Chapter 4

 Visual stimulation is a wave of electromagnetic energy  Visual spectrum has a point along a wavelength  Wavelength determines hue (color) – nm  Amplitude determines brightness  Pure colored wavelengths are said to be saturated  May be diluted with achromatic light (gray)  e.g., pure red diluted with achromatic light yields pink  Measurement of brightness or intensity of stimulus reaching the eyeball is more complex  Luminous intensity/flux1 candela or lumens  IluminanceFoot candle or LUX  LuminanceCandela/M 2 or foot lambert  Reflectanceluminance/iluminance  BrightnessActual experience of intensity

1. Location – Retina center Fovea (cones) & Periphery (mostly rods) 2. Acuity (ability to resolve fine detail) – much greater when image on cones 3. Sensitivity (ability to detect light) – rods much more sensitive  Scotopic vision – night vision where only rods active  Photopic vision – enough light for both rods & cones 4. Color sensitivity – only cones can discriminate all wavelengths 5. Adaptation – Light stimulation causes rods to rapidly lose sensitivity (slow response); cones insensitive to changes (sometimes hypersensitive with little stimulation causes night glare) 6. Differential wavelength sensitivity – cones sensitive to all wavelengths; rods are particularly insensitive to long wavelengths (red)

 Contrast sensitivity – ability to detect contrast is essential to detect and recognize shapes  C = (L-D)/(L+D)CS = 1/C M  Contrast itself  Level of illumination

 Reading Print – optimum print size >= 3 cycles/degree (stroke width 1/6 th degree); use familiar fonts; don’t use all uppercase or blocked letters  Color Sensation – best in well illuminated environment; 7% of males colorblind (protanopia). Most prevalent red-green  Simultaneous contrast – when two colors next to each other look the same  Negative After Image – occurs when focusing on one color too long.  Night Vision –  loss of contrast sensitivity due to age and low illumination is big problem  at night rods are actively used – lack of perception leads to speeding or overdriving head lights

 Bottom-up – stimulus that is there; Top – down – what we expect to be there.

Pictorial Cues  Linear perspective – converging parallel lines  Relative size – objects known to be similar size appear be different size  Interposition – one object obscures contour of another  Light & shading – shadows provide evidence as to location  Textured gradients – distant objects have finer gradient  Relative motion or motion parallax – distant object appear to move slower across the visual field

 Eye movements  Pursuit (following a moving object – plane in the sky)  Saccadic  Characteristics – initiation latency, destination, movement time, dwell duration, & useful field of view  Visual search  Serial search model – discriminating target from non- target (distracters) images, T=(NI)/2, top-down  Conspicuity – how well target stands out, bottom-up  Expectancies – experience/knowledge lead to target

 Knowledge of conspicuity should lead designer to enhance visibility of target  Knowledge of serial aspects should forewarn the designer about the cost of cluttered displays  Knowledge of the role of top-down processing should lead the designer to structure the search field to take advantage of past experience & intuition  Knowledge of all these influences should lead to visual search models that can predict how long it will take to find particular targets

 SDT assumes world can be modeled with the signal being present or absent (e.g., to luggage inspector weapon is signal and hair blowers, calculators, etc. are noise)  Combination of 2 states of the world present 4 joint events – hits, false alarms, misses, and correct rejections

 Other aircraft inconspicuous – occupies very small visual angle in field of vision  Two aircraft flying toward each other cover 1 mile in as little as 5 seconds  Two aircraft flying toward each other do not appear to be moving in the field of vision  Target may be camouflaged by clouds and ground noise  Not expecting other aircraft affects sensitivity because of top-down processing

 Ability to discriminate one signal from another  Recognize that long wave length colors are not easily recognized at night  Recognize that some letters and numbers are similar to others – 0 & O, E & F, 1 & l, etc.  Recognize that placement and design of signs & symbols can be confusing  Recognize that too close proximity can cause confusion  Design accordingly