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Chapter 6

Psych 101 Detailed Textbook Notes: Chapter 6

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Department
Psychology
Course
PS101
Professor
Kathy Foxall
Semester
Fall

Description
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 Def
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