perception

Question 1

Sensation

Answer 1

sensory processes detect (capture) information from the physical world and transform them into biological signals interpreted by the brain

Question 2

Perception

Answer 2

a 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 stimulus

private experience, hard to quantify (yellow, salty, heavy)

Question 3

Physical Stimuli

Answer 3

real and can be measured/quantified

Question 4

Methods used to study Sensation and Perception

Answer 4

Threshold - what is the minimum stimulus we can detect? (ex:faintest sound you can hear)

Scaling - measuring private experience (ex: rate your pain on a scale from 1-10, on how severe it is)

Signal Detection Theory - what factors influence your decision on if you saw something. Measuring difficult decisions - did you see a light, or was it your imagination?

Sensory Neuroscience - how are receptors activated, how do sensory receptors and nerves underlie our perceptual experience?

Neuroimaging - larger parts of the brain, what parts of the brain are activated during certain tasks?

Computational Methods - can we create models of sensory systems that adapt and learn, like humans?

Question 5

History of Neuroscience: Charles Darwin (1809-1882)

Answer 5

Theory of Evolution - suggested continuity in the structure and function of senses and nervous systems of model organisms and humans. Connects humans to animals, can study animals to learn about humans.

Question 6

History of Neuroscience: Johannes Müller (1801-1858)

Answer 6

Doctrine of Specific Nerve Energies - we are only aware of the activity in our nerves, and we cannot be directly aware of the world itself; it is most important which nerve is stimulated (not how). Everything we know about the world is related to our nervous system/specific nerves.

Question 7

History of Neuroscience: Hermann von Helmholtz (1821-1894):

Answer 7

first to effectively measure how fast neurons transmit their signals (ie: neurons obey normal rules of physics and chemistry). Measured AP conduction along neurons.

Question 8

History of Neuroscience: Santiago Ramón y Cajal (1852-1934):

Answer 8

made drawings of neurons and their connections - recreated what he saw in a microscope. Suggested neurons are discrete entities that do not actually touch one another (neuron doctrine)

Question 9

History of Neuroscience: Sir Charles Sherrington (1857-1952):

Answer 9

coined the term synapse. Nervous system is composed of individual neurons that communicate/connect

Question 10

History of Neuroscience: Otto Loewi (1873-1961):

Answer 10

discovered the 1st neurotransmitter (Ach), to prove that (most) neurons communicate using chemical, not electrical, signals. Communicate by releasing a substance that stimulates the next neuron

Question 11

History of Neuroscience: Sir Alan Hodgkin (1914-1998) and Sir Andrew Huxley (1917-2012):

Answer 11

discovered the ionic basis of resting potential and the AP (used squids)

Question 12

Transduction:

Answer 12

the first step in the sensory process. This is the conversion of external energy into an electrical signal (the receptor potential). Always mediated by opening/closing ion channels. (stimulus: light, odours, tastants, pain, heat, stretch, sound; will affect an ion channel - protein with a central pore that allows charged molecules to flow in and out - which changes membrane potential)

Question 13

Receptor Potential

Answer 13

a change in the membrane potential of the sensory receptor

Can depolarize cells to the action potential threshold

Can investigate what a neuron encodes by identifying the stimulus that gets a neuron to fire (the stimulus that allows the neuron to reach threshold) ex: some neurons in the visual cortex fire best to horizontal lines

Question 14

Synaptic transmission

Answer 14

sensory signals are relayed to other neurons this way.

