ASTM E1808-96(2021)

Standard Guide for Designing and Conducting Visual Experiments

ABSTRACT
This guide is intended to help the user decide on the type of viewing conditions, visual scaling methods, and analysis that should be used to obtain reliable visual experimental data. It is also intended to illustrate the techniques that lead to visual observations that can be correlated with objective instrumental measurements of appearance attributes of objects. This guide includes a review of issues regarding the choice and design of viewing environments, an overview of various classes of visual experiments, a review of experimental techniques for threshold, matching, and scaling experiments, a review for data reduction and analysis procedures. The three different threshold and matching techniques namely, the methods of adjustment, limits, and constant stimuli, are explained. Perceptual scaling techniques reviewed include ranking, graphical rating, category scaling, paired comparisons, triadic combinations, partitioning, and magnitude estimation or production. Brief descriptions and examples, along with references to more detailed literature, are given on the appropriate types of data analysis for each experimental technique.
SCOPE
1.1 This guide is intended to help the user decide on the type of viewing conditions, visual scaling methods, and analysis that should be used to obtain reliable visual data.  
1.2 This guide is intended to illustrate the techniques that lead to visual observations that can be correlated with objective instrumental measurements of appearance attributes of objects. The establishment of both parts of such correlations is an objective of Committee E12.  
1.3 Among ASTM standards making use of visual observations are Practices D1535, D1729, D3134, D4086, and E1478; Test Methods D2616, D3928, and D4449; and Guide E1499.  
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-May-2021
• ICS: 17.180.99 - Other standards related to optics and optical measurements
• Technical Committee: E12 - Color and Appearance
• Drafting Committee: E12.11 - Visual Methods

Relations

• Refers: ASTM D4086-18(2023) - Standard Practice for Visual Evaluation of Metamerism
• Effective Date: 01-Nov-2023
• Refers: ASTM D2616-19 - Standard Test Method for Evaluation of Visual Color Difference With a Gray Scale
• Effective Date: 01-Nov-2019
• Refers: ASTM D3134-15(2019) - Standard Practice for Establishing Color and Gloss Tolerances
• Effective Date: 01-Nov-2019
• Refers: ASTM D4086-18 - Standard Practice for Visual Evaluation of Metamerism
• Effective Date: 01-Oct-2018
• Refers: ASTM D3928-00a(2018) - Standard Test Method for Evaluation of Gloss or Sheen Uniformity
• Effective Date: 01-Jun-2018
• Refers: ASTM D3134-15 - Standard Practice for Establishing Color and Gloss Tolerances
• Effective Date: 01-Jan-2015
• Refers: ASTM D3928-00a(2014) - Standard Test Method for Evaluation of Gloss or Sheen Uniformity
• Effective Date: 01-Dec-2014
• Refers: ASTM D1535-14 - Standard Practice for Specifying Color by the Munsell System
• Effective Date: 01-Nov-2014
• Refers: ASTM E284-13b - Standard Terminology of Appearance
• Effective Date: 01-Nov-2013
• Refers: ASTM E284-13a - Standard Terminology of Appearance
• Effective Date: 01-Jun-2013
• Refers: ASTM D1535-13 - Standard Practice for Specifying Color by the Munsell System
• Effective Date: 01-Jan-2013
• Refers: ASTM E284-13 - Standard Terminology of Appearance
• Effective Date: 01-Jan-2013
• Refers: ASTM D1535-12a - Standard Practice for Specifying Color by the Munsell System
• Effective Date: 15-Jul-2012
• Refers: ASTM D4086-92a(2012) - Standard Practice for Visual Evaluation of Metamerism
• Effective Date: 01-Jul-2012
• Refers: ASTM D2616-12 - Standard Test Method for Evaluation of Visual Color Difference With a Gray Scale
• Effective Date: 01-Jul-2012

Overview

ASTM E1808-96(2021) is the Standard Guide for Designing and Conducting Visual Experiments, developed by ASTM International. This comprehensive guide provides methodologies and recommendations for selecting viewing conditions, visual scaling methods, and data analysis techniques to ensure reliable and reproducible results in visual experiments. It also offers guidance for correlating subjective visual observations with objective instrumental measurements, especially for appearance attributes such as color, gloss, and texture. The standard is vital for professionals involved in psychophysical evaluations, product quality assessment, visual sensory testing, and the development of visually-assessed standards across industries.

