Neural correlates of successfully encoded true and false information. from factual and social sources. Trey Hedden. Stanford University

Transcription

1 Truth and subsequent source memory -1 Neural correlates of successfully encoded true and false information from factual and social sources Trey Hedden Stanford University Angela H. Gutchess Harvard University and The Athinoula A. Martinos Center for Biomedical Imaging Carolyn Yoon University of Michigan Manuscript under review. Please do not cite or distribute without the authors permission.

2 Truth and subsequent source memory -2 Abstract Effective encoding of source information provides a powerful mechanism for later determination of the truth or falsity of a remembered statement. While undergoing functional imaging, 12 participants read statements accompanied by information explicitly indicating a statement s truth value, or whether it was provided by a trustworthy or dishonest person. Imaging data were back-sorted according to subsequent memory performance. Activation in medial temporal lobes and left prefrontal cortex was greater for statements correctly assigned to their source than those for which source memory failed. These memory-relevant areas were interrogated in region of interest analyses, which indicated that hippocampal activation was not modulated by truth value or type of source, whereas prefrontal activations differentially responded when the truth value of a statement was explicitly indicated or socially inferred. Results suggest that information from social sources is differently processed from non-social information, and that true information engages strategic encoding more than false information.

3 Truth and subsequent source memory -3 The successful execution of encoding processes is an important component in forming accurate representations of the world around us. Although those encoding processes may occur automatically, their likelihood of success may be guided by strategic allocation of attention, as when using deep encoding strategies (Craik & Lockhart, 1972). In everyday life, we are unlikely to engage in such strategic encoding unless we know that a fact or episode will be important to remember. How do we determine probable importance? Often, this information is gleaned through the source. If an authoritative or truthworthy source tells us that a fact is true, we are more likely to attempt to remember it. If an untrustworthy source communicates the fact, however, we are unlikely to expend energy attempting to encode that fact. If we do encode such a fact, we may wish to attach an associative tag denoting the source or that the fact is possibly untrue. In this way, source memory -- memory for where, how, or from whom information was obtained -- underlies how we learn from and interact with others. Research on brain-lesion patients has demonstrated that the medial temporal lobes (MTL) are necessary for the formation of stable memories (Milner, 1972; Squire, Stark, & Clark, 2004; Zola-Morgan, Squire, & Amaral, 1986). Building on this neuropsychological foundation, the neural correlates of successful encoding processes have been studied in normal humans using the subsequent memory paradigm, in which participants undergo functional neuroimaging during the initial presentation of to-be-remembered stimuli. The imaging data are then back-sorted according to subsequent performance on a memory task. Using this paradigm, researchers have confirmed the central role of MTL structures, including the hippocampus and the parahippocampal gyrus, in successful encoding processes (Brewer, Zhao, Desmond, Glover, & Gabrieli, 1998; Davachi, Mitchell, & Wagner, 2003; Wagner, Koutstaal, & Schacter, 1999). In

4 Truth and subsequent source memory -4 addition, these studies revealed the involvement of several regions of prefrontal cortex (PFC) in successful encoding. Prominent among these are two regions in left-lateralized ventrolateral PFC, one in the anterior portion of inferior frontal gyrus (Brodmann s areas (BA) 45, and 47), and the other in a more posterior portion of the inferior frontal gyrus (BA 9 and 44) (Brewer et al., 1998; Davachi, Maril, & Wagner, 2001; Fletcher, Stephenson, Carpenter, Donovan, & Bullmorel, 2003; Kirchhoff, Wagner, Maril, & Stern, 2000; Otten, Henson, & Rugg, 2001; Prince, Daselaar, & Cabeza, 2005; Wagner et al., 1998). Although all of the above-mentioned regions are invoked during encoding processes, some regions appear to be differentially involved in certain types of encoding. In particular, memory formation that involves associations among items or the association of an item with its source or context differentially depends on activation in the hippocampus and parahippocampal gyrus, although these regions also contribute to the non-associative encoding of individual itesm (Davachi et al., 2003; Davachi & Wagner, 2002; Prince et al., 2005). In contrast, perirhinal cortex displays activation whenever an individual item will be later remembered, regardless of whether source information will also be recollected (Davachi et al., 2003). It has been suggested that PFC subserves executive control processes, which contribute to the successful encoding of source information, even when an individual s goal is not specifically related to explicit encoding of an item and its source. The extent to which an individual engages in semantic or deeper-level processing of an item tends to increase the likelihood of successful source encoding (Otten et al., 2001; Paller & Wagner, 2002). Indeed, patients with PFC lesions have been found to exhibit similar item memory to control participants, but decreased memory for source information related to those items (Janowsky, Shimamura, & Squire, 1989). A recent study using transcranial magnetic stimulation has indicated that disruption of processing in left, but not

