w2 Flashcards
what is reception
Absorption of physical
energy – i.e. photons
what is transaction
Physical energy is
converted into an
electrochemical pattern
in the neurons
what is coding
One-to-one correspondence
between aspects of the physical stimulus and aspects of the resultant
nervous system activity
what element of vision involves rods
light and movement
what element of vision involves cones
colour and sharpness
where are the majority of cones located
the fovea
where are most rods located
outer regions of the retina
what colour range is human eye most sensitive to
green range
Hermann von Helmholtz
then proposed that…
there must be three types of
colour receptors in the
human eye, responding to
different wavelengths of
light
what did Thomas Young find
all colours of the
spectrum can be produced
by mixing 3 primary colours
what colour is short wavelength
blue
what colour is medium wavelength
yellow/green
what colour is long wavelength
red
what level does opponent-process theory work at
neurons
what is colour constancy
The tendency for a surface to appear to have the same colour despite a
change in the wavelengths contained in the illuminant
what are the 2 pathways after the retina
Parvocellular (P) Pathway
Magnocellular (M) Pathway
what is the P pathway sensitive to
Sensitive to colour and fine detail
which pathway has most input from cones
P pathway
what is the M pathway sensitive to
Most sensitive to motion
which pathway has the most inout from rods
M pathway
what are the steps in the pathway from the eye to the brain (5)
- Retina 2. Optic nerve 3. Optic chiasm
- Lateral Geniculate Nucleus (LGN) 5. cortical area V1
what is a receptive field
The region of the sensory space (i.e. retina) within which light will cause the neuron to fire
what is retinotopy
Things that are near to each
other in space are processed
in cells that are physically
near to one another
what is lateral inhibition
A reduction of activity
(inhibition) in one neuron
that is caused by a
neighbouring neuron
why is lateral inhibition useful
Useful for enhancing
contrast at edges of
objects
what does LGN stand for
Lateral Geniculate
Nucleus
what is LGN part of
the thalamus
what is the thalamus
a subcortical relay for most of the
brain’s sensory input and motor outpu
what do cells in the LGN have
a centre-surround receptive field
what does the centre-surround receptive field in LGN cells do
Responds to differences in light across their receptive field
what are the roles of the LGN
- Responds to differences in light across their receptive field
- maintains a retinotopic map
- correlates signals from the retina in space and time
what are the roles of V1 (the primary visual cortex)
- Extracts basic information from the visual scene
- send this information for stages of processing
- maintains retinotopy
what did single-cell recordings by Hubel and Wiesel (1979) indicate
in V1, some cells respond to simple features, and others combine those features into more complex ones
what does damage to V1 lead to
cortical blindness
what is cortical blindness
the patient cannot consciously report
objects presented in this region of
space
what can a patient with cortical blindness still do
the patient is still able to
make some visual discriminations in
the “blind” area
with cortical blindness, why is the patient is still able to
make some visual discriminations in
the “blind” area
there are other
routes from the eye to the brain
what is blindsight
Filling-in of ‘blind’ regions similar to filling-in of normal blind spot
what does the functional specialisation theory suggest
Different parts of the visual cortex are
specialised for different visual functions
V1 and V2 role
Early stage of visual perception (e.g.
shapes)
V3 and V3a role
Responsive to form (especially of moving objects)
V4 role
Responsive to colour
V5/MT role
Responsive to visual motion
who created functional specialisation theory
Zeki
what is the central assumption of functional specialisation theory
that colour, form, and motion are
processed in anatomically separate parts of the visual cortex
what did Zeki (1991) do
a brain imaging (PET) study
what did Zeki (1991) find about human V4
V4 more active for coloured than greyscale images- specialised for colour
what did Zeki (1991) find about human V5
V5 more active for moving dots
compared with static dots- specialised for motion
what is cortical achromatopsia
patients can’t see colour due to damage to V4, V2, or V3, despite a fully functioning retina
what do case studies of patients with cortical achromatopsia indicate
Case studies indicate intact implicit
colour processing in patients with
achromatopsia
what do we conclude from case studies of patients with achomatopsia
V4 is involved in colour
processing but the link between
colour processing and V4 is not
perfect
what is V5/MT involved with
motion processing in brain imaging studies of humans
what does damage to V5/MT lead to
akinetopsia
what could a patient with akinetopsia do/ not do
- can locate stationary objects
- can detect colour
- motion perception deficient
what is the binding problem
Sighted people don’t perceive the colour of things separately to
their shape, but in your brain those things are processed
separately… so where in the brain is the thing that is perceived?
what is the parietal (dorsal) pathway
the where pathway, concerned
with movement processing
what is the temporal (ventral) pathway
the what pathway, concerned with colour and form processing
what are the steps of the model of object recognition
- Early visual processing (colour,
motion, edges etc.) - Perceptual segregation: Grouping of
visual elements (Gestalt principles,
figure–ground segmentation) - Matching grouped visual description
onto a representation of the object
stored in the brain (called structural
descriptions) - Attaching meaning to the object
(based on prior semantic knowledge)
what is perceptual segregation
Separating visual input into individual
objects
when does perceptual segregation occur
Thought to occur before object
recognition
what are the 4 Gestalt Laws of Perceptual Organisation
a) The law of proximity
b) The law of similarity
c) The law of good
continuation
d) The law of closure
issues with gestalt psychology
- Most evidence only descriptive, not explanatory
- Relies heavily on introspection and
evidence from 2D drawings - Some segmentation clearly occurs via
top-down prior knowledge
what is agnosia
impairment in object recognition
(without primary visual
deficits)
what is apperceptive agnosia
Impairment in the process which constructs a perceptual representation from vision, can see parts but not the whole
what is apperceptive agnosia involved with
ateral occipital lobe damage
what is associative agnosia
Impairment in the process which maps a perceptual representation onto knowledge of the objects functions and associations, seeing the whole but not its meaning
what is associative agnosia involved with
occipito-temporal damage
when shown a drawing of an object, what would a patient with associative agnosia be able to do
preserved ability to
copy drawings of objects, but unable to
name them or show what they are fo
what are issues with research into object perception
- most Psych research comes from white male Western researchers and participants
- Westerners prioritise processing / categorising objects, while East Asians prioritise the relationships between objects and context
lesions to different areas of the brain in the ventral visual stream leads to
agnosia for different types
of objects
why are faces different to other objects
Face recognition is a within-category
discrimination (all faces look very similar), whereas other objects are between-category discrimination
why may facial recognition be different to other object discrimination
Faces are so important from a
social/evolutionary perspective that they may have a mechanism all to
themselves
what is prosopagnosia
Impairment of face processing that doesn’t come from damage to early visual processing
what is the fusiform brain area
- Part of the ventral (what) stream
- Responds to faces more than
other types of objects in
functional imaging experiments
what is evidence for holistic processing in face recognition
Sighted people are slower and less accurate at identifying inverted (upside down) faces
why does Gauthier suggest that faces are special
we have become experts at within-category discriminations
what is a criticism of the holistic processing model of facial recognition
not all prosopagnosic
patients are impaired on within-
category discrimination
