The McCollough effect in pigeons: tests of persistence and spatial-frequency specificity

Eight pigeons were trained on a conditional discrimination using red and gr een saturated and desaturated fields, and red and green saturated and desat urated vertical and horizontal black-on-colour gratings. The pigeons learne d to discriminate the stimuli on the basis of colour, to a high level of ac curacy, regardless of saturation or the presence of gratings. The pigeons w ere then repeatedly exposed to stimuli in which colour and grating orientat ion were correlated, following which they were tested for the presence of t he McCollough orientation-contingent colour after-effect, using black-on-wh ite vertical and horizontal gratings. Six of the birds showed convincing ev idence of the presence of the McCollough effect, and the effect was signifi cant across all birds. These findings support those of Roberts (1984), usin g a substantially different methodology. The six birds showing the McCollou gh effect were then tested for the persistence of the effect at delays of 2 4 to 96 h. Four of the birds showed evidence of the McCollough effect at le ast 24 h after the induction procedure. Three of these birds were also test ed to investigate the spatial frequency selectivity of the effect. The resu lts suggest a narrow tuning of the McCollough effect in pigeons of less tha n 0.36 log units. (C) 1999 Elsevier Science B.V. All rights reserved.