title: Low number of luminance levels in the luminance noise increases color discrimination thresholds estimated with pseudoisochromatic stimuli.
abstract: In pseudoisochromatic stimuli the presence of spatial and luminance noise forces the subject to discriminate the target from the background solely on the basis of chromaticity difference. Color-blind subjects may show difficulty to identify the target due to the elimination of borders and brightness clues caused by the luminance and spatial noise. Few studies have fully described the features of pseudoisochromatic stimuli. Fewer investigators have focused their studies in the effects of specific pseudoisochromatic parameters on color discrimination. We used the Cambridge Color Test (CCT) to investigate the influence on color discrimination thresholds due to the number of luminance levels present in the luminance noise. The CCT default has six luminance steps; however, in our investigation a total of eight different conditions were tested from 2 to 16 luminance steps. It was found that the CCT provided very robust values for color discrimination thresholds, which were degraded only for very small number of luminance steps. When the number of steps was increased, the color discrimination thresholds improved from 2 to 6 luminance steps and gradually reached a plateau for 10 or more luminance steps. The area of color discrimination ellipses as a function of luminance steps matches the relative proportion of ineffective contrasts between mosaic patches as a function of luminance steps, assuming that contrast becomes ineffective for values 18.6% or less. The lower number of color and luminance interactions in these conditions could explain the measured increase of color discrimination thresholds. The primary conclusion from this investigation was that results from pseudoisochromatic tests should have their parameters described in more detail. This type of description would allow a better understanding of the results provided, interpretations, and therefore cross study comparison of results obtained from different laboratories.
authors.affiliation: Instituto de Ciências Biológicas, Universidade Federal do Pará Belém, Brazil ; Núcleo de Medicina Tropical, Universidade Federal do Pará Belém, Brazil.
authors.forename: Givago S
authors.initials: GS
authors.lastname: Souza
authors.affiliation: Department of Biology, University of Memphis Memphis, TN, USA.
authors.forename: Felecia L
authors.initials: FL
authors.lastname: Malone
authors.affiliation: College of Medicine, University of Tennessee Health Science Center Memphis, TN, USA.
authors.forename: Teera L
authors.initials: TL
authors.lastname: Crawford
authors.affiliation: Instituto de Ciências Biológicas, Universidade Federal do Pará Belém, Brazil.
authors.forename: Letícia
authors.initials: L
authors.lastname: Miquilini
authors.affiliation: Instituto de Ciências Biológicas, Universidade Federal do Pará Belém, Brazil.
authors.forename: Raílson C
authors.initials: RC
authors.lastname: Salomão
authors.affiliation: Instituto de Ciências Biológicas, Universidade Federal do Pará Belém, Brazil.
authors.forename: Diego L
authors.initials: DL
authors.lastname: Guimarães
authors.affiliation: Instituto de Psicologia, Universidade de São Paulo São Paulo, Brazil.
authors.forename: Dora F
authors.initials: DF
authors.lastname: Ventura
authors.affiliation: Department of Biology, University of Memphis Memphis, TN, USA ; Department of Anatomy and Neurobiology, University of Tennessee Health Science Center Memphis, TN, USA.
authors.forename: Malinda E C
authors.initials: ME
authors.lastname: Fitzgerald
authors.affiliation: Instituto de Ciências Biológicas, Universidade Federal do Pará Belém, Brazil ; Núcleo de Medicina Tropical, Universidade Federal do Pará Belém, Brazil.
authors.forename: Luiz Carlos L
authors.initials: LC
authors.lastname: Silveira
keywords: Cambridge Color Test; P pathway; color vision; color-luminance interaction; compound stimulus; pseudoisochromatic stimulus