Transcript Cognition

Cognition
Human Factors
PSYC 2220
Michael J. Kalsher
Department of
Cognitive Science
Human Information Processing System
• Perceptual Stage
– Bringing information in through senses (sensory memory) for
comparison against existing knowledge in (long-term) memory
to give it meaning.
• Cognitive Stage
– Central processing (or thought stage) where we compare the
new information with current goals and memories.
– Transform the information, make inferences, solve problems,
consider responses.
• Action Stage
– Brain selects a response and then coordinates/sends motor
signals for action.
Generic Model for
Human Information Processing
Note: Assumes a linear progression of processing
Measuring Information Processing
• Cognitive psychology (science of the mind)
began to replace behaviorism in the late 1950s.
• Modeling “information processing” required the
use of special techniques (or dependent
variables) to make inferences concerning what
is going on “inside the head.”
– Reaction time (simple; choice)
– Verbal Protocol analysis (asking people to tell you
what they’re thinking before/during/after a task).
Memory: The Atkinson-Shiffren Model
Richard Atkinson & Richard Shiffrin, 1968
Sensory Register: where sensory info enters memory
Short-term store (WM or STM): receives and holds input from both the
sensory register and long-term memory.
Long-term store: where info is held indefinitely (levels of processing).
Sensory Memory
• Sensory Trace– temporary holding “bin”
– Visual trace is termed “Iconic memory”
– Auditory trace is termed “Echoic memory”
– Presumed to all be present for other sensory modalities
• Characteristics
– Veridical (accurate)
– Large storage capacity
– Brief time—decays and/or is interfered with by new
incoming information (clears for next input)
– Pre-categorical—before the information is interpreted (i.e.,
it in a “raw” form)
Iconic & Echoic SM: Some Distinctions
• Iconic held for briefer time (less than 1 sec)
than echoic (2-3 sec)
• Iconic memory is more spatially oriented
• Echoic memory is more temporarily oriented
Sensory Memory: Some Classic Findings
• Backward Masking
When subjects are presented with a “masking visual stimulus”
immediately after a “target visual stimulus” brief (< 50 msec) they fail
to consciously perceive the target stimulus.
• Suffix Effect
A weakening of the recency effect when an irrelevant item is
appended to the end of a to-be-learned list of words (Morton, Crowder &
Prussin, 1971).
Example: When asked to memorize a list, say: 1,5, 7, 9, 15, people
remember the first and last items best. If an additional number (e.g.,
20) is added to the end of the list—but is not part of the to-beremembered information, recall for the last item will be much weaker.
Sensory Memory: Object & Pattern Perception
• Perceptual recognition: Process by which sensory
elements are transformed into a mental representation or
code and then compared with stored information to
categorize it.
– Involves “Many-to-One” mapping
– Perception gives meaning to sensory input by aggregating many
simple information “bits” into fewer global representations.
• Characteristics of this process:
– Perception by feature analysis (bottom-up processing)
– Simultaneous top-down & bottom-up processing
Feature Analysis:
Bottom-up Processing
• Analysis of complex stimuli in terms of the
component parts.
• A three-stage process
– Break pattern into features
– Match features to patterns stored in LTM
– Decide which stored pattern is the best
match
Feature Analysis: Text Perception
• Features of letters are compared with features
of stored knowledge for the letters for possible
matches.
– Performed quickly and without awareness for familiar
objects (such as letters).
• Perception of print usually proceeds
hierarchically:
– Features combined into letters, letters into words, words
into sentences
– Exception: words seen frequently tend to be processed
holistically, a process termed unitization.
• DANGER, WARNING, CAUTION, NOTICE, ABC, CBS, NBC, FOX
Controlled vs. Automatic Processing
• Controlled Processing (Bottom-up)
– Effortful cognitive processes that require attention to initiate and
sustain them.
– Used to comprehend relatively unfamiliar or complex information.
• Automatic Processing (Top-Down)
– Cognitive processes that can be initiated and run with minimal
demand on attentional resources.
– For task to become automatic, it must exhibit consistent mapping
between its cognitively stored elements.
– When tasks are combined there will be less cross-interference in
time-sharing to the extent that one or both tasks are automated.
Design Implications: Textual Displays
• Feature compatibility
–
Accuracy and speed of recognition will be greatest when the features of a
display are in a format compatible with features and units in memory.