Key Topics

• Design of Visual Experiments: Recommendations on experimental setup, selection of viewing environments, and control of variables such as light source, viewing geometry, and observer consistency.
• Types of Visual Experiments:
  • Threshold and Matching Experiments: Methods to determine just-perceptible differences (JPDs) and equality between stimuli using adjustment, limits, and constant stimuli techniques.
  • Scaling Experiments: Strategies for deriving quantitative relationships between physical and perceptual attributes using methods such as ranking, category scaling, graphical rating, paired comparisons, triadic combinations, partitioning, and magnitude estimation.
• Data Analysis: Overview of procedures for reducing and interpreting experimental data, including Probit analysis, Thurstone's Law of Comparative Judgments, and multidimensional scaling (MDS) techniques.
• Standard Terminology & Definitions: Establishment of clear definitions for terms such as appearance, observer, sample, scale (nominal, ordinal, interval, ratio), and psychophysical concepts essential to experimental integrity.
• Observer Selection and Training: Guidance for the selection, evaluation, and training of observers to ensure their responses meet the standards required for accurate visual assessments.
• Safety and Compliance: Recommendations for establishing appropriate safety, health, and environmental practices before conducting visual experiments.

Applications

ASTM E1808-96(2021) is valuable across a wide range of industries and applications, including:

• Product Quality Control: Assessing color, gloss, or other appearance attributes in manufacturing (e.g., paints, textiles, plastics) to ensure consistency with standards.
• Color Science and Engineering: Providing methodologies for establishing visual tolerances and validating color-difference measurements using psychophysical experiments.
• Instrumental Correlation: Aiding in the correlation between subjective human assessments and objective instrumental readings, critical for developing reliable measurement protocols.
• Training and Selection of Visual Assessors: Outlining best practices for recruiting and qualifying observers, especially in environments where consistent and objective visual judgments are required.
• Research and Development: Facilitating the design of visual experiments in academic, industrial, or regulatory research, supporting new product development and standardization initiatives.

Related Standards

ASTM E1808-96(2021) draws on and complements several other key ASTM standards, including:

• D1535 – Practice for Specifying Color by the Munsell System
• D1729 – Practice for Visual Appraisal of Colors and Color Differences of Diffusely-Illuminated Opaque Materials
• D2616 – Test Method for Evaluation of Visual Color Difference With a Gray Scale
• D3134 – Practice for Establishing Color and Gloss Tolerances
• D3928 – Test Method for Evaluation of Gloss or Sheen Uniformity
• D4086 – Practice for Visual Evaluation of Metamerism
• D4449 – Test Method for Visual Evaluation of Gloss Differences Between Surfaces of Similar Appearance
• E1478 – Practice for Visual Color Evaluation of Transparent Sheet Materials
• E1499 – Guide for Selection, Evaluation, and Training of Observers

Referencing these standards ensures comprehensive coverage and compatibility with established methodologies in appearance measurement and visual assessment.

