Week 3.9 - Sensory Encoding Flashcards
Receptive fields, Tuning curves and Response Functions
What is a receptive field?
A neuron has a receptive field for a given input when that input modulates the neuron.
For a given neuron, it is the part of the input (sensory, cognitive, motor) space that, when activated, can elicit/inhibit spikes.
What is a tuning curve?
A tuning-curve shows the average response of a neuron (in spike frequency) for some feature dimension of input (orientation of a bar, e.g.).
Note: the more stimulus dimensions are presented, the more dimensions can figure in the tuning curve (or tuning ‘surface’).
What is transduction?
Transduction is the conversion of a physical source of energy (light, sound, touch,…) into spikes.
Sensory receptor neurons convert a type of stimulus energy (e.g. photon, sound wave) into an electrical impulse that can be interpreted by the brain.
What is a topographic map?
A topographic map is a map of something that retains spatial relationships (neighborhoods). For example, the map of the sensory surface is topographical because the neighborhood in the skin is like the neighborhood in the somatosensory cortex.
A topographic map is to be contrasted with a topological map, where relationships are kept, but the spatial arrangement may not be.
The sensation is topographically organized in the brain, meaning that neural activity appears as a map. For example, the neurons that respond to stimuli on your fingers are grouped and not randomly peppered throughout the brain.
The sensation is ______ organized in the brain
topographically
Describe the neural pathway involved in sound perception.
Receptors > Spiral ganglion > brainstem and midbrain nuclei > Thalamus > Primary Auditory Cortex
What are the common shapes of tuning curves?
Ideal tuning curves look like Gaussians or Sigmoids.
However, tuning curves can be quite complex and have many possible shapes.
What is the pathway for most forms of sensory perception?
Receptors > Ganglia > Brainstem > Thalamus > Cortex
What is a Reichardt detector?
A hypothetical neural circuit postulated to explain how the brain tracks motion.
Give examples of low-level features.
Edges
Contrast
Orientation
Color
What are these types of receptive fields called?
Categorize the left and the right receptive fields according to their preference for light.
On/Off-center receptive fields
Left - an on-center off-surround receptive field. Increases the firing rate when the light covers the center of the field.
Right - an off-center on-surround receptive field. Increases the firing rate when the light covers the surrounding of the field.
What is a mechanoreceptor?
A sensory cell that responds to mechanical pressure/distortion.
There are four mechanoreceptors in the skin of most mammals:
(1) Meissner corpuscle
(2) Merkel cell
(3) Pacinian corpuscle
(4) Ruffini endings
A tuning curve for retinal disparity has a form of…
a sigmoid (logistic) function
What is the frequency (F) of the stimulus if the period (T) of one cycle is 10ms?
F = 1/T
T=10ms=10/1000s
Therefore:
F=100Hz or 100 spikes in a second
What can you say about neuronal activity according to this inter-spike interval?
Graph from: Kostal, lansky, & Pokora, 2011
The neuronal firing depicted in this histogram appears to be regular, there is one clear peak of preferred interspike interval.
Will this circuit lead to motion detection? Why?
No, the information from two receptive fields arrives at different times. For the circuit to be able to detect motion, we must introduce a delay at axon A (see the example below).
