PSYC 212

Can we measure perception?

Unless it is the one who is being affected, no.

What is the difference between perception and sensation?

Sensation is the process of capturing information and transforming it to be processed by the brain.

Perception is how we interpret that information.

What is the usefulness of a quantitative relationship between a stimulus and the perception?

Allows comparison with other stimuli.

Allows comparisons among individuals and species.

What is a cross modal comparison?

Checking for similarities between sensory models (ex. comparing warmth to loudness)

What are the three ways to function perception vs stimulus intensity?

Linear, exponential and logarithmic.

Linear: increase in physical intensity \= increase in perceived intensity; proportion is constant.

Exponential: perceived intensity changes slowly at low physical intensity, but at higher physical intensities, the perceived intensity rises much more drastically. Proportion/slope increases with physical intensity.

Logarithmic: Slope is large at the beginning such that perceived intensities can change dramatically with small changes in stimulus intensity. However this effect diminishes and after a certain point, the sensory system would no longer be responsive to additional stimulus.

How can we obtain a these relationships?

Ask human subjects to rate each perceived intensity.

Try and minimize the difference between each stimulus and ask when they can detect the difference.

What are two basic characteristics of a relationship between stimulus and perception?

Starting point and slope.

Why does each graph not start at 0?

Because we are incapable of sensing really low stimuli.

What is the point called where the intensity has to reach a certain minimum level to be detected?

Absolute threshold.

What are stimuli called when they are below this point?

Subthreshold; will not produce detectable sensation.

What is above the absolute threshold?

Suprathreshold region; where sensation takes place. This is a region, thus the slope of each point may be different and must be determined to figure out overall change.

What is a difference threshold?

How small a change in stimulus intensity that is required to produce a discriminable change in sensation.

What is Psychophysics?

Developed by Gustav Fechner; relationship between physical and perceptual qualities.

What is the Method of Adjustment?

Human subject is told to adjust the physical intensity of a stimulus until it is barely detectable. This can determine the absolute threshold.

What is the Method of Limits?

Preferred if speed is not an issue; provides more reliable estimates. Subject presented with a stimulus whose intensity is chosen from an ascending or descending series.

Ascending starts from subthreshold and is increased until perceived.

Descending starts at suprathreshold and decreased until no longer perceived.

Transition could provide evidence of difference thresholds, and end point could determine absolute threshold.

What is the similarities between the method of limits and method of adjustment?

Both allow the subject to have an idea of what the next stimulus will be like compared to the last one, which may make the information less accurate (they expect the next one to be quieter).

What is the method of Constant Stimuli?

Neither scientist nor subject knows the value of the next stimulus and the subject merely response whether a sensation is felt and a frequency chart is established based on responses (random intensities).

What is a step function?

When the question is essentially yes or no. At low levels of stimuli, consistent answer of no when asked if it is felt, and once it passes the absolute threshold, consistent answer of yes.

What is an ideal detector?

When all subthreshold intensities fail to produce a detectable event while all suprathreshold consistently produce a positive sensation.

What is an S-shaped function or ogive?

Non-ideal detectors; while we can detect the high intensities and can't detect the low intensities, the middle ones have some uncertainty.

As the intensity increases, there is a progressive increase in the likelihood that it will be detected. This psychometric function provides a typical profile of how our sensory system response as a function of physical intensity.

What are some factors that result in uncertainty?

The source cannot provide a perfect stimulus.

Our nervous system/sensory system is inherently noisy.

We have to judge if it was perceived, based on physical, emotional and cognitive factors.

How do we determine threshold in a non-ideal detector?

Use an arbitrary value (ex. 50% perceived is taken, so the stimulus that causes this will be threshold)

This means that thresholds change with people and it is no longer an all-or-none.

What are some thresholds of human senses?

Touch: dimpling of skin by 10^-5cm

Smell: 40 molecules

Hearing: 10^-10cm eardrum movement.

Vision: 54-148 photons

How can we determine difference threshold in non-ideal detectors?

Place colors/images in front of subject: ask to decide which is dimmer/brighter

At a certain brightness, the subject cannot decide if the image is brighter or dimmer, thus is considered perceptually equal to another image.

The little bit of extra stimulus that requires for a difference to be perceived is called a "just noticeable difference" (JND).

Difference between two intensities is dI

What are the types of difference thresholds?

Increment threshold: the increase in stimulus that would cause a difference in perception.

Decrement threshold: the decrease in stimulus that would cause a difference in perception.

If we change the reference stimulus, does the difference threshold change?

