A flashed object presented in spatial alignment with a moving object is generally perceived as lagging behind the moving object. Previous studies of this flash-lag effect have compared stationary, flashed stimuli of exceedingly short duration to moving stimuli of long duration. We explored the flash lag effect in a moving Vernier task, where subjects must compare the alignment of two identical gratings, both drifting at equal velocity.

In this paradigm, each grating is windowed with a Gaussian temporal envelope of a different width, so that both gratings ramp on and off and drift for the period of time in which they are visible. This paradigm allows us to examine the “delays” that exist between stimulus pairs drawn from a spectrum that ranges from a single frame presentation to continuous motion. The stimulus construction also has a simple interpretation in the Fourier domain, which makes it easy to quantify the difference between the “moving” and “flashed” stimulus in terms of their spatio-temporal frequency content.

We found a flash-lag effect in moving Vernier judgments that is modulated by the difference in the widths of the Gaussian temporal envelopes. Our results are consistent with the hypothesis that greater processing delays exist at higher temporal frequencies.