5 Truth and subsequent source memory -5 right, ventrolateral PFC during encoding leads to a loss of subsequent memory accuracy (Kahn et al., 2005). Most studies of subsequent source memory have used materials or conditions that are abstract or unlikely to be encountered in everyday memory situations. It has been suggested that more natural conditions may lead to better source memory or different processing of source information under some circumstances (Rahhal, May, & Hasher, 2002). One recent study has investigated subsequent memory effects for factual statements of the sort that participants might routinely learn during class or while reading the newspaper (Mitchell, Dodson, & Schacter, 2005). These statements were presented as being either true or false, and participants were later presented with the originally-encoded statements and a second set of novel statements and were asked to indicate whether each statement was true, false, or whether they were unsure. The results indicated the presence of a phenomenon known as the illusion of truth, which occurs when previously seen, but false, statements are incorrectly judged as being true because they seem familiar and therefore believable (Begg, Anas, & Farinacci, 1992; Begg, Robertson, Gruppuso, Anas, & Needham, 1996; Gilbert, Krull, & Malone, 1990; Skurnik, Yoon, Park, & Schwarz, 2005). Using the subsequent memory paradigm, encoding-related activation in the hippocampus and ventrolateral PFC was found to be greatest when a false statement was subsequently remembered as false, thus avoiding the illusion of truth (Mitchell et al., 2005). These results suggest that effective encoding of source information can be used to reduce commonly-experienced memory misattributions. In addition to recent studies investigating everyday memory phenomena, a rising interest in social cognitive neuroscience has begun to emphasize the role of social and self-relevant information in the direction of attention and the ensuing formation of memories (Mitchell,

6 Truth and subsequent source memory -6 Macrae, & Banaji, 2004; Ochsner, 2004). In a recent study, activation in dorsomedial PFC (BA 6/8/9) was found to be greater during social (but not during non-social) judgments involving statements that were subsequently remembered versus those subsequently forgotten (Mitchell et al., 2004). Medial PFC regions also have been implicated in theory of mind tasks and related tasks that require consideration of others as social agents, including discerning deceptive intent in the actions of others (Gallagher & Frith, 2003; Grézes, Frith, & Passingham, 2004; Mitchell, Heatherton, & Macrae, 2002). These results suggest that socially-relevant information may be separately processed from purely semantic information, and that extent of dorsomedial PFC activation in response to social stimuli is related to subsequent memory formation. In the current study, we focus on the neural correlates of encoding processes leading to subsequent memory for the truth of statements received from social and nonsocial sources. The truth value of a statement was provided in one of two ways. It could be explicitly stated as being true or false, or it could be attributed to a trustworthy or dishonest source, in which case the statement is inferred to be either true or false from a nominally social context. We investigated neural regions that predicted subsequent memory in an effort to determine whether encoding processes would be modulated by the truth value or the type of source. For MTL regions, we expected relatively little modulation by source type, as these regions are likely to process associative information in an automatic fashion. Results from prior studies led us to hypothesize that ventrolateral PFC regions might be modulated by truth value, and that medial PFC regions might be modulated by the social or nonsocial nature of the source (Mitchell et al., 2005; Mitchell et al., 2004).

7 Truth and subsequent source memory -7 Methods Participants Twelve college-aged adults (aged years, mean age 20.5 years, 58% female) participated in the study. All participants gave informed consent and the study was approved by the University of Michigan Institutional Review Board. Materials and Procedure Task. Materials consisted of 240 true statements of health-related information for which participants were unlikely to have prior knowledge. False versions of each statement were constructed by altering one or a few words to make the statement factually untrue. The behavioral task consisted of an encoding phase and a retrieval phase. Before the encoding phase, participants were introduced to two hypothetical individuals, Pat and Chris. One of these individuals was introduced as being very honest and trustworthy, so that any information obtained from this individual can be considered to be true. The other individual was introduced as being very dishonest and who always tells lies, so that any information obtained from this individual should be considered to be false. Participants were told that they would be presented with statements and an indication of whether each was true or false and that they would later be shown the statements again and asked to remember whether each was true or false. The encoding phase, conducted inside the scanner, consisted of participants being presented with statements of health-related information, accompanied by either an explicit statement of its truth value ( TRUE or FALSE ) or by an indication of which individual conveyed the information ( PAT says: or CHRIS says: ). For each participant, one-half of the statements were factually true, while one-half were factually false. One-half of each set of true and false statements were accompanied by an explicit statement of truth value, while one-half were accompanied by an

