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Chapter 5

Psychology 1000 Chapter Notes - Chapter 5: Detection Theory, Subliminal Stimuli, Absolute Threshold

Course Code
PSYCH 1000
Terry Biggs

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Chapter 5
Sensory and Perception
Synaesthesia- “mixing of senses”, sounds a colours or tastes as touch sensations
o Provide glimpses into different aspects of how we “sense” and “understand” our world
Sensory and perceptual process
o Begin when specific types of stimuli activate specialized sensory motor receptors
o Whether the stimulus is light, sound waves, a chemical molecule or pressure, your
sensory receptors must translate this info into the “language” of nerve impulses
o Once this translation occurs, specialized neurons break down and analyze the specific
features of the stimuli
o These numerous stimulus “pieces” are reconstructed into a neural representation that is
then compared with previously stored info, such as our knowledge of what particular
objects look, smell or feel like
o This matching of a new stimulus with our internal storehouse knowledge allows us to
recognize the stimulus and give it meaning
o We then consciously experience a perception

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Sensation- environmental stimuli into nerve impulses that are sent to the brain
Perception- making “sense” of what are senses tell us –is the active process of organizing this
stimulus input and giving it meaning
Perception is an active an d creative process, the same sensory input may be perceived in
different ways at different times
o Your interpretation, or perception, is influenced by contex
5 classical senses
o Vision
o Audition- hearing
o Touch
o Gustation- taste
o Olfaction- smell
Immune system also has sensory functions that allow it to detect foreign invaders and to
receive stimulation from the brain
Human sensory systems are designed to extract from the environment the information that we
need to function and survive
Psychophysics- studies relations between physical characteristics of stimuli and sensory
capabilities, is concerned with 2 types of sensitivity
o Absolute limits of sensitivity
Softest sound or weakest salt solution humans can detect
o Differences between stimuli
Smallest difference in brightness that we can detect, how much difference must
there be in two tones before we can tell that they are not identical?
Stimulus Detection: The Absolute Threshold
We are often unsure of whether we have actually sensed very faint stimuli, researchers
designate the absolute threshold as the lowest intensity at which a stimulus can be detected
correctly 50% of the time
o Therefore the lower the absolute threshold the greater the sensitivity
Signal Detection Theory
Decision criterion- a standard of how certain for must be that a stimulus is present before they
will say they detect it
o can change from time to time, depending on factors such as fatigue, expectation, and
the potential significance of the stimulus

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Signal detection theory- is concerned with the factors that influence sensory judgement
At low stimulus intensities, both the participants and the situation’s characteristics influence
then decision criterion
Subliminal stimulus- one that is so weak or brief that although it is received by the senses it
cannot be received consciously
o The stimulus is well below the absolute threshold
STUDY, pg 173:
Prosopagnosia- unable to recognize familiar faces
3 points to take away from this study
o It would appear that the higher-order facial recognition is a complex process involving
several brain regions including the LOA( lateral occipital area) and the FFA( fusi-form
facial area), in addition to the primary visual cortex. Nonetheless, a person with severe
damage can still pick up certain information about the visual stimuli by using heuristic
rules to “identity” faces- oval, skin tone
o This research emphasizes the importance of the case study to investigate psychological
phenomena, fMRI imaging allows the researchers to precisely identify the regions and
deficits involved with this disorder
o The study highlights the subtle manner in which subliminal stimuli may have an effect,
it is argued that effect is one of biasing perceptionsubliminal cues can bias what we
perceive at a conscious level and may alter our conscious experience of those stimuli
The Difference Threshold
Distinguishing between stimuli can sometimes be as important as detecting stimuli
o Ex. a slight variation in taste might signal that the food is tainted or spoiled
o Professional wine tasters and piano tuners make a living by being able to make very
slight discriminations between stimuli
o Difference threshold- the smallest difference between two stimuli that people can
perceive 50% of the time
Sometimes called the just noticeable difference (jnd)
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