Visual Display Of Static Information

Copyright 2003 by Dr. Gallimore, Wright State University

Department of Biomedical, Industrial Engineering & Human Factors Engineering

Visual Display Of Static Information

Department of Biomedical, Human Factors, & Industrial Engineering


ANATOMY OF THE HUMAN EYE

• The eye is nearly spherical - diameter 20-25 mm

• It is surrounded by two membranes:• Cornea - covers the front surface of the

eye• Sclera - joins the cornea encloses the

eye



CORNEA

• The cornea is curved and clear.• Behind the cornea is the anterior chamber

containing the nutrient and oxygen liquid, aqueous humor.

• The cornea and aqueous humor constitute a strong fixed-focus lens system providing 2/3 of the refractive or focusing power of the eye.



LENS

• Under nervous and muscular control.

• Contributes to focusing power of the eye. Double convex lens, rear surface curves more sharply than its front surface.



LENS

• Behind the lens is a large chamber, filled with thin jelly-like substance, vitreous humor.

• Has variable refractive power . Changes shape and thickness through the process of Accommodation,

• Permits the eye to remain in focus as distance of objects change.



LENS

• What type of focus system is the LENS?• Variable focus



NEAR AND FARSIGHTED EYE



LIGHT PASSING THROUGH EYE

• Light enters eye at cornea, passes through the pupil, which is the aperture formed by the iris. Light then passes through the lens which focuses the light on the retina.

• The light must pass through network of nerve fibers and blood vessels before it reaches the photoreceptors.

• The photoreceptors are the RODS and CONES.• The optical image formed on the retina is transduced into nervous impulses then sent

to the brain through the optic nerve which joins the retinal at the optic disk.



RODS AND CONES

• Photoreceptors of the retina consist of RODS and CONES• Rods are primarily responsible for night vision (scotopic) • Cones are primarily responsible for daylight vision (photopic).• There are approximately 120 million rods. They contain the pigment rhodopsin• Cones mediate color vision. They contain one of three different pigments each of

which show maximum light absorption at different wavelengths. 7 million cones.



DENSITY OF RODS AND CONES



VISUAL ANGLE AND RETINAL SIZE

• Visual extent of an object on the retina is discussed in angular units or visual angle. Visual angles represent a constant relationship to retinal distances in a given eye and comparable from one eye to the next.– S = physical size of the object, meters or cm– D = distance of the target object from nodal point (N) of the eye– n = distance from corneal surface to nodal point, approx 7mm

aS

Ddeg arctan



VISUAL ANGLE AND RETINAL SIZE

• For small angles, a simple version is expressed in radians:•

• Simplified formula introduces some error. At 10 deg the visual angle will be overestimated by 1%; at 17 degree 3%.

• VA (minutes) = (3483 x H)/D

rad

SD



Vision Acuity

• Minimum separable acuity – smallest detail that can be discriminated

• Minimum perceptual acuity – detect a spot from a background

• Vernier Acuity –detect lateral displacement or slight offset of one line from another or it appears as continuous line

• Stereoscopic acuity – differentiate image on eye



Vision Acuity

• Contrast Sensitivity– Ability to distinguish

gratings as a function of their contrast and frequency.

– Modulation (M) = (Lmax - Lmin)/(Lmax + Lmin)



Conditions Affecting Visual Discrimination

• Luminance contrast– Also often called brightness. – Contrast – [(B1-B2)/B1], where

• B1 higher luminance of object or surface• B2 lower luminance of object or surface (usually background)

– Modulation = (Lmax-Lmin)/(Lmax + Lmin) where,• Lmax is maximum luminance• Lmin is minimum luminance

• Time– Acuity improves with increased exposure



Conditions Affecting Visual Discrimination

• Target Motion– Dynamic visual acuity – performance degrades as rate

of movement exceeds 60 degrees per second

• Age– Visual acuity and contrast sensitivity begin to decrease

after 40.

• Training– Train subjects to control focus has been shown to

improve acuty.



Dark Adaptation

• During adaptation the pupil size dilates increases to let in more light.

• A chemical reaction occurs in the eye within the rhodopsin (also know as visual purple).

• Rods take over. It takes approximately 20 minutes to dark adapt.



Display Features

• A. Visual display dimensions – Static versus dynamic

• Continuous vs discrete

– Coding• Pictorial, numeric etc.

– Technology used to transmit information.

• B. Units– Minimum discriminable unit (MDU) =required

maximum precision for operators task– Number of units required = (range) /MDU



Display Features

• C. In the physical characteristics of visual display units (VDU)– Light reflecting first light emitting

• D. large variation in display designs – Shape : linear, circular, semi circular, vertical,

horizontal – Fixed pointer, moving scale – Show full or partial scale– Variety of pointer and symbol designs – Scaled and linear, log, etc. units



Display Features

• E. Criteria for evaluating VDUs– Learning speed– Comfort– Absence of fatigue– Small individual differences it with effect– Performance stability– Speedy – Accuracy

• F. required properties – Visibility – Distinguishability – Interpretability



Alphanumeric Displays

• A. Criteria – Visibility – separate from surroundings – Legibility – distinguish characters – Readability/interpretability – ability to comprehend

• B. Typography (features of alphanumeric characteristics)– Stroke width

• thickness to letter height • Black on white 1:6 to 1:8• White on black 1:8 to 1:10

– Height• Width ratio 3:5




– Font type– Point size

• 1 point -= 1/72 inch

– Character size• 20-27 minutes of arc

• C. Case• D. Layout

• Interletterspacing• Interline spacing




• E. Hardware Considerations– Refresh rate, jitter, phosphor persistence – Polarity - black on white versus white on black – Color

• Use few colors• avoid extremes • chromostereopsis –false sense of depth • maximize color context of text




• F. Density – Search time increases with density – Use abbreviations, concise wording, and tables

• G. Grouping – meaningful groups of information

• H. Complexity– Visual scheme or organization– Using columns




• I. Highlighting– To reduce search time– Color, reverse video, blinking– Validity of highlighted material is important– Use blinking for extreme urgency (distracting)



Graphic Displays

• A. Display of text information– Instruction or procedures

• Pictorial for speed• Text for accuracy

– Multilingual

• B. Display of data- graphs– Elements don’t block each other– Scale should show order and range necessary

• Visual angle• Contrast

– Smallest unit must be visible



Graphic Displays

• C. Symbolic Displays– Pictures

• Show immediate meaning without need for recoding• Requires association of symbol to referent

– Criteria:– Recognition

– Matching

– Preferences



Symbols

• A. Symbolic sign is preferable to text if symbol can reliably depict what it is intended to represent (referent).

• B. strength of association between symbol and referent depends on – Already established association– Ease of learning

• Symbols (codes) need to be- Detectable - Compatible - Standardized

- Discriminable - Meaningful



Symbols• Criteria for Selecting Coding Symbols

– Recognition– Matching– Preferences and Opinions

• Perceptual Principles– Figure ground (Background remains stable (Necker

cube)– Figure Boundaries (solid is best)– Closure (closed figures are better)– Simplicity (keep it simple)– Unity (All parts of symbol should be as unified as

possible)



Coding Dimensions

• Single Coding – code on only one dimension– Shape– Size– Luminance (brightness)– Color– Flickering – etc

• Multidimensional Coding – code two or more dimensions (more than 2 can slow people down)– Color and shape (purple and square, green and circle)



Coding Dimensions

• Color Coding– Is very good for searching– Can distinguish approximately 9 items (Millers magical

number 7 +- 2)– Can be trained to distinguish more



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Visual Display Of Static Information