Can Implicit Post-Event Information Influence Explicit Eyewitness Memory?

This study examines whether unconscious processing of misleading post-event information can influence explicit and implicit eyewitness memory. Using the existing misinformation paradigm, false post-event information was presented to participants either under full or divided attention. Eyewitness memory was tested with both explicit (free recall and cued recall tests) and implicit memory tests (truth rating test). Participants who were misinformed under full attention recalled significantly more misinformation than their counterparts who were misinformed under divided attention and the control group. However, results from the truth rating test showed that both explicit and implicit forms of misinformation had no impact on implicit eyewitness memory. Since this study is the first to examine the effect of postevent information on implicit eyewitness memory, there is much room for improvement in the selection and design of the implicit memory test that is suitable for eyewitness setting. Other limitations and potential directions for future research are also discussed. UNCONSCIOUS PROCESSING OF POST-EVENT INFORMATION 4 Can Implicit Post-Event Information Influence Eyewitness Memory Explicitly? Eyewitnesses are an important source of evidence which helps identify suspects and prosecute offences (Buckhout, 1975; Engelhardt, 1999; Flowe, Mehta & Ebbesen, 2011; Wells & Olson, 2003). In the report, The Criminal Investigation Process (1975), one of the most important determinants of whether a case was solved is the presence of an eyewitness. However, a recent analysis on DNA exoneration cases, between 1992 and 2009, revealed that more than 70% of false convictions was a result of eyewitness misidentification (Kassin, Bogart & Kerner, 2012). For example, 88% of exonerations in rape cases and half of the exonerations in murder cases involved victims’ misidentification of the perpetrators (Gross, Jacoby, Matheson, Montgomery & Patil, 2005). These findings thus cast doubt upon the credibility and probative value of eyewitness evidence. Many studies have examined the possible mechanisms leading to erroneous recollections on the part of eyewitnesses (e.g., Cutler, Penrod & Martens, 1987; Loftus, Miller & Burns, 1978, Yuille & Cutshall, 1986). Some of the factors which might compromise eyewitness testimony include new information supplied after an event (i.e., post-event information) (Loftus, 1974; Loftus, 1975), a long retention interval (Yuille & Cutshall, 1986), and high weapon visibility during the event (Cutler et al., 1987). Of these factors, post-event information (PEI) has received substantial attention over the past 40 years’ (Loftus, 2005). The research examining the impact of PEI has shown that eyewitnesses are not only UNCONSCIOUS PROCESSING OF POST-EVENT INFORMATION 5 susceptible to memory loss over time, but also memory distortion due to misleading PEI (Yuille & Cutshall, 1986). The incorporation of PEI in eyewitness memory is referred to as the misinformation effect (Loftus & Hoffman, 1989). However, when examining the misinformation effect, the research to date has examined instances in which the participants are explicitly attending to the PEI. It is unclear, though, whether implicitly presented PEI may similarly lead to the misinformation effect. Indeed, witnesses may be bombarded with different types of information from various sources, e.g., when they talk to other cowitnesses, overhear others’ discussions, and receive new information from the media or interrogators (Loftus, 1991). It is unlikely that witnesses could attend to all sources of PEI, which, in turn, leads to the possibility that they may incorporate some PEI unconsciously. The present study therefore seeks to extend the literature on the misinformation effect by examining whether implicitly presented PEI may shape the extent to which eyewitnesses explicitly and implicitly recall a crime scene. In what follows I will discuss 1) the robust research examining PEI and eyewitness memory, 2) the mechanisms argued to lead to the misinformation effect, and 3) how implicitly presented PEI may be related to the misinformation effect. Misinformation Effect Research examining the misinformation effect typically followed a three-stage procedure: 1) participants first view an event, 2) they are then exposed to misleading UNCONSCIOUS PROCESSING OF POST-EVENT INFORMATION 6 information about the event, and finally 3) the participants take a memory test about the witnessed event (see, e.g., Loftus, 1991). In Loftus’ first study, which employed this threestage procedure, participants were presented with a series of slides depicting an autopedestrian accident (Loftus et al., 1978). One of the slides was altered so that half of the participants saw the car stopped at a stop sign while the other half saw the car stopped at a yield sign (Loftus et al., 1978). In the second stage of the experiment, all participants filled out a questionnaire asking them about the details of the accident. For half of the participants, one of the items in this questionnaire asked them whether they saw another vehicle passing the car while it was stopped at the stop sign. For the remaining participants, they were asked the same question with the words “stop sign” replaced by “yield sign”. The remaining items in that questionnaire were identical for all participants. In the final stage, all participants took a forced-choice recognition test about the accident they viewed earlier. In this test, 15 pairs of slides were presented; one of each pair was old and the other one was new (Loftus et al., 1978). Participants were instructed to select the slide that they had seen during the accident. One of the pairs was the critical pair: it included a slide showing the car stopped at the stop sign, and a similar slide which showed the car stopped at a yield sign (Loftus et al., 1978). The results showed that participants who were exposed to misinformation during the second stage were more likely to identify the slide with the wrong traffic sign (Loftus et al., 1978). This study demonstrated that when people are exposed to misleading information (e.g. UNCONSCIOUS PROCESSING OF POST-EVENT INFORMATION 7 suggestive questions) after they witnessed an event, their memory for the witnessed event might be distorted by information they come in contact with after the original event. Research has also shown how misinformation effect can be introduced through narratives containing false information, or through the discussions people have with cowitnesses (which is known as the social contagion effect) (e.g., Gabbert, Memon & Allan, 2003; Meade & Roediger, 2002, Zaragoza & Lane, 1994). In explaining why such instances of misinformation effect occur, researchers have argued that they are the result of failure of source monitoring.