Snap Shot
- The question: Can a person sincerely present as his or her own an idea, phrase, melody, or observed detail that actually came from someone else, and how does that bear on witness accounts and on claims of copying?
- What the research shows: In laboratory tasks, people sometimes claim another person’s idea as their own or offer it as new, at low but reliable rates, and some of those errors are held with confidence. The errors reflect failures of source monitoring and increase with distraction, similarity between people, and working on another person’s idea. Witnesses can likewise come to believe they saw details that were only suggested to them.
- What it does not show: Most ideas and details in these studies were correctly attributed, source errors are not inevitable after exposure, and orienting people to source reduces them. The research cannot show that a particular witness’s detail, or a particular song or text, was borrowed without awareness.
- The law: Copyright infringement does not require intent, and courts have accepted subconscious copying (Fred Fisher, Bright Tunes, ABKCO, Three Boys); the Ninth Circuit’s en banc decision in Skidmore overruled Three Boys on the separate inverse-ratio rule. Expert testimony on source errors in witness accounts is general and educational under Rule 702 and Houser, and in Arizona under Chapple and Nordstrom.
- Issues for each side: Prosecutors should document when and from whom a witness learned key details, without treating a confident first-hand report as proof of first-hand origin; defense counsel should tie any source claim to evidence of actual exposure, recognizing that most attributions are correct and that the same error can affect the accused.
Cryptomnesia, from Greek words meaning hidden memory, occurs when something remembered comes to mind without feeling remembered, and a person takes an idea encountered earlier as a new idea or as his or her own. It is the cognitive account of inadvertent plagiarism: a writer, musician, researcher, or group member reproduces something heard or read before while sincerely believing it to be original. Cryptomnesia is not deliberate copying, and it is not lying. It is an error about the source of a thought.
The phenomenon reaches court in two ways. In copyright litigation, courts have long held that copying can occur without awareness and still infringe, and the psychology of cryptomnesia explains how that can happen. In criminal and military cases, the same kind of source error can lead a witness, a complainant, or an accused to report as personally observed a detail that was learned from another person, an interviewer, or the media.
This paper describes the laboratory research on inadvertent plagiarism, its explanation in terms of source monitoring, the conditions that make it more and less likely, and its relationship to source errors in witness accounts. It then addresses the limits of the evidence and the law, including the subconscious-copying doctrine in copyright and the standards for expert testimony.
Source Monitoring and Hidden Memory
Memories do not carry labels identifying where they came from. Under the source monitoring framework, people infer the source of a memory at the time of remembering from its characteristics, such as perceptual detail, context, and the mental operations associated with it, usually through quick judgments and occasionally through more deliberate reasoning (Johnson et al., 1993). Errors are more likely when two possible sources are similar, when the original experience was encoded with limited attention, and when decisions are made quickly (Lane & Houston, 2021, pp. 61–66).
Cryptomnesia is one product of that system. Researchers have distinguished two ways it can arise. In one, the person forgets having encountered the idea at all and generates it again as if it were new. In the other, the person remembers the idea as old but misremembers who produced it, attributing another person’s contribution to himself or herself. Brown and Halliday (1991) linked inadvertent plagiarism to difficulties in remembering source, and Marsh and Bower (1993) proposed a single model in which the relative strength of memory traces accounts for both kinds of forgetting. A review of about two decades of experimental research concluded that the source monitoring framework provides the most plausible account of the phenomenon (Gingerich & Sullivan, 2013).
The Laboratory Evidence
Brown and Murphy (1989) developed the procedure most studies still use. Small groups took turns generating examples of a category, such as types of birds. Later, each participant was asked to recall the items he or she had generated and, separately, to generate new items not previously mentioned by anyone. In both tasks, participants sometimes plagiarized: they recalled another member’s item as their own, or offered an item already given by someone else as a new one. The rates were low, generally a few percent of responses, but they occurred despite instructions to avoid repetition, and items from the person who had spoken just before the participant were reported as particularly vulnerable.
Marsh and Bower (1993) had participants take turns with a computer partner at finding words hidden in letter grids. Participants then tried to recall their own words and to find new ones. Plagiarism was substantially more frequent than in the category task, and manipulations of the retention interval and of how thoroughly items were encoded reliably changed the rates. The errors are not always tentative. In one experiment, participants were less confident in plagiarized responses than in correct ones but gave high certainty ratings to a large share of them; in a second, correctly attributed responses carried more experiential detail on average, yet many plagiarized responses were accompanied by a confident memory of at least one such detail (Brédart et al., 2003).
