Linear mechanisms can produce motion sharpening

Human observers are not normally conscious of blur from moving objects [Nat ure 284 (1980) 164]. Several recent reports have even shown that blurred im ages appear sharper when drifting than when stationary and have suggested d ifferent non-linear mechanisms to explain this phenomenon [Vision Res. 36 ( 1996) 2729; Vision Res. 38 (1998) 2099]. We demonstrate here that even thou gh distortions of drifting narrow-band sine-wave gratings cannot be explain ed by linear mechanisms, these mechanisms may have an important role in sha rpening of moving edges. We show first that the effective spatial filter fo r a moving object that is formed by a simple difference-of-Gaussians spatia l filter and the typical biphasic temporal impulse response function can be approximated by a combination of Gaussian filters only. When this filter i s applied to moving, Gaussian-blurred edges, regions of blurring and sharpe ning are found over the same ranges of blur widths and velocities where rec ent experimental findings have shown them to exist. In general, that means that the output of the filter shows blurring in response to small blur widt hs and sharpening in response to larger blur widths. (C) 2001 Elsevier Scie nce Ltd. All rights reserved.