Implicit Memory – Arizona Forensic Services, LLC

Snap Shot

The question: Can a past experience that a witness does not consciously remember still shape what the witness perceives, believes, and identifies?

What the research shows: Prior exposure can speed and ease later processing (priming) without awareness, and people can experience a face or name as familiar without recollecting where they encountered it. That familiarity can be misattributed to the wrong source, producing false fame, illusory truth, unconscious transference, and mugshot-exposure errors. When people can recollect the true source, they can often set misleading familiarity aside.

What it does not show: The research does not show that a particular identification rests on misattributed familiarity, and in experiments transference is weaker when witnesses saw the perpetrator longer or the other person looked different. Implicit memory is not “implicit bias”; meta-analyses of the Implicit Association Test disagree about how well it predicts behavior and do not support conclusions about one person.

The law: Expert testimony on familiarity and source errors must satisfy Rule 702 as amended in 2023 (Daubert, Kumho) or Mil. R. Evid. 702 and Houser, and stays general. Police-arranged prior exposure is examined under Perry, Mil. R. Evid. 321, and Arizona’s Dessureault hearing; Chapple and Nordstrom govern eyewitness experts in Arizona.

Issues for each side: Prosecutors should document every exposure a witness had to the suspect’s face before an identification and rely on recollection-based detail, not familiarity alone; defense counsel should tie a familiarity claim to a specific, documented prior exposure rather than to the general possibility of error.

Most testimony rests on explicit memory: a witness consciously recalls an event and reports it. Psychologists have shown that experience also leaves a second kind of trace, one expressed in performance rather than recollection. A word read once is recognized faster later; a face seen briefly feels faintly familiar; a statement heard before seems more plausible. The person need not remember the earlier encounter for it to have these effects. This influence of the past without conscious recollection is called implicit memory.

Implicit memory reaches court mainly through identification. Feeling that a face has been seen before is part of what leads a witness to pick someone from a lineup, and that feeling can arise from an innocent encounter, a mugshot, a social media post, or an earlier procedure as well as from the crime. Because the witness cannot inspect where the feeling came from, an identification based on misattributed familiarity can be sincere and confident. The same research also explains why recognition of a genuinely known person is usually accurate, and why a witness who can recollect the circumstances of an encounter is on firmer ground than one who reports only a feeling of recognition.

This paper describes the explicit–implicit distinction, familiarity without recollection, the misattribution of processing fluency, and how these bear on unconscious transference and mugshot exposure. It briefly addresses implicit bias measures, which are often confused with implicit memory, and reviews the limits of the evidence and the governing federal, military, and Arizona law.

Explicit and Implicit Memory

Explicit (declarative) memory refers to deliberately retrieving facts and events. Implicit (nondeclarative) memory is shown when prior experience changes performance on a task that does not require, and may not involve, any conscious recollection of that experience (Graf & Schacter, 1985; Schacter, 1987). The best-studied form is repetition priming: after encountering a word, picture, or face, people identify or complete it more quickly or accurately on a later occasion (Tulving & Schacter, 1990). Skill learning and simple conditioning are also usually classed as nondeclarative, because they are expressed in what a person does rather than in what the person reports remembering (Squire & Wixted, 2011).

The strongest evidence that these forms of memory can come apart comes from amnesia. Patients with severe amnesia after medial temporal lobe damage, who perform poorly when asked to recall or recognize recently studied words, can show normal or near-normal benefits from prior study when given word fragments to complete (Warrington & Weiskrantz, 1970; Graf & Schacter, 1985). The patient H.M., who could form few new conscious memories after his surgery, improved on motor tasks with practice while having little or no memory of having done them before (Squire & Wixted, 2011). The brain basis of declarative memory is covered in The Hippocampus paper.

How to interpret these dissociations is still debated. The prevailing view treats explicit and implicit memory as reflecting separate brain systems (Squire & Wixted, 2011). An alternative account holds that a single memory-strength signal, combined with differences in how tasks are performed, can produce many of the same patterns; in formal model comparisons using data from healthy adults and from people with amnesia, a single-system model fit recognition and priming data better than a model with fully independent systems (Berry et al., 2012). For forensic purposes the debate matters less than the agreed observation: a person can be measurably influenced by an earlier exposure without being able to report it.

