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Chapter 5

Psychology 1000 Ch.5 Notes: Very Comprehensive and Organized


Department
Psychology
Course Code
PSYCH 1000
Professor
Dr.Mike
Chapter
5

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Chapter 5 Notes
Sensation and Perception
-Synaesthesia: “mixing of the senses” Experiencing sound as colours or tastes. 1 in
150 women have it, 1 in 7150 men have it
-These people provide glimpses into different aspects of how we sense and understand
our world
-Specific types of stimuli activate specialized sensory receptors.
-Stimulus can be light, sound waves/chemical molecule, whatever. These are
translated into nerve impulses, the only language the nervous system
understands.
-Stimulus is matched within an internal storehouse of knowledge which allows
us to recognize the stimulus and give it meaning.
-Then we consciously experience a perception
-Sensation: Stimulus detection process where our sense organs respond to and
translate environmental stimuli into nerve impulses that are sent to the brain.
-Perception: Making sense of what our senses tell us. The active process of organizing
this stimulus input and giving it meaning.
-The same sensory input may be perceived in different ways at different times because
perception is active and a creative procesess.
-For example: ABC: We perceive the middle symbol as B
12 13 14: We perceive the middle symbol as 13
Sensory Processes
-Senses: vision, audition, touch, gustation, olfaction. But there are more. Senses that
provide info about balance and body position; touch can be subdivided into pressure,
pain, temperature, etc.
-Human Sensory systems are designed to extract from the environment the info we
need to function and survive.
-We have specialized sensors that can detect different kinds of stimuli with
considerable sensitivity.
-Psychophysics: Relations between physical characteristics of stimuli and sensory
capabilities, and is concerned with 2 kinds of sensitivity:
-The first concerns absolute limits of sensitivity
-The second concerns with the difference between stimuli
Stimulus Detection: The Absolute Threshold
-Often unsure of whether we’ve actually sensed very faint stimuli, researchers
designate the Absolute Threshold: the lowest intensity at which a stimulus can be
detected correctly 50% of the time.
-The lower the threshold, the greater the sensitivity. Our senses are very sensitive
(imagine that)

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-Absolute Threshold for smell: One Drop of Perfume in a large apartment. We
can pick up on that
Signal Detection Theory
-Found that peoples sensitivity can fluctuate
-The concept of an absolute fixed threshold is inaccurate because there’s no single
point on a detection scale that separates non-detection from detection.
-There is a range of uncertainty, people set their own
-Decision Criterion: Standard of how certain they must be to determine a stimulus is
present before they’ll say they detect it.
-Can change based on fatigue, expectation, or significance of stimulus
-Signal Detection Theory is concerned with the factors that influence sensory
judgement.
-Perception, is, in part, a decision
Focus on Neuroscience: The Neurosciences of Subliminal Perception in
Propaganda
-Subliminal Stimulus: received by the senses but not noticed by you.
-These stimuli can however affect behaviour and attitudes without us knowing.
-Persuasive stimuli above the absolute threshold are far more influential than
subliminal attempts to sneak into our subconscious mind, maybe because we’re more
likely to get the message.
-Prosopagnosia: Inability to recognize familiar faces
-Visual Agnosia is specific for faces
-Higher order facial recognition involves LOA, FFA Brain regions.
-But you can give certain info about visual stimuli (faces) even if one of these areas are
damaged.
-Subliminal cues can bias what we perceive at a conscious level and may alter our
conscious experience of those stimuli (study showed that subliminal presentations of
aggressively tones words caused people to judge the ambiguous behaviours of others as
more aggressive and to increase their own tendency to behave aggressively)
-We may not be consciously aware of the stimuli, but aspects of the stimuli are
processed at a different level and available for us to use in subsequent decisions
The Difference Threshold
-Smallest Difference between two stimuli that people can perceive 50% of the time.
-Sometimes called the ‘just noticeable difference’ or jnd
-Weber’s Law: States that the difference threshold is directly proportional to the
magnitude of the stimulus with which the comparison is being made - expressed as a
Weber Fraction.
-JND value for weight = 1/50
-If you lift a weight of 50 grams, another weight must weigh 51 grams for
you to tell the difference.
-500 grams: other weight has to weigh 510 grams
-Weber Fractions show that humans are very sensitive to audition (tonal pitch) and
vision. But least sensitive to taste and smell.

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Sensory Adaptation
-Sensory systems finely attuned to changes in stimulation
-Sensory neurons engineered to respond to constant stimulus by decreasing their
activity.
-Sensory Adaptation: Diminishing sensitivity to unchanged stimulus (Adaptation =
Habituation)
-example: monotonous background sounds are unheard after awhile, you
eventually become used to swimming in cool water etc.
-Occurs in all sensory modalities, even vision. Without involuntary eye movements
that keep objects moving in the retina, they would just fade completely if we stared too
long at something
-Sensory Adaptation reduces sensitivity, but allows our senses to pick up informative
changes about our environment
In Review:
-Sensation is activities by which our sense organs receive and transmit information,
whereas perception involves the brains processing and interpretation of information.
-Psychophysics: Scientific study of how physical properties of stimuli are related to
sensory experiences
-Sensory sensitivity is concerned with limits of stimulus detectability (absolute
threshold) and ability to discriminate between stimuli (difference threshold). Absolute
threshold is intensity at which a stimulus is detected 50% of the time.
-Signal Detection Theory concerned with factors that influence decisions about
whether or not a stimulus is present.
-Subliminal Stimuli (not consciously perceived) can influence perceptions and
behaviour in subtle ways, but not enough to raise concern.
-Use of subliminal self-help materials sometimes results in positive behaviour
changes that may be a product of expectancy factors rather than subliminal
messages.
-Difference Threshold (JND): Amount 2 stimuli must differ for them to be considered
different 50% of the time.
-Weber’s Law: JND is proportional to the intensity of original stimulus and is
constant within given state of modality.
-Sensory Systems are responsive to changes in stimulation - adaptation occurs in
response to unchanging stimuli.
The Sensory Systems
Vision
-Normal stimulus for vision is electromagnetic energy (light waves) measured in
nanometers.
-Electromagnetic spectrum includes X-Rays, T.V and radio signals, infrared and
ultraviolet rays.
-Our visual system is sensitive to wavelengths extending from 700nm (red) to
400nm (blue-violet)
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