corritore, 7341

ITM 734

Human Factors in Information SystemsCh. 3 & 4: Vision, Perception, Object

RecognitionFall 2004Cindy Corritore, Ph.D.Creighton University

C.L. Corritore2

Human vision

• most important sense monkey people

• Two step: physical reception and processing/interpretation/perception

C.L. Corritore3

The eye

• parts retina rods vs. cones

Color (3 spectra of light) central and peripheralsensitivity to light (in light vs in dark)brightnessmovement

fovea [centralis]

C.L. Corritore4

The eye

• Cones give daytime vision and are colour sensitive. Have high acuity. Near centre of retina (fovea).

• Rods more sensitive to light, respond to brightness, but not colour. More about movement.

• Peripheral vision sensitive to movement.• Need awareness for non-standard lighting conditions

– e.g. don’t use colour dependence in dark conditions.

• There are fewer blue cones in foveal vision so use blue with care.

C.L. Corritore5

Perception

• Organise and interpret sensory information.

• Active process.

• Strongly influenced by past experience, education, cultural values, role requirements.

• Occurs in context.

C.L. Corritore6

Perception & Action

• 2 means of acting: Motor movements

Dominant in HCI

SpeechSpecialist

applications

• 5 senses: Vision

Dominant in HCI Hearing

Specialist applications

TouchVR, haptics, etc.

Taste Smell

Not used (yet…)

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Law of Prägnanz

‘Of several geometrically possible organizations, that one will actually be perceived is the one that possesses the best, simplest and most stable shape’.

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Law of Simplicity

perceive the top figure, not the bottom , more complexone.

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Gestalt thought

• perception is more than just a mirror image of the real world

• perceive groups of things, see well-organized patterns

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Gestalt Laws of Organization

• proximity – group close things• similarity – group like things• closure – fill in missing elements (complete

incomplete)• continuity – tend to see trends rather than

discrete elements (see a line, not two parts)• symmetry – tend to group items bounded by

symmetrical borders• familiarity – tend to group items that are

familiar together

C.L. Corritore11

law of similarity

lightness

shape

orientation

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Law of Familiarity

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Gestalt Laws of Grouping

• Good Continuation – objects arranged on a straight line or curve tend to be seen as following the smoothest path and the objects tend to be perceived together (as a unit)

• Proximity – objects that are close tend to be perceived together

• Common Fate – when objects move in same direction, we tend to perceived them together

• these can interact (not either or)

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Grouping

We see two lines, ab and cd – but not ad

Which grouping law?

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Grouping

see columns rather than rows.

Which grouping law?

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Grouping

see two groups of things –

What grouping law is this?

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Gestalt principles

• open question – what happens when the laws are in conflict (ie. more than one apply)?

• bottom line - user seeking structure in data

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is visual perception top-down (td) or bottom-up (bu)?

• TD: constructivists (Bruner, Neisser, Gregory) – perception active and constructive, internal and external (indirect theories) internal hypotheses, expectations, experience, context,

state of person prone to error

• BU: Gibson’s Direct Perception – optical input rich data (invariant) with little info processing required objects possess affordance see little error

C.L. Corritore19

Which is right? Depends ….

• Two types of perception: Perception for recognition

Often studied through illusionsDiscussion of link between bottom-up and top-

down processingLargely lab-based

Perception for actionE.g. Gibson’s work on affordancesMore top-down

• Perception is active

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Human vision

• eye movement moves in jumps, saccades, followed by

fixationsbrain adjusts for this movement in visual

field (sort of dampens it) jumps 30 ms, fixation 60-700 ms tend to fixate on part of visual screen

thinking about ability to perceive motion is innate

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Human Vision

• color hue (wavelength) brightness

(intensity) saturation (purity

of light)

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10 things to know about color

1. Color consists of three properties: hue (red, green, etc), brightness/lightness/value (light-dark) and saturation/chroma (vivid, pale, etc.)

2. Background has a strong influence on color appearance.3. Ambient light can affect color appearance.4. All humans divide hue into eleven basic categories: black,

white, red, green, yellow, blue, orange, pink, gray, brown and purple.

5. Color similarity is the best way to convey that two things are the same type. Color differences are the best way to convey that two things are different type.

6. People in all cultures, organize color the same.

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10 things to know about color

7. The meanings that people attach to color changes with culture. But it also changes with context in the same culture. I. E., blue can sometimes mean power and at other times sadness.

