Psych Chapter 6 amazonaws com
Psych Chapter 6 Sensation: the detection of physical energy emitted or reflected by physical objects; it occurs when energy in the external environment or the body stimulates Perception: the process by which the brain organizes and interprets sensory information
OUR SENSATIONAL SENSES
Our senses evolved to help us survive o Ex. pain alerts us to illness and injury o People born without the ability to feel pain are more susceptible to it o Often die early age because they can’t take advantage of pain’s warning signals
The Riddle of Separate Sensations Sensations begin with the sense receptors, cells located in the sense organs o Defn: specialized cells that convert physical energy in the environment or the body to electrical energy that can be transmitted as nerve impulses to the brain o The receptors for smell, pressure, pain, and temperature are extensions (dendrites) of sensory neurons o The receptors for vision, hearing, and taste are specialized cells separated from sensory neurons by synapses Sense receptors are like military scouts who scan the terrain for signs of activity o Cannot make their own decisions; they must transmit what they learn to field officers – sensory neurons in the peripheral nervous system; they then must also report to generals at a command centre – the cells of the brain, which analyse, combine information from scouts, and deciding what it means Sensory nerves use the same form of communication, a neural impulse The nervous system encodes the messages o One kind of code, anatomical was first described by Johannes Muller Doctrine of specific nerve energies o Defn: the principle that different sensory modalities (vision, hearing, etc) exist because signals received by the sense organs stimulate different nerve pathways leading to different areas of the brain o Ex. signals from the eye cause impulses to travel along the optic nerve to the visual cortex o Implies that what we know about the world reduces to what we know about our nervous system We see with our brain, not the eyes If sound waves could stimulate nerves ending in the visual part of the brain, we could see sound o Maurice Ptito Device that translates images from a camera into a pattern of electronic pulses that is sent to electrodes on the tongue
Then sends information about the pattern to the areas of the brain that process images Results: blind people have made out shapes, visual areas become active Called sensory crossover
Synesthesia o Defn: condition in which stimulation of one sense also evokes another o “perceptual crossover” o A person with synesthesia might say the colour purple smells like a rose, the aroma of cinnamon feels like velvet, the sound of a note on a clarinet tastes like cherries o People who see digits or letters in different colours (the number 2 in red) might have trouble naming the colour of a digit or letter if printed in another colour (2 printed in blue) o Runs in families, more common in females Theory that all people display some degree of synesthesia early in development, and those who aren’t synesthetes lose the dual perceptions as our brains mature and the connections diminish Two leading theories about the neurological basis of synesthesia 1. A lack of normal disinhibition in signals between different sensory areas of the brain 2. A greater number of neural connections between different sensory brain areas The doctrine of specific nerve energies fails to explain variations of experience within a particular sense (pink vs. red, pinprick vs. kiss) o Therefore another kind of code is necessary – functional Functional codes rely on the fact that sensory receptors and neurons fire, or are kept from firing, only in the presence of certain stimuli. How to form a functional code: o Which cells are firing? o How many cells are firing? o The rate at which cells are firing? o The patterning of each cell’s firing? Think of neurological equivalent of Morse Code
Measuring the Senses Absolute Thresholds Defn: the smallest quantity of physical energy that can be reliably detected by an observer To find out how sensitive the senses are, people are shown a series of signals that vary in intensity and are asked which ones they can detect Absolute is a bit misleading because some borderline signals are detected and some aren’t – “reliable” detection is when a person can detect a signal 50% of the time Ex. a person would be asked to sit in a dark room and look at a wall or screen, you would then be shown flashes of light varying in brightness, task would be to say whether or not you noticed a flash Would miss some flashes you’ve previously already detected
Despite our sharp sensory skills, our senses are tuned in to only a narrow band of physical energies Ex. only visually sensitive to some electromagnetic energies Difference Thresholds Defn: the smallest difference in stimulation that can be reliably detected by an observer when two stimuli are compared; aka just noticeable difference (jnd) Ex. a person might be asked to compare the weight of two blocks, the saltiness of two liquids, or the brightness of two lights When comparing two stimuli, A and B, the difference threshold will depend on the intensity or size of A The larger or more intense A is, the greater the change must be before you can detect a difference Comparing the difference of a few grams in two pebbles would not be detectable if comparing boulders Signal-Detection Theory Defn: psychophysical theory that divides the detection of a sensory signal into a sensory process and a decision process Response measurements can be affected by: Whether people are habitual yea-sayers, willing to gamble Ex. impressing the experimenter Whether people are habitual nay-sayers, cautious and conservative Alertness, motives, and expectations Ex. waiting for an important call and thinking you hear the phone ring while in the shower but it didn’t Different methods of dividing the response into sensory processes and decision processes Ex. researcher can some trials in which no stimulus is present and others in which a weak stimulus is present Four kinds of responses are possible: 1. Person detects a signal that was present (a hit) 2. Says was there when it wasn’t (false alarm) 3. Fails to detect when it was present (a miss) 4. Says its absent when absent (correct rejection) Assumes there is no single threshold because a person’s sensitivity to a stimulus depends on an active decision made by the person Many real world applications – screening job applicants for jobs that require keen hearing to training air traffic controllers