Conditions That Make It More and Less Likely
Because cryptomnesia is a source error, conditions that make sources harder to distinguish increase it. In three experiments, inadvertent plagiarism varied with the perceptual similarity between the participant and the other person (for example, a partner of the same sex), with cognitive distraction, and with the context in which ideas were retrieved (Macrae et al., 1999). Plagiarism during idea generation has been tied to inadequate monitoring of the source of ideas at the time they are produced (Marsh et al., 1997).
Working on another person’s idea also matters. In a study using creative problem solving, participants who generated improvements to some of another person’s ideas were later more likely to recall those ideas as their own, while simply imagining the ideas did not have that effect; a financial incentive not to plagiarize did not change the pattern (Stark et al., 2005). The authors concluded that the kind of elaboration performed on an idea, rather than its familiarity alone, influenced whether it was later claimed. This finding has practical relevance wherever people develop ideas together, including group discussions of an event: the person who elaborated on what another said may later remember it as his or her own contribution.
The research also identifies protective conditions. Elaborating on an idea, whether by imagining it or improving it, reduced the chance of later offering it as new (Stark et al., 2005), and, as described below, orienting people to the source of their memories at test reduces source errors in eyewitness tasks (Lindsay & Johnson, 1989). Most ideas in these studies were correctly attributed, and the errors that did occur were concentrated in conditions that degraded source information.
Source Errors in Witness Accounts
The same process has been studied in eyewitness research, under the heading of source misattribution. In five experiments, participants who viewed an event and then received misleading suggestions sometimes came to believe that they remembered seeing the suggested details in the event itself, not merely that they had read or heard about them (Zaragoza & Lane, 1994). The authors emphasized that the size of the effect varied and that source misattributions were not an inevitable consequence of exposure to suggestion. In an earlier study, suggestibility effects found with an ordinary recognition test were eliminated when participants were instead given a test that oriented them to the sources of their memories, although misled participants still sometimes attributed suggested details to the original event (Lindsay & Johnson, 1989).
In legal settings, the analogue of inadvertent plagiarism is a witness who reports, sincerely and sometimes confidently, a detail that entered his or her memory from another source: a co-witness’s description, a question that contained the detail, a news report, a social media post, or a discussion among friends. The process can affect complainants, accused persons, and third-party witnesses alike; an accused who learns details of an allegation from investigators can come to remember them as part of his or her own experience. The External Sources of Memory Distortion and Source Monitoring papers in this hub address these mechanisms in more detail.
These findings do not imply that first-hand reports are generally unreliable. Most details in source-monitoring studies are attributed correctly, and the confidence and vividness of a report, while not a guarantee of first-hand origin, are not evidence of borrowing either. The research supports a narrower question in any case: whether the witness had an opportunity to acquire the detail from another source before reporting it, and whether the record shows when the detail first appeared.
Limits of the Evidence
The core studies of cryptomnesia use university students generating category examples, puzzle words, or problem solutions in brief laboratory sessions, with low stakes and delays of minutes to a week. Rates of plagiarism are low and depend heavily on the task (Marsh & Bower, 1993). The research is mostly from the 1989–2013 period; searches for this paper did not identify substantial new experimental work on inadvertent plagiarism from 2022 to 2026, so these findings have not been tested with current methods such as preregistration and large online samples. The connection between laboratory plagiarism of ideas and source errors in eyewitness reports is a theoretical one, supported by eyewitness source-misattribution research (Zaragoza & Lane, 1994) but not by studies that test both in the same people. Neither body of research provides a method for determining whether a particular idea, melody, or detail was borrowed without awareness, deliberately copied, or independently produced.
Questions to Ask About This Research
If Brown and Murphy (1989) is offered as support for the idea that a witness took over another person’s detail, counsel should ask how large the effect was in absolute terms: plagiarism appeared in a small fraction of responses, the large majority of attributions were right, and participants were naming category members aloud with peers, not observing an event. When Brédart et al. (2003) is offered to show that a borrowed detail can feel like a confident memory, counsel should ask whether the conclusion follows from the design, because correctly attributed responses carried more detail and confidence on average even though many plagiarized responses were confident. When Zaragoza and Lane (1994) is cited, counsel should ask whether the finding applies to this witness, since the authors stressed that source misattributions varied in size and were not an inevitable result of suggestion, and ask whether there is evidence that the witness was actually exposed to the detail before reporting it. In copyright disputes, counsel should ask whether testimony about cryptomnesia is being used to explain how innocent copying could occur, which the research supports in general terms, or to establish that copying did occur, which it cannot. These questions are explained in “Reading Research Claims: A Guide for Attorneys” on this site.
