perception Flashcards
how much do we use our brains
brain weighs 2% of body
accounts for 20% of daily energy consumption
about 20 billion neurons in the cortex
each neurons makes thousands of connections
about 20 trillion connections in the brain
which part of the brain is related to sensation and perception
back half of the brain
what is perception
information processing
what is the first step in perception
sensation
sensation is transduction
what is transduction
turning one signal into another
what is sensation
changing physical stimuli in the world into electrical signals in the brain
how many sense are there and why do we define it as this many
5
as there are 5 visible sense organs
how is an alternative way at looking at how many sense are there
look at physical sensation that are transduced by the body
list full set of transduced stimuli = senses
chemoreception - smell and taste mechanoreception - pressure / vibration proprioception - muscle location thermoreception - temp equilibrioception - balance photorecption - vision nocioception - pain audition - hearing
what the brain does for perception
the brain filters sensory information
the brain constructs the world we perceive
sensory information is ambiguous - why we fall for visual illusions
what is rationalism - in terms of perception
some propositions are knowable by us by using intuition alone; still other are knowable by being deduced from intuited propositions
what is empiricism - in terms of perception
we have no source of knowledge other than sense experience
keu=y concepts on vision from democritus
vision is done by the eyes and slo the soul
vision is one of the many sense
things come into the eye and are transmitted onwards
some colours are special
all other colours can be made from combinations of the special colours
colour is a relagive, not an absolute sensations and depends on the relations of objects tp each other
kwy concepts on vision from plato
colour and vision are very complicated
you cannot predict how colours will mix to make other colurs
even if you could you shouldnt
alhazen’s views on colour/vision
you do not see as a result of things coming out of your eye
neither does matter enter your eye
instead light rays originating at each point on the surface of an object, carry information to you
light travels in a straight line
white light is composed of many colours
who tried to understand colour in europe in the 1600s ish
artists
da vinci
then newton tried
how did newton try to understand colour
what did poking his eye with a needle tell newton about the experience of colour - not much
then he experimented on colour in light
theory - white light is pure, gets colured by prism
prediction - placing another prism in front of coloyred light should add more colour
result - white light is made from the coloured light
=falsification of prediction from precious theory
= his paper on optics
key concepts on vision from newton
white light contains a combination of many spectral colours
light of a single spectral colour contains just one wavelenght - bigness
the colour of objects is a result of their reflectin certain combinations of spectral lights - if only a single wavelength is present, only a single solour can be seen
only three lights required to match any observed colour
3 primary colours
what were people starting to work out
but what ere they missing
many people were discovering that all colours could be produced by combination of three wavelenghts
but they didn’t know why
the missing key was trichromacy
name three people who were working out the trichromacy thing
palmer
lomonosov
thomas young - we named the theory after him but he didnt really care about understanding light…
what are metametres
stimuli that are physically diffferent
but are perceived to be identical
what is the central result of colour vision theory
the trichromacy of colour mixing is due to the fact that we have three types of photorecpetor
subtractive colour mixing - why does something look blue
because it absorbs (subtracts) most of the long wavelengths and some of the medium wavelengths. the short and medium light that is reflected to the eye appears blue
so basically it reflects blue light and absorbs the other wavelenghts
colour mixing - why does a patch look green
mix the two pigments together and what you have lft when each has subtracted its wavelenghts are some remaining medium wavelengths that look green
additive colour mixing
mix lights together and what you get is the addition of the light being reflective off the surface
you can get additive mixture from paints
what is the principle of univariance
the response of a photoreceptor is a function of just one variable (number of photons absorbed). thus this response can be identical for
- a weak light at a wavelength of peak sensitivity
- a strong light at a wavelength of a lower sensitivity
how do we see a different colour
you need to compare difference between the L M and S cones
key concepts of young-helmholtz
