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Lecture 8

Psychology 1000 Lecture Notes - Lecture 8: Oval Window, Additive Color, Umami

Course Code
PSYCH 1000
Derek Quinlan

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Chapter 5 Psych 1000 Week 4
Sensation & Perception
Synesthesia: mixing of the senses
Sounds as colors, tastes as touch sensations with different shapes
More prevalent in F
Some sort of “cross-wiring”
fMRI shows hearing certain words associated with activity in visual cortex
Theories for sensory mixing:
o (1) Pruning of neural connections that occurs in infancy has not
o (2) Deficit in neural inhibitory processes in the brain that ordinarily
keep input from one sensory modality from “overflowing” into
other sensory areas and simulating them
Steps of sensation perception:
(1) Stimulus is received by sensory receptors
(2) Receptors translate stimulus into nerve impulses (i.e., transduction)
(3) Feature detectors analyze stimulus features
(4) Stimulus features are reconstructed into neural representation
(5) Neural representation is compared with previously stored info in brain
(6) Matching process results in recognition and interpretation of stimuli
Binding problem:
How do we bind all our perceptions into one complete whole while
keeping its sensory elements separate?
Sensation: stimulus-detection process by which our sense organs respond to and
translate environmental stimuli into nerve pulses 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
Same sensory input can be perceived in many different ways: fig. 5.2 (p.138)
Thus, perception of characters is influenced by their context
Sensory Processes
Sensitivity of stimuli vary considerably between animals
Many species have senses that humans lack altogether
Transduction: characteristics of stimuli are converted into nerve impulses
Human senses:
(1) Vision
(2) Audition (i.e., hearing)
(3) Touch
o Subdivided into: (a) pain, (b) pressure, and (c) temperature
(4) Gustation (i.e., taste)
(5) Olfaction (i.e., smell)
(6) Body senses (i.e., balance and body position)
Psychophysics: studies relations between physical characteristics of
stimuli/sensory capabilities
Concerned with two kinds of sensitivity:
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Chapter 5 Psych 1000 Week 4
o (1) Absolute limits of sensitivity (e.g., what is the softest sound or
weakest salt-solution that humans can detect?)
o (2) Differences between stimuli (e.g., what is the small difference
in brightness we can detect?)
Stimulus Detection: The Absolute Threshold
Absolute threshold: lowest intensity at which a stimulus can be detected correctly
50% of the time
Lower value = greater sensitivity
Signal Detection Theory
People’s apparent sensitivity can fluctuate
Concept of a fixed absolute threshold is inaccurate
No intensity scale separates non-detection from detection of a stimulus
There is a range of uncertainty
People set their own decision criteria
i.e., standard of how certain they must be that a stimulus is present before
they will say they detect it
Can change from time to time depending on…
o (1) Fatigue
o (2) Expectation
o (3) Potential significance of the stimulus
Signal detection theory: studies the factors that influence sensory judgments
Warning light, barely perceptible tone may or may not be presented
Tell experimenter if they heard it or not
When tone is actually present:
o “Yes” = hit
o “No” = miss
When tone is not actually present:
o “Yes” = false alarm
o “No” = correct rejection
At low stimulus intensities, both the participant’s and situation’s characteristics
influence the decision criteria
Bold participants: have more hits, but also more FARs than conservative subjects
Can be influenced to become more bold or conservative with rewards/costs
Increasing rewards for hits or costs for misses = lower detection thresholds
o i.e., more “Yes” responses at low intensities
Higher detection thresholds = more conservative in their “Yes” responses
as costs for FARs are increased
Experience also plays a role in signal detection
The Difference Threshold
Distinguishing b/w stimuli can be just as important as detecting them
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Chapter 5 Psych 1000 Week 4
Difference threshold: smallest difference between two stimuli that people can
perceive 50% of the time
Sometimes called just noticeable differences (jnd)
Ernst Weber:
There is some degree of lawfulness in the range of sensitivities within our
sensory systems
Weber’s Law: difference threshold is directly proportional to the
magnitude of the stimulus with which the comparison is being made and
can be expressed as a Weber fraction
e.g., jnd value for weights is a Weber fraction of 1/50
o If you lift a weight of 50 g, a comparison weight must weight at
least 51 grams in order for you to be able to judge it as heavier
o If weight were 500 g, a second weight would have to weigh at least
510 g for you to discriminate between them
o Thus, 1/50 = 10/500 (just add the zero)
This law holds up reasonably well within the most frequently encountered
range, therefore, providing a reasonable barometer of our abilities to
discern differences in the various sensory modalities
*The smaller the fraction, the greater the sensitivity to differences
Sensory Adaptation
Sensory systems are finely attuned to changes in stimulation
Sensory adaptation: sensory neurons are engineered to respond to a constant
stimulus by decreasing their activity, and the diminishing sensitivity to an
unchanging stimulus
e.g., wristwatch against your skin eventually recedes from awareness
Adaptations occur in all sensory modalities
R.M. Pritchard:
Attached tiny projector to contact lens worn by participant
Visual images would remain in constant position on the retina, even if the
eye moved
Result: participants reported that the image appeared in its entirety for a
time, then began to vanish and reappear as parts of the original stimulus
Sensory adaptation frees our senses from the constant and the mundane to pick up
informative changes in the environment
Important to our well-being/survival, e.g., study:
Sensory adaptation was mostly absent in animals while they were alert and
engaged in a behavioral learning task, whereas after the task was learned
and had become routine, levels of alertness and sensory adaptation
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