Final Exam - PSYCH 2E03

Perceptual process

1) environmental stimulus 2) light is reflected and transformed  3) receptor processes 4) neural processing 5) perception 6) recognition 7) action

Transduction

transformation of environmental energy into electrical energy by sensory receptors

Internal stimuli

hunger, oxygen levels, blood pressure, fatigue are all interceptors

Perception to action

Electrical signals are transformed into conscious awareness = recognition = involved motor activities (behavioural response)

Sensation

sensory processes detect (capture) informaiton from the physical world and transform them into biological signals

Perception

single unified awareness of a stimulus that in turn arises from the sensation produced by our sensory systems; gives meaning and/or purpose to the detected sensation

Afferent

towards CNS

Efferent

away from CNS

Transduction

conversion of external energy into an electrical signal, mediated by opening/closing ion channels

Ligand-gated channel

ligand ion/molecule binds, opens channel pore that allows specific ions to pass though

G-protein coupled receptor

ligand binds to GPCR, GPCR activates a G-protein, G-protein initiates a signal cascade that ultimately opens ion channels

Types of receptor cells (3)

Lignad-gated

G-protein coupled receptor

Stretch/pressure-gated

Stretch/pressure gated channel

deformation of the plasma membrane causes protein to change conformation, opening a channel pore that allows specific ions to pass

How do receptors create action potential?

Receptor allows influx of Na+, depolarizing cells to the action potential threshold

How does a signal pass form one neuron to the next?

synaptic transmission

Law of dynamic polarization

APs only transmit in one direction

Nuerotransmitter

chemical messenger packed into vesicles; bind to specific receptors on post synaptic cells

Receptor

specialized proteins with high specificity for neurotransmitters

activation changes membrane potential of post-synaptic cell

Step of synaptic transmission

1. AP arrives at terminal

2. Depolarization opens voltage-gated CA2+ channels

3. CA2+ entry triggers vesicle fusion

4. Neurotransmitters diffuse across synaptic cleft and binds to receptors

5. Response in postsynaptic cell (Usually included changes in Na, K, Cl, or Ca permeability)

How is synaptic transmission/response terminated?

removal of NT from cleft:

6. Broken down by enzymes

7. Re-uptake into presynaptic terminal or y surrounding glial cells

8. Diffusion out of synaptic cleft

Excitatory (membrane potential)

bring membrane potential above threshold = cause firing

Inhibitory (membrane potential)

bring membrane potential below threshold = inhibit firing

Peripheral vs central end of sensory neurons

peripheral axos gathers info, central axon is in spinal cord

Bipolar neuron

generally sensory

dendrite and axon

Pseudounipolar neuron

generally sensory

central and peripheral axon

Multipolar neuron

generally motor and interneurons

many dendrites emerge from cell body, one axon

Principles of sensory coding (4)

1. stimulus location

2. intensity

3. duration

4. modality

Principles of sensory coding - Stimulus location

Topographical relationships are maintained from the sensory organ to the primary cortical site

Principles of sensory coding - Intensity

• Absolute threshold is largely determined by minimum receptor potential

• More intense stimulus = larger receptor potential = greater AP frequency) to a point)

Receptive field

each neuron in the cortical areas for touch of vision is stimulated only if a particular site on the corresponding sensory surface (skin or retina) is stimulated

Adaptation

continued exposure to a stimulus leads to a reduced awareness, often attributed to adaptation of sensory receptors

Principles of sensory coding - modality

Sensory receptors are only sensitive to a specific type of energy (recall Muller’s doctrine of specific nerve energies)

E.g. different types of touch: pressure, pain, temperature

Coronal axis

splits front-back

Sagittal axis

splits left-right

transverse/horizontal axis

splits top-bottom

4 lobes of the brain (front to back)

frontal, temporal, parietal, occipital

Which lobe is the olfactory cortex in?

frontal lobe

Which lobe is the somatosensory cortex in?

parietal lobe

Which lobe is the audiotry cortex in?

temporal lobe

Which lobe is the visual cortex in?

occipital lobe

Gyri

crests of cortical tissues

Sulci

grooves dividing gyri

What is the first destinationfor all sensory inputs?

