Summary Sensation and Perception - chapters 1-6, 10-12, 14, 15 PDF

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Chapters 1-6, 10-12, 14, 15...

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Chapter 1: Introduction to Perception Why Read This Book?    

Helpful for the future (career, researcher, teacher, etc.) Medical applications (hearing/vision aids, robots, facial recognition) Increase awareness of personal perceptual experiences In order to sense things, your receptors must be stimulated: perception depends on the properties of the sensory receptors

The Perceptual Process 

Perceptual process: journey from stimuli to response of perceiving

Stimuli (Steps 1 and 2)     

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Environmental stimuli: i.e. a tree, perception based on light reflected Principle of transformation: stimuli and responses created by stimuli are transformed, or changed, between environmental stimulus and perception Nature of reflected light depends on: properties of the light, properties of the tree, properties of atmosphere through which light is transmitted Cornea (at the front) and lens (right behind it) focuses light, form sharper image of tree on receptors in the retina Principle of representation: everything a person perceives isn’t based on direct contact with stimuli but on representations of stimuli that are formed on receptors and on activity in person’s nervous system Step 1 is the environmental stimulus (transformation onto retina) and step 2 is the stimulus on receptors (representation in the person’s eyes)

Receptor Processes/Transduction (Step 3) 

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Sensory receptors: cells specialized to respond to environmental energy o Visual receptors transform environmental energy into chemical o Shape perception by the way they respond to stimuli Visual receptors contain visual pigment which is a light-sensitive chemical that reacts to light, transformation of one energy to another is transduction Perception wouldn’t occur without transduction

Neural Processing  

Neurons transmit signals from receptors, through the retina, to the brain and then within the brain; changes (processes) the signals as they’re transmitted Neural processing: change in signals occurring as they’re transmitted via neurons

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Primary receiving area: area in the cerebral cortex for a specific sense where the electrical signals arrive o Occipital lobe: PRA for vision o Temporal lobe: PRA for hearing o Parietal lobe: PRA for skin senses (touch temperature and pain) o Frontal lobe: PRA for all other senses, coordination of 2+ senses

Behavioral Responses (Steps 5-7)       

Electrical signals are transformed into conscious experience Perception: conscious awareness of the tree (step 5) Recognition: placing an object in a category (step 6) Dr. P (patient) had visual form agnosia, which is the inability to recognize objects, and was caused by a brain tumor (could perceive but not recognize) Action: involves motor activities (step 7) Milner and Goodale propose that early on the goal of visual processing was to help animal navigate (perform the action to survive) The process of perception is constantly changing

Knowledge   

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Knowledge: information perceiver brings to a situation, can be information acquired years ago or recently acquired Rat-man demonstration: priming can influence perception Bottom-up processing (data-based processing): processing based on stimuli reaching receptors, stimuli provide basis for perception (receptor activation) Top-down processing (knowledge-based processing): processing based on knowledge Pharmacist reads scribble on prescription: start with patterns created on the retina (bottom-up), then pharmacist uses knowledge of the names of drugs and past experience to understand squiggles (top-down) Top-down may not be involved if it’s simple stimuli (i.e. seeing a flash of light), more complex stimuli involved top-down

How to Approach the Study of Perception 

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Psychophysical approach (psychophysics): measures relationship between stimuli (steps 1-2) and behavioral response (steps 5-7) o Oblique effect: better detail vision for vertical/horizontal lines compared to slanted lines Physiological approach: measures 2 different relationships o Relationship between stimuli (steps 1-2) and physiological responses (steps 3-4)

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Optical brain imaging in ferrets: found horizontal/vertical lines (stimuli) caused greater brain responses (physiological) o Relationship between physiological responses (steps 3-4) and behavioral responses (steps 5-7)  Used humans with brain scanner: brain response larger (physiology) when detecting horizontals than when detecting slanted (perception) Cognitive influences on perception: factors like knowledge, memories and expectations that people bring to a situation that influence their perceptions o Rat-man demonstration: primed with rat or primed with person

