SENSORY

Stimulus - NS - Response

Sensory coding
tuning at the receptor level - specialist, generalist
processing - lateral inhibition, feature detection
projection to CNS - question of "localization of function"
History (of general sensory mechanisms)-
Ernst Weber (1934)- DI/I = k
Gustav Fechner (1860) psychophysics - exponential
Modalities - (e.g. vision and audition, but there can be multiple submodalities in one modality, like, for somesthesis (touch), pressure is very different than nociception
Johannes Muller - 1830's law of specific nerve energies - like if you could transplant so that optic nerve connected up to brain through auditory nerve, then light would be perceived as if it were sound, so it is based on central connectivity rather than receptors that qualities are perceived, and, for submodalities of somesthesis, even the ascending tracts in the spinal cord are separated
Muller was an expert witness at a trial where a witness claimed to see his assailant by light of the phosphene from getting hit over the head
Stimulus - notion of "adequate" stimulus - Sherrington -the stimulus for which the least amount of energy works, like you see if you press on your eyeball, but it takes much less light energy, so rod is for light.
Receptors - Transduction -
receptor potential
generator potential
amplification
low threshold = high sensitivity
the most famous work on high sensitivity: S. Hecht, S. Schlaar & H. Pirenne, 1942, Energy, quanta and vision, J. Gen. Physiol. 25, 819-840 - a person can see 6 - 14 quanta over an area of 500 rods => each rod can see 1 photon
acuity (vs. sensitivity)
adaptation
phasic - rapidly adapting - Pacinian corpuscle
tonic - slowly adapting - muscle receptors
Receptive field the sensory field converging on the central neuron studied
each receptor would diverge to many neurons in the brain by lateral connections, and, by the same token, each cell high up in the nervous system would get input from many receptors
excitation and inhibition
Lateral inhibition -
H. K. Hartline (US) (1967 Nobel)
"primary physiological and chemical visual processes in the eye"
Feature abstraction -> pattern recognition

This page was last updated on Dec. 19, 2001

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