In several experiments we have shown that the pairings of seed with food are essential for the development of normal pecking.   Three groups of squab reared on the powder diet are shown in this figure.  The paired subjects were exposed to the sight of seed for 20 minutes and then immediately fed by the experimenter on days 14-20.  The explicitly unpaired subjects were also exposed to seed for 20 minutes but were fed after a 2 hour delay.  The context subjects were exposed to the test arena with no seed but fed immediately after the exposure.  The data show that only subjects for whom feeding occurs in close proximity to exposure to the seed come to peck at high rates when they are tested on PD21.