Exposure to a flickering uniform field can reduce flicker sensitivity even when the adapting oscillation is imperceptibly fast, suggesting that sensitivity to high temporal frequency modulations is regulated at a pre-conscious stage of processing. In an effort to place further limits on the sites of flicker sensitive mechanisms and conscious awareness we examined the orientation specific sensitivity loss induced by exposure to counterphasing grating stimuli at a range of temporal frequencies. We tracked contrast thresholds for both a parallel (to the adaptating grating) and an orthogonal grating at regularly spaced time intervals of exposure. Perhaps surprisingly, substantial orientation-specific adaptation occurred even for imperceptibly fast counterphasing gratings. This places the site of adaptation atleast at the stage where orientation is first encoded (input layers of primary visual cortex), and places the site of conscious perception of grating flicker beyond that. The build up of the effect consists of an initial, large, rapid ([[lt]]4s) component followed by shallow, exponential growth with a 20-30s time constant. Consistent with previous studies we found no evidence for a long-term persisting effect of adaptation.