Prisoner’s Dilemma:
Thoughts on Harvesting
Robert L. West & Matthew Kelly
Institute of Cognitive Science
Carleton University
Prisoner’s Dilemma
Cooperate
Defect
Cooperate
+1 +1
+10 -10
Defect
-10 +10
-1 -1
Lebiere, Wallach & West
1
13
25
37
49
61
73
85
97
109
121
133
145
157
169
181
193
205
217
229
241
253
265
277
289
Failure to Replicate
100
90
80
70
60
CC
50
CD
40
DC
DD
30
20
10
0
Problem
• Shared memory in original model
• Too noisy without it
– Important lesson for multi-agent simulations
– Sensitive to initial conditions
• Solutions
– Blending
– Lags
– Rock = 2
– Harvesting
1
12
23
34
45
56
67
78
89
100
111
122
133
144
155
166
177
188
199
210
221
232
243
254
265
276
287
298
Lag 0: Blend
70
60
50
40
#REF!
#REF!
30
#REF!
#REF!
20
10
0
Lag 0: Blend + Harvest
70
60
50
Series1
40
Series2
Series3
30
Series4
20
10
1
13
25
37
49
61
73
85
97
109
121
133
145
157
169
181
193
205
217
229
241
253
265
277
289
0
1
13
25
37
49
61
73
85
97
109
121
133
145
157
169
181
193
205
217
229
241
253
265
277
289
Lag 0: Blend + Double
60
50
40
CC
30
CD
DC
20
DD
10
0
1
12
23
34
45
56
67
78
89
100
111
122
133
144
155
166
177
188
199
210
221
232
243
254
265
276
287
298
Lag 0: Blend + Double + Harvest
60
50
40
CC
30
CD
DC
20
DD
10
0
1
13
25
37
49
61
73
85
97
109
121
133
145
157
169
181
193
205
217
229
241
253
265
277
289
Lag 1: Blend
70
60
50
40
CC
CD
30
DC
DD
20
10
0
1
13
25
37
49
61
73
85
97
109
121
133
145
157
169
181
193
205
217
229
241
253
265
277
289
Lag1: Blend + Harvest
80
70
60
50
CC
40
CD
30
DC
DD
20
10
0
Lag 1: Blend + Double
45
40
35
30
CC
25
CD
20
DC
DD
15
10
5
0
0
50
100
150
200
250
300
350
1
12
23
34
45
56
67
78
89
100
111
122
133
144
155
166
177
188
199
210
221
232
243
254
265
276
287
298
Lag 1: Blend + Double + Harvest
45
40
35
30
25
CC
CD
20
DC
15
DD
10
5
0
Stochastic Resonance
0.4
0.38
0.36
0.34
0.32
0.3
0
0.5
1
0
0.5
1
0.4
0.38
0.36
0.34
0.32
0.3
Rational Analysis
• Harvest a prediction
– Chunk activation increased
• Confirm prediction
– Chunk activation increased again
• Disconfirm prediction
– Correct chunk gets activation increased
– But not more than the incorrect chunk
• Does not map activation to actual results