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Chapter 5

chapter 5

12 Pages
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Department
Psychology
Course Code
PSYA01H3
Professor
Ingrid L.Stefanovic

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CHAPTER 5- SENSATION
SENSORY PROCESSESING
Sensation (simple sensation): detection of elementary/simple properties of stimuli (brightness, colour, warmth,
sweetness)
Perception (complex perception): detection of objections (both animate& inanimate), their locations, mvments, &
background/ nature that involves learning
Example: seeing red colour = sensation
Seeing red apple= perception
Belief: perceptions depend on learning VS sensation involves innateprewiredphysiological mechanisms
TRANSDUCTION
Transduction: conversion of physical stimuli into changes in the activity of receptor cells of sensory organs
Convert energy from environmental events into neural activity; through receptor cells or somatosenses
Each sense organ responds to a particular form of energy from environment + translate the energy into
neural firing for the brain to respond
In most senses, Receptor cells neuron that directly responds to physical stimulus (light, vibration,
aromatic molecules)== release chemical transmitter substances that stimulate other neurons, which
alters the rate of firing in their axons
Other senses such as somatosenses (body senses) doesnt require receptor cells, the dendrites of neurons
respond directly to physical stimuli w/o receptor cells
**in order for us to know whats going on in the outside; specific actions are required in order to see & understand the
outside world. This info is gathered by sense organs located outside the brain
Task of sense organ: transmit single to brain then the brain does it job to analyze the info and reconstruct what
occurred
Sense organs detect stimuli (light, sound, odour, taste) stimuli info transmit to brain through neural impulses axn
potential
TYPES OF TRANSDUCTIO BY SENSE ORGANS
LOCATION OF SENSE ORGANENVIORNMENTAL STIMULIENERGY TRANSUDCTED
Eye LightRadiant energy
EarSound Mechanical energy
Vestibular systemTilt/ rotation of head Mechanical energy
Tongue TasteRecognition of molecular shape
NoseOdourRecognition of molecular shape
Skin, internal organsTouch
Temperature
vibration
Mechanical energy
Thermal energy
Mechanical energy
MusclePain
StretchChemical rxn
Mechanical energy
SENSORY CODING
Because axn potentials and the duration cannot be changed, codes must be used to transmit specific info to the brain
(example: how do sense organs tell the brain that a red apple vs yellow lemon was seen?) through 2 forms anatomical
coding and temporal coding
ANATOMICAL CODING
www.notesolution.com
The firing of a specific neuron tells the brain where the body is being touched
By the means our brain represents the outer world
Brain uses anatomical coding to locate which sense organ was activated. b/c the brain has no direct info
about physical energy. Example: you rub your eye, then you mechanically stimulate the light receptors that
are in the eye area
Definition: a means by which the nervous system represents information, different features are coded by
the activity of different neurons
TEMPORAL CODING
The rate at which these neurons fire (whether fast or slow), tells us how intense the touch is
The coding of info based on time
Example: light touch= low firing rate of neurons === forceful touch= higher rate of neurons
PSYCHOPHYSICS (physics of the mind)
Is the study of the relation btw physical characteristics of stimuli and sensations they produce? To study perceptual
phenomena, there are 2 methods
1.The principal of the Just-Noticeable Difference
2.Signal Detection Theory
Ernst Weber- investigated the ability of humans to discriminate btw various stimuli/ measured it based on just
noticeable difference
Jnd= smallest difference btw 2 similar stimuli that can be distinguished or detected by a person, AKA difference
threshold (example: to see whether ppl can tell the difference btw a 400 gram weight to 410 gram weight)
- each dot marks another jnd. The amount of physical energy necessary to produce a jnd
increases w/ magnitude of stimulus
Weber Fractions: ratio btw jnd and magnitude of stimulus, reasonably constant over the middle range of most
stimulus intensities
Jnd is the difference btw the starting weight and the weight that ppl notice a difference. Example, starting weight is
100 and at 110 is when ppl start to notice the difference, TF the JND is 10. But instead of saying that the difference is
10, they use `Weber`s fraction` the ration of 10:100 where 10 is the difference, and 100 is the initial starting weight.
