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Midterm 1- Lecture+ Textbook Notes

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Department
Psychology
Course
Psychology 2015A/B
Professor
Patrick Brown
Semester
Winter

Description
Psych 2015: Lecture 1: Why study perception? - Sometimes the nervous system makes mistakes à illusions (ted talk- Beau Lotto), no one is an outsider, colour is important in determining differences, brain adapted to colour because it is a useful way to see the world (see predators) - Neil Harbisson à colour blind, sound instead of colour - Perception is limited - Knowledge in CNS, past experiences and constant environment in past - Understanding how you perceive the world o Color vision (mating displays, camouflage, evolved to touch at a distance) o Depth perception (planning, peri-personal space, space of navigation, binocular disparity) o Hearing (clue to information in world, language, writing is recent, spoken language to communicate without light or arms) o Touch (social reasons, way of bonding with people, synesthesia- feel it when they see the touch happen to other people) o Smell and taste (useful for survival, draw to good foods, taste for fat because ancestors did not have negative effects only the pros to lots of energy) o Language processing - Medical applications o Devices to assist people with vision and hearing loss o Supplement vision with another sense- system for drawing images on a persons back using pressure points - The perceptual process: o We distinguish among: The stimulus, Neural activity caused by the stimulus (electricity), Experience and action related to neural activity o The steps are arranged in a circle to emphasize that the process is dynamic and continually changing. o Subjective experience is different from action o Note that experience and action should not really be conflated – they are quite different - Stimulus: o Stimuli in the environment o Attended stimulus (increase gain of information gathering apparatus, ex: focus image on fovea), stimulus is transformed when hit by light and reflected into retina o Stimulus on the receptor surface (e.g., retina) o Many objects in the environment are available to an observer o The observer selects some of these objects for attention for some reason o Stimulus energy arrives at receptors resulting in first internal representations o Internal representation: in your mind, contains information about some object or process in the world  Internal: contained in your nervous system  Representation: contains information about the stimulus o Neurons fire or they don’t fire, that contains information, their firing pattern does, not a picture of what’s out there, internal representation of your car will match up with what you see in the parking lot o Processing refines representations  E.g., vision – going from patterns of light and dark à visual features à perceived objects  Don’t know where one thing ends and one thin begins  Other processing is required for recognition, little bits are put together  Visual processing occurs quickly  But at each stage you still have a representation of the stimulus, you get closer to what it actually is as you go further  Representations at different levels contain different kinds of information about the stimulus  This slide refers to a system of brain structures involved in visual perception. These structures are organized in a sequence – each refines the representation it receives from the previous one  A lot of processing is done in the retina  Temporal lobe identifies the object and its meaning  Can also go to motor cortex for visually directed movement  Physiological  This slide refers to the tasks the visual system has to carry out in order to generate your visual experience of the world  A representation does not resemble a stimulus – it contains information about the stimulus o Environmental stimulus is transformed into the image on the retina, and this image represents the stimulus in the person’s eyes (first transformation) - Neural activity caused by the stimulus (electricity) o When the visual receptors receive light reflected from the stimulus they transform environmental energy into electrical energy and they shape perception by the way they respond to stimuli o Transduction: occurs when the receptors create electrical energy in response to the light  Or in response to other types of stimulus for other senses  Rods and cones contain light pigment molecules that absorb photons of light at a particular wavelength, which triggers a signal cascade that sends AP to the brain that results in information  Ear came from fluid filled sac in fish who used it to hear if a predator is coming close  Ears are very delicate  Transduction changes environmental energy to electrical nerve impulses  changes environmental energy to (electrical) nerve impulses o Transmission: occurs as one neuron activates the next one  This electrical energy is processed through networks of neurons.  