Contrast inconstancy across changes in polarity.

C P Benton; A Johnston

doi:10.1016/s0042-6989(99)00110-8

Home/Archive/PubMed

PubMed · 10748940

Contrast inconstancy across changes in polarity.

C P Benton·A Johnston

View original source ↗Export metadata ↓

Abstract

In this study, we show that negative polarity noise patterns appear to have a higher contrast than positive polarity noise patterns with identical expected Fourier amplitude spectra. This demonstrates a failure of contrast constancy over changes in pattern polarity. An examination of local contrast measures shows that negative polarity noise has a wider distribution of local contrast values than positive polarity noise. We propose that the difference in apparent contrast between the two patterns may be based upon spatial non-linearities in the combination of local contrast measures.

Explore related subjects

Contrast Sensitivity Humans Lighting Models, Psychological Pattern Recognition, Visual Photic Stimulation Sensory Thresholds Journal Article

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

C P Benton, A Johnston. 1999. Contrast inconstancy across changes in polarity.. https://doi.org/10.1016/s0042-6989(99)00110-8

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2007

Shift in spatial scale in identifying crowded letters.

Crowding refers to the increased difficulty in identifying a letter flanked by other letters. The purpose of this study was to determine if the peak sensitivity of the human visual system shifts to a different spatial frequency when identifying crowded letters, compared with single letters. We measured contrast thresholds for identifying the middle target letters in trigrams, for a range of spatial frequencies, letter separations and letter sizes, at the fovea and 5 degrees eccentricity. Plots of contrast sensitivity vs. letter frequency exhibit spatial tuning, for all letter sizes and letter separations tested. The peak tuning frequency grows as the 0.6-0.7 power of the letter size, independent of letter separation. At the smallest letter separation, peak tuning frequency occurs at a frequency that is 0.17 octaves higher for flanked than for unflanked letters at the fovea, and 0.19 octaves at 5 degrees eccentricity. This finding suggests that the human visual system shifts its sensitivity toward a higher spatial-frequency channel when identifying letters in the presence of nearby letters. However, the size of the shift is insufficient to account for the large effect of crowding in the periphery.

Contrast Sensitivity↗

PubMed2007

Developmental delay and magnocellular visual pathway function in very-low-birthweight preterm infants.

This study investigated the effect of very preterm birth (gestation < or =30wks) and very low birth weight (< or =1500g) on the development of magnocellular and parvocellular visual processing streams. Participants were preterm infants (n=55: 31 females, 24 males) born between 24 and 30 weeks'gestation (mean 27.4wks [SD 1.3]), weighing between 720 and 1470g (mean 1015g [SD 215]) and term infants (n=52: 27 females, 25 males) born between 38 and 42 weeks'gestation (mean 39.4wks [SD 0.9]), weighing between 2670 and 4405g (mean 3549g [SD 440]). Visual-evoked potentials to phase-reversing sine-wave gratings, varying in spatial frequency and contrast, were used to elicit magnocellular and parvocellular specific responses. Previous studies found that the N1 component reflects the parvocellular response, while P1 reflects the magnocellular response in adults and infants. Findings from the current study indicate significantly lower P1 amplitudes in preterm compared with term infants under most conditions. No difference was found for the amplitude of the N1 waveform. Results indicate that, for the age-range tested, preterm birth has little effect on the development of parvocellular function, while it appears to disrupt the development of magnocelluar function.

Contrast Sensitivity↗

PubMed2006

Perceived direction of plaid motion is not predicted by component speeds.

It has been shown that the perceived direction of a plaid with components of unequal contrast is biased towards the direction of the higher-contrast component [Stone, L. S., Watson, A. B., & Mulligan, J. B. (1990). Effect of contrast on the perceived direction of a moving plaid. Vision Research 30, 1049-1067]. It was proposed that this effect is due to the influence of contrast on the perceived speed of the plaid components. This led to the conclusion that perceived plaid direction is computed by the intersection of constraints (IOC) of the perceived speed of the components rather than their physical speeds. We tested this proposal at a wider range of component speeds (2-16deg/s) than used previously, across which the effect of contrast on perceived speed is seen to reverse. We find that across this range, perceived plaid direction cannot be predicted either by a model which takes the IOC of physical or perceived component speed. Our results are consistent with an explanation of 2D motion perception proposed by [Bowns, L. (1996). Evidence for a feature tracking explanation of why Type II plaids move in the vector sum direction at short durations. Vision Research, 36, 3685-3694.] in which the motion of the zero-crossing edges of the features in the stimulus contribute to the perceived direction of motion.

Contrast Sensitivity↗