Question 15

Neurotransmitter

Answer 15

chemical messenger packaged into vesicles; bind to specific receptors on postsynaptic cells

Question 16

Receptors

Answer 16

specialised proteins with high specificity for neurotransmitters. Their activation either directly or indirectly changes the membrane potential of the postsynaptic cell

Question 17

AP process

Answer 17

1. AP arrives at terminal
2. Depolarization opens voltage-gated Ca2+ channels
3. Ca2+ entry triggers vesicle furion and release of NT
4. NT diffuses across synaptic cleft and binds to receptors
5. Response in postsynaptic cell (usually includes changes in Na+, K+, Cl-, Ca2+ permeability)

Response terminated by removal of NT from cleft
6. broken down by enzymes
7. reuptake into presynaptic terminal, or by surrounding glial cells
8. Diffusion out of synaptic cleft

Question 18

Synaptic Potential

Answer 18

caused by the binding of neurotransmitter to postsynaptic receptors

Question 19

Principles of Sensory Coding (S.D.M.I acronym)

Answer 19

1. Stimulus Location: Topographical relationships are maintained from the sensory organ to the primary cortical site. Receptive field: each neuron in the cortical areas for touch or vision is stimulated only if a particular site on the corresponding sensory surface (skin or retina) is stimulated
2. Intensity: Absolute threshold is largely determined by minimum receptor potential. More intense stimulus → larger receptor potential → greater AP frequency (to a point)

3.Duration: Adaptation: continued exposure to a stimulus leads to a reduced awareness, often attributed to adaptation of sensory receptors

4.Modality: Sensory receptors are only sensitive a specific type of energy (recall Müller’s doctrine of specific nerve energies)

Question 20

Cerebral Cortex

Answer 20

destination for all sensory signals. All sensory outputs first arrive in the primary receiving area in the cerebral cortex.

Then, info is transmitted to other cortical areas (association areas)

Polysensory: info from more than one sense is combined
Operations that take place in the cortex ultimately produce perceptual experiences

Cortex: sheet-like arrays of neurons. Cerebral cortex is a thin layer of neural tissue that covers the entire cerebrum
Neocortex: 6 layers that the cortex is made up of (vs phylogenetically older paleocortex and archicortex (3 layers, e.g., hippocampus))

Question 21

Thalamus

Answer 21

large, paired structure. Composed of anatomically distinct nuclei. All sensory signals (except smell) travel via the thalamus en route to the cortex

Question 22

Brainstem

Answer 22

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

Spinal Cord: transmits sensory and motor info to and from the brain

Question 23

Cranial nerves

Answer 23

2 pairs of nerves that pass through openings in the skull
(ssmmbmbsbbmm)
(ooottafvgvah) Olfactory (I), Optic (II), Oculomotor (III), Trochlear (IV), Trigeminal (V), Abducens (VI), Facial (VII), Vestibulocochlear (VIII), Glossopharyngeal (IX), Vagus (X), Accessory (XI), and Hypoglossal (XII).

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

MOTOR: 3 cranial nerves are dedicated to muscles that move the eyes (III, IV, VI)

BOTH: remaining 6

Question 24

Methods to study nervous system:
Electrophysiological Recording:

Answer 24

Intracellular Recording (measure voltage changes across cell membrane. Compare voltage inside vs outside. Signal amplitude: 1-100mV)

Extracellular Recording (measure voltage changes solely outside the cell. Compare activity near the cell to activity at distant, inactive, place. Signal amplitude: 10-500mV)

Question 25

EEG: electroencephalography

Answer 25

(measures electrical activity through dozens of electrodes placed on the scalp. Different scalp electrodes record from different parts of the brain. Can locate populations of neurons that respond to a stimulus - ERP event related potential is the average activity resulting from many responses to the same stimulus, delays of ERP tell us something isn't working properly) Pros: less invasive, high temporal resolution (millisecond scale) Con: lower spatial resolution

Question 26

MEG: magnetoencephalography

Answer 26

(measures changes in tiny magnetic fields across populations of neurons in the brain. Magnetic field changes accompany small electrical changes during neuronal firing. MEG instrument - SQUID superconducting quantum interference device. MEG can localize populations of active neurons) Pros: better localise deeper brain activity, while EEG is closer to the surface. Cons: very expensive