you can match any visible colour with a combination of three spectral lights becuase
3 classes of light detector in the eye
all colours are represented by the amplitudes of responses in these three photoreceptors
there are infinitely many spectra that will give rise to the same colours - these are called metametres
but there seem to be four unique hues (6 if you count black and white)
opponent processing - what
who came up with it
there are three cone types
but there seem to be four unique hues - 6 with black and hiwte
three cones can code three pieces of information about a stimulus - think of them as three coordinates in a cone space
ewald hering
seeing opponent processing through adaptation
neurons adjust their firing to adapt to the average stimulus
for colour this happens in the retina - the different cones adapt to the colour they are sensing
normally when a neutral background is shown opponent channels are balanced and respond around 0
after adapting they now respond less than they otherwise would have
this reveals which colours are opponent
how would we expect opponent processing to work and why does it not quite act like this
dimesion of colour space to be determined by 3 axes as three photoreceptor classes. so would expect 6 end points
but cones do not have nicely-spaced absorption spectra
L and M cones are especially close so they convey almost the same information
this is very inefficient (think of it as bandwidth out of the eye is expenvie as more wires = fatter optic disk = thicker nerve fibre layer = expensive to build, more to maintain, more to go wrong
so M L and S cones signal by using the differences between the cone responses
how opponent processing works in humans and other old world primates
three receptor types
three dimensions of colour vision constructed from different combinations of those cones
L-M: called opponent red/green axis signals differences in the quantal catches of the L and M cones
L+M: the luminance axis - signals the sum of the L and M cone catches
S-(L+M): an opponent blue/yellow axis
pattern colour interactions
colour is visible over a limited range of spatial-temporal frequencies
pattern colour interactions
-when luminance changes edge is visible
even for high frequencies
-when colour changes it is difficult to see bounday, especially for high frequency patterns
colour blindness - when
generally happens when individuals have missing or abnormal opsin genes
almost always the genes involved are the L and M cone opsin genes
because there are on the X chromosome, men are affected by colour blindness far more than women - men have no backup gene to rescue them if something goes wrong
what is colour vision
it is not usually the absence of colour
instead people lose a single dimension of colour
most common deficit is anomalous trichromacy where discrimination is poorer along the red/ green axis but still present
rarest type (<1 in 1000) is trianopia where individuals lack functioning s cones
losing either of the L or M opsins damages opponent what systems leaving which systems
red green damaged
blue yellow left
losing the S cone leaves only which system
red green`
what does protanopic mean
lost L opsin
what does deuteranopic mean
lost M opsin
what does trutanopic mean
lost S opsin
who was john dalton
chemist
described his own colour blindness
dies 1844
donated hi eyeballs to science
DNA from his preserved eyeballs was sequenced mid 1990s
found to lack an M opsin gene
we now sometimes call lack of M cone daltonism
colour deficits can be stimulated
brettel vienot and mollon 1994
computersied stimulation of colour appearance for dichromats
matching the internal precept can be hard. one solution is to use people who are colour blind in only one eye and ask them to match percepts between the stimulation in the good eye and real thing in the bad eye
online simulations also exist
ecology of colour vision (animals)
many animals only have two photoreceptors L and S
these animals often habe one colour channel and one luminance channel
this can distinguish light vs dark and blue vs yellow but not green vs red
primate colour vision
trichormatic vision exists in both old worls primates and new world primates
but in old world (african) it is present in all animals - X chromosomes have gene duplication of an L-cone pigment to generate an M-cone pigment
in the new world, only females can be trichromats: they carry different cone pigments on their X chromosome and these are expressed randomly through X inactivation
how had primate colour vision evolved
to support frugivory
the eating of fruit
in this sense primates are useful to trees just as honeybees are to flowers
trichromacy would also be useful in identifying edible foliage (old world monkeys) - perhaps both factors are important
the visible spectrum of light is a small part of ….
the wide range of wavelengths in the electromagnetic spectrum
wavelength of light is …
a continuous variable
photoreceptors in the retina are sensitive to a single wavelength?
