1. Seeking Consistent Stories By Reinterpreting or Discounting Evidence: An Agent-Based Model^ CSCN Presentation

2. Agenda The Phenomenon Agent-Based Model (ABM) Primer The Model Sample Run Experiments

3. Research Interests • Goal: psychology, law, computational modeling • persuasion and decision making • law classes => persuasion techniques • storytelling • narrative coherence • metaphors • Story model of jury decision making (Pennington & Hastie, 1986)

4. Real-Life Scenario: Bench Trial Prosecution (p) Defense Lawyer (d) “Guilty!” “Innocent!”

5. Sequential Evidence – What’s Normative Official Deliberation Story/ Verdict Evidence 1 Evidence 2 Evidence 3 Evidence N …

6. Empirical Literature on JDM • Form “coherent” stories that support option/verdict (Pennington & Hastie, 1988) • Confidence in option/verdict increases with “coherence” (Glockner et al., under review) • Decision threshold: “sufficiently strong” (supported by many consistent evidence) or “sufficiently stronger” than other stories (review by Hastie, 1993 • Narrative coherence: • consistency • causality • completeness • “Consistency” aspect of “good” stories • consistency between evidences in a story • consistency of evidence with favored story

7. Example Case (Pennington & Hastie, 1988) Scenario: Defendant Frank Johnson stabbed and killed Alan Caldwell • Evidence := facts or arguments given in support of a story/verdict • Facts— “Johnson took knife with him” ; “Johnson pulled out his knife” • Arguments—”Johnson pulled out knife because he wanted revenge” vs. “Johson pulled out knife because he was afraid” • Story := set of evidence supporting a given verdict • Same evidence can be framed to support multiple verdicts/stories!

8. Sequential Evidence – More Descriptive Official Deliberation Story/ Verdict Evidence 1 Evidence 2 Evidence 3 Evidence N Premature Story/ Verdict @ Evid n < N Compare, Deliberate, Interpret … (Brownstein, 2003; Russo et al., 2000)

9. People don’t just take evid @ face value, but are selective! Possible Reactions to New Evid in Light of Old: “reinforce” each other “reinterpret” less plausible one (Russo et al., etc.); e.g., misremember the info “discount” less plausible one (Winston) actively “seek” more evidence (not modeled here) Existing evidence A: “Johnson was not carrying a knife.” New evidence B1: “Johnson is nonviolent.” Inconsistent new evid B2: “Johnson pulled a knife.” Reinterpret B2: “Johnson grabbed a knife from Caldwell.” (i.e., explain it was Caldwell’s knife, not Johnson’s) Discount B2: “Witness must be mistaken.” Judge asks layers follow-up questions How People Deal with Incoming Evidence

10. Agenda The Phenomenon Agent-Based Model (ABM) Primer The Model Sample Run Experiments

11. What is Agent-Based Modeling? • agents + interactions^ • start simple; build up^ • Key terminology • agents • system • dynamics • agent births and deaths • interactions/competitions • parameters

12. Symbiotic relationship: Behavioral Experiments ABM Contributions ABMs Can Make Input Test description: informs base assumptions understanding: study processes in detail parsimony: demo emergence of seemingly complex phenomen from small set of simple rules predictions: new observations/predictions

13. (Other Models (Hastie, 1993))

14. (Contrast with Bayesian & Algebraic Models) • Algebraic (additive), Bayesian (multiplicative): • “single meter” of overall plausibility • ABM allows: • revisiting and reconsidering previously-processed evidence • interaction/competition between new evidence and individual pieces of previous evidence (not just conglomerate)

15. Contrast with Story Model & ECHO • Explanatory Coherence Model := Thagard’s Theory of Explanatory Coherence (TEC) + Story Model • Only implemented discounting, not reinterpretation • ABM enforces lower evidence-agent-level consistency, as opposed to higher story-level consistency • Unlike previous ABMs, model agents within individual as system

16. Motivations • Study emergence of consistent stories via reinterpretation, discounting, reinforcement mechanisms • Adaptive? • aid consistency? • speed-accuracy tradeoff? avoid indecisiveness • increases convergence rates? • order effects hurt accuracy?

