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Chapter

chapter reading5


Department
Psychology
Course Code
PSY100H1
Professor
doldeman

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CHAPTER 5: SENSATION, PERCEPTION, AND ATTENTION
Sensation
-How our sense organs respond to external stimuli and transmit responses to brain
-DETECTION
Perception
-Processing of detected sensory signals that result in internal representation of stimulus
-CONSTRUCTION of useful info about environment
-Based on PRIOR EXPERIENCE, shapes our expectation during identification of sensory
experience
-What we see or hear is the result of brain processes that actively construct perceptual
experience
How do we sense our world?
-convert physical energy into signals brain can understand i.e. nocturnal animals: poor vision,
superb hearing
-Sensory coding: how sensory organs translate stimulus’s physical properties into neural
impulses
-diff features coded by DIFF patterns
Receptors are specialized neurons
-transduction: sensory receptors produce neural impulses when receive physical/chemical
stimulation
oneural impulses interpreted as sight, smell, sound, touch or taste
-Sensation: transducted messages carried by nerve impulses
Sensory coding
-Quantitative:
oIntensity, brightness, loudness
oIndexed by neural firing FREQUENCY
oAlso more intense stimuli tend to recruit more neurons
-Qualitative
oColor, taste
oDifferent sensory receptors respond to different qualities of a stimulus
oIn most sensory systems (EXCEPT sense of SMELL) receptors provide coarse coding:
sensory qualities are coded by only a few receptors, each responds to broad range of
stimuli. By comparing and integrating activity get final percept.
Psychophysics
- examines PSYCHOLOGICAL experiences of PHYSICAL stimuli
-test limits of human sensory systems
Threshold
Absolute threshold: minimum intensity of stimulation that must occur before we can experience a
sensation
Difference threshold: difference between two stimuli, minimum amount of change required to detect a
difference
-Weber’s law: the size of a just noticeable difference is based on a relative proportion of
difference rather than a fixed amount of difference
oE.g. exam score 6/10 vs. 96/100. percentage, not absolute size, is imp
opicking up one-ounce letter vs. two-ounce easy to detect VS one pound package and one
pound + 1 ounce
Classical psychophysics based on idea of threshold: either see smthg or not
-had ignored important variable: HUMAN JUDGEMENT
-absolute threshold was WRONG
Signal-detection theory
-detecting a stimulus requires making a judgment about its presence or absence, based on a
SUBJECTIVE interpretation of AMBIGUIOUS info
othis is daily tasks of radiologist looking for early signs of cancer
oknowledge of patient’s age/sex affects judgment, level of motivation and attention
-Involves series of trials in which stimulus is presented on some and not on others. Research
participant states whether they observed it or not. Each trial ONE of FOUR outcomes:
osignal present, observer detects it: HIT
osignal present, failed detect: MISS

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osignal not present, erroneous detection: false alarm
osignal not present, no detection: correct rejection
*** SENSITIVITY measured by comparing HIT RATE to FALSE ALARM rate
-correct for any bias
-response bias: participant’s tendency to report detecting the stimulus on ambiguous trials
oe.g. radiologist checking for tumor is extra cautious about accepting abnormality b/c
treatment is dangerous vs. checking for signs of broken bone willing to make more
positive diagnosis because treatment does not endanger life
oalso expectations affect bias: soldier expecting imminent attack likely to err on side of
responding, many false alarms
Sensory Adaptation
-when an observer’s sensitivity to a stimuli decreases over time
-when aspect of environment changes, it is important to be able to detect change than for
unchanging stimulus.
oNOTE: when continuous stimulus stops, large response as well
Sensory Processes
-No neurons beyond sensory organs respond DIRECTLY to the world.
Gustation (sense of taste)
-keep poisons out of digestive system, receptors are part of taste buds
-stimuli: chemical substances that dissolve in saliva
-microvilli: short, hairlike structures at tip of each taste bud, come into direct contact with
saliva
-when stimulated, send electrical signals to medulla thalamus cortex experience of
taste
-4 “primary” sensations: sweet, sour, salty, and bitter.
-Every experience composed of mixture of these 4
-In general, near-infinite variety of perceptual experience from activation of unique combinations
of small number of receptor types using coarse coding
-Taste relies heavily on smell
-Also texture, extent of discomfort (spicy), cultural beliefs
-Entire taste experience happens in BRAIN not mouth
-Supertasters: people who experience intense taste sensations (genetic), more likely to feel
pain when eating spicy food, picky eaters
Olfaction (sense of smell)
-Goes DIRECTLY to the brain, bypass thalamus
-olfactory epithelium: thin layer of tissue embedded with olfactory receptors
-olfactory bulb: brain centre for smell below the front lobes
-Prefrontal cortex: process info smell is pleasant or aversive
-Amygdala: process intensity of smell
-These regions involved in emotion and memory formation
oOlfactory stimuli can evoke powerful memories and feelings
-Pheromones: chemicals released by animals and humans that trigger physiological or
behavioral reactions in other animals
oDon’t “smell” but processed in same way, but specialized receptors in nasal cavity respond
omajor role in sexual signaling
omay explain why menstrual cycles of women living together synchronize
Haptic sense (touch)
-Tactile info: anything that makes contact with skin gives rise to integrated experience of touch
-haptic receptors: sensory neurons that terminate outer layer of skin
otheir long axons enter CNS by spinal or cranial nerves
oseparate receptors for hot and cold
-haptic experiences: integration of various signals
-Brain areas involved in touch sensation respond LESS to self-produced tactile stimulation than
to external
Pain
-warning system, experience created by brain
-most painful experience comes from damaging skin