8 Truth and subsequent source memory -8 indication of the speaker. Each statement and its truth value indication remained on the screen for 6 seconds, during which time participants verified whether the statement was true or false by pressing one of two buttons. Before scanning began, participants viewed and responded to four practice statements. Each scan consisted of 60 statements, pseudorandomly interspersed with baseline periods of 2-12 seconds (in multiples of the TR), consisting of a fixation cross presented on the screen. The order of conditions and baseline periods was determined using the optseq2 program (Doug Greve, MGH NMR Center, Charlestown, MA). After scanning of the encoding phase and of the anatomical reference images, participants exited the scanner and completed the retrieval phase. Approximately minutes separated the encoding and retrieval phases. During the retrieval phase, participants were presented with each of the 240 statements viewed during encoding with no accompanying indication of truth value. Participants indicated via a four-choice button press whether they were confident that the statement was true, guessing that it was true, guessing that it was false, or confident that it was false. Participants were reminded of the true and false indications associated with each individual (e.g. If you remember that Pat said it, it must be true; if Chris said it, it must be false. ) and were informed that they had seen all 240 of the statements before and that half were true and half were false. Stimulus presentation was programmed using E- prime 1.1 SP3 (Psychological Software Tools, Pittsburgh, PA) and IFIS 9.0 (MRI Devices, Waukesha, WI). Image acquisition. Data were acquired using a 3-Tesla General Electric LX MR scanner (GE Signa 9.0 VH3 software, General Electric, Milwaukee, WI) paired with a whole-head coil. Functional data were obtained in 4 runs, each consisting of 270 volumes, using a gradient-echo spiral acquisition sequence for measurement of blood oxygen level-dependent (BOLD) effects

9 Truth and subsequent source memory -9 (TR = 2000ms, TE = 25ms, flip angle = 80, 64 x 64 matrix, FOV = 200mm). Thirty-two contiguous oblique slices of 4mm thickness were acquired parallel to the plane defined by the anterior and posterior commissures. Anatomical images were obtained using a Spoiled GRASS sequence consisting of 120 sagittal slices (0.9375mm in-plane resolution) of 1.5mm thickness. Statistical analysis. Behavioral data were analyzed using SPSS software (SPSS Inc., Chicago, IL) using an α-level of.05. For analysis purposes, responses to a statement involving a confident correct true or false attribution were classified as a correct source memory for that statement. Guessing responses and incorrect attributions were classified as indicating failed source memory for that statement (Otten et al., 2001). Functional volumes were slice time corrected using an 8-point Hanning windowed sinc interpolation implemented in C++. Intrasubject motion correction was performed using AIR 3.08 (Woods, Cherry, & Mazziotta, 1992). Remaining analyses were conducted using SPM2 software (Wellcome Department of Cognitive Neurology, London, UK) and associated programs incorporated into the Gablab Toolbox (Stanford University, Stanford, CA). The anatomical image was coregistered to the fifth functional volume and normalized to MNI space using a standard T1 template image with 2mm 3 voxels. The normalization parameters determined from the anatomical image were applied to the functional volumes, which were then smoothed with a 6mm isotropic Gaussian kernel. Condition effects for the 8 stimulus conditions were estimated using event-related regressors convolved with a canonical hemodynamic response function. Unless otherwise specified, all results reported are from group-level, random-effects analyses using an uncorrected threshold of p =.005 with a cluster size greater than k = 11, providing an approximate cluster-level threshold of p =.05 as estimated using Alphasim (B. D. Ward, Medical College of Wisconsin, Milwaukee, WI). Anatomical regions were identified using the WFU

