Computational methods Flashcards
Physiological measure of sensation and perception
Start with stimulus and look at where it is processed
Computational (psychophysics) measure of sensation and perception
Mathematical transformation of the physical stimulus (ex. Fechner’s law)
Transduction
The stimulus is transduced into an electrical signal : the physical stimulus interacts with a specific receptor/transducer located on a peripheral sensory neuron and causes the neuron to fire
Action potential
Rapid, temporary electrical signal that travels along the membrane of a neuron or muscle cell.
Action potential occurs when there is enough ______ that get activated
Transducers
As you present a stimulus, the neuron will increase the frequency of its firing rate corresponding with the ______ of the stimulus.
Intensity
Once the physical intensity of the stimulus has been encoded into the _____ ____of a certain neuron, we can say that the physical stimulus has been transduced or encoded.
Firing rate
Following transduction, nerve impulses will travel along the axon of the sensory neuron and enter the …
Central nervous system (CNS)
Almost all sensory neurons have their cell bodies located in the periphery with their ____ projecting into the CNS, except the retina and optic nerve, which are considered part of the CNS.
Axon
For most of our senses, the sensory neurons are located in the head, and they enter the CNS through their respective pair of _____ nerves
Cranial
Cranial nerves can be either _____, _____, or both.
Sensory, motor
Tactile information coming from the body reaches the CNS through peripheral somatic nerves entering the …
Spinal cord in between each of our vertebra
Signal transmission from one neuron to another occurs at the ______.
Synapse
A synase is where the _____ ______ of a presynaptic neuron is close to the ______ of the postsynaptic neuron.
Axon terminal of presynaptic neuron, dendrite of postsynaptic neuron
When an _____ ______ reaches the end of a neuron (the presynaptic terminal), it triggers the release of neurotransmitters.
Action potential
The ________ bind to receptors on the postsynaptic neuron, causing changes in its membrane potential (excitation or inhibition)
neurotransmitters
Transmission
When there is excitation or inhibition of the postsynaptic neuron
If the signal is strong enough, it generates a new action potential in the postsynaptic neuron, continuing the ________.
Transmission
First relay in the brain for most senses
Thalamus
The thalamus is organized into different _____
nuclei
Main function of nuclei
Send information from the outside to the right part of the cortex
Modulation during transmission
The brain can increase or decrease the signal it is receiving from peripheral sensory neurons. The thalamus is a site of modulation.
Perception
When sensory signals reach the cortex
Primary sensory cortices
First place where sensory information is being relayed, where conscious perception emerges
3 sensory cortices
Primary visual cortex : occipital lobe
Audition : temporal lobe
Somatosensation : parietal lobe
Modulation during perception
Our perception can be influenced by expectations : for example the placebo effect happens at the cortical level
Stanley Smith Stevens
In proportion, how much more/less intense two stimuli of different intensities are perceived based on a standard number
Not all sensory modalities have the same logarithmic shape (speed of growth decreases with stimulus intensity), some have an ______ shape (speed of growth increases with stimulus intensity)
Exponential
Why do some stimuli have an exponential shape and others a logarithmic one ?
Some physical stimulus intensities matter more to us to perceive (e.g. small differences in stimulus intensity do not matter for low intensity pain because there is no risk of injury = exponential shape)
Stanley Smith Stevens exponential law version of Fechner’s law
ψ = kI^a
psy: subjective percept
I: stimulus intensity
a: controls the curvature of the function
k: corrects for the scaling of measurement units used for I
Meaning of a value in Stanley’s law
If a is higher than 1, the shape is logarithmic
If a=1, it will be linear (as if perceiving it directly)
If a is lower than 1, the shape is exponential
Magnitude ranking
Rating stimuli on a scale
Visual Analog Scale
For comparing stimuli within subjects
Cross Modality Matching
For comparing stimuli between subjects
Why did researchers at first find no difference between tasters and super-tasters ?
The upper boundary (sweetest taste ever tasted) is based on past experiences
- Even if super testers taste more sugar, there won’t be a difference because the sweetest thing they ever tasted would also be higher than for a normal taster.
Solution to the tasters/ super-tasters measure problem
People were asked to rate the sweetness of a coke based on a sound scale. For supertasters, the intensity of the taste compared to a train whistle, others a telephone.
General labeled magnitude scales GLMS
For between subjects comparison
- rescale for comparison to the worst pain experienced (differs across people), or scale with multiple sensory modalities can reduce between subject differences
Prothetic sensations
Sensory experiences that vary in intensity or magnitude, such as loudness, brightness, or weight. They are often measured on a continuous scale and are additive in nature.
Prothetic perceptions are thought to rely on additive processes whereby increased activity in sensory neurons produce parallel increases in …
Subjective perception of intensity
Metathetic sensations
Sensory experiences that vary in quality or kind, such as changes in pitch, color, or taste. They involve categorical or qualitative changes rather than variations in intensity.
Metathetic experiences seem to be associated with different patterns of activities across different sub-populations of ______.
