From neurons to psychophysics

Question 1

What type of potentials are receptor potentials:

Answer 1

Receptor potentials are examples of graded potentials

Question 2

Describe generation of receptor potentials:

Answer 2

Generated by selective opening of ion channels causing an ionic current to flow across the membrane

Exception: vertebrate photoreceptor RPs are generated by selective closing of ion channels

Question 3

What is receptor potential limited by:

Answer 3

By the reversal potential of the ionic current that generates it (reversal potential is typically near 0 mV)

Point at which the direction of net current flow reverses is called the reversal potential

The same as the equilibrium potential in a single ion system

Question 4

Define the rate of net current flow of an ion:

Answer 4

Rate of net current flow for a particular ion is proportional to the difference between the membrane potential and the equilibrium potential for that ion

Rate of net current flow = k(Vm-Eion)

Question 5

Describe the link between range and sensitivity:

Answer 5

Large dynamic range comes at cost of less sensitivity to intensity differences

Question 6

Describe how to measure sensation and perception:

Answer 6

First step is to separately conceptualize physical stimulus and associated sensation

Two methods:

• Thresholds: measuring limits of sensitivity
• Scaling: ordering stimuli along a perceptual dimension

Question 7

Describe the units used for intensity in measuring sensation and perception:

Answer 7

Physical intensity: power per unit area

SI unit: Watts per square meter. In principle many physical stimuli can be expressed as such (light intensity, sound intensity, etc.)

In practice other measures may be more convenient

Question 8

Describe the use of psychophysical thresholds in measuring sensation and perception:

Answer 8

Absolute threshold: weakest stimulus intensity

Difference threshold: smallest difference between two stimuli that an observer can discriminate (also called difference limen, or just-noticeable difference, JND).

Question 9

Describe the limitation of response bias and how to overcome this:

Answer 9

Near threshold, stimulus is difficult to detect

Yes/no – observers may be more or less conservative in deciding

Two-alternative forced choice (2AFC) can get round this

(2AFC) is a method for measuring the sensitivity of someone to some particular sensory input, stimulus, through that observer’s pattern of choices and response times to two versions of the sensory input

Question 10

Describe the calculation used for difference threshold:

Answer 10

What is the smallest change in stimulus intensity that leads to a change in sensation (just-noticeable difference, jnd)?

Weber’s law: jnd is a proportional, not an absolute amount

If i is stimulus intensity and ∆i is jnd

∆i / i = C where C is a constant

Question 11

Define psychophysical correlation:

Answer 11

Identifying specific patterns of neural activity and correlate with specific sensations and perceptions

Question 12

Describe the aim and method of microneurography in humans:

Answer 12

Aim = visualize and record the normal traffic of nerve impulses that are conducted in peripheral nerves of waking human subjects

Fine tungsten needle electrode is inserted into the nerve

And connected to a high gain recording amplifier

Position of electrode tip within the nerve is adjusted in minute steps

Until electrode discriminates impulses of the neural system of interest

Subjects are fully awake and able to cooperate in tests requiring mental attention

While impulses in a representative nerve fiber or set of nerve fibers are recorded