Source Monitoring – Arizona Forensic Services, LLC

Snap Shot

The question: How do people know where a memory came from, whether they saw something, heard it from someone else, or imagined it, and how often do those judgments go wrong?

What the research shows: Memories carry no built-in label of their origin; people infer the source from a memory’s qualities, and most of the time the inference is correct. Errors are more likely when sources are similar, when encoding was hurried or divided, after delay, under quick decisions, and in young children and older adults. Asking specifically about source, warnings, and, for some school-age and preschool children, source-monitoring training reduce errors without eliminating them.

What it does not show: A source error is not a lie, and the framework identifies conditions of risk, not a finding about a particular witness. Neither confidence nor vividness, nor content-based credibility criteria nor brain imaging, can determine whether a particular person’s memory came from the source the person names.

The law: Testimony on source monitoring is assessed under Rule 702 (as amended in 2023), Daubert, and Kumho Tire, and in courts-martial under Mil. R. Evid. 702 and Houser; Arizona’s Chapple and Nordstrom allow general testimony on memory factors, and Lindsey bars opinions on a particular witness’s credibility.

Issues for each side: Prosecutors can show that a witness’s account was given before any identifiable outside source and that source attributions are usually accurate; defense counsel can show conditions that favor source confusion, but should tie the claim to an identified alternative source rather than to the possibility of error alone.

Remembering what happened is only part of remembering. A witness must also know where each piece of a memory came from: whether a detail was seen at the scene or heard later from another witness, an investigator, or the news; whether an action was performed or only planned or imagined; whether a person was seen at the crime or somewhere else. Psychologists use the term source monitoring for the processes by which people make these attributions. The process usually works well and without effort, but when it fails, the content of a memory can be accurate while its origin is wrong.

Source attributions matter in court because the legally important question is often not whether a witness knows a detail but how the witness came to know it. A detail that a witness perceived is evidence of what happened; the same detail learned from a co-witness or a question is not. The framework also explains how a sincere witness can be confident in a detail that came from somewhere other than the event.

This paper explains the source-monitoring framework, reality monitoring (distinguishing perceived from imagined events), confusions among things seen, heard, and imagined, the conditions and ages associated with more errors, source-monitoring training and source-focused questioning, and the forensic relevance of the research. Where outside information comes from (co-witnesses, media, investigators, family) is covered in External Sources of Memory Distortion; the classic misleading-information paradigm in The Misinformation Effect; and specific attribution errors in Misattribution of Memory, Imagination Inflation, and Unconscious Transference.

The Source-Monitoring Framework

The framework set out by Johnson, Hashtroudi, and Lindsay (1993) holds that memories are not stored with a tag identifying their origin. Instead, people infer the source when they remember, from the characteristics of the memory itself: perceptual detail (sights, sounds), spatial and temporal context, emotional reactions, semantic content, and traces of the mental operations that produced it. A memory rich in perceptual and contextual detail is likely to be attributed to something experienced; one carrying traces of deliberate thought is likely to be attributed to something imagined or reasoned out. Because the features of memories from different sources overlap, an attribution is a judgment, not a readout, and it can be wrong (Lane & Houston, 2021, pp. 61–66).

The framework describes two kinds of judgment. Most attributions are quick and heuristic, based on how a memory feels. Slower, systematic judgments draw on reasoning and other knowledge, such as recalling that a detail could not have been seen from where one stood, or that one first heard it from a friend. Systematic checking can catch heuristic errors, but it takes motivation, time, and relevant knowledge, and it can itself err when a person’s beliefs about what genuine memories feel like are mistaken (Johnson et al., 1993; Lane & Houston, 2021, pp. 65–66).

Reality Monitoring: Perceived Versus Imagined

Reality monitoring, the earlier and narrower idea from which the framework grew, refers to distinguishing memories of external events from memories of internally generated ones, such as thoughts, imaginings, and dreams (Johnson & Raye, 1981). The theory predicts, and research has generally found, that memories of perceived events tend to have more sensory and contextual detail, while memories of imagined events tend to carry more information about the cognitive operations that created them. When an imagined event is vivid and detailed, or when the effort of imagining it has faded from memory, it can be mistaken for something that happened.

