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.
What is the Gestalt approach?
top down - there is something else that marr’s approach is missing. the whole is greater than the sum of it’s parts.
concerned with rules of perceptual organisation.
what is a computational model?
3 levels.
computational theory - what is the goal of the processing?
algorithmic level - what processing is needed to do this?
mechanism level - what mechanism is needed to implement the algorithm?
what are the steps of marr’s approach?
Retinal Image
Grey level description – measuring intensity of light at
each point in image.
Primal sketch -representation of contrast change (blobs,
edges, bars etc) over range of spatial frequencies)
Identify edges and primitives
21/2D sketch - representation of orientation, depth,
colour relative to the observer
3D representation - representation of objects
independent of observer
what are advantages of the computational approach?
a system is better understood by understanding the problem that needs to be solved rather than the mechanism.
to understand perception by studying neurons is like understanding bird flight by looking at feathers.
why do optical illusions support the gestalt approach?
sensory input doesn’t change, yet we can interpret it differently.
what are the laws of perceptual organisation?
need 2 learn these m8 exam
- Similarity - can a jist of what’s out there.
- Good continuation - connecting things appear to be part of the same entity. more likely than two seperate.
- Proximity - spacial configuration manipulates what we see.
- Connectedness - things physically connected are perceived as a unit.
- Closure - closed figures are preferred to open ones. if we see 4 dots with no lines we see a square, even though it could be a X.
- Common Fate - things moving together/same orientation are grouped together.
- Familiarity - we form images we recognise, ie the dog dots.
- Invariance - recognising objects, really hard for AI. CAPTCHA tests.
- Prägnanz – “good figure” - central law of gestalt psychology.
some objects are prominent, some are background. this implies top down processing.
???
what is reification?
more spatial info than is present, relevant for continuation.
objects appear to be there but it’s not, look up eg cos it could be in exam m8.
what are problems with the gestalt approach?
Underplay the parallel processing and unconscious
processing that the brain does
Explanation of how some of their laws worked was
wrong.
Their laws provide a description of how things work
rather than an explanation.
Their laws are ill defined – Prägnanz – what is the
simplest and most stable shape?
Stating the obvious?
positives from Gestalt psychology?
Their laws actually appear to be generally correct.
Percepts can be analysed into basic elements.
The whole is greater than the sum of its parts.
Context and experience effect perception
what is bottom up processing?
Start from the bottom, considering physical
stimuli being perceived and then work their
way up to higher-order cognitive processes
(organizing principles and concepts)
- Higher cognitive processes can not directly
influence processing at lower levels
• E.G. Marr’s computational approach
what is top down processing?
The perceiver builds (constructs) a cognitive understanding (perception) of a stimulus, using sensory information as the foundation for the structure but also using other sources of information to build the perception.
what is figure ground segregation?
Gestalt psychologists also interested in how we separate figure from ground.. Usually no doubt – but some reversible figure-ground patterns.
• These are extreme examples
• Normally in a visual scene some objects
(figures) seem prominent, and other aspects
of field recede into the background (ground).
• Lecturer (figure), other objects (background)
• Gestalt interested in this because it infers topdown
process
Properties that affect whether area seen as figure or
ground are:
- Symmetry: symmetrical areas usually figure.
- Convexity: convex shapes usually figure.
- Area: stimuli with comparatively smaller area usually
figure.
- Orientation: vertical and horizontal orientations
usually figure.
- Meaning/Importance: meaningful objects more likely
to be seen as figure. Implies attention - top-down
what is an oculomotor cue?
cues that depend on our ability to sense the position of our eyes and tension in our eye muscles.
bringing finger towards your eye.
chamaeleo calyptratus only has this cue.
what is a pictorial or monocular cue?
cues that can be depicted in a still picture.
Pictorial Cues (also called monocular cues) do not require viewing with both eyes in order to work, usually better with 1 eye.
