MEC 325 Chapter Notes - Chapter 5: Binary Logarithm, Microwave Oven, Naturalistic Decision-Making
3 May 2018
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Chapter 5
Human information processing (HIP) - second stage of human design interaction cycle
-associated w computing systems, info displays, mobile phones
- Principle of cognitive psychology
- Observations of naturalistic decision making
Common problems:
- Too much info in interface design
- Ie. Microwaves
1. Too many controls—not all are required.
2. Rather than turning a dial, you have to key in the cooking time.
3. Too many contingent actions—even the “start” button has to be pressed. It is no longer
automatic after step 2 above.
4. Functions that seem deceptive. For example, if you want to heat up your cup of
coffee—press “beverage”. It will then cook for 1 min 20 sec. But the microwave oven
does not know your cup is half full, and that you want the temperature to be less than
- burning hot—about 65°C.
performance measure in HF= human reaction time, measures how complex decisions are
Hick’s law – rxn time is a function of the # of choices in a decision (directly related)
RT=a+b log2N
RT is reaction time, N is the number of alternatives, and a and b are constants. The
Equation
Info theory- maximize search time
Info= uncertainty or entropy
The amount of information in a stimulus depends on the probability that the stimulus
carries relevant information.
For example, a statement such as “The sun went up this morning” carries no
information, since the sun goes up every morning
The probability of an event therefore affects the amount of information.
The general formula for calculating the number of bits of information is hence
tied to the probability:
Hs=log2 N
where Hs is the amount of information and N is the number of equal probability
outcomes. For N events the probability that each may occur is therefore p=1/N.
RECALL to solve : 2 to the power of WHAT VALUE gives you N = H
Hs=log2 (1/p)
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To summarize the information for all N events we obtain:
Hs=log2 (1/p)
Examples:
If 2 stimuli are equally likely to occur with p=0.5, there is an information
uncertainty of 1 bit. If there are 4 possible events, each with a probability of p=0.25, there
are 2 bits.
EXAMPLE 1
Start with a deck of 64 cards—16 cards in 4 suits. Ask a person to think of card. Your
task is to identify the card the person is thinking of. You can ask the person for hints.
First, let us note that the amount of information uncertainty in the single card that you
will try to identify is as follows:
Hs=log2 N =log2 64=6 bits
We can also do the calculations using probabilities. The probability to find a single
card is p=1/64:
Hs=log2 (1/p)=log2 (1/1/64)=log2 64=6 bits
Given the hint that the card is red, the uncertainty is reduced from 64 to 32:1 bit.
Given that the card is a heart: 1 bit; lower 8 hearts: 1bit; lower 4 cards: 1 bit, lower 2
cards: 1 bit; ace of hearts: 1 bit; 6 bits altogether. This is in agreement with the
calculations above.
For events that have unequal probabilities:
hi=log2 (1/pi)=−log2 (pi)
where pi is the probability of the ith event and hi is the information of the ith event. The
variable hi is also called surprisal—obviously, the lower the probability for a single event
to occur, the greater the surprisal.
EXAMPLE 2
A bent coin is tossed and it comes up heads 90% of the time and tails 10% of the time.
Calculate the amount of information in this coin, considering both outcomes. Consider:
To perform the calculation we use the conversion from log2 to log10;
log2x=3.332 log10 x
Hhead=p log2(1/0.9)=0.9×0.0453×3.332=0.135 bits
Htails=p log2 (1/0.1)=0.1×1×3.332=0.332 bits
The total information uncertainty of tossing the coin is 0.135+0.332=0.467 bits.
Consider a regular coin:
Hs=2×0.5 log2 (1/0.5)=1.000
Because the bent coin comes up with heads almost all the time, there is less surprisal
than in a regular coin.
We can now understand that the amount of information can be calculated, and we can
apply Hick’s law to compare different designs, realizing that the more information, the
longer the reaction time will be for making decisions. A calculation exercise is presented
at the end of this chapter.
Human Info Processeing Cycle
1. perceptual processor (to see and hear)
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2. cognitive processor (to think)
3. motor processor (to act)
average time for each component of the processing cycle: 100 ms for perception; 70 ms for
cognition; and 70 ms for action.
CAP= Capacity , T- average processing time
the range of variability in perceptual and cognitive
processors is about 25–200 ms, and in motor processors about 30–100 ms
-working memory is short term memory – used when preforming a task; half time of the working
memory is 7sec, after 7sec, half the memory had been forgotten
- working memory deals w daily routine things (temp info stored while activiely acting on it) –
actions and responses are preprogrammed. Sensor processors such as seeing and hearing are
interpreted by the working memory and what motor response one should have to the specific
scenario they’re in is insticitively clear.
W. running memory, no need for retention
Perception and working memory of how to complete a task correctly is enhanced w experience.
(use of mnemonics-the study or development of a system in order to improve/assist memory..
associated w words/meanings of things.) As people learn tasks, they form large chunk- units of
info
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find more resources at oneclass.com
Document Summary
Human information processing (hip) - second stage of human design interaction cycle. Associated w computing systems, info displays, mobile phones. Microwaves: too many controls not all are required, rather than turning a dial, you have to key in the cooking time, too many contingent actions even the start button has to be pressed. It is no longer automatic after step 2 above: functions that seem deceptive. For example, if you want to heat up your cup of coffee press beverage . It will then cook for 1 min 20 sec. But the microwave oven does not know your cup is half full, and that you want the temperature to be less than. Burning hot about 65 c. performance measure in hf= human reaction time, measures how complex decisions are. Hick"s law rxn time is a function of the # of choices in a decision (directly related)
