Abstract
Filler siphoning theory posits that the presence of fillers (known innocents) in a lineup protects an innocent suspect from being chosen by siphoning choices away from that innocent suspect. This mechanism has been proposed as an explanation for why simultaneous lineups (viewing all lineup members at once) induces better performance than showups (one-person identification procedures). We implemented filler siphoning in a computational model (WITNESS, Clark, Applied Cognitive Psychology 17:629–654, 2003), and explored the impact of the number of fillers (lineup size) and filler quality on simultaneous and sequential lineups (viewing lineups members in sequence), and compared both to showups. In limited situations, we found that filler siphoning can produce a simultaneous lineup performance advantage, but one that is insufficient in magnitude to explain empirical data. However, the magnitude of the empirical simultaneous lineup advantage can be approximated once criterial variability is added to the model. But this modification works by negatively impacting showups rather than promoting more filler siphoning. In sequential lineups, fillers were found to harm performance. Filler siphoning fails to clarify the relationship between simultaneous lineups and sequential lineups or showups. By incorporating constructs like filler siphoning and criterial variability into a computational model, and trying to approximate empirical data, we can sort through explanations of eyewitness decision-making, a prerequisite for policy recommendations.
Highlights
Researchers have begun using receiver operating characteristic (ROC) analysis to assess the degree to which eyewitnesses distinguish innocent from guilty suspects when tested with simultaneous lineups, sequentialWells, Smalarz, et al (2015) proposed two arguments for why discriminability was an inappropriate interpretation of the lineup advantage
We focus on the comparison of simultaneous lineups and showups because this is where we found some support for filler siphoning theory, and because this comparison remains central to Smith et al.’s (2017) arguments for their theory
The primary goal of the present research was to determine if filler siphoning theory can explain why simultaneous lineups result in superior performance compared to showups
Summary
Researchers have begun using receiver operating characteristic (ROC) analysis to assess the degree to which eyewitnesses distinguish innocent from guilty suspects when tested with simultaneous lineups, sequentialWells, Smalarz, et al (2015) proposed two arguments for why discriminability was an inappropriate interpretation of the lineup advantage. Because ROC analysis focuses on suspect identifications (IDs) (correct IDs of the guilty suspect from target-present lineups and false IDs of a designated innocent suspect from a target-absent lineup), Wells et al argued that the positive selection of a filler was treated as a rejection, which made ROC analysis misleading (see Rotello & Chen, 2016, for a counterargument). This ignoring of fillers is central, given the explanation that Wells et al favor
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