What is a motion produced cue?
cues that depend on movement of the observer or object.
what is binocular disparity?
a cue that depends on the fact that slightly different images of a scene are formed on each eye.
for close vision what do the ciliary do?
contract, causing the lens to relax.
what are the types of pictorial cues?
overlap/interposition. relative size. atmospheric perspective relative height. familiar size. Linear perspective
how does retinal image size change with distance?
increase distance - decrease retinal size.
what is size constancy?
the fact that an object can look the same size regardless of changing retinal image size.
examammamam
what is emmerts law?
Emmert’s Law states that objects that generate retinal images of the same size will look different in physical size if they appear to be located at different distances.
Specifically, the perceived size of an object increases as its
perceived distance from the observer increases.
An object of constant size will project progressively smaller retinal images as its distance from the observer increases.
Similarly, if the retinal images of two different objects at different
distances are the same, the physical size of the object that’s farther away must be larger than the one that is closer.
describe atmospheric perspective.
Distant objects appear less sharp because more
air and particles to look through.
describe relative height
IF the objects are below eye height the highest object
is furthest away
If the objects are above eye height then the lowest object
is further away
describe shading and shows.
attached shadows - shadows within objects/casted upon itself.
assume light comes from above - sun.
detached shadows - shadows you project onto other surfaces, nasty tricksies.
what is an attached shadow?
shadows within objects.
what is texture gradient?
repeated patterns become finer in texture as distance increases.
causes you to perceive things that aren’t there.
describe motion parallax.
As an observer moves relative to a 3-D scene, nearby objects appear to move rapidly whereas far objects appear to move slowly.
imagine a train.
used often by animals that don’t have binocular overlap - no converging. ie eyes on side of head.
squirrels run parallel to things they’re interested in.
what is optical expansion?
combination of parallax and retinal size.
ball coming towards face.
what is deletion and accretion?
As one object moves in front of another, deletion occurs
whereby the front object covers more of the back object.
As one object moves away from another, accretion occurs whereby the front object covers less of the back object.
what is binocular disparity?
Cue depends on two eyes & fact that our eyes see the world from slightly different positions determined by the distance between them.
we see a combo of 2 images.
what is binocular rivalry?
one image is dominant over the other.
what are corresponding retinal points?
Regions on the two retinae that would overlap if you slid one retina on top of the other.
When you fixate on an object it will stimulate corresponding
points in the two eyes.
what are stereo blind people?
2-5%.
shit binocular disparity?
not always aware since we have multiple cues.
what is hyperstereo?
increased distance between the two eyes allows for increased depth perception for further away.
what is colour good for?
(1) Scene Segmentation: Variations in colour often
signal object boundaries
(2) Camouflage: Animals use this fact to disguise
themselves by colour markings
(3) Perceptual Organisation: Our visual system uses
colour to group elements in a scene
identifying food
what is hue?
The wavelength of the light reflected only determines
the hue which is seen.
what determines the perceived colour we see?
intensity of the reflected light (how bright it is)
the saturation of the colour (how much white light is mixed in with the pure hue).
what determines hue?
wavelength
ie red/blue
what determines brightness?
intensity
ie light blue/dark blue
what determines saturation? (how much colour/how much white)
spectral purity
ie red/pink
what are additive and subtractive colour mixing?
additive - light sources all add to white.
subtractive - paint adds to black
what is the trichromatic theory?
helmholtz.
There are three receptor types and their combined
responses account for all colours.
Blue-sensitive cones maximally responsive to short
wavelengths. (S-Cones).
Green-sensitive cones maximally responsive to
medium wavelengths. (M-Cones).
Red-sensitive cones maximally responsive to long
wavelengths. (L-Cones).
not RGB, refer to them as S, M and L. (shrot med long)
what light are rods not sensitive to?
red
what is the explanatory gap?
is my red the same as your red?
where are cones present?
in the fovea.
compare rods and cones.
rods
- very sensitive to light
- very sensitive to intensity (black/white)
- 20:1 rods:cones across whole retina.
cones
- respond to 3 wavelengths.
- found on fovea
support for trichromatic theory?
three forms of dichromatism (colour blindness).
what is the opponent process theory?