Signals from the receptors are transmitted to the brain o Processing: occurs during interactions among neurons in the brain  Things can go wrong with any of these operations –producing different forms of visual impairment  Person cannot recognize object but can use vision to make muscles move to pick it up works fine, found someone with the opposite (can talk about the object but cannot pick it up) o Cell phone #1 sends an electrical signal that stands for “hello.” The signal that reaches cell phone #2 is the same as the signal sent from cell phone #1. The nervous system sends electrical signals that stand for the moth. The nervous system processes these electrical signals, so the signal responsible for perceiving the moth is different than the original signal sent from the eye. Note that a microphone and a speaker work on the same principle – but the retina and visual cortex are very different from each other (to say nothing of subjective visual experience) - Experience and action: o The observer has conscious perception of the moth – now she knows something is there o She then recognizes the moth – now she knows what it is o She takes action by walking toward the tree to get a better view o Perception occurs as a conscious experience o “Experience” here means subjective experience (what is happening in your head, what it’s like to be you) o Recognition occurs when an object is placed in a category giving it meaning, have seen it before, re-know it, have to remember it though o Action occurs when the perceiver initiates motor activity in response to recognition, - Two interacting aspects of perception: o Bottom-up processing: Processing based on incoming stimuli from the environment, Also called data-based processing o Top- down processing: Processing based on the perceiver’s previous knowledge (cognitive factors), Expectation and hypotheses, Also called knowledge-based processing - Did you see a “rat” or a “man”? Looking at the more rat-like picture on slide 30 increased the chances that you would see this one as a rat. But if you had first seen the man version (slide 30), you would have been more likely to perceive this figure as a man o Recognition occurs when an object is placed in a category giving it meaning - In this example, (a) the image of the moth on Ellen’s retina initiates bottom-up processing; and (b) her prior knowledge of moths contributes to top-down processing. Both types contribute to what she sees. o It’s easier to see things you expect to see o Perception is determined by an interaction between bottom-up processing (what’s available at the receptors) and top-down processing (which brings knowledge into play). - The three relationships measured to study the perceptual process are the psychophysical (PP) relationship between stimuli and perception, the physiological (PH1) relationship between stimuli and physiological processes, and the physiological (PH2) relationship between physiological processes and perception. - Observing perceptual processes at different stages in the system: - Psychophysical approach (PP) - the stimulus-perception relationship, psychological response to outside world, how does it change when the stimulus changes, which parts of the brain are activated and what are they doing, Study in animals o Experiments that measure the relationships indicated by the arrows on the previous slide. (a) The psychophysical relationship (PP) between stimulus and perception: Two colored patches are judged to be different. (b) The physiological relationship (PH1) between the stimulus and the physiological response: A light generates a neural response in the cat’s cortex. (c) The physiological relationship (PH2) between the physiological response and perception. A person’s brain activity is monitored as he reports what he is seeing. o The psychophysical relationship (PP) between stimulus and perception: Two colored patches are judged to be different o Experiment that shows that vertical and horizontal lines result in better detail vision than slanted lines (oblique effect) due to larger brain responses (physiological approach) using a brain scanner on people while detecting lines of different orientations, - Physiological approach (PH1) - the stimulus-physiology relationship. Don’t ask them what happened, see exactly what happens in neurons o The physiological relationship (PH1) between the stimulus and the physiological response: A light generates a neural response in the cat’s cortex - Physiological approach (PH2) - the physiology-perception relationship, Only humans, must be able to give feedback, fMRI looks at activity of 250 000 neurons (voxel?), how do they respond to a stimulus o The physiological relationship (PH2) between the physiological response and perception. A person’s brain activity is monitored as he reports what he is seeing Important Terms: - Perceptual process: a sequence of steps leading from the environment to perception of a stimulus, recognition of the stimulus and action with regard to the stimulus - Environmental stimulus: the stimulus “out there” in the external environment - Principle of transformation: stimuli and responses created by stimuli are transformed, or changed, between the environmental stimulus and perception - Principle of representation: everything a person perceives is based not on direct contact with stimuli but on representations of stimuli that are formed on the receptors and on activity in the person’s nervous system - Sensory receptors: cells specialized to respond to environmental energy, with each sensory system’s receptors