Engineering Psychology PSY 378S

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Engineering PsychologyPSY 378S

• University of Toronto
• Spring 2006
• L8 Attention

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Outline

• Attention
• Three kinds of attention
• Selective attention
• Supervisory control sampling
• Visual/Target search
• Divided vs. focused attention
• Global (parallel) and local processing
• Emergent features
• Spatial proximity
• Response conflict
• Object-based proximity
• Proximity compatibility principle

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Attention as Spotlight

• We attend where beam falls
• Use this metaphor to distinguish among 3 types of
  attention

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Attention as Spotlight

• 1) Selective
• Information sometimes outside of beam we should
  attend to it
• need to attend to something else
• Need to change direction of spotlight
• e.g., so engrossed in task, forget about other
  things

Hey, over here!
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Attention as Spotlight

• 2) Focused
• Other irrelevant information in beam, need to
  narrow beam
• Need to concentrate on just one source
• Other sources of information in the environment
  serve as distraction
• e.g., someone is talking, youre trying to study

Must..focus!
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Attention as Spotlight

• 3) Divided
• Must get information from various sources, need
  to widen the beam
• Need to monitor many things at once
• e.g., driving car and listening to hockey game on
  the radio

Need..to..widen!
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Selective Attention
Hey, over here!
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Selective Attention

• Supervisory Control Sampling
• Operator scans display of a complex system in
  order to control it (e.g., dials in power plant)
• Location known, information unknown
• Target Search (aka Visual Search)
• Operator trying to locate target (radar, search
  and rescue)
• Information known, location unknown
• Directing Attention (read textbook)
• Cueing location (Hey over here!)
• Attention in Depth (read textbook)
• Potential for reduced clutter

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Supervisory Control Sampling
Which channel should be sampled more?
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Experimental Results inSupervisory Control

• Adjustment to event rate
• People sample channels with higher event rates
  more frequently
• e.g., speedometer vs. gas meter vs. engine
  temperature
• But
• Memory imperfect sampling imperfect
• Oversampling of channels with low event rates
  (sluggish beta)
• People forget to sample (undersampling)
  especially if must request/select info (channel
  info not directly observable)
• Importance of sampling reminders

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Experimental Results inSupervisory Control

• Mental model guides sampling
• When and where do events occur
• Improves with expertise
• Principles for design
• Frequently sampled displays should be placed
  centrally
• Sequentially sampled pairs of displays should be
  located together
• Processing strategiescognitive tunneling
• Downside of mental model
• When one channel fails, stop processing other
  channels
• Fixate (lock on to) channel being controlled

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Experimental Results inSupervisory Control

• Preview helps
• When observers given preview of scheduled events,
  sampling becomes more optimal
• Sampling affected by arrangement
• Operators more likely to make horizontal than
  diagonal scans
• Reluctant to diagonally scan to high event rate
  channel
• Event rate not enoughposition matters

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SDT and Supervisory Control Sampling

• Engineering psychologist divides world into
  channels along which events can periodically
  occur
• Signal detection problem Hit (detecting an
  event), Miss (do not observe an event), etc
• Ideal observer Optimal sampling
• Bias (mental model, event rate) (top-down, ?)
• Sensitivity (display arrangement factors)
  (bottom-up, d?)

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Implications

• Scanning results in supervisory control tell us
  about
• Importance of internal expectancies
• Novice vs expert scanning patternstell us about
  mental model/search strategy
• Diagnosticsfrequently watched instruments are
  those most important to operator
• Place in prominent location or close together

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Visual/Target Search
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Visual/Target Search

• Operator trying to locate target (radar, search
  and rescue)
• Target information known, location unknown
• Based on expectancies (top-down, ?)
• Novice vs. expert (quarterback, radiologist)
• Scan path will change with task
• Display factors and salience (bottom-up, d?)
• Large, bright, colourful, dynamic, abrupt onset ?
  attract attention
• Physical location (left to right, more
  concentrated in centre edge effect)
• Singletons (unique stimuli)

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Visual Fixations and UFOV

• Foveal area of fixation (approx 2 deg)
• Useful Field of View (UFOV)
• Effective area within which information can be
  extracted
• Min(distance between successive fixations) in
  visual search task
• Varies between 1 and 4 deg
• Check out http//www.visualawareness.com/Pages/wha
  tis.html