Sensory Adaptation Our senses are designed to respond to changes and contrast in the environment When a stimulus is unchanging or repetitious, sensation fades or disappears Sensory Adaptation o Defn: the reduction or disappearance of sensory responsiveness when stimulation is unchanging or repetitious o Spares us from responding to unimportant information ex. feeling a watch Sensory deprivation
o Defn: the focusing of attention on selected aspects of the environment and the blocking out of others o Experiment conducted on male volunteers, blocked off hearing, vision, and touch Results showed the men quickly felt edgy, some were so disoriented they quit the study the first day, the rest became confused and grouchy Some men had bizarre visions – like waking dreams Few were willing to stay in the study for longer than three days o Not always a bad thing, experiment procedures just aroused anxiety o The brain requires a minimum amount of sensory stimulation Sensing without Perceiving Too much stimulation can lead to fatigue and mental confusion “cocktail party phenomenon” – when people in a state of sensory overload block out unimportant sights and sounds, focusing only on interesting or useful Selective Attention o Defn: the focusing of attention on selected aspects of the environment and blocking out of others o All incoming messages are processed, so as to only pick up something like hearing your name being called Inattentional Blindness o Defn: failure to consciously perceive something you are looking at because you are not attending to it o We look, but we do not see o Ex. how many passes? Fail to see the gorilla suit
VISION What We See The stimulus for vision is light, which travels in the form of waves The physical characteristics of these waves affect three psychological dimensions of our visual world: 1. Hue Defn: the dimension of visual experience specified by colour names and related to the wavelength of light Shorter waves tend to be seen as violet and blue Longer waves tend to be seen as orange and red The sun produces white light (mix of all visible wavelengths), but when drops of moisture are in the air they act as a prism separating the white light into the colours of the visible spectrum – a rainbow is made 2. Brightness Defn: lightness or luminance; the dimension of visual experience related to the amount, or intensity, of light emitted from or reflected by an object The more light an object reflects, the brighter it appears Yellows appear brighter than reds and blues despite equal physical intensities
3. Saturation Defn: vividness or purity of colour; the dimension of visual experience related to the complexity of light waves o The wideness or narrowness of the range of wavelengths Pure light is when light only contains a single wavelength, and the resulting colour is said to be saturated o Extremely rare; usually we see a mixture of wavelengths White light lacks colour and is completely unsaturated An Eye on the World The cornea o Transparent; covers the front part of the eye o Protect the eye and bends incoming light rays toward a lens located behind it The lens o Works by subtly changing its shape, becoming more or less curved to focus light from objects that are close or far away The iris o Controls the amount of light that gets into the eye o The part of the eye that gives it colour o Surrounds the pupil The pupil o When you enter a dim room, the pupil dilates to let more light in The retina o Defn: neural tissue lining the back of the eyeball’s interior, which contains the receptors for vision o Contains special cells that communicate information about light and dark to the brain to regulate biological rhythms o The retina is an extension of the brain o The retinal image When we look at an object, the light pattern on the retina is upside down o Receptors in the retina Rods Defn: visual receptors that respond to dim light Long and narrow 120 million to 125 million in the retina More sensitive to light; allow us to see at night Occupy the outer edges of the retina Handle peripheral vision Cannot distinguish wavelengths of light, not sensitive to colour Cones Defn: visual receptors involved in colour vision The centre of the retina, or fovea, where vision is sharpest, contains only cones densely clustered together Differentially sensitive to different wavelengths and allow us to see colour
Need more light than rods to respond Not very sensitive
Dark Adaptation o Defn: a process by which visual receptors become maximally sensitive to dim light o Involves chemical changes in the rods and cones o 10 minutes for cones to adapt o 20 minutes for rods to adapt Rods and cones are connected by synapses to bipolar neurons, which communicate with neurons called ganglion cells o Defn: neurons in the retina of the eye that gather information from receptor cells (by way of the bipolar cells); their axons make up the optic nerve o Axons of ganglion cells converge to form the optic nerve o The optic nerve leaves the eye at the optic disk, where there are no rods or cones This produces a blind spot, we are unaware of it because i. The image projected on the spot is hitting a different “non-blind” spot in the other eye ii. Our eyes move so fast they pick up the entire image iii. The brain fills the gap
