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<p>different times of day and show <a href="page.php?w=Time-Place_learning">time-place learning</a>. After training, lab subjects were successfully able to peck specific keys at different times of day (morning or afternoon) in exchange for food, even after their sleep/wake cycle was artificially shifted. This suggests that to discriminate between different times of day, pigeons can use an internal timer (or <a href="page.php?w=Circadian_rhythm">circadian timer</a>) that is independent of <a href="page.php?w=Sensory_cue">external cues</a>. However,</p><p>
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