Figure 1.

Task protocol and stimuli. A, DMS task. The bird initiated a trial by keeping its head still in front of the monitor (automatically detected) to activate a go stimulus. After a 500 ms presample period, a sample stimulus was presented for 500 ms, followed by a 1000 ms delay. In the choice period, the crow chose the image identical to the sample item from an array of four items to receive a reward. All relevant task parameters were balanced. B, Rule-switching task. Go stimulus, presample, sample, and delay 1 are identical to the DMS task. After the first delay, a rule cue (either visual or auditory) indicated whether the bird was required to choose the same image as the sample image or a different image. The rule cue was followed by another 1000 ms delay. The choice period consisted of two images: the sample image and one other image from the daily set of four images. The shaded area (Encoding/Memory period) marks the analyzed sample and delay periods, which were completely identical in both tasks.