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PSY3108 Perception Midterm Notes Fall 2013.docx

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University of Ottawa
Levente Orban

Perception Midterm Lecture Notes Perception: the study of sensory processing What is perception? • Vision, audition, olfaction, gestation, nociception, proprioception, remote viewing, psychokinesis, telepathy, precognition, clairvoyance Recipe for Perception • Physical world – electromagnetic radiation, mechanical waves (ie acoustics) • An organ – to capture all this information o To detect some small aspect of the physical world – photons, vibrations, pressure changes • Neural processes o To make sense of the input – need to turn info from physical world o Organic capture info and turn into electrical processes o Basics: noise, simple sounds, frequency, pitch o Advanced: music & speech perception • Point of our sense was just to survive • Our perception is not perfect but it’s good enough • Its about measurement Is our perception perfect? • We did not drop into the Pleistocene period with all of our cognitive and perceptual abilities fully formed Cognition vs perception • Cognition = organization, identification, and interpretation of sensory information o Refers to the mechanisms by which animals acquire, process, store, and act on information from the environment • Perception = involves signals in the nervous system, which in turn result from physical stimulation of the sense organs Studying Sensation and Perception • Segment of the real world: absolute threshold, difference threshold, movement of the planets, efficacy of vaccines, etc • Segment of the real world  empirical generalizations o Weber’s law, Ekman’s law, mathematical descriptions, Weber’s ratio • Mathematical ratio used to describe their findings o What should the answer be on the top row if you wanted to make it perceptually equivalent?  100 to 50 if the bottom is 10 to 5  Weber discovered this – light intensity has to change by a ratio in order for us to perceive changes of the same distance in perception o If someone can just tell the difference between 100cd/m2 and 112cd/m2, she should be able to tell the difference between 200cd/m2 and _____cd/m2  (difference of 12%)  Between 200 and 224 (difference of 24%) o These are generalizations you can make by observing a segment of the world • How do you generalize? • Axiom system o Set of rules o A = A (a number is equal to itself), if a=b, then b=a • To verify mathematical equations – need logical consequences • • I = interpretation – bring mathematical conclusions back to the real world o Hypothesis or predictions to be tested • AMI – a model o Real world is an instance of the model • A = makes model become a theory about the real world • T = empiricism o Get experience and get meaning, but not truth • Logical and mathematical give you truth o But in truth you have no meaning • This is why two systems work together • Deductive reasoning and inductive reasoning • Weber and Fechner o First people who thought about quantitatively studying perceptive reasoning • 7/10 bees landed on a blue flower – chi squared test – you have taken empiricism route since you’ve observed and described with chi squared • If you write a program to mimic brain functions – you have taken the route of deductive reasoning o You would have to test the model – experiment and then test prediction of model to see if the artificial neural network is working properly Signal Detection Theory • You hear a crack in the woods – what do you do? o Reality check: if it was a turkey – you look you win, you run you lose  If it was a lion – you look you lose, you run you win • Decision making paradigm • Every time you’re presented with a signal there are 4 outcomes – two kinds of mistakes or two correct answer o False negative false positive, correct rejection or ... • 2 things involved in response o Sensitivity to signal (d’)  How well did you hear the crack in the woods?  Ability to identify two distributions of signals that are closely tied together  Sensitivity is high if noise and signal are close to each other  If you can only hear really loud cracks that’s low sensitivity o Criterion ()  How careful you are  If you’re very careful you have past experience  If you had a bad experience you would run away  If you haven’t had bad past experience you wil be less biased  Shifting criterion of being very careful or not very careful • The more careful you are the more likely you are to commit a false negative • The more jumpy you are the more likely you are to miss the turkey o Want to minimize both kinds of errors  One error has more negative consequences • The less costly mistake Biological & Information Processing Foundations The Sensory Neuron • Where information is processed o If you remove a single neuron ... • Cell body – where all info comes in – sums up the info that comes in from all other dendrites, fires