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The Information Processing Model A model for understanding human cognition.

from: Wickens, Lee, Liu, & Becker (2004) An Introduction to Human Factors Engineering. p. 122

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Assumptions in the IP Model Each stage transforms data and takes some time

Sensory processing• visual, auditory, kinesthetic• quality and quantity of input depend on limits of senses

Short-term sensory store• temporary storage at the sensory channel• requires no conscious attention

Perceptual encoding• stimulus is assigned to single perceptual category (from LTM)• levels of complexity of perceptual decisions

– absolute judgement (1 dimension)– loudness of a tone, crowd size

– pattern recognition (2 or more dimensions)– medical diagnosis, Sherlock Holmes

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Stages (cont.) Decision making

• what to do with perceived information• critical point in information processing

Memory• Working memory (short-term memory)• Long-term memory

Response execution• calling up and releasing necessary muscle commands to

perform actions• very complex

Feedback• monitoring the consequences of actions• not necessarily conscious

Assumptions in the IP Model

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Stages (cont.) Attention

• searchlight - which information source to monitor• resource of limited availability

Model not to be taken literally• Implies passivity; where are the goals?• Stages not sharply defined; overlap in time• Stages are not really "boxes" in the brain• Information flow may be right to left;

• e.g., expectations can influence perceptions

Assumptions in the IP Model

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The Information Processing Model The traditional driver for research and understanding. A useful organization scheme.

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Sensory Register, Part I: The Visual Sensory System

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The Visual Receptor System(see chapter 4)

The lens cornea – protective surface

pupil – opens (dilates) in darkness, closes (constricts) in light

accomodation: _______________________________• measured in diopters

The retina cones: ___________________________

rods: ____________________________

fovea: ___________________________

acuity: ___________________________

scotopic vision: ______________________

photopic vision: ______________________

adaptation: _________________________

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Example: driving at night

Specific hazards caused by: Glare Reduced contrast sensitivity Loss of color vision

Particularly bad for older drivers due to: Loss of contrast sensitivity due to age Loss of accomodation

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What affects Visibility?

1. Of print…

Good Bad

Good Bad

Good

Good

Bad

Bad

BAD Bad

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What affects Visibility?2. Characterizing and Measuring Light

Color• hue

– pure wavelength– visible spectrum ~400 – 700 nm

• saturation– amount of achromatic light mixed in

• brightness– amplitude

Design considerations • use color as a secondary source of information• design for monochrome first• consider

– simultaneous contrast– negative afterimage

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2. Characterizing and Measuring Light (cont.) Brightness measures (review)

• luminous intensity, luminous flux– energy at the source, candela

• illuminance– amount of energy striking an object, lux or foot-

candles (fc)• luminance

– amount of energy reflected from an object, foot-lambert (FL)

• reflectance– ratio of the amount of light striking the object to the

light reflected from the object,– illuminance

luminance

What affects Visibility?

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3. Characteristics of Visual Displays

Visual angle,• VA = tan-1(H/D)• VA = 3438H/D min

Example: reading ‘Good’ text from your notes page,

H = ______

D = ______

VA = ___________________________

What affects Visibility?

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3. Characteristics of Visual Displays (cont.)

Contrast,• Luminance of light areas, LL

• Luminance of dark areas, LD

• Contrast =

Spatial frequency• cycles of light and dark per degree of VA

Polarity• dark on light vs light on dark

(LL – LD)

(LL + LD)

What affects Visibility?

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4. Characteristics of Observers

Visual Acuity Age Contrast sensitivity Night vision

5. Characteristics of Environment

Ambient light • e.g., daylight vs night, glare, etc.

Movement Distractions

What affects Visibility?

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Your turn …

Define system requirements for your project based on this understanding of the visual sensory system.

Typical statements could include:1. The system must accommodate ____________________.

2. The system should allow for _______________________.

3. The system should include mechanisms that will _____________________.

Be careful not to start designing yet!