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http://pss.sagepub.com/content/21/9/1291The online version of this article can be found at:

 DOI: 10.1177/0956797610379860 2010 21: 1291 originally published online 5 August 2010Psychological Science

Isabel Lindner, Gerald Echterhoff, Patrick S.R. Davidson and Matthias BrandObservation Inflation : Your Actions Become Mine

  

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Remembering performing an action that was not actually per-formed is a particularly disconcerting type of memory failure. A false memory of locking a door, for instance, or of taking medication can have highly undesirable consequences. Imagi-nation is one well-known source of false memories of per-forming an action (Garry, Manning, Loftus, & Sherman, 1996; Goff & Roediger, 1998). For example, creating a mental image of taking a pill could induce someone to later misremember that she or he actually took it. The repeated imagining of self-performance is especially likely to induce such false memo-ries—an effect known as imagination inflation (Goff & Roediger, 1998; Thomas, Bulevich, & Loftus, 2003).

Here, we explore another potential source of false memories of action performance: mere observation of another person’s action. People constantly perceive other people’s actions, either in their immediate environment or in the media, and they typically do not mistake other people’s actions for their own (Jeannerod & Pacherie, 2004). Thus, it would seem counterintuitive and disadvantageous if observing other peo-ple’s actions were to easily induce false memories of

self-performance. Also, because imagination differs in some respects from observation, the effect may not be found for the latter: Compared with observation, imagination involves a higher degree of active self-generation, which has been sug-gested as a critical mechanism driving false memories of self-performance (Sharman, Manning, & Garry, 2005).

However, burgeoning research on motor simulation and mirror-neuron activity suggests another possibility. Echoing early ideomotor theory (James, 1890), research on motor representa-tions indicates that imagining actions involves their covert sim-ulation and thus approximates the motor experience of action performance (Decety & Grèzes, 2006). Notably, motor simula-tion can be engaged not only by imagining oneself performing actions, but also by observing other people performing actions (Grèzes & Decety, 2001; Jeannerod, 2001). Indeed, research on

Corresponding Author:Gerald Echterhoff, School of Humanities and Social Sciences, Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany E-mail: g.echterhoff@jacobs-university.de

Observation Inflation: Your Actions Become Mine

Isabel Lindner1, Gerald Echterhoff 2, Patrick S.R. Davidson3, and Matthias Brand4,5

1Department of Psychology, University of Cologne; 2School of Humanities and Social Sciences, Jacobs University Bremen; 3School of Psychology, University of Ottawa; 4Department of Computational and Cognitive Sciences, University of Duisburg-Essen; and 5Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen, Germany

Abstract

Imagining performing an action can induce false memories of having actually performed it—this is referred to as the imagination-inflation effect. Drawing on research suggesting that action observation—like imagination—involves action simulation, and thus creates matching motor representations in observers, we examined whether false memories of self-performance can also result from merely observing another person’s actions. In three experiments, participants observed actions, some of which they had not performed earlier, and took a source-memory test. Action observation robustly produced false memories of self-performance relative to control conditions. The demonstration of this effect, which we refer to as observation inflation, reveals a previously unknown source of false memories that is ubiquitous in everyday life. The effect persisted despite warnings or instructions to focus on self-performance cues given immediately before the test, and despite elimination of sensory overlap between performance and observation. The findings are not easily reconciled with a source-monitoring account but appear to fit an account invoking interpersonal motor simulation.

Keywords

false memory, social contagion, imagination inflation, action performance, observation, imagination, motor processes, interpersonal simulation, source monitoring

Received 7/27/09; Revision accepted 1/3/10

Research Article

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shared action representations (Schuetz-Bosbach & Prinz, 2007; Wilson & Knoblich, 2005) and on mirror-neuron responses to action perception (e.g., Gallese, 2005; Iacoboni, 2008; Rizzo-latti & Craighero, 2004) indicates that the observation of other people’s actions creates matching motor representations in observers. Overall, there appears to be a substantial overlap of motor representations in brain regions (e.g., the precentral gyrus; Jeannerod, 2001) that are activated during action perfor-mance, imagination, and observation.

The bulk of this research has focused on concurrent activa-tion elicited during the performance, imagination, and obser-vation of actions. However, little attention has been paid to the implications for subsequent memory. One of the few relevant studies found similar neural activity (event-related potentials) during source-memory tasks for previously performed, imag-ined, and observed actions (Senkfor, Van Petten, & Kutas, 2002).