• Upper and lower case
–
For isolated words: upper case letters are more recognizable.
–
In sentences: mixture of upper and lower case print is most easily perceived.
• Use print for text displays
–
Print is more easily recognized and read than cursive writing.
• Minimize abbreviations
–
Full words should be used for displays (ALAC, CCP, CISL, IRB, C&M)
–
Best abbreviations rule is truncation (use only first few letters of the word).
• Space between words or character strings
–
Ensuring there are gaps between words is crucial for accurate perception.
–
Make use of “Chunking” (e.g., arrangement of alphanumeric characters on license plates).
Feature Analysis: Geon Theory
Suggests everyday objects are recognized on the basis of
combinations of a set of 30 geometric shapes termed geons.
Role of Geons in Object Perception
Object recognition proceeds via the following steps:
– Objects broken down into component geons.
– Each geon categorized on the basis of feature matching.
– Objects are identified on the basis of the specific
configuration of their component geons.
Important Assumptions
(of Biederman’s approach)
• Only edges of geons are critical for object
recognition.
• Color and details may be necessary if subobject shapes for two objects are sufficiently
similar that the objects cannot be discriminated
on the basis of the component shapes alone.
Assumption #1:
Only edges of geons are critical for object recognition.
Assumption #2:
Color and detail necessary if sub-object shapes for two objects
are sufficiently similar that the objects cannot be discriminated on
the basis of the component shapes alone.
Basketball vs. an Orange
Design Implications:
Line drawings vs. photographs/pictures
Representing the human figure in safety symbols
The human figure is frequently the
main component in a safety
symbol. In other safety symbols, a
part of the human figure—a hand,
foot, or other body part—makes up
the main element of the symbol.
In either case, representation of the
human form must be simple,
consistent, and believable.
Interpretation must be instant and
must not require the viewer to study
the symbol to determine what part
of the body is involved or in what
way a hazard exists.
The Role of Context in Perception
• Higher level concepts or information are sometimes
needed to process “low level” perceptual features when
stimuli are unclear or incomplete.
• Use of top-down processing occurs simultaneously and
automatically along with bottom-up processing.
Perceiving a “6” or a “b” is determined by context
Top-Down Processing
• More critical for speech recognition than reading
printed words because of the “fleeting” nature of
speech (i.e.,, speech decays whereas print remains)
• Verbal context around critical spoken words
greatly facilitates recognition.
– In a study of recognition of warnings among pilots,
the verbal warning “Your fuel is low” was more
comprehensible than “fuel low” (Simpson, 1976).
Information Processing Trade-offs
• When stimulus quality is high, bottom-up
processing will predominate.
• As stimulus quality degrades, increased
contextual information and redundancy is
needed (top-down) to keep recognition
levels high.
Display Guidelines: Text Displays & Icons
• Optimize Bottom-up Processing
– Optimize factors such as size and contrast and quality of the stimuli.
• Optimize Top-Down Processing
– Use actual words rather than random text strings
– Restrict overall message vocabulary (fewer possibilities = higher efficiency)
– Provide contextual cues to aid recognition/comprehension.
• Evaluate Tradeoffs
– Given limited space, evaluate environment for degraded viewing conditions
& availability of contextual cues to determine appropriate trade-off between
bottom-up and top-down processing.
• Usability Testing
– Evaluate recognition & comprehension of icons.
– Conduct usability testing using the actual environment and/or elements of
the task context.
Pictures and Icons:
Important Tradeoffs
Advantages:
– Universal/Not Language Dependent
– Takes advantage of dual-coding (analog spatial image & semantic/meaning)
– Useful for many applications (e.g., highway signs, computer displays, warnings)
Potential Disadvantages:
– Legibility
• May be difficult to discriminate under degraded viewing conditions
• Pictorial messages should be distinctive, sharing a minimal number
of features with other pictorials.
– Comprehension
• Standardization and training (e.g., ANSI; ISO; GHS).
• Whenever possible, words should be used with symbols/icons.
The GHS: Breaking All the Rules?
Respiratory
Hazard
Explosive
Hazardous to
Aquatic Environment
Flammable
Compressed
Gas
Health Hazard
Health Hazard
Oxidizer
The GHS: Considering Alternatives
Which of the preceding shapes best communicates URGENCY to you? Please choose one.
