Tonic immobility in chicks during presentations and withdrawals of an imprinting stimulus

We investigated the effects of presentation and withdrawal of an imprinting stimulus on durations of the tonic immobility reaction in domestic fowl. In Experiment 1, presentation and withdrawal of the imprinting stimulus was compared to similar manipulations with a novel stimulus. Differences in the immobility reaction were due to specific effects of the imprinting stimulus. In Experiment 2, we demonstrated the effect of the presence or withdrawal of only the imprinting stimulus on the duration of the immobility reaction. The presence of the imprinting stimulus shortened the duration of the immobility reaction, while the withdrawal of the same stimulus lengthened the duration of the reaction, relative to a baseline condition. The results are interpreted in terms of central affective states which interact in simple ways.