PSYC-158 Perception Exam 1
questions and answers
What is an Absolute Threshold, what is the threshold for any sense, how does it
differ from JND?✔✔Minimum amount of stimulation necessary for a person to detect
a stimulus 50% of the time.
Just noticeable difference is the smallest detectable difference between two stimuli,
or the minimum change in a stimulus that can be correctly judged as different from a
reference stimulus; also known as difference threshold.
What is the Just Noticeable Threshold and what do the terms in the formula for K
mean?✔✔Just noticeable difference is the smallest detectable difference between
two stimuli, or the minimum change in a stimulus that can be correctly judged as
different from a reference stimulus; also known as difference threshold.
K is the Konstant•
Δ is the difference•
I is the stimulus intensity
What is the difference between a Step Function vs Sine Wave Function? What does
the SineWave function imply about perceived levels of intensity compared to the
physical level of intensity?✔✔Step wave is a different function, basically its more
squared.ie _|------|_ ___|------|_____ This is a step wave, the waves are
squares.|____|The mathematical function for a step wave consists of sine + cosine
functions. To get an exact step wave you need unlimited frequencies. But this doesnt
happen. You can get near a step wave with it being maded up of a high number of
sine and cosine waves.
sine wave:
In hearing, a waveform for which variation as a function of time is a sine function;
also called a "pure tone"
- In vision, a pattern for which variation in a property, like brightness or color as a
function of space, is a sine function
Amplitude: The height of a sine wave from peak to trough, indicating the amount of
energy in the signal.
-Increased intensity should result in increased perception of loudness.
What do the terms mean in the formula (e.g., I, S) for Fechner's Law and Steven's
Power Law?In general what do these laws imply about the perceived intensity of an
experience comparedwith the physical intensity of the stimulus?✔✔Fencher's Law: S
is sensation, k is constant and I isintensity of stimulus
-the magnitude of subjective sensation increases proportionally to the logarithm of
the stimulus intensity
Steven's power law: Perceived Intensity (S) is related to stimulus intensity (I) by an
exponent (b) multiplied by a constant (a)
, -Fechner's Law and Steven'sPower Law are nearlyidentical, but the Power
lawdescribes a wider range ofsensory comparisons, down tozero intensity
What are similarities and differences among Method of Limits Method of Constant
Stimuli,Method of Adjustment, Cross-Modality Matching✔✔Method of limits: The
magnitude of a single stimulus or the difference between two stimuli is varied
incrementally until the participant responds differently.
Method of constant stimuli: Many stimuli, ranging from rarely to almost always
perceivable, are presented one at a time.
• Method of adjustment: Similar to the method of limits, but the participant controls
the stimulus directly.
Cross-modal matching- the ability to recognize objects presented in two different
sensory modalities.
What are Bias and Sensitivity? What does Signal Detection Theory have to do with
them?✔✔Signal detection theory: A psychophysical theorythat quantifies the
response of an observer tothe presentation of a signal in the presence ofnoise.
-E.g., Where's Waldo: signal is Waldo, noise iseverything else.
Weak: measure response when Waldo was there• Stronger: measure response
when Waldo was thereAND NOT there.
Measuring responses in both conditionsSeparates the sensitivity from the bias
inperceptionThresholds and the Dawn of Psychophysics
Bias is the likelihood of detecting astimulus, and can shift outside of ourvoluntary
awareness,e.g., as number of beeps increases,threshold decreases - more biased
"infavor" of beeps.• To account for difference between sensitivity andbias ➔ Signal
Detection Theory
Give examples of Hits, False Alarms, Misses, Correct Rejections✔✔Hit: Stimulus is
present and observerresponds "Yes."•
Miss: Stimulus is present and observerresponds "No."•
False alarm: Stimulus is not presentand observer responds "Yes."•
Correct rejection: Stimulus is notpresent and observer responds "No."
What is the Criterion and what happens to the ratio of Hits to False Alarms as you
shift theCriterion to the right? To the left?✔✔An internal threshold that is set bythe
observer.▪ If the internal response is above criterion,the observer gives one
response.▪ Below criterion, the observer givesanother response.
