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Anisotropy of the Power Spectrum as a Cue in the Analysis of Visual Motion
Applied Math| Speaker: | Prof. Horace Barlow, Cambridge University |
| Location: | 693 Kerr |
| Start time: | Mon, Mar 18 2002, 4:10PM |
The eye's photoreceptors are astonishingly slow, for human cones take about 30 msec to reach their response to a brief flash, even in good light. In moving images there must as a result be a loss of high SPATIAL frequencies along the lines of motion; there is heavy attenuation at 50 Hz, so when an image moves at 5 deg/sec, there can be little spatial modulation above 10 cycles/deg, whereas a stationary gratings can be resolved up to 50 cyles/deg. There is no corresponding loss of high spatial frequencies at right angles to the direction of motion, so it follows that there is anisotropy of the power spectrum in moving images. Could this be detected and used by the visual system to determine the axes of motion in moving images? I shall review recent evidence (Ross, Babcock & Hayes, 2000; Geisler 1999; Burr and Ross, 2000) which indicates that this is the case,and show how older evidence (Gallant et al, 1996) together with the extensive literature on "Glass figures" (eg Wilson and Wikinson 1998), also supports this idea.
Professor Barlow is a UC Regent's Lecturer this year.