The effects of muting lesions on emotional behaviour and behaviour normally associated with calling

Bilateral intercollicular lesions in the chick abolish or depress not only calling, but also those phases of behaviour when calling would have been occurring. These include: long bouts of excited feeding immediately after food is made available; examining and pecking moving targets and novel objects; persistent scanning, and inhibition of other behaviour in a novel environment. Deaf birds behave precisely like controls, so that possible auditory deficits are not involved. During calling phases significant visual stimuli are treated as if they were starting or conspicuous. Conversely, continuous examination of a stimulus causes calling to diminish or disappear even though response continues; a brief period when the stimulus is not seen causes calling to begin again when it is once more perceived. In addition to the increased effectiveness of relevant visual stimuli, motor facilitation is usual in calling phases, as is inhibition of irrelevant responses. Emotional behaviour in man and other mammals is compared to calling phases in the chick.