L3,4,5 - Spatial Resolution of Vision

Question 1

In perception, how do you measure how good something is quantifiably?

Answer 1

• Assess how much signal is needed to successfully perceive the thing
  
  • SDT helps us quantify

Question 2

How can contrast alter the amount of signal?

Answer 2

• Amount of light difference via contrast
  
  • Different depths result in the light varying when it comes back to the eye
  • Distribution of light will remain the same
  • Less contrast = Less signal
• Contrast can be measure via the Pelli-Robson Contrast sensitivity chart that keeps letters at the same size, but downwards they decrease in contrast

Question 2

What are the different ways of measuring and testing for acuity (name only)?

Answer 2

• Testing the smallest size of object that no one can see
• Testing the smallest separation for which you can still distinguish two nearby objects
• Testing maximum density visibility of a series of lines (grating) against a background of the same average luminance
• Snellen eye chart

Question 2

What is spatial resolution (visual acuity?

Answer 2

• Resolution is the ability to distinguish differences in the spatial distribution of light in an image
• Visual acuity is the best known measure of resolution
• Visual acuity is the spatial resolving capacity of the visual system. This may be thought of as the ability of the eye to see fine detail.

Question 3

Is testing the smallest size of an object that no one can see a good measure?

Answer 3

• Not good – may not always disappear
• Blur makes it bigger on the retina, or neurons combining the neighbouring photoreceptors make it bigger in the brain

Question 4

Is testing the smallest separation for which you can still distinguish two nearby objects a good method? What is actually testing?

Answer 4

• E.g. Romans used to test sight by asking about whether they could see two stars that are close together or just the one
• It can depend on the size of your receptive fields. If they are larger, unsure that they are two stimuli as opposed to when RF are smaller
• The greater number of receptors contributing to the of a given ganglion cell, the larger that cells receptive field
• Smaller receptive field has superior visual acuity because convergence is more limited for this cell