Why the Visual System is Not a Camera Does not passively record the external world Feature detector cells o Defn: cells in the visual cortex that are sensitive to specific features of the environment, ex. spots of light and dark Different neurons were sensitive to different patterns projected on a screen in front of animals’ eyes Evolution has equipped us with an innate face module in the brain o Why infants show preference to looking at faces than scrambled ones o Vegetable face o Car pictures vs. bird pictures The Trichromatic Theory o Defn: a theory of colour mechanisms in the visual system, each sensitive to a certain range of wavelengths; their interaction is assumed to produce all the different experiences of hue o Aka Young-Helmholtz theory o Applies to the first level of processing in the retina o Retina has three types of cones Responds maximally to blue lengths Responds maximally to green And responds maximally to red o Colour blindness The Opponent-Process Theory o Defn: theory of colour perception that assumes that the visual system treats pairs of colours as opposing or antagonistic
o Applies to the second stage of colour processing in ganglion cells in the retina and in neurons in the thalamus and visual cortex of the brain; known as opponentprocess cells Respond to short wavelengths but are kept from firing by long ones, and vice versa Why we describe colours as bluish-green but not reddish-green Constructing the Visual World Form Perception o Gestalt Psychologists First to study how people organize the world visually into meaningful units and patterns Motto: “the whole is greater than the sum of its parts” People always organize the visual field into figure and ground o Gestalt Principles Defn: principles that describe the brain’s organization of sensory information into meaningful units and patterns 1. Proximity Things that are near each other tend to be grouped together Ex. dots 2. Closure The brain tends to fill gaps in order to perceive complete forms Ex. face, triangle, letter E 3. Similarity Things that are alike in some way (colour, shape, size) tend to be perceived as belonging together Ex. horizontal lines of stars 4. Continuity Lines and patterns tend to be perceived as continuing in time or space Ex. an oval on a line, and not two lines touching an oval Depth and Distance Perception o To estimate an object’s distance or depth, we rely on binocular cues Defn: visual cues to depth or distance requiring two eyes One such cue is convergence Defn: the turning inward of the eyes, which occurs when they focus on a nearby object o Retinal disparity Defn: the slight difference in lateral separation between two objects as seen from the left eye and the right eye Hold up two fingers one closer to face than the other o Binocular cues help us estimate distance up to 15 meters, any further and we use monocular cues Defn: visual cues to depth or distance that can be used by one eye alone
Interposition – when an object is interposed between the viewer and a second object, partly blocking the view of the second object, the first object is perceived as being closer Linear perspective – when two lines known to be parallel appear to be coming together or converging, they imply the existence of depth Light and shadow Motion parallax – the closer an object, the faster it seems to move Relative size Relative clarity – distant objects tend to look less detailed Texture gradients – distant parts of a uniform surface appear denser Visual Constancies: When Seeing is Believing o Perceptual constancy Defn: the accurate perception of objects as stable or unchanged despite changes in the sensory patterns they produce o Visual constancies 1. Shape constancy We see objects as having a constant shape even though the shape changes when we have a different point of view Round Frisbee in front of you, elliptical Frisbee on table 2. Location constancy We perceive stationary objects as remaining in the same place even though the retinal image moves as we move our eyes, heads, and bodies Looking at trees while driving on the highway 3. Size constancy We see an object as having a constant size even when its retinal image becomes smaller or larger A friend walking towards you on the street isn’t growing 4. Brightness constancy We see objects as having a relatively constant brightness even though the amount of light they reflect changes as the overall level of illumination changes Snow is still white on a cloudy day 5. Colour constancy We see an object as maintaining its hue despite the fact that the wavelength of light reaching our eyes from the object may change as the illumination changes An apple looks red whether you look at it in your kitchen or on the patio
