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Chapter 4

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Department
Psychology
Course
PSYA01H3
Professor
Steve Joordens
Semester
Fall

Description
Senses - touch is a short-range sense; have to be in contact w/something to have relevance - smell has intermediate range system, you smell better when you are closer  dogs have a history of smell and use their past to tell them what happened before coming into a room (for example) - vision and audition are long range system and are favored (avoiding a person to stay out of trouble or hunting can be used to prepare attack) - visual system must provide the stability in the face of rapid shifts in its input - sound is not so variable and intensity changes as we move toward or away from its origins; changes are more gradual than those face by visual system  sounds carry around obstacles in ways that light does not and auditory sense has more time to process signals - b/c they are attuned to different aspects of our world, sense contribute to the richness of experience Sensation vs. Perception – linked but description is a little false Sensation – raw sensory input that is striking the retina and it stimulates the retina and brought to the brain, which is then analyzed in perception – the detection of simple stimulus properties such as brightness, color, sound frequency, sweetness – seeing color red Perception – categorizing all things – the detection of objects, their location, their movements, their background. – Seeing a red apple – seeing purple and blue in the picture is sensation, whereas seeing beautiful fireworks is perception + seeing movement is sensation but seeing a soccer ball coming toward us and realizing that we will have to move the left to block it is perception How do these messages from the world get transferred into our body? - our senses are input from the world - through transduction Monday, October 23, 2006 Transduction Transduction – is the process by which sense organs convert energy from environmental events into neural activity, eventually ending up in the brain. - Sense organs detect stimuli provided by light, sound odor, taste or mechanical contact w/ environment – info. about these stimuli transmitted to the brain through neural impulses – action potentials carried by axons in sensory nerves - Sense organs differ in terms of the kinds of environmental energies they are sensitive to, and in the manner they transduce that energy. - Usually the transduction is accomplished via specialized receptor cells that release specialized neurotransmitters that stimulate other neurons. - Energy we’re able to pick up and turn into something else that makes sense inside the brain.  Light is out there in the real world and that is what our eyes can pick up, so it has to deal w/ radiant energy which goes to the neural system  Vestibular system is the tilt and rotation of head  Tongue is all about chemical analysis, recognizes various shapes of molecules and that’s what produces taste  Human is sensitive to a very narrow range of it (ie. We’re sensitive to light but we’re not sensitive to all light – infrared light) Location of Sense Environmental Energy Transduce Organ Stimuli Eye Light Radiant energy Ear Sound Mechanical energy Vestibular System Title and rotation of Mechanical energy head Tongue Taste Recognition of molecular shape Nose Odor Recognition of molecular shape Skin, Internal Organs Touch Mechanical energy Temperature Thermal Energy Vibration Mechanical Energy Muscle Pain Chemical Reaction Stretch Mechanical Energy - in most senses, specialized neurons called receptor cells release chemical neurotransmitter substances that stimulate other neurons, thus altering rate of firing of their axons Wednesday, October 25, 2006 Sensory Coding - How we take the rich source of information we see in front of us, reduce it to a bunch of firing patterns and somehow get it back a to a rich image. - Nerve cells can only send a message or not; they tell other neurons to fire or not. - The message does not vary in terms of what it says, or how it says it. - So how then can the same nerve cells transmit the fact that bananas are yellow, but carrots are orange? - In Morse Code complex, semantic messages were transmitted using simple clicks - In brain, through specific firing of nerve cells, able to capture the info. the richness of what’s out there and relay the information to the cortical areas, where it is somehow unpacked and turned into what we perceive. - A code is a system of symbols or signals representing info; as long as we know the rules of a code, we can convert a message from one medium to another w/o losing any information How does the brain code information? not absolutely sure yet; puzzle needs more unraveling Anatomical Coding – what is imp. is where the message originates and where it ends up. - Sensory organs located in different parts of the body send their signals to different locations in the brain; the brain uses this to interpret the signals correctly.  Example, rubbing your eyes & phantom limbs.  Tap your eye and you will see stars; eye is not getting light but by squeezing the fluid in your eyes, you are stimulating the sensory cells in your retina and the message is sent back to the visual cortex, which becomes the light pattern.  