Early vision Flashcards
Stimuli
proximal- information we have access to
distal- perception of the world
Size constancy
if something appears same size but know its further away then must be bigger
Light constancy
context determines perceived lightness
checkerboard illusions appears darker so correct for lightness
Colour constancy
context of lighting. inside artificial lighting vs sunlight
inside have more long wavelengths therefore expect white shirt to look redder
V4 area respond to surface of colour based on reflectance
surrounding colours influence perceived colour
Shape constancy
retain shape even when rotated
retina rarely sees actual shape as often distorted and seen from different angles
Retina
photosensitive cells
Cones
central vision field, daylight, acuity (fine detail) and colour
don’t have all cones else optic never too fat
Rods
periphery, night time, non acuity and monochrome
Blind spot
no receptors as wiring. eye movements (fixations) compromise
Edges
retinal level - areas of change. compare response of adjacent units and when differ there is an edge
Edge detectors
different scales of edges. either - inside and + outside (off-centre) or + inside and - outside (on-centre)
retinal ganglion cells
receptive field
what cell responds to
Parvocellular
small, small receptive field, colour, response sustained and distribution foveal
Magnocellular
large, larger field, monochrome, transient response (movement) distribution throughout retina
lateral geniculate nucleus
halfway between retina and primary visual cortex. separated visual fields. feedback to LGN to cortex
filter signals
Primary visual cortex (V1)
low level feature detector
single cell recording in cats
simple cells
different orientation and bar widths and fixed location for excitatory and inhibitory.
10% of cells in v1 and can have binocular input
Complex cells
bars and edges at particular orientation but no fixed location.
2/3 cells
can be direction selective
Hypercomplex cells
no fixed zones. tuned to orientation inhibitory end and binocular (too broad no longer interested)
monkey study
hide food under object. associate shape with food source. remove brain parts so can’t discriminate. can no longer find food source
ventral stream
Temporal what (object recognition)
Dorsal stream
Parietal where
where vs how behavioural evidence
red disc identical in size. context happens and sizes look difference. Gripometer grab central circle grip is not fooled so how pathway not fooled
Roelofs effects
x in boxes don’t look aligned. point at x is accurate. if response delayed then visual system overrides and gets it wrong.
Neuropsychological evidence
brain defects. double dissociation
issues of necessity and sufficiency
DF- ventral pathway damage can draw object from memory but cant copy. cant orientate object but can post. other patients with opposite