8. For people to be able to read words, there must be a lot of brightness (light-dark) contrast. Hue contrast is not much help. The biggest single mistake that designers make is insufficient brightness contrast.

9. When there are more than about 6 colors, ability to pick out individual elements declines.

10. Color is too important to consider only aesthetics. It greatly affects effectiveness, visibility and conspicuity

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Factors affecting color discrimination

• Doesn’t only depend on ‘actual’ colour

• Depends also on illumination and surrounding colours

• Important for web sitedesign (sometimes!) Be aware of colour deficiencies.

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Factors affecting color discrimination

• Spatial separationThe greater the separation, the worse the discrimination.

• Number of dimensions. Colors more discriminable if they differ in hue, saturation and

brightness than if they differ in only 1 or 2 dimensions.

• Spectral location. Varies across the spectrum. Most sensitive to changes around

yellow and at border between blue and green. poorest for colors from the edges of the spectrum: red and

violets. best when the colors are central members of each of the 11 basic

color categories.

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Factors affecting color discrimination

• Size poorer for small objects wrt hue, saturation and

lightness/brightness. effect greatest for yellow and blue.

• Saturation Hue discrimination worse as colors become less saturated.

• BrightnessHue discrimination declines at lower brightness.

• Time separationpoor for colors viewed successively and compared in memory. If

more than a few seconds elapse, people can easily discriminate only 10-12 colors.

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Factors affecting color discrimination

• Learned Color-Object Familiarityremember colors better when shown familiar objects (a red apple, green

leaf, etc.) or color is correct for object.

• Retinal locationbest when objects imaged in fovea - you are looking directly at it - and

falls as the image is seen further in the periphery. degrades first for red and green and then blue and yellow before failing

completely. only in large screens

• Brief presentationShort durations impairs discrimination of similar colors. effect is greater with reds and greens and smaller with blues and yellows.

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Mismatch

• Stroop effect: name the colour:REDGREENBLUEYELLOWBROWNPURPLE

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Human Vision

• Contrast Contrast is important for visual displays,

particularly for older users. Negative contrast (dark characters, light

background) is generally easier to read. Visual attention may be drawn by

flashing / movement, brightness, difference in a group

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Design Implications

• color should be redundant cue – why? color blind can only really differentiate 7-9 colors color interpretation varies warm appear to move towards, cool away cultural interpretations

red US/China

• which colors most sensitive to in foveal area (best with color)? red/yellow

• different colors require refocusing

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Design Implications

• visual resolution higher than monitors from 28”, letter height of .1-.2” recommended

• rods very sensitive to peripheral movement – draws attention

• brightness perception is individual PDA screen design? increase brightness, increase perception of

flicker• context (and expectations) allows us to

disambiguate interpretation

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Design Implications

• sans serif fonts

• grouping

• consistency

• simplicity

• clutter

• eye movement top left to bottom right

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Design implications:Competing Groupings

• Colour dominates shape

• Shape dominates texture

• Motion can dominate all other features

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Motion

• motion important real world - we control movement, use cues to

move through environment virtual world - must supply these cues

• key elements sense of location sense of locomotion (motion) sense of direction

can be in a virtual environment or an information space

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how do we judge our movement through ‘real’ space?

• egomotion - motion related to ourself

• visual input: foveal vision and peripheral limit peripheral, degrade performance peripheral good for perception of motion

(not focused information)

• integrate channels (eg. multiple displays) so user doesn’t have to do it in their

head

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ecological displays

• use naturally occurring cues in display these cues called optical invariants -

represent physical properties that don’t change like light deflection

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optical invariant 1: compression & splay

• compression of texture of a surface indicates distance indicates altitude of viewing

• splay is angle between two lines from front to back receding - depth

invariant – changeless, constant

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optical invariant 2: optical flow

• as we move, items flow past us

• how they move past tells us how fast we are moving and our heading (direction) expansion point - point from which all

streaming is occuring (ahead of us)stationary - cue for headingadd depth cues - more accurate

– binocular vision, motion parallax, etc.