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By following ASTM E1808-96(2021), organizations can ensure standardized practices in visual experiments, enhancing reliability, traceability, and the meaningful correlation of subjective visual data with objective measurements across various sectors.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1808 − 96 (Reapproved 2021)
Standard Guide for
Designing and Conducting Visual Experiments
This standard is issued under the fixed designation E1808; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope D4086 Practice for Visual Evaluation of Metamerism
D4449 Test Method for Visual Evaluation of Gloss Differ-
1.1 Thisguideisintendedtohelptheuserdecideonthetype
ences Between Surfaces of Similar Appearance
of viewing conditions, visual scaling methods, and analysis
E284 Terminology of Appearance
that should be used to obtain reliable visual data.
E1478 Practice for Visual Color Evaluation of Transparent
1.2 This guide is intended to illustrate the techniques that
Sheet Materials
leadtovisualobservationsthatcanbecorrelatedwithobjective
E1499 Guide for Selection, Evaluation, and Training of
instrumental measurements of appearance attributes of objects.
Observers
The establishment of both parts of such correlations is an
3. Terminology
objective of Committee E12.
3.1 The terms and definitions in Terminology E284 are
1.3 AmongASTM standards making use of visual observa-
applicable to this guide.
tions are Practices D1535, D1729, D3134, D4086, and E1478;
Test Methods D2616, D3928, and D4449; and Guide E1499.
3.2 Definitions:
3.2.1 appearance, n—in psychophysical studies, perception
1.4 This standard does not purport to address all of the
inwhichthespectralandgeometricaspectsofavisualstimulus
safety concerns, if any, associated with its use. It is the
are integrated with its illuminating and viewing environment.
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
3.2.2 observer, n—one who judges visually, qualitatively or
mine the applicability of regulatory limitations prior to use.
quantitatively, the content of one or more appearance attributes
1.5 This international standard was developed in accor-
in each member of a set of stimuli.
dance with internationally recognized principles on standard-
3.2.3 sample, n—a small part or portion of a material or
ization established in the Decision on Principles for the
product intended to be representative of the whole.
Development of International Standards, Guides and Recom-
3.2.4 scale, v—to assess the content of one or more appear-
mendations issued by the World Trade Organization Technical
ance attributes in the members of a set of stimuli.
Barriers to Trade (TBT) Committee.
3.2.4.1 Discussion—Alternatively, scales may be deter-
2. Referenced Documents
mined by assessing the difference in content of an attribute
with respect to the differences in that attribute among the
2.1 ASTM Standards:
members of the set.
D1535 Practice for Specifying Color by the Munsell System
D1729 Practice for Visual Appraisal of Colors and Color 3.2.5 specimen, n—a piece or portion of a sample used to
Differences of Diffusely-Illuminated Opaque Materials make a test.
D2616 Test Method for Evaluation of Visual Color Differ-
3.2.6 stimulus, n—any action or condition that has the
ence With a Gray Scale
potential for evoking a response.
D3134 Practice for Establishing Color and Gloss Tolerances
3.3 Definitions of Terms Specific to This Standard:
D3928 Test Method for Evaluation of Gloss or Sheen
3.3.1 anchor, n—the stimulus from which a just-perceptible
Uniformity
difference is measured.
1 3.3.2 anchor pair, n—a pair of stimuli differing by a defined
This guide is under the jurisdiction of ASTM Committee E12 on Color and
Appearance and is the direct responsibility of Subcommittee E12.11 on Visual
amount, to which the difference between two test stimuli is
Methods.
compared.
Current edition approved June 1, 2021. Published June 2021. Originally
3.3.3 interval scale, n—a scale having equal intervals be-
approved in 1996. Last previous edition approved in 2015 as E1808 – 96 (2015).
DOI: 10.1520/E1808-96R21.
tween elements.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.3.3.1 Discussion—Logical operations such as greater-
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
than, less-than, equal-to, and addition and subtraction can be
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. performed with interval-scale data.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1808 − 96 (2021)
3.3.4 law of comparative judgments—an equation relating 5. Viewing Conditions
the proportion of times any stimulus is judged greater, accord-
5.1 Light Source—The illumination of the specimens in
ing to some attribute, than any other stimulus in terms of
scaling experiments must be reproducible over the course of
just-perceptible differences.
the experiments. To achieve this, it is essential to control both
3.3.5 nominal scale, n—scale in which items are scaled
the spectral character and the amount of illumination closely in
simply by name.
both space and time. Failure to accomplish this can seriously
3.3.5.1 Discussion—Only naming can be performed with
undermine the integrity of the experiments.The spectral power
