Principles of Sensation

Question 1

What are the 3 fundamental steps of information processing?

Answer 1

1. transduction
2. transmission
3. perception

Question 2

Which is the conscious process: perception or sensation?

Answer 2

perception

Question 3

What is transduction?

Answer 3

It’s a multistep process where stimulus energy (electromagnetic, mechanical or chemical) is converted into electrical potentials that can be interpreted by the nervous system

Question 4

What is a receptor potential?

What needs to happen for it to fire?

Answer 4

It’s a graded response to a stimulus that can be depolarizing or hyperpolarizing, OR BOTH.

They have a threshold in stimulus amplitude that must be reached before they’ll fire

Question 5

What will happen to the receptor potentials when the stimuli is particularly intense?

Answer 5

Their amplitude will saturate

Question 6

What is a receptive field, and how is it defined anatomically?

Answer 6

FOr each receptor cell there is a small aprt of the world it encodes for - it’s the spatial region where a stimulus will produce a response

anatomically it’s defined by the dendrites to the receptor cells

NOTE: receptive fields can overlap = redundancy

Question 7

What makes up a sensory unit?

Answer 7

the primary afferent and any receptors that define its receptive field

Question 8

How can a receptor encode stimulus modality?

Answer 8

By responding to one form of energy more than any other

and

individual receptors responsing only to a narrow range of that energy

Question 9

The type of energy that a receptor responds to under normal conditions is called the ____, while an ____ is of a different typ eof energy that will cause the receptor to respond only if intense enough.

Answer 9

adequate stimulus (light for vision)

inadequate stimulus (pressure for vision)

Question 10

What theory explains why an inadequate stimulus is perceived as the adequate stimulus?

Answer 10

THe labelled line theory

We learn and “map” sensations in a way that our brain will perceive pressure on the eye as light because that’s the signal that is usually transmitted by that pathway

Question 11

What are the 3 main type sof energy humans can detect?

Answer 11

electromagnetic: light and thermal
mechanical: sound, gravity, head movement, tough, pressure, blood pressure
chemical: tastants, odorants, physiological modulators like O2 concentration

Question 12

How is stimulus intensity encoded - two ways…

Answer 12

1. frequency coding - firing rate of sensory neurons increases with increased intensity
2. population coding - nuber of primary afferents responding increases through recruitment with increased intensity

Question 13

If threshold is the minimal intensity ot produce a response and saturation is the maximal response, what is the difference between threshold and saturation?

Answer 13

dynamic range

Question 14

Describe recruitment in more detail…

Answer 14

THis goes back to the idea of receptive fields overlapping…

1 neuron at the center of the field responds “best” because it has the lowest threshold for the stimulus and it will respond first

the adjacent neurons within the receptive field will respond next - they have a higher threshold for the stimulus

the more intense the stimulus, the more neurons will be recruited and via population coding, the brain will register this increase in intensity

Question 15

What is adaptation and what is the difference between tonic adaptation and phasic adaptation?

Answer 15

Adaptation is the process by which the response of a receptor to a CONSTANT stimulus DECLINES over time

slow adaptation = tonic

rapid adaptation = phasic

Question 16

Do all of our senses undergo adaptation?

Answer 16

The vast majority do, but out sensation of gravity does not

Question 17

What is acuity?

Answer 17

the ability to localize a stimulus

Question 18

What are the two things that determine acuity?

Answer 18

receptive field size = smaller field size - greater acuity

Receptor density = more receptors - greater acuity

Question 19

What is the inherent paradox between intensity coding and acuity?

How is it solved?

Answer 19

the higher the intensity, the more neurons are recruited, the harder it should be to localize (in theory)

We solve this thorugh lateral inhibition

Question 20

Describe lateral inhibition

Answer 20

It’s a process that occurs IN THE CNS

Recruitment occurs in the PNS

the central axon sends out collaterals by inhibitory interneurons

As the action potential travels up the axon, the adjacent neurons are shut off and the difference in the action potential betin generated by the central neuron compared to the adjacent neurons becomes more pronounced

this preserves the fact that the center of the stimulus is generating excitation

ultimatley this depends on second order neurons