A comparison of pedestal effects in first- and second-order patterns

Pi Chun Huang, Chien Chung Chen

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)

Abstract

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/°) or a binary random dot pattern; they were either added to a vertical low-frequency (2 c/°) 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.

Original languageEnglish
Article number9
JournalJournal of Vision
Volume14
Issue number1
DOIs
Publication statusPublished - 2014

All Science Journal Classification (ASJC) codes

  • Ophthalmology
  • Sensory Systems

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