MT1 perception- neurons and neural codes Flashcards
STRENGTHS OF GRADED POTENTIALS
Instantaneous, omnidirectional, infinitely graded
WEAKNESSES OF GRADED POTENTIALS
VERY short range, ambiguous
STRENGHTS OF APs
Unidirectional (NMJ), long range
WEAKNESSES OF APs
Fixed amplitude so can’t encode value of stimulus by voltage, limited rate, slower
What proposes each sensory nerve gives rise to its own characteristic sensation regardless of how its stimulated
Muller’s Law of Specific Nerve Energies (1835)
Who mapped functions/sensations onto the cortex
Penfield and Rasmussen (1950)
Who extended the doctrine of law of specific nerve energies
V Helmholtz (1963)- each fibre in the auditory nerve was specific to a particular pitch, yet nature of neural excitation was the same
Who proposed the simplistic nature of doctrine of specific nerve energeis
Muller himself (1938)
ADVATNAGES OF FREQUENCY CODING
Cheap, log coding allows a wider range of stimulus values to be encoded
WEAKNESSES OF FREQUENCY CODING
Limited firing rate limits range, takes time to decode reliably, opposite case in photoreceptors
Study providing evidence for frequency coding from frog muscle
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
Who did the Limulus study
Hartline and Graham (1932)- showed logarithmic coding initially, then power coding
Evidence for log coding in taste
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
Evidence of the latency of respnose in monkey neurons in AIT
Desimone et al (1984)- latency was 80-100ms
Steve Carrell neuron
Quiroga et al (2008)- steve carrell neuron
Evidence for sparse coding
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
STRENGTHS OF PLACE CODING
Unlimited (well) range, faster to decode
STRENGTHS OF POPULATION CODING
Broadens range, reduced variablity from background noise/random firing from averaging, can code different stimulus attributes simultaneously
WEAKNESSES OF PLACE CODING
Expensive, resolution gained at the cost of packing in more and more neurons
STRENGTSH OF ENSEMBLE CODING
Compromise (reduces no of neurons needed), easier to decode reliably (less 0,9 vs 1 spike issue) and QUICKLY
Study suggesting colour is coded by place
Most electrophysiology suggests colour is coded by place (Zeki, 1973)
WEAKNESSES OF TEMPORAL ENCODING
Could take time to decode, can’t represent temporal and non-temporal qualities at once, unequally spaced impulses arrive more evely spaced (Brindley, 1970)
Study supporting concept of opponent processes
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
What is the consequence o light and dark adaption on what firing rate shows in auditory nerve fibres
Impulse rate doesn’t signal absolute light intensity, but intensity relative to the level the receptor ahs recently been exposed to
Evidence for the variation in light intensity vs reflectancy of light at a particular illumination level
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
Evidence of neuroanatomical basis of lateral inhibition in the eye
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)
