Psychological Research DOI 10.1007/s00426-015-0725-2

ORIGINAL ARTICLE

Collaboration in implicit memory: evidence from word-fragment completion and category exemplar generation Clelia Rossi-Arnaud1 • Vincenzo Cestari1,2 • Valeria Rezende Silva Marques1,3 Giulia Bechi Gabrielli1 • Pietro Spataro1

•

Received: 14 May 2015 / Accepted: 8 November 2015 Ó Springer-Verlag Berlin Heidelberg 2015

Abstract Recent studies have begun to investigate the effects of collaboration on explicit tests such as free recall, cued recall, and recognition. In contrast, little is known about the impact of this variable on implicit memory. To bridge this gap, the present study compared the performance of nominal and collaborative groups in two implicit memory tasks—word-fragment completion (WFCT) and category exemplar generation (CEGT). Both the disruption-of-individual-retrieval-strategies and the retrieval blocking hypotheses predicted no significant negative effects of collaboration on repetition priming; in contrast, the retrieval inhibition hypothesis predicted lower priming in collaborative than in nominal groups in both tasks. The results supported the former hypotheses, because priming scores in the WFCT and the CEGT did not differ between collaborative and individual groups. Interestingly; however, a significant collaborative inhibition was obtained in the CEGT (but not in the WFCT) when considering the raw proportions of studied and unstudied exemplars generated. The latter finding might indicate that the performance of collaborative groups can be significantly impaired by the disruption of within-category order resulting from the exposure to the exemplars generated by other group members, even when participants do not explicitly attempt to retrieve the stimuli presented at encoding.

& Clelia Rossi-Arnaud [email protected] 1

Department of Psychology, Sapienza University of Rome, Via dei Marsi 78, 00185 Rome, Italy

2

Cell Biology and Neurobiology Institute, CNR, Rome, Italy

3

CAPES Foundation, Ministry of Education of Brazil, Brası´lia, Brazil

Introduction Research in experimental psychology has been traditionally focused on individuals working in isolation. However, in recent years, there has been a surge of interests in the effects of group collaboration on memory retrieval (Harris, Paterson, & Kemp, 2008; Rajaram, 2011; Rajaram & Pereira-Pasarin, 2010; see Barber, Rajaram, & Aron, 2010, and Foley, Fried, Cowan, & Bays, 2014, for studies examining the effects of collaboration on memory encoding). In these experiments, participants independently study a list of items and are later administered an explicit task such as free recall, to be performed either individually (i.e., working alone) or collaboratively (i.e., working in group). The main focus resides in the comparison between the memory performance of collaborative and nominal groups. In the latter, the recall products of individuals working alone are pooled together in a non-redundant way by counting repeated items only once (Basden, Basden, Bryner, & Thomas, 1997). The usual, but counterintuitive, finding is that collaborative groups recall fewer items than nominal groups, a phenomenon referred to as collaborative inhibition (Weldon & Bellinger, 1997). The classical explanation for this phenomenon is that collaboration interferes with the use of individual retrieval strategies (Basden et al., 1997; Weldon & Bellinger, 1997). According to the disruption-of-individual-retrieval-strategies (DIRS) hypothesis, the order of recall of each person follows an idiosyncratic organization of the studied information. The disruption occurs because participants in the collaborative condition must listen to the output of the other members of the group, which is often misaligned with their own retrieval organization. As a consequence, they would be induced to switch from their spontaneous retrieval strategies towards less effective ones, thereby

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reducing the accuracy of the recall performance (Rajaram, 2011; Rajaram & Pereira-Pasarin, 2010). One of the key predictions of the DIRS hypothesis is that collaborative inhibition should be reduced, or eliminated, when the group members are provided with retrieval cues that minimize their reliance upon individual strategies (Finlay, Hitch, & Meudell, 2000). In agreement, Finlay et al. (2000, Exp.2) asked their participants to try to memorize pairs of unrelated nouns like ‘‘chair-TRAIN.’’ In the free recall task, they were required to retrieve the response term of each pair (e.g., ‘‘TRAIN’’), either individually or in collaborative dyads, whereas in the cued recall task, the stimulus words (e.g., ‘‘chair’’) were represented and participants were instructed to use them to retrieve the corresponding response items. The results showed that collaborative dyads remembered significantly fewer words than nominal dyads in free recall but not in cued recall. Finlay et al. (2000) argued that collaborative inhibition was abolished in the cued recall task because participants were less likely to use retrieval strategies based on their subjective organization of the study list when each item was cued separately. That is, cuing restricted the scope for mutual disruption of retrieval strategies during collaboration. A similar explanation has been advanced to account for the absence of collaborative inhibition in recognition tasks (Clark, Hori, Putnam, & Martin, 2000; Rossi-Arnaud, Pieroni, Spataro, & Cestari, 2011). Clark et al. (2000), in particular, showed that collaboration facilitated the recognition of targets, although it had variable effects on the rejection of lures. The authors proposed that recognition minimizes the role of the retrieval disruption mechanisms that are at the origin of collaborative inhibition in free recall, because the to-be-remembered items are represented during the test phase, implying that the memory performance should be less dependent on the use of individual retrieval strategies. Rather, an increase in the hit rates only requires that a person makes a compelling argument for why she/he is correct about the evaluation of an item as old (Clark et al., 2000; Clark, Abbe, & Larson, 2006). At the same time, not all types of retrieval cues result in the elimination of collaborative inhibition. Basden et al. (1997, Exp.1), for instance, reported that collaborative inhibition persisted in a category cued recall task in which participants were told to use the category names to retrieve the exemplars studied during the encoding phase— although the collaborative deficit was significant when the categories were large (15 exemplars) but not when they were small (6 exemplars). Likewise, Meade and Roediger (2009) found collaborative inhibition for categorized lists of 17 exemplars tested with both free- and forced-report category cued recall (in the latter condition, participants were required to retrieve a fixed number of exemplars from

