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Aaron Johnson, Bruce Hansen, Dave Ellemberg; Center-surround effects in human discrimination of amplitude spectrum slope. Journal of Vision 2007;7(9):967. doi: https://doi.org/10.1167/7.9.967.
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© ARVO (1962-2015); The Authors (2016-present)
The human visual system is capable of effectively discriminating between different slope exponents in the amplitude spectra of natural scene images. Many stimuli used in previous studies were designed to stimulate only the foveal or parafoveal regions of the retina. However, in real-world viewing conditions, images are rarely presented in isolation, and are almost always embedded in a similar visual context. It is therefore important to understand how the visual system can discriminate between different natural scene slope spectra when they are embedded in surrounds possessing different amplitude spectra slopes. Subjects performed a same-different task combined with a staircase procedure to measure the thresholds for discriminating changes in the amplitude spectra slope of a central target image (α=0.7,1.0,1.3) that was embedded in a larger surround image. The surround varied in amplitude spectra fall-off (same as target, higher [+ 0.6 α], or lower [− 0.6 α]). The results were compared to a condition in which the central target was presented alone, without the surrounding patch. The results showed that discrimination thresholds were lower when the surround amplitude spectral slope was similar to that of the embedded target patch. Converesely, an increase in discrimination thresholds was found for conditions in which the amplitude spectral slope of the surround was higher or lower to that of the embedded target. This pattern was similar for the three target α values. Finally, for the conditions in which the centre and surround had the same spectral slope, discrimination thresholds were lowest when the target patch amplitude slope had an exponent of 1.0, and highest when the exponent was 0.7. Together, these results suggest that the foveal and peripheral mechanisms receive simultaneous and comparable activation in order for the visual system to optimally discriminate between different natural scene spectra.
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