All sensory inputs first arrive at primary receiving area in the cerebral cortex, beofre being transmitted to association areas

Cerebral cortex

sheet-like array of neurons, covering the entire cerebrum in a thin layer of GREY MATTER

made of 6 layers

White matter

axon tracts and commissures (i.e. tracts that cross brain midline)

Nuclei (grey matter)

local accumulations of neurons that have roughly similar connections and functions

Thalamus

large paired structure composed of anatomically distinct nuclei

relay station where all sensory signals except smell travel en route to the cortex

Spinal cord

transmits sensory and motor information to and from the brain

Brainstem

Somatosensory, auditory and taste signals enter the brain via cranial nerves attached to the brainstem

Relays motor info from the brain

Which cranial nerves are dedicated to sensory info?

Cranial nerves I (olfactory), II (optic) and VIII (vestibulocochlear)

How many CN are motor vs sensory

3 motor

3 sensory

6 both

Ganglia

local accumulations of neurons and glia in the PNS

Spinal/peripheral nerves

bundles of peripheral axons ensheathed by glial cells

how many pairs of spinal nerves?

31 pairs

Electrophysiological recording

measure voltage change across cell membrane (inside vs outside) or near cell to distant, inactive place

intracellular can measure really small changes in electrical potentials

Extracellulars can only record bigger changes of action potential

Pro and cons of electrophysiological recording

very invasive - drilling into skull

only one neuron at a time

very high temporal and spatial resolution

Electroencephalography (EEG)

measures electrical activity through dozens of scalp electrodesl can roughly locate populations of neurons that respond to a stimulus

Event related potential (ERP)

The average EEG activity resulting from many responses ot the same stimulus

Pros and cons - EEG

Lower spatial resolution, not as much detail e.g. rough localization to a few millimeters

Pro: high temporal resolution, milliseconds

E.g. how activity flows through the brain over time

Pro: not invasive

Magnetoencephalography (MEG)

measures changes in tiny magnetic fields across populations of many neurons in the brain (since neuronal firing created electric flow and magnetic field); localize populations of active neurons

How to measure MEG?

superconducting quantum interference device (SQUID)

Pros and cons of MEG

• VERY costly, expensive device and dedicated, special room

• Slightly better spatial resolution, especially better for deeper structure because its not relying on scalp sensors; much better for deeper, subcortical structures

Magnetic resonance imaging (MRI)

magnet influences atom spin, sensors detect energy released as atoms realign to normal

tells us about water-rich (soft) tissues

Pros and cons of MRI

MRI is structural information, not activity

• Costly (compared to like an x-ray)

• Pro: doesn’t use radiation

• Better pictures of soft tissue vs x-ray

• Very uncomfortable: can’t move, claustrophobic, very loud; makes it hard to implement for many populations

• Because its loud, its hard to present auditory stimulus so it can’t be used for audition

Functional MRI (fMRI)

magnetic pulses pick up evidence of demand for more oxygen in the brain, creating a blood oxygen level-dependent (BOLD) signal;More active areas need more blood (oxygen)

Pros and cons of fMRI

• Low temporal resolution; because recording blood flow; neurons have to use up energy, then vascular system needs to supply more blood; so there is a delay

• Indirect measure; blood flow response to neuron activity

• Very helpful for subcortical structures

• non-invasive

Positron emission tomography (PET)

small amount of tracer (a biologically active, radioactive material) is injected into the patient’s bloodstream (2-deoxy-D-glucose, 2DG)

 Specialized camera detects the radiation emitted from brain regions using more of the tracer (i.e. metabolically active areas)

 E.g. type of glucose that the brain can use =where is it directed during various tasks

Pros and cons of PET

·        Poor spatial resolution

·        Can use auditory stimulus

·        Can look at deep structures

Efficient coding models

assume sensory systems become tuned to predictability in natural environments; compress redundant info and highlight less predictable bits

Bayesian models

assume earlier observations should bias expectations for future events; if predictions don’t match inputs, adjust model for future

Artificial neural networks

layers of heavily interconnected computational units (~neurson);

Strength of connections can increase or decrease with experience akin to learning

Includes AI, machine learning, neural networks, deep learning

Deep neural networks

have many ayers of units (nodes) with millions of connections; very good at taking lots of info and classifying it into categories

Psychophysics

the study of quantitative relationships between physical stimuli and psychological experiences

Why relate physical stimuli to perceptual experience using mathematical mdoels?

