Higher level vision: illusions Flashcards
When
dorsal stream
perception of time influenced by temporal dynamics of what’s being observed
e.g. fast flicker hangs around for a shorter period then slow flicker although opposite also found
order of processing
colour and form processed faster then direction change
might just be analogous to WEIRD
which stream
colour -ventral
motion - dorsal
Canonical views
not normal view so struggle to process
e.g. in basketball players struggle to process when coach draws court upside down to them
Specific brain areas
PET scans show colour V4 and motion V5
Stimulate MT in monkeys and trigger motion directions
IT damage leads to prosopagnosia
Fusiform Face Area (FFA)
neurons specialised for faces
However novel stimulus of greebles introduced and no response but after 7 hours of training become experts
FFA area goes from low response to high response
Particular coding
Each stimulus makes a particular neuron fire
objections to particular coding
many objects
many views of object
grandmother cells
multiplexing- single neurons often respond to more then one stimulus
Multiplexing
single cell cant distinguish between stimulus shown as it responds similarly to low contrast optimally orientated grating and a high contrast non-optimally orientated grating
a population of cells can collectively distinguish
Binding problem
If brain modular how do different properties come to a unitary experience
singer et al - synchronisation of neural firing
Plasticity
Phantom limb remapping- adjacent areas in somatosensory cortex
v1 used for high level language processing in blind people
v1 activation when braille reading
Effects of attention
feedback from visual cortex
visual effects subject to top-down modulation (motion aftereffect in V1)
feedback to LGN
if cognitive load being used up then miss things
Why care about illusions
- influence of context
- hypothesis testing
-top-down processing
-different levels of processing
Moon illusion
looks larger when nearer to horizon
- Size constancy (false distance estimates shown when experimented with flat sky)
-alternative explanation moon looks smaller when surrounded by more sky
Muller-lyer illusion
edges push towards or away
size constancy and depth cues
-think same size but further away so see line as larger
Horizontal/vertical illusion
vertical look longer then horizontal
aspect ratio of binocular world
vertical line takes up more of what you can see. when use just one eye effect reduced not abolished
Shepard’s table
don’t look same size due to perspective
Titchener/ Ebbinghaus circles
Circles look different sizes depending on surrounding circles
- size constancy
-contrast effect
Delboeuf illusion
inner bits of toilet roles appear different sizes depending on how much loo roll is left
Spirals or circles
looks like spirals but actually circles
local - small (makes sense) vs global- large (doesn’t make sense) info
Penrose triangle
triangle that can’t exist irl
sense from local but not overall (global)
Bistabiliy
two different interpretations without…
-duck/rabbit
-old women/young lady
-Necker cube
-coffer illusion
illusory contours
Kanizsa’s triangle
mostly reliable activation
Motion after effect
waterfall illusion
watch movement in one direction
neurons fire for this direction but adapt so rate decreases
when neutral neurons for other direction fire at baseline
motion illusion
effect of context (spinning vs pulsating)
snake illusion look like moving around black dot - fish also see
Wagon wheel illusion
rotating image based on time you sample will change direction its going
Hollow face
top-down knowledge faces not usually concave
dorsal not fooled completely
eyes follow illusion
despite view angle looks like eyes follow. as concave top down processing overrides
Café wall illusion
acts like a spiral so parralell lines look wonky
copy and pasted face
don’t notice all faces are the same
so individual facial features not used to identify
Thatcher illusion
face upside down looks normal but when flipped looks wrong
look at faces holistically
also works on countries
Gender face illusion
same face
appears more male if eyes/lips lightened and female is eyes/lips darkened
contrast difference or makeup