Gustav Fechner used Webers Idea of jnd to measure ppls sensations (example: he kept turning the light intensity
brighter and brighter to measure whether ppl can detect the difference and kept going until ppl couldnt stand the
brightness anymore)
Contribution to show how a logarithmic function could be derived from Webers principle
S.S Stevens- modified the formulation and suggested a power function to describe the relation btw physical intensity
and sensation
S= kIb
s= psychological magnitude of sensation
i= intensity of physical stimulus
k= mathematical constant that adjusts for the way physical intensity is measured
SIGNAL DETECTION THEORY
When calculating Reciever Operating Characteristic (ROC) curves, an experiment must be conducted first
www.notesolution.com
Participants sit in front of a computer and then a stimulus may or may not have been presented. Based on each
trial, whenever they think a stimulus occurred, they press yes or no
4 possibilities in a trial
1.Stimulus doesn`t occur and they say no = correlation rejection
2.Stimulus does occur and they say yes = hit
3.Stimulus doesnt occur and they incorrectly say yes= false alarm
4.Stimulus does occur and they incorrectly say no = miss
Sometimes the participant is just bias where its just easier for them to say yes even when they’re not so sure if
stimulus was there or not or vice versa, never saying yes. Being bias doesn`t allow the full sensitivity to be
observed`
ROC curves are easily calculated when there are pay offs, because with money involved, its easier to measure
how willingly people will say yes which TF can measure ppl`s different levels of sensitivity at different levels of
bias
Absolute threshold minimum value of a stimulus that can be detected
Signal detection theory: a mathematical theory of detection of stimuli, involves discriminating a signal from the
noise which is embedded and which takes into account of the participants willingness to report detection of the signal
Reciever operating characteristic curve (ROC curve)- a graph of hits and false alarms of articipants under
different motivational conditions; indicates people`s ability to detect a particular stimulus
VISION
Light
a stimulus to our vision
light consists of radiant energy similar to radio waves
wavelength- is the distance btw the adjacent (closest) waves of radiant energy, in vision
owavelength normally ranges from 380 to 760 nanometres (nm)
onm= 1 billionth of a metre
o380 nm light looks violet
o760 nm light looks red
oRadiant energy is normally invisible to our eyes (example: ultraviolent radiation, x-rays, gamma rays)
shorter wave lengths
oInfrared radiation, radar and radio waves have longer wave lengths
oElectromagnetic spectrum- entire range of wave lengths
oVisible spectrum- what we can see as light, what we can detect
The eye and its function
the eye is well protected; eye lashes from dust, eyebrows from sweater, eye lids
cornea- transparent tissue covering front of the eye which admits light
sclera- tough outer layer of the eyethe white of the eye
iris- pigmented muscle of the eye that controls the size of the pupil ; initially controls the amount of light
admitted into the eye
Aqueous humour- watery fluid in the eye located behind the cornea; nourishes the cornea. However if too
much of this liquid is produced the pressure in the eye can increase TF damage vision = GLAUCOMA its
supposed to be circulated and renewed since it filters the fluid from the blood
www.notesolution.com

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Description
CHAPTER 5- SENSATION SENSORY PROCESSESING Sensation (simple sensation): detection of elementarysimple properties of stimuli (brightness, colour, warmth, sweetness) Perception (complex perception): detection of objections (both animate& inanimate), their locations, mvments, & background nature that involves learning Example: seeing red colour = sensation Seeing red apple= perception Belief: perceptions depend on learning VS sensation involves innate prewired physiological mechanisms TRANSDUCTION Transduction: conversion of physical stimuli into changes in the activity of receptor cells of sensory organs Convert energy from environmental events into neural activity; through receptor cells or somatosenses Each sense organ responds to a particular form of energy from environment + translate the energy into neural firing for the brain to