Lindsay Lab Projects
The following is a sampling of some of the lines of research currently underway in my lab (and in the labs of collaborators). My aim here is just to give you a sense of the kinds of questions that interest me and the sorts of approaches I take to them.
Co-Witness Contamination Effects If two or more people witness a crime together, afterward they are likely to talk with each other about what they saw. Prior research demonstrates that if a witness's comments to a co-witness contain errors, there is some likelihood that the co-witness will later report those errors independently. We expect that under some conditions when people report details that they only heard a co-witness describe they are aware of that fact (i.e., they know that their reports are based on things the co-witness said) but that under other conditions they do not realize the true source of their memories (and may even experience illusory recollections of having witnessed detail that they had merely heard about). Our aim is to understand the cognitive mechanisms that underlie these various sorts of false reports. My doctoral student Tanjeem Azad is using something called the MORI technique to study these issues. It's very cool.
Study/Test Versus Continuous Recognition Most studies of recognition memory use a two-staged material: First there is a study phase, in which subjects are exposed to to-be-remembered materials (either with intentional or incidental learning instructions) and then later (often after a delay interval) there is a test phase in which subjects judge whether or not each test probe had appeared during the study phase. Everyday life doesn't separate out the study and test phases so clearly. As you move through the environment, you encounter some things you've seen before and some things you haven't ever seen before and you may recognize some of the things you've seen before and note the noveltly of some of the things you haven't seen before, but at the same time you are making those memory judgments you are also creating new memory records of your experiences with those items. Later, you may re-encounter and recognize something. In everyday life, the study and tests phases are one and the same. Helen Williams and I looked for direct, head-to-head comparisons of these two ways of testing recognition memory and came up with almost nothing, so we are giving it a go.
Influences of Eyewitnesses on Investigators Eyewitness identification evidence often plays a key role in police investigations and prosecutions. For example, the vast majority of the false convictions that have been overturned by DNA evidence in recent years involved faulty eyewitness identifications (see the Innocence Project website.). Much is known of the factors that affect the accuracy and confidence with which eyewitnesses perform identification tests (lineups), but little is known of how forensic investigators weigh witnesses' identification evidence in the context of other evidence. We speculate that investigators tend to be greatly swayed by eyewitness identification testimony (even when it is inaccurate, and even when there are other, more solid grounds for decisions). Because eyewitnesses are often wrong, this may lead both to accusations against innocent individuals and failures to prosecute guilty ones. To explore such issues, colleague Liz Brimacombe, grad student Leora Dahl, and I developed a new method in which participants role play being police investigators or witnesses. Subject/investigators interview witnesses before searching a computer data base of potential perpetrators with the aim of selecting a suspect. The data base includes information about each potential suspect's physical description, criminal record, whereabouts during the crime, and other probative details. The investigator selects a suspect and then rates the probability that the suspect is indeed the culprit, indicates the importance of various kinds of evidence for that conclusion, and reports whether s/he would arrest the suspect at that point in the investigation. Thereafter, investigators administer a lineup identification test to witnesses. Finally, investigators re-rate the probability that the suspect is the culprit, etc. We use changes from the pre- to post-ID ratings to index how much stock the subject/investigator places in the witness. This general procedure can be used in a wide range of potential studies (ranging from very "social" to quite "cognitive"). In the first set of experiments we completed (Dahl, Lindsay, & Brimacombe, 2006), the "investigators" were university undergraduates and the witness was a confederate. We found that investigators were greatly swayed by eyewitnesses' identification decisions (even though real witnesses perform extremely poorly on this lineup task). Mel Boyce, another recent grad student, took the lead on a version of the procedure in which the witnesses are not confederates; rather, subjects are tested in pairs with one member of each pair assigned to be the investigator and the other to play the role of witness. These studies yielded results that parallel those reported by Dahl et al. with confederate witnesses. Generally, undergraduate subject/ivestigators are greatly influenced by ID evidence and they put no more stock in witnesses who are accurate than in those who are in error. Ultimately, we hope to conduct versions of these studies in which the investigators are actual police officers. This is to be the central research project of new graduate student Mario Baldassari starting in the fall of 2011. It will be exciting to find out if police officers are better than naive undergraduates at weighing eyewitness identification evidence in this situation.