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each category, before proceeding to the next category). Basden et al. (1997) proposed that the negative effects of collaboration in this task were due to between-category shifting—i.e., the participants’ tendency to recall from a category different from that used by the previous participant. Such an explanation was supported by the finding that collaborative inhibition was eliminated when the group members were asked to retrieve from non-overlapping subsets of categories or to recall instances from a given category contiguously until recall output for that category was exhausted—two conditions that severely limited the possibility of category shifting (Basden et al., 1997). On the other hand, Meade and Roediger (2009) speculated that the use of high-taxonomic-frequency exemplars might have allowed participants to organize lists by category in all experimental conditions, rendering the cued recall task more susceptible to the negative impact of collaboration. This and other difficulties with the DIRS hypothesis (see Barber, Harris, & Rajaram, 2015, for more discussion) have led recent studies to investigate the possibility that additional mechanisms might also contribute to collaborative inhibition (Hyman, Cardwell, & Roy, 2013). Barber et al. (2015), in particular, tested the potential role of retrieval inhibition (a mechanism whereby the items produced by the group members during collaborative retrieval would cause long-term suppression of the remaining, unproduced items) and retrieval blocking (a mechanism whereby the continuous retrieval of the items already produced by other group members would block the conscious access to the representations of unproduced items). In their experiments, participants first collaborated to recall unshared lists of words; then, in a second phase, they were administered individual free recall and recognition tests. In line with the predictions of the retrieval inhibition hypothesis, the results showed that the negative effects of collaboration persisted in both individual tasks. However, consistent with the predictions of the DIRS hypothesis, the magnitude of collaborative inhibition was attenuated in recognition. While the impact of collaborative retrieval on explicit memory has been extensively investigated in literature (Rajaram, 2011), only one previous study has examined its effects on implicit memory (Andersson & Ro¨nnberg, 1996). Implicit tasks tap memories that are not available for conscious recollection (Tulving & Schacter, 1990); performance in these tests is typically measured via repetition priming—i.e., a facilitation in the accuracy and/or the speed of identification and generation of previously encoded (studied) vs. new (unstudied) items (Mulligan & Besken 2013). A distinction has been historically drawn between perceptually driven implicit tasks (such as wordfragment completion), which require the retrieval of the surface-level properties of the encoded stimuli, and

