Associative blocking of the mccollough effect

After exposure to two simultaneously presented achromatic grids (A and B) on a coloured field, subjects reported colour aftereffects on each of the separately presented grids. These aftereffects were shown to be examples of the McCollough effect, since they were contingent upon the subjects having experienced the grid in combination with the coloured field. Exposure to the coloured field in advance of combining the colour field with the grids attenuated the strengths of the aftereffects on the A and B grids. Moreover, exposure to the A grid on the coloured field in advance of combining the B grid with the A grid on the coloured field abolished the aftereffect on the B grid. The failure of the B grid to arouse the aftereffect was due to the presence of the already trained A grid, since exposure to the A grid on the coloured field followed by exposure to the B grid on that field yielded the aftereffect on the B grid. The conditions under which the McCollough effect was attenuated are those under which learning fails to occur in Pavlovian conditioning procedures. The results, therefore, supported the view that the pairing between the grids and the colour resulted in a learned association between the grids and some aspect of the response by the visual system to the colour.