A
B
C
D
Not sure
Comments (if any)
33.33%
51.28%
5.13%
10.26%
0.00%
0.00%
The GHS: Considering Alternatives
2. The following are possible examples of symbols for chemicals that are flammable.
Which of the preceding shapes best communicates a FLAMMABLE danger to you? Please choose one.
A
B
C
D
E
F
Not sure
Comments (if any)
31.58%
26.32%
5.26%
5.26%
26.32%
5.26%
0.00%
0.00%
The GHS: Considering Alternatives
Which of the preceding shapes best communicates a RESPIRATORY danger to you? Please choose one.
A
B
C
D
E
F
Not sure
Comments (if any)
35.90%
38.46%
7.69%
12.82%
5.13%
0.00%
0.00%
0.00%
The GHS: Considering Alternatives
A
B
C
D
E
Not sure
Comments (if any)
14.74%
65.26%
6.32%
10.53%
0.00%
3.16%
0.00%
Working Memory
• Term used to describe short-term store of information
that is currently active in central processing.
• Only a limited amount of information can be brought
from sensory register to working memory (1st bottleneck of
the information processing system).
• Relatively transient (decays rapidly) and limited in size.
• “Work bench” of consciousness in which we compare,
evaluate, and transform cognitive representations.
• Must be able to accommodate demands while supporting
active problem solving operations (e.g., hold a phone
number in memory until we have completed dialing it).
• Holds two different types of information
– Verbal & Spatial
Brown-Peterson Experiments
• Demonstrated that without rehearsal, the ability to
recall drops exponentially to an asymptote.
• Now-classic experiments conducted to test
characteristics and limitations of short-term
memory.
– One by John Brown in 1958 and another by Lloyd and
Margaret Peterson in 1959, hence the term “BrownPeterson paradigm”.
– Tasks used by the researchers were mostly the same and
yielded similar results.
•
•
•
Procedure: 24 participants (psychology students) were asked to
remember/recall trigrams (meaningless three-consonant syllables, e.g.,
TGH). To prevent rehearsal participants counted backwards in threes or fours
from a specified random number until they saw a red light appear. Participants
recalled trigrams after intervals of 3, 6, 9, 12, 15 or 18 seconds.
Findings: The longer the interval delay the less trigrams were recalled.
Participants were able to recall 80% of trigrams after a 3 seconds delay.
However, after 18 seconds less than 10% of trigrams were recalled correctly.
Conclusion: STM has a limited duration when rehearsal is prevented. It is
thought that this information is lost via trace decay.
Brown, J. (1958). Some tests of the decay theory of immediate memory. The Quarterly Journal of Experimental Psychology, 1012-21.
Peterson, L., & Peterson, M. (1959). Short-term retention of individual verbal items. Journal of Experimental Psychology, 58(3), 193-198.
Baddeley’s Working Memory Model
Strength of the model lies in its ability to integrate a large
number of findings from research on short-term/working
memory.
Alan Baddeley’s Model Components
– Central Executive: Overall control and regulation of cognitive
processes (e.g., binding information from numerous sources into coherent
episodes, coordination of the slave systems, shifting between tasks, selective
attention). Not as “Central” as once thought.
– Visuospatial sketch pad holds information about what we see.
Two components: Visual cache (stores info about form and color)
and Inner scribe (deals with with spatial and movement information
and transfers information to the Central Executive).
– Phonological loop deals with auditory information and consists of
two parts: a short-term phonological store that is subject to rapid
decay, and an articulatory rehearsal component (articulatory loop)
that can revive the memory traces (usually sub-vocally).
– Episodic Buffer links information across domains to form
integrated units of visual, spatial and verbal information with time
sequencing (e.g., memory of a story or movie scene).
Working Memory: Limitations
Ability to keep (verbal or spatial) information
in working memory is dependent on:
– Capacity (how much to-be-remembered information must be
kept active)
– Time (how long must it be kept active)
– Similarity (how similar is the to-be-remembered material to
other elements in working memory)
– Attention (how much attention is required to keep the to-beremembered material active)
Working Memory: Capacity
• Capacity of working memory = 7 +/- 2 “chunks”.
• Chunk = unit of working memory space defined
jointly by physical and cognitive properties
that bind items together.