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conceptually driven implicit tasks (such as category exemplar generation), which require the retrieval of the meaning of the encoded stimuli (Franks, Bilbrey, Lien, & McNamara, 2000; Roediger & McDermott, 1993; Spataro, Cestari, & Rossi-Arnaud, 2011). In the only relevant study, Andersson and Ro¨nnberg (1996, Exp.2) compared the performance of nominal and collaborative groups in the perceptually driven task of dot pattern completion. During the encoding phase, participants studied visuospatial patterns consisting of five lines connecting five dots in a 3 9 3 matrix. In the indirect test, they received a booklet of 5-dot patterns, with two lines already drawn, and were told to complete each stimulus with the first pattern they saw. The matched explicit version was a forced-choice recognition task, in which participants had to select the studied patterns among four alternatives. The results showed that collaborative groups performed significantly worse than nominal groups in the recognition task—replicating the usual negative effect of collaborative inhibition on explicit memory; by contrast, priming scores in the implicit memory task did not differ between collaborative and nominal groups. Andersson and Ro¨nnberg (1996) interpreted their findings to be consistent with the DIRS proposal that the disruption of individual retrieval strategies occurs at the level of ‘‘conscious communication’’ between the group members (Basden et al., 1997; Weldon & Bellinger, 1997); under this framework, implicit memory is expected to be less susceptible to the negative impact of collaboration, because, by definition, the Perceptual Representation System, which underlies repetition priming in perceptually driven tasks, is dissociated from conscious retrieval (Tulving & Schacter, 1990). Importantly, however, testing the impact of collaboration in implicit memory tasks may also have consequences for assessing the validity of the retrieval inhibition and retrieval blocking hypotheses (Barber et al., 2015). From this perspective, the absence of collaborative inhibition in implicit memory tests (Andersson & Ro¨nnberg, 1996) appears to be more consistent with the blocking than the inhibition account. This is because the blocking hypothesis predicts that collaborative retrieval should block only the conscious access to the representations of the unproduced items; however, these representations continue to be available in long-term memory and are therefore susceptible to be indirectly primed. In contrast, the inhibition hypothesis predicts that the representations of the unproduced items should be subject to a persistent, long-term inhibition, no matter how memory is probed (Barber et al., 2015); hence, there should be no room for priming them effectively with indirect tasks. In the present study, we examined the effects of collaborative retrieval in the perceptually driven task of wordfragment completion (WFCT) and the conceptually driven task of category exemplar generation (CEGT). In the

WFCT, participants encode a list of unrelated words under incidental instructions and are later presented with a series of unique-solution fragments to be completed with the first words that come to mind (Mulligan & Hartman, 1996; Spataro, Mulligan, & Rossi-Arnaud, 2010; Spataro, Mulligan, Longobardi, & Rossi-Arnaud, 2012). Repetition priming is measured as an increase in the probability to complete fragments with previously encoded words, relative to a baseline completion rate with new, unstudied words. Similarly, in the CEGT, participants encode a categorized list of exemplars under incidental instructions and are later presented with a series of category names to be used to generate the first exemplars that come to mind (Light, Prull, & Kennison, 2000; Mulligan, 2012). Repetition priming is indicated by an increase in the probability of producing the exemplars encoded during the study phase, relative to a baseline generation rate of new, unstudied exemplars. Different predictions can be advanced. First, consideration of the results reported by Andersson and Ro¨nnberg (1996) suggests that, in both the WFCT and the CEGT, repetition priming should be equally high in nominal and collaborative groups: such a result would support the DIRS hypothesis that the disruption of retrieval strategies occurs only when participants consciously try to retrieve the encoded items from memory (Basden et al., 1997). A similar outcome is expected on the basis of the retrieval blocking hypothesis (Barber et al., 2015), because collaborative inhibition should block only the conscious access to the studied items not produced by other group members, leaving implicit memory unaffected. In sharp contrast, the retrieval inhibition hypothesis predicts that priming in collaborative groups should be reduced in both implicit tasks, reflecting a long-lasting inhibition of the memory representations of unproduced items (Barber et al., 2015).

Experiment 1 Experiment 1 begins our investigation by testing the effects of collaborative retrieval in the WFCT—a perceptually driven implicit task (Spataro et al., 2010, 2012).

Method Participants A sample of 105 students of the University Sapienza of Rome (35 triads) was tested in the WFCT (74 females; age: M = 22.4 years). Fifteen triads worked individually (nominal condition), whereas the other twenty triads worked collaboratively.

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Design and materials The Experiment followed a 2 (Item Type: studied vs. unstudied words) 9 2 (Group Condition: nominal vs. collaborative groups) factorial design, in which Item Type was the variable manipulated within-participants, and Group Condition was the variable manipulated betweenparticipants. Thirty words, 7–9 letters in length, were selected from the LexVar database (Barca, Burani, & Arduino, 2002). They were divided in two critical sub-lists of 15 target words each (A–B), equated as closely as possible on the following variables: length in letters (M = 7.80–7.73), written frequency (M = 74.47–79.33), age of acquisition (M = 4.21–4.13), familiarity (M = 6.01–6.13), imageability (M = 5.22–5.42), and concreteness (M = 5.88–6.08). Values of the latter four variables were obtained from the LexVar database, as measured on 7-point Likert scales, whereas the estimates of written frequency were taken from the CoLFIS vocabulary (Bertinetto et al., 2005). For each word, a unique-solution fragment was constructed by randomly removing three to five letters [e.g., ‘‘c _ r _ _ o _ ia’’ for ‘‘cerimonia’’ (ceremony)]. The mean ratios between the number of letters provided in the fragments and the total length of the words ranged from 0.40 to 0.57. Within each sub-list, eight fragments contained the initial letter, whereas it was omitted in the other seven fragments (the presence of the first letter accounts for a significant portion of variance in the completion probability scores: Dasi, Soler, & Ruiz, 2004). Both the words and the fragments selected for Experiment 1 had been employed in previous studies (Spataro et al., 2010, 2012). The words included in the two sub-lists, and the corresponding fragments, were used either during the encoding phase (as studied words) or in the test phase (as the fragments corresponding to unstudied words) to compute the baseline proportions of completion. The assignment of the sub-lists to the roles was counterbalanced across participants. Procedure Each group was tested separately in a soundproof cubicle. The three participants sat in front of the computer monitor, at a distance of approximately 50 cm. At the beginning of the session, they were given standard instructions explaining that the experiment consisted of a number of unrelated tasks investigating attentional and perceptual abilities. During the encoding phase, a total of 70 words were presented (15 target items plus 55 fillers). Each trial included a fixation point for 500 ms, a word for 3 s and a pause for 4 s. The three group members were given