HEARING What We Hear The stimulus for sound is a wave of pressure created when an object vibrates The vibration causes molecules in a transmitting substance (usually air, but can be water and solids) to move together and apart This movement produces variations in pressure that radiate in all directions Dimensions of auditory experience: 1. Loudness Defn: the dimension of auditory experience related to the intensity (amplitude or maximum height) of a pressure wave Sound intensity is measured in decibels (one tenth of a bel) The average absolute threshold of hearing in humans is zero dB 2. Pitch Defn: the dimension of auditory experience related to the frequency (how rapidly the air vibrates – the number of times per second the wave cycles through a peak and low point) of a pressure wave; the height or depth of a tone One cycle per second is known as one hertz The healthy ear normally detects frequencies in the range of 16 Hz to 20 000 Hz 3. Timbre Defn: the distinguishing quality of a sound; the dimension of auditory experience related to the complexity of the pressure wave What makes a note played on a flue sound different from the same note played on an oboe When many sound-wave frequencies are present but are not in harmony, we hear noise When all the frequencies of the sound spectrum occur, they produce a hissing sound called white noise An Ear on the World The ear has an outer, middle, and inner section The eardrum o Very sensitive – can respond to the movement of a single molecule o Vibrates with the same frequency and amplitude as a sound wave o This vibration is passed along to three tiny bones: The hammer The anvil The stirrup – pushes on a membrane that opens into the inner ear The organ of Corti o Defn: a structure in the cochlea containing hair cells that serve as the receptors for hearing Defn: a snail-shaped, fluid-filled organ in the inner ear, containing the structure where the receptors for hearing are located o Contains receptor cells – look like bristles, called hair cells or cilia The hair cells of the cochlea are embedded in the rubbery basilar membrane
OTHER SENSES Taste: Savoury Sensations Aka gustation Receptor cells for taste are inside the taste buds, which are inside the papillae They are replaced every 10 or so days Basic tastes: sweet, salty, bitter, sour, and umami The centre of the tongue has no taste buds Supertasters o About 25% of people o Find many things bitter o Sweets are sweeter, salty things are saltier o Have more taste buds than other people, are smaller, and denser Smell: The Sense of Scents Aka olfaction Receptors are specialized neurons embedded in a tiny patch of mucous membrane in the upper part of the nasal passage, beneath the eyes Signals from the receptors are carried to the brain`s olfactory bulb by the olfactory nerve Distinct odours activate unique combinations of receptors Scent can have a non-conscious influence on what we think and do o Smelling a citrus cleaner, wipes crumbs off table o Hotels and malls install aroma diffusers to put people in a good mood Senses of the Skin Basic skin senses: o Touch (or pressure) o Warmth o Cold o Pain The Mystery of Pain The Gate-Control Theory of Pain o Defn: theory that the experience of pain depends in part on whether pain impulses get past a neurological “gate” in the spinal cord and thus reach the brain o The brain controls the gate o Thoughts and feelings can influence our reactions to pain Updating the Gate-Control Theory o Phantom pain Defn: the experience of pain in a missing limb or other body part The brain has reorganized itself o The brain is capable of generating pain on its own o An extensive matrix of neurons in the brain gives us a sense of our own bodies and body part o When this matrix produces abnormal patterns of activity, the result is pain:
Input from spinal cord Signals from brain centres Memories Emotions Expectations Attention o Mirror therapy tricks the brain into thinking that the missing limb is active and healthy – phantom pain vanishes The Environment Within Kinesthesis o Defn: the sense of body position and movement of body parts o Aka kinesthesia o Without it you could not touch your finger to your nose with your eyes closed Equilibrium o Defn: the sense of balance o Relies primarily on three semicircular canals Defn: sense organs in the inner ear that contribute to equilibrium by responding to rotation of the head Filled with fluid that moves and presses on hair-like receptors whenever the head rotates
PERCEPTUAL POWERS: ORIGINS AND INFLUENCES Inborn Abilities Infants can: o Distinguish sweet from salty o Discriminate among odours o Distinguish a human voice from other sounds o Will startle to a loud noise and turn towards the source To test an infant’s perception of depth, a visual cliff is used o Mother lures baby either across the shallow side, or the “cliff” o Most babies refused to cross the “cliff” Critical Periods If an infant misses out on a critical period, perception will be impaired Kitten study – horizontal and vertical lines Psychological and Cultural Differences Psychological factors that influence what we perceive and how we perceive it: 1. Needs When we need something, have an interest in it, or want it, we are very likely to perceive it Hungry people are faster at recognizing words related to food 2. Beliefs What we hold to be true about the world an affect our interpretation of unclear sensory signals
If you believe in aliens, you might think you see a spaceship 3. Emotions A small child afraid of the dark may see a ghost instead of a robe hanging on the back of a door, or a monster instead of a favourite doll Negative and positive emotions influence pain Ex. relief of being alive may offset anxiety and fear Ex. intentionally having your foot stepped on will hurt more 4. Expectations Previous experiences often affect how we perceive the world Perceptual set – habitual way of perceiving based on experiences o Help us fill in words in sentences we don’t fully hear Missing a misspelled word in a textbook
PUZZLES OF PERCEPTION Subliminal Perception: How Persuasive? Perceiving without awareness o A simple visual stimulus can affect your behaviour even when you are unaware that you saw it o Priming Defn: a method used to measure unconscious cognitive processes, in which a person is exposed to information and is later tested to see whether the information affects behaviour or performance on another task or in another situation Being subliminally flashed the word honesty, then describing a person as honest – they have been primed to evaluate the person that way Perception versus Persuasion o Subliminal persuasion technique improvements are due to expectation o Motivation is a big part of persuasion – subliminal words like dry and thirst make people drink more