• Physical binding:
– 8, 7, 5, 3 = 4 chunks
– 23, 27, 35, 46 = 4 chunks
• Cognitive binding:
– Example:
• M T V N B C F B I C I A I Q = 14 chunks
• MTV, NBC, FBI, CIA, IQ = 5 chunks
Working Memory: Time
• Strength of information in WM decays rapidly
unless it’s actively rehearsed (reactivated).
• Maintenance rehearsal is essentially a serial
process of sub-vocally articulating each item.
• The more chunks, the longer it .takes to cycle
through items in maintenance rehearsal.
• “Half-life” of working memory = the delay after
which recall is reduced by one-half.
– Half-life of 1 chunk = approx. 70 sec
– Half-life of 3 chunks = approx. 7 sec
Working Memory: Confusion and Similarity
Which list of letters is most likely to be
retrieved from working memory?
EGBDVC or ENWRUJ?
Items that sound like a to-be-remembered item
impair recall more than do items that sound
different from it.
The memory confusion occurs whether the list is
heard or seen.
Working Memory:
Attention and Similarity
Working memory is resource-limited.
– When attentional resources are diverted
to another task, rehearsal stops and
memory decays.
– If the competing activity uses the same
resources, disruption will be worse than
if it uses different resources
• Basis for development of Multiple Resource Theory.
WM: Implications for Design
• Minimize working memory load
– Items that operators need to retain in working memory during task
performance should be kept to a minimum
• Provide visual echoes (e.g., visual presentation of phone numbers)
• Exploit chunking
– Optimize physical chunk size (i.e., 3 or 4 numbers or letters)
– Use meaningful sequences (letters are more meaningful than numbers)
– Keep numbers separate from letters (e.g., license plate sequencing)
• Minimize Confusability
– (More confusion when lists sound similar; Use physical distinctions to reduce
confusability)
• Exploit different working memory codes
– Working memory retains 2 qualitatively different types of information: visual
spatial and verbal phonetic
• Each system processes information somewhat independently
• If one code is being used, it will be interrupted more by processing that same type of
info than by processing info in alternative code
Long Term Memory
LTM is Conceptualized as having 3 basic stages:
– Encoding
Input of sensory memory, short term memory, and attention
– Storage
Some memorial representation is laid down
– Retrieval
Remembering the output
(Output probably loops back into short-term memory)
Theories of LTM
• Levels of Processing
• Paivio’s Dual Code Theory
• Tulving’s episodic vs. semantic
memory theory
Levels of Processing
Memory strength depends on the strength of associations
made between to-be-remembered items and and existing
information in LTM. Deep processing is superior to other
more superficial types of processing.
Example
– Participants in an study employing the incidental memory
paradigm in which they are unaware that their memory will be
tested later.
– They are given one of 3 tasks involving, say—an apple
Surface task (Is it red? Is it small?)
Phonological task (Does it rhyme with chapel?)
Semantic task (Is it edible? Is it a Fruit? Is it good for you?)
• People remember the information best when engaged in
semantic processing, as opposed to superficial processing.
Paivio’s Dual Code Theory
• Based on the fact that our memory for pictures is
better than our memory for words.
– Words are coded in memory by a verbal code
– Pictures are coded visually (by their appearance) and verbally.
• Dual coding theory helps explain why concrete
words and concepts (chair) are easier to
remember than abstract words (honor).
– Concrete words/concepts are more easily transformed to a
pictorial image than abstract words.
Tulving’s Memory Theory:
Types of Memory
Episodic
– Knowledge of specific experiences as we move
about the world.
Semantic (Jeopardy knowledge)
– Conceptual memory (knowledge of world and how it works)
– Devoid of memories of particular instances.
Procedural (“Muscle memory”)
– Implicit and skill-based knowledge that is usually
associated with performing an activity or procedure
(e.g., riding a bicycle).
Episodic Memory
• Episodic memory represents our memory of
experiences and specific events in time in a serial form,
from which we can reconstruct the actual events that
took place at any given point in our lives.
• It is the memory of autobiographical events (times,
places, associated emotions and other contextual
knowledge) that can be explicitly stated. Individuals tend
to see themselves as actors in these events, and the
emotional charge and the entire context surrounding
an event is usually part of the memory, not just the bare
facts of the event itself.
Semantic Memory
• Semantic memory is a more structured record of facts,
meanings, concepts and knowledge about the
external world that we have acquired.