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different tasks: they were requested to covertly count the number of consonants, vocals, and letters contained in each word and to report the results on appropriate response sheets. These encoding tasks were always performed individually and aimed at directing the participants’ attention towards the perceptual (orthographic) properties of the studied words (Roediger, Weldon, Stadler, & Riegler, 1992). Learning was incidental, since participants were not required to remember the words and no mention was made about the subsequent memory task. The assignment of the two critical sub-lists to the studied/unstudied roles was counterbalanced across groups. The study phase was immediately followed by a visuospatial distractor task, which lasted about 15 min. Next, the WFCT was administered. Participants were presented with a total of 50 fragments, corresponding to 15 target studied words (presented during the encoding phase), 15 target unstudied words (not presented during the encoding phase, but included in one of the two critical sub-lists), and 20 filler words randomly intermixed (not presented during the encoding phase and not scored). They were instructed to complete the fragments with the first words that came to mind, and no mention was made about the relationship with the encoding phase. The first and the last five fragments could never be completed with studied words. The task was time-constrained since each fragment remained on the screen for 10 s, during which participants attempted to provide the correct solution; it was preceded by a fixation point for 500 ms and followed by a pause for 3 s. In the nominal condition, each participant received a different response sheet and completed the task alone. In contrast, in the collaborative condition, participants were asked to work as a group and one person was randomly chosen to record the joint output in a single response sheet. Following Weldon and Bellinger (1997), no specific instructions were given about the modalities of collaboration, and turn-taking was not explicitly required, favoring free-flowing discussion. To assess the possible confound due to explicit contamination, at the end of the WFCT each participant responded to a question intended to probe the use of intentional retrieval strategies (‘‘Did you intentionally retrieve the studied words when completing the fragments?’’) (Bowers & Schacter, 1990). Groups were classified as ‘‘intentional’’ if at least one of the three members responded ‘‘yes’’ to the latter question.

Results and discussion In the nominal condition, the responses of the three participants working alone were pooled together, with redundant items counted only once (Basden et al., 1997;

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Weldon & Bellinger, 1997). That is, if participant 1 completed the fragments corresponding to the target studied words A, C, D, and participant 2 completed the fragments corresponding to the target studied words B, D, E, their pooled performance was: A ? B ? C ? D ? E. This procedure was applied to both studied and unstudied words. The proportions of fragments completed with target studied and unstudied words (see the upper panel of Fig. 1) were analyzed through a mixed 2 (Item Type: studied vs. unstudied) 9 2 (Group Condition: nominal vs. collaborative groups) ANOVA. The results revealed only a significant main effect of Item Type [F(1, 33) = 89.27, MSE = 0.013, p \ 0.001, g2p = 0.73], indicating better overall performance for studied than for unstudied words [M = 0.56 vs. M = 0.30]—i.e., a significant priming effect was obtained. Neither the main effect of Group Condition (F \ 1) nor the interaction between Item Type and Group Condition reached the significance level [F(1, 33) = 2.78, p = 0.12], indicating that priming scores (i.e., the differences between the proportions of fragments completed with studied words minus the proportions of fragments completed with unstudied words) were equivalent in nominal and collaborative groups [M(nominal) = 0.22 vs. M(collaborative) = 0.31]. As illustrated in Fig. 1, the two groups differed neither in the proportions of fragments completed with studied words [M(nominal) = 0.54 vs. M(collaborative) = 0.59; t(33) = - 1.01, p = 0.32] nor in the proportions of fragments completed with unstudied words [M(nominal) = 0.32 vs. M(collaborative) = 0.28; t(33) = 1.10, p = 0.28]. A follow-up analysis was conducted by taking into account only the data from unintentional groups (i.e., those groups in which all three members denied the use of intentional retrieval strategies) (see the lower panel of Fig. 1). Twenty-four groups satisfied this condition, 14 in the nominal condition and 10 in the collaborative condition. However, the results of the ANOVA did not change, since the main effect of Group Condition and the two-way interaction between Item Type and Group Condition fell again below the significance level [F \ 0.07, p [ 0.79], confirming that priming scores did not differ between the two groups, M(nominal) = 0.22 vs. M(collaborative) = 0.24. A similar conclusion was reached when the priming differences between nominal and collaborative groups were analyzed with a non-parametric test (which is more appropriate with small samples), Mann–Whitney U = 65.50, p = 0.79. In summary, the results of Experiment 1 showed that repetition priming in the WFCT did not differ between nominal and collaborative groups. In the overall analysis, which included both intentional and unintentional

