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Marcia Grabowecky, Emmanuel Guzman-Martinez, Parkson Leung, Steven Franconeri, Satoru Suzuki; A simple technique to improve fixation performance in naïve observers. Journal of Vision 2009;9(8):433. doi: 10.1167/9.8.433.
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Maintenance of stable central eye fixation is crucial for a variety of behavioral, electrophysiological, and neuroimaging experiments. Naïve observers in these experiments are not typically accustomed to fixating and are often unable to reliably maintain fixation and this may produce confounds in experimental results. Verifying fixation requires the use of cumbersome and costly eye-tracking and results in loss of participants when they are unable to reliably fixate. We devised a simple flicker display consisting of a random-dot pattern (single pixels [.047 deg], 50% black, 50% white) rapidly alternating (37.5 Hz; 75 Hz refresh rate) with its video reversed complement (i.e. white dots became black and black dots became white). This display appeared as a uniform gray patch when the eyes were stable (due to temporal luminance summation), but produced an easily detectable momentarily static noise pattern (due to disrupted temporal summation of luminance) whenever the eyes moved or blinked. A few minutes of training using this display dramatically improved the accuracy of eye fixation when observers later performed a demanding peripheral attention-cueing task. Observers reliably detected their own eye-movements when their eyes deviated by as little as 0.5 degrees. In contrast, the same amount of training using control displays that were uninformative about fixation performance did not produce significant fixation improvements, and some observers consistently made eye movements towards the attention cue, contaminating the observed attention-cueing effect. Our results indicate that (1) eye fixation can be rapidly improved in naïve observers by providing contingent feedback about eye movements, and (2) our simple flicker technique provides an easy and effective method for providing this feedback.
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