Human Factors Engineering: Vision

• Vision is explored in the context of Human Factors Engineering, ISE 3614.
• Everyday driving showcases how it connects to research.

Limits of the Visual Sensory System

• Human Factors specialists should understand the limits of the visual sensory system.
• Nighttime driving illustrates potential sensory system limitations.

Overview of Topics

• Light and the receptor system in vision
• Visual limitations and sensation/perception
• Depth perception and visual search mechanics

Light as Electromagnetic Energy

• Light is a point on the visual spectrum defined by wavelength in nanometers (nm).
• Wavelength determines the color perceived.
• Physical characteristics of light contrast with the psychological experience of color.

Light Intensity and Perceptual Dimensions

• Intensity is the amount of radiant energy from a source.
• Illuminance is incident light on a surface, measured in meter-candles.
• Luminance is reflected light, measured in candela per square meter or milliLamberts.
• Perceptual dimensions include wavelength and intensity.

Layers of the Eye

• Three main layers exist in the eye: the sclera (outer), choroid (middle) and retina (inner).
• The cornea is part of the sclera.
• The choroid contains the iris, pupil, and lens.
• The retina includes the fovea and optic disc ( Blind Spot).

The Receptor System

• The Lens bends or refracts light.
• The lens changes shape to accommodate near or far vision.

Retina Receptors

• Retina is a thin layer of neural cells containing rods and cones.
• The fovea is responsible for highest resolution vision.
• Fovea contains only cones.
• Cones are approximately 6 million and concentrated in fovea, for focus and visual acuity.
• Cones are responsible for sensing color and for photopic vision (bright light).
• Rods are approximately 120 million and distributed all over the retina for sensitivity.
• Rods facilitate peripheral, movement, and scotopic vision (dark).

Visual Limitations

• Rods and cones differences are responsible for visual processing characteristics.
• Contrast, color, and night vision are vital for Human Factors.

Contrast Sensitivity

• It depends on spatial frequency, which is the number of dark/light pairs within a visual angle.
• Illumination level affects sensitivity.
• Lower contrast is more difficult to discern.
• Font familiarity matters.
• THIS IS VERY DIFFICULT due to Styles.

Color Sensation and Deficiency

• Color sensation happens best in good light.
• Rods are insensitive to red colors.
• Color deficiency exists, with types including protanope, deuteranope, and tritanope.
• Protanopes and deuteranopes confuse red and green colors.
• Designs should be monochrome first for inclusivity.

Dark Adaptation and Rhodopsin

• It takes 20-30 minutes for rods to reach peak sensitivity in the dark.
• Rhodopsin in rods reacts to light by breaking down or bleaching when exposed to light.
• Rhodopsin regenerates in darkness.

Night Vision and Glare

• Contrast sensitivity diminishes with age.
• Glare, irrelevant light of high intensity, is annoying, distracting and destroys rods' sensitivity.

Bottom-Up vs. Top-Down Processing

• Bottom-up sources include what the senses "see".
• Top-down sources are knowledge, experience, and expectancies.

Gestalt Laws of Organization

• Perceptual system organizes what is seen.
• Laws describe how the system organizes visual stimuli.
• Gestalt Laws apply to display or control layout design.
• The whole is something else than the sum of its parts.

Gestalt Law: Proximity

• Proximity is when closer objects are grouped together.

Gestalt Law: Similarity

• Similarity is when similar objects are grouped together.

Gestalt Law: Closure

• Closure is when objects forming closed units are grouped.

Good Continuation/Continuity

• Elements following the same direction (straight line, curve) form a group.

Gestalt Law: Good Continuation

• Good continuation is when objects in a line or smooth curve get grouped.

Depth Perception

• Depth perception is how a 3-D world is perceived from a 2-D image.
• Depth cues arise from the body/eyes and the external stimulus.

Depth Cues from Visual System

• Accommodation involves the lens changing shape.
• Convergence involves eyes rotating to keep the target in the fovea.
• Binocular disparity involves the difference in images between the eyes.

Accommodation of Lens

• Accommodation is defined as the lens's ability to change shape, bending light for focus.

Convergence Explained

• Eyes rotate to keep visual target in fovea.
• Cue results from eyes' rotation, projecting the image on each retina.

Binocular Disparity Explained

• Depth cue is based on difference between each eye's retinal images.
• Closer objects result in greater disparity between the image received by each eyeball.

Depth Cues from the Stimulus

• Depth cues include relative size, linear perspective, light & shading and interposition.
• Other cues are height in the visual field and relative motion or motion parallax.

Linear Perspective Explained

• Linear perspective is a depth cue from the stimulus.

Relative Size Explained

• Relative size is a depth cue from the stimulus.

Light/Shading and Textural Gradients Explained

• Texture gradients serve as a depth cue from the stimulus.

Interposition (Occlusion) Explained

• Interposition, or occlusion, gives depth cues from stimulus.

Height in Visual Field Explained

• Height in the visual field acts as a depth cue from stimulus.

Visual Search

• Eye movements involve pursuit movements and saccades.
• Pursuit movements involve tracking across the visual field.
• Saccades involve abrupt, discrete movements.

Saccades - Reading

• Pursuit movements are automatic, require physically moving stimulus and are smoothly executed but slow.
• Saccades are rapid eye movements.
• Small inter-word spacing requires smaller saccades and longer fixations.

Dwell in Saccades

• Initiation latency measures the time between a target appearing and saccade starting.
• Dwell or destination duration involves information content.
• The useful field of view (UFOV) defines surrounding fixation point area available for processing.

Visual Search Strategies

• It comprises pursuit and saccadic eye movements.
• Pursuit aids object tracking in visual field
• Saccades facilitate reading through discrete eye movements
• Saccades is time between target and saccade, and duration to extract target content/info.

Visual Search and Conspicuity

• Serial vs. parallel search strategies exist.
• Key factors complicating visual search include target conspicuity and expectancies.
• Conspicuity is a bottom-up (parallel search) factor and expectancies are top-down (prior knowledge).

Visual Search Time

• Search time is N x I / 2, with N as item number and I as time spent on each item.
• Strategies involve reducing N or I.

Finding a File

• Alphabetical order simplifies finding a file.

Visual Search Strategies

• Visual search strategy involves top-down/left to right reading, or random selection.

Important Factors Complicating Things

• Conspicuity of the target and parallel search may help.
• Expectancies and prior knowledge also influences search.

Visual Search Types

• Visual search includes serial and parallel.

Serial Search

• Serial search is attentive.
• Serial search means every item gets searched.
• Serial search may prove slow, effortful & error prone.

Parallel Search

• Parallel search involves searching items simultaneously (search at a glance).
• Parallel search may benefit UI.
• Pop-out effect, speed and efficiency, can influence error.
• The number of distractors do not matter.

Serial vs. Parallel Search & Automaticity

• Serial and parallel searches depend on target/distractor nature.
• Does the target have shared feature size, movement, or brightness?
• Automaticity is familiarity.

Upcoming Studies

• Read Chapter 4 (vision) & Bennett, K. B. & Flach, J. M. (1992).
• Read Wickens Chapter 2 Signal Detection, Information Theory, and Absolute Judgment.
• Norman Review 1 is due 2/17 (Friday) 11:59 pm.
• Project Milestone 2: Personas is due 2/24 (Friday) 11:59 pm.