OUR SENSATIONAL SENSES
Our senses evolved to help us survive o Ex. pain alerts us to illness and injury o People born without the ability to feel pain are more susceptible to it o Often die early age because they can’t take advantage of pain’s warning signals
The Riddle of Separate Sensations Sensations begin with the sense receptors, cells located in the sense organs o Defn: specialized cells that convert physical energy in the environment or the body to electrical energy that can be transmitted as nerve impulses to the brain o The receptors for smell, pressure, pain, and temperature are extensions (dendrites) of sensory neurons o The receptors for vision, hearing, and taste are specialized cells separated from sensory neurons by synapses Sense receptors are like military scouts who scan the terrain for signs of activity o Cannot make their own decisions; they must transmit what they learn to field officers – sensory neurons in the peripheral nervous system; they then must also report to generals at a command centre – the cells of the brain, which analyse, combine information from scouts, and deciding what it means Sensory nerves use the same form of communication, a neural impulse The nervous system encodes the messages o One kind of code, anatomical was first described by Johannes Muller Doctrine of specific nerve energies o Defn: the principle that different sensory modalities (vision, hearing, etc) exist because signals received by the sense organs stimulate different nerve pathways leading to different areas of the brain o Ex. signals from the eye cause impulses to travel along the optic nerve to the visual cortex o Implies that what we know about the world reduces to what we know about our nervous system We see with our brain, not the eyes If sound waves could stimulate nerves ending in the visual part of the brain, we could see sound o Maurice Ptito Device that translates images from a camera into a pattern of electronic pulses that is sent to electrodes on the tongue
Then sends information about the pattern to the areas of the brain that process images Results: blind people have made out shapes, visual areas become active Called sensory crossover
Synesthesia o Defn: condition in which stimulation of one sense also evokes another o “perceptual crossover” o A person with synesthesia might say the colour purple smells like a rose, the aroma of cinnamon feels like velvet, the sound of a note on a clarinet tastes like cherries o People who see digits or letters in different colours (the number 2 in red) might have trouble naming the colour of a digit or letter if printed in another colour (2 printed in blue) o Runs in families, more common in females Theory that all people display some degree of synesthesia early in development, and those who aren’t synesthetes lose the dual perceptions as our brains mature and the connections diminish Two leading theories about the neurological basis of synesthesia 1. A lack of normal disinhibition in signals between different sensory areas of the brain 2. A greater number of neural connections between different sensory brain areas The doctrine of specific nerve energies fails to explain variations of experience within a particular sense (pink vs. red, pinprick vs. kiss) o Therefore another kind of code is necessary – functional Functional codes rely on the fact that sensory receptors and neurons fire, or are kept from firing, only in the presence of certain stimuli. How to form a functional code: o Which cells are firing? o How many cells are firing? o The rate at which cells are firing? o The patterning of each cell’s firing? Think of neurological equivalent of Morse Code
Measuring the Senses Absolute Thresholds Defn: the smallest quantity of physical energy that can be reliably detected by an observer To find out how sensitive the senses are, people are shown a series of signals that vary in intensity and are asked which ones they can detect Absolute is a bit misleading because some borderline signals are detected and some aren’t – “reliable” detection is when a person can detect a signal 50% of the time Ex. a person would be asked to sit in a dark room and look at a wall or screen, you would then be shown flashes of light varying in brightness, task would be to say whether or not you noticed a flash Would miss some flashes you’ve previously already detected
Despite our sharp sensory skills, our senses are tuned in to only a narrow band of physical energies Ex. only visually sensitive to some electromagnetic energies Difference Thresholds Defn: the smallest difference in stimulation that can be reliably detected by an observer when two stimuli are compared; aka just noticeable difference (jnd) Ex. a person might be asked to compare the weight of two blocks, the saltiness of two liquids, or the brightness of two lights When comparing two stimuli, A and B, the difference threshold will depend on the intensity or size of A The larger or more intense A is, the greater the change must be before you can detect a difference Comparing the difference of a few grams in two pebbles would not be detectable if comparing boulders Signal-Detection Theory Defn: psychophysical theory that divides the detection of a sensory signal into a sensory process and a decision process Response measurements can be affected by: Whether people are habitual yea-sayers, willing to gamble Ex. impressing the experimenter Whether people are habitual nay-sayers, cautious and conservative Alertness, motives, and expectations Ex. waiting for an important call and thinking you hear the phone ring while in the shower but it didn’t Different methods of dividing the response into sensory processes and decision processes Ex. researcher can some trials in which no stimulus is present and others in which a weak stimulus is present Four kinds of responses are possible: 1. Person detects a signal that was present (a hit) 2. Says was there when it wasn’t (false alarm) 3. Fails to detect when it was present (a miss) 4. Says its absent when absent (correct rejection) Assumes there is no single threshold because a person’s sensitivity to a stimulus depends on an active decision made by the person Many real world applications – screening job applicants for jobs that require keen hearing to training air traffic controllers