specialized to respond to a specific type of energy - Visual pigment: a light-sensitive molecule contained in the rod and cone outer segments, the reaction of this molecule to light results in the generation of an electrical response in the receptors - Neural processing: operations that transform electrical signals within a network of neurons or that transform the response of individual neurons - Primary receiving area: areas of the cerebral cortex that first receive most of the signals initiated by a sense’s receptors, ex: occipital cortex for vision and temporal lobe for hearing - Occipital lobe: a lobe at the back of the cortex that is the site of the cortical receiving are for vision - Temporal lobe: a lobe on the side of the cortex that is the site of the cortical receiving area for hearing and the termination point for the ventral, or what, stream for visual processing - Parietal lobe: a lobe at the top of the cortex that is the site of the cortical receiving area for touch and is the termination point of the dorsal (where or how) stream for visual processing - Frontal lobe: receiving signals from all of the senses, the frontal lobe plays an important role in perceptions that involve the coordination of information received through two or more senses, it also serves functions such as language, thought, memory and motor functioning - Perception: conscious sensory experience - Recognition: the ability to place an object in a category that gives it meaning - Visual form agnosia: inability to recognize objects, can describe the object - Action: motor activities such as moving the head or eyes and locomoting through the environment, action is one of the major outcomes of the perceptual process - Knowledge: any information that the perceiver brings to a situation - Rat-man demonstration: the demonstration in which presentation of a “ratlike” or “manlike” picture influences an observer’s perception of a second picture, which can be interpreted either as a rat or as a man. This demonstration illustrates an effect of top- down processing on perception Lecture 2: Psychophysics - Psychophysics is the study of the relationship between external stimulation and internal (mental) states - The basic task for a sensory system is to detect energy changes in the environment - Nervous system is built for change - Habituation: ceasing of response to a stimulus that is unchanging - Eyes have a built in shutter so that the light is falling on different cells - A modality is a system that responds to energy of one particular kind, such as light - Most animals detect energy in multiple different modalities (vision, hearing, touch, taste, smell, proprioception) - Integration of senses to understand outside environment, person talking to you- hear and see, tires screeching- can see and hear it - How much stimulus energy must be present for an observer to detect the stimulus? - Experiment giving different stimulus intensities and ask if they observed the stimulus, the person may have forgotten whether or not they saw it or they may not be confident whether or not they saw the stimulus (don’t want people to think they are seeing things that aren’t there) - Some were below or just above a threshold of energy needed for you to be able to perceive the signal (threshold stimuli) - Original response to this question was the concept of absolute threshold - Step function: large step, no change in probability of detection of light intensity until a certain point, anything below the absolute threshold will never be detected and anything above will be - This theory is incorrect - The absolute threshold is the minimum stimulus energy necessary for an observer to detect the stimulus - In the oblique effect: the threshold is lower for horizontal and vertical gratings over slanted or oblique (exposed to more horizontal/ vertical orientations during development) - In what follows, the basic testing situation will have low-intensity stimuli presented to an adapted observer in a very quiet, very dark room (dark adepter eye) - Dark room increases sensitivity of eyes, takes about 15 mins to adapt - Method of limits o Start with an intensity that they can’t see then increase and decrease to see where they switch their results then average to find the absolute threshold o Present stimuli that vary in how much energy they contain o In ascending or descending series o Cross-over point is where response changes (e.g., from don’t see it” to “I do see it” or vice-versa) o Looking at the average cross over points in light intensity o Observer reports whether she perceived the stimulus o The dashed lines indicate the crossover point for each series of stimuli o The absolute threshold – the average of the crossover values – is 98.5 in this case o May get better with practice - In practice, the absolute threshold turns out not to be a fixed value, but to vary from series to series - Staircase method/ Method of Adjustment o Revised method of limits: experimenter changes direction each time the observer changes her response o Hover around centre, after several trials hone in on absolute threshold o This approach allows the experimenter to track the threshold if it changes (e.g., during adaptation) o Adaptation occurs when sensory receptors change their sensitivity