Psychophysical Assessment of Visual Function

LABORATORY 4:

The Temporal Contrast Sensitivity Function

Purpose

The purpose of this laboratory is to give you experience in determining your very own human "temporal contrast sensitivity function" (Temporal CSF).

Equipment

We will use the same Cambridge Research Systems machine that we used for the spatial CSF, located in room 417 HPB. This machine can present a variety of temporal frequencies. It also can change the contrast of the temporal frequencies from below the human threshold to well above threshold.

METHODS

Position yourself 57 cm from the screen with the keyboard on your lap. A series of 6 temporal frequencies will be presented. Each will be presented 3 times, in random order. A large patch on the monitor screen will flicker as its intensity changes sinusoidally over time. The temporal frequencies (flicker rates) will be 0.5, 1, 3, 8, 25and 40 Hz.

We will use the Method of adjustment to determine your threshold contrast for each temporal frequency. There is a little white fixation cross in the center of the monitor. Look at it (but no need to stare, this is just a reference point.) When we start the program, the computer will make a large patch of the monitor around the fixation spot flickerone of the six some temporal frequencies. If you do not see the flicker, press the “up” arrow on the keyboard until you do see it. Then use the “down” and “up” arrows to change the contrast until it is right at threshold – a contrast where you can “barely” see the flicker. If you want, you can increase the contrast a click and then back down a click or two to be sure that this is where your threshold is. Some flicker rates (temporal frequenies) are easier to see than others.

Data Analysis and Graphs

At the end of the testing, we will copy your data into an Excel spreadsheet that will convert your data into contrast sensitivity. We will give you a print-out listing the temporal frequencies at which you were tested and the contrast sensitivity values for each temporal frequency.

To complete this laboratory exercise, 1) transfer the contrast sensitivity valuesto the data sheet (next page) 2) plot the contrast sensitivity values on the graph below (note, the X-axis has marks indicating the six temporal frequencies we have used; the Y-axis is a log scale; 3) connect the data points with straight lines, 4) turn in the lab report to Dr. Norton.

Name ______

Temporal Frequency Contrast Sensitivity

0.5 Hz ______

1 Hz______

3 Hz______

8 Hz______

25 Hz______

40 Hz______

PSYCHOPHYSICAL ASSESSMENT: Temporal Contrast Sensitivity Function LaboratoryPAGE 1