Three methods to elicit sigma-optokinetic nystagmus in Java monkeys

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Abstract
Sigma-optokinetic nystagmus (σ-OKN) can be elicited in awake Java monkeys (Macaca fascicularis) when stationary periodic visual patterns (grid of black white stripes, row of equally spaced dots) are illuminated stroboscopically. Three methods were found to be useful in inducing the σ-OKN: postrotatory nystagmus, optokinetic afternystagmus (OKAN) following normal OKN and a gradual transition from ϕ-movement (ϕ-OKN) to σ-OKN. The properties found for σ-OKN in man are also present in monkeys with the one exception that monkeys have a long-lasting σ-OKAN in darkness which is not present in man. The average angular speed ¯Ve of σ-OKN slow phases was related to the flash frequency fs and the spatial period Ps of the stripe pattern according to the following equation: {ie519-01} The constant k was 1 or close to 1.