Spatial Localisation, Correspondence & Horopter

What is the egocentre?

The fixed reference point within the observer used to judge spatial location.

What are the two components of spatial localisation?

Bi-dimensional and tri-dimensional localisation.

What determines relative (oculocentric) localisation?

Position of the image on the retina.

What is the principal visual direction?

The direction of the fovea.

What is a local sign?

The visual direction assigned to each retinal point.

What is required for egocentric localisation?

Retinal position + registered eye position.

What happens if the eye is moved passively?

Mislocalisation occurs.

Where are eye proprioceptors located?

Muscle spindle cells in extraocular muscles.

Through which nerve do proprioceptive signals travel?

Trigeminal nerve (ophthalmic branch).

When is proprioception most important?

In darkness or low vision

What is corollary discharge?

An efference copy of the motor signal sent to eye muscles.

Why is corollary discharge important?

It informs the brain of voluntary eye movements.

What is stereopsis?

Fine depth perception from binocular disparity.

Name two monocular depth cues.

Motion parallax, overlapping contours.

What are corresponding points?

Retinal points in each eye with identical visual direction.

What is the law of sensory correspondence?

Corresponding points produce single vision.

What is the cyclopean eye?

The single central perceptual eye from which direction is localised.

Why do corresponding points project to the same cortical cells?

Nasal fibres cross at optic chiasm.

What is the horopter?

The locus of points that stimulate corresponding retinal points.

What happens to objects on the horopter?

They are seen singly.

What is the Vieth–Muller Circle?

The theoretical horopter assuming symmetrical correspondence.

What is the Hering–Hillebrand deviation?

The difference between empirical horopter and VMC.

What is the abathic distance?

The fixation distance (~2m) where the horopter is flat.

What causes physiological diplopia?

Stimulation of non-corresponding retinal points.

When does crossed diplopia occur?

Object closer than fixation.

When does uncrossed diplopia occur?

Object further than fixation.

Why are we usually unaware of physiological diplopia?

It is suppressed by the visual system.