If we can quantify what the standard is, we can identify when people may be experiencing deviations (e.g. usually hear X sound, or see at X distance)

Why gap in stimulus intensity vs perceived sensation - why doesn’t it start at origin?

The gap represents the threshold; minimum value of stimulus before it is detected

Absolute threhsold

minimum stimulus level required to be registered by the brain as a sensory event

Methods to measure thresholds?

method of adjustment

method of limits

method of constant stimuli

What is the most accurate method to measure limits? Why?

method of constant stimuli, as participants can’t predict based on previous stimuli, so responses are more accurate

Psychometric function

in reality, there is uncertainty around stimulus intensities near absolute threhsold, so 50% response level taken as absolute threshold (arbitrary)

Why is there uncertainty around absolute threshold?

• Attention can vary; can be bored or locked in

• Physical factors: eg variability in physical stimulus on computer screen

• Biological systems aren’t perfect; many neurons have some baseline level of firing; how much increase before attributed to stimulus

Just noticable difference (detla I)

how much does a stimulus need to change to produce a detectable difference?

proportional to standard intensity - as target/standard increase, the difference must be larger to be perceivable

2 alternative forced choice task

two stimuli are presented side by side and subject MUST make a comparative judgment

if 50-50, they feel the same - perceptual equivalence point

75% of the time = JND

Weber’s law (for JND = I)

delta I = k * I

What sensory dimension is the most sensitive?

pitch - it has the smallest weber fraction, only needs 0.03% change to detect a difference

Weber-Fechner’s Law (Sensation = S)

S = k ~ log (I)

Magnitude estimation

subject provides relative ratings of sensations; discovered that relationship between stimulus and subject can be directly measured

Magnitude estimation and power law

S = a * I^b

a is a scaling constant and b is power exponent

What determines power exponent (b)?

most stimuli are logarithmic (b<1), like Weber-Fechner model

but some are linear (b=1) or exponential (b>1), like pain

Sensory transducer theory

the idea that transduction of the physical stimulus into a biological stimulus is the basis of the power law

Cross-modality matching

• compare stimuli from one sensory modality to stimuli of another sensory modality

• electric shock at different values; “turn up sound to match the intensity of the shock”

Signal detection theory

how people detect stimuli based on stimulus intensity and person’s physical and psychological state

threshold depends on likelihood that signal > noise to produce a eprceptual event

takes into account non-sensory factors that may influence decision-making process: sensitivity of system + judgement

Four possible outcomes in an SDT experiment

hit = correct

false alarm

miss

correct rejection

S+N distribution affected by…

signal intensity and detection sensitivity

detection sensitivity (d’)

sensitivity measure by relationship of hits to false alarms

can differ for 1 person with signal strenght

or within multiple people with diff sensitivities to same signal

Receiver operating characteristic (ROC)

plots false alarms vs hits; for a fixed d’, changing your criterion changes the patterns of hits and false alarms in predictable ways

Do absolute threshold exist? (ROC)

There is a range or threshold that shifts based on context and cognitive factors, not a fixed absolute threshold to which you respond consistency

What does ROC tell us?

1. provides estimate of relative sensitivities of different individuals (d’)

2. provides measure of how non-senosry facotrs may influence judgements (beta)

Meaning of Pr(S/n)

Probability of identifying a signal when there’s actually just noise

Can ROC curve ever have more false alarms than hits?

In order for false alarm to be bigger, the signal+noise needs to be less than the noise alone =doesn’t make sense =so no, curve should never fall below chance performance (except chance isn’t perfect)

Types of touch

tactile

pain

thermal

itchiness

pleasant touch

kinesthesia

balance/position/coordination = proprioception