Inspired by this cognitive-neuroscience research, we inves-tigated whether false memories of self-performance could result not only from imagining self-performance, but also from merely observing other people’s actions. If this were the case, one would have to reckon with many more instances of false memories than has hitherto been assumed.

We were also interested in mechanisms underlying a possi-ble inflation effect. Action observation could lead to false memories because it increases familiarity with the action (Thomas et al., 2003). Alternatively, memories from action observation could be misattributed during retrieval because they possess sensory features diagnostic of self-performance (e.g., visual cues, sound); this is especially likely when source monitoring is lax or biased (Johnson, Hashtroudi, & Lindsay, 1993; Murnane & Bayen, 1996). Furthermore, research on motor simulation suggests that the observation of other people’s actions triggers motor representations similar to those engaged by self-performance, and these motor represen-tations might be reactivated later during a memory test.

We based our procedure on the imagination-inflation para-digm developed by Goff and Roediger (1998). In Phase 1 of each experiment, participants read action statements (e.g., “Shake the bottle”) and performed some of the described actions. In Phase 2 of each experiment, a group of participants observed videos showing another person performing actions, some of which the participants had not performed in Phase 1. To obtain a baseline and replicate the imagination-inflation procedure, we also included a group in Experiment 1 that imagined performing actions in Phase 2. To isolate the poten-tial effect of familiarity, we asked a third group to merely read action statements in Phase 2. To isolate the potential effect of active self-generation, we asked a fourth group to generate action statements by unscrambling scrambled ver-sions of the action statements in Phase 2. In Experiments 2 and 3, we created additional observation conditions to investigate potential underlying mechanisms of an inflation effect, such as source-monitoring effort and overlap of sensory features between performance and observation.

In all experiments, participants took a source-memory test after a 2-week delay. During the test, they indicated whether they remembered performing the actions in Phase 1. The critical outcome was the rate of false memories of self-performance, that is, the proportion of “performed” responses for actions that were presented but not performed or were not presented at all in Phase 1.

Experiment 1Method

Participants. Sixty University of Cologne students (mean age = 23.0 years; 49 females and 11 males) participated for partial fulfillment of course requirements.

Design. We created a mixed 3 (Phase 1 encoding of action statements: performed vs. only read vs. not presented) × 2 (Phase 2 presentation: presented vs. not presented) × 4 (Phase 2 processing: observe vs. imagine vs. generate vs. read) design, with the first two variables varying within participants.

Materials. Sixty action statements describing manipula-tions of objects with one or two hands were chosen from the imagination-inflation literature or constructed analogously. The action statements were divided randomly into 12 five-item sets, which were appropriately counterbalanced across experimental conditions. The videos of action performance (including sound) showed the actor’s torso, arms, and hands from a second-person perspective (Fig. 1, left panel). The actor performed the actions on a table. The gender of the actor was counterbalanced across sets of action statements.

Procedure. Participants were recruited for a study on every-day actions and tested individually. The experiment was computer based and consisted of two phases. In Phase 1, par-ticipants sat in front of a computer monitor next to a table with all of the action objects. To preclude the possibility that differences in later memories of whether or not actions were performed could reflect differences in memory for the differ-ent action objects, we always asked participants to pick up the appropriate object after its name appeared on the screen. Then, a perform instruction or a read instruction, along with an action statement, appeared on the screen in German (trans-lated into English, these statements included “Please perform: Shake the bottle!” or “Please read: Shake the bottle!”). Par-ticipants were asked to continue performing or reading the action statement for a period of 15 s and to confirm that they had followed this instruction after each presentation. Each participant received 30 different action statements (six five-item sets) in a random order; half of the action statements had a perform instruction and half had a read instruction (three five-item sets each). Six five-item sets were not presented in Phase 1.

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In Phase 2, following a 5-min filler task, 15 action state-ments (three five-item sets: one performed, one read, and one not presented in Phase 1) were presented in 15-s trials, in ran-dom order, and with no object visible. Each action statement was presented five times (e.g., Goff & Roediger, 1998).1 A beep signaled the beginning and end of trials. Participants received one of four processing instructions:

• Observe: Participants were asked to read each action statement once and then watch a video clip that re-peatedly showed the action described by the action statement. During each trial, actions were shown on average two times (M = 2.02, SD = 0.94).