Recognition Response Bias As explained above, on a yes/no test of recognition memory, subjects are to say “Yes” to test items that had been presented on a study list and “No" to test items that had not been presented on the study list. According to Signal Detection Theory, performance on such a test is determined by two things. One is the extent to which the test taker accesses more evidence of having studied an item for items that really had been studied than for items that had not been studied. If evidence-strength is equivalent for studied and non-studied items (e.g., because the person didn’t pay much attention to the items during the study phase), performance will be poor, and if evidence strength is much greater for studied than for non-studied items then performance will be good. Very often, average evidence strength is greater for studied than for non-studied items, but the two distributions overlap, meaning that there are some non-studied items for which the person experiences more evidence of having studied those items than they do for some of the studied items. This puts the test-taker in a tricky position, at risk of making false alarms (i.e., judging that a nonstudied item had been studied) and/or misses (i.e., judging that a studied item had not been studied). According to Signal Detection Theory, in this situation the test-taker sets a criterion: If there is X amount of evidence of oldness, then I’ll say Yes, and if there is less than X then I’ll say No. The idea is that this criterion can be set to be very high (only say Yes if there is a LOT of evidence of oldness, in which case false-alarms will be rare but misses will be common) or to be very low (say Yes even if there is just a little bit of evidence of oldness, in which case misses will be rare but false alarms common) or anywhere in between. We refer to this as a “response bias:” A conservative bias means that one only says Yes if there is a lot of evidence, a liberal bias means that one says Yes even if there is only a little bit of evidence, and a neutral bias (which could also be called an absence of bias) means that false alarm and miss rates are approximately equal. It is well established that in a straightforward recognition memory study with, say, common words or simple line drawings, on average response bias tends to be neutral. A couple of years ago we stumbled upon the finding that response bias to novel and rich materials (e.g., scans of great paintings) tends to be conservative (few false alarms, many misses). It turns out that similar effects had already been reported in the literature (rats!). Justin Kantner and I have been conducting studies to try to understand the cognition mechanisms that give rise to this materials-based difference in recognition response bias. In closely related work, also with Justin, we have been exploring recognition response bias as a stable individual difference variable or trait. Even with familiar materials that typically give rise to a neutral bias on average, individual subjects differ widely in response bias, with some being conservative, others liberal, and others neutral. That could simply be due to measurement error, but Justin Kantner and I found that individuals who are liberal on one recognition test tend to be liberal on another, even if the two tests are superficially different and widely separated in time. We are trying to understand how individual differences in response bias come about and what their implications are for models of recognition memory and for other, related judgments. Also, grad student Kaitlyn Fallow has joined us in an effort to understand why most people tend to be conservative in their recognition judgments when the stimuli are high-res scans of faces.
Trevor Greene's Brain Rehabilitation I am involved in a minor way in a study led by Ryan D'Arcy of the National Research Centre of Canada that is using functional magnetic resonance imaging (fMRI) to measure physiological and anatomical changes in the brain of Trevor Greene. Trevor Greene is an extraordinary individual. As a captain in the Canadian army, his skull was fractured by a stone axe wielded by a 16-year-old Afghanistani boy. Google him to check out his amazing story. In brief, it's surprising Captain Greene survived at all, but what is most wonderful is that much of the progress he has made (with the help of his incredibly dedicated wife Debbie) occurred years after the injury. We scanned Trevor every 3 months over a 3-year period to explore the relationships between changes in Captain Greene's physical abilities and changes in his brain. It is a thrilling honour to be involved in this study. We are now working on analyses and writing.