Study Questions: Spatial Frequency Channels



1.  What is an image?

2.  What is a sine wave grating?  Describe the properties of a grating. (a) Sketch a sinusoidal grating. (b) Sketch a grating of higher frequency than (a). (c) Sketch a grating of lower contrast than (a). (d) Sketch a grating perpendicular to (a). (e) Sketch a grating with a different phase to that shown (a). (f) How can one construct all kinds of visual patterns using sine wave gratings?

3.  Describe experiments which demonstrate the existence of multiple, independent spatial frequency channels.

4.  What is a (spatial) contrast sensitivity function? How is it measured?

5.  Sketch a typical human contrast sensitivity function. Describe the interrelationship you might expect between the results for the following tasks: contrast threshold for single sine wave gratings, contrast threshold for "pseudo-square-wave gratings" (which consists of a sine wave grating at one fundamental frequency f plus a second grating with triple the spatial frequency 3f, and 1/3 the contrast), and discrimination between a sine wave grating and a pseudo-square-wave grating which share the same fundamental f at the same contrast (but the square wave has the added 3f component). Do this for three values of f: low, medium and high spatial frequencies.

6.  How might one relate the so-called "feature detectors" (e.g., a center-surround receptive field, an edge or a bar detector) to the spatial frequency "filters" of Fourier analysis?

7.  Briefly define the following terms: contrast, contrast threshold, contrast sensitivity, and spatial contrast sensitivity function.

8.  Suppose you were shown a contrast sensitivity function with a dip at 8 cycles per degree.  Discuss at least two ways an experimenter could have induced such a situation, and how this is used as evidence for underlying spatial frequency mechanisms.

9.  Describe perceptual effects which can be explained by the theory of multiple spatial frequency channels.

10.  What physiological evidence supports the theory of multiple spatial frequency channels?