CMPUT 301: Lecture 12The Human

Lecturer: Martin JagersandDepartment of Computing Science

University of Alberta

Notes based on previous courses byKen Wong, Eleni Stroulia

Zach Dodds, Martin Jagersand

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What Next?

• So far, mostly computer and program developer’s perspective on design.

• For usable systems, we need to better understand the human user.

• HCI:– studying people, computer technology, and

ways these influence each other– designing, implementing, and evaluating

interactive computing systems for human use

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Studying People

• Humans are limited in their capacity:1. Sensory properties limit what information can

be inputted. Seeing, hearing, touching smelling etc.

2. Cognitive capacities limit what can be perceived, processed and stored

• This has important implications for design.

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Cognitive Models

• Knowing how people think, learn, reason, and communicate is critical to designing systems to ease cognitive tasks.

• Cognitive models provide a method of predicting user behavior and performance.

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Cognitive Model

• Model Human Processor:– perceptual subsystem

– handle sensory stimulus

– “input”

– motor subsystem– controls actions

– “output”

– cognitive subsystem– does the processing to connect the above

– “compute”

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Cognitive Model

• MHP basics:– interacting subsystems, each with processors

and memory– sometimes serial, sometimes parallel

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Input-Output Channels

• Focus on:– vision (visual channel)– hearing (auditory channel)– touch (haptic channel)– movement

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Visual Processing elements and Pathways

• Eye transforms light into nerve impulses

• Optic chiasm splits left and right visual fields

• LGN: Exact function unknown. May have to do with stereo.

• V1 (Striate cortex) performs spatial filtering / coordinate transforms

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The EyeThe Biological Camera

• Lens, cornea and fluids focus light.

• Six eye muscles orient the eye

• Iris adjusts light• Retina captures

images

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RetinaConverts light to nerve impulses

• Photoreceptor converts light

• Other cell layers perform image processing

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PhotoreceptorsRods and cones

Rods: Night vision, but no color.

125 million, none in fovea,

outnumber cones 20:1

Cones: Color sensitive, but poor light sensitivity

6.4 million, peak density in fovea

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PhotopigmentLarge molecule with two energy levels

• Cis retinal has low energy

• Trans slightly higher energy

• Incoming light photon adds energy => changes cis to trans state.

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Interneurons and Ganglion cells

Center-surround organization:

1. Light hyperpolarizes the rod and excites the bipolar cell below it

2. But inhibitory connections through horizontal cells suppress signals

3. Best response to localized “dot”

4. While stimulating surround only lowers firing rate

• What is this???

Convolution!!! Im*[-1 2 –1]

+- -

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Disappearing figure?

• Focus steadily on first the left then the right black dot

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Visual Perception

• Brightness:– visual acuity increases with luminance– perception of flicker also increases with

luminance– issue:

– flickering bright, large monitors?

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Visual Perception

• Color:– hue

– wavelength of light (470–640 nm)

– ~150 distinguishable

– lightness– ~240 luminance levels

– saturation– ~20 purity levels

– issue:– how many colors?

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Visual Perception

• Color wheel:– additive primaries

(light)– subtractive primaries

(pigments, dyes)– shade

(adding black)– tint

(adding white)– “relationships”

(harmonizing, contrasting, clashing)

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Visual Perception

• Perceiving color:– photopigments of cones

– “red” (558 nm peak), 64%, actually yellow

– “green” (531 nm peak), 32%

– “blue” (420 nm peak), 4%

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Visual Perception

• Perceiving color:– converted to opponent channels

– ratio of red to green

– ratio of blue to yellow

– ratio of black to white– from red and green levels

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Visual Perception

• Color:– acuity

– high to yellow, green, and orange

– low to deep blue

– issues:– color blindness

(red/green deficiency most common)

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Visual Perception

• Color blindness test:

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Visual Perception

• Color blindness test:

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Visual Perception

• Focus:– different hues focus at (physically) different

points (e.g., red versus blue)– Attention focus– can cause fatigue from refocusing

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Visual Perception

• Color guidelines:– colors are effective maximally when they are

used minimally

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Visual Perception

• Color guidelines:– use color consistently with user expectations

– stop

– go

– caution

– cold

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Visual Perception

• Color guidelines:– use foreground and background colors that

contrast well– e.g., highway signs

– color theory– clashing colors

– opponent color channels– red/green?