17. Agenda The Phenomenon Agent-Based Model (ABM) Primer The Model Sample Run Experiments

18. Goal • Model consistency-seeking process in story formation • Present evidence-agents to judge-system • Judge-system compares evidence-agents => keep, reinterpret, or discount evidence (agents “interact” & “compete”) • Until sufficiently strong/stronger story emerges

19. Agents Evid 1 Evid 1 Evid 2 Verdict (“G”,”N”,…) G N N Abstract features (binary) x x x x x y Plausibility index (0%-100%) 34% 14% 89% • Evidence-agents, composed of “features” • Operationalize consistency /b/ agents: • “similarity” in abstract features (Axelrod’s culture ABM, 1997) • “inverse Hamming distance” := % feature matches …

20. Parameters

21. (Java GUI)

22. System & Agent Births • Judge-system represents judge’s mind • Evidence presentation = “agent birth”: • Initialization of N0 Agents: • Set up randomly-generated agents, OR… • uniform distributions—even for plausibility index due to prior beliefs (Kunda, 1990) or knowledge (Klein, 1993) • User-specified

23. results\sysout_081118_0455.log Printing 8 agents: 01 02 03 04 05 06 07 08 N G I G N I N N y y y y y y y y y y y y y y y y 100% 100% 100% 100% 100% 100% 100% 80% Dead/Rejected Evidence--Printing 9 agents: 01 02 03 04 05 06 07 08 09 I G G I G I N N N y y x x y x x x y y x x x y x x y y 00% 00% 00% 00% 00% 00% 00% 00% 00% To keep track of evidence-agents and their order of presentation: lists of agents in order of birth/presentation to the system. latest-born agent always appears at the end of a list. no geographical “topology” (Topology)

24. Stories Evid 1 Evid 2 Evid 1 Evid 3 N N G N y x x x y y x x 14% 34% 51% 89% strength = 99% / 3 = 33% strength = 89% := {evidence-agents supporting a verdict} • Consistency = inverse Hamming distance amongst evidence (:= SevidencePairs # feature matches / # evidencePairs / F ) • Plausibility Index (“Strength”) = average of plausibility indices Story promoting “Innocent” verdict Story promoting “Guilty” verdict

25. Births & Interactions • If time period t = k * I, where k is some constant, birth new agent. • Random selection of agent to compare with newest-born. • Compare agents and compute consistency. If consistency… • = C, both agents are "winners“; increase both agents' plausibility indices by D • < C, "inconsistency conflict“ => competition. • higher plausibility index => "winner" (“draw” if indices identical). If consistency… • = N, "loser" is salvageable by “reinterpreting” one of its inconsistent features to match winner’s • < N, discount (decrease plausibility by D) • Agents with plausibility = 0% => death & removal from system • Gather stories in system. Check strengths. “Winning story found” if 1 ! story with strength >= S and/or |strength-strength | >= Sd for all competing stories; stop run early.

26. Possible Reactions to New Evid : Completely consistent (e.g., 100% features match) => “reinforce” both; “reward consistency” Inconsistent… but salvageable (50% features match) => “reinterpret” less plausible “loser”; “increaseinconsistency” not salvageable (0% features match) => “discount” “loser”; “punish inconsistency” => plaus(Evid1) > plaus(Evid2) => Evid2 “loser” Operationalizing Consistency--Examples Evid 2 Evid 1 Evid 2 Evid 1 Evid 2 Evid 1 Evid 1 Evid 2 Evid 1 Evid 2 Evid 1 Evid 2 x x x x x x y x y x x x y x y y y y y y y y x y 44% 51% 34% 24% 51% 61% 51% 34% 51% 51% 34% 34%

27. Agenda The Phenomenon Agent-Based Model (ABM) Primer The Model Sample Run Experiments

28. Sample Output^ • Live Evidence--Printing 8 agents: • 01 02 03 04 05 06 07 08 • N G I G N I N N • y y y y y y y y • y y y y y y y y • 100% 100% 100% 100% 100% 100% 100% 80% • Dead/Rejected Evidence--Printing 9 agents: • 01 02 03 04 05 06 07 08 09 • I G G I G I N N N • y y x x y x x x y • y x x x y x x y y • 00% 00% 00% 00% 00% 00% 00% 00% 00% • 3 stories found: • -Verdict N supported by 4 evidence, with 1.00 consistency => 0.48 strength • -Verdict G supported by 2 evidence, with 1.00 consistency => 0.25 strength • -Verdict I supported by 2 evidence, with 1.00 consistency => 0.25 strength • *** Found winning story! Verdict N supported by 4 evidence, with 1.00 consistency => 0.48 strength

29. Judge-System can get Stuck… results\sysout_STUCK.log Live Evidence--Printing 17 agents: 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 N G G I G I I I I N I G G N N N G x x x x x x x x x x x x x x x x x y y y x y y y y y y y y y y y y y 100% 100% 100% 90% 100% 100% 100% 100% 100% 100% 84% 100% 79% 100% 100% 98% 100% Dead/Rejected Evidence--Printing 10 agents: 01 02 03 04 05 06 07 08 09 10 I I I I N I I G N G y x y y y y y y y y y x x x x x x y x x 00% 00% 00% 00% 00% 00% 00% 00% 00% 00% 3 stories found: -Verdict N supported by 5 evidence, with 1.00 consistency => 0.29 strength -Verdict G supported by 6 evidence, with 1.00 consistency => 0.34 strength -Verdict I supported by 6 evidence, with 1.00 consistency => 0.34 strength No winning story found.

