Psychophysics Neuroscience

How do we measure sensation/perception

Thresholds

Scales

Signal Detection

Cellular/Neuronal Neuroscience

Systems Neuroscience

Systems Neuroscience

Psychophysics

The science of defining quantitative relationships between physical and psychological event

Can control the physical stimuli and then measure how a person responds

Extension from the philosophical ideal of Dualism

Invented by Gustav Fechner

Dualism

The mind exists separately from the material world and thus is not a pure representation of it

Gustav Fechner

1801-1887

Initially damaged his eyesight by staring at the sun doing vision research

Led to one of the earliest experimental psychology fields

Showed that the mind can be studied and quantified

Thresholds

Generally the minimum difference between stimuli (or between a stimulus and baseline) needed to be detected as different

A quantifiable measurement of our perceptual abilities

Two Point Threshold

Within the realm of touch

The minimum distance at which two separate sensations can be distinguished

Just noticeable difference (JND)

The smallest detectable difference between 2 stimuli, or the minimum change in a stimulus that can be correctly judged as different from a reference stimulus

i.e: difference threshold

Absolute threshold

Minimum amount of stimulation necessary for a person to detect a stimulus 50% of the time

Weber’s Law

The principle describing the relationship between stimulus and resulting sensation that says the JND is a constant fraction of the comparison stimulus

Larger stimulus values have larger JNDs and smaller stimulus values have smaller JNDs

Thus, larger amounts of a stimulus in the environment require larger changes for a JND, and in turn smaller stimulus values have smaller JND

“proportional” relationship

Fechner’s Law

A formalized version of Weber’s Law

A principle describing the relationship between stimulus magnitude and resulting sensation magnitude such that the magnitude of subjective sensation increases proportionally to the logarithm of the stimulus intensity

“logarithmic” relationship

Method of constant stimuli

Test many stimuli, one at a time, across a range including barely perceptible to always perceptible

There is no such thing as “perfect conditions” so it is the point at which you detect it 50% of the time

Method of Limits

Vary the magnitude of a stimulus (or difference between two) until participant notices

Scientist adjusts the magnitude change

Method of Adjustments

Let participant adjust a stimulus until it matches a target (e.g. color matching)

Participant adjusts the magnitude change

Scaling Methods

Measuring the “strength” of your sensation, rather than threshold of detection

Not all sensations have the same scale, or strength

Can measure this with magnitude estimation

• give participants a sensation and have them rate its strength

• Can do freeform, or give a starting baseline

Sensations have different scales

Stevens’s Power Law

S=aI^b

S = sensation

I = intensity of stimulus

b = exponent tied to stimulus type

a = constant adjusted to put different scales on the same axis

Fechner’s vs Stevens’ “Laws”

Fechner’s is logarithmic whereas Stevens’ is power

Both make broad assumptions about the “fit” of data to their metrics and about the scales they work on

Both are only approximations of data and turn out to not really be “laws”

Both show:

• People’s internal perception can be modeled

• Sensation is proportional to other parameters

Signal Detection Theory (SDT)

Our ability to detect a signal amongst noise

Accounts for the amount of noise, the discriminability of the signal, and biases in the person’s response patterns

Important to know the signal strength, noise, and criterion, and how they shift

Sensitivity in Signal Detection Theory

How discriminable the target is from the noise can shift results

Criterion in Signal Detection Theory

The decision threshold

Can be shifted be the subject

Receiver Operating Characteristic (ROC) Curves

Model of SDT data

Demonstrate both the sensitivity and criterion in one line

With greater sensitivity, curve moves closer to top left corner

Transductions

The translation process that all sensory organ due when they take physical stimuli and convert them to electrical/biochemical signals in our nervous system

The way is occurs is unique to each system, but has same basic tenets

The signal become part of our nervous system’s communication, and then relies on the building blocks of nervous system, neurons and nerves

What makes up the neuron

Axon terminals

Axon

Dendrites

Nucleus

Cell Body

Synapse

The space between 2 neurons

Neuronal Communication - Chemical

Neurons generally transmit signals via neurotransmitters at the synapse

Pre-synaptic neuron releases neurotransmitters into the synapse

Post-synaptic neuron has receptors that are then activated by neurotransmitters

Neurotransmission cues, and is cued by electrochemical action potentials

Neuronal Communication - Electrical

Cells polarized in resting state

When AP threshold reached, depolarization occurs down the axon

Neurotransmitters trigger an electrical shift in the post-synaptic neuron, leading to the neuron “firing” an action potential

