Optokinetic nystagmus and the accessory optic system of pigeon and turtle.

Optokinetic nystagmus (OKN) response functions were obtained in pigeon (Columba livia) and turtle (Chrysemys picta) before and after electrolytic lesions of the accessory optic nuclei (AON). Postlesion retinal input to the AON was evaluated using standard autoradiographic techniques. Bilateral destruction of AON in both pigeon and turtle did not abolish OKN, but was correlated instead with a reduction in OKN frequencies at high pattern velocities. A difference was observed between species with respect to the effects of partial lesions. Incomplete destruction of AON produced no observable change in OKN response functions in pigeon, but correlated with reduced OKN response functions in turtle. These results suggest that the AON mediate a portion of OKN in both pigeon and turtle, particularly at high pattern velocities, but are not essential for its occurrence.