Sensory Adaptation Our senses are designed to respond to changes and contrast in the environment When a stimulus is unchanging or repetitious, sensation fades or disappears Sensory Adaptation o Defn: the reduction or disappearance of sensory responsiveness when stimulation is unchanging or repetitious o Spares us from responding to unimportant information ex. feeling a watch Sensory deprivation
o Defn: the focusing of attention on selected aspects of the environment and the blocking out of others o Experiment conducted on male volunteers, blocked off hearing, vision, and touch Results showed the men quickly felt edgy, some were so disoriented they quit the study the first day, the rest became confused and grouchy Some men had bizarre visions – like waking dreams Few were willing to stay in the study for longer than three days o Not always a bad thing, experiment procedures just aroused anxiety o The brain requires a minimum amount of sensory stimulation Sensing without Perceiving Too much stimulation can lead to fatigue and mental confusion “cocktail party phenomenon” – when people in a state of sensory overload block out unimportant sights and sounds, focusing only on interesting or useful Selective Attention o Defn: the focusing of attention on selected aspects of the environment and blocking out of others o All incoming messages are processed, so as to only pick up something like hearing your name being called Inattentional Blindness o Defn: failure to consciously perceive something you are looking at because you are not attending to it o We look, but we do not see o Ex. how many passes? Fail to see the gorilla suit
VISION What We See The stimulus for vision is light, which travels in the form of waves The physical characteristics of these waves affect three psychological dimensions of our visual world: 1. Hue Defn: the dimension of visual experience specified by colour names and related to the wavelength of light Shorter waves tend to be seen as violet and blue Longer waves tend to be seen as orange and red The sun produces white light (mix of all visible wavelengths), but when drops of moisture are in the air they act as a prism separating the white light into the colours of the visible spectrum – a rainbow is made 2. Brightness Defn: lightness or luminance; the dimension of visual experience related to the amount, or intensity, of light emitted from or reflected by an object The more light an object reflects, the brighter it appears Yellows appear brighter than reds and blues despite equal physical intensities
3. Saturation Defn: vividness or purity of colour; the dimension of visual experience related to the complexity of light waves o The wideness or narrowness of the range of wavelengths Pure light is when light only contains a single wavelength, and the resulting colour is said to be saturated o Extremely rare; usually we see a mixture of wavelengths White light lacks colour and is completely unsaturated An Eye on the World The cornea o Transparent; covers the front part of the eye o Protect the eye and bends incoming light rays toward a lens located behind it The lens o Works by subtly changing its shape, becoming more or less curved to focus light from objects that are close or far away The iris o Controls the amount of light that gets into the eye o The part of the eye that gives it colour o Surrounds the pupil The pupil o When you enter a dim room, the pupil dilates to let more light in The retina o Defn: neural tissue lining the back of the eyeball’s interior, which contains the receptors for vision o Contains special cells that communicate information about light and dark to the brain to regulate biological rhythms o The retina is an extension of the brain o The retinal image When we look at an object, the light pattern on the retina is upside down o Receptors in the retina Rods Defn: visual receptors that respond to dim light Long and narrow 120 million to 125 million in the retina More sensitive to light; allow us to see at night Occupy the outer edges of the retina Handle peripheral vision Cannot distinguish wavelengths of light, not sensitive to colour Cones Defn: visual receptors involved in colour vision The centre of the retina, or fovea, where vision is sharpest, contains only cones densely clustered together Differentially sensitive to different wavelengths and allow us to see colour
Need more light than rods to respond Not very sensitive
Dark Adaptation o Defn: a process by which visual receptors become maximally sensitive to dim light o Involves chemical changes in the rods and cones o 10 minutes for cones to adapt o 20 minutes for rods to adapt Rods and cones are connected by synapses to bipolar neurons, which communicate with neurons called ganglion cells o Defn: neurons in the retina of the eye that gather information from receptor cells (by way of the bipolar cells); their axons make up the optic nerve o Axons of ganglion cells converge to form the optic nerve o The optic nerve leaves the eye at the optic disk, where there are no rods or cones This produces a blind spot, we are unaware of it because i. The image projected on the spot is hitting a different “non-blind” spot in the other eye ii. Our eyes move so fast they pick up the entire image iii. The brain fills the gap