Confusion can cross sensory channels. In two experiments, people were more likely to remember falsely that they had seen an event when they had both imagined seeing it and actually heard it than when they had only heard it or only imagined it; considering possible sources, or evaluating the features of a memory more carefully, reduced these errors (Henkel et al., 2000). The finding helps explain why asking a witness to picture or reconstruct a scene, a common step in some interviews, can add detail of uncertain origin. The cumulative effects of repeated imagining are covered in Imagination Inflation.

Seen, Heard, or Suggested: Source Confusion in Witnesses

Much witness error can be described as source error. In the misinformation paradigm, a witness who sees an event and later reads or hears misleading details may report those details as part of the event. Lindsay and Johnson (1989) found that misled participants made fewer such errors when the test asked them to identify where they had encountered each detail than when it asked only whether a detail had been in the original event, which indicated that some errors reflected confusion about source rather than loss of the original memory. Other experiments found that participants sometimes claimed to remember seeing details they had encountered only in post-event questions, even when asked directly about source (Zaragoza & Lane, 1994), so source questioning reduces but does not cure the problem.

A source error can also attach to an entire event. In the “crashing memories” procedure, people are asked a single leading question that presupposes they have seen a film that does not exist; in two recent studies, 25.7% and 38% of participants endorsed having seen the nonexistent film (so about 62% to 74% did not; the sample sizes were not given in the abstract reviewed), which is not necessarily a false memory, and endorsement was associated with measured suggestibility but not with acquiescence or compliance (Rassin, 2022). The same mechanism can attach a familiar face to the wrong context, as when a person seen innocently near a crime is later identified as its perpetrator (see Unconscious Transference).

Conditions That Make Source Errors More Likely

The research identifies several conditions under which source attributions are more often wrong (Johnson et al., 1993; Lane & Houston, 2021, pp. 65–66). Sources that are similar are harder to tell apart, such as two interviews, two speakers, or a scene and a photograph of it. Encoding that was brief, distracted, or divided binds less contextual detail to an event, leaving less to distinguish it from later information. Delay allows distinguishing features to fade, so memories from different sources become more alike. Decisions made quickly rely more on heuristic judgments. And when a related memory “imports” its features into another, a detail can borrow the vividness of something genuinely experienced.

Conversely, source attributions are usually more accurate when the sources were distinctive, when the witness paid attention to where information came from, when little time has passed, and when the witness is asked to consider source deliberately rather than to report everything that comes to mind.

Age Effects

Young children’s source monitoring is not uniformly poor. In one developmental study, 6- and 9-year-olds were as good as adults at distinguishing what they had done from what they had watched another person do, but had particular difficulty distinguishing what they had done from what they had only imagined doing (Foley & Johnson, 1985). Other work found that children’s source errors depended on how similar the sources were, so that the age difference was larger when sources were alike (Lindsay et al., 1991). Children’s skills improve with age, and the conditions of questioning matter a great deal; children’s suggestibility more broadly is covered in Suggestibility of Children’s Memory and Memory Development.

Older adults also show relative weakness in source memory. A meta-analysis of 46 studies found that age differences in memory for context, such as who said something or where it was encountered, were reliably larger than age differences in memory for content (Spencer & Raz, 1995). A 2026 meta-analysis of 150 articles found that healthy older adults showed more false memory than younger adults, both spontaneous and suggestion-induced, with moderate average effects (a different comparison from people with mild cognitive impairment or Alzheimer’s disease versus healthy older adults, where the suggestion-induced difference was not statistically reliable; see “Alzheimer’s Disease and Memory”), and its authors attributed part of the difference to declines in verbatim memory and in monitoring (Huan et al., 2026). These are averages; many older adults remember sources accurately, and age alone says little about a particular witness (see Aging and Memory).

