Sensation & Perception Flashcards
noumenal and phenoumenal world?
noumenal is the physical world.
what are receptor cells?
specialised neurons which
respond to a particular physical property of the
environment.
transform physical energy into electrical
energy
what is transduction?
the transformation of
environmental physical energy into electrical
energy in the nervous system.
carried out by receptor cells.
what is transmission?
action potentials and shitt
what is perception?
conscious sensory experience
what is recognition?
placing an object in a category
what is visual form agnosia?
an inability to recognise
objects. This disorder highlights the distinction
between perception and recognition.
what is top down processing?
processing based on prior
knowledge/ experience/ assumptions
what is bottom up processing?
processing based on
incoming sensory information
what is ames room?
uses top down processing to manipulate the viewer.
what is physiological?
what’s going on in the brain? study anatomy recording brain activity methods of imaging micro stimulation Lesioning & TMS
what is Psychophysical?
what do we perceive? Measures the relationship between stimuli (physical world) and perception (psychological world)
limited ecological validity
what are the types of threshold?
Absolute (Detection) – what is the smallest
magnitude that we can perceive?
Difference (Discrimination) – what is the
smallest difference that we can perceive?
• Not a constant value / quantity
• Instead, its related to the baseline level
– e.g. Adding a book to a bag of cotton wool vs. a bag of bricks
• However the difference as a proportion of the
baseline level is constant
– Weber’s law??
how do you measure absolute threshold?
adjustment, Problem – different people have different
criteria for saying ‘yes I see it!’
Forced Choice – which stimulus
contains the dot?
what is the Psychometric function threshold?
75% correct
is recognition required for action?
no. ie reactions, a ball flying towards your head will be avoided.
different types of imaging?
fMRI
• MEG
• EEG
• PET
what is the perceptual process?
stimulus –> electricity –> action
knowledge over arching all of it.
what are the properties of light?
Light is a form of electromagnetic energy.
physical psychological
Wavelength Colour
Intensity Brightness
why do we have a blind spot?
where fibres leave the retina to form the optic nerve there are no photoreceptors.
what controls the focus of the lens?
Ciliary muscle
Where are receptors located in the eye?
retina
what is the function of the eye?
to focus the intended image on the retina.
what is the purpose of the iris and the pupil?
pupil - hole in the centre to let light in
iris - size of retina
together create an adjustable aperture.
receptors in retina don’t work if too much or little light.
what are the cornea and the lens?
role is to focus light on the retina.
cornea is the outside layer, 80% of focusing.
can’t change the amount of focusing it does.
the lens is located behind the pupil, can change focusing power depending on what it’s looking at. Can change shape due to the ciliary muscles.
what is accommodation?
changing the shape of the lens.
closer - fatter
farther away - thinner
What are the type of refractive errors?
myopia - nearsightedness
can’t focus on far away, the light is focused in front of the retina, lens bends light too much.
corrected with a concave lens - glasses.
hyperopia - farsightedness
light not bended enough, light focuses behind retina.
convex lens in glasses.
convex - sauron eye shape
describe retinal ganglion cells.
long axons, form the optic nerve and take info to the brain.
describe photoreceptors.
carry out transduction, contain photopigment, reacts to light and triggers electrical signal.
form layer furthest from the incoming light, must pass bipolar cells, axons etc.
they are all transparent.
blood vessels do cast shadows on the retina, but retina ignores/fills in the gaps.
blind spots.
what are the types of photoreceptors?
rods - 120 million
longer outer segment
very sensitive, useful at night
monochromatic vision, only 1 type which responds best to medium wavelengths of light. closest to green.
cones - 6 million
less sensitive, useful in the day
responsible for colour perception.
3 types - red blue green
what is sensitivity?
ability to detect low levels of light.
what is scotopic, photopic and mesopic vision?
scotopic - only rods
photopic - only cones
mesopic - both rods and cones active.
describe dark adaption.
photopic to scotopic vision.
takes 20-30 minutes.
sensitivity is 100,000 greater. (ability to detect small changes in light)
what are the types of cones?
red cones, longer wavelengths of light.
green cones, medium wavelengths.
blue cones, sensitive to shorter wavelengths.