Phantom limb is where that part of the brain becomes randomly stimulated and you feel like you need to itch but you have no arm. - any information that ends up in the visual cortex, will produce a visual message - people on psychedelic drugs usually say things like the number 13 is a bluish color, or that light has a nice smell; signals get mixed up Temporal Coding – Information can be coded according to time - The easiest way to do this is with respect to rate of neural firing - By firing at a faster or slower rate according to intensity of a stimulus, an axon can communicate quantitative info. to the brain (ie. Light touch to skin can be encoded by low rate of firing and more forceful touch by a high rate) - Thus, firing of particular set of neurons (anatomical code) tells where the body is being touched; the rate at which these neurons fire (temporal code) tell us how intense the touch is - May be the main way to code the intensity of stimulation  Imagine grandmother in your mind; there are certain visual/auditory/smell patterns associated with her and all those things come to mind when you think of her; and all the nerve cells fire in synchrony and they are somehow glued together and maybe that is what underlies our conscious experience. Psychophysics – physics of the mind The systematic study of the relation between the physical characteristics of stimuli, and the sensations they produce. Just Noticeable Differences - Ernst Weber was the first to measure JNDs, the smallest change in the magnitude of a stimulus that can be detected. - found that the JND is directly related to the magnitude of the original stimulus - when examining people’s ability to detect differences in weights, he found that if the weights were within 1/40th of each other, no difference was detected. - [Used in modern times, to measure eye visions to see what prescription is needed] - Weber examined all the senses in this respect (example, to detect a diff. in brightness, the differ. must exceed 1/60 of the average brightness of the stimuli) - These ratios are now called Weber Fractions (b/w jnd and magnitude of a stimulus) - Construct graph indicating strength of sensation of brightness (in jnds) in relation to the intensity of a stimulus – graph relates strength of sensory experience to physical intensity - Each dot marks another jnd – amount pg physical energy necessary to produce a jnd increases w/ magnitude of stimulus; shape is characteristic of the mathematical function of a logarithm - This was a big deal in psychology because ability to experience difference in brightness, sound, heaviness follows a mathematical rule and can be studied. Measuring Sensitivity via Thresholds - The JND is a threshold aka difference threshold. - It reflects how big a difference has to be before it is detected. - There are more simple thresholds as well, how intense does a stimulus have to be before the subject claims to see, hear, smell, taste, or feel it? - Simple threshold – just being able to detect the presence of sound - Absolute threshold – minimum value of stimulus that can be detected – discriminated from no stimulus at all. - Threshold was not a fixed value; it is the point at which a participant detects the stimulus 50% of the time - We may have a conscious and unconscious system where unconscious system has a lower threshold and it takes less to detect presence of energy (ie. A message for an ad in lighter color, in background can be detected by our unconscious system to do something – such as travel on an airplane because of hot airhostess) - These sorts of thresholds have been used to assess the sensitivity of our sensory apparatus, and have lead to areas of research such as subliminal perception. How do we know if a message is subliminal? Subliminal - so subtle a sensory stimulus that one is not aware of its existence but may in some manner respond to it. - if you want to make, real lasting changes in any area of your life, you must reach the subconscious mind where the changes begin  simple threshold approach – establish the ‘limon’, the point where it is noticed half the time you notice something, and half the time you can’t  subliminal – point (more than half the time) where you can’t notice the stimulus th  Advertising expert for a theater put ‘eat popcorn’ 1/60 of a second, and the popcorn sales increased  You can somehow stimulate the unconscious mind w/o the conscious mind being aware and it causes hunger  It got everyone interested in subliminal perception, they wanted to not be controlled and went to go see movies to see if they got hungry  The statement of ‘eat popcorn’ was made up; but his sales increased The Problem with Simple Thresholds - Jastrow’s (1897) Subliminal Perception Experiment (first empirical study in N.A) - You sit there and he started walking backwards and you have to tell him when you can’t see the word - At that point, he would show the cards and you had to guess what they said – saw that the results were 60% correct, which is above chance - He concluded that this is strong evidence for some existence of some entity other than our primary waking self – somebody that is good at telling us letters from digits, when you cant see them - This is a very controversial area because of method; the way the experimenter presents the whole stimuli to people - subject may get tired and may not be telling the truth; experimenter has no way in verifying the truth of the subject - Demand characteristics and response bias can prevent accurate measurements of a threshold – subject has to make up