Psychology 2115A/B Lecture Notes - Lateral Inhibition, Foveal, Retina

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Published on 20 Apr 2013
School
Western University
Department
Psychology
Course
Psychology 2115A/B
Chapter 3 Review: Intro to Vision, Part 2
By the end of this section, you should know about:
- Neural convergence: the connections expand laterally across the retina
- Lateral inhibition: what happens after phototransduction from receptor to the ganglion cell out of
the retina to the cortex
Neural Responses to Light
The output of the photoreceptors (hyperpolarization) is transmitted to the retinal ganglion cells
Convergence of rod and cone signals onto the ganglion cells
o Way more rods than cones in the retina
o As a result, rods show greater convergence than cone cells
o A lot more rods feed into one ganglion cells than cones
o This means that rods do greater spatial summation: many rods summate (add up together) their
responses and feed them to a single ganglion cell, while this doesn’t often happen in cones
o Greater spatial summation means that we can detect specks of light all across our visual fields
and it doesn’t have to be particularly intense for us to sense that it is there
o The cones don’t have this sensitivity to dim spots of light
o This great spatial summation we trade off for detail we can detect that spot of light but we
aren't very good at knowing what or where the spot of light is
o Cones give us a lot of very good detail/acuity
Neural Convergence
120 million rods and 5 million cones convergence to 1 million ganglion cells
Higher convergence of rods than cones
o Average of 120 rods to one ganglion cell
o Average of six cones to one ganglion cell
o Cones in fovea have one to one relation to ganglion cells
The reason why the fovea is the most visually acute part of the eye
Rod Sensitivity > Cone Sensitivity?
Why is it the case that the sensitivity of the rods to light in comparison to the rods?
Rods take less light to respond fewer photons of light to generate a response in a rod than we would
in a cone
Rods have to add together all of their responses to create a response in a ganglion cell increase
likelihood of the ganglion cell responding
Visual Acuity
The ability to see fine detail
Foveal acuity vs. peripheral acuity
o Best acuity in the fovea since it is full of cones
o Acuity largely reduced in low light levels
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Document Summary

Chapter 3 review: intro to vision, part 2. By the end of this section, you should know about: Neural convergence: the connections expand laterally across the retina. Lateral inhibition: what happens after phototransduction from receptor to the ganglion cell out of the retina to the cortex. The output of the photoreceptors (hyperpolarization) is transmitted to the retinal ganglion cells. 120 million rods and 5 million cones convergence to 1 million ganglion cells. Higher convergence of rods than cones: average of 120 rods to one ganglion cell, average of six cones to one ganglion cell, cones in fovea have one to one relation to ganglion cells. The reason why the fovea is the most visually acute part of the eye. Rods take less light to respond fewer photons of light to generate a response in a rod than we would in a cone.

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