We studied the cervico-ocular reflex (COR) alone and in combination
with the optokinetic (OKN) reflex in head-fixed pigeons. We analyzed
these responses in two behavioral conditions: (1) animals were hung in
a harness (“resting” condition); and (2) animals were
additionally submitted to a frontal airflow that provoked a flight
posture (“flying” condition). In both conditions, cervical
stimulation provoked a slow phase of very low gain (around 0.05) in the
opposite direction to that of the stimulation and fast phases triggered
near the head–body alignment in the same direction as the
stimulation. The slow phase showed a phase lag of 20 deg at 0.5 Hz. The
gain of the slow phase was not modified by the velocity, amplitude, or
frequency of the stimuli. This gain was not changed by the presence of
a fixed visual surround.
When cervical stimuli (0.05–0.5 Hz) were added to an
optokinetic stimulation (30 deg/s) in the “resting”
condition, the slow phase velocity (SPV) of the optokinetic reflex was
modulated with a time course close to that produced by the
cervico-ocular reflex alone. The SPV was alternately increased and
decreased round the SPV level corresponding to the steady-state OKN. In
the “flying” condition, optokinetic-cervical stimulation
provoked an eye beating field and a strong SPV modulation synchronized
with the position of the cervical stimulation. The number of nystagmic
beats (OKN) and the amplitude and velocity of the fast phases were
modulated in correlation with the SPV. Consequently, the optokinetic
response was increased or decreased according to whether the cervical
stimuli were in the reverse direction or in the same direction as the
optokinetic stimulation, respectively.
These data are interpreted as an improvement of gaze stabilization by
the COR. This mechanism is context dependent, since it is strongly
reinforced during the flight.