eyewitness memory

Eyewitness MemoryDr. Anne Cybenko

University of Dayton Research Institute

“The Innocents” Taryn Simon

There have been 289 exonerations in the US◦ www.innocenceproject.org

Over 70% of those have been due at least in part to a mistaken identification

It’s a unique situation that tests human memory and decision making

Why do People Care?

Ronald Cotton

CORRECT IDENTIFICATION

FALSEIDENTIFICATION

Picking Cotton

This guy commits a crime and someone witnesses it.

The Basics: What Happens when there’s a witness to a crime?

Police get a description from the witness


He was about 6’ tall, brown hair, brown eyes, no facial hair…

Police find a suspect who may be: Guilty or Innocent


Witness is shown a lineup that is eitherPerpetrator Present

Perpetrator Absent


Perpetrator Present

Perpetrator Absent

Picks the suspect CORRECT IDENTIFICATIONBad guy goes to trial

FALSE IDENTIFICATIONInnocent guy goes to trial

Picks a foil FOIL PICKBad guy may go free

FOIL PICKInnocent guy may go free

Rejects the lineup

FALSE REJECTIONBad guy may go free

CORRECT REJECTIONInnocent guy may go free

The Basics: Possible Outcomes of a Lineup

Type of Lineup

Witn

ess’s

Dec

ision

Mostly undergraduate participants Participants watch a mock crime (video or

live) Participants usually give a description Filler task Presented with a lineup Make an Identification

How is it studied?

Witness interview techniques Child interview techniques Showups Foil selection Lineup Presentation Lineup Instructions Multi-modality lineups Double-blind lineups

What Exactly do People Study

Simultaneous or Sequential Lineups Accuracy and Response Time Verbal Overshadowing Effect Interference Theory

Topics for today

Sequential vs. Simultaneous Lineups

I am going to show you six photographs. Please look at all six photographs before making any comment.

The person who committed the crime may or may not be among those shown in the photographs you are about to see. If you recognize any of the persons in the photographs as the suspect, go back and pick out the person you recognize.

If you recognize any of the persons please do not ask me whether your choice was ‘right’ or ‘wrong’, as I am prohibited by law from telling you.

SAN BERNARDINO COUNTY SHERIFF PHOTO LINE-UP

1 2 3

4 5 6

I am going to show you some photographs.

The person who committed the crime may or may not be among those shown in the photographs you are about to see. If you recognize any of the persons in the photographs as the suspect, please tell me and we will stop the lineup.

If you recognize any of the persons please do not ask me whether your choice was ‘right’ or ‘wrong’, as I am prohibited by law from telling you.

SAN BERNARDINO COUNTY SHERIFF PHOTO LINE-UP

Decision PP Simultaneo

us

PP Sequential

PA Simultaneo

us

PA Sequential

Suspect ID .58 .50 .43 .17Foil ID .12 .02 .15 .18Reject .30 .48 .42 .65


Lindsay & Wells (1985)

Results depend on:◦ Similarity of the innocent suspect to the

perpetrator ◦ Innocent suspect position in the sequential lineup

(Clark & Davey, 2001)


Decision

PPSimultaneo

us

PPSequenti

al#2

PPSequenti

al#4

PASimultaneo

us

PASequential

#2

PASequential

#4

Suspect .417 .292 .667 .313 .292 .458

Foil .438 .500 .167 .354 .208 .334

Reject .146 .308 .167 .333 .500 .208

Innocent suspect is medium similarity to perpetrator

Decision

PPSimultaneo

us

PPSequenti

al#2

PPSequenti

al#4

PASimultaneo

us

PASequential

#2

PASequential

#4

Suspect .250 .292 .625 .417 .417 .250

Foil .542 .583 .208 .312 .208 .542

Reject .208 .125 .167 .271 .375 .208

Innocent suspect is high similarity to perpetrator

The Mecklenburg Report (2006)


Simultaneous (N = 319)

Sequential(N = 229)

Suspect .599 .45Foil .028 .092Reject .376 .472

Absolute vs relative decision making


WITNESS model (Clark, 2003) to generate predictions

Perpetrator is represented as a vector of features, P.

Memory of the perpetrator (M):◦ Feature j of P is stored correctly in M with probability a.◦ Feature j of P is stored incorrectly in M with probability 1 – a.

Innocent suspect and foils:◦ Feature j matches the perpetrator with probability s◦ Feature j mismatches the perpetrator with probability 1 – s.

Match each lineup member to memory (M).◦ m(L1,M), m(L2,M), … , m(L6,M) (for six person lineup)

Apply decision rule to make a decision.

