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Chapter 6

Study Guide of chapter 6 for PSYA01

by

Department
Psychology
Course Code
PSYA01H3
Professor
Steve Joordens
Chapter
6

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CHAPTER 6 ! SENSATION
CHAPTER OUTLINE:
Sensory Processing: Primary function of senses to provide info. to guide behaviour. Translation of neural activity
is called transduction. Two types of neural codes: anatomical or temporal. Subliminal perception refers to
behavioural effects of a stimulus that cannot be consciously detected.
Vision: Images of visual scene focused on retina, inner layer at back of eye. Photoreceptors contain chemicals
(photopigments) that tranduce light into neural activity. Three types of cones in retina, each most sensitive to
particular wavelength of light, detect colours.
Audition: Bones of middle ear transmit sound vibrations from eardrum to cochlea, which contains auditory
receptors (hair cells). Left-right localization accomplished by 2 means: arrival time & differences in intensity.
Gustation: Taste receptors along with olfactory system provide us with info. about complex flavours
Olfaction: detection of aromatic molecules!odour may have several hundred dimensions
The Somotosenses: sensory receptors (touch, pressure, vibration, changes in temp. and stimuli that cause tissue
damage). Sensory endings along joints, internal organs, muscles convey info about own movements and about
events occurring in organs. Vestibular system helps us maintain our balance and make compensatory eye
movements to help us maintain fixation when our heads move.
OPENING CASE STUDY:
-little girl injuring her thumb wishes she didnt feel pain
-father explains that without pain, she wouldnt know when she was injuring herself, and serious damage
could occur
-when parts of body are damaged, injured cells make chemical thats picked up by nerve endings, and nerves send
messages to brain to warn it that something bad is happening
-brain gets us away from whatever is hurting us; become afraid of it
-hard to survive without pain
-senses are means by which we experience world
-without sensory input, brain would be utterly useless: learn nothing, think no thoughts, etc.
-vision most import sense modality-provides info. about shape, size, colour, and movement of objects nearby and
at a distance.
-other senses deal with events close by
SENSORY PROCESSING:
Sensation: detection of elementary properties of stimulus. Ex. brightness, colour, warmth, and sweetness
Perception: detection of more complex properties of a stimulus. Ex. location & nature; involves learning
Animate & inanimate objects, movements, backgrounds
Ex. seeing a movement is sensation, but seeing a baseball coming toward us and realizing that we will have to
move to left to catch it is perception
-experience is essential to development of some of most elementary features of sensory systems
-traditionally we think we have 5 senses, but in fact we have several more
Transduction: process by which sense organs convert energy from environmental events into neural activity;
conversion of physical stimuli into changes in activity of receptor cells of sensory organs
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-only sense receptors brain possesses detect such things as temperature, salt concentration of blood; receptors
cannot inform about what is going on outside
-sense organs detect stimuli provided by light, sound, odour, taste, or mechanical contact with environment
-transmitted to brain through neural impulses-action potentials carried by axons in sensory nerves
receptor cells: release chemical transmitter substances that stimulate other neurons, thus altering rate of firing of
axons; directly responds to physical stimulus, such as light, vibrations, or aromatic molecules
-somatosenses (body senses), dendrites of neurons respond directly to physical stimuli without intervention of
specialized receptor cells
** refer to table 6.1 on pg. 166 for types of transduction
Sensory Coding:
-diff. stimuli cannot be translated into diff. types of action potentials
-code is system of symbols or signals representing information. Ex. spoken English, magnetic fields on recording
tape, electrical zeros and ones in memory of computer
means by which nervous system represents info:
Anatomical Coding: interpret location, type of sensory stimulus according to which incoming nerve fibres are
active; diff. features coded by diff. neurons. Ex. rubbing eyes automatically stimulates light receptors there
-distinguishes among sense modalities but also stimuli of same sense modality
-sensory coding for body surface is anatomical: diff. nerve fibres serve diff. parts of skin
Temporal Coding: coding of info. in terms of time; diff. features are coded by pattern of activity of neurons
-rate: by firing at faster or slower rate according to intensity of stimulus, axon can communicate quantitative info