Source-Monitoring Training and Source-Focused Questioning

Because many errors reflect poor source judgments, researchers have tested whether people can be helped to make better ones. In one study, children aged 3 to 8 took part in science demonstrations and then heard their parents read a story describing both experienced and nonexperienced events. Many children described fictitious events in response to open-ended prompts, with no age differences at that stage, and accuracy declined further with direct questions, especially for younger children. After source-monitoring instructions, the older children retracted many of their false reports, but the younger children did not (Poole & Lindsay, 2001). In another study, 3- and 4-year-olds who were given practice distinguishing events seen live from events seen on video were later more accurate than control children in answering both misleading and non-misleading questions about a target event (Thierry & Spence, 2002). Reviews of this work describe source-monitoring training as one promising way to help young witnesses (Lane & Houston, 2021, pp. 157–158).

The benefits have limits. Warnings, source-focused tests, and instruction about the features of true memories reduce errors but rarely eliminate them (Lane & Houston, 2021, pp. 81–87). In a recent study of 294 adults, 18.4% made a false report about a suggested childhood event; a source-sensitization training given before a second attempt did not reduce false reports, and false beliefs and memories increased in both groups (Bücken et al., 2026). Training procedures differ, and results from one population and procedure do not transfer automatically to another. For investigators, the most consistent lesson is procedural: ask about source directly, avoid supplying details, and record when and from whom a witness first learned a contested fact.

Forensic Relevance

Source monitoring bears on two different questions that courts face. The first is whether a witness perceived a detail or acquired it later. The framework explains how a witness can be sincere, confident, and partly accurate while attributing a detail to the wrong origin, and it directs attention to the record of what the witness was exposed to. The second is whether an account describes an experienced event at all. Credibility-assessment methods built on reality-monitoring ideas rate statements for sensory and contextual detail; meta-analytic research has found large average differences between experienced and fabricated statements at the group level (Oberlader et al., 2016), but these methods were designed to distinguish truthful accounts from deliberate fabrication, and they performed less well on suggested memories than on invented accounts, though findings differ across studies (Lane & Houston, 2021, pp. 94–96). A sincerely held source error may have the same features as a genuine memory.

Brain imaging has identified regions, particularly in the prefrontal cortex and medial temporal lobes, that are engaged when people remember source (Mitchell & Johnson, 2009). These are group-level findings from simple laboratory materials, and imaging cannot classify an individual witness’s memory as true or false (Lane & Houston, 2021, pp. 93–94).

Limits of the Evidence

Most source-monitoring research uses students or children in laboratory settings, simple materials such as words, pictures, or short videos, and short delays. Real witnesses often have more at stake, more distinctive experiences, and much longer delays, and their sources (a friend’s account, a news report, an interview) are more varied than those in experiments; the research does not settle whether those differences make attributions more or less accurate. The child studies used specific events and procedures, and the effects of training varied with age and method.

The findings are group averages. Most attributions in most studies were correct, and the framework identifies conditions that raise the risk of error rather than a test for any particular memory. An expert can describe those conditions and explain why confidence does not guarantee correct attribution; an expert cannot determine from an account alone whether a particular detail came from the event.

Questions to Ask About This Research

When Lindsay and Johnson (1989) or Zaragoza and Lane (1994) is cited to suggest that a detail came from post-event information, counsel should remember that these experiments demonstrate a possibility under controlled conditions and ask what the record shows this witness was exposed to and when the detail first appeared. When a confident, detailed account is put forward to establish that the witness perceived its contents, ask how the framework treats vividness, since it describes source as a judgment drawn from a memory’s features, and vivid memories can be assigned to the wrong origin (Johnson et al., 1993). When age is offered as a reason to doubt a child’s or an older adult’s attributions, ask who was studied and how large the effect was: Foley and Johnson (1985) found children as good as adults on some source distinctions, and the Huan et al. (2026) meta-analysis reports moderate average differences, not a rule for individuals. When source-monitoring training is said to have made a child’s account reliable, ask whether the procedure resembled those tested by Poole and Lindsay (2001) and Thierry and Spence (2002), and whether the child’s age matches the ages that benefited. When a content-based credibility method is offered, ask whether it was validated against sincerely held false memories rather than deliberate lies. These questions are explained in “Reading Research Claims: A Guide for Attorneys” on this site.