no
what is motion perception good for
determines motion of objects in the world
attracts attention
figure-background segmentation
estimate depth - motion parallax
infer from and 3D structure
bio motion can be used to infer action and type of actor
5 types of motion
ego (self) - motoin induced by the movement of the observer
object - movement of objects in the world
apparent motion - when a stationary object appears to be moving
biological motion - specific motion patterns of living things
motion parallax - depth from motion
what are the components of motion
depth
speed
velocity is a vector, vector’s direction = direction of motion, vectors size = speed
what us motion aftereffect
the illusion of a stationary object that occurs after prolonged exposure to a moving object
what does the existence of the motion aftereffect suggest
an opponent processing systme like that of colour vision
what are interocular transfer
the transfer of an effect (EG adaptation) from one eye to another
what does interocular transfer tell us about the locys of the MAE in the visual system
result of activities of neurons in a part of the visula system where information collected from two eyes is combined
input from both eyes is combined in V1
recent studies - locate site of motoin aftereffects more precisely
what is optic flow
flow field induced by motion on the retina
arrows indicate direction of motion and speed
optic flow patterns differ whent he observer moves and when something in the scene moves
how should we think about how to process motion information
eg models for motion detection (what are the models, don’t explain)
spatiotemporal energy models for the perception of motion
elabotaed reichardt detectors
model of human visual-motion sensing
in terms of axis how should we think about motion
motion is like orientation but in time
important features of a motor detector
like an orientation detector
but involves changes in position over times
so strat with two adjacent receptors separated by a fixed distance
the two big problems of the motion detector
correspondance problem - which feature in frame 2 corresponds to a particualr feature in frame 1
appeture problem - when a moving object is viewed through an aperture (receptive field), the direction of motion of a local feature or part of the object may be ambiguous
saccadic supression - reduction of visual sensitivity that occurs when one makes a saccadic eye movement; eliminates smear from retinal image motion during an eye movement
how does the motor system solve the problem of why an object in motion may appear stationary
sends out two copies of each order to move eyes
one copy goes to each eye muscle
another efference copy goes to an area of visual systme that has been dubbed comparator
comparator can then compensate for image changed caused by eye movement, inhibiting any attempts by other parts of the visual system to interpret changes as object motion
what did Newsome and Pare discover
experiment with mokeys
trained mokeys to respond to correlated dot motion displays
activity in MT is directionally selective
activity in MT also corresponds with monkeys behaviour
MT areas of monkeys were lesioned
result - monkeys needed about ten times as many dots to correctly identify direction of motion
the man who couldnt see motion
what
akinetopsia - a rare neuropsychological disorder in which the affected individual has no perception of motion
is caused by disruptions to the human cortical homolog of MT
man sees streams of multiple frozen images
as soon as motion is ceased the images collapsed into each other
what did gladstone notice about homer’s writing
didnt use blue, just wine-dark to colour the sea
used several weird terms to describe colour
what was whorf’s idea on language (overarching idea)
language influences cogntion
the words you use shape your thoughts
stronger and weaker forms of this hypothesis
what is the weak version of whorf’s idea
language primes thought
language that has obligatory gender terms may encourage its speakers to pay more attention to gender
languages with stronger tenses may encourage people to attend to time more
words with more than one meaning may prime people to adopt different assumptions
what is the stronger version of whorf’s idea
language contrains thought
if you dont have a word for it its harder to think about
what is the strongest version of whorf’s idea
language alters percetion
words can alter what you hear, see or remember
if you dont have a word for a colour for example you cant see it?
the sapir-whorf hypothesis
all three forms of whorfs idea are supported by some experimental evidence
it is also true to say language is not a tight constraint on human cognition
you can still see blue even if youre from ancient greece
gender in language
german and spanish both assign genders to objects
spanish observers assign gender traits to objects
gender in memory
people given object-name pairings to learn remember them better if its consistent with the appropriate gender
german speakers learn the apples name is patrick easier than if its patricia with the reverse for spanish speakers
even if testing proficient english speakers in english
how do english speaking children tend to assign gender terms to objects
male as artifical
female as natural
language perception
direction terms
spatial terms influence time perception?
-kuuk thaayorre language spoken by people from northern australia
- these and many other groups have an excellent sense of direction
- positions are given in absolute terms rather than relative
is this really an effect of lnaguage or something else?