• Imagine: Participants were asked to read each ac-tion statement once and then close their eyes and repeatedly imagine performing the action as vividly as possible.

• Generate: Participants were asked to unscramble a scrambled or fragmented version of each action statement (Table 1), type the solution, and repeatedly read it. After each presentation, the correct solution was shown. The task was initially easy but became increasingly difficult, so as to maintain participants’ engagement.

• Read: Participants were asked to read each action statement repeatedly. To reduce elaboration, we in-structed them to count the consonants once (see also Thomas et al., 2003).

To standardize processing duration, we asked participants to keep repeating the process they received during each 15-s trial. Two weeks later, we administered a forced-choice source-memory test, in which all 60 action statements were presented in a random order. Participants indicated whether they per-formed or did not perform each action described in the statements.

Results and discussionWe conducted standard parametrical tests (pair-wise compari-sons) and, in addition, nonparametric tests when conditions for the former were jeopardized. To provide conservative deci-sions, all tests were two-tailed.

Mean proportions of participants’ “performed” responses are given in Table 2. These responses were coded as false when the action statement was only read or was not presented in Phase 1. An inflation effect occurred when the proportion of false “performed” responses for action statements presented (i.e., observed, imagined, generated, or read) in Phase 2 was significantly higher than the proportion for corresponding action statements not presented in Phase 2. The critical differ-ences (proportion for items presented minus proportion for items not presented in Phase 2), which represent the size of the inflation effect, are depicted in Figure 2 (left panel). Because the same pattern emerged for the two kinds of nonperformed items (read and not presented) from Phase 1, proportions were collapsed for these item types (as in Goff & Roediger, 1998).

Shake the Bottle! Shake the Bottle!

Fig. 1. Screenshots of action videos taken from a second-person perspective (left; Experiments 1–3) and from a first-person perspective (right; Experiment 3 only).

Table 1. Example of Material Given to Participants Who Received a Generate Instruction in Experiment 1

German original Translation Easy unscrambling Difficult unscrambling

Schütteln Sie die Flasche! Shake the bottle! Sie3Schütteln9die5Flasche! d__ fl_sche sch_tt_ln s_e!

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We found an inflation effect for both the imagine condition, F(1, 14) = 14.47, p = .002, η2 = .51, and the observe condition, F(1, 14) = 13.06, p = .003, η2 = .48, but not for the generate condition (F < 1) or the read condition (F = 1.90). Pair-wise comparisons revealed that the inflation effect was significantly higher in the observe condition and the imagine condition compared with the read condition and the generate condition, respectively, Fs(1, 28) > 7.84, ps < .009, ηp

2s > .22. No signifi-cant difference was found between the read condition and the generate condition, F(1, 28) = 1.10, p = .303. There was a

trend toward a greater effect in the imagine condition than in the observe condition, F(1, 28) = 2.55, p = .121.

Beyond replicating the imagination-inflation effect (Goff & Roediger, 1998), our study revealed false memories of self-performance after subjects observed another person’s actions. By analogy, we refer to this as the observation-inflation effect. Reading and generating action statements in Phase 2 did not produce more false memories of self-performance relative to responses for statements not processed in Phase 2. These findings do not support the notion that the effect is due

Table 2. Experiment 1: Mean Proportion of “Performed” Responses as a Function of Phase 1 Encoding, Phase 2 Processing, and Phase 2 Presentation of Action Statements

Phase 2 processing

Observe Imagine Generate Read

Phase 1 encoding Presented Not presented Presented Not presented Presented Not presented Presented Not presented

Performed .91 (.10) .61 (.19) .91 (.20) .70 (.25) .80 (.17) .81 (.18) .69 (.20) .69 (.16)Only read .23 (.29) .06 (.10) .33 (.26) .05 (.09) .08 (.11) .09 (.13) .01 (.05) .00 (.00)Not presented .12 (.13) .04 (.08) .21 (.24) .01 (.05) .01 (.05) .01 (.05) .03 (.07) .00 (.00)

Note: Phase 1 encoding was varied within participants, Phase 2 processing was varied between participants, and Phase 2 presentation was varied within participants. Proportions represent frequencies of “performed” responses (from a source-memory test) divided by the number of all responses for the corresponding item type. Standard deviations are given in parentheses.