Hering, Hurvich-Jameson
Hering noticed that when people are presented with large number of colour samples and asked to pick out those that are
pure (not a mix), then:
The pick a red a green and a blue (as predicted by trichromatic theory)
But also Yellow! Also cones and fatigue were not understood, so it was unclear how trichromacy could explain afterimages.
red/green receptor
blue/yellow receptor
white/grey receptor
opponent in nature, can’t signal both at same time.
support for opponent process theory?
(1) Non-existence of certain colours, e.g., bluish-yellow
(2) Colour confusions in colour blindness (ie problems with red and green)
(3) Complementary afterimages
(4) Colour context effects (surrounding context changes perception)
trichromancy versus opponent process?
both are correct.
trichromacy at the level of the cones.
opponent processes at the level of LGN (lateral geniculate nucleus) and cortical cells.
what are the types of colour blindness?
EXAM
more like colour deficiency
anopias - insensitive to L, M or S wavelengths of light (missing a cone)
anomalies - misalignment of L or M in trichromats (distribution or deficiency)
more likely in males
what is the blindness that means you only see black and white?
cortical colour blindness.
what are the types of anopia?
protanopia - L cone missing
deuteranopia - M cone missing
tritanopia - S cone missing
what are the types of anomilies?
protanomaly - L cone pigment deficiency. Need more red in red-green to match yellow
deuteranomaly - M cone pigment deficiency. need more green in red-green to match yellow
what does colour blindness support?
1)Whole fact of anopia points to 3 cone types.
2)Opponent process theory supported by the fact that
people who have trouble with RED also have trouble with GREEN etc
what are human tetrachromats?
have 4 types of cones, almost all females.
what are Hertz?
the number of waves per second
how does frequency relate to wavelength?
high freq = short wavelength high pitched
low freq = long wavelength
human hearing range?
20-20,000 Hz
amplitude and loudness?
high amplitude - loud
decibells
what is Fundamental
frequency?
the wavelength of the longest component that determines the pitch of the sound.
what do harmonics do?
determine the timbre,
the sound quality
what do the semicircular canals do?
vestibular system.
balance and movement of the head.
3 in each ear.
contain endolymph, fluid moves the cupula, AP.
what are the ossicles?
three of them.
when the eardrums move, they also move and amplify the sound.
the Stapes is attached to the oval window and it moves this
describe the cochlear.
looks like a snail, all coiled.
also filled with fluid.
describe why your voice hears different to when you hear it played back.
bone conduction.
we hear it conducted through the skull aswell as through the eardrums.
what is the basilar membrane
contains cochlear.
when the stapes opens the oval window, it generates a wave in the basilar membrane.
different frequencies change different parts of the membrane.
hairs are attached to BM, detect vibrations in BM, fire to brain.
what does tonotopic mean?
Hair cells respond preferentially to a particular frequency They are Tonotopic (this differs from the visual system which is retinotopic)
describe auditory transduction.
• Air pressure changes (kinetic) • Vibration of eardrum -> middle ear -> oval window (mechanical) • Cochlear fluid flows (kinetic) • Hair cells bend (mechanical) • Auditory nerve fires (neural)
what does pitch depend on?
frequency
what does loudness depend on?
amplitude
describe the relationship between pitch and intensity?
More intense low frequency sounds are perceived as lower pitch.
Perception of loudness affected by frequency.
not independent.
thus Low frequency sounds need to be more intense to be perceived as equally loud
equal loudness curve
describe space perception of hearing.
monoaural (one ear).
loudness.
doppler effect - car zoom
cant locate phone by sound alone
describe binaural space perception.
Needed to perceive direction
Interaural intensity differences - different distances from source.
what is the precedence effect?
When a sound is followed by another sound separated by a sufficiently short time delay (below the listener’s echo threshold), listeners perceive a single fused auditory image; its perceived spatial location is dominated by the location of the first-arriving sound (the first wave front).
what is auditory grouping or streaming?
group sounds together by proximity in:
space
time
frequency
what is galloping streaming?
same source
what is seperate streaming/morse?
2 simultaneous streams independent of each other.
what is continuity in sound?
