Psychology of Perception
Psychology 4165-100
Spring 2016
11:00–12:15 TR
Lewis O. Harvey, Jr.–Instructor
Scott M. Schafer–Teaching Assistant
Vincent Mathias–Learning Assistant
Steven M. Parker–Consultant
Homework 2: Contrast Sensitivity
10 Points: Due at the beginning of class, Thursday, 4 February 2016
There are two parts to this homework assignment. Each part counts 5 points.
Late homework will receive a grade of zero. Your homework must be prepared
with a word processor, not handwritten. Graphs must be prepared with
computer software (e.g., R), not hand-drawn. Turn in a hard copy at the
beginning of class and upload an electronic version (pdf if possible) to the course
Dropbox in D2L.
Part 1: In the table below are given the threshold (i.e., d-prime = 1.0) contrasts for
detecting sine wave gratings patches (Gabor patches) of various spatial
frequencies. Assume that stimuli having amplitude less than these values would
not be visible.
cpd
contrast
cpd
contrast
1.0
0.00409
9.00 0.00208
1.25
0.00377
10.65 0.00278
1.90
0.00274
15.00 0.00489
2.65
0.00229
18.50 0.00845
3.75
0.00175
21.25 0.0150
5.50
0.00157
26.50 0.0377
7.50
0.00164
30.00 0.0702
8.00
0.00198
40.00 0.362
a.
b.
Will a 3.0 cpd sine wave grating with contrast of 0.005 be visible? Why?
Will a 30.0 cpd sine wave grating with contrast of 0.005 be visible? Why?
Part 2: Using the contrast threshold data in the table, plot (using any computer
graphing program, R for example) a graph of the contrast sensitivity function
(CSF). Put contrast sensitivity (S = 1/contrast) on the vertical axis and spatial
frequency on the horizontal axis. Make two graphs. In the first graph plot
frequency on a linear scale and sensitivity on a logarithmic scale (in R use
log=”y” as an argument in the plot() command). In the second graph plot
both the x- and y-axes on logarithmic scales. (in R use log=”xy” as an argument
in the plot() command). Compare these graphs with CSFs shown in class and
in Figures 3.7, 3.9, 3.32, 3.36 and 3.37 of the textbook. Are they the same or are
there differences?