what the experimenter wants (ie. When can you not see the words on the paper // not knowing what the experimenter means) - Introspection – relying on subject to give you data is scientifically dangerous Freud – one of his ideas; in conscious minds we like to think of ourselves as pure people - but there are perceptual defense mechanisms; try to keep dirty stuff out of minds - experiment was done where words were presented and the person had to blurt out word when he/she saw it – showed that it took longer to say the swear word; Freud may have been right - or it could have been that the person saw the swear words around the same time as the other word but the willingness to say it took longer - there could have been a response bias – willing to say it may have been reduced or taken longer because it was uncomfortable to say it out loud (emotionally charged words) - response bias is a personal thing Friday, October 27, 2006 Separating Bias from Sensitivity - 1974 Green & Swets came up w/ a way of measuring sensitivity free of resp. bias - approach called signal detection theory - theory involves presenting stimulus on some trials, and not on others; then asking subjects on each trial to state (guess) whether or not a stimulus was presented - every stimulus event requires discrimination b/w signal (stimulus) and noise (consisting of both background stimuli and random activity of nervous system) - It is a mathematical theory of the detection of stimuli, which involves discriminating a signal from the noise in which it is embedded and which takes into account participants’ willingness to report detecting the signal. This leads to four possibilities – stimulus was either present or it was not 1. Hit – saying a stimulus is present when it is. 2. Miss – saying a stimulus is not present when it is. 3. False Alarm – Saying a stimulus is present when it is not. 4. Correct Rejection – Saying a stimulus is not present when it is not. So far bias can still have an effect, but it affects both hits and false alarms. Conservative – less likely to say yes; even when stimulus is present Liberal – more likely to say yes when it is present, but it also increases the false alarm. Graph on pg. 170, is a receiver operating characteristic curve (ROC) – graph of hits and false alarms of participants under different motivational conditions; indicates people’s ability to detect a particular stimulus. - difference b/w two curves demonstrates that louder tone is easier to detect – detectability is measured by relative distances of the curves from 45-degree line - signal detection method is best way to determine person’s sensitivity to occurrence of particular stimulus (dimmest light eye can pick up; lightest sound that ear can pick up – best sensitivity to avid bias) - signal detection theory emphasizes that sensory experience involves factors other than the activity of the sensory systems, such as motivation and prior experience In the signal detection theory, which bias is the null sensitivity line constructed under? Is it the 50 cents for hits and -50 cents for false alarms? The null sensitivity line is really just a theoretical thing. It is a line depicting all points on the graph where hits equal false alarms. So it goes from .00 hits and .00 false alarms to 1.00 hits and 1.00 false alarms. Again, the idea is that if one is saying yes just as often when something was presented (a hit) as when nothing was presented (a false alarm) then they are apparently insensitive to whether a stimulus has or has not been presented. Thus, whenever the proportion of hits equals the proportion of false alarms this implies null sensitivity, and the null sensitivity line merely connects all of these pairs of points. How do we get rid of bias? Trick here is to use some manipulation that will vary response bias & test given subject under a number of levels of this mani. (Payoffs) - Hits are greater than false alarms - When below the line – more likely to say yes when its not there, no when there is - Maximum sensitivity when bias is at a level that allows us to show the best sensitivity you can show; you always have bias - Want to know what’s the maximum sensitivity of the system, under the best possible systems – you can find the best sensitivity of every sense receptor this way - Graph shows results from different levels of response bias (5) and you can compute a curve and see the sensitivity from the null sensitivity - Two sources of information – one is any information you get from sense organs; two is the general willingness to say yes or no - Sum up: the whole issue is what if you want to know how good a system is at picking up information – point of signal detection theory Vision – Near and Far - Some of our senses are primarily concerned with providing information about stimuli and events in our immediate environment (touch, perhaps smell). - Others provide info. about stimuli/events that are further away (vision, audition). - Frontal lobe – we got good at planning things because our hands became free and were able to get into mischief but we needed advance information. - Vision gives us a lot of information in advance on what is happening and allows us to plan our actions better. - knowledge about things not in our immediate environment can be critical as actions can than be taken that either bring the stimulus close if it is desirable, or make sure it stays far away if it is undesirable. - Of our “early