10 Truth and subsequent source memory -10 PickAtlas tool (Maldjian, Laurienti, & Burdette, 2004; Maldjian, Laurienti, Kraft, & Burdette, 2003). Clusters of functional activation were identified as regions of interest (ROIs) and smoothed with a 4mm isotropic Gaussian kernel. Parameter estimates for each experimental condition were extracted from these ROIs for each participant. Results Behavioral Results Two behavioral measures were used to assess memory performance. First, the proportion of correct source memory judgments (confident correct attributions) was calculated. Second, the false alarm rate was calculated as the proportion of statements incorrectly assigned a confident attribution. Means for each measure are displayed in Table 1. Each of these measures was subjected to a repeated-measures ANOVA with source type (social inference vs. explicitly stated) and truth value (true vs. false) as independent variables. For correct source memory judgments, there was no main effect of source type, F (1, 11) = 0.03, MSE =.007, and no interaction, F (1, 11) = 2.99, MSE =.003. There was a significant main effect of truth value, F (1, 11) = 37.82, MSE =.008, p <.001, with participants exhibiting better source memory for true than for false statements. For false alarm rates, there was no effect of source type, F (1, 11) = 0.00, MSE =.003, and no interaction, F (1, 11) = 0.16, MSE =.009, but there was a significant main effect of truth value, F (1, 11) = 11.20, MSE =.005, p =.007, with a higher incidence of originally false statements being confidently remembered as true. This latter effect indicates the presence of an illusion of truth, in which familiar yet false statements are incorrectly remembered as true.

11 Truth and subsequent source memory -11 Imaging Results All reported functional imaging results involve brain regions that displayed differential activation for statements whose truth value was correctly and confidently remembered versus statements for which subsequent memory of the truth value failed. Functional data were first analyzed through the overall subsequent memory contrast (correct source > failed source), designed to identify regions for which correct source memory produced greater activation than did failed source memory, regardless of truth value or source type. As shown in Table 2, this analysis revealed significant activations in MTL regions, including the right hippocampus and bilateral parahippocampal gyri, in left lateral temporal cortex, and in several left-lateralized PFC regions, including posterior ventrolateral PFC (inferior frontal gyrus, BA 9), dorsomedial PFC (superior frontal gyrus, BA 8), and anterior ventrolateral PFC (inferior frontal gyrus, BA 47). These activations were then used as ROIs, and parameter estimates of activation attributable to each individual condition were extracted and compared. These comparisons were conducted through repeated-measure ANOVAs in which source type (social inference vs. explicitly stated), truth value (true vs. false), and subsequent memory (correct source vs. failed source) were independent variables. This analysis provides a conservative estimate of differences between source type and truth value conditions, as ROIs were defined in a manner that was unbiased with respect to any individual condition. Because of the conservative nature of this analysis, we report regions with marginal differences among conditions (p <.10). The ROI analyses revealed that although many of these regions were more active in individual conditions when source information was correctly remembered compared to when source memory failed, very few of these regions demonstrated differential activity across truth values and source types (see

12 Truth and subsequent source memory -12 statistical effects in Table 2). Indeed, no regions displayed a main effect of truth value, and only three regions displayed a main effect of source type. Of interest, the hippocampus did not differentially respond across source type or truth value, although it did differentiate between correct and failed source memory. In contrast, two regions in the parahippocampal gyrus displayed differential activation across conditions. In the right parahippocampus, the subsequent memory effect was primarily evident when a statement was inferred to be true or false. In a region of left parahippocampus, the subsequent memory effect was larger when truth value was explicitly stated than when it was inferred (see Figure 2). These results suggest that MTL activity outside of the hippocampus proper may be modulated by the source of information, with right MTL regions being more responsive to social sources and left MTL regions more responsive to unambiguous nonsocial sources. In the PFC, two ventrolateral regions displayed differential activation across source types. Both anterior and posterior ventrolateral PFC exhibited greater subsequent memory effects when truth value was explicitly stated compared to when it was inferred (see Figure 3). In contrast, a dorsomedial region (BA 8) displayed a main effect of source type, in that explicit statements of truth value produced greater activation than did socially inferred truth values. Whereas anterior and posterior ventrolateral PFC only displayed reliable subsequent memory effects when encoding information from explicitly stated sources, this dorsomedial PFC region also displayed a reliable subsequent memory effect for socially inferred true, but not false, statements. This may suggest that dorsomedial PFC differentiates between information from trustworthy and dishonest social sources. In addition, lateral temporal regions also had activation related to subsequent memory. These lateral temporal regions were the only ones to display a differential subsequent memory

