Cognitive and social influences on lay judges' decision processes

2015 Fiscal Year Final Research Report

• Project Area: Law and Human Behavior
• Project/Area Number: 23101008
• Research Category: Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
• Allocation Type: Single-year Grants
• Review Section: Humanities and Social Sciences
• Research Institution: Keio University
• Principal Investigator: Itoh Yuji 慶應義塾大学, 文学部, 教授 (70151545)
• Co-Investigator(Renkei-kenkyūsha): FUCHINO Takao 立命館大学, 法務研究科, 教授 (20271851) ; MURAYAMA Aya 近畿大学, 国際学部, 特任講師 (10609936)
• Research Collaborator: MATSUO Kayo 慶應義塾大学, 先導研究センター, 研究員 ; HINE Kyoko 理科学研究所, 研究員 ; MIURA Hiroshi 慶應義塾大学, 先導研究センター, 研究員
• Project Period (FY): 2011-04-01 – 2016-03-31
• Keywords: 裁判員制度 / 事実認定 / 感情 / 被害者の意見陳述 / 説示

Outline of Final Research Achievements

We examined the influences of inflammatory information in courts on lay judges' verdict decisions with a series of mock lay judge experiments. Inflammatory information such as victim's family's statements of opinion or photographs of dead bodies made the mock lay judges' negative emotions stronger and increased guilty verdicts. However, for mock lay judges with high need for cognition, inflammatory information did not elicit negative emotions nor increase guilty verdicts. Careful legal instructions, pressure for rational decision, and enough thinking time seemed to remove the influences of inflammatory information in courts. However, our data suggested the possibilities that pressure for rational thinking caused irrational judgments or excessive suppression of negative emotions. More psychological experiments are required for the reexamination on Japanese lay judge system and its proper applications.

Free Research Field

認知心理学・司法心理学