EFFECT OF TARGET SIZE ON MONOCULAR FIXATION

The method used by Boyce [1] has been used to examine the accuracy of fixation of the centre of a disc target as a function of the angle subtended by the disc at the eye. Angular diameters from 19′–240′ were used. The R.M.S. deviation of the direction of the visual axis from its mean direction increases by less than a factor of two between the extreme sizes of the target. There is an unexplained reduction in accuracy of fixation when the diameter of the target is about equal to the diameter of the fovea. Experiments have also been carried out on the accuracy of fixation of the centre of two small dots separated either vertically or horizontally at function of distance between the dots. The accuracy of fixation for these targets is unexpectedly good. © 1969 Taylor & Francis Group, LLC.