up or doesn’t fire up • Dendrites – receive info from different neurons, sometimes fire all at same time or sometimes different times o Excitatory or inhibitory  Positive or negative reaction • Engine of the cell – axon hillock – where the action potential or signal starts • Axon o Two parts  Nodes of ranvier – interaction occurs to amplify action potential first emitted  Myelin sheath – fatty insulators that prevent axon to have contact with extra cellular space • What is the most common disease that causes demylination of the axon o MS – multiplesclerosis • Parkinsons • Synapse o Every action potential ends in synapse o Connection with parts of neuron o 3 parts of synapse  Terminal  Synaptic cleft – neurotransmitters travel through here  Postsynaptic dendrite  Fires off another action potential • Action potential o Based on presence of positive and negative ions inside cell o Creates gradient between interior and exterior o Cell fires in response to voltage change  Other channels open up and difference between positive and negative ions – other space becomes neutral o Spike train (or spy train?) – a block of action potential  Where all the info is conveyed o Each neuron has a threshold – if the change is beyond the threshold then axon hillock emits an action potential and fires • Types of dendrites – affects voltage change in cell body – excitatory and inhibitory • A) Neuron 7 is active and sends a positive shock. This leads to a discharge in depolarization -- or excitation. If this single neuron is strong enough, it could lead to an action potential. o neuron 7 is an excitatory neuron • B) Next, neuron 3 becomes active and sends a negative discharge. This discharge causes hyperpolarization -- or inhibition. o inhibitory – sends a weakening signal, will not fire • C) Finally, we see that Neuron 7 and 3 are active simultaneously. The end result is a moderate effect. Not as strong as if Neuron 7 fired alone, but stronger than the effect of Neuron 3 alone. o if both excitatory and inhibitory fire at same time may or may not fire depending on the threshold • Neuron adds up effects of all incoming inputs o If one cell has a threshold of 2, it needs a minimum of 2 to fire and only receives a signal of 1 then it will not fire The artificial neuron • Cell body o Excitatory – will always be a positive value o Inhibitory – will always be a negative o Theta = threshold at which neuron will fire (dif thresholds) o Incoming and outgoing connections  Can be expressed mathematically • 1 or 0 depending on threshold o If activation value is greater than threshold then output value will be 1, if activation value is less than threshold the output value will be 0 o Ex: have two +1, -1, theta =1, it equals sum of all its inputs, so output value will also be 1 since it reached the threshold o Ex: threshold 2, then output value is now 0 since you didn’t reach the threshold (sum of inputs is 1) o Ex: 1, 1, 1, threshold 2 – input sum of 3, threshold 2, output is 1 since reached the threshold o ^ this is an excitatory neuron o F(a) = 1 if a is greater than or equal to theta o F(a) = 0 if a is less than theta • Exercise 1 o AND function: both neurons must fire for the output to fire  If only 1 or none of the inputs fire then the output is 0  X1 =? And x2 =? To get theta=2 • X1 = 1, x2 = 1, so 1+1=2 which is the threshold of theta which is 2 • Exercise 2 o OR function: output will fire if either one input is active, even if both are active o Output will fire if either is active, or both o X1 = ? , x2 =?  theta=2  Either both or one • The smallest single value that would satisfy both of those is 2 • X1 and x2 are both 1  The neuron should work for all the conditions in the truth table (1 means on, 0 means off) • Exercise 3 o AND NOT function: output will fire only if either one input fires o One is an excitatory neuron the second one is inhibitory neuron – the second one has to be negative (dot means inhibitory, arrow means excitatory)  X1 =?, x2 =?  theta=2 • X1 = 3, X2 = -1 (?) • X1 = 2, x2 = 0 • Exercise 4 o XOR function: output should fire if the inputs differ. Known as “exclusive OR” function, a combination of AND NOT and OR – output fires whenever both inputs differ (ie one input fires but the other does not) o X1 =?, x2 =?, z1 =?, z2=?, theta =2  2 for the four outside ones and -1 for the inside ones • Hot and cold – mccullogch & pitts model o Momentary feeling of hotness when something is actually cold (or other way around?) o Time o At each time point only the adjacent neurons can be outputting (?) o At time one z2 is activated, at time 2 x2 is not receiving any more signal so not emitting inhibitory signal, but z2 sent signal to z1 o Time 1 – receive input to the cold, at time 2 you stop the cold it turns 0 but you had z2 firing to z1  At each time step you can update only the adjacent neuron - only z2 is active  Then neurons are already in motion and they activate hot o X2 sends