participants, there was a non-significant numerical trend towards greater priming in collaborative than in nominal groups, which echoes the collaborative facilitation reported by Clark et al. (2000) in recognition memory (see MacLeod & Kampe, 1996, for a discussion of the similarities between WFCT and recognition tasks). However, this numerical advantage disappeared when the analysis was limited to unintentional participants, confirming that the Perceptual Representation System does not depend on the same conscious retrieval processes that underlie recognition memory (Tulving & Schacter, 1990; Tulving, Schacter, & Stark, 1982).

Experiment 2 Experiment 2 sought to replicate the results of Experiment 1 in the CEGT, a conceptually driven task. To reiterate our hypotheses, only the retrieval inhibition hypothesis predicted lower priming in collaborative than in nominal groups (Barber et al., 2015), whereas the DIRS and the retrieval blocking hypotheses predicted equal priming levels in the two groups.

Method Participants A different sample of 72 students of the University Sapienza of Rome (24 triads) was recruited for the CEGT. They were 15 males and 57 females (mean age: M = 23.4 years). Twelve groups worked individually, whereas the other twelve groups worked in the collaborative condition. Materials Ten exemplars were selected from each of 14 categories (animals, colors, fruits, emotions, flowers, occupations, vegetables, diseases, geometrical shapes, trees, musical instruments, sports, atmospheric phenomenon, body parts), yielding a critical set of 140 target words. The mean scores of taxonomic frequency ranged from 20.7 to 43.2 (the maximum possible value being 200), as assessed on the basis of the Boccardi and Cappa’s (1997) norms for Italian language. This database reports, in descending order of taxonomic frequency, all the exemplars spontaneously produced by 200 Italian-speaking university students between 18 and 25 years in response to single category labels (e.g., frutta [fruit]). None of the exemplars selected for the present study ranked among the six most common

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Fig. 1 Experiment 1: mean proportions of fragment completion, as a function of Item Type (studied vs. unstudied words) and Group Condition (nominal vs. collaborative groups), for all groups (upper panel) or only the unintentional groups (lower panel). Bars represent standard errors. WFCT word-fragment completion task

category members. There was substantial variability in both the length and the written frequency of critical words (between 4 and 11 letters for length and between 6.8 and 50.5 occurrences for frequency, with the latter values drawn from the CoLFIS vocabulary). Each category was further divided into two sub-sets of 5 exemplars (A and B), to counterbalance items across old and new conditions. Procedure The encoding procedure was similar to that illustrated in Experiment 1. Participants were presented with a total of 70 exemplars (5 members from each of the 14 critical categories). Each trial included a fixation point (a black cross at the center of the screen) for 500 ms, a word for 3 s, and a pause for 4 s. The tasks were again to covertly count the number of consonant, vocals, and letters contained in each word (Roediger et al., 1992) and to report the results on appropriate response sheets. As in Experiment 1, learning was incidental. In both the nominal and collaborative conditions, half of the groups studied the exemplars included in the list A, while the exemplars of the list B were used to compute the baseline proportions of category generation; for the remaining groups, the assignment of the lists to the studied/unstudied roles was reversed. The order of exemplars in the study lists was randomized anew for each group.

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Following the study phase, participants were involved in the same 15-min distractor task employed in Experiment 1. Next, the CEGT was administered. Each trial began with a fixation point for 500 ms, followed by a category name (e.g., ‘‘FRUIT’’), which remained on the screen until participants produced the first ten exemplars that came to mind (to be sure that exemplars other than the most common were generated: Mulligan, 2012). A total of 20 category names were presented, corresponding to 6 practice categories (at the beginning of the task) plus 14 studied categories. No mention was made about the relationship between the study and test phases. In the nominal condition participants worked alone and wrote their responses on separate sheets. In contrast, in the collaborative condition they were asked to work as a group and one person was randomly chosen to record the collective output in a unique response sheet. As in Experiment 1, no specific instructions were given about the modalities of collaboration, and turntaking was not explicitly required, favoring free-flowing discussion (Rajaram & Pereira-Pasarin, 2007;Weldon & Bellinger, 1997). At the end of the CEGT, participants responded to the same question illustrated in Experiment 1, to assess retrieval intentionality.

