PSY100H1 Chapter Notes - Chapter 5: Stereopsis, Binocular Disparity, Moon Illusion

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16 Feb 2011
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Sensation, perception and attention
-Sensation refers to how the sense organs respond to the external stimuli and
transmit those responses to the brain
-Perception refers to the processing, organization, and interpretation of sensory
signals that result in an internal representation of the stimulus
-Sensation is detection, whereas perception is construction
-The bodily systems convert stimulus energy into useful information
-Most of the time perception is based on past experiences, and this shapes our
expectations during the identification of sensory experiences
-The brain does not passively record information about the external world, rather,
how we see and hear is a result of the brain processes that actively construct
perceptual experiences to allow adaptation to an environment
oThis system can get details wrong, or fill in information that does not exist
oBut it does so in efficient and intelligent way so to produce a meaningful
understanding of what is going on around us
How do we sense our worlds?
-Sensory organs gain information about the environment by converting forms of
physical energy into signals that the brain can understand
oThis process has been shaped by evolution to
Access potential dangers
Identification of items
-Because different species face different adaptive challenges, each species is
sensitive to different types of physical energy
oThe information we sense and perceive has solved adaptive problems for
humans over the course of the evolution
1. Stimuli must be coded to be understood by the brain
-Sensory coding is the way sensory organs translate stimuli informations physical
properties into neural impulses
oDifferent features of the physical world are coded by different patterns of
neural impulses
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Example: green light will be coded by one pattern, sensation of a
hot skillet on your arm by another
-Receptors are specialized neurons in the sense organs that pass impulses to
connecting neurons when they receive chemical or electrical stimulation
-Transduction is a process by which sensory receptors produce neural impulses
when why receive physical or chemical stimulation
oAfter transduction, the sensory neurons pass their information to the brain
in form of neural impulses
Most of the sensory information enters the thalamus and is then
passed on to the cortex
In the cortex, the incoming neural impulses are interpreted
as sight, smell, sound, touch or taste
oSensation, then, refers to the transduced messages
that are carried by the nerve impulses
-Sensory coding can be divided into two categories, quantitative and qualitative
oQuantitative factors such as intensity, brightness, and loudness
Often indexed by the frequency of neural firing
The higher the frequency the more intense is the stimulus
The amount of neurons triggered also related to the
quantitative category, more intense stimulus tends to recruit
more neurons
oNot useful for color and taste
oQualitative coding is possible because different sensory receptors respond
to different qualities of stimulus
Example: one class of receptors responds to red light and another
to green
But if this was the case for all the sensory systems, then we
would need to have an enormous number of different
receptors
oAnd in most sensory systems, with exception of the
olfaction, receptors provide a coarse coding, in
which sensory qualities are only coded by a few
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receptors, each of which respond to wide range of
different stimulus
Only by comparing and integrating activity
across the whole range of receptors do we
compute the final percept
2. Psychophysics relates stimulus to response
-Psychophysics examines our psychological experiences of physical stimuli
oAsses such things as how much physical energy is required to detect that
energy and how much change is required for us to notice a change in the
stimuli
a.Sensory threshold
-Absolute threshold refers to the minimum intensity of stimulation that must occur
before one can experience a sensation
oExample: hearing threshold can be, how loud does a whisper have to be for
you to be able to perceive it, or a quietest whisper you can hear
-Difference threshold refers to the minimum amount of change required in order to
detect a difference between the intensity of the stimuli
oJust noticeable difference between two stimuli
Difference threshold increases as the stimuli increases
Example: easier to tell a difference between an one once
object and a two ounce object than is it easier to tell the
difference between a 5 pounds and 5pound and 1 ounce
object
oThis principle is known as the Weber’s law and it
states that the size of just noticeable difference is
based on the relative proportion of difference rather
than a fixed amount of difference
Getting 6 our of 10 of getting 96 out of 100
b. Signal detection theory
-Threshold is judged by human judgment
-Concept of absolute threshold was flawed because sometime people perceived a
stimulus when there wasnt one and sometimes missed one when there was one
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