Analogous to visual system filling in behind an occluder
Hear sound as continuous through noise
what are the two types of skin?
glabrous - palms of hands/feet
hairy - everywhere else.
where in the brain does pain go to?
the somatosensory cortex on the opposite of the body.
what is proprioception?
is the sense of the relative position of neighbouring parts of the body and strength of effort being employed in movement.
describe merkel’s disc
responds to fine details - ie braille.
very close to surface of the skin
describe meissner corpuscle
flutter - ie objects slipping through fingers. or holding an egg?
fast changes.
small receptive fields
describe ruffini organs
stretching - ie picking up something/holding something heavy.
buried further down.
describe paccinian corpuscles
vibration, running your hand over a fine texture - ie writing.
large receptive fields.
why do you have multiple receptor types?
A single stimulus can activate many different receptor systems.
describe the receptive fields of paccinian corpuscles compared to meissners corpuscles.
Paccinian corpuscles have larger receptive fields than Meissner’s corpuscles.
what is the two point threshold?
the smallest separation
of 2 separate but adjacent points of stimulation on the skin that just produces two
distinct impressions of touch
Finger tip 2mm
Arm 3.5 cm
what is the homunculus?
diagram showing amount of primary somatosensory cortex dedicated to body parts.
can change with experience, ie learning an instrument.
what is the difference between active and passive touch?
Active touch – active exploration of environment.
Passive touch – body is stationary.
what are the advantages of active touch?
- More parts of body contact object
- You can search for the most diagnostic parts of objects to feel
- Kinesthetic senses are also engaged
what are spatial cues?
texture
bumps and grooves, when
finger is stationery or moving
what are temporal cues?
texture
only when move finger
across surface
Paccinican corpuscles – adaptation to high frequencies impairs performance
Can perceive texture via a tool, ie writing a pen you can sense texture of paper.
what is double dissociation?
one system tells you what it is, the other where. can only do one.
tactile agnosia - cannot identify objects by touch, but know where it is.
tactile extinction - don’t know where but can recognise it.
describe what areas of the brain were active when identifying what an object is.
primary and secondary somatosensory cortex.
describe what areas of the brain were active when identifying where an object is.
superior parietal areas.
describe how top down influences may change our perception of touch.
emotional effects - same sensation can be pleasurable or unpleasant depending on context.
expectation influences a lot - ie holding a furry tarantula.
body position - aristotle’s illusion
what is aristotle’s illusion?
fingers crossed, eyes closed.
brain ignores posture, object comes into contact with outside of both fingers. feels like 2 objects.
what is the cutaneous rabbit illusion?
tapping wrist/arm evenly.
perceive as if the stimulus has jumped.
activity in primary somatosensory cortex as if the forearm had actually been stimulated.
what is the traditional view of pain?
over stimulation of a system.
two types of pain?
A delta fibres - fast myelinated.
C fibres - slow burning pain
stimulus can stimulate both.
what is kinesthesis?
movement of limbs in space.
what is gustation?
taste.
what are taste and smell?
chemosenses.
what causes each taste type?
Sweet: sugars (fructose, glucose, saccharose...) artificial sweeteners (aspartame, saccharin...)
Sour: all acids (acetic acid, citric acid, ascorbic
acid, phosphoric acid, lactic acid…)
Bitter: no unique chemical class: quinine,
caffeine, peptide, phenols
Salty: salts like table salt (NaCl), or NH4Cl, KCl
Umami: Mono sodium glutamate, Inosine 5’-
monophosphate, Guanosine 5’-monophosphate
what is the traditional view of tasting?
different areas of the tongue are more responsive to the core taste.
wrong boi.
what is Henning’s smell prism?
flowery, putrid, fruity, spircy, resinous, burned.
Why is there no satisfactor classification of odours?
can differentiate but not classify all smells - 10,000
what are the two routes to smelling?
orthonasal - inhalation through nose.
retronasal - during chewing and swallowing.
both go to olfactory membrane.
describe top down effects on smell.
labelling/context - same odour smells worse when labelled as body odour rather than cheese
learning - wine tasting
what is the proust effect?
vivid memories brought back by the smell of biscuits.
background noise and taste?
