Frequency= Cycles/second = Hertz

Relative Sensitivity

• Low modulation steady (non-flickering) stimulus

• High modulation flickering stimulus

• Relative Sensitivity = 1/ (% Modulation)

• As the % modulation increases , the relative sensitivity decreases

No flicker

Threshold

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

Low frequency CFF

Hi frequency CFF

No flicker Flicker No flicker

High Low

• Loss at low frequencies

– Troxler phenomenon

– Purkinje tree visualization

Troxlex phenomenon

• http://upload.wikimedia.org/wikipedia/commons/6/6e/Lilac-Chaser.gif

• Loss at high frequencies

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

Broca-Sultzer effect

Stimuli with duration between 50 and 100 ms are perceived brighter than shorter or longer stimuli

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

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

Masking

• Simultaneous masking

– Example: Crowding phenomenon in amblyopes

• Backward masking

– Example: Metacontrast

• Forward masking