Why the Visual System is Not a Camera Does not passively record the external world Feature detector cells o Defn: cells in the visual cortex that are sensitive to specific features of the environment, ex. spots of light and dark Different neurons were sensitive to different patterns projected on a screen in front of animals’ eyes Evolution has equipped us with an innate face module in the brain o Why infants show preference to looking at faces than scrambled ones o Vegetable face o Car pictures vs. bird pictures The Trichromatic Theory o Defn: a theory of colour mechanisms in the visual system, each sensitive to a certain range of wavelengths; their interaction is assumed to produce all the different experiences of hue o Aka Young-Helmholtz theory o Applies to the first level of processing in the retina o Retina has three types of cones Responds maximally to blue lengths Responds maximally to green And responds maximally to red o Colour blindness The Opponent-Process Theory o Defn: theory of colour perception that assumes that the visual system treats pairs of colours as opposing or antagonistic
o Applies to the second stage of colour processing in ganglion cells in the retina and in neurons in the thalamus and visual cortex of the brain; known as opponentprocess cells Respond to short wavelengths but are kept from firing by long ones, and vice versa Why we describe colours as bluish-green but not reddish-green Constructing the Visual World Form Perception o Gestalt Psychologists First to study how people organize the world visually into meaningful units and patterns Motto: “the whole is greater than the sum of its parts” People always organize the visual field into figure and ground o Gestalt Principles Defn: principles that describe the brain’s organization of sensory information into meaningful units and patterns 1. Proximity Things that are near each other tend to be grouped together Ex. dots 2. Closure The brain tends to fill gaps in order to perceive complete forms Ex. face, triangle, letter E 3. Similarity Things that are alike in some way (colour, shape, size) tend to be perceived as belonging together Ex. horizontal lines of stars 4. Continuity Lines and patterns tend to be perceived as continuing in time or space Ex. an oval on a line, and not two lines touching an oval Depth and Distance Perception o To estimate an object’s distance or depth, we rely on binocular cues Defn: visual cues to depth or distance requiring two eyes One such cue is convergence Defn: the turning inward of the eyes, which occurs when they focus on a nearby object o Retinal disparity Defn: the slight difference in lateral separation between two objects as seen from the left eye and the right eye Hold up two fingers one closer to face than the other o Binocular cues help us estimate distance up to 15 meters, any further and we use monocular cues Defn: visual cues to depth or distance that can be used by one eye alone
Interposition – when an object is interposed between the viewer and a second object, partly blocking the view of the second object, the first object is perceived as being closer Linear perspective – when two lines known to be parallel appear to be coming together or converging, they imply the existence of depth Light and shadow Motion parallax – the closer an object, the faster it seems to move Relative size Relative clarity – distant objects tend to look less detailed Texture gradients – distant parts of a uniform surface appear denser Visual Constancies: When Seeing is Believing o Perceptual constancy Defn: the accurate perception of objects as stable or unchanged despite changes in the sensory patterns they produce o Visual constancies 1. Shape constancy We see objects as having a constant shape even though the shape changes when we have a different point of view Round Frisbee in front of you, elliptical Frisbee on table 2. Location constancy We perceive stationary objects as remaining in the same place even though the retinal image moves as we move our eyes, heads, and bodies Looking at trees while driving on the highway 3. Size constancy We see an object as having a constant size even when its retinal image becomes smaller or larger A friend walking towards you on the street isn’t growing 4. Brightness constancy We see objects as having a relatively constant brightness even though the amount of light they reflect changes as the overall level of illumination changes Snow is still white on a cloudy day 5. Colour constancy We see an object as maintaining its hue despite the fact that the wavelength of light reaching our eyes from the object may change as the illumination changes An apple looks red whether you look at it in your kitchen or on the patio
HEARING What We Hear The stimulus for sound is a wave of pressure created when an object vibrates The vibration causes molecules in a transmitting substance (usually air, but can be water and solids) to move together and apart This movement produces variations in pressure that radiate in all directions Dimensions of auditory experience: 1. Loudness Defn: the dimension of auditory experience related to the intensity (amplitude or maximum height) of a pressure wave Sound intensity is measured in decibels (one tenth of a bel) The average absolute threshold of hearing in humans is zero dB 2. Pitch Defn: the dimension of auditory experience related to the frequency (how rapidly the air vibrates – the number of times per second the wave cycles through a peak and low point) of a pressure wave; the height or depth of a tone One cycle per second is known as one hertz The healthy ear normally detects frequencies in the range of 16 Hz to 20 000 Hz 3. Timbre Defn: the distinguishing