Yes; it increases in a linear fashion with stimulus intensity:

Weber's law:

dI \= kI

dI: difference threshold
k: proportion (Weber's fraction)
I: intensity

How do we determine k?

Experimentally determined; k is the slope of a plot between dI and I.

k can change dramatically in extreme situations at very high or low intensities, so Weber's law no longer applies.

What is Fechner's law?

Higher intensity of levels require a greater change in physical stimulus (dI) to produce identical changes in sensation (dS).

A JND occurs through identical changes in sensation from progressively greater changes in stimulus intensity.

dS is constant at all levels for a JND

What type of relationship is the stimulus-sensation function?

Logarithmic (because for an equal change in sensation, there must be progressively larger increases in stimulus intensity).

Thus:

S \= klog(I)

At low intensities, magnitude of our sensations change rapidly with small changes in stimulus intensity, but we become less sensitive at higher intensities.

What is modern psychophysics?

Developed by Stevens who rejected Fechner's psychophysics. A set of direct methods for studying sensation.

Exact relationship between stimulus and sensation could be directly obtained. Established a set of procedures that is known as scaling. Stevens asked his subjects to provide a direct rating of sensation experienced (magnitude estimation).

What is a modulus?

The standard stimulus that represents a certain value in modern psychophysics.

Then, subjects rate the other stimulus based on the modulus (like rating from 1-10).

What is the power law?

S \= (k)(I^b)

S is the sensation by the subject
I the physical intensity of the stimulus
k is the scaling constant that takes into account the units used to represent the stimulus intensity
b is the exponent value.

According to this relationship, sensation is related to intensity raised to a certain power. But there is no general exponent; different sensory experiences are related to stimulus intensity by a particular exponent (ex. taste, sight, touch, etc vary in exponent, as well as subsections like salty, bitter, etc).

What does the power law say about brightness and loudness?

Brightness perception grows rapidly at first with increasing light intensity, though further increments will gradually reduce the rate at which perceived brightness increases. (b \= 0.33)

Loudness perception is related to sound intensity by a negatively accelerating function (b \= 0.67)

What is implied about the power law?

Reflects the sensory system at their lower levels, thus the interface where physical stimulus becomes converted into biological signal. The exponent is determined by the nature of transformation at this site.

What is the sensory transducer theory?

Psychophysical magnitude functions are not only related to low-level transformation processes but also at the highest levels of the mind where judgments are made on mental impressions.

The exponent can be affected by judgments.

What is intramodal matching?

Demonstrated how sensitive a particular sensory system is to diverse kinds of stimulation.

What is cross-modality matching?

Subjects are asked to compare stimuli from one sensory modality to those of another (ex. loudness vs brightness).

The equal sensation function shows different slopes depending upon the power function for the sensory parameter that was being compared.

ex. Electric shock shows a steep relationship for cross-modal matching with loudness, implying that small changes in electric current requires large changes in sound setting for a judgement in equality.

What is the difference between prothetic and metathetic sensations?

Prothetic: when subjects can judge it by "how much".

Metathetic: when the sensory experience changes entirely (ex. colors. There isn't a 10 red, or 1 red).

Which follows the power law?

Prothetic processes.

How does prothetic processes differ from metathetic processes?

Prothetic is additive; additional neurons activated for more sensation.

Metathetic is different neuons activated, which changes in quality

What is the method of triads?

For metathetic perception: subjects are presented with 3 options and asked to figure out which is more similar. Thus a similarity map can be created.

What is multi-dimensional scaling?

Psychological similarity represented by physical distance in a spatial map.

What are nonsensory variables?

Complex aspects that are not directly sensory (ex. value of art, seriousness of crime). Intramodal and cross-modality matching may also be applied to nonsensory variables.

What is discrimination scaling?

Each increment in discrimination, measured as a JND, produces equivalent increases in subjective impression; the variability in psychological units is constant along a linear psychological continuum.

What is ratio scaling?

Psychophysical power functions are based on the notion that equal unit of discrimination along the stimulus continuum does not represent equal distances, but equal ratios along the subjective continuum.

What is Ekman's law?

Ekman proposed that detectable changes in sensation (JND) rather than being constant at all levels were actually related to sensation in a linear manner. In other words, the relationship between changes in sensation that are just detectable at a particular at a particular sensation level is analogous to Weber's law:

dS \= kS

What affects the threshold?

Noise (internal or external). The signal must exceed the noise and cross threshold to cause a sensation.

What is signal detection theory?

Uses statistical concepts that take into account cognitive factors that may influence a subject's decision-making process.