to a stimulus o Fastest method - Method of constant stimuli o Uses a set of stimuli ranging from clearly perceptible to definitely imperceptible o These stimuli are presented one at a time in irregular order a fixed number of times o Not in order of increasing or decreasing intensity o For each level of intensity you have the probability that the subjects said they saw it o Absolute threshold is (arbitrarily) set at intensity leading to “Yes” response 50% of the time o Due to chance, above will be seen and below will not o Results of a hypothetical experiment in which the threshold for seeing a light is measured by the method of constant stimuli. o Need to draw function to determine threshold o Using this method, a candle flame can be seen at a distance of 48 km on a clear night o Using this method, an observer can detect the ticking of a wristwatch in a quiet room at 6 meters o Using this method, an observer can taste one teaspoon of sugar dissolved in 7.5 liters of water o Using this method, an observer can smell one drop of perfume diffused through an average 3 room apartment o Most accurate method due to a high n and randomization but is time consuming - Why is the threshold so variable? o Other stimuli are also present, even in a quiet and dark room. These are exogenous noise. (generated outside the nervous system) o There is spontaneously generated endogenous noise in the nervous system (random nerve firings), increases information carrying capacity of the nervous system o Noise is not just sound - What must happen in order for a stimulus to be detected? o Hundreds of millions (perhaps billions) of neurons and many more connections among neurons are involved o For an absolute threshold to exist, those neurons would pretty much all have to respond in the same way to a stimulus just above the threshold. This is unlikely! o Doesn’t have to work the exact same way for us to be adapted - If we don’t have absolute thresholds for sensory stimuli, then: o Something else must determine whether we see (or hear, or smell...) a given stimulus o Our ability to detect a stimulus of a given intensity may vary across occasions - In fact, there are two things that determine whether we detect a given stimulus: o Sensitivity – in vision, a function of the light-gathering power of our visual system (touch- heat/pressure, etc.), We can change sensitivity to environmental energy signals by mechanical means – e.g., glasses or a hearing aid, Changing sensitivity to social signals may be more difficult – but might be possible with training (e.g., clinical psychologist or cop) o Criterion (bias) – a function of the importance the signal has for us, We can change response criterion by changing payoffs - Signal detection theory: o Differs from a classical psychophysical experiment in that there is only one stimulus intensity presented and on some of the trials, no stimulus is presented (loudness may vary) o Classical psychophysics did not study the probability of detection – it studied the probability of a YES response  Suppose the observer wants to appear sensitive  He might say YES on almost every trial, “super vision”  Some people are less confident with uncertainty and may say no on every trial unless it is definite o Thus, to study perception we must take into account the observer’s decision- making behavior and we do this through signal detection analysis o Signal detection theory is based on the idea that there is no absolute threshold (no minimum amount of energy in a signal needed for the signal to be detected) o Rather, detection probability is a function of signal strength, criterion, and one other thing: noise o Signal detection theory is a mathematical system for separating an observer’s sensitivity from her response bias o Sensitivity completely free of bias and bias completely free of sensitivity o Can change bias (can’t change sensitivity except by glasses) by changing the reward structure, get $1000 for every correct true, hit or false alarm reward or taking away o Only one stimulus intensity is presented – but it is presented on a large number of trials o On some trials, no stimulus is presented o 4 possible outcomes: present/say present, not present/ say not present, present/ say not present or not present/ say present o Want hits (present/ say present) with few false alarms (not present/ say present) o Because stimuli are presented at very low intensity – just above or just below threshold – observer might think that stimuli are presented on all or most trials. They might then say YES on a trial when no stimulus was presented, because they think it was just a very low intensity stimulus. o The two kinds of trials are randomly mixed and occur in equal numbers. Thus, the probability of correct guessing is 50% o So the question is, on signal-absent trials will the noise be interpreted as signal? The answer is determined by the observer’s bias. o On signal-present trials the observer “sees” (or “hears”) the stimulus plus any noise in the sensory system o On signal-absent trials the observer “sees” (or “hears”) only noise in the sensory system o So the question is, on signal-absent trials will the noise be interpreted as signal? The answer is determined by the observer’s sensitivity and bias o Consider two