Copyright Catherine M. Burns 1 VISION PART 2
Copyright Catherine M. Burns2 Visual Search Idea that people look through the environment to detect certain things Perspectives: Eye movements (physical) Visual search (cognitive) Signal detection theory
Copyright Catherine M. Burns3 Eye movements Pursuit movements (moving target) Saccadic movements (static target) TargetPursuit movement Think finger tracking exercise from controls lecture
Copyright Catherine M. Burns4 Saccadic movements Initial point Destination Movement time Dwells
Copyright Catherine M. Burns5 Key aspects Movement times are very rapid (ms) 3-4 dwells per second Destination reflects goals (top down) or salience (bottom up) Dwell time reflects information content or extraction difficulty
Copyright Catherine M. Burns6 Visual Search Identification of targets in a field of non-targets (distractors) Time (1 target) = (number of items x inspection time)/2 Average time, based on probability of finding a target Key points: more items=more time Only applies to very itemized searches (e.g.phone books)
Copyright Catherine M. Burns7 Other types of search Organized search People will search left-right and top-bottom Unorganized searches (inspection tasks, maps) Prob of detection Time 1 0
Copyright Catherine M. Burns8 Basic principles More items, search time takes longer But – diminishing returns with longer searches Modify with Salience (conspicuity) Organization
Copyright Catherine M. Burns9 Signal detection theory Adds to visual search by distinguishing between Target location Target identification Applies to environments with signals and noise elements Material inspection, baggage inspection, reading xrays
Copyright Catherine M. Burns10 Based on the idea that people may identify correctly (hit), miss the target, identify noise as target (false alarm), ignore noise (correct rejection) TargetNo Target Respond Y Respond N HITFA MissCR
Copyright Catherine M. Burns 11 Lighting Ergonomics (not in text)
Copyright Catherine M. Burns12 Direct Lighting light straight from a source lamps, desk lights, "task lighting" high local luminance strong shadows tends to create glare if illumination is too high if people have to work with bright task lighting in a dim room they get a "relative" glare effect good to add illumination in already high illuminated areas
Copyright Catherine M. Burns13 Indirect Lighting throw light onto the ceiling or walls then it is reflected back diffuse light, no shadows low glare need bright ceilings and walls Combining both Filters (aka shades!) help diffuse light, remove shadows
Copyright Catherine M. Burns14 Incandescent Lighting work by heating up a filament primarily red-yellow spectrum (think of metal heating) alot of waste energy to heat "warm" light
Copyright Catherine M. Burns15 Fluorescent Lighting electricity passes through a gas, or metal vapour (sodium vapour) neon, yes like the signs argon mercury vapour (arenas, large facilities) tube covered with a fluorescent phosphors converts uv rays to visible light low luminance, general non-directional lighting primarily yellow green spectrum
Copyright Catherine M. Burns16 Full Spectrum Lighting simulates daylight less visual fatigue greater visual acuity improved mood/ Seasonal affective disorder colour, skin tones look better
Copyright Catherine M. Burns17 Determining lighting levels generally all surfaces in visual field should be equally bright luminance ratios (3:1 in middle of visual field, 40:1 across room) choose furnishings based on reflectance levels windows with blinds and curtains to reduce glare matt surfaces, not smooth shiny no source of light should be right in the visual field
Copyright Catherine M. Burns18 Lighting by Type of Work Fine detailed work: needs high lighting levels light to the front to reduce shadows Computer work indirect lighting is better to reduce glare lighting level should consider need to switch tasks
Copyright Catherine M. Burns19 Exercise: Lighting Analysis CharacteristicE2RCH Natural sources? Reflectance Size of room Artificial sources Levels Flicker? Key tasks?