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UFOV

• Affected by
• Density of information
• Discriminability of target from background
• Aging ? UFOV
• http//www.psych.ucalgary.ca/PACE/PCA-Lab/research
  .stj94.html
• Affects
• Driving Behaviour (smaller UFOV?visual search,
  driving)
• Search and Rescue
• Coverage not Exhaustive Observers dont blanket
  area with UFOVs
• Only 53 of terrain covered (Stager Angus,
  1978)
• Targets may not be identified in UFOV
• Fixated but not detected (implies decision
  criterion XC)
• Training as solution

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Dwell Time

• Typical fixation 250-500 ms
• Survey vs. examination dwell (Kundel Nodine,
  1978)
• Longer examination dwells occur with
• Less legible displays
• Less familiar, less frequent, out-of-context
  words or objects (information theory!)
• More difficult text, or difficult to interpret
  display instruments
• Critical display instruments (greater information
  pickup)controlling aircraft vs check-in-bounds
• Longer dwells for novices Novices pilots dwell
  twice as long as experts on attitude directional
  indicator (Bellenkes et al., 1997)

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Visual Search Task

• Shown target
• Look for target in randomly arranged set of
  distractors

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Factors Affecting Search Rate

• Number of items
• Typically serial search
• Target distinguished by single level of
  dimension/simple rule
• Feature vs conjunction search
• Typically a parallel search
• Discriminability
• Hard to distinguish ? serial (inefficient)
• Easy to distinguish ? parallel (efficient,
  preattentive, pop-out)

Serial
RT
Parallel
Set Size
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Factors Affecting Search Rate (contd)

• Absence/presence of target features
• Absent (O in Qs) ? serial
• Present (Q in Os) ? parallel
• Spacing
• Little effect scanning and clutter trade off
• One or more targets
• Generally less time if single type of target
• Unless all targets discriminable along single
  dimension (e.g., diagonal stroke in K, X)

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Factors Affecting Search Rate (contd)

• Training
• If one can train to automaticity, leads to
  parallel processing
• Only where targets are consistent, must maintain
  mapping

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Visual Search Applications

• Industrial inspection
• Icons on desktop, maps, tables, commercial and
  information signs
• Vehicle dispatcher
• Scanning digital map to locate the vehicle that
  is not in service and has large capacity
• Military commander
• Find infantry platoons on digital terrain model
• Symbol coding

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Selective Attention Summary

• Supervisory Control Sampling
• Operator scans display of a complex system in
  order to control it (power plant, aircraft)
• Location known, information unknown
• Target Search (aka Visual Search)
• Operator trying to locate target (radar, search
  and rescue)
• Information known, location unknown
• Directing Attention, Attention in Depth (covered
  in book)

Hey, over here!
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Break
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Divided vs. Focused Attention

• Often good to divide attention (multi task)
  e.g., in high demand air traffic control
• However, sometimes impossible to narrow when
  needed
• Divided attention mandatory rather than optional
• Display designs or principles that facilitate
  divided attention impair focused attentiona
  tradeoff

Need..to..widen!
Must..focus!
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Parallel Processing and Divided Attention

• Preattentive phase
• Automatic
• Organizes visual world into objects, groups,
  patterns
• Global or holistic processing
• Short term sensory store
• Subsequent selective attention
• More focused
• Further elaboration
• Higher level perception, cognition
• Local processing

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Pre-attentive
Selective
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Display on right allows for preattentive grouping
of elements
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Organized Displays

• Follow Gestalt principlesproximity, similarity,
  etc.
• Probability in context redundancy (Garner, 1974)
• Knowledge of location of one display item allows
  better prediction for another
• And information theory
• Information theory based measures of display
  organization (Palmiter Elkerton, 1987 Tullis,
  1988)

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Global and Local Processing

• Global processing
• All items of organized display processed together
  in parallel (pre-attentive)
• Local processing
• Processing single object in display (selective)

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What is small letter?
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What is small letter?
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What is large letter?
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What is large letter?
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Global and Local Processing

• Response Conflict (Navon, 1977)
• Global?Local
• We automatically process global information, this
  affects local processing
• Asymmetric interference from small does not
  affect large (Local does not affect Global)

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Emergent Features

• Related to global processing concept
• Emergent feature is global property of set of
  stimuli (or displays) not evident as each is seen
  in isolation
• Speeds processing (because preattentive)
• Only works if
• Organization is compatible with task
• Gestalt principles (based on information theory
  expectation/redundancy constructs) upheld

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Spatial Proximity and Divided Attention

• How can display designers help users divide
  attention?
• Putting information sources in the same location
  (? spatial proximity) should support parallel
  processing (and thus divided attention)
• There is evidence that it does
• Head-Up Displays (HUDs) as example
• HUD superimposes aircraft instrument information
  on view of real world

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Do HUDs Help?