Measuring Perception 

Absolute threshold: minimum stimulus intensity that can be detected, stimulus level above zero necessary to detect stimulus o Making lines thinner at different orientations, decreasing light (sound) intensity until it can barely be seen (heard) o If finer lines can be detected, the threshold is lower when gratings are horizontal/vertical

Measuring Thresholds 

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Fechner: first to say we could measure the mind using thresholds o Classical psychophysical methods: used to measure relationship between stimuli and perception METHOD: Determining the Threshold o 3 methods are limits, adjustment and constant stimuli o Method of limits: present stimuli in ascending order (intensity increases) or descending order (intensity decreases)  Change from YES to NO is the crossover point (threshold)  Advantage: most accurate method, involves many observations, random order of stimuli  Disadvantage: time-consuming o Method of adjustment: present stimuli in increasing or decreasing order but the observer adjusts it until they can’t detect it  Advantage: faster, observers determine threshold themselves o Method of constant stimuli: experimenter presents 5-9 stimuli with different intensities in random order  Set so the highest intensity is always detected, lowest is never  Threshold determined by intensity detected 50% of the time Difference threshold: minimum difference between 2 stimuli necessary to be able to tell the difference between them o Weber proposed the DL ratio to the standard is constant o Weber fraction: ratio of DL/Standard for lifting weights is .02, remains relatively constant for each sense

o Weber law: the fact the Weber fraction remains the same as the standard is changed Estimating Magnitude 

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Magnitude estimation: developed by S.S. Stevens to determine relationship between doubling a stimuli and it’s perception of if it doubled o Experimenter presents “standard” stimulus and assigns a value, then presents different intensities and subjects assigns a number o The number is the perceived magnitude of the stimulus o Note: intensity is a physical measure (how much), perceived magnitude is a perceptual measure of what observer perceives Response compression: increase in perceived magnitude is smaller than increase in stimulus intensity (i.e. doubling intensity doesn’t double perceived magnitude, perceived magnitude will be smaller) Response expansion: increasing intensity results in more of an increase in perceptual magnitude (i.e. doubling intensity more than double perceived magnitude)

Power functions: relationship between intensity of stimulus and our perception of its magnitude o Steven’s power law: P = KSn where P is perceived magnitude, K is a constant, S is the stimulus intensity, n is the power o Exponents less than 1 are associated with response compression, greater than 1 are associated with response expansion o Response compression: for brightness, don’t perceive it as doubly bright, helps eyes to adjust o Response expansion: for shock, perceive it as more than doubly bright, rapid increase in pain warns us of danger

Beyond Threshold and Magnitudes 

Phenomenological method: person describes what he is perceiving or to indicate when a perception occurs, basic level of description of properties (i.e. name color of light, taste is bitter or sweet)

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o Used when testing people with brain damage: Dr. P could describe (perceive) the glove but not recognize it Visual search: find one stimulus among many as quickly as possible o Reaction time: measured to provide information, time between presentation of stimulus and person’s reaction

Threshold Measurement Can Be Influenced by How a Person Chooses to Respond 

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People decide to answer two ways: o Choosing to respond “yes” if there’s a slight possibility, gives more yes responses, ends up with lower threshold o Choosing to respond “yes” only if you’re sure Response criterion: subjective magnitude above which the participant will indicate a stimulus is present o Low says yes if there’s a slight change; high says yes only when sure o Problem if comparing 2 people’s responses and their RC differ Appendix

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Method of constant stimuli can depend on subject’s response criterion

A Signal Detection Experiment  

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Note: at least 5 different intensities of stimuli are presented in method of CS In signal detection experiment: o Only one stimulus intensity is presented o On some trials, no stimulus is presented Tone present: say yes = hit, say no = miss Tone not present: say yes = false alarm, say no = correct rejection o If presented with 100 trials with a tone saying yes on 90, there’s 90% hit rate; if presented with 100 trials with no tone saying yes on 40, there’s a 40% false alarm rate Payoffs: affect motivation o Give reward for hits, take away rewards for other 3  Person with higher response criterion becomes more liberal and says yes more often o Give rewards for correct rejection, take away for other 3  Person raises response criterion again, bigger reward for saying no o Give rewards for hit and correct rejection, take away for false alarm and miss  Receiver operating characteristic (ROC) curve: L is for liberal, C is for conservative, N is for neutral

o Use curve to determine if two people’s sensitivities are equal if the shape of the ROC curve is identical Signal Detection Theory 

