Critical fusion frequency in the central visual field.

The critical fusion frequency (CFF) was measured across the central visual field. Stimulus parameters were adjusted to ensure an increase in CFF at the fovea. Comparison was made between the foveal and extra-foveal CFF values. The study showed that, while the CFF may be highest at the fovea when the CFF values are generally low, stimulus parameter changes that increase the CFF result in a greater increase extra-foveally. Ultimately, then, the CFF maximum shifts from the fovea to an extra-foveal area. Under the experimental conditions used in the study, the maximum occurred approximately 10 degrees from fixation.