to measure and see how acuity deteriorates as the stimulus is moved
farther from the fovea
to gain some experience in calibration or making sure the stimulus works
the way your think it does
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.
Calibration is the process of checking out the equipment and the stimuli
to make sure that they are doing what they ought to be doing.
In studying our sensation, sometimes the calibration has to include the
The stimulus being used in this experiment is a checkerboard.
When the checks are too small, the checkerboard is supposed to blend in
with the background.
It should be easy to make this happen, have the white and black squares
equally different from the background. However, monitors do not make it
easy. Each monitor is different and monitors change over time.
So, before the experiment, each participant will calibrate their monitor
so that a checkerboard that is too small to see will blend into the
This is a very simple and basic type of calibration.
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 Type: Your Pick of Either Grating or Checkerboard
Number of Positions: in your groups you will pick
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
Upper limit of staircase: leave as default but record (the unit is in
Method (Method of Limits):
Number of Levels to Test: 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: 9 to 15
Type of MOL: Traditional
Stare at the middle of the top of the screen area for the experiment
In the upper right corner is a grating made up of alternating bright and
Using the slider at the bottom of the screen, adjust the brightness of the
gray background until you cannot see the grating or at least it is minimally
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 closest to the fovea that it
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 computer will track the staircases and when each position is done it
will move to the next position.
The threshold are calculated and a summary of the results will be
displayed at the end of the experiment.
Press the Show Data button and record your results