Errors in pigeons' memory for number of events

In Experiment 1, pigeons were trained in a within-subjects design to discri minate sequences of light flashes (illumination of the feeder) that varied in number, but not in time (2f/4sec and 8f/4sec), and in time, but not in n umber (4f/2sec and 4f/8sec). Number samples required a response to one of t wo comparison dimensions (either color or line), whereas time samples requi red a response to the remaining comparison dimension. Delay testing reveale d a significant choose-small bias following number samples and a significan t choose-long bias following time samples. In Experiment 2, testing confirm ed that in the absence of a sample, there was a bias to respond small to th e number comparisons and long to the time comparisons. Additional tests ind icated that the birds were discriminating time samples on the basis of the number of light flashes occurring during the last few seconds of the time s amples, rather than on the basis of the total duration of the flash sequenc e. Consequently, the choose-long bias observed for time samples during dela y testing was really a choose-small bias. In Experiment 3, the birds receiv ed baseline training with a 5-sec delay and were subsequently tested at sho rter and longer delays. A choose-large bias occurred at delays shorter than the baseline training delay, whereas a choose-small bias was again observe d at delays longer than the baseline delay. These findings provide addition al empirical support for the conceptualizing of memory for number and time in tenus of a common mechanism.