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Chapter 1

PSYCH 2000 Chapter 1: Chapter 1

Course Code
Nikol Piskuric

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Chapter 1
Why Measure Percepon?
-Even though percepon is not a feature of the physical world, psychologists have developed
methods to quanfy and compare our percepons
-May oer clues about the nature of the brain, the way it processes informaon, and ulmately,
the biological processes that lead to sensaon and percepon
Relang Physical Intensity of a Smulus to
Perceived Sensaon
-Funcon: mathemacal descripon
of how one variable is related to
another; generally expressed as a
-Starts pass 0, what is the minimum amount of intensity needed for us to perceive that
-Absolute threshold: where
you perceive the stimulus 50%
of the time
-Subthreshold: less intense
than the absolute threshold
-How small of a change do we
need in our stimulus intensity
for us to perceive it?
-Psychometric function: relation
of psychological experience
and a physical stimulus
Determining Threshold

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1. Method of Adjustment
oEx. Parcipant sees a light, adjust intensity
bright or lower unl they can no longer detect it
= absolute threshold
2. Method of Limits
oParcipant presented with a subthreshold
smulus, keep increasing unl they can see it =
absolute threshold
oStarng for upper limit, going down or starng
from lower limit, going up
3. Method of Constant Smuli
oShown dierent intensies, do you perceive it?
Graph it
-Why might methods 1 & 2 be less accurate than 3?
oKnow intensies increasing in method 2, and we’re able to control intensies in method
1 so we know when to expect to see the light or not
oMethod 3 has no expectaons, not sure if its brighter or weaker than the smulus just
-Step funcon = ideal absolute threshold
-Large variability around absolute
threshold for humans
oBiological systems are noisy (neuron
part of visual pathway, baseline /res 1-2
AP, smulus only changes frequency
very slightly – is this small increase
something real or just the noise of the
biological system?)
oSmulus could be noisy (device ejecng
light on the screen, intensity may vary
oJudgement can play a role (cognive
-Di,erence Threshold (Weber): How much a
smulus needs to change in order to produce a
detectable change in sensaon
oBirthday cake of a two year old, add
another candle – noce dierence in light
oGrandmas birthday, 100 candles – add
another one – do not noce dierence
-Sound with intensity a is perceptually
equivalent to reference sound – no different to
the control sound
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