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Stephen J. Ross 1 , Roy S. Malpass 2 , & Lisa D. Topp 3 1 Florida International University

The importance of context and stimulus sampling in mockwitness tasks: Perceptual similarity may not be enough. Stephen J. Ross 1 , Roy S. Malpass 2 , & Lisa D. Topp 3 1 Florida International University 2 University of Texas at El Paso 3 Stephen F. Austin State University.

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Stephen J. Ross 1 , Roy S. Malpass 2 , & Lisa D. Topp 3 1 Florida International University

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  1. The importance of context and stimulus sampling in mockwitness tasks:Perceptual similarity may not be enough Stephen J. Ross1, Roy S. Malpass2, & Lisa D. Topp3 1Florida International University 2University of Texas at El Paso 3Stephen F. Austin State University

  2. Evaluating Lineup Fairness Using mock witnesses An individual who did not witness a crime but is asked to view a lineup and select the suspect Rationale If a lineup is constructed appropriately, each person in the lineup should have an equal chance of being selected Determining Fairness Biased if proportion of suspect identifications differs from chance expectancy Lineup can also be considered unfair if the fillers in the lineup are not reasonable alternatives to the suspect

  3. Lineup Fairness What is the MW task concerned with? Focus should be on having MW determine “who is the accused?” (Wells & Bradfield, 1998) “Suspect stands out” or “Suspect stands out compared to the description of the perp”? Similarity is associated with lineup fairness estimates Perceptual similarity is not just physical similarity Individuals also use inferred connotative information from individuals when forming similarity judgments (Rhodes, 1988; Ross, 2008) MW report “criminality” as a contributor to choice (McQuiston & Malpass, 2002)

  4. Three Questions…. Does description presence influence lineup fairness? Do MW use different information depending on presence absence of description? Does filler pool source influence MW evals? Are college student filler pools equivalent to criminal filler pools? Do they vary in similarity & inferred characteristics? How does this variation influence lineup fairness assessments? Does context influence lineup fairness? Do MW use different information depending on the context the photoarray is presented in (i.e., criminal v. volunteer)?

  5. Method - Materials Constructed 13 lineups 8 criminal 5 layperson Varied in similarity

  6. Very Dissimilar

  7. Dissimilar

  8. Moderately Similar

  9. Very Similar

  10. Very Dissimilar 1 --------- 2 --------- 3 --------- 4 --------- 5 Very Similar

  11. Very Dissimilar 1 --------- 2 --------- 3 --------- 4 --------- 5 Very Similar

  12. Very Dissimilar 1 --------- 2 --------- 3 --------- 4 --------- 5 Very Similar

  13. Very Dissimilar 1 --------- 2 --------- 3 --------- 4 --------- 5 Very Similar

  14. Very Dissimilar 1 --------- 2 --------- 3 --------- 4 --------- 5 Very Similar

  15. Method – Participants & Procedure 689 undergrads 129 trait/similarity raters 560 mockwitnesses Trait/Similarity ratings Rated each individual on 7 characteristics Assessed similarity of potential fillers with target individual Mockwitness evaluations Assessed lineup fairness (bias & size)

  16. Results – Bias (desc) r = -.81

  17. Results – Size (desc) r = .64

  18. Results – Bias (no desc) r = .21

  19. Results – Size (no desc) r = -.34

  20. What are MW basing decision upon? When told suspected of committing a crime Description provided: similarity # of MW choices No description provided: criminality # of MW choices

  21. Do college students differ from criminals? p = ns p < .05

  22. College students produces lineups that are more unfair even though similarity is the same Do college students differ from criminals?

  23. College students produces lineups that are more unfair even though similarity is the same Do college students differ from criminals?

  24. Take-home Message Information used by MW varies as a function of description presence and question asked While college students did not differ from criminals in their perceived similarity to the target, they did differ on key inferred traits Lineups using college students as fillers were evaluated to be more unfair than lineups using criminal mugshots even though the perceived similarity was the same What is the appropriate question to be asked? Does the suspect stand out in the lineup? OR Taking into account the description provided by the witness, does the suspect stand out?

  25. Current/Future Research Replication Similarity structure across various construction techniques

  26. Thank You!! sross@fiu.edu http://www.fiu.edu/~ascl/

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