-in english we dont order time left to right linguistically, left to right is determined by writing
for kuuk thaayorre speakers direction may be a fundamental concept influencing language not the other way round
strong whorf - colour perception
what experiment was carried out
different languages, cultures have many different numbers of colour terms
the berlin kay world colour survey
24 native speakers of 110 unwritten languages were asked to name each of 330 munsell chips
identified languages with between 2 and 11 unique colour terms
different languages, cultures have many different numbers of colour terms
strong whorf - colour perception
what does this say about colour perception in relation to language
does your colour vocab alter the way you see? - yes
when tested at a coarse level there is little difference in colour discrimination acorss cultures
but there are top down influences on colour perception
discrimination across perceptual categories are better than within a category
language influences perceptual categories and maybe only in the right visual field
how do all languages tend to develop names for colours and in what order
2 names - light/warm vs cool/dark
3 names - white, red/yellow, black/blue/green
4 names - white, red/yellow, black/blue, green
5 names - white, red/yellow, black/blue, green, pink
scientific study - what is it tending towards
towards reductionism
methodology required that the phenomena under study be measureable
biological phenomena and behavioural responses are measureable
but personal experience of perception is not measureabel
what is psychophysics
the scientific study of the relationship between physical stimuli and the psychological effect of these stimuli
this field has developed highly controlled mechanisms to investigate this
these methods have wide applications across the physical and social sciences
what is webers law
the ratio of the difference threshold to the background intensity is a constant
your ability to detect a difference is best thought of as a percentage difference
what is a psychometric curve and what is it trying to do
characterses the relationship between a physical stimulus parameter and the probability to detect the stimulus
what are the four results in the medical world
diagnostic test positive vs negative
against
disease condition vs no disease condition
hit = positive result and disease is there
correct rejection = negative result and disease is not there
type 1 error = positive result and no disease
type 2 error = negative result and disease is there
what does type 1 and errors have to do with the study of perception and psychophysics
shows how we need to ask participants the right questions
if we just show one stimulus and see how often people get it right we would only have part of the story
what is the forced choice
present signal on some trials and no signal on others (detection)
the subject is forced to say yes i saw it or no i did not on every trual
this way we can count both the number of hits and false alarms
what does noise in data result in
uncertainty
what is the JND
just noticeable difference
the smallest change a person cna detect
what does webers law suggest about the JND
is a fixed percentage of the stimulus level
what is the law of specific nerve energies
cortical neurons all communicate by spikes
all spikes are pretty much the same
how do we know the nature of the stimulus that originated the neural event
the neural pathway carrying the signal determines the sensation
theories of pitch perception
placed code theory
temporal code theory
basilar membrane
for pure tones each point on the basilar membrae oscilates up and down at the same frequency as the tone. what differs from point to point is the size of oscillation
with different points on the basilar membrane being tuned for different frequencies
place code theory
simpley the most important aspect is the place on the basilar membrane that is activated
what is cochlear microphonic
a small electrical signal that can be measured near hair cells discovered by ernest wever
low frequency tones - slow firing rates
high frequency tones - high firing rates
what is temporal code theory
pitch is coded by the firing rates of cells in the 8th auditory nerve
low frequency tones = slow firing
high frequency tones = high rate
what is the problem with temporal code theory
single celss firing rate is limited to 1,000 hz
hearing range is 20 - 20.000 hz
so how could temporal code work?
how could temporal code work (brief what are the theories)
volley principle
what is the volley principle
an idea stating hat multiple neurons can provide a temporal code for frequency ig each neuron fires at a distinct point in the period of a sound wave but does not fire on every period
reconciles the fact cochlear microphonic mimics the sound pressure waves with the implausability of the temporal code
wever suggested that while one neuron alone could not carry the temporal code for 20,000hz tone, 20 neurons with staggered firing rates could
each neuron would respond on average to ebery 2th cycle of the pure tone, and the pooled neural response would jointly contain the information that a 20,000hz tone was being presented
mechanisms we carry out auditory scene analysis by
interaural level difference
interaural time difference
what is interaural level difference
the difference in level (intensity) between sound arriving at one ear versus the other
sounds are more intense at the ear closer to the sound because the head blocks the sound
- bigger effect for high frequencies
- this is becuase low frequencies are wider than the head and high frequencies have to vibrate through the head
where is ILD largest
90 degress and -90 degrees
non existent for 0 and 180 degrees
what is interaural time difference
the difference in time between sound arriving at one ear versus the other
most useful for low frequency sounds, or brief broadband sounds
because we need to be able to link features ( similar to correspondance problem for motion)
sound localization
ILD and ITD are great for determing azimuth
but what about elevation?