Foods rated as less sweet and salty in presence of background noise.
Foods taste crunchier and fresher when the sound is amplified or the high frequencies increased
benefits to multisensory integration?
- Can allow detection of weak stimulus in another modality
- Can make sense of an ambiguous stimulus in another modality
- Can alter the quality of a stimulus in another modality
what is the McGurk effect?
Watch lips moving to make sound ‘ga-ga’
Hear sound ‘ba-ba’
Subjects perceive ‘da-da’
Visual information is affecting the sound that you hear
how is proprioception using multisensory integration?
Eyes signal motion (relative to background).
Muscles, skin, & joints of neck indicate tilt.
Otoliths (vestibular system) also indicate tilt.
Semicircular canals (vestibular system) signal start and end of movement.
what is kinaesthesia?
the illusion of speed, we perceive changes in speed more than a constant speed.
describe multisensory receptive fields.
Orbitofrontal cortex – taste and smell.
Taste of banana and sight of banana
Posterior parietal cortex – touch, vision, audition
describe multisensory receptive fields.
A cell which responds to touches to the index finger may also respond to visual stimuli close to the index finger
what are random dot kinematograms?
Instead of presented each simultaneously to the right and left eye, we now present the first and then the second after a short time lag.
Here we perceive a central square to move rightward,
even though we cannot perceive a square in either
frame alone .
what is the correspondence problem highlighted by random dot kinematograms?
The ‘correspondence problem’ highlighted by RDKs
suggest that motion detection is direct.
We cannot imagine a visual system matching point for point over time in these displays.
what are the 5 ways to make a spot of light move?
real movement apparent movement induced movement autokinetic movement movement afereffects
describe real movement
Light physically moves, i.e. is physically displaced from one place to another.
- We perceive movement when the eyes are stationary, so that the image moves across the retina.
- When an image moves across the retina, it stimulates a series of receptors.
- There are neurons in visual system that respond best when a stimulus moves in a particular direction.
Excitation and inhibition interact to create a cell that responds only to movement from right to left. diagram in lecture.
can also work by delay, both cells need simultaneous activation, only works if travelling in right direction.
trying to find out what determines:
Threshold for perceiving movement
Perception of velocity
what is the aperature problem?
cells only detect a tiny part of movement, all must be integrated for the object to make sense.
square problem.
middle temporal area does this.
what can movement detectors not explain?
(1) There is no movement on the retina
– as when you follow a moving object with your eyes so your eye movements keep the object’s image stationary on fovea.
(2) When you perceive no movement when there is movement on retina
- as when you move your eyes to look at different parts of the scene or as you walk through a scene.
outflow theory
what is Helmholtz outflow theory?
you get two copies of commands, one to eye one to brain.
if there is no difference then we don’t perceive movement.
what evidence is there for the outflow theory?
Convincing evidence from:
1. Afterimages move when we move our eyes (Eye muscle movement signal no retinal movement).
- The world moves when we passively wobble our eyes (retinal movement, no eye muscle movement signal).
- Immobilizing eye-ball results in attempted eye- movement leading to apparent movement of world in opposite direction (Eye movement signal, no retinal movement).
what is apparent movement?
(stroboscopic movement)
Illusion of movement between two lights by flashing one light on and off, waiting between 40 & 200 msec, then flashing other light on and off.
Perception of movement in film = series of static images.
what is the critical flicker fusion frequency threshold?
lowest frequency at which a flickering light source is seen as constant.
human - 60Hz
what is induced movement?
Surround spot with another object and then move this object.
ie Sitting on train – feel it move backward, only to realize that your train is actually standing still, and the one next to you is moving forward.
describe autokinetic movement
Turn out all room lights. When the surrounding framework of the room is not visible, the small stationary light appears to move, usually in an erratic path.
eyeballs can’t stay completely stationary.
describe movement after effects.
Supports idea of movement detectors, which respond only to movement across the retina.
background firing rates, illusions wear out one set of detectors, once it stops it has a refractory period, the other direction bg rate is greater.
scotopic and photopic vision?
scotopic - rods
photopic - cones