Neurons
Difference Threshold
The smallest detectable difference between two stimuli that a person can perceive, also known as the just noticeable difference (JND).
Detection Threshold
The minimum intensity of a stimulus required for a person to perceive its presence.
True or false : there is no particular intensity at which we start perceiving all stimuli
True
Probabilistic detection threshold
Difference in stimulus intensity for which a difference is expected to be perceived 50% of the time (logistic regressionfunction to the data from the thresholding procedure)
Methods of constant stimuli
- 10 different stimuli
- 10 intensities
- Randomly present different intensities to avoid bias
- Accurate but long
Methods of limits – ascending/descending
- Ascending/descending cycles; start with high or low intensity and switch direction of intensity until the participant switches their answer.
- A bit less accurate, but faster (less data)
Staircase = start either very low or very high and go up/down until participant changes their answer, then alternate intensity for every answer (e.g. if participant says yes, switch stimulus for one with lower intensity)
Method of adjustment
- Let the participant increase/decrease intensity in order to identify the threshold
- Really fast
- Not very accurate
A perceptual rating is a ______ : there may be a difference between what we perceive and what we choose to report
Decision
Signal detection divides the ______ and the reporting
Perception
What changes in signal detection theory is not the ______ ______, but the subjective experience due to noise
Stimulus intensity
Signal
The true sensory information coming from the external world.
Noise
The various physiological or psychological processes influencing our perception of that external stimulus in an unpredictable manner
The detection threshold is probabilistic because of _____
Noise
Physiological source of noise
Spontaneous activity in our sensory nerves (even in no stimulus context, the neurons will discharge action potentials, creating noise/randomness in the nervous system)
Psychological sources of noise
Spontaneous fluctuations in attention that alter the perception of sensory stimuli in an unpredictable manner (e.g. expectations, fatigue)
From a statistical perspective, noise is …
Whatever is not measured and that contributes variability to participants’ responses.
True or false : once you control for a part of noise, that part is gone. But it is impossible to get rid of all the noise.
True
People that are more conservative will tend to withhold correct identifications until it is completely clear that they have perceived something. This will cause them to have ____lower/higher thresholds which could be erroneously interpreted as them having ____lower/higher sensory sensitivity.
Higher threshold, could be misinterpreted as lower sensory sensitivity
People that are more liberal will tend to wrongfully detect the presence of a sensory stimulus when there is none. . This will cause them to have ____lower/higher thresholds which could be erroneously interpreted as them having ____lower/higher sensory sensitivity.
Lower threshold, could be misinterpreted as higher sensory sensitivity
Sensitivity (d’)
An individual’s ability to distinguish between signal and noise, reflecting how well they can detect a target stimulus. Higher sensitivity indicates better discrimination.
Criterion
The decision threshold set by an individual in SDT, determining whether they report the presence of a signal. It reflects their response bias, influenced by factors like expectations or consequences of false alarms and misses.
False alarm
No signal but report perceiving it
Correct rejection
No signal and no reporting of signal
Hits and misses are _____ related.
Inversely (more misses = less hits ; more hits = less misses)
Correct rejections are inversely related with ____ _____
False alarms
In an SDT graph, the x and y axes are …
X : strength of felt sensation
Y : probability
In an SDT graph, the blue distribution is when…
There is no stimulus
In an SDT graph, the green distribution is when …
There is a stimulus
The area to the left of the criterion is when …
The participant does NOT report detecting the signal
The area to the right of the criterion is when …
The participant does report detecting the signal
The fact that there is an overlap between the two distributions means that…
Sometimes the presence or absence of a stimulus feels exactly the same, leading to false alarms (right) or misses (left)
Usually hits and correct rejections are associated with what levels of subjective perception ?
Hits : a medium-to-high subjective sensation
Correct rejections : a medium-to-low subjective sensation.
If you put your criterion at the complete left
Response to all trials will be yes = 100% hits but also 100% of false alarms (because will always say yes when it is not there)
If you put your criterion all the way to the right
Response will always be no. You will never perceive the stimulus even if it is there (100% misses and 100% correct rejections)
With a criterion in the middle, you have more ____ than _____
More hits than false alarms
In a ROC receiver operation characteristics curve, X and Y axes are …
X : probability of false alarm
Y : probability of a hit
This point in the ROC means perfect discrimination : all hits, no false alarms : criterion at the place with the most accuracy.
Top left corner
At d’ (sensitivity) =___ : same number of hits and false alarms due to picking at random
d = 0.05
Smaller sensitivity means the ROC curve will go more to the ____left/right, the curves will overlap more and discrimination will decrease
Right
d’ corresponds to the ratio of ____ and ____
Hits and false alarms. For example, 40% of hits and 20% of false alarms will fall on the ROC curve for d’ = 0.5
Meaning of d’ being on the left vs on the right of d’=0 (straight line)
On the left : stricter criterion where the participant was more likely to say that he/she didn’t perceive a stimulus (less hits, less false alarms)
On the right : more liberal criterion, more hits, more false alarms
The less the green and right distributions overlap, the ___less/more sensitivity
More
d’= ___ to maximize hits
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