Chapter 2 pt.2 Flashcards
How does the method of adjustment work?
The observer controls the level of the stimulus and “adjusts” it to be at the perceptual threshold. The participant does so by increasing or decreasing the level of the stimulus until it feels as if it is just at the detectable level.
eg. adjusting volume control to just where you can hear it
What is a pro and con for the method of adjustment?
pro = its fast to do
con = its the least accurate method as it varys from patient to patient, and its not good to rely on them
What is the methd of adjustment good for determining?
For determining the Point of Subjective Equality
eg. In vision research, the experimenter may present a stimulus of particular brightness. The participant would have to adjust another stimulus to be equally bright to the first one
Explain the concept of Sensitivity in the context of perception
Sensitivity is the ability to percieve a particular stimulus. As the threshold goes down, the observer is deemed to be more sensitive.
eg. a person who can hear a sound at 10 decibels (dB) is more sensitive than a person who can hear the sound only at 15
Explain Magnitude estimation
Its a psychophysical method where participants judge and assign numerical estimates to the perceived strength of a stimulus
eg. An experimenter presents a standard tone and assigns it a particular loudness value, say 20. Then the participant must judge subsequent tones and give them numerical values, in comparison with the standard. Thus, if the participant thinks the new tone is twice as loud as the standard, it should be assigned a 40. If the next tone is just a bit softer than the standard, it may be assigned a 15.
What is Response Compression?
Where if the strength of a stimuli increases, the participant will notice the increase, but not assume it to be as big as double.
eg. if you judge the first sugar-water solution as a 5 on the sweetness scale, doubling the sugar in the solution will cause an increase in your sweetness judgment but not a doubling of the perceived sweetness. In fact, you will likely judge the 2-teaspoon solution as a 7 or an 8 on the sweetness scale.
What is Response Expansion?
As the strength of a stimulus increases, the perceptual response increases even more (opposite of response compression). This is usually seen in pain perception
eg. If a person receives an electric shock of physical intensity 10 and judges it to be 5 on a pain scale, increasing the physical intensity to 20 will lead to a more than doubling of the judgment, to perhaps 15 on the pain scale.
What is Linear Relation?
Where the magnitude of response matches the changes in physical quantity (not response compression or expantion, its just right)
eg. the person experirences double and says its double
Stevens developed an equation to try to anaylyze how we perceive different things compared to their actual intensity, what mathematical equation is this called?
Stevens Power Law
Explain Stevens Power Law
Its P = KS to the power of n
p = how strong we percieve the stimuli
k = the number that adjusts the scale
S = the actual intensity
n = an exponent that changes how we experience the intensity.
Response bias can interfere with results (eg.someone saying that can hear something they actually cant just to impress) and people will respond differently. What is the solution for this? Explain it?
Catch trial = a trial where the stimulus is not presented, and if the presenter ever says they an see it in the catch trial, you can dismiss this participant as an unreliable observer
Explain the Forced-choice method and why its different than a catch trial
In every trial, the subject is asked to report either when the stimulus occurred or where it occurred.
Instead of determining whether a light was present or not, the participant must decide if a light was present in one location or another or at one time slot or another time slot
Why does the forced-choice method prevent the need for catch trials?
Because the observer cannot simply say “yes” in every trial, regardless of the presence of a stimulus in that trial.
Explain what a “false alarm” is and what a “miss” is
False alarm = occurs when the observer mistakes a nonsignal for an active signal
Miss = occurs when the observer mistaks an active signal for a nonsignal
Explain what a “correct rejection” and a “hit” is
Correct rejection = occurs when a nonsignal is percieved as a nonsignal
Hit = occurs when a signal is correctly percieved as occuring
What is a Criterion? And what does it mean for it to be high or low?
The difference of judgement of a signal based on the situation. its a bias that can affect the rate of hits and false alarms (also called internal cutoff)
If there is likely to be a variety of hits, misses, correct rejections, or false alarms, the criterion will be high, but if its more likely to be one more than the others, the criterion will be lower.
Signal detection theory states that we must consider _______ ______ __________ to successfully measure thresholds.
All four possibilities
What does it mean by the “sensitivity” of a signal
How easy or difficult it is to distinguish signal detection, to tell if it is present or absent.
An observer with high sensitivity will be able to make mostly hits and correct rejections
In psychophysics, if you know the relation of hits to false alarms, you can determine ________, which is a mathematical measure of sensitivity.
D-prime
To simplify seeing all of the possible outcomes for a given signal strength, researchers have developed a way to summarize all of the possible outcomes for this situation across all possible criteria. This summary is called the receiver-operating characteristic (ROC) curve. Explain it
The ROC curve is a graphical plot of how often false alarms occur versus how often hits occur for any level of sensitivity.
Sensitivity (d) is captured by the bow of the curve, and moving along the bow captures the criterion
Why are ROC curves good?
They capture all aspects of signal detection theory in one graph
Why do people respond when there is no stimulus present?
Their either dumb or because there is background noise in the sensory system
What are the teo goals of neuroimaging?
To reveal where perception happens in the brain, and how it unfolds through the brain over time
To reveal the particular area(s) in the brain where a specific process occurs, scientists use neuroimaging to develop _______ ______ of the brain, which show the areas that are active during perceptual tasks.
Spatial maps
How does Electroencephalography work? (EEG)
Electrodes (about 256) are positioned on a persons scalp and detect electrical signals in the brain.
Areas of the brain that are active generate faster electrical signals and by that we can see where perceptual processes are occuring.
What is an advantage of EEG
because it picks up a continuous electrical signal, which allows measurments to be made every milisecond, we can determine the time course of perceptual processes
EEG uses intra/extracellular recording, what does this mean?
it measures activity of a single neuron (using micro electrodes)
How does Magnetoencephalography (MEG) work?
Magnetic sensors detect small magnetic fields produced by the electrical activity in the brain (shows neural activity)
MEG uses arrays of ______ to detect weak signals
SQUIDs
MEG has better ______ ______ than EEG
Spacial resolution
How does Magnetic resonance imaging (MRI) and functional magnetic resonance imaging (fMRI) work?
Large magnetic fields align the oxygen molecules in our brain. Blood flows to the areas that are more activated.
The fMRI scanners take a picture every 30 milliseconds which allows us to pinpoint where and what time course perceptual processes are happening
How does Transmagnetic stimulation (TMS) work?
A magnetic coil is used to stimulate electrically a specific region of the brain and activates that regions neurons which can give us information on how this area functions
For fMRI’s, __________ (that carries oxygen to the blood) contains an iron atom that has magnetic properties
Hemogoblin
fMRI’s show _________ activity
Metabolic
What was one of the first ways to measure the brain?
PET (positron emission tomography) scans
How do PET’s work?
glucose gets intected into the patient and radioactivly the x-ray detects it. X-rays casue positron to be emitted and it shows metabolic activity.
(not good spacial resolution)
Why wouldnt you recconmend PET?
Because of the radiation