Cryptomnesia and the Law
Federal and Military Standards
Expert testimony about source monitoring and inadvertent plagiarism is governed by Federal Rule of Evidence 702, as amended December 1, 2023, under which the proponent must show the court that it is more likely than not that the rule’s requirements are met, including that the opinion reflects a reliable application of reliable methods to the case. Daubert v. Merrell Dow Pharmaceuticals, Inc. (1993) made the trial judge a gatekeeper, and Kumho Tire Co. v. Carmichael (1999) extended that obligation to all expert testimony, including testimony based on technical or other specialized knowledge. In courts-martial, Military Rule of Evidence 702 tracks the federal rule, the 2023 federal amendment took effect in the military rule in 2025 through Military Rule of Evidence 1102 (Joint Service Committee on Military Justice, 2025), and practitioners should confirm current text; military judges apply the six factors of United States v. Houser (1993). A lay witness may testify only to matters within personal knowledge (Fed. R. Evid. 602; Mil. R. Evid. 602). A witness who has misattributed the source of a detail sincerely believes the detail is within his or her personal knowledge, so the issue is ordinarily one of weight, explored through cross-examination and, where admissible, general expert testimony, rather than a ground for excluding the witness.
Arizona
Arizona Rule of Evidence 702 adopted the federal formulation and 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) is Arizona’s leading case on expert testimony about memory and eyewitness reliability; excluding such testimony was an abuse of discretion on its facts, while admission otherwise remains within the trial court’s discretion, and State v. Nordstrom (2001) approved limiting an expert to general factors without opinions on the accuracy of a particular witness. An expert may not tell the jury whether a particular witness is truthful (State v. Lindsey, 1986, 149 Ariz. at 475).
Copyright: Subconscious Copying
Copyright infringement requires copying of protected expression, usually proved circumstantially by access to the earlier work and similarity between the works; intent to copy is not an element. Judge Learned Hand held a composer liable while finding that the borrowing had probably occurred without awareness, reasoning that “everything registers somewhere in our memories” (Fred Fisher, Inc. v. Dillingham, 1924). In the case concerning George Harrison’s “My Sweet Lord,” the district court found that Harrison had subconsciously copied “He’s So Fine,” a song he had heard about six years earlier, and held that the subconscious copying infringed (Bright Tunes Music Corp. v. Harrisongs Music, Ltd., 1976). The Second Circuit affirmed the finding of infringement, declined to retreat from its position that copying can be subconscious, explained that innocent intent is not a defense, and held that the lapse of time did not preclude a finding of access (ABKCO Music, Inc. v. Harrisongs Music, Ltd., 1983).
The Ninth Circuit relied on that line of cases in affirming a jury verdict that Michael Bolton’s 1991 song “Love Is a Wonderful Thing” infringed the Isley Brothers’ earlier song of the same name, holding that a long interval between exposure and creation does not by itself preclude a finding of subconscious copying (Three Boys Music Corp. v. Bolton, 2000). Three Boys also applied the “inverse ratio rule,” under which a high degree of access lowers the proof of similarity required, and on that point it has been overruled (Skidmore v. Led Zeppelin, 2020, en banc). In Skidmore, the en banc Ninth Circuit abrogated the inverse ratio rule and overruled its prior cases to the contrary, citing Three Boys; the court noted that access may still serve as circumstantial evidence of copying but cannot prove substantial similarity, and its ruling on the inverse ratio rule did not concern subconscious copying. Three Boys therefore remains an illustration of subconscious copying, but it is no longer good law in the Ninth Circuit on the inverse ratio rule. Because sincerity is not a defense, cryptomnesia research bears less on liability than on related questions such as access, credibility, and willfulness; the Copyright Act permits increased statutory damages for willful infringement and reduced statutory damages when an infringer was not aware and had no reason to believe that the conduct infringed (17 U.S.C. § 504(c)).
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. Inadvertent plagiarism and source misattribution occur at low rates in laboratory studies, most ideas and details are attributed correctly, and source errors are not an inevitable consequence of exposure to another person’s account. A confident, detailed report is not evidence of borrowing. Prosecutors are well positioned to establish the first-hand origin of key details by interviewing witnesses separately and promptly, recording first accounts, avoiding questions that supply details, and documenting what each witness was told and when. A detail that appears in a recorded account before any opportunity for exposure carries particular weight.
The research also counsels caution. Borrowed information can be reported sincerely and with confidence, so the first-hand feel of an account does not establish that each detail was first-hand, and the errors are more likely when the source was a similar person, such as a friend who discussed the event, or when the witness elaborated on what another person said. The same principle applies to an accused: a detail in a statement is probative of first-hand knowledge only if it can be shown that the accused did not learn it from investigators, discovery, or others.