Model-Based Predictions

◦ Best Above Criterion (BAC): A witness identifies the best matching lineup member if the match to memory is above criterion. (Absolute judgment)

◦ Relative Difference Model (RD): Best matching lineup member is identified if the difference between the best match and the next-best match is above a difference criterion. (Relative judgment)

WITNESS model

Dunning & Perretta (2002) Four eyewitness studies using a

combination of videotaped and live crimes. Measured response time and accuracy

Accuracy and Response Time

Witnesses making their ID’s faster than 10-12 seconds were nearly 90% accurate

Witnesses that took longer than 12 seconds were 50% accurate

Automatic vs Deliberative processes


Study N Accurate Inaccurate t1 201 38.4 63.9 -3.07**2 96 11.1 15.7 -2.46*3 41 13.2 23.5 -2.78*4 50 13.3 36.4 -4.26**

* p<.05 ** p<.01Study 1 participants had think aloud task

Optimal response time changes with:◦ An increase in retention interval (Brewer et al., 2006)

◦ An increase in the size of the lineup (Brewer et al., 2006)

◦ Confidence of the witness (Weber et al., 2004)

◦ Age (Weber et al., 2004)


Verbalizing the appearance of previously seen visual stimuli impaired subsequent recognition performance

Verbal Overshadowing Effect

Experiment 1◦ Does describing a perpetrator affect ones ability

to identify him?

Schooler & Engstler-Schooler (1990)

Description NoneCorrect ID .38 .64Foil ID .37 .22Rejection .25 .14

Experiment 3◦ Do these results apply to all stimuli that are

difficult to describe?

Description

Visualization

None

Correct ID .33 .64 .73Foil ID .67 .36 .27


Experiment 5◦ Does this pattern of results change if there’s a

limited amount of time to ID the suspect?

Description NoneUnlimited Recognition .50 .805 Second Recognition .73 .76


Meta-analysis on 29 published and unpublished verbal overshadowing studies

Zr = -.12, a small but significant negative effect of verbal overshadowing

Meissner & Brigham (2001)

Long delay between description and ID (Finger & Pezdek, 1999)

More than 1 trial (Fallshore & Schooler, 1995; Houser et al., 1997; Melcher & Schooler, 1995)

Following re-presentation of visual stimulus(Schooler et al., 1996)

When a cognitive interview is used(Finger & Pezdek, 1999; Meissner et al., 2001)

Studies that don’t find verbal overshadowing

Availability assumption◦ Visual representation remains available in

memory despite the temporary verbal impairment Modality mismatch hypothesis

◦ Competing representations in memory from different modalities

Possible Mechanisms

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Proactive interference: When information that is presented BEFORE a target event interferes with the memory for that target event

Retroactive interference: When information that is presented AFTER a target event interferes with the memory for that target event

Retroactive interference is stronger than proactive interference (Schemeidler, 1939; McGeoch and Underwood,1943; Melton and Von Lacrum, 1941)

Types of Interference

41

Changed-trace hypothesis: Outside information interferes with target information because it changes the memory trace of the target information.

Multiple-trace hypothesis: Outside information interferes with target information because it creates a separate memory trace that is recalled instead of the target trace.

Hypotheses of Interference

42

Argued that the Loftus et al. results could have been due to 2 other issues:◦ Original stimulus never encoded◦ Remembered both, trusted/responded with the

one from the narrative

McCloskey & Zaragoza (1985)

43

Participants were presented with slides depicting a maintenance man enter an office, fix a chair, then steal $20.

4 Critical items within the slides ◦ tool (hammer, wrench, or screwdriver)◦ soda can (Coke, 7-up, or Sunkist)◦ coffee jar (Folgers, Maxwell House, or Nescafe)◦ magazine (Glamour, Vogue, or Mademoiselle)

Participants presented with written account of what they just saw. This written account contained misinformation for 2 of the items.


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Two types of tests: ◦ Traditional Recognition Test: Target vs. Interfering

Saw Coke, read about 7-up, Test: Coke or 7-up◦ Modified Recognition Test: Target vs. Novel

Saw Coke, read about 7-up, Test: Coke or Sunkist Traditional Recognition test – Picked 7-up Modified Recognition test – Picked Coke Participants could not have picked Coke in

the modified test if reading about 7-up changed their memory trace


45

Replicated McCloskey and Zaragoza (1985) with 2 changes

Gave either incorrect or neutral information in the recap of the slides (“7-up” or “soda” )

Test was in the form of open ended questions: “The key to the desk was next to a ____ can?”

participants performed equally well on the recall tests

If the misinformation really changed the memory trace, participants should have performed considerably worse on the recall test for the misinformation items.

Zaragoza, McCloskey, and Jamis (1987)

46

Replicated McCloskey and Zaragoza’s (1985) experiment Testing was in the form of Yes/No statements: “Below the magazine

rack there was a copy of Vogue magazine.” Tversky and Tuchin asked about the critical item (the one from the

slides), the misinformation item (the one from the summary of the slides), and the novel item (the one that did not appear at all)

Belli asked about the critical item, and the novel item. Misleading postevent information reduced the "Yes" responses to

the question about the original item. T & T Subjects were equally good at rejecting the novel item T & T Similar number of subjects responded yes to original item as

responded yes to the misleading item. Belli - misled subjects were better than control subjects at rejecting

the novel item Belli concluded memory trace was changed, T & T did not.

Tversky & Tuchin (1989)Belli (1989)

47

McCloskey and Zaragoza’s results could have been a product of their stimuli having too many unique discernable features such that even if the trace was altered, some of those features would remain unchanged.