Familiarity Without Recollection

Recognition, the judgment that something has been encountered before, is widely thought to draw on two kinds of information. Familiarity is a fast, graded sense that an item is old; recollection is a slower retrieval of where and when it was encountered (Mandler, 1980; Yonelinas, 2002). The two can be separated experimentally. In the process-dissociation procedure, participants are asked either to include or to exclude items from a particular source; familiarity pushes them to accept old items in both conditions, while recollection allows them to reject items they can place in the wrong source (Jacoby, 1991). A review of 30 years of this research concluded that recollection and familiarity differ in their properties and are affected differently by many variables (Yonelinas, 2002). Some researchers argue instead that the two reflect differing amounts of a single memory strength rather than distinct processes (Lane & Houston, 2021, pp. 49–50).

The everyday illustration is meeting a familiar-looking person out of context, such as the butcher from one’s local shop on a bus, and knowing the face without knowing why (Mandler, 1980). Lane and Houston (2021, pp. 48–51) apply the distinction to identification: accurate source attribution generally depends on recollection, and a decision based on familiarity alone is made without any basis for knowing where the familiarity came from. Familiarity is not therefore inaccurate. Most of the time a familiar face is familiar for the right reason, and people who know someone well recognize that person with high accuracy even from poor-quality video, while strangers viewing the same footage perform far worse (Lane & Houston, 2021, pp. 52–53). The risk lies in a particular combination: a face that is familiar, a witness who cannot recollect the source, and a setting, such as a lineup, that suggests a source.

Fluency and Its Misattribution

One account of how implicit memory produces familiarity holds that previously encountered material is processed more fluently, and that people interpret this ease of processing according to the situation. When the situation invites a judgment of memory, fluency is felt as familiarity; when it invites a judgment of fame or truth, fluency can be experienced as fame or truth. Experiments support this account. In one study, briefly flashing a test word just before it appeared on a recognition test increased the likelihood that participants called it “old” when they were unaware of the flash; when the flash was long enough for them to notice it, the effect was reduced or reversed (Jacoby & Whitehouse, 1989).

The false-fame studies show the same process unfolding over time. Participants read a list of names they were told were nonfamous and later judged which names on a mixed list were famous. On an immediate test, the names they had read were less likely than new nonfamous names to be called famous, which the authors attributed to participants recollecting that the names came from the study list. After a 24-hour delay the pattern reversed: the previously read nonfamous names were more likely to be judged famous, consistent with familiarity outlasting recollection of its source (Jacoby et al., 1989). The finding cuts both ways: recollecting the true source lets people oppose misleading familiarity, and conditions that preserve recollection reduce the error.

Repetition also increases belief. In a classic study, statements repeated across sessions were rated as more likely to be true than new statements (Hasher et al., 1977). A 2026 meta-analysis of 182 studies (31,184 participants) found a small but reliable effect after correcting for small-study bias (g = 0.37), with substantial variation depending on the type of statement and the instructions at first exposure (Ye et al., 2026). A 2024 review noted that repetition increases belief even in implausible claims, and that instructions to focus on accuracy reduce the effect (Udry & Barber, 2024). The Illusion-of-Truth Effect paper covers this research; its relevance here is that a statement a witness has heard repeatedly may come to feel credible for reasons unrelated to its accuracy.

Neuroimaging research suggests why witnesses cannot simply introspect on these influences. In laboratory studies reviewed by Lane and Houston (2021, pp. 91–92), early visual areas associated with perceptual priming responded more strongly to correctly recognized studied shapes than to falsely recognized similar new shapes, yet participants’ experience of remembering did not reflect the difference. These are group averages from simple materials and cannot be applied to an individual witness.

