Stimuli Accommodation & Vergence Responses

What is the primary stimulus to accommodation?

Defocus blur (even-error signal)

Why is blur an even-error stimulus?

Gives magnitude but not direction

What spatial frequency range is peak CSF?

3–7 c/deg

Contrast Control hypothesis?

Accommodation maximises spatial contrast

Fine Focus hypothesis?

High spatial frequencies give best directional cue

Why are square waves better at low SF?

Contain odd harmonics → steeper contrast gradient

Does reducing contrast amplitude reduce accommodation?

Not unless below threshold

What provides direction cue?

Chromatic aberration, spherical aberration, astigmatism, microfluctuations

Effect of removing chromatic aberration?

Reduced gain, increased phase lag

What happens when CA reversed?

Accommodation severely impaired

Primary vergence stimulus?

Binocular disparity

What is Panum’s area?

Region where disparity still allows fusion

Fixation disparity?

Small residual disparity during fixation