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optical invariant 3: time-to-contact (tau)

• time we estimate until we reach an object related to our perception of the size of

objects

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optical invariant 4: global optical flow

• flow as it depends on person’s velocity and altitude fly low, things move faster

• bias - we estimate speed by global flow bus vs. motorcycle high cockpit plane taxi speeds problem -

too fast as global cues different - appeared they were going slow

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optical invariant 5: edge rate

• no. edges that pass by visual field per unit time

• use this to judge speed related to global flow and/or texture broken lines in highway vs. static wheat

field

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3-D Displays

• represent item in reality or third dimension uses depth as another quantity value

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Depth Judgements

• based on perceptual cues linear perspective - converging lines are receding in depth * interposition - obscuring item is closer height in plane - higher are farther away light & shadow - shadows indicate position relative size - based on experience. Smaller than expected

- farther away textural gradient - grain finer as go farther away

* most dominant cues

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Depth Judgements

• based on perceptual cues proximity-luminance covariance - brighter, closer aerial perspective - hazier in distance * motion parallax - as track eyes across image, items closer

move faster so judged to be closer (relative)scan this room

• all rules from the ‘real world’ with physiological roots that humans apply to displays

http://www.yorku.ca/eye/toc-sub.htm (motion after-effect) - stare at red square and when lines stop, they will reverse direction and move upwards – your system habituating)

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Depth Judgements and Humans

• built-in depth cues * binocular display - we get disparate input from

two eyes (slightly off) and merge. Degree to which ‘off’ implies distance

convergence - converge eyes, degree to which do this implies distance of object to brain

accommodation - degree to which lens accommodate to focus implies distance

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Perceptual hypotheses and ambiguity affect it

• depth/distance perception colored by our expectations/assumptions (hypotheses) automatic cues redundantly support our hypotheses

• great example: rear end collisions with small cars misperceive distance because expect larger car some European cars

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Perceptual hypotheses and ambiguity

• idea - you often make faulty assumptions, and then use cues (cycle through them) to support it. particularly true with 3-D mappings onto

2-D space3-D graphs (also have area/volume and

proximity problems)

• lesson - not great to use depth to represent a variable value

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3-D displays

• great for representing 3-D data where third dimension is distance (realism) CAD design why? pictorial realism, for example

also minimizes mental load

• great with integrative tasks less cognitive overhead

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3-D displays in 2-D: problems

• not great with focused tasks too gestalt representation of 3-D in 2-D imprecise and

requires interpretation (not exact) help by adding artificial guides (ticks, etc)

C.L. Corritore50

3-D displays in 2-D: problems

• may get misinterpretation if false hypotheses formed because of missing/inaccurate depth cues hard to represent all of these must disambiguate with artificial

elements strongest cues: interposition, motion

parallax, binocular disparity (requires special visual hardware)

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so what?

• how does this apply to interfaces? obviously in virtual reality data mining visualization mis-interpretation of graphs

Banking, finance pie graphs others ?

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Pattern recognition (2-D)

• Distinguish like things from every angle First National Bank bldg from airplane

• Seems to be top-down: general to detailed but can be other way also

• Features, edges, elemental components, context, experience, expectations

• Templates in memory?

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Object recognition

• People naturally ‘fill in’ with continuity where none exists; this works better for gentle curves than sharp ones.

• This can be exploited in constructing computer images.

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Object recognition

• Components feature coding feature integration Accessing stored structural object descriptions accessing semantic knowledge about object

• Size and shape constancy see elephant as same size and shape no matter

the orientation or distance (inborn?)

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Face recognition

• Special case of object recognition store info about the person/face that is

more accessible than name name comes after general person info recognise holistic (face) before specifics

(analysis byparts; job, name)

• Built-in predisposition

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Sound Output

• Novel Area current uses limited to beeps/twerps no real mapping between sounds and object/activity

• Humans good at sound perception; perhaps best at noticing changes in background/expected sounds driving car, notice an unusual noise father and well pump

• Sound good when other senses being used (another sensory channel - has own analysis path), glut of info to monitor, background things can become imp. at any time

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Sound Output

• Research on sounds scattered good aspects

different sensory channel so richer experience (better memory)good when sound maps to real things or things that make sense

(alarm for bad items) - real sounds (have meaning)tried to use in lieu of visual animation (eg. algorithm analysis)data sonification (explore data by listening to it); blind

bad aspectstoo much noise - can’t differentiate soundsnoisy environmentacclimate/habituate to noises (car alarms)

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Speech Output

• Problematic• strategies

words/phrases storedphone co. : sounds artificiallimited vocabulary

phonemes (sounds) - about 40 in Englishbuild wordsdifficult as requires natural language precepts

• problems may imply intelligence if can talk well

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Future Developments

• Earcons opportunistic, mobile communication http://www.hubbubme.com/

• multimedia - kind of a vast unknown

• multimodal - speech, vision, gesture haptic interface

real world examplemovie clip