Mental Simulation in Thinking about “What if …” Clare Walsh, University of Plymouth & Steven Sloman, Brown University

Outline What is a mental simulation? How do people mentally simulate possibilities when they think “what if..”? ExperimentsConclusions

Mental Simulation Imagine something were different, e.g., On Sunday, there was no queue at the ice-cream shop What else would be different if this were the case? –Would the ice-cream shop have made a profit? –Would it have been a hot day?

Mental Simulation Important in many aspects of higher cognition: PlanningDecision-making Hypothesis Generation and Testing Belief Revision

Lewis / Stalnaker Theory of Conditionals Imagine the actual world Imagine the antecedent occurred Make any necessary additional changes to accommodate this (should be minimal!) Check whether the consequent occurred

Lewis Imagine a world that is as similar as possible to reality Hot Queue at Large Day Ice-cream Shop Profit

What are Causal Models? Causal Models represent causal relations between events (Pearl, 2000) Hot Queue at No DayIce-cream Profit Shop Shop

Causal Models and Mental Simulation Mental simulation involves updating our causal models Hot Queue at No DayIce-cream Profit Shop Shop

Experiment 1 Present a scenario where there are two possible alternative worlds Do people consistently judge one to be closer? Is this influenced by the consequent that you ask about?

Experiment 1 - Scenario Fires cause the alarm to go off and the sprinkler system to come on. AlarmFireSprinkler In fact, there was a fire, the alarm went off and the sprinkler system came on. Ann thinks there was a fire, that the alarm went off and that the sprinkler system came on but she’s not sure.

Experiment 1 - Scenario AlarmFireSprinkler According to Ann, what is the probability that if the alarm didn’t go off, then … there still was a fire? the sprinkler still came on?

Alternative Possibilities Possibility 1 AlarmFireSprinkler Possibility 2 AlarmFireSprinkler

Scenario - OR Fires cause either the alarm to go off or the sprinkler system to come on (depending on whether there are people in the building). AlarmFireSprinkler In fact, there was a fire and the alarm went off. Ann thinks there was a fire and the alarm went off but she’s not sure.

Scenario - OR AlarmFireSprinkler According to Ann, what is the probability that if the alarm didn’t go off, then … there still was a fire? the sprinkler still didn’t come on?

Alternative Possibilities Possibility 1 AlarmFireSprinkler Possibility 2 AlarmFireSprinkler

Results Probability that there was a fire And Fire 33 Sprinkler 47

Results Probability that there was a fire And Or Fire 3347 Sprinkler 4757

Lewis / Stalnaker Theory of Conditionals Imagine the actual world Imagine the antecedent occurred Make any necessary additional changes to accommodate this (should be minimal!) Check whether the consequent occurred

Implications The consequent determines which possibility people think about Hence, people think about the consequent before simulating an alternative Principle 1: People are more likely to undo events if there is a direct causal link between the antecedent and consequent

Experiment 2 What happens if there are alternative causes available?

Experiment 2 Producing smoke causes the alarm to go off. The alarm going off causes the occupants to evacuate. The occupants evacuated. SmokeAlarm Evacuate

Experiment 2 Producing smoke causes the alarm to go off. Producing smoke causes the sprinkler system to come on. The alarm going off causes the occupants to evacuate The sprinkler system coming on causes the occupants to evacuate The occupants evacuated. Alarm Alarm SmokeEvacuate Sprinkler Sprinkler

Questions If the alarm hadn’t gone off, would the occupants have evacuated? Yes or No If the alarm hadn’t gone off, would there have been smoke? Yes or No Alarm Alarm SmokeEvacuate Sprinkler Sprinkler Smoke Alarm Evacuate

Alternative Possibilities If the alarm hadn’t gone off, would the occupants have evacuated? Yes or No Alarm Alarm SmokeEvacuate Sprinkler Sprinkler Alarm Alarm Smoke Evacuate Sprinkler Sprinkler

Results Linear Linear Smoke20 Evacuate13 Consequent influences which possibility people think about

Results Linear Diamond Linear Diamond Smoke2022 Evacuate1373 Consequent influences which possibility people think about

Diamond Model Smoke First Evacuate First Smoke First Evacuate First Smoke22 53 Evacuate39 73 Alarm Alarm SmokeEvacuate Sprinkler Sprinkler

Implications Once again the consequent influences which possibility that people imagine Principle 2: Alternative Causes reduce the probability that people will undo an event When we simulate alternatives we construct a model and we make further updates assuming that previous inferences hold

Conclusions We have little evidence that people seek to make minimal changes when they simulate alternatives Instead mental simulation depends on the causal models that people have in mind They are guided by some straightforward principles: –They undo events if they are causally related to the antecedent –If they do not have alternative causes