What is the purkinje shift?
red looks darker than green in the dark.
At night rods are present, more sensitive to green so green appears brighter.
How do rods and cones differ in terms of retinal distribution?
fovea - small central area of the retina that contains only cones.
when directly looking at an object it falls on the fovea.
rods distributed in the periphery.
What is nerual convergence?
Describe it in the retina.
one neuron receiving signals from lots of neurons.
120 rids send signals to 1 ganglion cell.
6 cones send signals to 1 ganglion cell.
in the fovea 1 cone:1 ganglion cell.
neural convergence determines acuity.
what is acuity?
ability to detect fine details of a stimulus.
high acuity - can detect fine details.
high convergence - low acuity.
low convergence - high acuity. specificity.
Where is the highest acuity?
fovea.
1 cone:1 ganglion cell.
acuity decreases in the peripheral.
describe acuity in scotopic conditions.
it decreases.
better acuity in daylight/photopic.
describe ganglion cells.
far fewer than photoreceptors, around 1:126.
must condense raw info from the photoreceptors - convergence.
sort out important info and send to the brain.
2 types - M/magnocellular cells
large, carry info about dynamic aspects ie movement/flicker
P/parvocellular cells
small, carry info about colour.
what is the optic nerve?
what is the optic tract?
ganglion cells have axons that clump together to form the optic nerve. (blind spot)
2 optic nerves, one from left one from right.
some cross over at the optic chiasm, after this it is the optic tract.
in the optic nerve, it carries all the info.
in the optic chiasm, left visual field goes to the right hemisphere.
how can damage cause blindness?
damage to the optic nerve would cause blindness in one eye.
damage to optic tract would cause hemianopia - unable to see half the visual field.
What is the lateral geniculate nucleus?
first brain region to recieve info from the eye.
one in the left hemisphere one in the right.
each LGN recieves info from both hemispheres but keeps them seperate.
LGN has six layers, each eye has axons terminating in 3 layers each.
2 magnocellular layers
4 parvocellular layers
retinotopic mapping, preserves order of the world.
LGN receives signals from the retina and the cortex.
Sends signals to the cortex.
Regulate info flow from retina to cortex.
describe retinal ganglion cells.
1:126 photoreceptor.
condense raw info from the photoreceptors.
baseline activity - always active
find region that causes an increase or decrease in AP - receptive field.
don’t have a response in overall levels of light, only care about changes within the receptive field.
what are single cell recordings?
physiological approach, electrode inserted into a neuron, measures electrical activity of a single neuron.
what is a receptive field?
A cell’s receptive field is that part of the visual field(or that part of the retina) in which a visual stimulus elicits a change in the firing rate of the cell.
excitatory and inhibitory regions, excitatory in the centre
why are ganglion cells influenced by a region on the retina?
due to convergence
what is lateral inhibition?
inhibitory synapses at some receptors.
what is centre surround antagonism?
excitatory in the centre, inhibitory in the outside due to lateral inhibition.
OR inhibitory in the centre excitatory in the outside.
what is the response profile of a receptive field?
mexican hat shaped.
like normal but dips below 0
what kinda of image do retinal ganglion cells transmit?
center surround receptive fields, emphasise edges.
edges most important
how do receptive fields explain the hermann grid?
centre surround antagonism
varying receptive field sizes
when at an intersection more light falls on the inhibitory region, less response interpreted as less bright sot he dark spot appears.
when looking at the dots they dissapear -
high peripheral vision with large receptive fields.
looking at the dot is precise and falls on the fovea.
describe acuity in receptive fields.
small fields have little peripheral vision.
describe the simultaneous contact illusion.
brighter outer square causes lots of inhibition around the edge of the inner square. cells fire less so it appears darker.
darker outer square causes little inhibition around the edge of the inner square, cells fire more and it appears brighter.
explain mach bands.
although a single shade it appears to gradually change due to its neighbour either inhibiting or not.
