beer, Erin A. Krizay, Donald I. A. MacLeod; Spatiotemporal averaging along a moving trajectory. Journal of Vision 2007;7(9):1043. doi: 10.1167/7.9.1043.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
We find that changes in luminance are detected with impaired sensitivity when they belong to an object in apparent motion. A disc was viewed in an orbit around the point of fixation. It appeared sequentially in eight locations at 45 degree intervals around fixation. Luminance modulation was introduced by increasing luminance on the major axes and reducing it on the diagonals, or vice versa. Vivid large-scale apparent motion results at intermediate interstimulus intervals, but not at very short or very long ISIs.
In one experiment, subjects matched the luminance of the lighter, or the darker, disks of a fixed-modulation stimulus using a central disc. The difference between the matches is a measure of the apparent luminance modulation. The apparent modulation was reduced at ISIs that gave strong apparent motion.
In a second experiment, subjects matched the diagonal to the major axis discs, effectively adjusting the luminance modulation to zero. The reciprocal of the standard deviation of the settings is a measure of modulation sensitivity. By this criterion, modulation sensitivity was sharply reduced at ISIs that gave strong apparent motion. Also, the task of making the setting was experienced as far more difficult in the presence of the motion.
We conclude that detectability of a spatial luminance modulation can be severely compromised when the luminances compared appear to belong to a single moving object. The large visual angle between successive discs in our experiment precludes spatio-temporal averaging in the afferent pathways or V1, so evidently high-level vision incorporates a bias toward constancy in the properties of moving objects. The constancy assumption is usually correct, and allows economy in representation.
This PDF is available to Subscribers Only