2.7 Basic Visual Functions Flashcards
Pre-req for normal vision
at least one edge
stimulation changes over time
high level processes and experiences
Edges
area with sudden change in brightness or colour
without = ganzfeld vision (no vision)
encouraged through lateral inhibition
Lateral Inhibition
process that highlights edges through activation of photoreceptors by light sources producing a reduction in nearby photoreceptors
this emphasized the contrast of edges
occurs through interactions between horizontal and amacrine cells
example: Mach band illusions
Stimulation Changes Over Time
area of retina that is stimulated changes
if same retinal area is constantly stimulated it will fade (decrease) image
- this could be due to refractory period of photoreceptors
- equipped to fix this through involuntary eye movement (micosaccades)
High Level Processing and Experiences
Early visual experiences favour better developed of neural structures involved in higher level processes
happens in association areas (temporal) not prim. cortex
evidence: those who lost vision and restored had issues with higher complex processes (example: face recognition and motion perception )
Plasticity
the ability to adapt to change
loss of ability, other areas will pick it up
Stratton experiments: inverted lenses
only took 7 days to adapt quickly
Light Detection Elements
Adaptation Time Size Locus Cognition
Light Detection: Adaptation
Duplicity Theory
– affects ability to detect light
(The combination Rod + cone Curve)
Light Detection: Time
Broch’s Law
Duration and Intensity = threshold
Light Detection: Size
Better at detection light when large area is stimulated
Ricco’s Law
Light Detection: Locus
Detection is easier when its on the periphery of the retina
- stiles crawford effect
Stiles Crawford Effect
light entering near the edge of the pupil produces lower photoreceptor response compared to direct on
due to shape and size and refractive indices of the various parts of photoreceptors (needs to hit straight on)
Light Detection: Cognition
Lightness constancy
Brightness Contrast
assimilation
Light constancy
how sensory perception and cognition interact
- unconscious inference (algorithm)
- relative illumination
either way cognition is involved
Brightness contrast
receptive field are at certain level
less inhibition in black than white and therefore it looks brighter
- relative ratio of foregrownd to background
