This document discusses properties of flicker perception and critical flicker frequency (CFF). It defines CFF as the temporal frequency at which a flickering stimulus is perceived as non-flickering. It notes that CFF increases with retinal illumination per the Ferry-Porter law and that stimuli between 50-100 ms appear brighter than shorter or longer stimuli per the Broca-Sultzer effect. Examples of different types of masking phenomena are also provided.

2. Frequency= Cycles/second = Hertz

4. Relative Sensitivity Low modulation  steady (non-flickering) stimulus High modulation flickering stimulus Relative Sensitivity = 1/ (% Modulation) As the % modulation increases , the relative sensitivity decreases

6. No flicker Threshold

7. Critical Flicker Frequency For a specific % modulation, temporal frequency is increased until the stimulus does not flicker (fuses) This is called CFF = Critical Flicker Frequency

8. Low frequency CFF

9. Hi frequency CFF

10. Low High No flicker No flicker Flicker

11. Loss at low frequencies Troxler phenomenon Purkinje tree visualization

13. Troxlex phenomenon http://upload.wikimedia.org/wikipedia/commons/6/6e/Lilac-Chaser.gif

15. Loss at high frequencies

16. Ferry-Porter law: CFF increase with log of retinal illumination

17. Broca-Sultzer effect Stimuli with duration between 50 and 100 ms are perceived brighter than shorter or longer stimuli

18. Brucke-Bartley Effect: A flickering 10 HZ light appears brighter than a steady light of the same luminance (example of Broca- Sultzer effect)

19. Talbot-Plateau law: brightness of a fused temporally modulated stimulus is equal to the brightness of a steady light of the same average luminance

20. Masking Simultaneous masking Example: Crowding phenomenon in amblyopes Backward masking Example: Metacontrast Forward masking