Special Issues for Defense
The research supports several propositions defense counsel can legitimately present. People can come to believe that they remember seeing details that were only suggested to them, and they can claim another person’s ideas as their own while sincerely believing the ideas are theirs. These errors are more likely with distraction, similarity between people, delay, and elaboration of another’s idea, and confidence is only a partial guide to whether a detail was borrowed: in one study plagiarized responses were held with lower average confidence, but many were held with high confidence. Evidence of when and from whom a witness heard a detail, combined with general expert testimony on source monitoring, is a legitimate way to help the factfinder evaluate an account.
The research also counsels caution about its limits. Rates of inadvertent plagiarism are low, most attributions are correct, and the research cannot show that a particular detail was borrowed. A source claim is fairly raised only with evidence of actual exposure to the detail before it was reported. The same mechanism can affect the accused’s account and defense witnesses who have discussed the case with the accused or with each other.
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
Brédart, S., Lampinen, J. M., & Defeldre, A.-C. (2003). Phenomenal characteristics of cryptomnesia. Memory, 11(1), 1–11. https://doi.org/10.1080/741938174
Brown, A. S., & Halliday, H. E. (1991). Cryptomnesia and source memory difficulties. American Journal of Psychology, 104(4), 475–490. https://doi.org/10.2307/1422937
Brown, A. S., & Murphy, D. R. (1989). Cryptomnesia: Delineating inadvertent plagiarism. Journal of Experimental Psychology: Learning, Memory, and Cognition, 15(3), 432–442. https://doi.org/10.1037/0278-7393.15.3.432
Gingerich, A. C., & Sullivan, M. C. (2013). Claiming hidden memories as one’s own: A review of inadvertent plagiarism. Journal of Cognitive Psychology, 25(8), 903–916. https://doi.org/10.1080/20445911.2013.841674
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
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
Macrae, C. N., Bodenhausen, G. V., & Calvini, G. (1999). Contexts of cryptomnesia: May the source be with you. Social Cognition, 17(3), 273–297. https://doi.org/10.1521/soco.1999.17.3.273
Marsh, R. L., & Bower, G. H. (1993). Eliciting cryptomnesia: Unconscious plagiarism in a puzzle task. Journal of Experimental Psychology: Learning, Memory, and Cognition, 19(3), 673–688. https://doi.org/10.1037/0278-7393.19.3.673
Marsh, R. L., Landau, J. D., & Hicks, J. L. (1997). Contributions of inadequate source monitoring to unconscious plagiarism during idea generation. Journal of Experimental Psychology: Learning, Memory, and Cognition, 23(4), 886–897. https://doi.org/10.1037/0278-7393.23.4.886
Stark, L.-J., Perfect, T. J., & Newstead, S. E. (2005). When elaboration leads to appropriation: Unconscious plagiarism in a creative task. Memory, 13(6), 561–573. https://doi.org/10.1080/09658210444000232
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
ABKCO Music, Inc. v. Harrisongs Music, Ltd., 722 F.2d 988 (2d Cir. 1983).
Bright Tunes Music Corp. v. Harrisongs Music, Ltd., 420 F. Supp. 177, 180-81 (S.D.N.Y. 1976), aff’d sub nom. ABKCO Music, Inc. v. Harrisongs Music, Ltd., 722 F.2d 988 (2d Cir. 1983).
Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993).
Fred Fisher, Inc. v. Dillingham, 298 F. 145 (S.D.N.Y. 1924).
Kumho Tire Co. v. Carmichael, 526 U.S. 137 (1999).
Skidmore v. Led Zeppelin, 952 F.3d 1051 (9th Cir. 2020) (en banc).
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).
Three Boys Music Corp. v. Bolton, 212 F.3d 477 (9th Cir. 2000), overruled in part by Skidmore v. Led Zeppelin, 952 F.3d 1051 (9th Cir. 2020) (en banc).
United States v. Houser, 36 M.J. 392 (C.M.A. 1993).
17 U.S.C. § 504(c).
Fed. R. Evid. 602.
Fed. R. Evid. 702.
Mil. R. Evid. 602.
Mil. R. Evid. 702.
Mil. R. Evid. 1102.
Ariz. R. Evid. 702.
Ariz. Sup. Ct. Order R-23-0004 (amending Ariz. R. Evid. 702, effective Jan. 1, 2024).
Related topic papers: Source Monitoring · Misattribution of Memory · Implicit Memory · External Sources of Memory Distortion · Unconscious Transference · The Misinformation Effect
Related topics from Arizona Forensic Services: Courts-Martial