to both adjacent z1 and z2 o X2 = +1, z2 = +1, z1 =0, y1=0 o X2 = 0, z1=1, z2=1, y1=1 The Brain • Different techniques to study the brain o FMRI, EEG, etc • What technique is the first image using? o FMRI  Whats good about FMRIs? • Lights up the parts that are being used • Special image of which areas are lighting up • Not invasive • What is it measuring? o Something happening in the brain • Spatial resolution  What is the weakness • The time aspect – doesn’t give us info about the timing of events abut whats happening when o 4 or 5 second delay – the neuron may have already stopped communicating • Can tell where, but we don’t know what – we just know something happened • Poor temporal resolution • Second image – head of human and electrodes attached to head o This is an EEG  What are the advantages? • High temporal resolution o Shows activity in area associated with electrodes – shows at the microsecond level  What is the weakness • Poor spacial resolution o You get the activity from millions of neurons – don’t know if they’re near the surface or deep inside • Spatial resolution = how precise of an image you can get of the brain – can precisely tell where something happened • Temporal resolution = the precision of time – seconds vs microseconds • 3 image – microscopic imaging o Can only cover very small areas o Good for small animals o Flourescent imaging o Combines the temporal resolution of EEG and the special resolution of FMRI (but even better) Somatosensory System The Skin and its Receptors • Somatosensory system o 3 types of perceptions:  1) from skin – give you info about mechanical contact with skin  2) proprioception – give you info about position and status of limbs  3) noceception – pain • Different dimensions by which we can say one receptor is different from another o The receptor can differ in looks, response, physical, incapsulation (wrapping), or free nerve endings o The kind of receptive field they have – what is the area that they cover – how big is the area that one receptor is responsible for o The temporal – how fast can you sense before it feels like a continuous touch o Sensitivity – what is the min amount of stimulation you need to apply before the receptor fires (and you can feel) o Response adaptation – idea that some receptors will get used to the stimulation  When you’re wearing clothes don’t feel them all the time since neurons got used to it • Can be slow or fast adapting neurons o Fast adapting = stop feeling it after a while o Its affect – the receptor responds either excitatory or inhibitory o Or it can have both affects o How is the information carried – fast or slow – depends on how important the info is  If its critical info you have to act quick on then it will be fast  Speed of info is determined by the amount of mylination – how well insulated • Also by the diameter of the fibre – the bigger the fiber the faster the info will be processed o If info is travelling slowly you will feel pain longer • Receptive field (RF) o Area which affects firing of neuron  Directly related to spatial resolution o Exists for all sense organs (skin, retina, inner ear, etc) o Can be excitatory and inhibitory, or both o One receptor is either responsible for larger or smaller area o The larger the receptive field = the harder our sensations are to locate  Ex: hands have many receptors – receptive fields are smaller  Back – receptive fields are larger o Different receptive fields can overlap one another  Some are perceiving vibrations, touch, pressure • All overlapping one another o Receptive field resolution  Spatial resolution • How many receptors are there for a particular area? • The bigger the receptive field the smaller the spatial resolution o Temporal resolution  How often can a receptor fire when it receives input?  Different from sensitivity  If you tap your arm, at some point you could tap so fast that all you would feel is a continuous touch • The faster it fires the higher the temporal resolution • Centre-surround receptive fields o Receptive fields that are both excitatory and inhibitory o Common in visual sense o If you receive a stimulation around the receptor there will be pos or neg affect and at a certain distance it will have an opposite effect • Response adaptation o How do receptors respond to continuous stimulation?  