• It refers to general factual knowledge, shared with others
and independent of personal experience and of the
spatial/temporal context in which it was acquired.
Semantic memories may once have had a personal
context, but now stand alone as simple knowledge. It
includes such things as types of food, capital cities,
social customs, functions of objects, vocabulary,
understanding of mathematics, etc. Much of semantic
memory is abstract and relational and is associated with
the meaning of verbal symbols.
Procedural Memory
• Procedural memory (“knowing how”) is the
unconscious memory of skills and how to do things,
particularly the use of objects or movements of the
body, such as tying a shoelace, playing a guitar or
riding a bike.
• Typically acquired through repetition and practice,
procedural memory is composed of automatic
sensorimotor behaviors that are so deeply embedded
that we are usually unaware of them. Once learned,
these "body memories" allow us to carry out ordinary
motor actions more or less automatically.
Memory and the Brain
• The different types of LTM are stored in different regions of
the brain and undergo quite different processes.
• Declarative memories (episodic and semantic) are encoded
by the hippocampus, entorhinal cortex and perirhinal
cortex (all within the medial temporal lobe of the brain), but
are consolidation and stored in the temporal cortex and
elsewhere.
• Procedural memories, on the other hand, do not appear to
involve the hippocampus at all, and are encoded and stored
by the cerebellum, putamen, caudate nucleus and the
motor cortex, all of which are involved in motor control.
Long-Term Memory:
Basic Mechanisms
• Strength
– Determined by frequency and recency of use.
• Associations
– Retrieval of information in LTM dependent on the number and
richness of associations with other items. (related to depth of
processing)
• Forgetting
– Exponential function; most forgetting occurs quickly, then reaches
an asymptote.
– Major reasons for memory retrieval failure:
•
•
•
•
Weak strength due to low frequency or recency
Weak or few associations with other information
Interfering associations
Recall vs. Recognition
Information in LTM is organized around
central concepts
Schema: term used to describe a person’s knowledge structure
about a particular topic.
-- Example: The knowledge structure I have concerning my role as a college
professor.
– Schemas that describe a sequence of activities are called scripts
(e.g., interactive warnings; goal is to interrupt existing “unsafe” scripts).
Mental Models: type of schema that describes our understanding of
system components, how a system works, and how to use it.
Mental models that are shared by a large group of people are termed
population stereotypes.
Cognitive Maps: mental representations of spatial information (e.g.,
layout of a city, campus, workplace).
-- Edward Tolman’s work with rats
-- Orientation usually reflects our view point
-- Re-orienting our perspective through mental rotation is effortful.
Tolman’s Procedure
3 groups of rats placed in a complex maze ending at a food box.
Group 1: Food reward every time they reached the end of the maze.
Group 2: Day 1 – 10 = No reward; Day 11 – 17 = Rewarded.
Group 3: No reward
Long-Term Memory: Implications for Design
1.
Encourage regular use of information to increase
frequency (of use) and recency.
2.
Encourage active verbalization or reproduction of
the to-be-remembered information (deep processing
to form strong associations is best!).
3.
Standardization can reduce memory load
(e.g., equipment, environments, displays, symbols,
operating procedures).
- Results in development of strong yet simple schemas and
mental models that are applicable to a wide variety of
circumstances.
- Question: Are there any down sides to standardization from a
cognitive perspective?
Long-Term Memory: Implications for Design
4. Use Memory Aids
– Particularly important for infrequent or safety-critical tasks.
– Putting “knowledge in the world” so that people don’t have to rely on
“knowledge in the head” (LTM) Norman, 1988.
5. Carefully design to-be-remembered information
– Info that must be remembered and retrieved unaided should have
characteristics such as:
•
•
•
•
•
•
Be meaningful to an individual and semantically associated with other information
Use concrete rather than abstract words whenever possible
Use distinctive concepts and information (to reduce interference)
Well-organized sets of information (group or otherwise associated)
An item should be able to be guessed based on other info (Top-down Processing)
Limit technical jargon
6. Design to support development of correct mental models
– Apply the concept of visibility: users should immediately be able to
determine the state of a device and the alternatives for action.
Facilitating Memory:
Storage
Memory is better if the “to-be-remembered”
information is organized prior to memorization.
– Material induced organization
Organization is already provided in the stimuli
– Subjectively induced organization
Organized by having individuals use their own personal
memories to help process to-be-remembered
information. That is, by integrating it into existing mental
structures, such as schemas, scripts, mental models.