Results and discussion As in Experiment 1, the responses of the three participants working in the nominal condition were pooled together, with redundant items counted only once (Basden et al., 1997; Weldon & Bellinger, 1997). This procedure was applied to both studied and unstudied exemplars. The proportions of correct generation (see Fig. 2, upper panel) were submitted to a mixed 2 (Item Type: studied vs. unstudied) 9 2 (Group Condition: nominal vs. collaborative) ANOVA, which found significant main effects of both Item Type [F(1, 22) = 168.31, MSE = 0.005, p \ 0.001, g2p = 0.88] and Group Condition [F(1, 22) = 61.63, MSE = 0.004, p \ 0.001, g2p = 0.73], indicating that performance was greater for studied than for unstudied exemplars (a significant priming effect was obtained: M = 0.49 vs. M = 0.23) and greater for nominal than for collaborative groups (M = 0.43 vs. M = 0.29). However, the two-way interaction between the two variables did not reach the significance level [F(1, 22) = 1.85, p = 0.18], suggesting that repetition priming did not differ between nominal and collaborative groups [M(nominal) = 0.28 vs. M(collaborative) = 0.23; t(22) = -1.36, p = 0.19]. Only four groups were classified as intentional in the CEGT—two nominal and two collaborative triads. When these groups were eliminated from analysis, the results did not change (see Fig. 2, lower panel). In particular, the main

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exemplars recalled [M = 0.65 vs. M = 0.53, t(22) = 2.95, p = 0.007] and in the mean number of exemplars recalled per category [M = 3.28 vs. M = 2.71, t(22) = 2.78, p = 0.011], thus replicating the results reported by Basden et al. (1997) and Meade and Roediger (2009).

General discussion

Fig. 2 Experiment 2: proportions of exemplars generated, as a function of Item Type (studied vs. unstudied words) and Group Condition (nominal vs. collaborative groups), for all groups (upper panel) or only the unintentional groups (lower panel). Bars represent standard errors. CEGT category exemplar generation task

effect of Group Condition and the two-way interaction between Item Type and Group Condition continued to fall below the significance level [F \ 1.36, p [ 0.29]. To summarize, the results of Experiment 2 confirmed those obtained in the WFCT, because repetition priming was not affected by collaborative inhibition, consistent with the predictions of the DIRS and retrieval blocking hypotheses (but in contrast with the predictions of the retrieval inhibition hypothesis). Interestingly, however, the raw proportions of studied and unstudied exemplars generated by collaborative groups were significantly lower than those generated by nominal groups (we will discuss this finding in more details in the General discussion). It is unlikely that the absence of significant effects of collaboration on CEGT priming reflects a general ineffectiveness of our experimental manipulation, because we obtained the standard collaborative inhibition when using an explicit category cued recall task. For this follow-up experiment, we tested an independent sample of 24 triads (20 males and 52 females; mean age: 22.8 years)—12 in the collaborative condition and 12 in the nominal condition. The procedure was the same as that illustrated for the CEGT, with the exception that at the time of test participants were told to use the category labels to retrieve the exemplars presented at encoding. A series of t tests for independent samples showed that nominal groups outperformed collaborative groups in the total proportions of

The present study investigated the effects of collaborative retrieval in two verbal implicit tasks, the WFCT (perceptually driven) and the CEGT (conceptually driven). The results showed that repetition priming did not differ between nominal and collaborative groups in both tests, confirming and extending to verbal implicit memory the conclusions previously reached by Andersson and Ro¨nnberg (1996). Motivational explanations, such as evaluation apprehension, free riding (the feeling that one’s own contribution is less identifiable and more dispensable when working in group: Diehl & Stroebe, 1987) and social loafing (Weldon & Bellinger, 1997; Weldon, Blair, & Huebsch, 2000), cannot be easily reconciled with our findings, because these mechanisms are expected to be at work with both explicit and implicit memory tasks. As illustrated above, the DIRS hypothesis can account for the absence of collaborative inhibition in implicit memory, because it assumes that the performance decrease typically observed in collaborative groups depends on the disruption of consciously adopted retrieval strategies which occurs when participants are exposed to the recall products of the other group members (Basden et al., 1997; Finlay et al., 2000). By definition, implicit memory processes are not available to conscious recollection (Tulving & Schacter, 1990) and thus are expected to be immune to the negative consequences of collaboration (Andersson & Ro¨nnberg, 1996). In a similar vein, the retrieval blocking hypothesis proposes that the repetitive recall of the items already produced by the other group members leads to a blocking of the conscious access to the representations of unproduced items (Barber et al., 2015). However, these representations continue to be available in memory, meaning that they can be primed in indirect tasks. Distinction between these two perspectives awaits future research. On the other hand, our data are clearly in contrast with the predictions following from the retrieval inhibition account (Barber et al., 2015). More specifically, the fact that priming was not reduced in collaborative groups suggests the conclusion that collaboration does not produce a permanent inhibition of the representations of studied items—if this were the case, a significant collaborative deficit should have been apparent even in implicit tasks. In this respect, it is worth noting that the use of both perceptually and conceptually driven implicit tests allowed us