Slowly or quickly? o “receptor gets used to the stimulation” o How fast receptor gets used to presence of a stimulation o Figure shows presentation of a stimulus – fa = fast adapting, sa= slow adapting  Fast adapting – stops firing after, but a bit at end when you release  Slow adapting – receptor never gets used to presence of stimulus action potentials still going on o  Figure shows number of action potentials that occur at a given point  Bottom one is only showing the presence of the stimulation o Which pattern of action potentials on the left match up to the ones on the right  Match the spike trains (patterns of action potentials) to the fast or slow adapting response • A another kind of fast adapting response ( the middle) • B  slow adapting response • C  the middle one – bursts of patterns with nothing in between – the fast adapting response • Big spike on top figure tells you there are a lot of action potentials happing in a few milliseconds • • Diagram of hair in skin – Hair Follicle o Nerve has grown around roots of hair follicle – detecting an emotion in the hair o Similar to the inner ear o Why it hurts so much to pull out hair – nerves attached o Goosebumps – nerves attached  Idea was to trap air in between hair if it puffs up o Merkel nerve endings – are slow adapting – can feel stimulation for long time – detect touch and steady pressure o Ruffini receptors – slow adapting, positioned deeper in skin  Respond to steady pressure – can feel harder touch with these o Meissner receptors – fast adapting cells  lose the sensation quite fast after initial presentation of stimulus  detect emotion and flutter  large receptive fields o Pacinian – fast adapting  detect vibration  large receptive fields  low spatial resolution  not easy to locate feeling o Free nerve endings – not encapsulated – they are just there – designed to detect things like temperature warm cold burning pain and different kinds of pain  They use the C class – slower – onset of perception later/slower o All other ones above are A class • Table summarizing all the information (receptors, location, etc) = on the exam! Neural Signals • After receptors fire, info gets passed along into spine then into brain • Efferent fibers – sensing fibers taking info in • Afferent fibers - • From lower parts of body info is fed lower • Epidurals during birth – which area would this go through? o Anywhere between L2 and L5 on the diagram  Anesthetic spreads up a bit o What is blocked out?  Everything below L2 since info is temporarily blocked so nothing can travel up • Efferent fibers are fed into dorsal portion of spine column o Dorsal = back portion o Anterior = opposite of dorsal o Ventral = pointing towards abdomen • L = lumber , C = cervical • Information travels up into brain into post-central gyrus • Areas where different kinds of sensation relate to • • How could they come up with image of parts of gyrus related to parts of body sensation o Can look at which part of the brain is active – FMRI  But a cruder way is to cut open someone’s head and poke at different parts of the brain and see what it affects while they are awake – feel the sensations in the body from stimulating brain  When people are brain damaged look at what was affected • Efferent means sensing – all info going from nerves and neural system – used to detect something, detect sensations Proprioception • Position sensing • Muscle spindle receptor: detects stretching & contraction • Ex: a recptor that detects stretching • Golgi tendon organ – located between muscle spindles and tendons – can feel tension if you stretch out o Muscle tension • Fastest fibers you can have o Travel at highest speed – called AAlpha class fibers – they are twice as fast as other skin receptors – extremely fast response • Nociception – Pain perception TED talk: • Disorder of thinking things are imposters o Face area of the brain – when its damaged you cant see faces  Amygdala (emotional core of brain) – gages the emotional significance of what you are looking at • Goes down autonomic nervous system • Channel to amygdala could be cut – not experiencing the emotion attached to the person you are seeing • No delusion through the phone – different pathway to hearing centres than vision pathways  Recognizes mother through hearing o Phantom limb – continue to vividly feel presence of limb that is no longer there  Ex: phantom menstrual cramps if uterus removed  Half of the people claim they can move the phantom – vivid sensations  Half of them don’t have this – say its paralyzed • Why would a phantom limb be paralyzed o The original limb was paralyzed because of peripheral nerve injury – had an actual painful arm – amputated to get rid of pain o Nerve supplying arm has been cut and pain for months gets carried over into the phantom  When it was attached the brain was telling the arm to move, but it was parlayzed • Learned paralysis – associative link – command to move arm creates sensation of paralyzed arm  How do you treat this syndrome? • How do you unlearn the learned paralysis o Send command to phantom but give visual feedback that it is following command  Mirror box – looking at phantom being resurrected because in the mirror he sees it – gives visual impression that phantom is moving and the pain is relieved because they think the phantom is moving • Critical rule of visual input Chemosensory System • Taste and smell • Gustation = taste • Olfaction = smell • Gustation + olfaction = chemosensory system • Origins of chemoreception o Ability started with other organisms - detecting