Social facilitation of pecking following differential rearing

White-Leghorn × Black-Orpington chicks were reared socially, in isolation, or were isolated and exposed to an artificial stimulus at 16 h. They were tested at 24, 48, or 72 h for pecking in the presence of another chick, of the artificial stimulus, or in isolation. Socially reared chicks pecked more during pair-testing than in isolation, and showed no increase in pecking with the artificial stimulus. Imprinted chicks pecked most with the artificial stimulus, but showed a slight increase in pecking during pair-testing compared with isolation. Isolates showed similarly low peck rates under all conditions. These results, showing the importance of familiarity with test conditions in facilitation, were interpreted as consistent with an arousal-reduction account of facilitation. The importance of stimulus movement was also discussed, both as a potential dimension of stimulus generalization and as a factor in maintaining a minimum level of arousal essential to responding.