Neurons fire in an all-or-none fashion for each action potential, or “spike”

The number of spikes per second indicates how excited the neuron is

Each action potential starts near the cell body of a neuron and propagates down the axon towards the axon terminal

Electrochemical process involves Na+ & K+ ions moving in/out of the neuron

Entire populations of neurons work in concert to process information

Cellular Neuroscience

Neurons themselves still follow the laws of physics

Neuronal signals often compete

• Can have excitatory and inhibitory signals

Can research how particular cells function, how they’re organized, what neurotransmitters are involved in particular types of communication, and much more

Nerves

Generally bundles of neurons, typically that extend into the peripheral nervous system

12 Cranial Nerves

Nerves that connect the brain stem to various organs/muscles

Some send information to the brain (afferent; sensory) and some send information from the brain (efferent; motor) and some do a bit of both

Afferent nerves

Sensory

Send information to the brain

Efferent nerves

Motor

Send information from the brain

Sensory Cortices

Just as there are different nerves related to different senses, so too are there different parts of the brain that process that information

But this does not mean they never interact

Other regions integrate information between senses

Electroencephalography (EEG)

B placing electrodes on your scalp, we can directly measure the electrical activity generated by neuronal firing, only we’re measuring the firing of large populations of neurons

Can assess Event-Related Potentials (ERP), which are the change in EEG signal as a result of an event, such as a sensation

Need many trials of the event to average across, as the signal is noisy

Excellent temporal resolution (millisecond range), poor spatial resolution

Magnetic Resonance Imaging - Structural

Uses shifts in powerful magnetic fields to asses the atomic structure of tissue

No X-Ray radiation like a CT scan

But magnet dangerous if metals brought in

Magnetic Resonance Imaging - Functional

When neurons fire more, they require more oxygen

fMRI tracks the Blood Oxygen Level Dependent (BOLD) signal, which is the ratio of oxygenated to deoxygenated hemoglobin that shifts in response to neuronal activity
This is an indirect measure of brain activity

Can measure increases and decreases in response to a sensation

Also requires a large # of trials to average

Excellent spatial resolution (millisecond range), poor temporal resolution (1-2s period)

Positron Emission Topography (PET)

Similar resolution to fMRI but based on metabolism of brain cells (requires injection but can track particular neurotransmitters)

Magnetoencephalography (MEG)

Sort of between EEG and fMRI, that measures changes in magnetic activity across populations of many neurons in the brain

Good temporal resolution, and good spatial resolution for at least the surface of the brain

Velma is searching for clues with Scooby and the Gang, when she, as always, breaks her glasses. According to signal detection theory, what MUST have changed with regards to her vision by losing access to her glasses?

A) Her criterion becomes more lax, and she is more likely to accept stimuli as real even if they are not.

B) Her criterion becomes more strict, and she is less likely to accept stimuli as real, even if they really are.

C) Her sensitivity increases, as she is more able to distinguish between signal and noise

D) Her sensitivity decreases, as she is less able to distinguish between signal and noise

D) Her sensitivity decreases, as she is less able to distinguish between signal and noise

Bjorn is expecting a phone call. After repeatedly accidentally checking his phone, he has started using a stricter criterion, wanting to avoid false alarms. Which of the following statements reflects what may also happen now that he has a stricter criterion?

A) He is more likely to false alarm to noise, accepting as signal.

B) He is less likely to detect a real call, missing it as noise.

C) He is more likely to detect a real call, discriminating it from noise.

D) He is less likely to correctly reject noise, mistaking it as a phone call.

B) He is less likely to detect a real call, missing it as noise.

Which statement is true about EEG:

A) It is a direct measure that has good spatial resolution

B) It is an indirect measure that has good spatial resolution

C) It is a direct measure that has good temporal resolution

D) It is an indirect measure that has good temporal resolution

C) It is a direct measure that has good temporal resolution