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Information Theory (aka Communication Theory) Grew out of the study of problems of electrical communications

(especially telegraphy) and statistical mechanics.

The message source selects one of a possible set of messages, encodes it, and transmits the resulting signal through a channel. The message is decoded and then received by the receiver.

Information display: decision complexity

messagesource

encoder channel decoder messagereceiver

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Information Theory: definitions

Information: “reduction of uncertainty” (that the receiver has about the message transmitted by the source.)

Bit: a single unit of information, equivalent to a choice between two alternatives (yes/no, on/off)

Entropy (H): measure of information in bits (typically, bits per second, bits per word, bits per symbol) "a measure of our ignorance" H is based on the number of possible messages (or events or

stimuli) N, the probabilities of those messages, and the context (i.e., the probabilities of all messages).

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% Redundancy:

SO WHAT? Why should we care? Because if we can quantify information, we can quantify human

information processing!! In terms of performance, we can look at choice reaction time (how long it takes to make a choice or decision) as a function of the amount of information.

Example: A tetris-like game is being designed in which the probability of

appearance of each shape is directly proportional to the number of edges. If the pieces are shaped as follows, what is the average amount of information and the % redundancy in the system?

100* )H

H - (1 = Redundancy % av

max

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Quantifying Information For N equally likely

alternatives,

If known probabilities:

The "average entropy" of a system:

For example: If equally likely,

H =______________

If pi = [0.13, 0.2, 0.27, 0.4]

H1 = _________________

Hav = _____________________

________________________

2

N = N = H

10

102 log

loglog

p - = )p

1( = H i2

i2 loglog

)]p

1( [ p = H

i2iav log

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Principles of Display Design Based on research findings from …

physical and psychophysical characteristics, capabilities, and limitations

visual system hearing & loudness etc.

memory perception attention

The principles listed on the following slides are discussed in detail in Buck & Lehto, chapter 18

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Principles based on Sensory Modality Use the most appropriate sensory modality

based on: intended function, e.g. …

warnings instructions labels data

sensory demands of background task(s)

sensory capability of the intended audience

Combine sensory modalities when possible to account for changing conditions

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Principles based on Location & Layout Locate visual displays where they can be seen

and put more important visual displays in more central locations within 30° of typical line of sight clear away visual obstacles

avoid visual clutter

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Principles based on Location & Layout Provide information at the time it needs to be

used.

Group displays and display elements consistently with the sequence of use by the operator.

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Principles based on Location & Layout Tasks requiring information integration are better served

by object-like displays. AKA, Proximity compatibility principle (Wickens & Carswell,

1995). Promote integration of information (where appropriate.) gestalt - human tendency to perceive complex configurations as

complete entities

Note: This carries over into design of controls, in that the spatial arrangement of displays should be preserved in the controls. (Example: stove controls.)

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Principles based on Location & Layout Objects that are placed together will be more

likely to be viewed as being related. e.g., recall …

Position displays or display elements so they have obvious spatial referents

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Related principles (not found in B & L) Principle of pictorial realism (Roscoe, 1968).

Displayed quantities should correspond to the human's internal model of these quantities.

Continuous variables should have analog displays; discrete variables should have digital displays.

Also, high values of the variables should be on the top of the display (or right); low values on the bottom (or left).

Other factors to consider: required precision, rate of change information.

Examples to discuss: altimeter, thermometer, scale, watch, speedometer.

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Principle of the moving part (Roscoe, 1968). The direction of movement of an indicator on a

display should be compatible with the direction of movement of an operator's internal representation of the variable whose change is indicated.

Example: Thermometer's mercury rises as temperature rises. Violation: Fixed pointer-moving scale display.

120

118

116

114

112

112

114

116

118

120

vs.

Related principles (not found in B & L)

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“Sticky” example from aviation Display of the aircraft's bank angle

to pilots. "Outside-in" "ground-referenced" "bird's-

eye" display (moving plane, fixed ground) - conforms to the principle of the moving part, but violates the pilot's frame of reference.

"Inside-out" "pilot's eye" "moving horizon" display - violates the principle of the moving part but congruent with the pilot's frame of reference.

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“Sticky” example from aviation (cont.)

A compromise: The Frequency-Separated Display Rapid control movement induces "outside-in" display change. When the pilot enters into a gradual turn, the horizon and

plane slowly rotate to an "inside-out" format.

Thus, at high frequencies, when motion perception is dominant, the principle of the moving part is followed. At low frequencies, the static principle of compatibility of frame of reference is followed.

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See also … Legibility principles – pp. 664-668

Information content and coding – pp. 668-673

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Other examples to discuss …