Spatial Vision Flashcards
Visual Acuity
A measure of the finest detail that can be resolved by the eyes
Cycle
A repetition of black and white stripe
Amblyopia
Disorder characterised by reduced spatial vision in an otherwise healthy eye even with proper correction for refractive error (lazy eye)
Why is central vision slower than a peripheral vision?
Foveal cones have longer axons than peripheral cones in order to allow dense packing in the central fovea, the longer axons transmit slow signals better than fast one
Spatial Frequnecy
Refers to the number of times, a pattern such as a sine wave grating repeats (a cycle) given unit of space (degree of visual angle)
How is spatial frequency measured?
It is measured as the number of cycles per degree of visual angle
Contrast Sensitivity Function
The ability to perceive sharp and clear outlines of very small objects. CS helps detect objects without a clear outline and distinguish them from their background contrast.
Factors Affecting CFS
1)Adaptation level of the eye
2) Temporal modulation of targets (how it varies over time)
3) Age
- Reduces contrast sensitivity because of the reduction in rods, which are eye structures responsible for vision in low-lit areas
4) Refractive State
Why does the visual system break down real world images into?
A vast number of components, each of which is essentially a sine wave grating with a particular spatial frequency
Fourier analysis
A mathematical procedure by which any signal can be separated into component sine waves at different frequencies.
Phase
The position of a grating relative to a fixed position measured in degrees, where one complete cycle is 360 degrees
How does a ganglion cell respond when the spatial frequency of the grating is too low?
The ganglion cell responds quickly because part of the fat, bright bar of the grating lands in the inhibitory surround, damping the cell’s response.
How does a ganglion cell respond when the spatial frequency of the grating is too high?
When the spatial frequency is too high, the ganglion cell responds weakly because both the dark and bright stripes fall within the centre receptive field centre, washing out the response
How does the cell respond when the spatial frequency is just right?
When the spatial frequency is just right, the bright bar filling the centre with dark bars filling the surround, the cell responds vigorously
How is each retinal ganglion cell “tuned” to spatial frequency?
Each cell acts like a filter responding best to a specific spatial frequency that matches its receptive field size and responding less to both higher and lower spatial frequencies