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-nerve fibers that convey pain info are THINNER than those for temp and touch
-2 kinds of nerve fibers for pain
oFast Fibers: for sharp immediate pain
oSlow Fibers: for chronic, dull, steady pain
Distinction: MYELINATION
Gate-Control Theory
-theory: in order to experience pain, pain receptors must be activated and a neural “gate” in
the spinal cord must allow these signals through to the brain
-Close Gate: stimulate other haptic receptors, overwhelm signals from pain receptors
oReduce pain through rubbing or distraction
- midbrain controls gate: endorphins, painkillers stimulate this region, making gate close
Hearing/Audition
-second to vision in info about world
-stimulus: displacement of air molecules caused by changes in air pressure
-pattern of changes in air pressure through time called sound wave
-amplitude = LOUDNESS
-frequency = PITCH
ohumans detect 20 Hz to 20,000 Hz
-can predict response of auditory system to a complex sound from way it responds to component
tones
-*if tree falls and no one around to hear it, causes changes in air pressure, but if not registered
by brain, there is no sound.
-Ear transduces sound waves into brain activity, making sound
-Sound waves Outer ear down auditory canal to ear drum, marks beginning of middle ear
eardrum vibrates bones called ossicles (hammer, anvil, stirrup) oval window,
membrane of cochlea: inner ear, fluid-filled tube snail shape ossicles AMPLIFY vibrations so
1000 times greater in pressure
Pitch coding
TWO mechanisms for encoding frequency work at same time in basilar membrane: temporal coding and
place coding
Temporal coding
-encodes low frequencies, e.g. sound of tuba
-firing rates of cochlear hair cells strictly match frequency of pressure wave
-can only occur for up to 4000 Hz
-at higher frequency, hair cells fire in volleys
Place coding
-different frequencies activate similar receptors at different LOCATIONS on basilar membrane
-stiffness decreases along its length, SO higher frequencies vibrate better at membrane’s base,
lower frequencies at tip
-hair cells at base activated by high freq, at tip by low
-frequency of a sound wave is encoded by receptors on the area of basil membrane
that vibrates the most.
-BOTH temporal and place coding involved in perception of pitch. System is vulnerable to injury
and loss through intense sounds and aging.
Locating origin of sound
-the sensory receptors DO NOT code where event occurs
-brain integrates different sensory info coming from each two ears
-know from examining barn owl, use fine-tuned hearing to locate prey
ouse two cues to locate sound:
difference in timing between its arrival in each ear
difference in intensity in each ear
-unless sound comes from exactly front or back of owl, reaches one ear first
-separate neural pathways process TIMING CUE and INTENSITY CUE
Vision
-what is called seeing is more than transducing energy
-when you open your eyes, nearly half of your brain in action
-focus light to form image on retina
olight passes through cornea focuses light by refraction bent rays form image on retina
omore refraction happens at cornea than lens, but lens is adjustable while cornea is not
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