Optokinetic nystagmus suppression as an index of the allocation of visual attention.

PURPOSE To use the suppression of optokinetic nystagmus (OKN) as an objective measure of subjects' ability to distribute their visual attention to different elements-static or dynamic, simple or complex-in their visual environment. METHODS Large-field, constant-velocity projected images, along with a stationary central fixation target were presented to 25 young participants (13 women). Images were either black O's with a few X's or red C's, blue T's, and a few red T's, with the X's and red T's as the search targets. Stationary targets at either 0° or ±12.5° were either blinking squares or a rapid succession of colored shapes-blinks or green stars were the target events. Central fixation was maintained at all times. OKN gain was calculated for all tasks and analyzed in a mixed 4-way ANOVA, with the sex of the subjects as the group variable and dynamism, location, and complexity as within-subject effects. RESULTS There was no effect of sex; all three main within-subject effects were significant, as were the two-way interactions between them and an interaction between dynamism and sex. The most striking result was that there was little difference across static tasks but that dynamic tasks showed significantly more OKN breakthrough, particularly for the complex search presented centrally. CONCLUSIONS In this group of normal-sighted young subjects, OKN breakthrough was sensitive to a range of stimulus characteristics. This finding allows a single outcome measure to be used across a wide range of possible tasks and may be useful in assessing the effects of age and disease.