30. Output of a Run^

31. Agenda The Phenomenon Agent-Based Model (ABM) Primer The Model Sample Run Experiments

32. 5 Experiments • Experiment 1: Emergence of consistency Decision Speed • Experiment 2: Speedup • Experiment 3: Accuracy tradeoff Decision Accuracy—Order Effects • Experiment 4: Emergence of order effects • Experiment 5: Extending deliberation

33. Obtaining Consistent Stories – Q1 Q1: Evidence-level consistency sufficient? Which of the 3 mechanisms? Implementation: No rules DV: Consistency of stories

34. Obtaining Consistent Stories – Q1 Results Reinterpret > Discount > Reinforcement

35. Speed-Accuracy Tradeoff – Q2 Q2: Reinterpretation & Discounting increase speed? Prediction: Reinterpretation & Discounting allow much faster convergence DV: Time to Converge, Max nEvid (Max Consistency) Implementation: Both rules; all cases have reinforce

36. Speed-Accuracy Tradeoff – Q2 Results Results of 10 Runs—Time to First Convergence, Maximum Number of Evidence, Maximum Story Consistency

37. Speed-Accuracy Tradeoff – Q2 Results Medians of 10 Runs—Time to First Convergence, Maximum Number of Evidence, Maximum Story Consistency Reinterpret > Discount > Reinforcement only

38. Speed-Accuracy Tradeoff – Q3 • Q3: What would happen if allow process to continue even after having found winner? Any point to "holding off judgment" until all evidence presented? • DV: Which story wins? (Strength) • Prediction: Leader will only be strengthened; competing stories never get a foothold. • Implementation: Allow system to continue running even if found winner

39. Speed-Accuracy Tradeoff – Q3 Results^ Figure 2. Example run where winner switches • Over 20 runs, # runs same winner:# runs different winner = 15:1 • => Good heuristic to stop deliberation, for less time & effort

40. Order Effects – Q4 p d d d p d p d p d Heuristic may be ok only if randomized evidence…what if biased evidence? Q4: Is there an Order Effect? Took {20 randomly-generated evidence} and then “doctored” it; % D win = “accuracy” IV: Presentation order--P goes first, followed by D vs. interwoven evidence Prediction: earlier, weaker side (e.g., P) beats out later, stronger side (e.g., D); "Accuracy" of D…P… > PDPDPD… > P…D… DV: Time to Converge, (Projected) Winner

41. Order Effects – Q4 Results Figure 3. Sample random presentation order run.

42. Order Effects – Q4 Results Figure 4. Sample D…P… biased presentation order run.

43. Order Effects – Q4 Results Figure 5. Sample P…D… biased presentation order run.

44. Order Effects – Q4 Results Table 4. Results of 10 Runs Varying Presentation Order of Evidence • Strong primacy effect • Exper3 conclusion no longer holds; longer deliberation DOES help!

45. Increasing Deliberation – Q5 Q5: Can deliberating more often between births reduce order effects (i.e., increase "accuracy")? Implementation: Use P…D… model from Exper4 IV: Varied I (I = 0 => wait till end to deliberate) DV: % runs that P wins

46. Increasing Deliberation – Q5 Results Too much lag time during trials can be detrimental!

47. Summary of Key Findings • Why reinterpret and discount evidence? • Maximizes consistency (Experiment 1) • Hastens convergence on decision (Experiment 2) Reinterpret > Discount > Reinforcement • Speed-accuracy tradeoff? Yes… • Accuracy ok if evidence balanced (Experiment 3) • Not ok/primacy effect if biased (Experiment 4) • => Important to interweave evidence, like in real trials! • Can reduce primacy effect by decreasing premature deliberation (Experiment 5) • All achieved by modeling consistency @ evidence level, not story level

48. (Future Expansions) • Q6: What happens when introduce bias toward certain verdicts? • Prediction: Verdict-driven process takes less time to converge • DV: Time to Converge (Consistency of Stories) • Implementation: Add favoredVerdict • Q7: In general, what conditions lead to indecision?

49. BACKUPS

50. Agenda The Phenomenon Agent-Based Model (ABM) Primer The Model Sample Run Experiments