nominal-scale data.
distribution of the illumination should be known or, if this is
notpossible,thelightsourceshouldbeidentifiedastotypeand
3.3.6 ordinal scale, n—a scale in which elements are sorted
manufacturer. Information such as daylight-corrected fluores-
in order based on more or less of a particular attribute.
cent light, warm-white fluorescent light, daylight-filtered in-
3.3.6.1 Discussion—Logical operations such as greater-
candescent light, incandescent light, etc., together with param-
than,less-than,orequal-tocanbeperformedwithordinal-scale
eters such as correlated color temperature and color rendering
data.
index, if available, should be noted in the report of the
3.3.7 psychometric function, n—the function, typically
experiment.
sigmoidal,relatingtheprobabilityofdetectingastimulustothe
stimulus intensity. 5.2 Viewing Geometry—Almost all specimens exhibit some
degreeofgonioapparentorgoniochromaticvariation;therefore
3.3.8 psychophysics, n—the study of the functions relating
the illuminating and viewing angles must be controlled and
the physical measurements of stimuli and the sensations and
specified. This is particularly important in the study of speci-
perceptions the stimuli evoke.
mens exhibiting gloss variations, textiles showing
3.3.9 ratio scale, n—a scale which, in addition to the
directionality, or gonioapparent (containing metallic or pearl-
properties of other scales, has a meaningfully defined zero
escent pigments) or retroreflective specimens, among others.
point.
This control and specification can range from correct position-
3.3.9.1 Discussion—In addition to the logical operations
ing of the source and observer and the elimination of any
performable with other types of data, multiplication and
secondary light sources visible in the specimens, for the
division can be performed with ratio-scale data.
judgment of gloss specimens at and near the specular angle, to
3.3.10 scale, n—a defined arrangement of the elements of a
more elaborate procedures specifying a range of angles and
set of stimuli or responses.
aperture angles of illumination and viewing for gonioapparent
and retroreflective specimens. When fluorescent specimens are
4. Summary of Guide
studied, the spectral power distribution of the source must
4.1 This guide provides an overview of experimental design closely match that of a designated standard source.
and data analysis techniques for visual experiments. Carefully
5.3 Surround and Ambient Field—For critical visual scaling
conducted visual experiments allow accurate quantitative
work, the surround, the portion of the visual field immediately
evaluation of perceptual phenomena that are often thought of
surrounding the specimens, should have a color similar to that
asbeingcompletelysubjective.Suchresultscanbeofimmense
of the specimens.The ambient field, the field of view when the
value in a wide variety of fields, including the formulation of
observer glances away from the specimens, should have a
coloredmaterialsandtheevaluationoftheperceivedqualityof
neutral color (Munsell Chroma less than 0.2) and a Munsell
products.
ValueofN6toN7(luminousreflectance29to42);seePractice
4.2 This guide includes a review of issues regarding the
D1729).
choice and design of viewing environments, an overview of
5.4 Observers—Guide E1499 describes the selection,
various classes of visual experiments, and a review of experi-
evaluation, and training of observers for visual scaling work.
mental techniques for threshold, matching, and scaling experi-
Of particular importance is the testing of the observers’ color
ments. It also reviews data reduction and analysis procedures.
vision and their color discrimination for normality. Color
Three different threshold and matching techniques are
vision tests for this purpose are described in Guide E1499.
explained, the methods of adjustment, limits, and constant
stimuli. Perceptual scaling techniques reviewed include
6. Categories of Visual Experiments
ranking, graphical rating, category scaling, paired
6.1 Visual experiments tend to fall into two broad classes:
comparisons,triadiccombinations,partitioning,andmagnitude
(1) threshold and matching experiments designed to measure
estimation or production. Brief descriptions and examples,
visual sensitivity to small changes in stimuli (or perceptual
along with references to more detailed literature, are given on
equality), and (2) scaling experiments intended to generate a
the appropriate types of data analysis for each experimental
psychophysical relationship between the perceptual and physi-
technique.
cal magnitudes of a stimulus. It is critical to determine first
4.3 Forreviewsoftopicsinotherthanvisualsensorytesting
which class of experiment is appropriate for a given applica-
within ASTM, see Refs (1, 2).
tion.
6.1.1 Threshold and Matching Experiments—Threshold ex-
periments are designed to determine the just-perceptible dif-
The boldface numbers in parentheses refer to a list of references at the end of
this guide. ference in a stimulus, or JPD.Threshold techniques are used to
E1808 − 96 (2021)
measuretheobservers’sensitivitytoagivenstimulus.Absolute 6.1.2.3 Interval Scales—Intervalscaleshaveequalintervals.
thresholds are defined as the JPD for a change from no On an interval scale, if a pair of specimens were separated by