- the cone of confusion, regions in space where all sounds procude the same ILD and ITD
how is the cone of confusion rectified
shape and form of pinnae helps determin localization of sound
head-related transfer function - describes how pinnae, ear canal, head and torso change intensity of sounds with different frequencies that arrive at each ear from different loction in space
how do listeners know how far away a sound is
simplest cue - relative intensity of sound
inverse-square law - as distance from a source increases, intensity decreases faster such that decrease in intensity is distance squared
spectral composition of sounds - higher frequencies decrease in energy more than lower frequencies as sound waves travel from source to one ear
realtive amounts of direct vs reverberant energy
complex pitch perception - what happens in natural situations
acoustic environments can be a busy place with multiple sound sources
so source segregation or auditory scene analysis needs to occur
strategies to segregate sound sources
spatial separation between sounds
separation ased on sounds spectral or temporal qualities
auditory strem segregation - perceptual organization of a complex acoustic signal into separte auditory events for which each stream is heard as a separate event
auditory filling in
conituiity and restoration effects
auditory stream segregation`
what is head related transfer function
breaks the cone of confusion and determine elevation of a sound
what is distance in terms of sound determined by
the spectral content
how can visual information be influenced by auditory information
the McCGurik effect
the video where you are hearing the same word but what you hear is influenced but the word the man in the video is making with his lips demonstrating how visual information influences auditory information
4 types of sensation in terms of touch
somatosensation - sensory signals from the body
proprioception - perception mediated by kinesthetic and vestibular receptors
nociception - pain sensation
thermoception - temperature sensation
where are the touch receptors
embedded on outer layer (epidermis) and underlying layer (dermis)
what are the three attributes each touch receptor has
type of stimulation the receptor responds to
size of receptive field
rate of adaptation (fast =transient, slow = sustained)
roles of the four types of receptors
Slow adapting 1 - responds to steady downwards pressure, fine spatial details and low frequency vibrations (reading braille)
slow adapting 2 - sustained pressures, particularly skin stretching (grasping a cup)
fast adapting 1 - vibrations between 5 and 50 hz (cup is slipping from your grip)
fast adapting 2 - responds to vibrations between 50-700 hz (something lands on your arm)
how do the four touch recpetors work
they work in unison
in addition to these tactile receptors there are other types of mechano receptors within musclesm tendons and joints.
kinesthetic receptors play important role in sense of where limbs are, what kind of movements are made
importance of kinesthetic receptors
ian waterman - patient
cutaneous nerves connecting waterman’s kinesthetic mechanorecpetors to brain destroyed by viral infection
lacked kinesthetic sense, dependent on visions to tell limb position
importance / what are thermoreceptors
sensory receptors that signal information about changes in skin temperature
two distinct populations of thermoreceptors - warmth and cold fivres
body is consistently regulating internal temperature
thermoreceptors kick into gear when you make contact with object warmer or colder than your skin
methanol in mint activates vold fivres
capsaicin in chili activates warmth fibres
how does touch information reach the brain
to get to the brain information must first pass through spinal chord
-axons of various tactile receptors combine into single nerve trunks
-several nerve trunks from different areas of the body
but spinal chord is not just a cable
touch sensation travel as far as 2m to get from skin and muscles of feet to brain
this can take a long time
to enable faster processing there are spinal chord mediated reflexes
example of monosynaptic reflex
knee jerk
mediated by a single (mono) connection (synaptic)
useul for protecting muscles from sudden forces
not under conscious control
example of postsynaptic reflex
pulling hand away from a hot stove
mediated by interneuron
can be consciously modulated
how are touch sensations represented
somatopically
analogus to retinotopy found in vision
-adjacent areas on the skin connected to adjacent areas in the brain called hominculus
brain contains several sensory maps of body, different subareas of S1 secondary areas as well
phatom limb
perceived sensation from a physically amputated limb of the body
parts of the brain litsening tomissing limbs not fully aware of altered connections so they attribute activity in these areas to stimulation from missing limb
pain
pain sesation truggered by nociorecpetors
response to noxious stmiuli can be moderated by anticipation, religious belief, prior experince, watching others respond, excitement
nocioreceptors transmit information about things that cause damage or potential damage to the skin
what are the two groups of nocioreceptors
a-delta fibres - respond to strong pressure or heat -myelinated so conduct signals rapidly -quick shallow pain c fibres -respond to various intense stimulation: pressure, heat, cold, chemicals -throbbing pain
what type of touch recpetor are nocioreceptors
bare receptors in the epidermis
what are the benefits of pain perception
sensing dangerous objevys
who was miss c
reported by melzack and wall 1973
born with insensitivity to pain
did not sneeze, cough or gag or protect eyes reflexively
suffered many childhood injuries
as an adult developed joint problems as a result from standing too long in one position
she died age 29 from infections that could have been prevented in someone who was alerted to injury
in general smelly molecules are…
small volatile hydrophobic (don't mix with water)
what is the physiology of smell and smelling
odors bind to the olfactory cilia
there are part of the OSN -olfacotry sensory neuron
each OSN will have a single type of odour receptor
there are about 5 million OSNs in your head
OSNs will fire once 8 of their binding sites are filled
signals are sent to the olfactory bulb
no thalamus, direct line to the cortex
what is the main theory on smell receptors
is based on shape
odorants have the right shape to fit in the lock of a receptor and activate it
what is an alternative to shape theory on how our receptors understand smell
our receptors sense molecule vibration
problems with shape theory for describing how our receptors understand smell
scientists are rubbish at predicting sell from structure
if shape theory is correct there shouldnt be any difference between the smell of isotopes
recent experiments suggest that flies can tell the difference between isotopes
changing the shape of some molecules does not change their smell
each OSN……
expresses one type of olfactory receptor
each glomerus….
