ASSESSMENT OF VISUAL-ACUITY AND CONTRAST SENSITIVITY IN THE CHICK USING AN OPTOKINETIC NYSTAGMUS PARADIGM

While the chick is one of the widely used animal models for eye growth studies very little is known about its visual spatial resolution perf ormance. Using optokinetic nystagmus responses as an indicator of stim ulus visibility, we estimated the visual acuity of young chicks to be between 6.0 and 7.7 cycles deg(-1) at 2 and 4 days of age and slightly higher, between 7.7 and 8.6 cycle deg(-1), at 8 days. Contrast sensit ivity measured using the same experimental paradigm was greatest at ar ound 1.2 cycle deg(-1), for which the contrast threshold lay between 4 % and 11%. Sensitivity became progressively poorer for frequencies bot h higher and lower than this. These data suggest that the visual perfo rmance of the chick is slightly poorer than that of the pigeon which h as a similar eye size and exhibits similar foraging behaviour. (C) 199 8 Elsevier Science Ltd. All rights reserved.