What are names for the primary visual cortex?
V1, Striate cortex (cos stripey)
where does V1 receive it’s input from?
LGN, so left hemisphere is right visual field.
who first researched visual stuff with EEGs?
Hubel and Weisel
Describe the V1 cell response.
at baseline with no stimulus it responds a little bit, like ganglion.
tried to stimulate with dots (like ganglia) but couldn’t excite it.
they got a bit response when the edge of a slide moved across the receptive field.
they respond to lines, not spots.
what makes V1 cells respond best?
they prefer lines at particular orientations.
they are aligned in columns.
what is retinotopic mapping?
things close together in the visual scene are imaged on neighbouring parts of retina and will be analysed by neighbouring parts of V1.
what you see is essentially mapped onto the V1 cells.
what is cortical magnification?
the amount of the cortex devoted to representing each part of the retinal field is distorted.
ie fovea represented by large area of the cortex.
fovea is only 0.01% of the retina but is represented by 10% of V1.
what are orientation columns?
the organisation of orientation preferences of V1 cells.
perpendicular to the surface of V1 the cells all have the same preferences as you move down - ie a column.
what are ocular dominance columns?
80% V1 cells are binocular, but respond better to one eye compared to the other.
Cells with the same ocular dominance are arranged in columns perpendicular to the orientation columns.
what are LGN cells?
monocular, only respond to input from either eye, not both.
are V1 cells binocular or monocular?
80% binocular
what are the types of cells in V1?
simple cells
complex cells
hypercomplex cells
what are simple cells?
respond to oriented bars and edges.
the receptive field has elongated regions.
thus have orientation selectivity, ganglion/LGN cells do not.
some have on centre, some have off centre.
edge and bar detectors
what is orientation tuning?
they respond best to a preferred orientation, but also respond to other orientations just have a weaker response.
what is the difference between bar and edge detectors?
3 stripes - bar
2 stripes - edge
where do V1 cells receive their input from?
lots of converging LGN cells.
describe complex cells.
respond to oriented lines but no discrete on or off regions.
it’s phase insensitive.
respond best to particular direction aswell as orientation.
where do complex cells receive their input from?
simple cells converging.
can have simple cells with different preferences.
makes sense to look at mate.
what are hypercomplex cells?
called End-stopped cells.
respond to bars of particular orientation and length.
length should fit the receptive field.
where do hypercomplex cells get their information from?
complex cells, lines that are too long could extend into other complex cells.
what does v3 specialise in?
form
what does v4 specialise in?
colour
what does v5 specialise in?
motion
what is the inferotemporal cortex (IT)?
sensitive to face cells.
what is the grandmother cell hypothesis?
as we move higher into the visual system neurons respond to more complex stimuli.
do we have specific neurons that only fire when we see ie your grandmother?
probs not no.
too many individual things to recognise for this to be practical, also how do you deal with new stimuli?
2 processing streams of the brain?
what - features like colour
where - location, speed
processed by different pathways, but both connected in many ways. signals can flow upwards and back.
what is the pathway for what/where?
both start at V1.
what - travels ventrally to the inferotemporal cortex.
where/how - travels dorsally to posterior parietal cortex.
what is visual form agnosia?
can’t identify objects.
damage to ventral pathway - ie what stream.
what is optic ataxia?
damage to dorsal pathway - where stream.
cannot reach to grasp objects but can recognise and describe them.
essentially opposite of visual form agnosia.
what is the rod and frame illusion?
illusionnnnn. 2 vertical lines in 2 tilted frames, it makes the lines appear tilted.
affects you differently depending on the task you’re asked to do.
affected when asked to reorientate it, but not when asked to touch it - shows distinction since one pathway subject to the illusion and one not.
why is the idea of perception of a camera a fallacy?
idk its shit tho.
we’re much more complex
What is Marr’s approach?
bottom up - mechanical/computational approach, look at the input and try to determine how the output was created.
concerned with the representation of edges, contours and other areas of contrast change.
not inherently human, AI could simulate.
series of algorithms that depend on the previous one.