Facilitating Memory:
Encoding Specificity
Cues that are present when the to-beremembered event occurs are effective
retrieval cues.
– The learning environment (studying and testing in
the same room is better then changing rooms).
– State-dependent memory (study wired; test
wired?)
– Mood-dependent memory.
Facilitating Memory:
Memory Mnemonics
Method of Loci
– Select a well-known location and mentally walk
through and visualize a specific number of objects at
that location (e.g., furniture in each of several rooms of your apartment or
house).
– Establish an ordered list of these items that you
commit to memory.
– Learn to attach to-be-remembered items to the list.
– Later, when you want to recall, take a walk back
through the location and “see” what was placed there.
Facilitating Memory:
Memory Mnemonics
Pegword Method
– Commit an ordered set of pegs to memory
• Rhyming: One is a bun, two is a shoe, three is a
tree…Well-known list: A is an apple, B is a bird, C is a
cat…
• New List:
– 1 = tree
– 2 = light switch
– 3 = stool, and so on ….
– Then visualize each to-be-remembered
item interacting with your pegs (e.g., a
grocery list, terms for a test, etc.).
• Important to use elaborate imagery. Humor often
helps!
Memory Failures: Episodic Memory for Events
• Personal knowledge of memory of a specific
event or episode is acquired by a single
experience (high school prom; traumatic event).
• Biases observed in episodic memory
– Similar to top-down biases in perception; guided by expectations, mood, …
• May be biased by plausible scenarios of how the episode in question might have been
expected to unfold
• Biases toward the “typical” may become more pronounced as time passes
• May be influenced by suggestion
• Applications
– Eye-witness testimony
• The Biggers Criteria (A Supreme court decision [Neil vs. Biggers, 1972]
established 5 factors that should be considered when evaluating eyewitness
testimony accuracy: certainty, view, attention, description, and time.
– Accident investigation
Memory Failures: Sources of Bias at Each Stage
Process
Example
Encoding
Attention
Witnesses tend to focus on the weapon used in a crime
(salience) instead of on the perpetrator’s face or other features.
Expectancy
Witnesses may see what they expect to see.
Storage
Degraded memory/schema modification
A degraded visual recollection may be replaced by an LTM schema of
what a “typical criminal” looks like, or that an auto crash typically occurs
at a high speed (causing the person to overestimate the actual speed).
Biasing Events
Chance encounter with a suspect in handcuffs prior to the line-up
Retrieval
Recognition
Analogous to a signal detection task. We should maximize “hits” and
“correct rejections, but should we also aim for minimizing a guilty bias?
Memory Failures:
Prospective Memory for Future Events
Failures of prospective memory: forgetting to do
something in the future.
– Reminder strategies
• Low tech - String around the finger? Post-its?
• High tech – Smart phones
– Cognitive/behavioral strategies
• verbally stating or physically taking some action regarding the
required future activity the moment it is scheduled
Situation Awareness
Definitions:
– Users’ awareness of the meaning of dynamic
(unexpected) changes in their environment.
– The perception of the elements in the environment
within a volume of time and space, the
comprehension of their meaning, and the projection
of their status in the near future (Endsley, 1995).
Importance of SA for Human Factors:
Perception (What’s going on?)
Understanding (Interpret the meaning of existing cues)
Prediction (Predict the future implications of the available
information).
Attention and Mental Resources
• Selective attention allows us to process important
information. We usually attend to one (auditory)
channel at a given time.
• Focused attention allows us to filter out unwanted
information.
• Sustained attention (Vigilance tasks; infrequent signals).
• Divided Attention (Time-Sharing) allows us to perform
more than one cognitive task by attending to both at
once or by rapidly switching attention.
– Time sharing among multiple tasks usually causes performance
drop for one or more tasks, relative to baseline task performance.
– Four factors determine the extent to which two or more tasks can
be time-shared: Resource demand, Task Structure, Similarity,
Resource allocation (or task management).
Performance Improvement Guidelines:
Selective Attention Tasks
• Reduce number of channels that must be monitored.
• Emphasize relative importance of each channel to
effectively focus attention.
• Reduce stress to ensure appropriate channel sampling
and train to ensure optimal channel scanning patterns.
• Provide guidelines regarding probable location of signals.