two units, and a second pair at some other point on the scale
stimulus, while difference thresholds represent the JPD from a
were also separated by two units, the differences between the
particular stimulus level greater than zero. The stimulus from
pair members would appear equal. However, there is no
whichadifferencethresholdismeasuredisknownasananchor
meaningfulzeropointonanintervalscale.Acommonexample
stimulus. Often, thresholds are measured with respect to the
ofanintervalscaleistheCelsiustemperaturescale.Inaddition
difference between two stimuli. In such cases, the difference of
to the mathematical operations listed for nominal and ordinal
apairofstimuliiscomparedtothedifferenceinananchorpair.
scales, addition and subtraction can be performed with
Absolute thresholds are reported in terms of the physical units
interval-scale data.
used to measure the stimulus, for example, a brightness
6.1.2.4 Ratio Scales—Ratio scales have all the properties of
threshold might be measured in luminance units of candelas
the above scales plus a meaningfully defined zero point. Thus
per square metre. Sensitivity is measured as the inverse of the
it is possible to equate ratios of numbers meaningfully with a
threshold, since a low threshold implies high sensitivity.
ratio scale. Ratio scales are often impossible to obtain in visual
Threshold techniques are useful for defining visual tolerances,
work. An example of a ratio scale is the absolute, or Kelvin,
such as color-difference tolerances. Matching techniques are
temperature scale. All of the mathematical operations that can
similar, except that the goal is to determine when two stimuli
be performed on interval-scale data can also be performed on
are not perceptibly different. Measures of the variability in
ratio-scale data, and in addition, multiplication and division
matching can be used to estimate thresholds. Matching experi-
can be performed.
ments provided the basis for CIE colorimetry through the
metamericmatchesusedtoderivethecolor-matchingfunctions
7. Threshold and Matching Methods
of the CIE standard observers.
7.1 Several basic types of threshold experiments are pre-
6.1.2 Scaling Experiments—Scaling experiments are in-
sented in this section in order of increasing complexity of
tended to derive relationships between perceptual magnitudes
design and utility of the data generated. Many modifications of
and physical magnitudes of stimuli. Several decisions must be
thesetechniqueshavebeendevelopedforspecificapplications.
made, depending on the type and dimensionality of the scale
Experimenters should strive to design an experiment that
required. It is important to identify the type of scale required
removes as much control of the results from the observers as
and decide on the scaling method to be used before any scaling
possible, thus minimizing the influence of variable observer
dataarecollected.Thisseemstobeanobviouspoint,butinthe
judgment criteria. Generally, this comes at the cost of imple-
rush to acquire data it is often overlooked, and later it may be
menting a more complicated experimental procedure.
foundthatthedataobtaineddonotyieldtheanswerrequiredor
7.1.1 Method of Adjustment—The method of adjustment is
cannot be used to perform desired mathematical operations.
the simplest and most straightforward technique for deriving
See Refs (3, 4) for further details. Scales are classified into the
threshold data. In it, the observer controls the stimulus mag-
following four classes:
nitude and adjusts it to a point that is just perceptible (absolute
6.1.2.1 Nominal Scales—Nominal scales are relatively threshold) or just perceptibly different (difference threshold).
The threshold is taken to be the mean setting across a number
trivial in that they scale items simply by name. For color, a
of trials by one or more observers. The method of adjustment
nominalscalemightconsistofreds,yellows,greens,blues,and
has the advantage that it is quick and easy to implement.
neutrals. Scaling in this case would simply require deciding
However, it has a major disadvantage in that the observer is in
which color belonged in which category. Only naming can be
control of the stimulus. This can bias the results due to
performed with nominal data.
variability of observers’ criteria and adaptation effects. If an
6.1.2.2 Ordinal Scales—Ordinal scales are scales in which
observer approaches the threshold from above, adaptation
elements are sorted in ascending or descending order based on
might result in a higher threshold than if it were approached
more or less of a particular attribute. A box of multicolored
from below. Often the method of adjustment is used to obtain
crayons could be sorted by hue, and then in each hue family,
a first estimate of the threshold, to be used in the design of
say red, the crayons could be sorted from the lightest to the
more sophisticated experiments. The method of adjustment is
darkest. In a box of crayons the colors are not evenly spaced,
also commonly used in matching experiments.
so one might have, for example, three dark, one medium, and
7.1.2 Method of Limits—The method of limits is only
two light reds. If these colors were numbered from one to six
