Physiology of the Visual System Flashcards
Look at an object with both eyes –> perceive it as singular. Why so?
Visual scene –> stimulating points on our retina that share a common visual direction
The region in visual space over which we perceive single vision is known as “Panum’s fusional area”, with objects in front and behind this area being in physiological diplopia (i.e. double vision). Our visual system suppresses this diplopia and hence we do not perceive double vision under normal viewing conditions. In order to understand the discussion on the horopter and Panum’s fusional space, the sense of direction will be introduced. Two terms describing
These points on our retina are called?
retinal corresponding points
Where do these points have to fall on?
An area called the horopter
What if the points fall outside?
Don’t have the same visual direction –> retinal disparity –> depth
Region in visual space which we perceive single vision is called?
Panum’s fusional area
Objects that are in front and behind this area result in?
diplopia
Why don’t we experience diplopia then?
suppression
3 terms describing direction sense are?
Principal Visual Direction
Oculocentric Visual Direction
Egocentric Visual Direction
Describe Principal visual direction.
Represented by a line that joins the object and the fovea Another name: visual axis
Describe oculocentric visual direction.
Based on the principal visual direction, the direction of all other objects in the subjects visual field is determined.
Each point of the retina has its own sense of direction. E.g. look at an object –> imaged on the fovea
below object –> imaged above the fovea
above object –> imaged below the fovea
Describe egocentric visual direction.
What is it determined by? (4)
The direction of an object in space relative to one self, rather than the eyes.
Determined by the eye, head and body position and the vestibular apparatus.
Information from egocentric visual direction allows us to determine what?
If change in retinal position is due to object moving or eye or head movement
Stationary object, head and body. Object is imaged on the fovea. When eye moves the stationary object is imaged on a new retinal position (no longer in fovea). What has changed? What remains the same?
Changed- oculocentric direction
Same- egocentric direction
Why hasn’t egocentric direction changed?
Bc the object is stationary
Eye tracks a moving object. The object is imaged on the fovea at all times. What has changed? What remains the same?
Changed- egocentric direction
Same- oculocentric direction