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Fig. 2. Magnitude of the inflation effect in Experiments 1, 2, and 3. For Experiment 1, results are shown for the four Phase 2 processing conditions; for Experiment 2, results are shown for the four combinations of Phase 2 processing and retrieval instructions; and for Experiment 3, results are shown for the three combinations of sensory overlap and interpersonal character of observation. The magnitude of the inflation effect was calculated as the difference between the proportion of false “performed” responses for action statements presented in Phase 2 and the proportion of false “performed” responses for corresponding action statements not presented in Phase 2.

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Observation Inflation in Action Memory 1295

to mere familiarity with or active self-generation of action statements.

According to one prominent account, false memories like those we observed could be due to lax source monitoring (Johnson et al., 1993): Participants misremember performing an action that they merely observed or imagined because they do not take sufficient care to determine the source of action repre-sentations during the memory test. A related reason for source misattributions is a response tendency biased toward a specific source (Murnane & Bayen, 1996). Indeed, we found a pattern consistent with this possibility: Observation and imagination not only increased false “performed” responses but also increased correct “performed” responses. Perhaps repeated observation and imagination generally encouraged participants to claim actions as self-performed—a source-memory response bias.

We designed Experiment 2 to examine these possibilities. One group of participants was instructed to carefully monitor the source of their memories during the memory test; specifi-cally, they were told to focus on features indicating self-performance (following Thomas & Bulevich, 2006). If false memories are due to lax source monitoring, they should be reduced by such instructions (Echterhoff, Hirst, & Hussy, 2005; Henkel, Franklin, & Johnson, 2000). Another group of participants was explicitly warned about the observation-inflation effect. Such a warning should reduce or eliminate a bias to claim actions as self-performed (see McDermott & Roediger, 1998). We investigated whether the observation-inflation effect would persist despite these additional instruc-tions. Furthermore, we replicated the observe condition and the read condition from Experiment 1.

Experiment 2Method

Participants. Fifty-six University of Alberta undergraduates (mean age = 19.7 years; 33 females and 23 males) participated for partial fulfillment of course requirements.

Design. As in Experiment 1, we manipulated Phase 1 encoding of action statements (performed vs. only read vs. not presented) and Phase 2 presentation (presented vs. not presented) within partici-pants. Three groups of participants observed action performance in Phase 2. Retrieval instructions were varied across these partici-pants: Some were told to monitor the source of their memories (observe/source-monitoring group), some were explicitly warned about the observation-inflation effect (observe/warning group), and others received only the standard instruction (observe/ standard group). A control group only read action statements in Phase 2 and took the standard memory test (read/standard group).

Materials. The same materials as in Experiment 1 (translated into English) were employed, except that, to enhance homoge-neity of the material, only one male actor was shown in all the videos.

Procedure. The procedure was the same as in Experiment 1, except for the following modifications. To further standardize the procedure in Phase 1, the experimenter, rather than the par-ticipants, picked the objects. To minimize differences in mem-ory for the action objects themselves, we asked all participants, prior to both reading and performing actions, to look at a pho-tograph of each object. Each action statement was encoded (performed or read) only once in order to control the frequency of encoding better than in Experiment 1. To reduce differences in mere motor activity between reading and performing, we asked participants in the only-read trials to imitate, after read-ing an action statement, meaningless hand movements shown by the experimenter. (The hand movements were performed next to the object and for approximately the same duration as when participants performed actions.)

The same pattern emerged in Experiment 1 for items that were only read or were new (i.e., not presented in Phase 1); thus, to increase parsimony, we did not employ new items in Phase 2. To increase similarity to the observe condition, we presented participants in the read condition with meaningless visual stimuli after they read action statements once.

Immediately before the source-memory test, participants in the observe/source-monitoring group were asked to focus on self-performance cues during the test (e.g., to remember how actions felt, looked, or sounded; see Thomas & Bulevich, 2006). They were urged not to confuse actions they performed with actions performed by the person in the video. Participants in the observe/warning group were informed about the observation-inflation effect and encouraged to be careful to avoid such errors.