13 Truth and subsequent source memory -13 effect across truth values (as seen by the truth value by subsequent memory interactions in Table 2). In these temporal regions, the subsequent memory effect was larger for true statements than for false statements (see Figure 3), which may suggest that these regions are involved in semantic encoding of reliable information. Discussion The overall pattern of results confirms the importance of MTL and ventrolateral PFC regions for successful encoding of source information. In particular, hippocampal activation during encoding reflected whether the source (truth value) would subsequently be remembered or not, and did not differ for explicitly stated and socially inferred truth values. This suggests that hippocampal activation is related to the successful formation of associative memories between an item and its source, and this associative activation occurs largely automatically, without regard for strategic control (Davachi et al., 2003; Davachi & Wagner, 2002; Ryan, Althoff, Whitlow, & Cohen, 2000; Stark & Okado, 2003). Parahippocampal activation, in contrast, showed subsequent memory effects that were greatest for statements explicitly stated to be true, with smaller subsequent memory effects for false statements, whether they were explicitly stated or socially inferred. This suggests that parahippocampal activation may be modulated by strategic control based on an individual s interpretation of how information from a given source should be evaluated and encoded. PFC activation displayed a general trend of greater subsequent memory effects for statements accompanied by an explicitly stated truth value than for socially inferred truth values. This suggests that when the truth value is known, strategic encoding processes may be brought to bear in order to facilitate memory for the semantic information and its associated source. However, when the truth value is provided through social inference, even if that inference is

14 Truth and subsequent source memory -14 based on a trustworthy source, uncertainty about the verity of a statement may remain. Participants are therefore more likely to engage in processing related to the social situation than to semantic knowledge specific to the statement. No PFC regions displayed a subsequent memory effect for socially-inferred false statements, suggesting that in this situation, participants did not associate the truth value derived from the source with the statement. In particular, activation in a dorsomedial PFC region, identified in a previous study as being related to memory for social judgments (Mitchell et al., 2004), was observed to be more related to subsequent memory for true statements whose truth value was socially inferred than for socially inferred false statements. This dorsomedial region was also related to subsequent memory for explicitly stated truth values, suggesting that activation in this region may reflect the engagement of encoding processes when information is obtained from a reliable source. A lack of activation in this region may therefore signal uncertainty in the information and may serve as a potential marker of inferences of deceit in the actions of others. Lateral temporal regions were observed to display greater activation during successful encoding of true than false information. Lateral temporal cortex has been previously implicated in semantic memory (Kirchhoff et al., 2000; Levy, Bayley, & Squire, 2004; Schmolck, Kensinger, Corkin, & Squire, 2002). The current results suggest that when true information is encountered, lateral temporal regions are engaged to append novel facts to an individuals existing semantic knowledge base. One somewhat surprising finding was that no regions displayed greater activation during successful encoding of false information than true information. In another functional imaging investigation of true and false statements, subsequent memory effects were found to be largest for correctly remembered false statements, thus assisting participants in avoiding expression of

15 Truth and subsequent source memory -15 an illusion of truth (Mitchell et al., 2005). Although the behavioral data from the current study showed evidence of an illusion of truth, memory for true and false statements did not differentially express a subsequent memory effect in any region, as shown by the absence of a main effect of truth in all ROIs. One possible explanation for this difference in findings across these studies is that the study by Mitchell and colleagues (2005) considered all statements judged with low confidence to indicate successful memory, whereas the current study includes only high confidence response as correct. Because the illusion of truth is predicated on familiar statements being more likely to be judged as true, and true statements may therefore be correctly judged as true without an explicit memory of their truth (this is particularly likely for low confidence responses), the analyses from the previous study may have inadvertently reduced the likelihood of observing activation related to subsequent memory for true statements. The findings from the current study suggest that truth value per se is of less importance during encoding of source information and differentially affects activation in very few regions, while the certainty with which a truth value can be assigned (where explicitly stated truth values are more certain than those obtained from social inferences) affects activation in a somewhat larger set of regions. In summary, subsequent memory for truth value was associated with activation in MTL and PFC regions identified in previous studies as subserving effective encoding processes. Within these regions, observed differences in subsequent memory effects across conditions indicated that both the reliability and social relevance of a source leads to differential processing of the information obtained from that source. Hippocampal activation did not discriminate among specific types of sources, although it was generally involved in associating a statement with its truth value. Right parahippocampal activation only demonstrated subsequent memory effects during encoding of a trustworthy social source, while left parahippocampal activation