molecules o In water everything is in dissolved form so distinction between taste and smell is not very clear o Senses (taste and smell) diverged when medium changed from water to air • Grocery store – how can food producers focus on good looking fruits rather than good tasting fruits? o Since you cant taste before you buy o If it looks perfect we will buy it o Distinct order of sense playing their roles: visual, tactile, olfactory, gustation  Gustation • Animals started to smell through pheromones (through glands) – useful for setting up territory, predator avoidance, sexual excitation/repulsion • Olfaction has little effect compared to other senses in humans o We can’t smell very well, we have better vision o Freud said that because we stood up we are no longer close to the ground and most smells happen near the ground – so we are not where the action is in terms of smell o Actually, we can smell as well as dogs but we don’t go around crawling on the ground  Chocolate sniffing experiment showed that we are capable • Gustation • 5 distinct tastes: sweet, sour, bitter, salty, umami (savory) • 5000 receptors on the tongue • No hard distinctions for areas of tastes on the tongue • Heightened sensitivity for bitter tastes in back • Papillae = taste buds o Protrude at the tip of tongue • Back of tongue, vallaie are V shaped • Microvillai are activated when mechanism touches molecules • Neuron fires and action potential travels to receptors • Activators and Mechanisms o Salt  Simplest receptor is for salt  Since it’s compatible with the neural system since action potentials naturally activate through rushes of sodium  Different amounts of salt fire different patterns – lots of salt continues to fire neurons • Sour o Fairly simple o Acidic, contains hydrogen ions o Hydrogen rushes in and activates action potential • Sour and salty compete for the channel, you can only taste one at a time • Sweet and Bitter o More complicated /complex o They activate multiple kinds of compounds o Series of biochemical interactions o Special receptor that takes in multiple kinds of compounds o Sweet takes all kinds of sugars o Receptors use g protein to play a role in activating action potential o Receptor  g protein  action potential • Coding o Carrying signal to the brain o Differences – not using spine, just feeds from tongue to brainstem o Cross-fiber coding: instead of each fiber feeding into brain we have convergence where signals file into one fiber – each taste produces a response profile o Ex: vanilla ice cream fires off a special pattern of receptors – look at total and get response profile (special combo of response pattern) o Response profile is the reason why we can differ between tastes even though its filing into the same fiber – since they have different profiles • Y axis = detection threshold, x axis = temperature of solution • Which taste has highest sensitivity? – bitter o Salty is lowest • Temperature related effect – can detect better or worse depending on temp • Right chart: debunks myth of distinct regions of tongue for different tastes • It’s a gradient – clusters of sensors where its more intense but can also taste it anywhere Olfaction • Biological mechanisms of olfaction • Perceptual shifts in olfaction during pregnancy • Olfaction takes place on small mucus membrane called olfactory epithelium – high up, under frontal lobe but not in brain • Air comes through nostrils or from back of mouth (exhaling) – a lot of molecules mixed in through mouth o Taste is influenced significantly through olfactory system – taste is a combo of everything happening in mouth • Olfactory epithelium o 3 kinds of cells:  1) cilia – tiny branches that blanket • Where action potential is initiated, molecular bind here  2) basil cells – help regenerate sensory neurons every 30-60 days • Whole sensory neuron is replaced • Makes up to 5% of epithelium  3) supporting cells – make this layer wet • Fat repellent because wet • Doesn’t let fat molecules in o Cant smell through fat molecules • Odorant binding protein • Maintains ionic content  Similar to what happens in tongue • There are some molecules that look similar but are sensed differently, and there are some that look different but smell the same – no pattern, it’s a puzzle • 2 olfactory bulbs o All signals from epithelium arrive here o Glomenulus – bundle of neurons  Fibers are converging – receives sensory neurons from all areas of epithelium, from multiple sensory neurons  But a single sensory neuron will only connect to one glomenulus  Feature extraction – info coming in, and glomenulus is extracting  2000 glomenuli, but 12million neurons  Info passed onto primary olfactory cortex • Anterior olfactory nucleus – enables communication between the two olfactory bulbs • Piriform cortex – sensory stimuli – lights up when given scents • Amygdale, tubercule, entorhinal – higher cognitive functions of olfaction, not restricted to just