receives inputs from OSNs expressing the same surface receptor
explain the connections between the OSNs and the olfacotry bulb
connections are incredibly specific
each OSN expresses just one type of receptor
axons from the OSNs project to glomeruli in the olfactory bulb
each glomerus recieves inputs from OSNs expressinf the same surface receptor
the code for odor
we can distinguish thousands of smells
but we only have about 300 individual receptor types
they generate a pattren of activity elsewhere in the cortex (entorhinal, piriform cortex)
we learn to associate the response pattern with the object
why is smell different to other sensory systems
doesnt go through the thalamus
strong link to memory
what did Cain 1982 study into odor identification find out
asked men and women to identify smells of visually-masked objects
also asked them to estimate before hand how well they expected both sexes to score
both groups expected women to do better overall but for men to score well on scents in the male domain
and this was true
what is blindsmell
does the brain respond to odors in concentrations below our potentilas threshold
using an fmri compatible olfactometer sobel et al presented subjects with sub-threshold levels of odoratn in the scanner
found brain activation to smells that were not noticeable to participants
what is the VNO
the vomeronasal organ
parallel olfactory system in many animals including rodents and horses
contains a separate set of heavy chain odoratn receptors that bind a class of molecules caled phermones
animals will exhibit speciifc sniffing behaviour in order to drive air over the VNO
the VNO does not appear to function in adult humans (the anatomical structure is degenerate and many of the genes necessary for it function are pseudogenes
it is present (like gills) during fetal development
are humans insensitive to pheremones?
MHC / HLA
mice and many other animals express a group of proteins from a group of genes called the major histocompatibility complex
this gene is also present in humans
it is called the human leukocyte antigen
in both mice and humans this gene similarity appears to affect mate choice
human mate choices and the HLA
1995 wedekind et all
HLA difference was correlated with mate choice in humans
females preffered males with different HLAs unless on oral contraceptives then they preffered males with similar HLAs
but
roberts et al 2008 = mate preference depends on relationship status
in mice tears contain what chemical
chemosignal
what is androstadienone
a metabolite of testosterone found in sweat
saxton et al ound that pre-exposure to this chemical affeted speed dating results
how might hormones be detected
liberles and buck 2006 showed that a second class of receptors present in the mouse olfactory epithelium genes for these receptors were also present these receptors detect volatile amines found in urine ... stress... pheromone? possible mechanism for human chemosignalling
smell of tears experimetn
gelstein et al collected sad tears from female subjects (different to poke tears)
men could not onsciously tell tears from salt water
but
after sniffing tears men rated pictures of women as less attractive
self reported lower rates of sexual arousal
had lower level of testosterone
and showed reduced brain activity in substrates of sexual arousal in response to porn
what happens if something hits you in the front of the head and pushes your nose back
can push the cribiform plate backwards
this will shear all your OSN axons making you anosmic
what is the McClintock effect
one of the most famous effects in the field
1971 mcClintock reported female students who lived together synchronized their menstral cycles
1998 studied claimed the effect could be driven by pheromones found in sweat
this effect has becomes more or less established in the literature and has entered popular scientific consciouseness
evidence against the McClintock effect
more recent studies have thrown doubt
original studies were barely significant
if account is taken of probablity of random synchronisations, the effect dissapears
no support from large scale, long term chinese study (yang et all 2006)
where does taste occur
on the tongue
what is taste largely made up of
what we can smell
what does retronasal flow do
brings olfactory molecules from your mouth to your nasal cavity
what is responsible for flavour
retronasal olfaction combined with taste
what is orthonasal olfaction
smells coming from the front
what is retronasal olfaction
smells coming from behind the mouth
what \re the 5 basic tastes and what makes them up
sweet - glucose, fructose sour - protons salt - sodium ions bitter - no single molecule, poisons umami - amino acids, glutamate etc
taste buds
create neural signals conveyed to brain by taste nerves
where are tast buds embedded