Results and discussionTable 3 gives the proportions of “performed” responses. Figure 2 (middle panel) depicts the critical difference repre-senting the inflation effect. As in Experiment 1, we found sig-nificantly more false “performed” responses after participants in the observe/standard group had processed action statements than after they had not processed action statements in Phase 2, F(1, 13) = 15.13, p = .002, η2 = .54, but we found no such effect in the read group, F(1, 13) = 1.32. An observation-inflation effect was also found in both the observe/source-monitoring group and the observe/warning group, F(1, 13) = 33.97, p < .001, η2 = .72, and F(1, 13) = 5.52, p = .035, η2 = .30, respec-tively. Pair-wise comparisons revealed that the observation-inflation effect was significantly higher in each observe group than in the read/standard group, Fs(1, 26) > 7.11, ps < .013, ηp

2s > .22.2 No significant differences in the magnitude of the effect emerged between the three observe groups, Fs < 1.6. Participants rarely misremembered action statements as self-performed when those statements were presented neither in Phase 1 nor in Phase 2. These proportions did not differ sig-nificantly among the four groups.

In sum, we replicated the observation-inflation effect found in Experiment 1, and the effect persisted despite a source-monitoring instruction or a warning about the effect

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given immediately before the test. These results suggest that participants were reasonably confident that they had actually performed the nonperformed actions. The findings do not sup-port the possibility that the effect is due to lax source monitor-ing or a bias toward claiming actions as self-performed.

However, the persistence of the effect under increased source-monitoring effort does not rule out other mechanisms suggested by source-monitoring accounts. Source confusion may occur because memories from self-performance and memories from observation share perceptual features (e.g., an object’s visual appearance, concomitant sound). The features of observation-based memories could be falsely taken as cues diagnostic of self-performance. A similar account has been proposed to explain the imagination-inflation effect (Thomas et al., 2003). To examine this possibility, in Experiment 3 we manipulated the overlap of perceptual features between encoding (Phase 1) and processing (Phase 2). Overlap was high when participants performed actions with their eyes open in Phase 1 and observed videos that included sound and showed action performance from a first-person, ego-centric perspective in Phase 2. Overlap was low when partici-pants performed actions with their eyes closed and observed videos without sound from a second-person, allocentric perspec-tive. A source-monitoring account predicts decreased observa-tion inflation for low perceptual overlap.

It has been argued that the covert simulation of action repre-sentations serves important interpersonal functions, such as pre-dicting other people’s actions (Graf, Schuetz-Bosbach, & Prinz, in press) and understanding the goals underlying those actions (Blakemore & Decety, 2001; Iacoboni et al., 2005; but see Lingnau, Gesierich, & Caramazza, 2009). Because the interpersonal character of action observation is reduced with a first-person perspective (vs. a second-person perspective), an interpersonal mirroring account would predict greater observation inflation for a second-person perspective (vs. a first-person perspective).

Experiment 3Method

Participants. Fifty-four University of Cologne students (mean age = 25.3 years; 39 females and 15 males), none of

whom took part in Experiment 1, participated for partial ful-fillment of course requirements.

Design. In addition to the same within-participants manipula-tions as in Experiments 1 and 2, Experiment 3 included a manip-ulation of the overlap of sensory features between encoding (Phase 1) and processing (Phase 2). Participants were divided into three groups. Participants in the high-sensory-overlap group performed actions with their eyes open in Phase 1, and they watched videos with sound that depicted actions from a first-person perspective (i.e., with a low interpersonal character) in Phase 2. Participants in the partial-sensory-overlap group also performed actions with their eyes open in Phase 1, but they watched videos depicting actions from a second-person perspec-tive (i.e., with a high interpersonal character), as in Experiments 1 and 2. Participants in the low-sensory-overlap group performed actions with their eyes closed in Phase 1 (see Hornstein & Mulligan, 2004) and watched second-person-perspective videos without sound in Phase 2. This design pitted the overlap of sen-sory features against the interpersonal character of the observed actions; the interpersonal character is lower with a first-person perspective than with a second-person perspective.

Materials. The same materials were used as in the previous experiments. Action performance was videotaped simultane-ously from a first- and a second-person perspective.