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to rule out a variant of the retrieval inhibition hypothesis borrowed from past research about two well-known effects that bear close similarity with the memory deficit observed in collaborative groups—namely, the part-set cuing effect (the fact that providing people with a partial set of studied items impairs recall for the remaining items: Nickerson, 1984) and the retrieval-induced forgetting effect (the fact that retrieving a partial set of items lowers recall for the remaining items: Anderson, Bjork, & Bjork, 1994). The similarity between these two effects and collaborative inhibition is due to the fact that, in all cases, a subset of previously encoded items is provided to participants before or during the memory performance (Barber et al., 2015). As concerns retrieval-induced forgetting, Perfect, Moulin, Conway, & Perry (2002) found that poorer performance for unpracticed items was observed in the implicit conceptually driven tasks of category generation and category verification, whereas the effect did not occur in the perceptually driven tasks of perceptual identification and word stem completion (see Butler, Williams, Zacks, & Maki, 2001, for a similar result with word-fragment completion). Data on the effects of part-set cuing in implicit memory are more sparse. However, Sloman (1991) and Watkins and Allender (1987) reported a significant negative impact of part-set cuing in the category generation task, whereas Basden, Basden, Church, & Beaupre (1991) and Peynirciog˘lu and Moro (1995) reported no influence or even a facilitation (for participants who did not use explicit retrieval strategies) in word-fragment completion. Taken together, these two lines of investigation suggest the possibility that collaboration during the retrieval phase may inhibit the conceptual, but not the perceptual, traces of the studied items. Our results are inconsistent with this modified version of the retrieval inhibition hypothesis, because the CEGT is clearly a conceptually driven task and yet priming was unaffected by group collaboration. At the same time, a significant inhibitory effect was observed in the raw proportions of exemplars generated in the CEGT. The fact that this collaborative inhibition held for both studied and unstudied exemplars suggests that it cannot be solely considered as a memory effect. As previously mentioned, the DIRS hypothesis suggests that collaborative inhibition should be minimized when participants are provided with an effective structure which supports retrieval (Clark et al., 2000; Finlay et al., 2000). However, different types of retrieval cues provide different levels of retrieval support. Word fragments severely constrain memory search to a limited number of solutions (Weldon, 1993; Nelson, Canas, Bajo, & Keelean, 1987) and virtually eliminate the utility of using retrieval strategies. In contrast, asking participants to generate exemplars exhaustively from single category eliminates the disruption produced by between-category switching (the mechanism

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that, according to Basden et al. (1997), produces collaborative inhibition in the category cued recall task) but does not reduce the potential disruption produced by the alteration of within-category order (Basden et al., 1997). Unlike Basden et al. (1997), Meade and Roediger (2009) showed that collaborative groups remembered fewer studied exemplars than nominal groups even when the cued recall task was blocked by category. Thus, the question of whether the exposure to the exemplars produced by other group members interferes with the individual within-category order of retrieval awaits further clarification. In the case of the CEGT, a mechanism similar to the alteration of withincategory order might occur both when sampling exemplars from a subset of studied items and when retrieving unstudied exemplars from semantic memory. However, the reasons of the discrepancy with the Basden et al. (1997)’s results remain unclear. Category size might be a potential moderator, because it has been shown that the size of collaborative inhibition is greater with large than with small categories (Basden et al., 1997, Exp.1). However, we obtained significant inhibitory effects when presenting only 5 exemplars during the study phase, whereas Meade and Roediger (2009) obtained similar results by presenting 17 exemplars. Thus, the disruption of within-category order appears to be equally effective with small and large categories. A second possibility is that discrepancies in the results are driven by differences in the taxonomic frequency of studied exemplars. Meade and Roediger (2009) speculated that the use of high-taxonomic-frequency exemplars increased the participants’ tendency to encode study lists by category—a factor which in turn enhanced the susceptibility to collaborative inhibition (Basden et al., 1997, employed low-taxonomic-frequency exemplars). In the present study taxonomic frequency was medium to low, suggesting that this second explanation cannot fully account for the overall pattern of results. Finally, a third variable to be considered is the type of procedure (turntaking vs. unstructured) adopted during collaboration. Thorley and Dewhurst (2007) reported that collaborative false recall was significantly higher when using a turntaking procedure, as compared with a free-flowing, unstructured procedure. However, both the studies by Basden et al. (1997) and Meade and Roediger (2009) utilized a turn-taking method, whereas we adopted an unstructured method1. Hence, an explanation in terms of procedural differences seems to be unconvincing. Clearly, additional research is needed to clarify this issue.

