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APPENDIX C: BASIC CONCEPTS IN FOURIER ANALYSIS
Pages 44-48

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From page 44...
... The most widely used stimulus transform is the logarithm; for example, the logarithm of stimulus luminance or contrast often has a linear relationship with the z-score of percentage correct in the psychometric function. The second approach to stimulus specification developed in the past 15 years and is based on a rather complicated mathematical transformation of the luminance distribution of the stimulus: the two-dimensional Fourier transform.
From page 45...
... Third row: a two-dimensional spatial frequency filter based on the two-dimensional contrast sensitivity function. Bottom row: The amplitude spectra after being filtered by the contrast sensitivity function.
From page 46...
... The basis for the use of sinusoidal gratings as test stimuli in the measurement of the contrast sensitivity function is rooted in the desire to apply linear systems analysis in order to understand the functioning of the visual system. Since the elementary signals of Fourier analysis are sinusoidal gratings, they are the stimuli of choice, since it is necessary to know how the visual system responds to these elementary signals if predictions concerning complex stimuli are to be made.
From page 47...
... first suggested that cells in the visual cortex have receptive field sensitivity profiles that are of the form of Gabor functions, and further electrophysiological measurements in the visual cortex of monkies support this idea (Kulikowski et al., 1982; Pollen and Ronner, 1982; Pollen et al., 1984)
From page 48...
... APPENDIX C: BASIC CONCEPTS IN FOURIER ANALYSIS 48 FIGURE 22 Sinusoidal gratings that have been windowed by a Gaussian function, called Gabor signals or Gabor functions. These stimuli are optimally localized both in space and in spatial frequency.


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