Anomalous recognition of flicker-fused letters

Flash sequences appear as steady emission of light if the frequency is above the flicker-fusion threshold. One can display flicker-fused letters against a background, and using the Talbot-Plateau law, vary the average luminance of the letters to control degree of match to background luminance. We have previously reported that the visual system can identify letters that have an average luminance that equals background luminance, which can be described as an anomalous contrast discrimination. The present work confirms the earlier report, and provides additional evidence that the phenomenon is not based on a shift in luminance balance. We discuss the possible role of ON and OFF retinal channels in registering the anomalous contrast.