possible set-ups:  Signal is present on most trials (& observer knows): When unsure – respond YES, You’ll be right most of the time  Signal is absent on most trials (& observer knows): When unsure – respond NO, You’ll be right most of the time o Observer might adopt different strategies for these different situations o If such a pattern occurs that tells us that the observer’s expectations influence her performance – not just the actual stimulus event. In such a case we can change performance by changing expectations o Ex: Suppose the stimulus is presented on 20 out of 200 trials, In 200 trials this observer says NO 188 times. Why? He has a bias – in this case, to say NO. This observer does not often use the YES response, but when he does he is much more likely to be right than to be wrong. This pattern suggests sensitivity in the presence of a bias to respond “No”. That bias makes sense since the stimulus is present only 10% of the time. This observer’s YES responses are useful, out of the yes answers they were correct 11/12 times which shows that they have sensitivity o Ex: Suppose the stimulus is presented on 100 out of 200 trials. This observer has 5 times as many hits as the previous one (55 vs. 11) – but when she uses the YES response she is as likely to be wrong as to be right. Not much of a bias, even distribution, not much sensitivity (as much of a chance to be right then to be wrong). This observer does not appear to have a bias to either response – nor does she appear to be very sensitive. This observer’s yes responses have very little value. o Ex: Suppose the stimulus is presented on 100 out of 200 trials. This observer’s YES responses are quite useful – she is 3 times as likely to say YES when a signal actually occurs as when there’s no signal. This observer clearly has no bias to either response (she uses each 100 times) but she does demonstrate sensitivity o Ex: Suppose the stimulus is presented on 100 out of 200 trials. This observer’s NO responses are useful – she does not say NO very often, but when she does she is very likely to be right. The point is that separate aspects of the data are used to assess sensitivity and bias. Yes bias, yes sensitivity o Bias is assessed by looking at how many times the observer makes a given response (YES, or NO) o Sensitivity is assessed by comparing hit rate to false alarm rate – that is, what proportion of YES responses is correct? o Conclusion 1: In order to assess an observer’s performance you have to consider both hits and false alarms o Conclusion 2: Response patterns like these can occur for the same observer and the same stimulus intensity – as a result of changing the payoff o Note that you could do exactly the same with misses and correct rejections – there is no information in the set of hits and false alarms that is not also in the set of misses and correct rejections o Costs of misses and hits may be different based on the situation o Payoff: Suppose you reward hits but don’t punish false alarms – a sensible observer will say YES on every trial, Suppose you punish false alarms but don’t reward hits– a sensible observer will say NO on every trial o So far this is all conceptual. We need a way to calculate the observer’s sensitivity and strategy (= bias) o Lack of sensitivity is the straight diagonal line (a YES response is equally likely on signal present & signal absent trials), blue is high sensitivity o This is called a receiver operating characteristic (ROC) curve: if two people have the same curve they have the same sensitivity o This observer can “buy” a lot of hits at the cost of very few false alarms, up to about a 90% hit rate o After that point, a few more hits cost a lot of false alarms o The red curve is less “bowed” – meaning that, at first, as false alarms increase, you get fewer hits than when the curve is more bowed o If signal strength or sensitivity increases the ROC curve becomes more bowed o How are these curves produced? What is the psychological process? o When present, the signal adds to the activity in the sensory system produced by noise o When present, the signal adds to the activity in the sensory system produced by noise o That’s why the signal + noise distribution is shifted toward higher values of activity in the sensory system o The criterion is the level of activity in the sensory system above which the observer will report that she saw the signal o If activity in the sensory system exceeds the criterion, the observer will say YES; otherwise she will say NO o Putting on glasses moves bottom function to the right, more accurate answers o Poorer sensitivity than the previous slide, more sensitivity= higher levels of sensory activity o d’ (sensitivity) is the difference between the mean of the noise distribution and the signal +noise distribution o The distance between the peaks of the noise and (signal + noise) distributions is a measure of sensitivity, called d’ (d – prime), You can increase d’ by (for example) putting on glasses, or turning up the volume on the radio o D’ can be measured by comparing the experimentally determined ROC curve to standard ROC curves or from proportions fo this and false alarms o The location of the criterion gives a measure of bias towards one response or the other (YES or NO) o