to brain
-firing of specific set of neurons tells where body is being touched; rate at which these neurons fire (temporal code)
tells us how intense that touch is
Psychophysics: branch of psychology that measures quantitative relation between physical stimuli and perceptual
experience
The Principle of the Just-Noticeable Difference (JND): smallest change in magnitude of a stimulus that a person
can detect; JND directly related to magnitude of that stimulus
Ex. distinguishing between a 40 gram weight and a 41 gram weight; feels pretty much the same, hard to notice any
difference
-different senses have different ratios: ex. ratio for detecting differences in brightness of white light is approx. 1 in
60!Weber fractions: ration between a JND and magnitude of stimulus; reasonably constant over the middle
range of most stimulus intensities
-Fig 6.1 on pg. 167!provides a mapping between physical and psychological worlds
-x-axis is something measured with respect to objective world
-y-axis is very different
-amount of physical energy necessary to produce a JND increases with magnitude of stimulus
-Fig 6.2 on pg. 168! relationship between stimulus and perception when less energy is required to produce a
JND at higher intensities
-points of physical energy that produce more intense sensation are closer together at higher
levels of physical sensation
-S.S. Stevens power function: S=kIb
-provides systematic way of comparing different sensory systems
-only substantive diff. is value of b-between zero and 1 (fig 6.1); greater than 1
(fig 6.2)
Signal Detection Theory:
Mathematical theory of detection of stimuli, which involves discriminating a signal (stimulus) from noise
(consisting of both background stimuli and random activity of nervous system) in which it is embedded and
which takes into account subjects willingness to report detecting signal
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-best way to determine persons sensitivity to occurrence of particular stimulus
-concept of threshold not used
-involves factors such as motivation and prior experience
Threshold: line between not perceiving and perceiving; point at which stimulus, or change in value of a stimulus,
can just be detected; detects stimulus 50% of time
Difference threshold: alternate name of JND; minimal detectable difference between 2 stimuli
Absolute threshold: minimum value of a stimulus that can be detected-discriminated from no stimulus at all;
minimum value of a stimulus that can be detected
-response bias-your tendency to sayyes orno when you are not sure whether you detected the stimulus
-hits-sayingyes when stimulus is presented!correct response
-misses”- sayingno when it is presented!incorrect response
-correct negatives-sayingno when stimulus is not presented!correct response
-false alarms-sayingyes when the stimulus is not presented!incorrect response
-persons response bias can seriously affect investigators estimate of threshold detection
!person with response bias to avoid false alarms will appear to have a higher threshold
!to avoid this, deliberately manipulate response biases and observe results of these manipulations on
peoples judgement
Receiver operating characteristics curve (ROC curve): graph of hits & false alarms of subjects under different
motivational conditions; indicates peoples ability to detect a particular stimulus
EVALUTATING SCIENTIFIC ISSUES:
Subliminal Self-Help:
-messages so faint that cannot be consciously heard or seen
Claims:
-doing ordinary activities and listening to tapes will provide self improvement in a variety of aspects
-requires no effort or work
Evidence in support:
-testimonials from customers who use product
-but can testimonials be taken as evidence that self-help really works?
Does evidence support?:
No! 3 reasons:
-simply making a purchase indicates a commitment to self-improvement
-once people have expended some effort toward reaching a goal, they tend to justify their effort by perceiving
positive results
-if a person expects an effect to occur, he/she is easily convinced that it really did
-subliminal-below threshold
-subliminal perception: perception of a stimulus, as indicated by change in behaviour, at an intensity insufficient to
produce a conscious sensation; behavioural effect of stimulus that falls below threshold of conscious detection
-thus, persons satisfaction is no indication that subliminal perception has really taken place
What should we conclude?:
Subliminal tapes DON’T WORK!
VISION:
Light:
-consists of radiant energy!oscillates and is transmitted from its source
wavelength: distance between adjacent waves of radiant energy; in vision, most closely associated with perceptual
dimension of hue
-wavelength of visible light is short ranging from 380-760nm
-electromagnetic spectrum-entire range of wavelengths; the part we see is visible spectrum
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