In search of the elusive initial model

A key assumption of Mental Model theory (Johnson-Laird & Byrne, 1991, 2002) is that reasoners should use a minimal representation of the premises, called the initial model, in order to reduce the cognitive load involved in the processing of more than one model. However, there is no direct evidence for this postulate. In the following studies, we modified the ability of participants to process conditional (if-then) inferences in more complex ways by varying the degree of arbitrariness of the conditionals and by restricting the time allotted. Study 1 used premises with arbitrary relations with explicit negations in both terms in order to control for a possible matching strategy, with 9 s, 15 s, or unlimited processing time. Results show a significant number of initial model patterns, which increased with time. No evidence for use of a matching strategy was found. Study 2 involved arbitrary relations without negations, with 6 s or 8 s processing time. This study showed a significant increase in initial model patterns at the longer times. Study 3 used premises with familiar relations with either very limited processing times (5 s, 7 s) or an unlimited time condition. Results show very low numbers of initial model patterns in the three time conditions. Overall, these studies provide clear evidence that reasoners do use an initial model form of reasoning, and suggest that this is done mostly because of difficulty of processing more abstract content.