Influence of the behavioural context on the optocollic reflex (OCR) in pigeons (Columba livia).

We investigated the effects of several behavioural conditions on the properties of the horizontal optocollic reflex (OCR) in pigeons. The head reflex was triggered by rotating the visual surroundings at different velocities (stimuli steps of 30-300 deg. s(-1)) and the characteristics of the slow and fast phases of the OCR were analysed during, (i) the 'resting condition', in which animals were hung in a harness, (ii) the 'standing condition', in which animals were freely standing, (iii) the 'walking condition', in which animals were walking on a treadmill at different velocities, and (iv) the 'flying condition', in which animals were hung in a harness and subjected to a frontal air-stream, provoking a flying posture. In the 'resting' condition, irregularities were observed in the amplitude of nystagmic beats, in the beating field and in the slow phase velocity (SPV) of the OCR. These irregularities diminished progressively when the behavioural condition changed from 'standing' to 'walking', and disappeared in the 'flying' condition. Correlatively, the working range of the OCR (evaluated by its gain at the plateau of SPV) was progressively extended toward higher stimulation velocities. The velocity of the fast phases of the OCR (measured for all the conditions except the 'walking condition') also increased in correlation with the SPV. The walking speed did not influence the OCR in the treadmill velocity range of 0.20-0.40 m s(-1). The presence of a frontal airstream in the 'standing condition' did not change the OCR properties. This fact (and other observations discussed in the paper) suggests that the adaptation of the OCR to the behavioural context is mediated by internal signals generated by each behavioural condition.