warning” senses, vision is primary. Vision – what you see, and what you don’t - First of all, we often believe that we see all there is to see in the world. That is simply false - Light is the stimulus and consists of radiant energy similar to radio waves, ad oscillates as it is transmitted from its source - the light spectrum ranges from short wavelength signals like Gamma Rays, up to long wavelength like AC television and radio waves - We see only a small part of this called the visible spectrum. It ranges from light with wavelengths of between 380 nanometers (violet) up to 760 nanometers (red). - This is really a narrow, tiny part of the light spectrum, other beasties are sensitive to what we don’t pick up and can see more. Basic Anatomy of Outer Eye a) Cornea – fluid filled outer coating of eye; admits light into eye; can fix far-sighted if b) Sclera – white part of the eye, tough membrane (structure) serves as protection for eye itself. c) Iris – colored part of your eye, a muscle that controls the size of the pupil; when there’s little light, iris opens pupil; when a lot of light – iris reacts by closing down the pupil. d) Aqueous Humor – now focused light passes through eyeball which is filled with a liquid called aqueous humor (watery fluid). Fluid nourishes front of eye in a way that blood vessels normally would. - if it is produced too quickly, or if passage that return it to the blood becomes blocked, pressure w/in eye can increase and cause damage to vision – disorder known as glaucoma, nutrients not delivered properly. e) Pupil – black part in the middle of the eye; opening in iris that allows light into the eyeball. f) Lens – transparent organ situated behind the pupil of the eye; helps focus incoming light onto the retina. This lens is flexible and slight alterations in it can alter the focus of it, a process called accommodation (as an example, squint). - Becomes brittle/stiff as we age – no surgery, still need glasses. - b/c it must remain transparent, lens contains no blood vessels and is therefore functionally dead tissue g) Retina – If eye is properly shaped, nicely focused image lands on inner coating of the back of the eye. This inner coating is the retina, and it is the part that transmits the light signal (focused or not) into a neural signal. – performs sensory functions of the eye - has three principal layers 1) ganglion cell layer (front) 2) bipolar cell layer (middle) and 3) photoreceptor layer (back) OK, so now the light is in the eye, what happens next? Visual problems can be fixed by reshaping the cornea, at young age. People whose eyes are too long (front to back) are nearsighted; need a concave lens to correct the focus. People whose eyes are too short are farsighted; need convex lens. As people get older, the lenses of their eyes become less flexible and it becomes difficult for them to focus on objects close to them. These people need reading glasses w/ convex lens. Wednesday, November 1, 2006 - Info. from photoreceptors is transmitted to neurons that send axons towards one point at back of the eye – optic disc. All axons leave eye at this point and join optic nerve, which travels to the brain. - Photoreceptors respond to light and pass info. on by means of a transmitter substance to the bipolar cells, the neurons with which they form synapses - Bipolar cells transmit this info. to ganglion cells, neurons whose axons travel across the retina and through optic nerves (back of eye) - Thus, visual info. passes through a 3-cell chain to the brain: photoreceptor  bipolar cell  ganglion cell  brain. Vision – Transduction The process of transducing a light signal into a neural impulse comes about through several interim steps: Step 1 - Photoreceptors - Light strikes the back of the eye stimulating photoreceptor cells which can be either rods or cones – energy is translated to nerve impulses here - Rods are not responsive to color, but they are very responsive to dim light, great for low light situations, allow you to see mostly shades of gray – in periphery area - Cones are sensitive to color and provide a much more detailed image, great for high light, detailed imaging; need a lot of light – primarily in centre of retina - The Fovea which is a small pit in the back of the retina, approx. 1 mm in diameter, contains only cones and most are connected to only one ganglion cell apiece. - Fovea is responsible for our finest, most detailed vision – when we look at a point in our visual field, we move our eyes so that the image of that point falls directly on the cone-packed fovea. - Further away from fovea, number of cone decreases and number of rods increase. Up to 100 rods may converge on a single ganglion cell. A ganglion cell that receives info. from so many rods is sensitive to very low levels of light. - transduction is done via a bleaching process in which the photopigments are split, causing an action potential There are actually three kinds of photoreceptors in the retina. - Rods have one type, a type that is only sensitive to brightness (shades of grey) - Cones come in three varieties, one roughly sensitive to the color red, another to green, and a third to blue (approximately) - photoreceptors of cones are sensitive to color in the inverse way that a TV (or computer monitor) displays color. Step 2 - Bipolar Cells - signal from photoreceptors is then passed on to the bipolar cells which reprocess
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