Person’s sensitivity to a stimulus is indicated by the shape of ROC curve

Signal and Noise Signal = stimulus, noise = all other stimuli in environment, cause false alarms SDT: in terms of signal plus noise (S+N) or noise (N) o False alarm = yes on a noise trial, hit = yes on sound + noise trial Probability Distributions  

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Red = probability a perceptual effect will be caused by noise Green = probability that perceptual effect will be caused by signal + noise Perceptual effect (loudness) is what person experiences on each trial In SDT tone has same intensity always but loudness can vary What are the chances a given loudness is due to N or S+N? o At 10, there’s a high chance that what’s heard is due to noise o At 20, could be due to noise or sound + noise o At 30, there’s a high chance that what’s heard is due to sound + noise

The Criterion

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Liberal criterion: o Present N: most of the probability distribution for N falls to the right of criterion, good chance of saying yes when N is present (false alarm) o Present S+N: entire probability distribution for S+N is to the right of criterion, probability of saying yes when S+N is present is high (hit) Neutral criterion: o Present N: person answers yes rarely when N present, only small part of N distribution is to the right, low false-alarm rate o Present S+N: person answers yes frequently when S+N present, most of S+N distribution to the right of criterion (high hit rate) Conservative criterion: o Present N: false alarms low because none of N curve falls right of criterion o Present S+N: low hits because only small portion of S+N falls to right of criterion According to SDT, persons sensitivity is determined by distance (d’) between peaks of N and S+N distributions

The Effect of Sensitivity on the ROC Curve 

If someone has super sensitive hearing, her S+N curve is far to the right, indicated by large d’ between the probability distributions, also makes ROC curve more bowed o Liberal criterion:  Present N: high false alarms  Present S+N: high hits o Neutral criterion:  Present N: low false alarms  Present S+N: high hits (almost all S+N is to the right) o Conservative criterion:  Present N: low false alarms  Present S+N: low hits

Chapter 2: The Beginnings of Perception Starting at the Beginning 

Stimuli trigger a process that ends up with perception occurring due to the activity in the brain (Figure 2.1)

Light and Focusing Light: The Stimulus for Vision 

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Vision is based on visible light, which is a band of energy within the electromagnetic spectrum (continuum of electromagnetic energy that’s produced by electrical charges and radiated as waves) o Wavelength: distance between peaks of the electromagnetic waves, associated with specific colors Visible light: energy within EM spectrum that humans can perceive, 400700 nanometers (nm) Light can also be described as photons (smallest packet of light energy)

The Eye       

Eye: contains receptors for vision Pupil: light reflected from objects in environment enters through here Cornea and lens: focus the light to form sharp images on the retina Retina: network of neurons on back of the eye, contains receptors for vision Rods and cones: visual receptors, contain visual pigments that react to light and trigger electrical signals Optic nerve: where signals from the receptors end at in the back of the eye, conducts signals toward the brain Eye creates 2 transformations: o Transformation from light reflected from object into image of the object o Transformation from the image of the object into electrical signals

Light Is Focused by the Eye 

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Two-element optical system: cornea and lens o Cornea: fixed (can’t adjust focus), accounts for 80% of focusing power o Lens: uses ciliary muscles to change shape and adjust focus for objects at different distances, accounts for 20% of focusing power Why the eye needs to adjust: o If viewing an object far away, the light rays are coming in parallel and reach the retina

o If an object is closer, the rays come in at an angle, which would cause the light to converge past the retina o Accommodation: change in lens’s shape when ciliary muscles tighten, increase curvature of lens so it’s thicker, allows you to focus o Near point: distance your lens can’t accommodate objects into focus anymore Loss of Accommodation With Increasing Age 