Question 27

MRI magnetic resonance imaging

Answer 27

(patient placed in a large, powerful magnet that produces a strong magnetic field that influences how atoms spin. Aligns atoms (usually hydrogen) to that magnetic field. A radiofrequency current pulsed through the patient causes atoms to spin out of equilibrium. When the pulse is turned off, MRI sensors detect the energy released as atoms realign with the magnetic field. Tell us about water rich, soft (hydrogen) tissues. Get a snapshot of the brain from a living person, can reconstruct 3D images.) Pro: no radiation (less invasive than x-ray), high spatial resolution Cons: very costly, claustrophobic, loud, limits who can do it - kids

Question 28

fMRI functional MRI

Answer 28

(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), can record the functional information/ activity of the living brain) Pro: non invasive Cons: lower temporal resolution, response is slower

Question 29

PET positron emission tomography

Answer 29

(a small amount of tracer (2-deoxyglucose), biologically active radioactive material, is injected into a patient's bloodstream to get to the brain. Specialised cameras detect radiation emitted from brain regions using more of the tracer - metabolically active areas. More tracer = more activity) Pros: looks at structures deep in the brain, better for auditory tests ex.. Cons: lower spatial resolution, very invasive

Question 30

Mathematical Models:

Answer 30

mathematical language, concepts, equations to closely mimic psychology and neuronal processes w/mathematical prescission (ex: Hodgkin & Huxley’s model described how AP’s in neurons are initiated and propagated)

Question 31

Computational Models:

Answer 31

use mathematical language, equations to describe steps in physiological and/or neuronal processes - often implemented on computer

Question 32

Computational Models: Efficient Coding Models

Answer 32

Efficient coding = the brain tries to reduce redundancy and maximize information in the way it processes sensory input. Sensory systems adapt to their environments by focusing on the most useful information. They process predictable inputs by compressing/minimizing their representation while giving more attention to unexpected or less predictable inputs, which might be more important or informative. How computers compress/store data

Question 33

Computational Models: Bayesian (statistical) Models

Answer 33

The brain combines prior knowledge (what it already expects) with new sensory input to form a best guess about the world. assume earlier observations should bias expectations for future events - build a model of the world (sensory inputs). Predictive coding: models predict future events. If predictions dont match inputs, prediction error, the model is adjusted to improve future predictions

Question 34

Computational Models: Artificial Neural Networks

Answer 34

Made up of layers of highly interconnected computational units similar to neurons, linked by connections resembling axons, dendrites, and synapses. These connections strengthen or weaken with experience, mimicking the process of learning. Deep Neural Networks: many layers of units (nodes) w/millions of connections; very good at taking lots of info and classifying it into categories (ex: AI tech in google home or facial recognition software) number of nodes (depth) of a network distinguishes a single neural network from a deep learning model. Neural Network has: inputs, weights (how important is this input to the outcome), threshold (minimum output of a single node in order for data to be sent to the next layer), output Deep neural network at feed-forward and some can also be trained through feedback

Question 35

Gustav Fechner: Psychophysics

Answer 35

pioneered classical psychophysics. Father of experimental psychology. Psychophysics: study of quantitative relationships between physical stimuli and psychological experiences Relationship between Mind over Matter Function: mathematical description of how one variable is related to another; generally expressed as a formula

Question 36

Absolute threshold

Answer 36

minimum stimulus level required to be registered by the brain as a sensory event; where the function begins Subthreshold: below level of detection Suprathreshold: above level of detection

Question 37

How to measure thresholds? 3 ways

Answer 37

Method of Adjustment: adjust knob just so you can detect light (stimulus) Method of Limits: light keeps getting dimmer till you cant see it. Say yes if you detect, no if you can't. Threshold - average of last stimulus you can detect and first of which you can't detect. Method of Constant Stimuli: can't predict the next one, diff intensities are presented. Very random. Most accurately cause no order, not predictable. Better at detecting.