1

The conversations between the members of collaborative groups could not be recorded for technical reasons in the area in which participants were tested, and thus, we cannot judge the extent to which they adopted a turn-taking procedure.

Psychological Research

Collaborative inhibition in the proportions of unstudied exemplars generated in the CEGT represents a novel finding in the literature concerning collaborative inhibition, since previous studies have always examined the recall of studied exemplars (Basden et al., 1997; Meade & Roediger, 2009). In many respects, the request to produce new exemplars from an unstudied category resembles a semantic task. Extant research suggests that the retrieval of shared, semantic information from long-term memory is less vulnerable to the negative effects of collaboration, when compared with the retrieval of episodic information (Harris, Keil, Sutton, Barnier, & McIlwain, 2011). In an episodic task, the group members cannot cue each other efficiently, because the best cues for retrieval of an event are those self-generated by each individual (based on the encoding specificity principle: Tulving & Thomson, 1973). As mentioned above, the result of such a deficit of communication is that participants tend to give up their idiosyncratic strategies of retrieval in favor of different, sub-optimal strategies (Basden et al., 1997; Weldon & Bellinger, 1997). In contrast, shared knowledge does not need to be cued with the same precision to promote or reinstate effective retrieval (Andersson & Ro¨nnberg, 1996). The reason is that, in a semantic task, the collaborating members will activate similar, shared cognitive representations: in these conditions, if one of the participants knows the correct response, communication between the group members will affect the success of retrieval to a minimal extent. In agreement, Andersson and Ro¨nnberg (1996, Exp.1) found that collaboration did not reduce performance in a semantic retrieval task in which participants were requested to answer Swedish history questions, and Harris et al. (2011) reported that nominal and collaborative couples of older spouses recalled a similar amount of names from their Rotary or Probus club. The present results are inconsistent with these data, but may support other evidence indicating that, when asked to recall lists of categorized words, collaborative groups display more limited exploration than nominal groups (Hyman et al., 2013). Although in this study the notion of limited exploration was taken to reflect the tendency of collaborative groups to sample items from a restricted number of categories, it might potentially extend to indicate the tendency to spontaneously sample a lower number of exemplars from the same category. In conclusion, we must note that the present study has a number of limitations. First, we did not test the performance of nominal and collaborative groups in the explicit versions of the WFCT (word-fragment cued recall) and CEGT (category cued recall) using a within-group design (although in the Discussion of Experiment 2 we reported the results of a follow-up experiment testing explicit memory in an independent sample of triads), and thus, we could not assess the question of whether retrieval support moderates the effects of collaborative inhibition in explicit memory. Working

retrospectively, we expected a significant negative influence of collaboration in the explicit version of he CEGT, but no inhibition or even a facilitation in the explicit version of the WFCT (Basden et al., 1997; Finlay et al., 2000). Second, a high number of collaborative groups reported to have employed explicit retrieval strategies in Experiment 1. This finding was unexpected and was not replicated in Experiment 2, although we can speculate that the members of collaborative groups might have been more likely to share their ideas about the real aims of the study, perhaps leading to mutual contamination. Lastly, the two tasks differed substantially in their time constraints, since the fragments in the WFCT were to be completed within 10 s, whereas in the CEGT, the category labels remained on the screen until participants produced 10 exemplars. We cannot exclude the possibility that this methodological confounding influenced the present findings, although the similarity in the priming results argues against this hypothesis. Despite these limitations, our study extends current knowledge about the memory effects of retrieval collaboration by showing that repetition priming in two verbal implicit tasks was unaffected by collaborative inhibition. This finding supports the DIRS proposal that the detrimental effects of collaboration depend upon the use of conscious retrieval strategies but is in contrast with the notion that collaboration inhibit the representations of unproduced stimuli (Andersson & Ro¨nnberg, 1996; Barber et al., 2015). In addition, we found that, compared to nominal groups, collaborative groups produced a lower number of studied and unstudied exemplars. To account for these results, we speculated that the performance of collaborative groups was significantly impaired by the disruption of within-category order resulting from the mutual exposure to the exemplars generated by other members (Basden et al., 1997; Meade & Roediger, 2009).

Notes 1.

The conversations between the members of collaborative groups could not be recorded for technical reasons in the area in which participants were tested, and thus, we cannot judge the extent to which they adopted a turn-taking procedure.

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