Criterion is labeled β: liberal (says yes more often, higher false alarms and hits), neutral (say yes and no equally, low false alarm, high) or conservative (says no more often, low false alarms, low hits) o By choosing a stricter criterion you reduce the false alarm rate, at the cost of increasing misses o When the peaks of the two distributions are closer, you either increase the miss rate in order to avoid increasing the false alarm rate, or else you have to increase the false alarm rate to maintain your hit rate. o By choosing a laxer criterion you increase the hit rate, at the cost of also increasing false alarms o Placement of the criterion β depends upon expectations and payoffs o It’s important to note that sensitivity (d’) and bias (β) are totally independent of each other o Two observers who have the same sensitivity but different bias might have very different performance o This means that we can assess the sensitivity of someone’s sensory system regardless of any response bias they may have. - Why is SDT useful? o Consider an evening in a bar downtown. There’s a guy there who believes he is God’s gift to women. This guy thinks that if a girl touches her hair it means that she wants him to approach her. He thinks that if she sips her drink she sips it at him.In other words, he’s making “stimulus present” judgments o Consider an evening in a bar downtown. There’s a cute guy there who is really shy. This guy might not respond if a girl were to smile at him. Even if she were to do her very best flirting, he wouldn’t draw the appropriate conclusion. o What is the difference between these two guys? o #1 has no sensitivity but a very lax criterion. In order to find girls who actually enjoy his attention he has to accept many false alarms. Perhaps we should say impose his false alarms on many girls o The shy guy has no sensitivity and a very strict criterion. In order to avoid being turned down by a girl he will ignore lots of girls who might actually like him. Not a lot of false alarms or hits o Presumably this is what a girl would actually prefer – a guy who is reasonably sensitive, in the sense of pretty good at telling whether she is interested – not too many false alarms, but not too many misses either o The moral of the story: how things go for you in the chase depends upon your d’ and your β, not just your outward appearance - Identification: o Identification is the task when the stimulus is clearly above threshold and the issue is, what is it? o The difficulty of the task depends upon the number of things the stimulus might be o Suppose someone claims she can identify her favorite cola. We present two different brands and ask her to say which is her favorite. Her success would not impress us. o Suppose someone claims she can identify her favorite cola. We present two different brands and ask her to say which is her favorite. Her success would not impress us. o Information theory says that an observer’s identification of a stimulus depends upon the nature of both the channel and the signal o It is useful to think of the observer as a channel through which information is transmitted (like a telephone line) o The channel is the observer’s sensory system. The signal is the stimulus out in the world. o We describe the signal in terms of how complex it is – that is, how much information it contains o We quantify information in terms of how many questions we must ask to discover the identity of the stimulus o Suppose there are only two alternatives – as in a coin flip. You only need to ask one question: “Is it heads?” Regardless of the answer, you will know what the up- face is o Suppose I think of an English letter. How many questions must you ask to identify that letter? 5: Is the letter in the first half of the alphabet (A – M)? Yes. Is the letter on of the first 7 (A – G)? No. Is the letter in the range H – J? No. Is the letter either K or L? Yes. Is it K ? No. (want to reduce uncertainty by half each question o Each question eliminates half of the alternatives and defines 1 bit of information o So the amount of information in a stimulus identity depends upon the number of possible stimuli - Discrimination: o Discrimination problems ask the question, “Is this stimulus different from that one?” o An important issue is, by how much must two stimuli differ in order for the observer to notice the difference? o The absolute threshold measures the stimulus level above 0 that is necessary for detecting a stimulus. There is also a minimum difference that must exist between 2 stimuli nefore we can tell the difference between them (difference threshold, DL) o In discrimination studies, the observer compares a standard stimulus with each of a set of comparison stimuli more or less like the standard o The difference threshold (DL). (a) The person can detect the difference between a 100-gram standard weight and a 102-gram weight but cannot detect a smaller difference, so the DL is 2 grams. o With a 200-gram standard weight, the comparison weight must be 204 grams before the person can detect the difference, so the DL is 4 grams o The Weber fraction, which is the ratio of DL to the weight of the standard, is constant o Electric shock 0.01, lifted weight 0.02 (2%),
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