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Related Concept Videos

Perceptual Constancy01:12

Perceptual Constancy

Perceptual constancy is the ability to recognize that objects remain consistent and unchanged even when their appearance varies due to changes in sensory input. There are four main types of perceptual constancy: size constancy, shape constancy, color constancy, and brightness constancy.
Size constancy is the recognition that an object remains the same size, even when its image on the retina changes. For instance, a bus is perceived to be large enough to carry people, even if it looks tiny from...
Linear time-invariant Systems01:23

Linear time-invariant Systems

A system is linear if it displays the characteristics of homogeneity and additivity, together termed the superposition property. This principle is fundamental in all linear systems. Linear time-invariant (LTI) systems include systems with linear elements and constant parameters.
The input-output behavior of an LTI system can be fully defined by its response to an impulsive excitation at its input. Once this impulse response is known, the system's reaction to any other input can be calculated...
Calibration Curves: Linear Least Squares01:20

Calibration Curves: Linear Least Squares

A calibration curve is a plot of the instrument's response against a series of known concentrations of a substance. This curve is used to set the instrument response levels, using the substance and its concentrations as standards. Alternatively, or additionally, an equation is fitted to the calibration curve plot and subsequently used to calculate the unknown concentrations of other samples reliably.
For data that follow a straight line, the standard method for fitting is the linear...
Light Acquisition02:16

Light Acquisition

In order to produce glucose, plants need to capture sufficient light energy. Many modern plants have evolved leaves specialized for light acquisition. Leaves can be only millimeters in width or tens of meters wide, depending on the environment. Due to competition for sunlight, evolution has driven the evolution of increasingly larger leaves and taller plants, to avoid shading by their neighbors with contaminant elaboration of root architecture and mechanisms to transport water and nutrients.
Flame Photometry: Overview01:02

Flame Photometry: Overview

Flame photometry, also known as flame emission spectrometry, is a technique used for the qualitative and quantitative analysis of elements present in a sample using a flame as the source of excitation energy. The concept of flame photometry was realized in the early 1860s by Kirchhoff and Bunsen, who discovered that specific elements emit characteristic radiation when excited in flames. The first instrument developed for this purpose was used to measure sodium (Na) in plant ash using a Bunsen...
Relation between Poisson's ratio, Modulus of Elasticity and Modulus of Rigidity01:15

Relation between Poisson's ratio, Modulus of Elasticity and Modulus of Rigidity

Deformation occurs in axial and transverse directions when an axial load is applied to a slender bar. This deformation impacts the cubic element within the bar, transforming it into either a rectangular parallelepiped or a rhombus, contingent on its orientation. This transformation process induces shearing strain. Axial loading elicits both shearing and normal strains. Applying an axial load instigates equal normal and shearing stresses on elements oriented at a 45° angle to the load axis.

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Enabling High Grayscale Resolution Displays and Accurate Response Time Measurements on Conventional Computers
06:50

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Published on: February 29, 2012

Lightness constancy: ratio invariance and luminance profile.

Alessandro Soranzo1, Alessandra Galmonte, Tiziano Agostini

  • 1School of Social Science and Law, University of Teesside, Middlesbrough TS1 3BA, England. a.soranzo@tees.ac.uk

Attention, Perception & Psychophysics
|March 24, 2009
PubMed
Summary

Simultaneous lightness constancy, the visual system's ability to perceive surfaces equally under different lighting, is enhanced by gradual illumination edges. However, wider light ratios impair this visual constancy.

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Area of Science:

  • Visual perception
  • Color science
  • Computational neuroscience

Background:

  • Simultaneous lightness constancy enables consistent perception of surface lightness across varying illumination.
  • Lightness constancy failure occurs when identical surfaces appear different under different lighting conditions.
  • The impact of illumination edge luminance profiles on lightness constancy remains an open research question.

Purpose of the Study:

  • To investigate how the luminance profile of illumination edges influences simultaneous lightness constancy.
  • To determine if ratio invariance of illumination edges is sufficient to maintain lightness constancy.
  • To explore the role of edge homogeneity and luminance ratio amplitude in visual perception.

Main Methods:

  • Two experiments were conducted using bipartite illumination displays.
  • The luminance profile of illumination edges (gradual vs. sharp, homogeneous vs. inhomogeneous) was manipulated.
  • The luminance ratio amplitude between illumination fields was systematically varied.

Main Results:

  • Simultaneous lightness constancy improved with gradual and homogeneous illumination edge profiles.
  • Increased luminance ratios between illumination fields led to a decrease in lightness constancy.
  • Edge profile characteristics significantly impact the visual system's decomposition of luminance.

Conclusions:

  • Gradual and homogeneous illumination edges facilitate the visual system's decomposition of luminance into lightness and illumination components.
  • Wider luminance ratios impede this decomposition process, leading to compromised lightness constancy.
  • The findings support the layer decomposition schema in explaining visual perception of lightness.