Relies on the sensitivity of the sensory system, but also the decision of the subject to whether the signal is worthy of being considered as happening.

What are the basic foundations to SDT?

Sensation magnitudes evoked by noise (N) and signal + noise (S + N). Thus the distribution of sensation magnitude of S + N is always to the right of N (because subject always reads signal with background of noise).

What issues arise with weak stimulus?

Distributions overlap because noise could be loud enough to be mistaken as a signal.

What are the two possibilities with detecting noise?

Recognizing the noise: correct rejection

Mistake noise for signal: false alarm.

What are the two possibilities with detecting a signal?

Subject recognized signal: hit

Subject could not recognize signal: miss

What is a criterion?

Certain value of sensory magnitude is chosen as a cut-off point that in turns, governs the response.

If the trial evoked a sensation that is greater than the criterion, then the response is yes.

If it fails to pass the criterion, the response is no.

How does criterion help with detection?

By adding a criterion, the overlap of the noise and signal + noise becomes less impactful.

If the detected sensation is above the criterion, there is a higher probability the signal is a hit, than a miss because there are more signals above the criterion than there is just noise.

What can affect the criterion?

Subject opinion: ex. if the subject does not expect a lot of signals, they move the criterion to the right (make it more conservative), meaning the signal must be fairly obvious to be considered as "yes, a response must be made". On the other hand, if the probability of stimulus appearing is higher, than the criterion is reduced.

What is a receiver operating characteristic curve (ROC)?

Plots the probability of a false alarm vs the probability of a hit. Each point on the curve is specified by the subject's criterion because it determines relative value of hits and false alarms.

A higher criterion will be further down the curve because there is very little probability of false alarms, but also a low probability of hits (because cutting off most signals with criterion.)

What affects criterion?

Motivation: If there is no punishment for getting a false alarm, then just make a really low criterion.

What is a response bias?

Response based on motivation and stimulus expectancy; which poses a problem with threshold.

What occurs when signal gets progressively larger?

Distance between curves of noise and signal + noise gets larger and larger (d'). d' is the separation between the two distribution peaks.

A larger d' value is taken to represent an individual with a high detection sensitivity. A less sensitive the subject is to the stimulus, the closer the two distributions.

What is the important of d'?

Provides a numerical estimate of a person's sensitivity and therefore allows comparisons among different individuals.

Unlike threshold, which can change with criterion, d' is generally stagnant.

What is two-alternative forced choice (2AFC)?

Two presentations: 1 with signal, 1 without signal. The impact of criterion is reduced because one is guaranteed to have a signal. The proportion of correct responses can then be used as a measure of sensitivity because nonsensory factors do no affect the hit rate.

What is a staircase procedure?

Stimulus level varied in relation to subject's response. If the subject keeps guessing wrong, stimulus increases, or if the subject keeps guessing right, stimulus decreases. The changes continue until a specific number of response reversals take place. This signal intensity can be used as a measure of sensitivity.

What are the two views of the brain?

1. Heterogenous collection of functionally specialized structures

2. Homogenous organ in which various functions of the mind are diffuse and synergistic.

What is phrenology?

Behavioural characteristics could be assessed by external landmarks on the skull; individuals blessed with large measure of attribute, that part of the brain is well developed.

What was the result of brain lesion studies?

Conclusion that there was no localization of function, and injury to any one part of the brain affects all higher functions equally rather than selectively.

What is aphasia?

The loss of the ability to speak; Broca's area damaged: responsible for the production of speech (articulation).

What is Wernicke's area responsible for?

Comprehension; also produced aphasia; could articulate properly but spoke gibberish.

What is functional anatomy?

The study of how the brain is organized to carry out various functions.

What is parallelism?

A large number of mental functions are simultaneously processed along two or more pathways, each having their own set of dedicated anatomical modules.

Prominent in visual, auditory and somatosensory system.

However, parallelism arises early into sensory processing, and once in cortex, there are multiple pathways.

What is lateralization?

The functional difference between two hemispheres in cerebral.

What is the composition of the brain?

White matter inside, grey matter outside.

What are some important, interior portions of the cerebral hemisphere?

Large tracts of grey matter; hippocampal formation, amygdala and basal ganglia

Important for memory, emotion and movement control.

Where do all sensory inputs first arrive?

Primary cortical area: primary auditory cortex in temporal lobe, primary visual cortex in occipital, etc.

What are the convolutions of the cerebral cortex?

Grooves: sulcus

Elevated regions: gyrus

What is cytoarchitectonics?