emebeddded in structures - papillae (bumps on the tongue)
each taste bud contains…
taste receptor cells
how is taste information sent to the brain
via cranial nerves
which chemicals we taste enter through ion channels
salt - NaCl, Na+ is important for cell function
H+
how are sweet and bitter tasted
sweet and bitter compounds are too big to fit through ion channels
these tastes are sensed by G-coupled proteins
coding of taste quality - labelled lines
a theory of taste coding in which each taste fibre carries a particular taste quality
(remeber the law of specific nerve energies)
major source of controvery in the literature
other posibilities for theories behind taste coding
patterns of activity across many different taste neurons
if labelled lines theory of taste coding is true what does that mean for research
we can measure neural response in primates and predict patterns in humans
where does our confusion over labelled lines come from
confusion stemmed from the non-pure responses to pure tastes
caused by imperfect receptors
labelled lines are important because a pattern or synthesis mechanism would make identifying behaviourally useful taste information difficult to detect
umami and MSG
MSG is glutamate - a neurotransmitter
concerns have been raised about its safety
“chinese restaurant syndrome”
current evidence - MSG in large doses may be a problem for some sensitive individuals but not serious for the general population
how fat molecules are dealt with by the taste system
fat molecules (like protein molecules) are too large to stimulate taste and olfaction
fat molecules stimulate the trigemial nerve in the mouth - tactile sensations like creamy, oily, viscous
but there are fatty acid receptors in the tongues of rats
just like MSG / protein fat in the gut produces a conditioned preference
explain various studies looking into genetic variation in taste experience
arthur fox 1931 - difference of perception for phenylthiocarbamide PTC
bitter to some but not others
Dennis Drayna 2003 found the gene that codes for PTC/PROP receptors
- nontasters (two recessive copies) vs supertasters (two dominant copies)
flavour preferences
nature vs nurture?
hedonic responses to odours inate or learnt?
evidence from infants
cross-cultural data supporting associative learning
evolutionary argument
learned taste aversions
hardwired taste expressions
the pleasure of taste - hardwired affect: evidence from newborn facial expression for the different tastes
olfactory system is functional by first trimester so is difficult to separate learned from innate
cross cultural preferences for tastes and odours
there is agreement about taste preference
no agreement for odours
many people from asian cutures dislike the smell of cheese
japanese eat natto that most westerners find awful
both high in protein and similarly nutritious
vision and flavour
huge impact
white wine with added red food colouring will be described like red wine
what is gain control
lets neurons control their sensitivity
we need it because neurons have to code things that have large dynamic ranges
the brain and gain control
brain has similar structures everywhere
maybe similar operations happen across the cortex
limited number of universal or canonical computations get everything done
vision as a model system for investingating the brain and gain control
why is it so good
vision is a window into the brain
visual stimuli are cheap and easy
visual system is big and well organised - so you can record from it
people are good at accessing their visual system consciously (unlike olfaction)
100 years of prior data and publications
what is contrast
the average luminance in part of the visual field
often expressed as a decimal or a percentae
what is the currency of the early visual system
contrast and not lminance
contrast gain control
explains pretty much everything
says that neuronal inputs are divided by the sum of the local average response
the model is agnostic as to how this happens
but it describes its computation perfectly
early contrast gain control
the gain pool for early contrast normalization does not care about spatial frequency or orientation
we think that it is happening at or before the LGN
short-range gain control is very different when you put the mask onto the other eye or another precortical pathway
gain control in the visual cortex
gain control and normalization continues through the visual cortex
neural activity is moderated by the local activity of the group - averaged over both space and times
receptive fields in cortex are large so normalization happens over wide regions
different visual pathways are combined in cortex so they can interact
structure in cortical gain control
long range tuning (orientation) slow (neurons in cortex dont like fast flicker - unlie the LGN) complex features (facial expressions, blur, gender..)