quality of a sound; the dimension of auditory experience related to the complexity of the pressure wave What makes a note played on a flue sound different from the same note played on an oboe When many sound-wave frequencies are present but are not in harmony, we hear noise When all the frequencies of the sound spectrum occur, they produce a hissing sound called white noise An Ear on the World The ear has an outer, middle, and inner section The eardrum o Very sensitive – can respond to the movement of a single molecule o Vibrates with the same frequency and amplitude as a sound wave o This vibration is passed along to three tiny bones: The hammer The anvil The stirrup – pushes on a membrane that opens into the inner ear The organ of Corti o Defn: a structure in the cochlea containing hair cells that serve as the receptors for hearing Defn: a snail-shaped, fluid-filled organ in the inner ear, containing the structure where the receptors for hearing are located o Contains receptor cells – look like bristles, called hair cells or cilia The hair cells of the cochlea are embedded in the rubbery basilar membrane
OTHER SENSES Taste: Savoury Sensations Aka gustation Receptor cells for taste are inside the taste buds, which are inside the papillae They are replaced every 10 or so days Basic tastes: sweet, salty, bitter, sour, and umami The centre of the tongue has no taste buds Supertasters o About 25% of people o Find many things bitter o Sweets are sweeter, salty things are saltier o Have more taste buds than other people, are smaller, and denser Smell: The Sense of Scents Aka olfaction Receptors are specialized neurons embedded in a tiny patch of mucous membrane in the upper part of the nasal passage, beneath the eyes Signals from the receptors are carried to the brain`s olfactory bulb by the olfactory nerve Distinct odours activate unique combinations of receptors Scent can have a non-conscious influence on what we think and do o Smelling a citrus cleaner, wipes crumbs off table o Hotels and malls install aroma diffusers to put people in a good mood Senses of the Skin Basic skin senses: o Touch (or pressure) o Warmth o Cold o Pain The Mystery of Pain The Gate-Control Theory of Pain o Defn: theory that the experience of pain depends in part on whether pain impulses get past a neurological “gate” in the spinal cord and thus reach the brain o The brain controls the gate o Thoughts and feelings can influence our reactions to pain Updating the Gate-Control Theory o Phantom pain Defn: the experience of pain in a missing limb or other body part The brain has reorganized itself o The brain is capable of generating pain on its own o An extensive matrix of neurons in the brain gives us a sense of our own bodies and body part o When this matrix produces abnormal patterns of activity, the result is pain:
Input from spinal cord Signals from brain centres Memories Emotions Expectations Attention o Mirror therapy tricks the brain into thinking that the missing limb is active and healthy – phantom pain vanishes The Environment Within Kinesthesis o Defn: the sense of body position and movement of body parts o Aka kinesthesia o Without it you could not touch your finger to your nose with your eyes closed Equilibrium o Defn: the sense of balance o Relies primarily on three semicircular canals Defn: sense organs in the inner ear that contribute to equilibrium by responding to rotation of the head Filled with fluid that moves and presses on hair-like receptors whenever the head rotates
PERCEPTUAL POWERS: ORIGINS AND INFLUENCES Inborn Abilities Infants can: o Distinguish sweet from salty o Discriminate among odours o Distinguish a human voice from other sounds o Will startle to a loud noise and turn towards the source To test an infant’s perception of depth, a visual cliff is used o Mother lures baby either across the shallow side, or the “cliff” o Most babies refused to cross the “cliff” Critical Periods If an infant misses out on a critical period, perception will be impaired Kitten study – horizontal and vertical lines Psychological and Cultural Differences Psychological factors that influence what we perceive and how we perceive it: 1. Needs When we need something, have an interest in it, or want it, we are very likely to perceive it Hungry people are faster at recognizing words related to food 2. Beliefs What we hold to be true about the world an affect our interpretation of unclear sensory signals
If you believe in aliens, you might think you see a spaceship 3. Emotions A small child afraid of the dark may see a ghost instead of a robe hanging on the back of a door, or a monster instead of a favourite doll Negative and positive emotions influence pain Ex. relief of being alive may offset anxiety and fear Ex. intentionally having your foot stepped on will hurt more 4. Expectations Previous experiences often affect how we perceive the world Perceptual set – habitual way of perceiving based on experiences o Help us fill in words in sentences we don’t fully hear Missing a misspelled word in a textbook
PUZZLES OF PERCEPTION Subliminal Perception: How Persuasive? Perceiving without awareness o A simple visual stimulus can affect your behaviour even when you are unaware that you saw it o Priming Defn: a method used to measure unconscious cognitive processes, in which a person is exposed to information and is later tested to see whether the information affects behaviour or performance on another task or in another situation Being subliminally flashed the word honesty, then describing a person as honest – they have been primed to evaluate the person that way Perception versus Persuasion o Subliminal persuasion technique improvements are due to expectation o Motivation is a big part of persuasion – subliminal words like dry and thirst make people drink more
