Afferent signals from the extraocular muscles affect the gain of the horizontal vestibulo-ocular reflex in the alert pigeon

We have shown previously that the gain of the horizontal vestibulo-ocular reflex (HVOR) is modified by afferent signals from extraocular muscle proprioceptors in the decerebrate pigeon. We have now analysed the variability of the HVOR in intact, alert pigeons and, using the artificial vestibulo-ocular reflex method, have found that in all of the pigeons tested afferent signals from the extraocular muscle proprioceptors modify the gain, but not the phase, of the HVOR. While this effect was seen in a given bird only on some occasions, when present it was consistent in magnitude and direction and closely similar to our previous observations on decerebrate pigeons. These results from alert, intact birds strengthen the evidence that extraocular muscle afferent signals play a part in the control of the vestibulo-ocular reflex.