olfactory, emotional, and memory components • • Populations of neurons are small, densely packed, bundled together o Info processing happens o Result of this gets transferred to other areas o Small strands allow integration of other info – ex: memory • Case of suprathreshold function o Morning sickness st  Happens a lot in 1 trimester  Functional theory of pregnant sickness: st • timing of symptoms (1 trimester) • Sensitive period of fetal development – heart, brain, etc • Miscarriage – women who experience moderate amount of morning sickness have fewer miscarriages than those who have none or far too much o <20 weeks fetal death o Food cravings & aversions • Olfaction becomes super sensitive • Foods high in toxic substances elicit the sickness (coffee, meats, some vegetables) • Embryos that have just formed – little bits of toxic substances could be fatal o Absolute threshold technique  Longitudinally studied, test women 4 times at each trimester and once after birth  Scent – phenyl-ethyl alcohol  Results: pregnant women are capable of detecting scents earlier than non pregnant women  Sensitivity shifts back after birth  Mechanism? • Estrgogen modulates olfaction – affects permeability of epithelium – some molecules can pass through faster • Brain region responsible for toxic substances – elicits nausea and region becomes more sensitive • Women experience nausea in order to limit toxins for fetus – that’s the theory o Embryo protection hypothesis • Visual ability also becomes more acute in pregnancy – make far less mistakes on the test  Used the staircase method • Olfactory abnormalities o Hyposmia: reduced smell perception due to inflammation, infection, or trauma o Anosmia: complete loss of smell sensation  Genetic, born that way Auditory Sensation What is sound? • Vibration of particles o Particles vibrating back and forth in a medium (could be air, or water for dolphins) • Longitudinal waves • Sound waves: • • If the first particle is pulled down, it also pulls down the particle next to it • Air particles are travelling in same direction as energy transfer • Longitudinal waves represent sound • Earthquakes moves in a longitudinal direction • Air molecules in throat – vibrate all air molecules around it Sound intensity • Intensity = how loud is the sound? o The louder the sound the more compressed the air frequencies are o Sections of compressed air and sections behind it is rarefaction – sequence of pressure changes o The amplitude of the graph – the larger the change the bigger the amplitude o Detecting changes in pressure o Intensity is measured in decibels: a proportion between the pressure the sound is making divided by a reference value (the smallest audible signal we can hear – low compression)   Equation – called a Bell (named after Alexander Graham Bell) on a scale of 1-18 instead of millions without the log. To convert to decibels, multiplied by 10 Sound Frequency • What makes sound low or high • How squished the signals are, • How long does it take for one cycle to complete • Range that humans can hear is 20-20,000hz o Measured in hertz – a one hertz sound means one cycle takes one second to complete o • Low frequency sounds not as likely to be stopped by objects such as mountains – animals have better hearing Pitch • As frequency goes up, pitch goes up (but it’s not a 1 to 1 mapping) • • Many theories • Relationship between pitch and frequency – graph above o Y axis is frequency o Looks like a Weber’s Law situation, the frequency is the objective physical quality of the sound waves, pitch is the subjective quality that is perceived by humans Speed of sound • Why put ear on steel of train tracks? o Sound travels faster in different materials:  Air: 331m/s (at 0 Celsius)  Sea water: 1522m/s  Aluminum: 6420m/s • What happens to intensity as sound is travelling away from the source? o Takes a larger and larger area, and as the area increases the intensity dissipates, sound gets thinner and thinner in larger area • It is rare for sound to travel without any obstacles o What could happen to sound waves?  Could get an echo – a reflection, waves can bump into objects and be reflected  Could be absorbed – hits something and doesn’t get reflected  Can be diffracted – will get bent (like looking at a fish in water) Sound interactions • Reflection o Echo – large rooms especially if empty  Less to absorb o Bats use echolocation – emit sound that reflects from insects o Can humans use echolocation?  Some humans can! Identical to bats – airborne sonar  Controversy and skepticism • But just needs to be activated in humans and then its possible • Absorption o Sound proofing rooms, barrier around highways, recording studios o Bats – different climates and seasons/different environments = absorption changes as well as speed of sound  Different environments have different rates of absorption – when absorption is high bats emit lo
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