how you can measure visual perception and neural response
a CRT screen
what did nachmias and sansury 1974 do
asked if measuring contrast detection would tell them somethin about neural transducer functions
a transducer function tells you how a neuron (or population of neurons) converts inputs to outputs
found the dipper function (had to repeat more than 1000 times)
adjust the contrast difference at each test level until it is barely detectable
= a contrast discrimination threshold
plots discrimination threshold as a fuunction of test contrast = dipper function
what is the dipper function
not everything obeys weders law
the dip in the dipper function is the point at which the visual system is most sensitive to contrast
it tells you where the steepest part of the response curve is
when do we witness abnormal gain control
has been observed or proposed in epilepsy, autism, shizophrenia, parkinsons as well as normal ageing
may be an indicator of neural dysfunction - the canary in the mineshaft
but abnormal gain control may also be the cuase of some neruological diseases
epilepsy and gain control
some forms of epilepsy may be due to abnormal neuronal gain control
photosensitive epilepsy can be triggered by high contrast visual flicker
do patients with non-photosensitive ‘idiopathic generalized epilepsy’ IGE exhibit abnormal gain control?
what is ESP
extrasensory perception
what is telekinesis
affecting things with our mind
precognitino
seeing (affecting?) the future
telepathy
reading other minds or projecting owns thoughts onto others
what if ESP is true
the presence of verified ESP would overthrow our understanding of vast domains of science
why should/ shouldnt we study esp
no reason in principle but there is a cost to every human endeavour time money confusion the history of esp research is littered with failure
brief history of esp research
-who was first
henry sidgwick
founded the society for psychical research
first group to propose applying modern scientific methods to study psychic phenonmena
brief history of esp research
1970s
lots of research into esp US stargate project at least 20 million dollars remote viewing ganzfeld conducted at sri
brief history of esp research
1980s
fragmented research prgrams
de-emphasis from most uni
disappeared from textbooks
uk is something of an exception
PEAR’s esp experiment
on random numbers
random numbers generated by hardware will fall into a distribution
PEAR claimed a participant could changethe random number distribution
claimed highly significant results
why did PEAR make significant results
n was high, not a large effect
independent analysis indicate that the entire effect is driven by a few events out of several thousand
the experiments are particularly suseptible to any form of experimental irregularity - file drawer effect, instrment bias or outright fraud
should we pay more attention to effect sizes than p values
yes
small experimental biases can give rise to high p if n is high
you dont necessarily have a real result]no
if you have controlled your experiment well then even small effects are interestnig - especialy if they overthros all existing scientific thought
daryl bem
lots of minor flaws in paper lead to false conclusion
7 types of experimental error there could be in psychological experiments
p-value hacking the texas sharpshooter fallacy the file drawer problem multiple comparisons post-hoc statistical tests improper analysis of interactions fraud
what is p-value hacking
exploiting researcher degrees of freedom chosing this such as -when to stop recording data waht variables to follow - what comparisons t make - waht statistica methods to chose if you monitor the data or outcomes in any way while making these decisions you can consciously or unconsciously explout their degrees of freedom to reach the magic p-value
what is the texas sharpshooter fallacy
post-hoc definition of success
eg throw darts then put the bulls eye on the dart board
example is notice some people tend to give significantly below chance responses to zener card tests. or sucessfully predict the next but one card
what is the file drawer problem
bad data is not included in the study
at first sight would ppear to be manifestly fraudulent
but sometimes there are valid reasons to exclude participants (eg they didnt understand the task or mucked about on purpose)
who makes the decisions
when do pilots become data
what is multiple comparisons and tests
you are very likely to get a significant result if you carry out 14 experiments
in other words no matter how bad your experiment is, if you run it 14 times you are likely to get at least one positive result - which of the 14 results is liekly to get published ….
solution to multiple comparisons
publishing or at least noting the null results
replication!
higher standards than 5%
reproducibility
core principle of scientific progress
scientific claims gain by the replicability of their supporting evidence
scientific debate is meaningless if the evidence being debated is not reporduceable
how reproduceable is literature… not very….
what did they do and find in the reproduceability project 2015
massive project of direct replications
270 people did 100 replications
replication was very different from original studies
also did it with cancer research and had to abandon the studies because they couldn’t even work out the methods sometimes..
