The Problem Space Model Explanation Of Suppression Effect In Conditional Reasoning

Suppression effect in conditional reasoning was explained by mental model theory and probability theory. But both theories only explain a few of studies. The problem space model proposed by Zhang qinglin can made a more reasonable explanation of the suppression effect. The aim of present study is to explore the cognitive and brain mechanism of the problem space affecting suppression effect from both behavioural and ERP experiments.In Behavioural experiments, we manipulated the number of alternative conditionals and the number of disable conditionals that were implied in the major premise to form four types of problem space. We test four types of problem space on suppression effect using three-type response index and rating scale response index. The results showed: (1) Under both response indexes, when there were many alterative conditionals, the participants less accepted the DA and AC, which revealed obvious suppression of invalid inference; When there were many disable conditionals ,the participants tended to less accept the MP and MT, which revealed obvious suppression of valid inference.(2) Under both response indexes, when there were many alterative conditionals, the Participants not only less accepted the invalid inference but also they less accepted the valid inference. When there were many disable conditionals, the participant less accepted MP and MT, however, they more accepted the DA and AC.In ERP experiment, we investigated the neural mechanism on the suppression of invalid inferences (AC,DA) in conditional reasoning in the presence of alternative conditionals by using abstract proposition materials. We obtained the averaged ERP of invalid inference task and baseline task and the difference waves were obtained by subtracting the averaged ERP of invalid reasoning task from that of the baseline task, so the difference waves of AC and DA were only related to pure reasoning processing. The results revealed that there were no significant difference in the early components (P1,N1) of both tasks. But AC and DA elicited a more negative ERP deflection than baseline task in the time windows between 200～800ms .The difference waves and topographical maps showed that there were a N250 in the time windows between 200—300ms at the frontal,frontal-central and central areas, which was possibly related to conflict-monitoring in the reasoning processing. There was a LNC(late negative component) in the time windows between 300～800ms at the central,central-parietal and parietal areas, which possibly reflected deeper integrating and processing to premises.From the point of time processing, the cognitive processing in AC and DA reasoning showed a dynamic activity from the frontal area to parietal area. To a certain degree, the present results showed that brain mechanism of the problem space affecting suppression effect was two-stage processing. In the first stage, participants found the conflict between the alternative conditionals and major premise. The second stage made the final inference by integrating the premises and the alternative conditionals.To sum up, the results of behavioural experiment showed that problem space model can better explained the suppression effect in conditional reasoning than other theories.Further more, it revealed that searching more the alternative conditionals or disable conditionals in bigger problem space would cause the bigger suppression of conditional reasoning. The ERP results possibly showed that brain mechanism of the problem space affecting suppression effect was two-stage processing.