Figure 4. Mean percentage of correct choices made by individual pigeons during each session of the initial conditioning series.

a) Mean percentage of correct choices for the two groups, for which rewarded feeder choices were either associated with increasing (up-gradient) or decreasing (down-gradient) intensity changes (chance level 25%). Because of extensive pre-training exposure to the reinforcement contingencies (see text), there was no evidence for gradual response acquisition typically associated with the learning of a discrimination task. b) Combined mean percentage of choices made at either feeder associated with the intensity gradient of the virtual magnetic intensity (VMI) map (note chance level of 50%). c) Mean percentage of correct choices calculated only for trials during which the pigeons chose either of the two feeders associated with the direction of the intensity gradient of the virtual magnetic intensity (VMI) map (chance level of 50%).