Our eyes are moving constantly, even when we try to keep our gaze fixed on a stationary target. We can classify these unvoluntary tiny eye movements into tremor, drift and micro-saccades. In a recent study (Thaler,L., Schütz, A.C., Goodale, M.A. & Gegenfurtner,K.R (2013). What is the best fixation target? The effect of target shape on stability of fixational eye movements. Vision Research,76,31-42.[download as pdf]) we investigated if the shape of a fixation target affects variability (2D-dispersion) and stability (micro-saccade frequency) of fixational eye movements. We found (a) that target shape affects variability and stability of fixational eye movemts and (b) that there is an 'optimal' target shape, which minimizes variability and maximizes stability of fixational eye movemts.
The results are interesting from an applied point of view, because (a) micro-saccades can cause artifacts in fMRI, MEG and EEG data analysis and (b) unvoluntary tiny eye movements may render the assumption that a target was perfectly fixated invalid, which may have consequences for the interpretation of behavioral data. Thus, an 'optimal' fixation target may be useful for research that requires the eyes to be as steady as possible.
The results are also interesting from a conceptual point of view, because they may help to understand the neural mechanisms underlying fixational eye movements.