Question 38

Ideal Detector

Answer 38

always senses suprathreshold stimuli. Not typical psychophysics results. An ideal detector would always detect any stimulus above the threshold—perfectly, with no mistakes. ➡️ For example, if a sound is loud enough (suprathreshold), the ideal detector always hears it. In reality… : uncertainty around stimulus intensities near abs. threshold. Select a 50% response level as abs. threshold (arbitrary). S-shaped function or ogive. Why the variability around 50%?: cognitive factors (you may not be paying attention and miss it, may get bored), physical factors (variability in how computer shows images), biological system (some neurons fire more/less, membrane potentials wobble)

Question 39

Shape of Psychometric Function

Answer 39

Absolute threshold: starting point suprathreshold : slope slope changes with increasing intensity

Question 40

Difference threshold (or just noticeable difference, JND), ΔI (Ernst Weber):

Answer 40

How much does a stimulus need to change in order to produce a detectable change in perception? Ex; how much weight needs to be added for you to notice that weight was added (stimulus was changed)? Present subject with 2 stimuli and ask which one is heavier (i.e., greater stimulus “intensity”) → repeat (e.g., 50x) Calculate % of times the subject said the target was heavier than the reference 2 alternative forced choice: two stimuli are presented side by side and subjects must make a comparative judgment. MUST pick between “it’s heavier” or ”it’s lighter

Question 41

Perceptual Equivalence point:

Answer 41

we perceive the weights as the same, even though they aren't If we change the weight of the standard: Need a larger change in weight to detect a change at all. What happens to the functions as a result of increasing the standard light intensity? Curve gets flatter. Need to add more weight to notice a difference What happens to the difference threshold? Increases w/larger standard intensity

Question 42

Scaling

Answer 42

Stanley Smith Stevens (1930): proposed a new set of methods for studying perception. Began the era of modern psychophysics Believed that you could directly measure sensations (vs. Fechner’s indirect approach) Scaling: procedure to estimate the amount of something related to perception Magnitude estimation: scaling approach in which subjects provide direct ratings of their sensations Experiment: Subject assigns a number to the standard stimulus (modulus) and provides a relative numerical rating for other stimuli of varying intensities

Question 43

value of the power exponent (b)

Answer 43

specific exponent that related each sensory experience to a stimulus intensity. Nature of the relationship, or “power function”, is linear, increasing, or decreasing

Question 44

What determines the exponent in the power function: Sensory transducer theory:

Answer 44

transduction of a physical stimulus into a biological stimulus is the basis of the power law Note: for exponents >1, Fechner’s law does not hold, thus must use Stevens power law. (accelerating function, not logarithmic)

Question 45

Other scaling techniques: cross-modality matching

Answer 45

compare stimuli from one sensory modality to those of another sensory modality (relationships seem to be similar across individuals, with normal hearing and vision)

Question 46

SDT (signal Detection Theory)

Answer 46

how we make judgments on if stimulus is real or not Abs. threshold can very, and it depends on likelihood that signal>noise to produce a perceptible event SDT: takes nonsensory factors into account that can affect signal detection. It uses statistical concepts to consider cognitive factors that may influence decision-making. Accuses the decision depends on sensitivity of sensory system+judgment by subject Ex: On a mammogram, cancer appears as a fuzzy white region (= signal), there are other fuzzy regions of the mammogram not due to cancer (= noise) Ex: you’re in the shower, waiting for an important phone call. Water is making a constant sound (=noise), sound of the phone ringing (=signal)

Question 47

4 possible outcomes in SDT experiment

Answer 47

correct rejection (no noise, no response) false alarm (response to no noise) miss (noise but not response) hit (noise and response)

Question 48

ROC (receiver operating characteristic curve)

Answer 48

plots hits vs false alarms for signal of fixed intensity. Shows effects of different criterion effects in an SDT experiment Response bias: simply changing nonsensory factors can affect signal detection Provides estimate of relative sensitivities of different individuals (d’) - Can figure out by matching hit and false alarm rates to appropriate ROC curve - Increasing d’ increases separation between distributions and the likelihood of a hit Provides measure of how nonsensory factors may influence judgments (β)

Question 49

Do actual thresholds exist?

Answer 49

there is no fixed absolute threshold, thresholds change depending on situational factors. There is a range.