• Both information channels (instruments and view
  out the windshield) can be attended in parallel,
  or at least reduce transition time
• HUDs improves control of position during landing
  (Wickens Long, 1995)

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Conformal imagery Correspondence of objects
across views (creates new shared object)
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Expectation

• HUD helps divided attention when pilot expects
  stimulus
• However, spatial proximity does not guarantee
  that parallel processing will occurit hinders
  when the stimulus is unexpected
• Airplane poised to move out less likely to be
  seen with HUD (Wickens Long, 1995)

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Response ConflictEriksen Eriksen (1974)

• Control
• H
• Perceptual Competition
• K H K

• Redundancy Gain
• H H H
• Response Conflict
• F H F

H Right button F Left button
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Response ConflictEriksen Eriksen (1974)

• Perceptual Competition
• Increased display clutter leads to failure to
  focus between relevant and irrelevant
• Response conflict and redundancy gain
• Proximity allows two channels to be processed in
  parallel, even if undesired
• Information competes at perceptual level when
  there are different implications for action
• If they disagree, RT ? -- leads to response
  conflict
• If they agree, RT ? -- leads to redundancy gain

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Object-Based Proximity

• Similarity can be based on more than spatial
  proximity
• What if different information channels are
  different dimensions of the same stimulus?
• Colour, shape, location, size, etc.
• Stroop task (demo) name ink colour
• XXXX XXXX
• GREEN RED
• Stroop effect RT and error ? when colour name
  and ink colour conflict (relative to neutral
  control)
• Redundancy gain also observed

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Object-Based Model

• Multiple dimensions belonging to single object
  likely to be processed in parallel
• Likely to help if parallel processing required
• But hinder if one dimension is irrelevant
• GREEN RED
• Attention not just space-based (spotlight)
• Object-based model says concurrent processing
  occurs when elements lie within single object,
  independent of its spatial dimensions
• Judgments about two parts of same object made
  faster than when parts are from different
  objects, even when distance constant (Behrmann et
  al., 1998)

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Object Displays

• So we can take advantage of this object based
  proximity
• Integrating information sources into one display
  if parallel processing required (divided
  attention)
• Emergent features property of whole, not seen
  when parts in isolation
• Connect spokes to form polygon

Safety parameter display (Westinghouse)
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Focused Attention Tasks?

• What if the task requires focussed attention,
  will the object display be good?
• Not really
• Use appropriate object type for task(s)
• E.g., bar graph

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SummaryTowards an Attention-Based Display
Design Principle
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Integrating Information

• Integrating multiple information sources by
  proximity or common representation (objectness,
  colour, etc.) results in
• Increased probability of parallel processing
  (divided attention)
• Increased likelihood of emergent features with
  improved performance if they are mapped to the
  task
• Possible creation of clutter or response conflict
  if the task requires focussed attention on one
  dimension

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Separating Information

• Separating multiple information sources by moving
  them apart or putting them in separate objects
  results in
• Increased probability of local processing
  (focused attention)
• Reduction of clutter or response conflict if the
  task requires focussed attention on one dimension
• Decreased likelihood of emergent features (but
  still possible--bars in bar graph)

vs.
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Putting it TogetherProximity Compatibility
Principle(Wickens Carswell, 1995)

• If task requires HIGH processing proximity, then
  should have HIGH display proximity
• If task requires LOW processing proximity, then
  should have LOW display proximity
• Processing proximity extent to which
  information sources are used in the task
• Display proximity how close display elements
  are (distance or object-based)

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Summary

• Attention
• Three kinds of attention
• Selective attention
• Supervisory control sampling
• Visual/Target search
• Divided vs. focused attention
• Global (parallel) and local processing
• Emergent features
• Spatial proximity
• Response conflict
• Object-based proximity
• Proximity compatibility principle