– blue/yellow

– black/white

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Visual Perception

• Color guidelines:– avoid blue text, fine lines, small shapes

– lens absorbs blue

– saturated blue cannot be made to focus

– only 4% of cones are blue-sensitive

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Visual Perception

• Color guidelines:– avoid saturated colors

– “angry fruit salad”, “circus”

– visual fatigue

– allow users to focus on their content

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Visual Perception

• Color guidelines:– use color redundantly

– with brightness, shape, texture, etc.

– color blindness

– monochrome monitors

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Visual Processing

• Processing:• Scan• Filter• Interpret– 2D to 3D– fill in missing

information

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Dorsal and Ventral PathwaysWhere/What or Action/Perception?

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Visual Processing

• Reading:– saccades, fixations, regressions– issues:

– type size

– line length

– leading

– word shape (varying or NON-VARYING)

– typeface (serif type, sans serif type)

– contrast (black on white or white on black)

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Hearing

• Sound:– characteristics:

– pitch (20 Hz to ~20 kHz)

– loudness

– timbre

– processing:– cocktail party effect

– issue:– could be used more effectively in user interfaces

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Touch

• Sensory receptors:– thermoreceptors

– heat and cold

– nociceptors– intense pressure, heat, and pain

– mechanoreceptors– pressure (force feedback)

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Touch

• Mechanoreceptors:– rapidly adapting

– responds to immediate pressure, but stops responding with continuous pressure

– slowly adapting– responds to continuous pressure

– acuity:– two-point threshold test

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Motor and Sensory areas

Central sulcus: Where sensory and motor information (somehow) is unified.

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Short and long control loops

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Sensory-motor alignment

• Somatosensory and primary motor areas aligned across central sulcus

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Pareital associationIntegration of sensory information

• Exaple: Reaching to a visual goal

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Movement

• Reacting:– stimulus sensed– brain processes and produces response– brain signals appropriate muscles to move– time taken involves reaction and movement

time

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Movement

• Speed and accuracy:– tradeoff?– Fitt’s law

– time taken to hit a target (e.g., menu item) depends on the size of the target and the distance to be moved

– e.g., menus, pie menus, linear menus

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Human Memory

• Humans remember substance and meaning over details.

• Humans tend to remember the unexpected over the expected.

• Humans recognize patterns and form associations.

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Human Memory

• Types of memory:– sensory buffers– short-term or working memory

– via attention (selective focus, interest)

– long-term memory– via rehearsal

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Sensory Memory

• Sensory memory:– iconic, echoic, and haptic memories– constantly overwritten by incoming information

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Short-Term Memory

• Short-term memory:– scratch pad for temporary recall of information– rapid access (70 ms), but rapid decay– limited capacity

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Short-Term Memory

• Memorize:5358979323846

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Short-Term Memory

• Recall.

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Short-Term Memory

• Average performance:7 2 digits in order

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Short-Term Memory

• Memorize:780 492 5202

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Short-Term Memory

• Memorize:HEC ATR ANU PTH ETR EET

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Short-Term Memory

• Exploit chunking and pattern abstraction.

• Recency effect (word recall):– most recently presented words

versus words presented in the middle versus words presented earlier

• Recency effect affects short-term memory.

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Short-Term Memory

• Characteristics:– letters or words that rhyme are difficult to

distinguish– rate of forgetting increases with task complexity and

amount of information– even small amounts of information can be quickly

lost if there is distracting new information– recall of names of items is usually better when

presented as pictures rather than words

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Long-Term Memory

• Long-term memory:– stores everything we “know”– huge capacity– relatively slow access (~100 ms)– slow decay– issue:

– do we really forget ordo we just find it harder to recall some things?

