Human Computation (Slides)

What is computation?

Milk carton computer

http://madwriter.livejournal.com/795010.html

Pask on Computation

The modern computer is a 'black box'. The abacus user in contrast slides beads along wires at each stage of calculation and can see exactly what is going on. The history of computing is one of increasing delegation of control and increasing machine inscrutability. Every increase in automation has required a corresponding increase in man-machine communication. We have had to find ways of telling machines what to do, and when they have completed tehir obscure ballet, they have to tell us the result. They must interface with us at a practical level (we put something in, take something out) and at an intelligible level (they must make sense of what we put in, and we must understand what they put out).

Put at its simplest, a modern computer manipulates symbols by adding, subtracting and comparing them, and it does so via instructions known as a program.

Pask, Curran, Microman (1982), p. 7

http://en.wikipedia.org/wiki/Gordon_Pask

Counting beans

http://en.wikipedia.org/wiki/Abacus

http://en.wikipedia.org/wiki/Mancala

Pickerings Harem

The word computer was originally used (circa 1900's) to describe a person whose job it was to compute.

http://www.cfa.harvard.edu/~jshaw/pick.html

"Pickerings Harem" was a group of women computer's who translated astronomical data recorded on photographic films into tables of data in standardized units.

Digital

Digital refers to our fingers, in the sense of counting

Digital is described as discrete rather than continuous in the sense that the numbers represent separate ideas (one, two, three are each distinct and "disconnected"), rather than continuous in the sense of for instance a precise distance between two objects (which in written form, we might express as a number with fractions.)

Separation of Meaning from Representation

The concept of "one" is universal (in relation to two, or three)

Speech

wehn, ayn, ehn

Writing

one, een, un

1, b0001, 0x01

Decimal

We are used to writing and thinking of numbers using a system of Arabic numerals, a technology that originated in Persian mathematics in the 1st and 2nd century. In this system, 10 discrete symbols (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) are used to express an infinite number of concepts of quantities.

An important step is to (re) make the separation between the notion of a particular quantity (say the number of days in the month of February, or twenty-eight) and the numeric notation of that concept ("28"). "28" is simply one way of expressing this concept. In Roman numerals, the same concept could be expresses as "XXVIII".

Rules (Decimal):
1. When tapped on your shoulder, count.
2. When you get to 10, tap the shoulder of the person next to you and "zero" your count.

Exhibit 1: Human computers Lieven, Amy, and Natasa count the number of people in the room.

File:HumanCountingMachine decimal.ogv

Result:
8, 1
...
(reversing order)
18
...
Decoding:
10's  1's
1     8

18 = decimal representation of "eighteen"

Binary

Binary, a system of expressing numbers using only two discrete symbols (typically: 1, and 0), is the system used by modern digital computers for simple numeric quantities. It was Claude Shannon who made the connection between George Boole's work on logical systems based on true and false values and using electronic circuits to implement them as circuitry. Using a binary system makes a physical implementation much simpler than a decimal system such as Charles Babbage's Difference Engine.

Rules (Binary):
1. When tapped on your shoulder, raise your hand.
2. When you get tapped and your hand is raised, tap the shoulder of the person next to you put your hand down.

Exhibit 2: Human computers Lieven, Amy, Natasa, Inge, Danny, and Fabien count the number of people in the room, in binary.

File:HumanCountingMachine binary.ogv

Result:
0, 1, 0, 0, 1
...
(reversing order)
1  0  0  1  0
...
Decoding:
16's 8's 4's 2's 1's
1    0   0   1   0

10010 = binary representation of "eighteen"

Logic

• Propositional Logic
• Basic building blocks, True and False, and operations: and, or, not
• Truth tables

True or False?

Instead of representing quality, another kind of "digital" representation exists in propositional logic based on "binary" notion of "True" and "False".

Happy? True, False

NOT!

Not True, False

Not False, True

NOT

An "operation"

   INPUT   OUTPUT

   Veg?    Carn?
   F   =   T
   T   =   F

NOT

LET Y BE NOT X

  X?     Y
  F      T
  T      F

AND: Principled Katherine

Katherine is happy when the food is vegetarian and cheap.

• Vegetarian? (True or False)
• Cheap? (True or False)
• Happy?

AND: Truth Table

   Veg?  Cheap?  Happy?
   ----------------------
   F     F       F
   F     T       F
   T     F       F
   T     T       T

The concepts (Veg, Cheap, Happy?) can be changed to represent anything, the operation of the and remains the same.

   V     C       H
   ----------------------
   F  +  F   =   F
   F  +  T   =   F
   T  +  F   =   F
   T  +  T   =   T

Virtue AND Chastity = Holy

Venomous + Circular pattern = H Snake

OR: Opportunistic Gordon

Gordon is happy when the good is vegetarian or cheap.

OR

Gordon is happy when the good is vegetarian or cheap.

   V     C       H
   ----------------------
   F  +  F   =   F
   F  +  T   =   T
   T  +  F   =   T
   T  +  T   =   T

Vice OR C = Hell

Encode/Decode

In these simple example of "logic machines", there is a process of translating, where a given situation in the world is encoded according to a particular representation (in this case logical propositions veg?, and cheap?). The machine then proceeds to "do its thing" on this representation of the situation. The result (in this case a logical proposition happy?) is in turn interpreted, or decoded from the machine representation to some "external" meaning (Will Katherine be happy?).

De Morgan's Law

Who needs AND, you can replace it with NOT + OR

A and B == not ( (not A) OR (not B) )

Restaurant Logic

Katherine is happy if the food is vegetarian and cheap.

is equivalent to

Katherine is not happy if the food isn't vegetarian or cheap.

---

Gordon is happy if the food is vegetarian or cheap.

is equivalent to

Gordon is not happy if the food is not vegetarian and is not cheap. (He's only unhappy when it's neither vegetarian nor cheap).

Exercise: Human Adding Machine

Human Computation: Adding Machine

For next week

Take a (digital) photograph which depicts counting in a public space.

Binary Digits

Understanding binary allows how to count much higher than just four using the fingers of one hand. The word "bit" is a shortened form of "binary digit", and the word "digit" is another name for a finger. If we think of a raised finger as a binary "1" and a lowered finger as a "0", imagine how high you could count with four fingers (much higher than just four). In other words, how many unique signs can you make using the four fingers of one hand (where you only either raise or lower each finger, independent of the others). How would you teach someone to systematically work through all of the possibilities? The question "how high can you count using all 10 fingers" could be rephrased, how many unique discrete states can you form using your hands by raising and lowering each finger independently.