Procedure. The procedure was the same as in Experiment 2, except for the following changes. To reduce differences in experience with the objects for action statements that were read and action statements that were performed during Phase 1 in the low-sensory-overlap group, we used the following procedure. First, the name of an action object appeared on the screen. Then, participants closed their eyes, and the experi-menter handed the object to them. This was done so partici-pants could get a tactile impression of the object—regardless of whether they performed or did not perform the correspond-ing action statement. Then, participants read the action state-ment, closed their eyes again, and either performed the action with the object (perform trials) or performed a combination of meaningless hand movements as instructed verbally by the

Table 3. Experiment 2: Mean Proportion of “Performed” Responses as a Function of Phase 1 Encoding, Phase 2 Processing and Retrieval Instruction, and Phase 2 Presentation of Action Statements

Phase 2 processing/retrieval instruction

Observe/standard Observe/source monitoring Observe/warning Read/standard

Phase 1 encoding Presented Not presented Presented Not presented Presented Not presented Presented Not presented

Performed .87 (.17) .74 (.21) .91 (.13) .77 (.23) .74 (.28) .86 (.20) .84 (.21) .83 (.21)Only read .29 (.28) .06 (.09) .29 (.20) .03 (.07) .23 (.17) .07 (.19) .09 (.15) .04 (.09)Not presented — .02 (.02) — .00 (.01) — .01 (.03) — .01 (.02)

Note: Phase 1 encoding was varied within participants, Phase 2 processing and retrieval instruction was varied between participants, and Phase 2 presentation was varied within participants. Proportions represent frequencies of “performed” responses (from a source-memory test) divided by the number of all responses for the corresponding item type. Standard deviations are given in parentheses.

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experimenter (only-read trials). Careful probing ensured that participants, as if blindfolded, did not see the objects or their own performance at any time during Phase 1.

Results and discussionTable 4 gives the proportions of “performed” responses. Figure 2 (right panel) shows the critical differences represent-ing the observation-inflation effect. In all three experimental groups, participants gave significantly more false “performed” responses for action statements that they had processed (vs. not processed) in Phase 2—high-sensory-overlap group: F(1, 17) = 7.56, p = .014, η2 = .31; partial-sensory-overlap group: F(1, 17) = 32.00, p < .001, η2 = .65; and low-sensory-overlap group: F(1, 17) = 13.07, p = .002, η2 = .44. As the effect sizes indicate, the smallest observation-inflation effect was found in the high-sensory-overlap/low-interpersonal-character condition, and rela-tive to that condition, there was also a trend toward a significantly greater effect in the partial-sensory-overlap/high-interpersonal-character condition, F(1, 34) = 3.40, p = .074, ηp

2 = .09 (two-tailed, pair-wise comparison). There were no further significant differences in the magnitude of the effect, Fs < 1.

In sum, observation inflation was found regardless of the amount of sensory overlap (minimal, maximal, or partial) between self-performed actions (Phase 1) and observed actions (Phase 2). Also, when overlap was maximized and the inter-personal character of observation was low, the effect was not higher but, if anything, lower than it was in a condition in which sensory overlap was partial and the interpersonal char-acter of observation was high. These findings are inconsistent with an account invoking feature-based source misattribution and can be better reconciled with an account invoking inter-personal motor simulation.

General DiscussionIn three experiments, we found that merely observing another person’s actions, such as shaking a bottle, induced people to

falsely remember having performed the action, as indicated by substantial rates of false “performed” responses in a source-memory test. This finding extends research on the imagination-inflation effect (Garry et al., 1996; Goff & Roediger, 1998) by revealing a hitherto undiscovered source of false memories that is ubiquitous in everyday life: observation of other peoples’ actions. This is not a transient effect, as it occurred after a 2-week delay.

Beyond demonstrating a novel type of false memory, our findings are also informative about possible mechanisms that might account for this effect. Experiment 1 suggests that false memories of self-performance are not due to the familiarity of action statements or active self-generation of action state-ments. Further findings do not support the view that the effect is due to lax source monitoring or a source-response bias dur-ing the test (i.e., a bias to claim nonperformed actions as per-formed): In Experiment 2, the effect persisted when participants were urged to focus on self-performance cues or were explic-itly warned about the effect. In Experiment 3, the effect was, if anything, lower when there was high sensory overlap (vs. par-tial sensory overlap) between performance and observation. When visual and auditory overlap was reduced to a minimum, the effect persisted. Thus, the similarity of sensory features alone cannot account for the effect, which is inconsistent with the notion of feature-based source confusion.