slightly more complex than the method of adjustment. In the
in increasing lightness, an ordinal scale would be created. Note
method of limits, the experimenter presents the stimuli at
that there is no information on such a scale as to the magnitude
predefined discrete magnitude levels in either ascending or
of difference from one of the reds to another, and it is clear that
descending series. For an ascending series, the experimenter
they are not evenly spaced. For an ordinal scale, it is sufficient
presents a stimulus, beginning with one that is certain to be
that the specimens be arranged in increasing or decreasing
imperceptible, and asks the observer if it is visible. If the
amountsofanattribute.Thespacingbetweenspecimenscanbe
observer responds no, the experimenter increases the stimulus
large or small and can change up and down the scale. Logical
magnitude and presents another trial. This continues until the
operations such as greater-than, less-than, or equal-to can be
observer responds yes. A descending series begins with a
performed with ordinal-scale data. stimulus magnitude that is clearly perceptible and continues
E1808 − 96 (2021)
until the observer responds no, the stimulus cannot be per- 7.1.3.3 Staircase Procedures—Staircase procedures are
ceived. The threshold is taken to be the average stimulus modifications of the forced-choice procedure designed to
measureonlythethresholdpointonthepsychometricfunction.
magnitude at which the transition between yes and no re-
Staircase procedures are particularly applicable to situations in
sponses occurs for a number of ascending and descending
which the stimulus presentations can be fully automated. A
series. Averaging over both types of series minimizes adapta-
stimulus is presented and the observer is asked to respond. If
tion effects. However, the observers are still in control of their
the response is correct, the same stimulus magnitude is
criteria since they can respond yes or no at their own
presented again. If the response is incorrect, the stimulus
discretion.
magnitude is increased for the next trial. Generally, if the
7.1.3 Method of Constant Stimuli—In the method of con-
observer responds correctly on three consecutive trials, the
stant stimuli, the experimenter chooses several stimulus mag-
stimulusmagnitudeisdecreased.Thestimulusmagnitudesteps
nitude levels (usually five or seven) around the level of the
are decreased until some desired precision in the threshold is
threshold. These stimuli are each presented to the observer
reached. The sequence of 3-correct or 1-incorrect response
several times, in random order. The frequency, over the trials,
prior to changing the stimulus magnitude results in conver-
with which each stimulus is perceived is determined. From
gence to a stimulus magnitude that is correctly identified in
such data, a “frequency-of-seeing” curve, or psychometric
79 % of the trials, very close to the nominal threshold of 75 %.
function, can be derived that allows determination of the
Often several independent staircase procedures are run simul-
threshold and its uncertainty. The threshold is generally taken
taneously to randomize the experiment further. A staircase
to be the stimulus magnitude at which it is perceived in 50 %
procedure can also be run with yes-no or pass-fail responses.
of the trials. Psychometric functions can be derived for either
a single observer (through multiple trials) or a population of
8. Scaling Methods
observers (one or more trials per observer). Two types of
8.1 Dimensionality—Scaling methods can be divided into
response can be obtained: yes-no (or pass-fail) and forced
two groups: unidimensional (one-dimensional) and multidi-
choice.
mensional scaling.
7.1.3.1 Yes-No Procedures—In a yes-no or pass-fail method
8.1.1 Unidimensional Scaling—This method assumes that
of constant stimuli procedure, the observers are asked to
both the attribute to be scaled and the physical variation of the
respondyesiftheydetectthestimulus(orstimuluschange)and
stimulus are unidimensional. The observers are asked to make
no if they do not. The psychometric function is the percent of
their judgments on a single perceptual attribute. In color work,
yes responses as a function of stimulus magnitude. Fifty
common examples include judging the color difference in a
percent yes responses would be taken as the threshold level.
pair of specimens or judging the lightness of one specimen
Alternatively, this procedure can be used to measure visual
relative to that of another in a series of colors in which hue and
tolerances above threshold by providing a reference stimulus
chroma are constant.
magnitude (for example, a color-difference anchor pair) and
8.1.1.1 Cross-Modality Scaling—It is also possible in color
asking the observers to pass stimuli that fall below the
work to judge one attribute of a pair of specimens but express
magnitude of the reference (have a smaller color difference
the results in terms of another attribute, displayed on a scale
than the anchor pair), and fail those that fall above it (have a
made up of anchor pairs.An example is the use of a gray scale,
larger color difference). The psychometric function is the
inwhichdifferencesintotalcolordifference,orchroma,orhue
percent o
...