16 Truth and subsequent source memory -16 reflected encoding of non-social source information. Activation in several PFC regions was associated with encoding of non-social source information, while only dorsomedial PFC activation distinguished between true and false information from social sources. No PFC regions displayed a significant subsequent memory effect for information from untrustworthy social sources, indicating that information from deceptive individuals is processed differently from true or false information from reliable sources.

17 Truth and subsequent source memory -17 Author Note Trey Hedden, Psychology Department, Stanford University; Angela H. Gutchess, Psychology Department, Harvard University and The Athinoula A. Martinos Center for Biomedical Imaging; Carolyn Yoon, Ross School of Business and Institute for Social Research, University of Michigan. Trey Hedden and Angela Gutchess are supported by NRSA fellowships from the National Institutes of Health. The authors thank Cory Crane, Ki Goosens, and the University of Michigan Functional Imaging Center. Address correspondence to: Trey Hedden, Psychology Department, 434 Jordan Hall, Building 420, Stanford University, Stanford, CA

18 Truth and subsequent source memory -18 Table 1. Behavioral memory performance. Correct Source False Alarms Failed Source M SD M SD M SD Inferred True Inferred False Stated True Stated False Note. False alarms indicate incorrect confident source attributions. Failed source memory is equivalent to (1 correct source).

19 Truth and subsequent source memory -19 Table 2. Activations related to subsequent memory for correct source > failed source MNI Coordinates Cluster Statistical Effects Anatomical Region L/R BA x Y z T size (k) S SxT SxM TxM SxTxM Superior Frontal Gyrus L Middle Temporal Gyrus L Superior Frontal Gyrus L * Inferior Frontal Gyrus L Middle Temporal Gyrus L Middle Frontal Gyrus L Parahippocampal Gyrus L Middle Temporal Gyrus L * Inferior Frontal Gyrus L Hippocampus R Uncus L Parahippocampal Gyrus L Parahippocampal Gyrus R Superior Frontal Gyrus L Cerebellum Parahippocampal Gyrus L Middle Frontal Gyrus L * Note. Statistics for peak voxels and surrounding ROIs from each significant cluster of activation. Clusters were identified from each contrast with an uncorrected threshold of p =.005, k = 11. Anatomical labels were derived from the location of the majority of gray-matter voxels within a cluster. Each cluster was defined as an ROI and was interrogated for activation in each of the six experimental conditions. Repeated-measure ANOVAs were performed to determine which ROIs displayed differential activity across conditions. No ROIs displayed a main effect of truth, while all ROIs had a significant main effect of subsequent memory. BA = Brodmann s Area, S = source type, M = subsequent memory effect, T = truth value. * p <.05 p <.10

20 Truth and subsequent source memory -20 Figure Captions Figure 1. Examples of stimuli used in each condition. Stimuli were health-related statements that consisted either of true or false information. Each statement was accompanied by either an explicitly stated declaration of its truth value, or was attributed to one of two individuals. One of these individuals was known to be trustworthy, and therefore all statements attributed to this individual were considered to be true. The other individual was known to be dishonest, so all statements attributed to this individual were considered to be false. Figure 2. Parameter estimates for MTL regions of interest. Parameter estimates attributable to each experimental condition were extracted and normalized to baseline activation. Statistics associated with each ROI are reported in Table 2. Error bars represent average within-subject standard error. The x-axis indicates baseline activation. MNI coordinates for each ROI are given in brackets. IT = socially inferred true, IF = socially inferred false, ST = explicitly stated true, SF = explicitly stated false. Figure 3. Parameter estimates for left PFC regions of interest. Parameter estimates attributable to each experimental condition were extracted and normalized to baseline activation. Statistics associated with each ROI are reported in Table 2. Error bars represent average within-subject standard error. The x-axis indicates baseline activation. MNI coordinates for each ROI are given in brackets. IT = socially inferred true, IF = socially inferred false, ST = explicitly stated true, SF = explicitly stated false.

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