Familiarity and Eyewitness Identification

Unconscious transference is the identification, as the perpetrator, of someone the witness knows from another context, such as an innocent bystander at the scene. In experiments in which participants watched a filmed event involving both a perpetrator and a bystander, participants shown a lineup without the perpetrator chose the bystander more often than control participants, and most of those who erred reported believing that the bystander and the perpetrator were the same person (Ross et al., 1994, pp. 923–924). Lane and Houston (2021, pp. 48–49) describe the innocent-bystander effect as replicated and as a form of source-monitoring error. The effect has limits. In a study with more than 31,000 participants, transference occurred but was much weaker when the bystander looked different from the perpetrator and when participants viewed the perpetrator for longer; accounts based on familiarity and on failed source retrieval had the most support, and transference weakened the relationship between confidence and accuracy (Carlson et al., 2024).

Prior exposure to photographs works in a similar way. In an early study, people who had seen mugshots of individuals they had never seen at the original event sometimes later identified those individuals in a lineup (Brown et al., 1977). Across 32 independent tests in two meta-analyses, viewing mugshots before a lineup reduced correct identifications and increased false identifications, with the larger effect on false identifications; whether the witness had identified someone from the mugshots was a substantial moderator of both effects. Viewing mugshots that did not include the culprit, when no one from the mugshots reappeared in the lineup, did not significantly impair identification of the culprit (Deffenbacher et al., 2006). More recent experiments found that seeing an innocent suspect’s image on mock social media increased misidentification of that person in a later lineup (Kruisselbrink et al., 2023). The practical lesson is that a witness’s exposure history before an identification is part of the evidence needed to interpret it; these procedures are discussed in the Mug Books and Mugshot Exposure paper.

Implicit Bias Measures: A Separate Question

“Implicit memory” is sometimes confused with “implicit bias,” but they are different research areas. Implicit bias research asks whether people hold evaluative associations toward social groups that they do not report, and it relies heavily on the Implicit Association Test (IAT), which measures how quickly people sort words and images when categories are paired in different ways (Greenwald et al., 1998). Whether IAT scores predict behavior is contested. One meta-analysis concluded that IATs were poor predictors of most measures of discrimination and performed no better than simple explicit measures (Oswald et al., 2013). The test’s developers responded that both meta-analyses produced average correlations, about .15 to .24, that could still have societally significant effects when applied across many people or many occasions (Greenwald et al., 2015). A larger meta-analysis of 217 research reports found small, highly heterogeneous correlations with intergroup behavior, with IAT and explicit measures each contributing uniquely, and noted that most studies were underpowered (Kurdi et al., 2019).

These are modest group-level correlations; none of the meta-analyses supports inferring from a test score how a particular person behaved on a particular occasion, and the IAT does not measure implicit memory for an event. Testimony that moves from the memory research in this paper to claims about a witness’s or a party’s attitudes moves to a different and more disputed literature.

Limits of the Evidence

Most implicit memory research tests university students on words, names, statements, or pictures minutes to days after study, and transference and mugshot studies use staged or filmed events with low stakes. These designs establish that familiarity can be misattributed and identify conditions that make it more or less likely; they do not establish how often the error occurs in actual cases, and they cannot determine whether a particular witness’s identification reflects memory of the crime or familiarity from another source. Effect sizes vary: the illusory truth effect is small on average and heterogeneous, transference depends on bystander similarity and viewing time, and IAT correlations with behavior are small. Whether priming and recognition reflect separate systems is unsettled, and neuroimaging differences between true and false recognition cannot classify an individual memory.

Questions to Ask About This Research

When unconscious transference is offered to explain an identification, counsel should ask what documented contact this witness had with the defendant before the identification, how long and under what conditions the earlier encounter occurred, and whether the defendant resembles the person the witness saw, because Carlson et al. (2024) found transference much weaker when the bystander looked different and the perpetrator was seen longer. When Deffenbacher et al. (2006) is cited, counsel should ask whether the witness selected a photograph and whether any face from the mugshots reappeared in the lineup, since choosing was a substantial moderator and exposure without that overlap did not significantly impair identification. When the false-fame studies (Jacoby et al., 1989) are cited, counsel should ask whether the conditions that allowed recollection to oppose familiarity, such as a short delay and full attention, were present here. When IAT research is raised, counsel should ask which meta-analysis is relied on, what correlation it reported, and whether the witness is drawing an inference about a group or about one person. These questions are explained in “Reading Research Claims: A Guide for Attorneys” on this site.