What mechanism, then, could account for observation inflation? Research on motor simulation and interpersonal mirroring suggests that the observation of another person’s action may trigger a covert simulation of the action and thus activate motor representations similar to those produced dur-ing self-performance (e.g., Iacoboni, 2008; Schuetz-Bosbach & Prinz, 2007; Wilson & Knoblich, 2005). Evidence suggests that mirrored motor representations can shape observers’ self-related motor memory (Stefan et al., 2005) and that neural cor-relates of conscious memory for these representations are similar to those of memory for self-performed actions (Senkfor et al., 2002).When, on a memory test, participants reactivate mirrored action representations, they could—erroneously—remember having performed the action.

Table 4. Experiment 3: Mean Proportion of “Performed” Responses as a Function of Phase 1 Encoding, Sensory Overlap and Interpersonal Character of Observation, and Phase 2 Presentation of Action Statements

Sensory overlap/interpersonal character of observation

High sensory overlap/low interpersonal character

Partial sensory overlap/high interpersonal character

Low sensory overlap/high interpersonal character

Phase 1 encoding Presented Not presented Presented Not presented Presented Not presented

Performed .89 (.14) .77 (.20) .92 (.12) .78 (.29) .89 (.14) .78 (.23)Only read .17 (.21) .03 (.08) .28 (.21) .02 (.06) .20 (.24) .00 (.00)Not presented — .01 (.01) — .01 (.02) — .01 (.01)

Note: Phase 1 encoding was varied within participants, sensory overlap and interpersonal character of observation was varied between participants, and Phase 2 presentation was varied within participants. Proportions represent frequencies of “performed” responses (from a source-memory test) divided by the number of all responses for the corresponding item type. Standard deviations are given in parentheses.

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Our findings are generally consistent with such accounts, which emphasize the interpersonal functionality of motor sim-ulation. We found robust false memories of self-performance after action observation from a second-person perspective, which is the perspective that individuals experience in inter-personal encounters. Also, there was a trend toward a lower false-memory effect when the observation situation was less characteristic of social interaction (i.e., first-person perspec-tive vs. second-person perspective).

On a general note, we think that these findings indicate how investigations of false memory can be extended and enriched by drawing on advances in social cognitive neuroscience. Neuroscientific methods may help researchers further explore the role of interpersonal motor simulation in observation inflation.

Acknowledgments

These studies were part of I.L.’s dissertation. We thank Bill Hirst, Walter Hussy, Amina Memon, Suparna Rajaram, Henry Roediger, and Gün Semin for helpful comments; Gerhard Mutz for technical assistance; and Michael Mentzner and Alexandra Hill for serving as actors.

Declaration of Conflicting Interests

The authors declared that they had no conflicts of interest with respect to their authorship or the publication of this article.

Funding

The Faculty of Science, University of Alberta, and the Natural Sciences and Engineering Research Council of Canada provided research funding to P.S.R.D.

Supplemental Material

Additional supporting information may be found at http://pss.sagepub .com/content/by/supplemental-data

Notes

1. Three additional five-item sets (one performed, one read, and one not presented in Phase 1) were presented once in Phase 2 in each experiment. The results for these items paralleled the results for items presented five times (see Tables S1 to S3 in the Supplemental Material available online), except that in Experiment 1 there was no inflation effect in the observation group. Finding the effect for once-presented items in Experiments 2 and 3 but not in Experiment 1 is consistent with the effect for items presented five times being lower in Experiment 1 than in the other experiments. A possible reason for this cross-study difference is suggested by research on memory-enhancing effects of self-performance (Cohen, 1989; Nilsson, 2000): The memory advantage for self-performed items (vs. control items) is greater for longer stimulus lists (Engelkamp & Zimmer, 1997). Assuming that more accurate memory reduces the likelihood of false responses, the present false-memory effect might be attenuated with longer item lists. Indeed, there were 50% more Phase 2 trials in Experiment 1 than in Experiments 2 and 3.

2. An analysis of variance did not yield a significant difference in the false-memory effect between the observe/warning and the read/standard group (F = 2.23), but a corresponding nonparametric test did show a difference, Mann-Whitney’s U(28) = 47.5, p = .019, rrb

2 = .27 (rrb is the rank-biserial correlation coefficient).

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