-shifted left= more yes responses less no... more false hits
questions and answers
What is an Absolute Threshold, what is the threshold for any sense, how does it
differ from JND?✔✔Minimum amount of stimulation necessary for a person to detect
a stimulus 50% of the time.
Just noticeable difference is the smallest detectable difference between two stimuli,
or the minimum change in a stimulus that can be correctly judged as different from a
reference stimulus; also known as difference threshold.
What is the Just Noticeable Threshold and what do the terms in the formula for K
mean?✔✔Just noticeable difference is the smallest detectable difference between
two stimuli, or the minimum change in a stimulus that can be correctly judged as
different from a reference stimulus; also known as difference threshold.
K is the Konstant•
Δ is the difference•
I is the stimulus intensity
What is the difference between a Step Function vs Sine Wave Function? What does
the SineWave function imply about perceived levels of intensity compared to the
physical level of intensity?✔✔Step wave is a different function, basically its more
squared.ie _|------|_ ___|------|_____ This is a step wave, the waves are
squares.|____|The mathematical function for a step wave consists of sine + cosine
functions. To get an exact step wave you need unlimited frequencies. But this doesnt
happen. You can get near a step wave with it being maded up of a high number of
sine and cosine waves.
sine wave:
In hearing, a waveform for which variation as a function of time is a sine function;
also called a "pure tone"
- In vision, a pattern for which variation in a property, like brightness or color as a
function of space, is a sine function
Amplitude: The height of a sine wave from peak to trough, indicating the amount of
energy in the signal.
-Increased intensity should result in increased perception of loudness.
What do the terms mean in the formula (e.g., I, S) for Fechner's Law and Steven's
Power Law?In general what do these laws imply about the perceived intensity of an
experience comparedwith the physical intensity of the stimulus?✔✔Fencher's Law: S
is sensation, k is constant and I isintensity of stimulus
-the magnitude of subjective sensation increases proportionally to the logarithm of
the stimulus intensity
Steven's power law: Perceived Intensity (S) is related to stimulus intensity (I) by an
exponent (b) multiplied by a constant (a)
, -Fechner's Law and Steven'sPower Law are nearlyidentical, but the Power
lawdescribes a wider range ofsensory comparisons, down tozero intensity
What are similarities and differences among Method of Limits Method of Constant
Stimuli,Method of Adjustment, Cross-Modality Matching✔✔Method of limits: The
magnitude of a single stimulus or the difference between two stimuli is varied
incrementally until the participant responds differently.
Method of constant stimuli: Many stimuli, ranging from rarely to almost always
perceivable, are presented one at a time.
• Method of adjustment: Similar to the method of limits, but the participant controls
the stimulus directly.
Cross-modal matching- the ability to recognize objects presented in two different
sensory modalities.
What are Bias and Sensitivity? What does Signal Detection Theory have to do with
them?✔✔Signal detection theory: A psychophysical theorythat quantifies the
response of an observer tothe presentation of a signal in the presence ofnoise.
-E.g., Where's Waldo: signal is Waldo, noise iseverything else.
Weak: measure response when Waldo was there• Stronger: measure response
when Waldo was thereAND NOT there.
Measuring responses in both conditionsSeparates the sensitivity from the bias
inperceptionThresholds and the Dawn of Psychophysics
Bias is the likelihood of detecting astimulus, and can shift outside of ourvoluntary
awareness,e.g., as number of beeps increases,threshold decreases - more biased
"infavor" of beeps.• To account for difference between sensitivity andbias ➔ Signal
Detection Theory
Give examples of Hits, False Alarms, Misses, Correct Rejections✔✔Hit: Stimulus is
present and observerresponds "Yes."•
Miss: Stimulus is present and observerresponds "No."•
False alarm: Stimulus is not presentand observer responds "Yes."•
Correct rejection: Stimulus is notpresent and observer responds "No."
What is the Criterion and what happens to the ratio of Hits to False Alarms as you
shift theCriterion to the right? To the left?✔✔An internal threshold that is set bythe
observer.▪ If the internal response is above criterion,the observer gives one
response.▪ Below criterion, the observer givesanother response.
-shifted left= more yes responses less no... more false hits
