Perception/Natural Design Flashcards
absolute threshold
minimal limit of a sense modality- minimum stimulus energy detected 50% of the time(Start out with lo intensity and increase until they can see itBut it’s not clear when perception happensso we look at probabilities, where do people perceive something HALF the time, half the time yes, half the time no)
difference threshold
- minimum difference needed to discriminate between two stimuli, 50% of the time- judgment made between standard and comparison stimuli (both are well above absolutethreshold)- a.k.a. “just noticeable difference,” or JND-JND depends on what specific sense/stimulus it is
weber’s law
k=JND/S (k=constant, S=stimulus intensity)e.g., for a 100 g weight, JND = 3 g (difference = 3%)for a 1,000 g weight, JND = 30 g (difference = 3%) Weber fraction = 3/100 = 0.03
Fitt’s law
- intended to measure the information capacity of the human motor system- original task: participants tapped a stylus back and forth between two metal plates; were told to“emphasize accuracy rather than speed”- definition: the time to acquire (or move to) a target is a function of the distance to and size of the target– applied to computers with pointing systems (e.g., mouse, trackpad, touch screen, etc.)- referenced in Apple’s Macintosh Human Interface Guidelines (2012) and Microsoft’s Windows UserExperience Interaction Guidelines (2010)
Fitt’s Law & computer menus
- poor design: menus (that are not at the edge of the screen, dead space at bottom) take longer to correctly activatee.g., Apple Mac OS Dock good design: menus that are at the extreme edges of a screeneg., Microsoft Windows taskbar at the bottom of the screen has “infinite” target size, so is quickand easy to activate, can move mouse down a mile and still target icon- better design: menus that are in the corner of the screene.g., Windows 8’s “hot corners”: upper-right corner opens Charm bar
Fitt’s law and computer menu items
- poor design: small buttons are harder to click e.g., typical pull-down or pop-up menu (boring grey)- good design: menus closer to the mouse pointer lead to faster performance e.g., pie menus (same distance to all options in pie from mouse)- better design: executing commands without needing to reach a particular target e.g., mouse or touch gestures can be performed anywhereGood design should take perceptual abilities into consideration!!!!
ClearviewHwy Typeface
- ClearviewHwy® typeface developed over 10 years to be more readable, even with degraded vision (due to aging population, poor viewing conditions, etc.)- first, existing typefaces were reviewed and rejected- new design emphasized certain geometrical characteristics of letters “a”, “e”, and “s” to aiddistance viewing– design also reduces HALATION: spreading and blurring of light from headlights
ClearviewHwy Typeface research methods
• experimental design: tests of recognition (e.g., looking for a street name) and legibility (identification); recognition distances are up to twice as much as legibility distances• recognition procedure: particular word appeared on a panel with two other words; RT measured• legibility procedure: read a sign from moving vehicle on test track; record maximum distance for identification• subjects: half were older drivers - results:• nighttime sign reading distance improved by up to 16% (vs. FHWA Standard Alphabet); at ~70 km/h, extra 24 m of reading distance, or 1.2 s of reading time• upper/lowercase Clearview gave 14% improvement over all-CAPS FHWA typeface• greatest improvement came in older drivers!concs• lab and field experimentation are both valuable• psychophysical research can have important applications!
affordances (background)
J.J. Gibson (1977)• influenced by evolutionary theory• “ecological approach”: how does individual interact with environment?• in general, stressed importance of “stimulus array”• downplayed role of cognition in perception• study INVARIANTS: properties of an object that remain constant despite changes in perceiver’sPOVe.g., large object covers up lots of background• basic principles:1) consider perception from POV of moving observer (like in real life)-(lots of vision research isolated someone’s head in a frame, that’s not real life bro!)2) consider info in dynamic “optic array”, not just static image on a screen3) optic array is rich with information; mental processing unnecessary: perception is directdownplay cognition, IT ALL JUST HAPPENSstimulus array: flat picture of what we perceive
affordances
real (or perceived) set of actions that a specific object or environmental situation makes available to the perceiver• cups drinking• buttons  pushing• handles  push/pull/hold- depends on perceiver- no distinction between “natural” and “artificial” world; constructed world is a form of thenatural world transformed by humans-what functions can i do with this object?-cultures independently came up with cups for drinking, like language of color progression!-Gibson admitted that affordances are probabilistic-can be errors in perceiving affordances-e.g., thin ice covered with snow
affordances origins
Kurt Lewin: Aufforderungscharacter translated as: “invitation character”, “valence”, or “demandcharacteristic” Koffka (1935):“To primitive man each thing says what it is and what he ought to do with it…a fruit says ‘Eat me’; water says ‘Drink me’; thunder says ‘Fear me’; and woman says ‘____ me’ ”- mailbox has a valence only if you want to mail a letter - for Gibson, affordances deal with the POSSIBLEe.g., can you put the letter in the mailbox?(Need doesn’t matter, but the physicality. Can you put that letter, in a mailbox, whether or not its appropriate for you at that time.)
affordances of the terrestrial environment
1) The air- atmosphere  breathing- also visual, auditory, olfactory perception2) The substances- water  drinking, washing, pouring- solids (clay)  shaping, moulding- harder substances  chipped, ground, whittled3) The surfaces (and their layouts)- horizontal, flat, rigid surfaces  support- vertical surfaces  barriers- obstacles  circumvented (if paths visible)4) The objects (“Everyday Things”) - may be attached or detachede.g., 5-inch cube can be grasped; 10-inch cube cannot (unless it has a handle)- objects not ___________ by their qualities; certain qualities are afforded by certain objects - alternatively: object can have several affordances• a special type of object is…people!- they lead to certain affordances  social behavior, which is based on available stimulus informatione.g., physical attractiveness has commonalities across culture and age• affordances of places, especially hiding places:- affords privacy (remaining unseen) via opaque enclosure
affordances research evidence
Eleanor J. Gibson & Walk (1960): visual cliff experiment- sheet of glass placed across apparent drop-off - infants tended to avoid deep side- affordances don’t require much learningWarren (1984): stair climbing- formula from 17th century used up to 1978:2 × R (riser height) + T (tread depth) = 24 in.- not optimal for all people- observers judged pictures of various stairs- optimal: R = L (leg length) × 0.25- visual judgments matched energy expenditure (direct perception?)-had ppl go up and down while measuring energy expenditureno mountain of evidence here
how did norman take on theory of affordances after gibson’s death?
- mistaken perceptions  inappropriate actions (errors)e.g., glass door perceived to be open air- designers should use PERCEIVED affordancese.g., real affordances: what are the actions you can actually do?vs. perceived affordances: what are the actions you think you can do? - no signs, pictures, labels should be required (“natural design”)Norman later changed perceived affordance to the word SIGNIFIER: “any perceivable sign for appropriate behaviour, whether intentional or nonintentional”
principles of natural design: visibility
visibility– important parts must be visible- parts must provide correct messagee.g., good: “S” = salt, “P” = pepper (better: clear container) - natural signals, interpreted naturally- may indicate relation between intended and actual operations– allows discrimination of different actionse.g., car climate control: red = hot, blue = cold(Floss, poorly designedGet to end of floss, and only get 3cm, shit, do you rewash it?So now there are windows into the floss box to avoid that at the endEven clear floss boxesAlso, salt and pepper. Sometimes indicated by holes… Never sure which one. The best one is if the containers are clear so you can easily see what is salt and pepper just by looking!)
