期刊
JOURNAL OF VISION
卷 14, 期 1, 页码 -出版社
ASSOC RESEARCH VISION OPHTHALMOLOGY INC
DOI: 10.1167/14.1.9
关键词
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资金
- NSC [99-2410-H-002-081-MY3]
- [96-2413-H-002-006MY3]
- [NSC-101-2401-H-006-003-MY2]
The human visual system is sensitive to both luminance (first-order) and contrast (second-order) modulations in an image. A linear-nonlinear-linear model is commonly used to explain visual processing of second-order patterns. Here we used a pattern-masking paradigm to compare first-order and second-order visual mechanisms and to characterize the nonlinear properties underlying them. The carriers were either a high-frequency horizontal grating (8 c/8) or a binary random dot pattern; they were either added to a vertical low-frequency (2 c/8) sinusoidal grating (firstorder stimuli) or multiplied by it (second-order stimuli). The incremental discrimination threshold of the target was measured with pedestals whose spatial properties matched those of the target, with the exception of contrast (in the first-order pedestal) or modulation depth (in the second-order pedestal). The threshold function showed a typical dipper shape for both firstand second-order stimuli. The results for the first-order stimuli with different types of carrier and the secondorder stimuli with a grating carrier were well explained by a divisive inhibition model in which the facilitatory input was divided by the sum of broadband inhibitory inputs. The results for the second-order stimuli with a random-dot carrier were explained by a modified divisive inhibition model that operated on modulation depth. Our results suggest that divisive inhibition is required to explain visual discrimination in both firstand second-order patterns. However, the source and nonlinearity of the divisive inhibition may be different for these two types of patterns and carrier.
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