to measure and see how acuity deteriorates as the stimulus is moved
farther from the fovea
to develop some understanding of what is an experiment
To begin to learn how to design an experiment to answer a question
to compare data to hypothesis
Acuity and Retinal Physiology
From class and chapter 3 of the text, we learn that the number of cones
get fewer as the distance from the fovea increases.
Since we will be testing in the day time, it is the cones that are the
principal receptors involved in what we see
The density of cones is by far the greatest in the fovea
It has also been observed that receptive fields are smaller at the fovea
than in the periphery
Acuity and receptive fields are examples of spatial summation so should
Question: It would seem that if the density of the cones is greatest in
the fovea and the receptive fields are smallest in the fovea that our acuity
would be highest at the fovea and decrease in the periphery.
Scientist use many types of methods to collect their data.
One type of research method unique to the sciences is the experiment.
In simple terms that means the research changes something and sees what
happens. I will introduce a lot of formal language, but that is the
basic idea, hold onto it.
The thing that the experimenter changes is called the Independent Variable
The thing that the experimenter measures to see what happened is the
dependent variable (DV)
See if you can figure out the IV and DV for this experiment.
Stimulus Settings: Note all values
Stimulus Type: Checkerboard
Contrast: Leave unchanged but note for your stimulus section
Stimulus Position: in your groups you will pick both number of positions and where
What you want:
To cover the possible range
To determine how acuity changes over range
Pick at least 3.
Issues to Consider:
Too few levels will not allow you to know what is going on in your data
Too many will cause unnecessary wear and tear on your participants
The goal is good clear data with as few measures as necessary
Background Level: Leave unchanged
Method Settings (this is Method of Limits): Note all values
Number of Levels of Critical Feature Size: You pick in your groups
too few and you will not have a good measure of the threshold
Too many and you bore and tire your participants which can lead to sloppy
The goal is clear, accurate measures
Number of staircases: Same Issues as above
Minimum Value of Critical Feature Size: Lowest value in staircases
Set to 1.
Maximum Value of Critical Feature Size: Largest value in staircases
Set to 10.
Every member of the group should use the same browser this week and next.
Make the browser fill the screen.
Place your head centered on the screen 24" from the monitor surface.
Fixate on the red fixation mark. Do not move your eyes from that
The stimulus will be presented at the position you chose for this condition.
If you see it, press the yes button or the z key.
If you do not see it, press the no button or the / key.
The threshold is calculated at the end of the experiment.
Press the Show Threshold button to display the threshold and then record your results.