Used stimuli that were very similar to each other.

Conducted 10 Experiments

Chandler (1989 & 1991)

48

Nature photographs Cut in thirds

Chandler - Stimuli

A A’ A”

49

Variables between experiments: ◦ Proactive or Retroactive interference◦ Presentation time◦ Retention interval◦ Number of stimuli

Chandler’s Methodology

50

Chandler’s Methodology (Retroactive Interference)

Target List Interfering List

Retention

Test

51

Found Retroactive interference when:◦ Presentation time was long(7.5 and 10 seconds)◦ Delay was short (3 – 15 minutes)

Did not find Retroactive Interference when◦ Presentation time was short (4 seconds)◦ Lots of stimuli (140 not 48)◦ Delay was long (48 hours)

Did not find significant evidence of proactive interference under any conditions

Chandler’s Results

52

Participants tested in groups of 1-8 All stimuli presented on overhead Responses were made on paper

Experiments 1-6 Method

53

Experiment 1 was conducted to gather evidence for/against item specific retroactive and proactive interference in a modified recognition test.

Replicate Chandler’s results

Experiments 1 & 2- Purpose

54

Participants: 60 Undergraduates Materials: 48 Color Photographs of Nature

Scenes. Each scene was divided into thirds (A, A’, A”)

Experiments 1&2 - Method

55

Experiments 1&2 - Stimuli

A A”A’

56

Experiments 1&2- Stimuli

A A”A’

57

Experiments 1 & 2 - Method Experiment 1

Math Phase Study Phase Interfering Phase Math Phase Test Phase

Interfering Phase Study Phase Math Phase Math Phase Test Phase

Experiment 2

58

Experimental Accuracy: M = 68.7, SD = 11.1

Control Accuracy: M = 75.8, SD = 8.8 t (31) = 4.682, p < .001, r = -.644 Significant evidence of retroactive

interference

Experiment 1 - Results

59


Control Accuracy: M=72.77, SD = 10.43 t (27) = .486, p = .631, r = -.093 No evidence of proactive interference


60

See if the results of Chandler (1989, 1991) and Experiments 1&2 are found when the stimuli are words instead of images

Find support for/against the changed-trace and multiple-trace hypotheses

Experiments 3&4 - Purpose

61

Participants: 60 Undergraduates Materials: 144 words from Van Overschelde,

Rawson, and Dunlosky’s (2004) updated category norms. The 18 most common words from 8 categories(animals, colors, body parts, fruits, sports, clothing, countries, and car models) were used.


62

Experiments 3 & 4 - MethodExperiment 3

Math Phase Study Phase Interfering Phase Math Phase Test Phase


Experiment 4

63


Control Accuracy: M = 85.62, SD = 10.86 t (28) = 2.139, p = .013, r = -.375 Evidence of retroactive interference was

present


64


Control Accuracy: M = 82.33, SD = 9.94 t (30) = 2.66, p = .013, r =- .437. Evidence of proactive interference was

present

64


65

Find evidence for/against the Threshold Theory of Interference

Experiments 5&6 - Purpose

66

Participants: 39 Undergraduates Materials: Same as Experiments 1 & 2

(nature pictures)


67

Experiments 5 & 6 - MethodExperiment 5

Math Phase Study Phase Interfering Phase (4 or 1) Math Phase Test Phase


Experiment 6

68

Experimental (4) Accuracy: M = 67.78, SD = 12.33


Control Accuracy: M = 76.79, SD = 14.35 F(2,34) = 8.534, p = .001 Tukey test revealed that all groups are

significantly different from each other.


69



Control Accuracy: M = 75.05, SD = 10.80 F(2,34) = 8.534, p = .001 Tukey and paired samples t-tests:

◦ Control = Experimental (1)◦ Control > Experimental (4)◦ Experimental (1) > Experimental (4)


70

Contrasts

Predictions:◦ Control = Experimental (1)◦ Control > Experimental (4)◦ Experimental (1) > Experimental (4)

t (20) = 3.16415, p = .047, r =- .578


71

Retroactive interference is found when the stimuli are pictures and words and when there is a single or multiple presentation of interfering information.

Proactive interference is only found when there are multiple presentations of interfering information.

Summary of Results

72

An interfering stimulus only interferes with a target stimulus IF the difference in strength between the memory trace of the interfering stimulus and the memory trace of the target stimulus crosses a threshold.

Threshold Theory of Interference

73

Support for a modified version of multiple trace hypothesis

Threshold Theory of Interference is supported◦ Evidence of proactive interference found with

multiple presentations of interfering stimuli◦ Evidence of retroactive interference ◦ No evidence of retroactive interference after 48

hours (Chandler, 1991)

Discussion

74

What determines the strength of the memory trace?

If Experiments 5 & 6 had more than 4 repetitions, would they cause even more interference?

Future Directions

75

Thank you!

eyewitness memory

Documents

mock crime video

foilfoil pickbad guy

lineupfalse rejectionbad

freefoil pickinnocent

freethe basics

witnessthe basics

innocentthe basics

people studysimultaneous