Source Monitoring and the Law

Federal and Military Standards

Expert testimony about source monitoring 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, is the product of reliable principles and methods, and reflects a reliable application of those methods to the case. Daubert v. Merrell Dow Pharmaceuticals, Inc. (1993) assigned trial judges the gatekeeping role, and Kumho Tire Co. v. Carmichael (1999) extended it to all expert testimony, including technical or other specialized knowledge. Testimony on source monitoring ordinarily describes general principles and the conditions present in a case; it may not tell the factfinder that a particular witness’s memory came from the wrong source.

In courts-martial, Military Rule of Evidence 702 tracks the federal rule; under Military Rule of Evidence 1102 the 2023 amendment became part of the military rule in 2025 (Joint Service Committee on Military Justice, 2025; practitioners should confirm current text), and military judges apply the six factors of United States v. Houser (1993), including proper basis, relevance, reliability, and probative value. The Court of Appeals for the Armed Forces has held that expert testimony amounting to an opinion that a witness is truthful is impermissible (United States v. Brooks, 2007), and the same principle limits testimony that a witness’s memory is or is not accurate.

Arizona

Arizona Rule of Evidence 702 adopted the Daubert standard effective January 1, 2012, and was amended effective January 1, 2024, to conform to the 2023 federal amendment (Ariz. Sup. Ct. Order R-23-0004). State v. Chapple (1983), Arizona’s leading case on memory and eyewitness expert testimony, held that excluding such testimony was an abuse of discretion on facts in which contested identifications were critical, while leaving admission otherwise to the trial court’s discretion. State v. Nordstrom (2001) upheld limiting an eyewitness expert to the general factors affecting reliability without an opinion on the accuracy of a particular witness, and experts may not opine on whether a particular witness is truthful (State v. Lindsey, 1986, 149 Ariz. at 475). Testimony on source monitoring fits within that space when it explains the general conditions under which source errors occur and leaves the application to the jury.

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. Most source attributions are correct, children as young as 6 can match adults on some source distinctions, and errors concentrate in identifiable conditions such as similar sources, divided attention, long delays, and suggestive questioning (Foley & Johnson, 1985; Johnson et al., 1993). A detail recorded in an early account given before any identifiable outside source stands on firmer ground than one first reported after exposure. In non-suggestive mock-crime studies, details first reported later were often accurate, and peripheral details that received little attention are less likely to have been stored, so a detail that first appears after repeated questioning or exposure requires attention to how it emerged. Prosecutors and investigators can protect the value of an account by recording first statements, asking witnesses how they know each key detail, avoiding questions that supply information, and documenting what each witness was told or shown.

The research also counsels caution. A sincere, confident, and detailed memory can be attached to the wrong source, so confidence alone does not show that a witness perceived what the witness reports (Zaragoza & Lane, 1994). Asking a witness to imagine or reconstruct a scene can add detail of uncertain origin (Henkel et al., 2000). Source-monitoring training helped some children in some studies but did not help the youngest children in one study or adults in another (Bücken et al., 2026; Poole & Lindsay, 2001), and testimony presenting training as a guarantee of accuracy goes beyond the research. Content-based credibility assessments do not reliably distinguish genuine memories from sincerely believed false ones.

Special Issues for Defense

The research supports several propositions defense counsel can legitimately present. Memories carry no built-in label of origin, and people can confidently attribute suggested or imagined details to an event (Johnson et al., 1993; Lindsay & Johnson, 1989). Source errors are more likely when sources are similar, when encoding was brief or divided, after delays, and in young children and older adults (Huan et al., 2026; Spencer & Raz, 1995). Expert testimony explaining these conditions, combined with evidence of what a witness was exposed to and when, is a legitimate aid to the factfinder, particularly where the witness gave no recorded account before encountering other sources.

The research also counsels caution about its limits. Source confusion is possible, not inevitable; most attributions in the research were correct, and the framework describes conditions of risk, not conclusions about any witness. A source-monitoring argument is strongest when it identifies a specific alternative source for a specific detail and shows that the exposure preceded the detail’s first appearance, and weakest when the detail was recorded before any identifiable exposure. An expert cannot testify that a particular memory came from the wrong source, and age-related differences are averages that do not describe a particular child or older adult. The same principles apply to the accused’s own account.