Discrete areas of cortex had a common cytoarchitectonics appearance that could be distinguished from neighbouring regions.

What is a subcortical structure?

Collection of brain cells that reside below the cerebral cortex. Given title of nucleus (ex. Thalamus, which has extensive connections with the cortex and is composed of a set of anatomically distinct nuclei, each serving different functions in the transmission of sensory and motor information to and from the cortex).

What are the three brain stem areas?

Midbrain, pons and medulla. Cranial nerves allow signal transmission and brain stem also contains networks of fibre pathway that carry sensory and motor signals to and from the brain.

How many spinal nerves are there?

31 pairs.

What is the law of specific nerve energies?

Sensory signals from each modality are trasmitted by a specific set of nerve fibers (mechanical (touch), chemical (taste and smell), sound (auditory), and light (visual))

Where is the somatotopic map located?

Behind the central gyrus.

What is the representation of the somatotopic map?

Brain allocates larger amounts of cortical tissue to certain parts of the body that have greater sensitivity to touch.

What is the neuron doctrine?

The unification of nerve fibers and nerve cells into a single anatomical unit.

What is the law of dynamic polarization?

Unidirectional nature of information.

What is the law of connectional specificity?

Each neuron is a specific entity and there is no physical continuity between one neuron and the next.

What is the difference between bipolar and multipolar neurons?

Bipolar only has 1 dendrite, multipolar has many dendrites (most common).

What are the 3 types of neurons?

Sensory neurons: triggered by stimulus from environment and send to brain.

Interneurons: Process the signals locally within a particular module or transmit to other brain sites. This makes up the largest number in the cerebral cortex.

Motor (efferent) neurons: Carry signal to various muscles in the body so coordinated motor action can be taken in response to sensory information.

What are glia?

AKA neuroglia, also in the brain and outnumber neurons but have no function in signal processing. For example, myelin, astrocytes (gives structural support and firmness, and maintains environment; toxin free), oligodendrites (form myelin sheath in CNS by wrapping around with cell body), Schwann cells (forms myelin sheath by production).

Only axons are myelinated.

What is transduction?

When specialized receptor neurons transform the energy in a physical stimulus into a neural signal; this creates a depolarizing signal or receptor potential.

How do we distinguish between feelings at different locations in the body?

Different axonal fibers that conduct messages from different parts of the body; a separation that is maintained at the thalamus and cortex.

Each neuron in the cortical areas for touch or vision is stimulated only if a particular site on the sensory surface is stimulated; a receptive field.

What is adaptation?

Continued stimulus to the point of ignoring the stimulus.

What is the labelled-line principle?

The idea that because specific modalities are perceived differently due to the specific set of connections made to ultimately stimulate our cerebral cortex.

What is electrophysiology?

Probe the activity of one or a few neurons at a time and use that information to decipher local processing at the cortical site or record the summated activity of large clusters of neurons using techniques that sample electrical changes over a larger part of the brain.

What is single-unit recording?

A single electrode placed in the neighborhood of the neuron to detect the change in ionic environment brought about by the neural activity.

What is electroencephalography?

Uses electrodes attached to the scalp, which picks up changes in potentials that occur when a stimulus is applied or cognitive task is initiated. The voltage fluctuations may be caused from summated synaptic potentials in the cell body and dendrites of an ensemble of neurons.

What is event-related potential (ERP)?

The electrical responses that are tied to a particular sensory stimulus or behavioral output.

What are the advantages and disadvantages of EEG?

Advantages: non-invasive and offers excellent temporal resolution

Disadvantage: offers poor spatial resolution; the localization of electrical activity in the cortex can only be done in the broadest sense; limits its use when more precise function localization is required.

What is functional brain imaging?

Basis is that neuronal activity increases the local amount of blood.

What is fMRI?

Resonance and relaxation depends on local molecular environment. The magnetic qualities of hemoglobin that is deprived of oxygen is different from when oxygen is present. Thus when there is more oxygenated blood during activity, the magnetic resonance increases and blood flow can be imaged.

What is positron emission tomography?

PET is non-invasive in vivo functional imaging technique. PET uses probes tagged with special radioactive element that decays with time and releases highly energetic anti-electron particles (positrons). The positrons get annihilated when they come in contact with electrons in neighboring atoms, which releases gamma rays. This can be then detected and form an image of the brain. This can pick up hot-spots of activity in the brain as there is an increase in blood flow.

What is optical imaging?

Use voltage-sensitive dyes; change fluorescence properties in response to membrane depolarization. This way, fluorescence change was monitored during activity.