Implicit Memory and the Law

Federal and Military Standards

Expert testimony about familiarity, source errors, and mugshot exposure is governed by Federal Rule of Evidence 702, as amended December 1, 2023, which requires the proponent to show that it is more likely than not that the testimony rests on sufficient facts or data, reflects reliable principles and methods, and reflects a reliable application of those methods to the case. Daubert v. Merrell Dow Pharmaceuticals, Inc. (1993) assigns the trial judge a gatekeeping role, and Kumho Tire Co. v. Carmichael (1999) extends that obligation to all expert testimony, including technical or other specialized knowledge. Such testimony describes general principles; it may not tell the factfinder that a particular identification is mistaken. Familiarity from an encounter police did not arrange does not trigger the due process screen for identifications, and in Perry v. New Hampshire (2012) the Supreme Court left the reliability of such identifications to cross-examination, jury instructions, and expert testimony. Familiarity created by a police-arranged mugshot viewing or earlier array is part of the procedural history a court examines. Neuroimaging offered to show what a person remembers raises separate Rule 702 issues, discussed in The Hippocampus and Detecting Deception papers.

In courts-martial, Mil. R. Evid. 321 makes an identification inadmissible if it results from an identification process so suggestive as to create a substantial likelihood of misidentification, or if due process requires exclusion. Expert testimony is assessed under Mil. R. Evid. 702 and the six factors of United States v. Houser (1993). The December 1, 2023 amendment to Federal Rule 702 became part of Mil. R. Evid. 702 in 2025 through Mil. R. Evid. 1102 (Joint Service Committee on Military Justice, 2025); practitioners should confirm the current text.

Arizona

When a defendant challenges a pretrial identification, an Arizona trial court holds a hearing outside the jury’s presence under State v. Dessureault (1969); if the pretrial procedure was unduly suggestive, the State must show by clear and convincing evidence that the in-court identification is not tainted by it. State v. Chapple (1983) is Arizona’s leading case on eyewitness expert testimony: excluding such testimony was an abuse of discretion in that case, where identification was the central disputed issue, and admission otherwise remains discretionary. State v. Nordstrom (2001) approved allowing an expert to explain factors affecting reliability while barring opinions on a particular witness’s accuracy. Arizona Rule of Evidence 702 adopted the Daubert standard effective January 1, 2012 and was amended effective January 1, 2024 to track the 2023 federal amendment, and State v. Lindsey (1986) bars expert opinion on whether a particular witness is telling the truth.

Special Issues in Legal Practice

The principles described above apply with equal force to every party in a legal proceeding. The science operates the same way regardless of who is asking the questions, and the research summarized here does not by itself favor either side. What differs between the parties is not the science but the vantage point — the particular places where these issues tend to surface, and the particular errors each party is best positioned to guard against. The two summaries below identify those recurring issues. They are offered for orientation, not as litigation strategy; in every case the controlling question is what the evidence in that case will, and will not, support, and the expert’s role is to inform the trier of fact rather than to advocate for either side.

Special Issues for Prosecutors

The research supports several propositions prosecutors can legitimately present. Familiarity is usually familiar for the right reason, recognition of well-known people is highly accurate, and transference from an innocent encounter is weaker when the witness viewed the perpetrator longer or the other person looked different. Recollection of where and when a face was seen allows people to set misleading familiarity aside, so an identification accompanied by specific, independently verifiable detail about the encounter rests on more than familiarity. Prosecutors are well positioned to protect identifications by ensuring that witnesses are not shown the suspect’s image before a lineup, by recording what photographs, social media, or news coverage the witness saw, and by obtaining the witness’s confidence statement at the first identification.

The research also counsels caution. A witness’s sincere feeling that a defendant is familiar does not show that the familiarity came from the crime, and confidence does not resolve the question, because transference and mugshot exposure can weaken the relationship between confidence and accuracy. When the record shows a prior mugshot viewing, especially one in which the witness selected the defendant, or an earlier encounter in a setting near the crime, the factfinder is entitled to weigh that history. Testimony that treats implicit bias measures as evidence about a particular person goes beyond the research in either direction.

