August 2009
Volume 9, Issue 8
Vision Sciences Society Annual Meeting Abstract  |   August 2009
A comparison of the pedestal effects in the 1st- and 2nd-order patterns
Author Affiliations
  • Pi-Chun Huang
    Psychology Department, National Taiwan University
  • Chien-Chung Chen
    Psychology Department, National Taiwan University
Journal of Vision August 2009, Vol.9, 1011. doi:
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      Pi-Chun Huang, Chien-Chung Chen; A comparison of the pedestal effects in the 1st- and 2nd-order patterns. Journal of Vision 2009;9(8):1011.

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      © ARVO (1962-2015); The Authors (2016-present)

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Purpose. Human visual system is sensitive to both luminance (the first-order) modulations and contrast (the second-order) modulations in an image. A linear-nonlinear-linear (LNL) model is commonly used to explain the visual process of the 2nd-order stimuli. Here we used pattern masking paradigm to compare the 1st-order and the 2nd-order visual mechanisms and to characterize the nonlinear properties of their underlying mechanisms. Methods. The stimuli were a high frequency horizontal grating (8 cyc/d) either added to (1st-order stimuli) or multiplied with (2nd-order stimuli) a vertical low frequency (2 cyc/d) Gabor function. The discrimination threshold of the target was measured with pedestals whose spatial properties as that of the target except contrast (1st-order pedestal) or modulation depth (2nd-order pedestal) of either the low or the high frequency components. Results. The threshold function showed a typical dipper shape for both the 1st- and the 2nd-order stimuli: the threshold first decreased (facilitation) and then increased (suppression) with pedestal contrast or modulation depth. The results for the 1st-order stimuli were well explained by divisive inhibition model in which the facilitatory input was divided by the sum of broadband inhibitory inputs. The results for the 2nd-order stimuli were also well explained by a modified that operated on modulation depth rather than contrast in the input images. Conclusion. Our result suggests that divisive inhibition is required to explain visual discrimination in both the first- and the second-order patterns. However, the source and the nonlinearity of the divisive inhibition may be different for these two types of patterns.

Huang, P.-C. Chen, C.-C. (2009). A comparison of the pedestal effects in the 1st- and 2nd-order patterns [Abstract]. Journal of Vision, 9(8):1011, 1011a,, doi:10.1167/9.8.1011. [CrossRef]
 Supported by NSC 96-2413-H-002-006-MY3 and NSC 097-2811-H-002-005- to CCC.

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