MT1 perception- neurons and neural codes

Question 1

STRENGTHS OF GRADED POTENTIALS

Answer 1

Instantaneous, omnidirectional, infinitely graded

Question 2

WEAKNESSES OF GRADED POTENTIALS

Answer 2

VERY short range, ambiguous

Question 3

STRENGHTS OF APs

Answer 3

Unidirectional (NMJ), long range

Question 4

WEAKNESSES OF APs

Answer 4

Fixed amplitude so can’t encode value of stimulus by voltage, limited rate, slower

Question 5

What proposes each sensory nerve gives rise to its own characteristic sensation regardless of how its stimulated

Answer 5

Muller’s Law of Specific Nerve Energies (1835)

Question 6

Who mapped functions/sensations onto the cortex

Answer 6

Penfield and Rasmussen (1950)

Question 7

Who extended the doctrine of law of specific nerve energies

Answer 7

V Helmholtz (1963)- each fibre in the auditory nerve was specific to a particular pitch, yet nature of neural excitation was the same

Question 8

Who proposed the simplistic nature of doctrine of specific nerve energeis

Answer 8

Muller himself (1938)

Question 9

ADVATNAGES OF FREQUENCY CODING

Answer 9

Cheap, log coding allows a wider range of stimulus values to be encoded

Question 10

WEAKNESSES OF FREQUENCY CODING

Answer 10

Limited firing rate limits range, takes time to decode reliably, opposite case in photoreceptors

Question 11

Study providing evidence for frequency coding from frog muscle

Answer 11

Adrian and Zotterman (1925)- increasing the weight suspended from a thread attached to a frog muscle containing a single stretch receptor caused more frequent nerve impulses

Question 12

Who did the Limulus study

Answer 12

Hartline and Graham (1932)- showed logarithmic coding initially, then power coding

Question 13

Evidence for log coding in taste

Answer 13

Sato (1971)- at first, firing of a taste fibre of a rat was related to the log of the conc of the salt solution, then after 5 seconds the relationship followed a power function

Question 14

Evidence of the latency of respnose in monkey neurons in AIT

Answer 14

Desimone et al (1984)- latency was 80-100ms

Question 15

Steve Carrell neuron

Answer 15

Quiroga et al (2008)- steve carrell neuron

Question 16

Evidence for sparse coding

Answer 16

Olhausen and Field (2004)- there is evidence the code for representing objects in visual system and tones in auditory system involves a pattern of activity across a small no of neurons

Question 17

STRENGTHS OF PLACE CODING

Answer 17

Unlimited (well) range, faster to decode

Question 18

STRENGTHS OF POPULATION CODING

Answer 18

Broadens range, reduced variablity from background noise/random firing from averaging, can code different stimulus attributes simultaneously

Question 19

WEAKNESSES OF PLACE CODING

Answer 19

Expensive, resolution gained at the cost of packing in more and more neurons

Question 20

STRENGTSH OF ENSEMBLE CODING

Answer 20

Compromise (reduces no of neurons needed), easier to decode reliably (less 0,9 vs 1 spike issue) and QUICKLY

Question 21

Study suggesting colour is coded by place

Answer 21

Most electrophysiology suggests colour is coded by place (Zeki, 1973)

Question 22

WEAKNESSES OF TEMPORAL ENCODING

Answer 22

Could take time to decode, can’t represent temporal and non-temporal qualities at once, unequally spaced impulses arrive more evely spaced (Brindley, 1970)

Question 23

Study supporting concept of opponent processes

Answer 23

De Valois et al (1966)- stimulation with light from different parts of the spectrum will increase or decrease base AP firing rate in cells in dorsal LGN of monkeys

Question 24

What is the consequence o light and dark adaption on what firing rate shows in auditory nerve fibres

Answer 24

Impulse rate doesn’t signal absolute light intensity, but intensity relative to the level the receptor ahs recently been exposed to

Question 25

Evidence for the variation in light intensity vs reflectancy of light at a particular illumination level

Answer 25

de Valois and de Valois (1990)- intensity of light varies oer 9 log units, while reflectancy of light within a particular level of illumination varies over only a 20-fold range

Question 26

Evidence of neuroanatomical basis of lateral inhibition in the eye

Answer 26

Collateral branches spread sideways from each receptor cell axno in a layer just below th eommatidia, making inhibitory synaptic contact with other nearby cells (Purple and Dodge, 1965)