Presbyopia: the distance of the near point increases with age, loss of ability to accommodate, due to the lens hardening and ciliary muscles weakening

Myopia 

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Myopia: inability to see distant objects clearly, parallel rays of light focus at a point before reaching the retina, caused by one of two factors: o Refractive myopia: cornea and/or lens bends the light too much o Axial myopia: eyeball is too long Moving an object closer pushes the focus point back further, causing it to come into focus Far point: distance at which light becomes focused on the retina, person with myopia can see clearly at this distance Corrective lenses bend the light so it focuses as if it were at the far point (light becomes the same angle as if it were at the far point) Laser-assisted in situ keratomileusis (LASIK): procedure that involves sculpting the cornea with an excimer laser

Hyperopia   

Hyperopia (farsightedness): trouble seeing nearby objects, focus point for parallel rays of light is behind retina, possibly because eyeball is too short Corrective lenses can bring the focus point forward onto the retina Vision doesn’t occur in the retina, but in the brain

Receptors and Perception 

Light entering visual receptors triggers electrical signals when light is absorbed by visual pigment molecules

Transforming Light Energy Into Electrical Energy  

Transduction: transformation of one form of energy into another form, for vision it’s transforming light energy into electrical energy via rods and cones Outer segments: contains millions of molecules of a light-sensitive visual pigment

o Visual pigments have 2 parts: long protein called opsin, smaller lightsensitive component called retinal o Retinal and opsin combine, resulting molecule absorbs visual light o Retinal changes shape from being bent to straight when visual pigment molecule absorbs one photon of light o Isomerization: change of retinal shape, creates chemical chain reaction that activates charged molecules to create electrical signals in receptors  Isomerization of one visual pigment molecule triggers a chain of chemical reactions that releases as many as a million charged molecules, which leads to activation of the receptor Adapting to the Dark  

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Dark adaptation: in the dark, you gain an increase in sensitivity Distribution of the Rods and Cones: o Fovea: contains only cones o Peripheral retina: retina outside of fovea, contains rods and cones o Peripheral retina contains many more rods than cones o Macular degeneration: destroys cone-rich fovea and small area around it, creates blind region in central vision o Retinitis pigmentosa: degeneration of the retina, attacks peripheral rod receptors and results in poor vision in the peripheral visual field, later foveal cone receptors are attacked resulting in complete blindness o Blind spot: contains no receptors, don’t see it because brain fills it in Measuring the Dark Adaptation Curve: o Dark adaptation curve: function relating sensitivity to light to time in the dark, as time goes on the sensitivity increases o Light-adapted sensitivity: sensitivity measure in the light  High threshold = low sensitivity o Dark-adapted sensitivity: sensitivity at the end of dark adaptation, dark adapting one eye made it easier to see with that eye in the dark  The first part of the dark adaptation curve is caused by cones, the second part is caused by rods Measuring Cone Adaptation: o Both rods and cones curve has 2 phases because test light is on peripheral retina (which has rods and cones), looking at cone sensitivity, it increases and then levels out o Green curve due only to cone adaptation because test light was focused on all-cone fovea, cones are more sensitive to light in beginning Measuring Rod Adaptation:

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o Need to measure dark adaptation in a person with no cones (rod monochromats), all-rod retinas light sensitivity measured before turning light off aka rod light-adapted sensitivity o Rods less sensitive than cones, once dark adaptation begins rods increase sensitivity o Summary: when light turns off the sensitivity of cones and rods increases, because cones are more sensitive at the beginning we see with our cones right after lights go out o Rod-cone break: place where rods begin to determine dark adaptation curve Visual Pigment Regeneration: o Visual pigment bleaching: retinal changes shape and separates from opsin, causes molecule to become lighter in color o As light remains on more pigment’s retinal is isomerized and breaks away from opsin, when in bleached state they’re not useful for vision o Visual pigment regeneration: retinal returns to bent shape and becomes reattached to opsin, in order to change light energy into electrical energy o When lights are out, bleached visual pigment continues to regenerate, no more isomerization, eventually retina cont...