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Chapter 4

Chapter 4 Notes Notes on chapter 4 in point form


Department
Psychology
Course Code
PS101
Professor
Eileen Wood
Chapter
4

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Chapter 4- Psychology Notes
By: Yen Hoang
Sensation: the stimulation of sense organs
The process through which the senses detect visual, auditory and other sensory stimuli
and transmit them to the brain
Involves the absorption of energy such as light or sound waves by sensory organs such as
the eyes or ears
Perception: the selection, organization and interpretation of sensory input
The process by which sensory information is actively organized and interpreted by the
brain
Involves organizing and translating sensory input into something meaningful such as
your best friend’s face or other environmental stimuli
Psychophysics: Basic Concepts and Issues:
Psychophysics: the study of how physical stimuli are translated into psychological
experience
Thresholds: looking for limits:
o Sensation begins with a stimulus, any detectable input from the environment
o A threshold is a dividing point between energy levels that do and do not have a
detectable effect
An absolute threshold for a specific type of sensory input is the minimum
amount of stimulation that an organism can detect
They define the boundaries of an organism’s sensory capabilities
o The difference between being able to perceive a stimulus
and being able to just barely perceive it
Researchers had to arbitrarily define the absolute threshold as the
stimulus intensity detected 50% of the time
Weighing the difference: the JND
o Difference threshold: the smallest increase or decrease in a physical stimulus that
is required to produce the “just noticeable difference” (JND) in sensation that is
detectable 50% of the time
JND is the smallest difference in the amount of stimulation that a specific
sense can detect
As stimuli increase in magnitude, the JND becomes larger
Weber’s law states that the size of a just noticeable difference is a
constant proportion of the size of the initial stimulus
o This constant proportion is called the Weber fraction
Amount of increase needed to make a difference
Ie if you are carrying 20 kg, 1 additional
gram will not make a difference
o Whereas if you’re carrying only 20
g, 1 g will make a difference
o Weber’s law applies not only to weight perception but to all
of the senses
The flaw with these classic measures:

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o Focus on the physical stimulus:
How strong/weak it is
How much/little there is
o What about individual variations?
Individuals differ from each other
Individuals can differ depending on context
Psychophysical scaling:
o Feschner’s law states that the magnitude of a sensory experience is proportional to
the number of JNDs that the stimulus causing the experience is above the absolute
threshold
Constant increments in stimulus intensity produce smaller and smaller
increases in the perceived magnitude of sensation
o Perceptions cannot be measured in absolute scales
In the domain of sensory experience, virtually everything is relative
Signal-detection theory:
o The fact that perceptions can’t be measured on absolute scales applied not only to
sensory scaling but to sensory thresholds as well
o Signal-detection theory proposes that the detection of stimuli involves decision
processes as well as sensory processes, which are both influenced by a variety of
factors besides stimulus intensity
Detection of sensory stimulus involves noticing a stimulus from
background noise and a decision about whether the stimulus is present
Decision= the probability of stimulus occurrence and potential
gain/loss with deciding whether the stimulus was present/not
Real life example: picking up your cousin, whom you’ve never met at the
airport having only a description/old photo
There are four possible outcomes:
o Hits (detecting signals when they’re present)
o Misses (failing to detect signals when they’re present)
o False alarms (detecting signals when they’re not present)
o Correct rejections (not detecting signals when they are
absent)
Perception without awareness:
o Subliminal perception: the registration of sensory input without conscious
awareness
Is it possible?
Yes and no
o If just at threshold, it works, but very, very tiny
Subliminal stimulation generally produces weak
effects
o Below threshold, technically not possible
Sensory adaptation:
o The process of sensory adaptation is yet another factor that influences registration
of sensory input
o Sensory adaptation is a gradual decline in sensitivity due to prolonged stimulation

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It is an automatic, built in process that keeps people tuned in to the
changes rather than the constants in their sensory input
It allows people to ignore the obvious and focus on changes in their
environment that may signal threats to safety
Ie allows us to shift attention
Our Sense of Sight: The Visual System:
o The stimulus: light:
o For people to see, there must be light
Light is a form of electromagnetic radiation that travels as a wave
Light waves vary in amplitude and in wavelength
Amplitude affects mainly the perception of brightness while
wavelength affects mainly the perception of colour
o Therefore light can also vary in its purity
Most objects do not emit light, they reflect it
o The eye: a living optical instrument:
o The eye serves two main purposes:
They channel light to the neural tissue that receives it (retina)
They house that tissue
Parts of the eye:
Cornea:
o Tough
o Transparent
o “herds”
o Muscles in iris contract/expand to adjust the size of pupil
o Pin-head to eraser-head:
Pin-head= bright light
Eraser-head= darkness
Lens: the transparent eye structure that focuses the light rays
falling on the retina
o Made up of relatively soft tissue capable of adjustments
that facilitate a process called accommodation
Accommodation occurs when the curvature of the
lens adjusts to alter visual focus
When you focus on a close object, the lens
of your eye gets fatter (rounder/bulge)
When you focus on distant objects, the lens
flattens out to give you a better image of
them
o Nearsightedness: close objects are seen clearly but distant
objects appear blurry
Focus of light from distant objects falls a little short
of the retina
Focusing problem occurs when the cornea
or lens bends the light too much or when the
eyeball is too long
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