• Arrange visual channels to optimize scanning efficiency.
• Prevent potential “masking” problems given multiple
auditory channels.
• Optimize rate of signal presentation (not too slow or too
fast) and where possible, allow personal control over rate.
Performance Improvement Guidelines:
Focused Attention Tasks
• Make competing channels distinct
(salience).
• Physically separate irrelevant channels
from channel of interest (organization).
• Reduce the number of competing
channels (information density).
• Make the channel of interest different
(salience).
Performance Improvement Guidelines:
Sustained Attention Tasks
• Vigilance tasks – human operators are very bad
at tasks requiring sustained attention in order to
detect infrequently occurring signals.
• Consider the following:
– Arrange appropriate rest-work schedules
– Maximize signal conspicuity
– Reduce uncertainty regarding signal
occurrence/location
– Arrange frequent training/feedback sessions
– Maintain environmental conditions at optimal levels
Performance Improvement Guidelines:
Divided Attention Tasks
• Minimize potential sources of information
• Prioritize task importance ahead of time
• Minimize task difficulty and select
dissimilar dual tasks
• Capitalize on “automatic processing” via
over-learning
Mental Workload
• Amount of cognitive resources available
in a person versus amount of resources
demanded by the task
• Measuring mental workload
– Primary task measurement
– Secondary task measurement
– Psychological measures
– Subjective measures
Limitations
• Can’t assume that information will be
processed just because it is presented.
• People can only process so much
information per period of time.
• For complex displays-only a small amount
of info will be attended to at one time.
– The information most critical to task
performance must be provided in a way that
will attract attention (conspicuity/salience).
Multiple Resources
• Visual and auditory processing requires
separate resources.
• There are multiple kinds of informationprocessing resources that allow time sharing
to be more successful.
– Time Sharing (optimize resources optimally)
– Stages: Early vs. Late (resources for perceptual
processing/central processing separate from those used for
response selection/execution).
– Input Modalities: Visual vs. Auditory
– Processing Codes: Spatial vs. Verbal in Early
Processing and Manual vs. Vocal in Responding
Input Modalities
• Humans are generally better at dividing
attention between one visual and one
auditory input (cross-modal time-sharing) than
between 2 visual or 2 auditory channels
(intramodal time-sharing).
• Dual task interference is generally
reduced by spreading input across
visual and auditory modalities
Effect of presentation modality in direct-to-consumer
(DTC) prescription drug television advertisements
Applied Ergonomics, 45(5), 1330-6, Wogalter, M.S., Shaver, E.F., Kalsher, M.J.
Direct-to-consumer (DTC) drug advertising markets medications requiring a
physician's script to the general public. In television advertising, risk disclosures
(such as side effects and contraindications) may be communicated in either
auditory (voice) or visual (text) or both in the commercials.
This research examines presentation modality factors affecting the
communication of the risk disclosures in DTC prescription drug television
commercials.
The results showed that risk disclosures presented either visually only or both
visually and auditorily increased recall and recognition compared to no
presentation. Risk disclosures presented redundantly in both the visual and
auditory modalities produced the highest recall and recognition. Visual only
produced better performance than auditory only. Simultaneous presentation of
non-risk information together with risk disclosures produced lower recall and
recognition compared to risk disclosures alone-without concurrent non-risk
information. Implications for the design of DTC prescription drug television
commercials and other audio-visual presentations of risk information including
on the Internet, are discussed.
Processing Codes
• Spatial and verbal processing (codes)
depend on distinct resources
• To the extent that any two tasks draw on
separate, rather than common
resources, time-sharing is more efficient
– Less likely to impact performance of
concurrent tasks
Confusion
• When the same resources are used for two
tasks, the amount of interference between
them is increased or decreased by the
difference in similarity of the information
being processed.
• Similarity induces confusion.
• When two tasks are confused, it sometimes
produces cross-talk
– Output intended for one task inadvertently gets
delivered to the other.
Guidelines for maximizing
performance for concurrent tasks
1. Task Re-design. Do careful assessment of timesharing requirements and make them less resourcedemanding whenever possible.
2. Interface re-design. Off-load heavily demanded
resources (e.g., supplement voice display if visual
display is too attention-demanding).
3. If we are performing a primary task that imposes a
heavy mental workload—it is unlikely we will be able
to add a second task successfully.
4. Training.
5. Automation.