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

Bücken, C. A., Riesthuis, P., Caon, G., Cucu, A., & Otgaar, H. (2026). Trained but still tricked: Source sensitisation training fails to reduce false memory reports. Memory, 34(1), 19–33. https://doi.org/10.1080/09658211.2025.2585095

Foley, M. A., & Johnson, M. K. (1985). Confusions between memories for performed and imagined actions: A developmental comparison. Child Development, 56(5), 1145–1155. https://doi.org/10.2307/1130229

Henkel, L. A., Franklin, N., & Johnson, M. K. (2000). Cross-modal source monitoring confusions between perceived and imagined events. Journal of Experimental Psychology: Learning, Memory, and Cognition, 26(2), 321–335. https://doi.org/10.1037/0278-7393.26.2.321

Huan, S.-Y., Otgaar, H., Howe, M. L., Liu, Y.-R., Xu, H.-Z., Wang, J., & Yu, J. (2026). A meta-analysis of false memory in healthy and pathological cognitive aging. Psychology and Aging, 41(4), 497–524. https://doi.org/10.1037/pag0000966

Johnson, M. K., Hashtroudi, S., & Lindsay, D. S. (1993). Source monitoring. Psychological Bulletin, 114(1), 3–28. https://doi.org/10.1037/0033-2909.114.1.3

Johnson, M. K., & Raye, C. L. (1981). Reality monitoring. Psychological Review, 88(1), 67–85. https://doi.org/10.1037/0033-295X.88.1.67

Joint Service Committee on Military Justice. (2025). Amendments to the Military Rules of Evidence since 1984 (G. E. Maggs, Ed.; 2025 ed.). https://jsc.defense.gov/Portals/99/MRE%20Amendments%202025.pdf

Lane, S. M., & Houston, K. A. (2021). Understanding eyewitness memory: Theory and applications. New York University Press.

Lindsay, D. S., & Johnson, M. K. (1989). The eyewitness suggestibility effect and memory for source. Memory & Cognition, 17(3), 349–358. https://doi.org/10.3758/BF03198473

Lindsay, D. S., Johnson, M. K., & Kwon, P. (1991). Developmental changes in memory source monitoring. Journal of Experimental Child Psychology, 52(3), 297–318. https://doi.org/10.1016/0022-0965(91)90065-Z

Mitchell, K. J., & Johnson, M. K. (2009). Source monitoring 15 years later: What have we learned from fMRI about the neural mechanisms of source memory? Psychological Bulletin, 135(4), 638–677. https://doi.org/10.1037/a0015849

Oberlader, V. A., Naefgen, C., Koppehele-Gossel, J., Quinten, L., Banse, R., & Schmidt, A. F. (2016). Validity of content-based techniques to distinguish true and fabricated statements: A meta-analysis. Law and Human Behavior, 40(4), 440–457. https://doi.org/10.1037/lhb0000193

Poole, D. A., & Lindsay, D. S. (2001). Children’s eyewitness reports after exposure to misinformation from parents. Journal of Experimental Psychology: Applied, 7(1), 27–50. https://doi.org/10.1037/1076-898X.7.1.27

Rassin, E. (2022). Suggested false memories of a non-existent film: Forensically relevant individual differences in the crashing memories paradigm. Memory, 30(9), 1205–1211. https://doi.org/10.1080/09658211.2022.2085750

Spencer, W. D., & Raz, N. (1995). Differential effects of aging on memory for content and context: A meta-analysis. Psychology and Aging, 10(4), 527–539. https://doi.org/10.1037/0882-7974.10.4.527

Thierry, K. L., & Spence, M. J. (2002). Source-monitoring training facilitates preschoolers’ eyewitness memory performance. Developmental Psychology, 38(3), 428–437. https://doi.org/10.1037/0012-1649.38.3.428

Zaragoza, M. S., & Lane, S. M. (1994). Source misattributions and the suggestibility of eyewitness memory. Journal of Experimental Psychology: Learning, Memory, and Cognition, 20(4), 934–945. https://doi.org/10.1037/0278-7393.20.4.934

Legal Authorities

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

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

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

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. Brooks, 64 M.J. 325 (C.A.A.F. 2007).

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

Fed. R. Evid. 702.

Ariz. R. Evid. 702.

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

Mil. R. Evid. 702.

Mil. R. Evid. 1102.

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