Special Issues for Defense

The research supports several propositions defense counsel can legitimately present. Prior exposure can create familiarity without recollection, people can misattribute that familiarity to the wrong source, and this can produce a sincere and confident misidentification. The effect of viewing mugshots before a lineup is well documented, falls more heavily on false identifications than on correct ones, and depends substantially on whether the witness chose a photograph (a commitment effect); commitment, familiarity, and source misattribution are not mutually exclusive mechanisms (see “Mug Books and Mugshot Exposure”); exposure through social media can have a similar effect. Expert testimony explaining these principles, combined with evidence of what the witness saw before the identification, is a legitimate way to help the factfinder evaluate an identification.

The research also counsels caution about the limits that apply to the defense. Laboratory demonstrations show that misattribution can occur, not that it occurred in a given case, and a familiarity argument is strongest when tied to a specific, documented exposure rather than to the general possibility of error. An expert cannot tell the factfinder that a particular identification is mistaken, and transference is less likely when the witness had a good view of the perpetrator and the other person looked different. The IAT literature does not support conclusions about how an individual witness or juror perceived or remembered a defendant.

This paper is for educational purposes only and is not legal advice. The author is a psychologist, not an attorney; summaries of law are general and must be verified against current authority or with a licensed attorney.

References

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Brown, E., Deffenbacher, K., & Sturgill, W. (1977). Memory for faces and the circumstances of encounter. Journal of Applied Psychology, 62(3), 311–318. https://doi.org/10.1037/0021-9010.62.3.311

Carlson, C. A., Wooten, A. R., & Carlson, M. A. (2024). Was he the perpetrator or a bystander? Testing theories of unconscious transference for eyewitness identification. Journal of Applied Research in Memory and Cognition, 13(4), 543–555. https://doi.org/10.1037/mac0000155

Deffenbacher, K. A., Bornstein, B. H., & Penrod, S. D. (2006). Mugshot exposure effects: Retroactive interference, mugshot commitment, source confusion, and unconscious transference. Law and Human Behavior, 30(3), 287–307. https://doi.org/10.1007/s10979-006-9008-1

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Greenwald, A. G., Banaji, M. R., & Nosek, B. A. (2015). Statistically small effects of the Implicit Association Test can have societally large effects. Journal of Personality and Social Psychology, 108(4), 553–561. https://doi.org/10.1037/pspa0000016

Greenwald, A. G., McGhee, D. E., & Schwartz, J. L. K. (1998). Measuring individual differences in implicit cognition: The implicit association test. Journal of Personality and Social Psychology, 74(6), 1464–1480. https://doi.org/10.1037/0022-3514.74.6.1464

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Kurdi, B., Seitchik, A. E., Axt, J. R., Carroll, T. J., Karapetyan, A., Kaushik, N., Tomezsko, D., Greenwald, A. G., & Banaji, M. R. (2019). Relationship between the Implicit Association Test and intergroup behavior: A meta-analysis. American Psychologist, 74(5), 569–586. https://doi.org/10.1037/amp0000364

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Legal Authorities

Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993).

Kumho Tire Co. v. Carmichael, 526 U.S. 137 (1999).

Perry v. New Hampshire, 565 U.S. 228 (2012).

State v. Chapple, 135 Ariz. 281, 660 P.2d 1208 (1983).

State v. Dessureault, 104 Ariz. 380, 453 P.2d 951 (1969).

State v. Lindsey, 149 Ariz. 472, 720 P.2d 73 (1986).

State v. Nordstrom, 200 Ariz. 229, 25 P.3d 717 (2001).

United States v. Houser, 36 M.J. 392 (C.M.A. 1993).

Ariz. Sup. Ct. Order R-23-0004 (2023) (amending Ariz. R. Evid. 702, effective Jan. 1, 2024).

Fed. R. Evid. 702.

Ariz. R. Evid. 702.

Mil. R. Evid. 321.

Mil. R. Evid. 702.

Mil. R. Evid. 1102.

Related topics from Arizona Forensic Services: Courts-Martial