respond In most senses, Receptor cells neuron that directly responds to physical stimulus (light, vibration, aromatic molecules)== release chemical transmitter substances that stimulate other neurons, which alters the rate of firing in their axons Other senses such as somatosenses (body senses) doesnt require receptor cells, the dendrites of neurons respond directly to physical stimuli wo receptor cells **in order for us to know whats going on in the outside; specific actions are required in order to see & understand the outside world. This info is gathered by sense organs located outside the brain Task of sense organ: transmit single to brain then the brain does it job to analyze the info and reconstruct what occurred Sense organs detect stimuli (light, sound, odour, taste) stimuli info transmit to brain through neural impulses axn potential TYPES OF TRANSDUCTIO BY SENSE ORGANS LOCATION OF SENSE ORGAN ENVIORNMENTAL STIMULI ENERGY TRANSUDCTED Eye Light Radiant energy Ear Sound Mechanical energy Vestibular system Tilt rotation of head Mechanical energy Tongue Taste Recognition of molecular shape Nose Odour Recognition of molecular shape Skin, internal organs Touch Mechanical energy Temperature Thermal energy vibration Mechanical energy Muscle Pain Chemical rxn Stretch Mechanical energy SENSORY CODING Because axn potentials and the duration cannot be changed, codes must be used to transmit specific info to the brain (example: how do sense organs tell the brain that a red apple vs yellow lemon was seen?) through 2 forms anatomical coding and temporal coding ANATOMICAL CODING www.notesolution.com The firing of a specific neuron tells the brain where the body is being touched By the means our brain represents the outer world Brain uses anatomical coding to locate which sense organ was activated. bc the brain has no direct info about physical energy. Example: you rub your eye, then you mechanically stimulate the light receptors that are in the eye area Definition: a means by which the nervous system represents information, different features are coded by the activity of different neurons TEMPORAL CODING The rate at which these neurons fire (whether fast or slow), tells us how intense the touch is The coding of info based on time Example: light touch= low firing rate of neurons === forceful touch= higher rate of neurons PSYCHOPHYSICS (physics of the mind) Is the study of the relation btw physical characteristics of stimuli and sensations they produce? To study perceptual phenomena, there are 2 methods 1. The principal of the Just-Noticeable Difference 2. Signal Detection Theory Ernst Weber- investigated the ability of humans to discriminate btw various stimuli measured it based on just noticeable difference Jnd= smallest difference btw 2 similar stimuli that can be distinguished or detected by a person, AKA difference threshold (example: to see whether ppl can tell the difference btw a 400 gram weight to 410 gram weight) - each dot marks another jnd. The amount of physical energy necessary to produce a jnd increases w magnitude of stimulus Weber Fractions: ratio btw jnd and magnitude of stimulus, reasonably constant over the middle range of most stimulus intensities Jnd is the difference btw the starting weight and the weight that ppl notice a difference. Example, starting weight is 100 and at 110 is when ppl start to notice the difference, TF the JND is 10. But instead of saying that the difference is 10, they use Webers fraction the ration of 10:100 where 10 is the difference, and 100 is the initial starting weight. Gustav Fechner used Webers Idea of jnd to measure ppls sensations (example: he kept turning the light intensity brighter and brighter to measure whether ppl can detect the difference and kept going until ppl couldnt stand the brightness anymore) Contribution to show how a logarithmic function could be derived from Webers principle S.S Stevens- modified the formulation and suggested a power function to describe the relation btw physical intensity and sensation b S= kI s= psychological magnitude of sensation i= intensity of physical stimulus k= mathematical constant that adjusts for the way physical intensity is measured SIGNAL DETECTION THEORY When calculating Reciever Operating Characteristic (ROC) curves, an experiment must be conducted first www.notesolution.com
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