Eye oscillations in strobe reared cats

Abstract

Cats reared from birth in stroboscopic illumination develop abnormal spontaneous eye oscillations of low amplitude. The present experiments were undertaken to define these eye movements as recorded in the dark, in stroboscopic light of various frequencies, after exposure to normal light and after attenuation of the vestibulo-ocular reflex (VOR) gain by optical reversal of vision. The interaction of spontaneous eye oscillations with voluntary saccadic eye movements, and optokinetic tracking (OKN), were also studied. Two cats, reared from birth to 18 months in 8 Hz strobe light, and one normally reared control animal, were used. Horizontal movement of the right eye was measured by the scleral eye coil method. The frequency content of eye movement records was determined by power spectral analysis. VOR gain was estimated in the dark, by rotating the animals sinusoidally at 1/8 Hz and 5 degrees/sec velocity amplitude. In the dark, both strobe reared cats had abnormal spontaneous eye oscillations at a frequency close to 8 Hz, with peak-to-peak amplitudes of 0.5--1.0 degrees. These abnormal eye movements did not interfere with, nor were they abolished by, normal oculomotor activity. The introduction of strobe light modified the spontaneous eye movements by entraining the oscillations at a given 'forcing' frequency, and by producing a number of harmonics or sub-harmonics. In one of the strobe reared animals, the effect of normal light was to reduce the characteristic 'dark' value of 9 Hz, to a new maintained 'light' value of 2.7 Hz. Adaptive attenuation of the VOR gain caused the abolition of regular spontaneous eye oscillations in the dark; nevertheless, transient oscillations to single strobe flashes could still be elicited in the VOR adapted condition. The results are interpreted as representing an organised attempt by the developing oculomotor system to attain the goal of stable visual perception in a new visual environment.