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Long-Term Memory

• Types of long-term memory:– episodic memory

– events and experience represented in serial form

– semantic memory– structured record of facts, skills, and concepts

(derived from episodic memories)

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Long-Term Memory

• Semantic memory model:– semantic network:

– entities, relationships, attributes

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Long-Term Memory

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Long-Term Memory

• Long-term memory processes:– storing information– forgetting information– retrieving information

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Long-Term Memory

• Storing information:– total time hypothesis

– time spent learning is directly proportional to the amount learnt

– distribution of practice effect– learning time is most effective if distributed

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Long-Term Memory

• Memorize:– list A

Faith Age Cold Tenet Quiet Logic Idea– list B

Boat Tree Cat Child Rug Plate Church– list C

Java Swing Class Object Interface Constructor Method

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Long-Term Memory

• Memorize:– list D:

The Midterm Exam Will Be on Oct 22

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Long-Term Memory

• Interesting and meaningful information is easier to remember.

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Long-Term Memory

• Why do we forget?– decay

– information held degrades over time until it is forgotten

– interference– new information causes old information to be lost

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Long-Term Memory

• Interference:– retroactive

– new information replaces old

– e.g., new phone number

– proactive– old memory interferes with new

– e.g., still thinking of the old phone number

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Long-Term Memory

• Retrieving information:– recall

– information is reproduced from memory

– recognition– information presented indicates that the information

has been seen before

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Long-Term Memory

• Memorize:– child– red– plane– dog– friend– blood– cold– bread– big– angry

• Peg list:– 1 bun– 2 shoe– 3 tree– 4 door– 5 hive– 6 sticks– 7 heaven– 8 skate– 9 wine– 10 hen

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Long-Term Memory

• Peg list:– 1 bun– 2 shoe– 3 tree– 4 door– 5 hive– 6 sticks– 7 heaven– 8 skate– 9 wine– 10 hen

• Recall vivid imagery.

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Long-Term Memory

• Visualize:The engines roared above the noise of the crowd. Even in the blistering heat people rose to their feet and waved their hands in excitement. The flag fell and they were off. Within seconds the car had pulled away from the pack and was cornering round the bend at a desperate pace. Coming down the straight the sun glinted on its shimmering paint. The driver gripped the wheel with fierce concentration. Sweat lay in fine drops on his brow.

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Long-Term Memory

• What color was the car?

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Thinking

• Two categories of thinking:– reasoning

– process by which we use knowledge to infer something new

– problem solving– process of finding a solution to an unfamiliar task,

using knowledge we have

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Reasoning

• Deductive reasoning:– deriving the logically valid necessary conclusion

from the given premises– e.g.,

If it is raining, the ground is dry.It is raining.Therefore, the ground is dry.

– e.g.,Some people are babies.Some babies cry.Some people cry?

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Reasoning

• Inductive reasoning:– generalizing from cases we have seen to infer

information about cases we have not seen– e.g.,

all elephants are gray?– positive versus negative evidence

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Reasoning

• Exercise:– each card has a number on one side and a letter on

the other (guaranteed)– verify the statement …

– if a card has a vowel on one side, it has an even number on the other

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Reasoning

• Abductive reasoning:– reasoning from a fact to the action or state that

caused it

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Problem Solving

• Gestalt theory:– beyond only reproducing known responses or

using trial and error– involves insight and restructuring the problem

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Problem Solving

• Problem space theory:– problem state space, with initial and goal states– apply transition operators– select operators using heuristics such as means-

end analysis– e.g., moving an office

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Problem Solving

• Analogy:– mapping knowledge relating to a similar known

domain to the new problem

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Problem Solving

• Story:A doctor is treating a malignant tumor. To destroy it, he needs to blast it with high-intensity rays. However, these will also destroy the healthy tissue surrounding the tumor. If he lessens the intensity of the rays, the tumor will remain.

How does he destroy the tumor?

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Problem Solving

• Analogous story:A general is attacking a fortress. He can’t send all his men in together as the roads are mined to explode if large numbers of men cross them. He therefore splits his men into small groups and sends them in along separate roads.

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End

• What did I learn today?

• What questions do I still have?