From Photons to Phenomena Flashcards
what are inferences and visual perceptions made from?
photons
stages of processing
- reception
- transduction
- coding
reception
physical photon energy hits the retina and interacts with photo receptors
transduction
converts physical photon energy into electrochemical pattern sent down the brain
coding
one-to-one correspondence between the physical stimulus and firing pattern of brain neurones
what are rods?
photoreceptors that provide vision in dim light and movement
where are rods?
peripheral regions of the retina
what are cones?
photoreceptors that provide colour and sharpness of vision
where are cones?
found particularly on the fovea
trichromatic theory
argues there must be three types of colour receptors in the human eye, as primary colours can produce all colours of the spectrum
opponent-process theory
inputs from cones are processed in an opposition manner, along scales at the level of neurones
what is colour constancy?
the tendency for a surface to appear the same colour, regardless of a change in wave lengths
where do signals from the retina travel down?
the optic nerve via two parallel pathways
- parvocellular pathway
- magnocellular pathway
parvocellular pathway
most input comes from rods
magnocellular pathway
most input comes from cones
pathways between the eye and the brain
- retina
- optic nerve
- optic chiasm
- lateral geniculate nucleus
- cortical area V1
what is receptive field?
region of sensory space within which light will cause the neurone to fire
what is retinotopy?
things near to each other in space are processed in cells close together
what is lateral inhibition?
reduced activity in one neurone caused by a neighbouring neurone, to enhance object contrast
what is the lateral geniculate nucleus part of?
the thalamus, involved in sensory input and motor output
what does the LGN contain?
- centre-surround receptive field
- retinotopic map
what does the LGN combine?
signals across space and time to determine whether objects are moving
what does the V1 extract?
low-level information from the visual scene for later stages of processing
what does damage to V1 result in?
cortical blindness, but patients can make blindsight judgements in the “blind” area
functional specialisation theory
different parts of the visual cortex are specialised for different visual functions
V1 and V2 function
involved in early visual perception
V3 and V3a function
responsive to form and moving objects
V4 function
responsive to colour
V5/MT function
responds to visual motion
what might challenge the idea of distinct visual processing modules?
sighted people do not perceive colour differently
however, synchronised temporal coding may explain the conscious experience of object processing
where pathway
(dorsal/parietal stream)
concerned with movement processing
what pathway
(ventral/temporal stream)
concerned with colour and form processing
damage to dorsal stream
result in optic ataxia
damage to ventral stream
results in visual form agnosia
stages of object recognition
- early visual processing
- perceptual segregation
- structural depictions
- attaching meaning to the object based on prior semantic knowledge
where is object information processed?
in the ventral visual ‘what’ stream
agnosia
deficits in object recognition without primary visual damage
apperceptive agnosia
impairment in constructing perceptual representations from vision
what is apperceptive agnosia associated with?
lateral occipital lobe damage
associative agnosia
impairment in mapping perceptual representations onto knowledge of object functions
what is associative agnosia associated with?
occipital-temporal lobe damage
prosopagnosia
impairment in face processing caused by damage further along the ventral stream
what may fusiform face area be specialised for?
complex visual processing, as humans are experts at within-category discrimination
holistic processing
features of the face are processed less than other types of objects
evidence of holistic processing
disruptions in spatial-relational inversion
