Ch. 3

• Hartline won the Nobel Prize in Physiology and Medicine in 1967 for his discovery of a property of neurons called the neuron’s receptive field.
• Hartline isolated a single ganglion cell axon in the opened eyecup of a frog.
• Hartline illuminated different areas of the retina and found that the cell he was recording from responded only when a small area of the retina was illuminated.
• Hartline called the area the receptive field of that RGC.
• The receptive field of a ganglion cell covers a much greater area than a single photoreceptor.
• There are many ganglion cells in the retina, who together take in information about what is happening over the entire retina
• A normal chest X-ray (CXR) may show a thin, well-defined, black line around one or both lateral margins of the heart, an optical illusion resulting from overlap of superimposed normal structures, known as the Mach Band or Mach Effect.
• Ganglion cells have center-surround receptive fields that are arranged like concentric circles in a center-surround organization.
• Stephen Kuffler measured ganglion cell receptive fields in the cat and reported a property of these receptive fields that Hartline had not observed in the frog.
• Receptive fields overlap, so stimulating at a particular point on the retina will generally activate a number of fibers in the optic nerve.
• Each ganglion cell monitors a small area of the retina.
• Cones recieves sensory information first, then bipolar cells & then horizontal cells process that information

  • sometimes result in firing of ganglion cells
  • sometimes enhance activity of certain cells & different parts of visual field
• Ganglion Cells' receptive fields differ in size

  • very small in the retina
  • the further from the fovea, the larger the receptive field
• 2 Point Discrimination Test: the two points have to be far apart for the person to feel the different point

  • At the tip of the finger, they can be close & differentiated - because the receptive fields are small at tip of fingers thus higher touch acuity
• • Light that hits "surround" is inhibitory --> less likely for neuron to fire
  • Light that hits "centre" is excitatory --> more likely for neuron to fire
• Stephen Kuffler found that whether the retinal ganglion cell attached to the receptive field fires, depends on the pattern of light & dark on the receptive field
• Lateral Inhibition: inhibition coming from sides

  • away from you
• Hermann Grid: you see grey spots in the periphery intersections but not at the intersection you're looking at

  • this is due to lateral inhibition
  • firing at a spontaneous rate, inhibiting the surrounding large receptive fields & permits you to see the grey
• Mach Band: at the point where the lighter area meets the darker area, the lighter area will appear even lighter near the boundary & darker will appear even darker near the boundary

  • occurs because neurons in the visual cortex suppress the activity of neighbouring neurons, enhancing the contrast at edges where light intensities differ sharply
  • ex. of lateral inhibition