That s a good idea, but let s keep thinking! Can we prevent our initial ideas from being forgotten as a consequence of thinking of new ideas?

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1 Psychological Research (2017) 81: DOI /s ORIGINAL ARTICLE That s a good idea, but let s keep thinking! Can we prevent our initial ideas from being forgotten as a consequence of thinking of new ideas? Annie S. Ditta 1 Benjamin C. Storm 1 Received: 29 September 2015 / Accepted: 19 April 2016 / Published online: 28 April 2016 Ó Springer-Verlag Berlin Heidelberg 2016 Abstract Four experiments examined participants ability to remember their own ideas in a modified Alternative Uses Task. Participants were asked to generate uses for objects, and on half of the trials participants were then asked to think of more uses. Memory for the initial uses they generated was then tested via a cued-recall task. Results demonstrated that participants forgot their initial uses as a consequence of thinking of new uses (referred to as the thinking-induced forgetting effect), and this effect persisted even when participants chose the subset of uses they thought were the most creative and to be remembered. The only scenario in which uses were protected from forgetting was when they were required to use their uses as hints for generating more ideas. Together, these findings demonstrate that one s own ideas are susceptible to forgetting when additional ideas must be generated, indicating that thinking is a modifier of memory despite one s motivation to preserve their ideas. Introduction The concept of creativity may seem nebulous and elusive, but it can be studied in the same way that any other cognitive phenomenon can be studied (Smith & Ward, 2012). When we generate a new idea or solve a problem, we do so by retrieving, connecting, and synthesizing information in memory, building on what we already know to create & Annie S. Ditta aditta@ucsc.edu 1 Psychology Department, University of California, Social Sciences II, Room 145, 1156 High Street, Santa Cruz, CA 95064, USA something new and useful to the situation at hand. Indeed, one might argue that creativity is at the very core of cognition. Whether in the context of remembering, solving problems, or generating ideas, the goal of cognition is often not to reduplicate, but to create something new (e.g., Bartlett, 1932; Schacter & Addis, 2007). In this way, the scientific study of creativity is not of incidental interest it is of critical import to developing a more complete theoretical understanding of human cognition. One challenge to thinking of new and creative ideas is the need to avoid reproducing old and inappropriate ideas. Although a certain degree of domain knowledge and experience is often necessary for creativity, this knowledge and experience can also serve as a source of mental fixation (Smith, 1995, 2003, 2008; Ward, Smith, & Finke, 1999). For example, the ability to solve problems or think of new and creative ideas can be impeded or constrained by what we already know (e.g., Duncker & Lees, 1945; Luchins & Luchins, 1959; Smith & Blankenship, 1989; Smith, Ward, & Schumacher, 1993; Wiley, 1998; but see, Sio, Kotovsky, & Cagan, 2015). One way people have been shown to be able to overcome mental fixation is by taking advantage of an incubation period, which typically involves time off from a task, allowing the heightened accessibility of information in memory or prior experience to dissipate (Smith & Blankenship, 1989; 1991; Vul & Pashler, 2007). More recently, research has suggested that we may rely on more active and goal-directed forms of forgetting to facilitate creativity, such as through processes related to inhibitory control (e.g., Angello, Storm, & Smith, 2015; Koppel & Storm, 2014; Storm & Angello, 2010; Storm, Angello, & Bjork, 2011; Storm & Patel, 2014). One form of goal-directed forgetting that has been implicated in the ability to overcome mental fixation is that of retrieval-induced forgetting (Anderson, Bjork, & Bjork,

2 Psychological Research (2017) 81: ). In studies of retrieval-induced forgetting, participants are exposed to category exemplar word pairs (e.g. fruit lemon, drinks gin, fruit orange, drinks beer) and then guided to retrieve (via repeated retrieval practice) a subset of the exemplars from a subset of the categories (e.g., fruit l ). Later, when a final test is administered, memory for unpracticed items from practiced categories (e.g., orange) is worse than for unpracticed items from unpracticed categories (e.g., gin, beer). Although the phenomenon of retrieval-induced forgetting has now been observed in a multitude of contexts and with a wide range of materials (Storm et al., 2015), theoretical explanations remain in contention. According to the inhibition account, which has garnered substantial support in recent years, retrieval-induced forgetting is caused by an inhibitory process that acts to resolve competition from non-target items that become inappropriately activated during retrieval practice (e.g., Anderson, 2003; Storm & Levy, 2012). Competing theoretical explanations have argued that forgetting is the consequence of non-inhibitory mechanisms such as strength-based interference and inappropriate contextual cuing (Jonker, Seli, & MacLeod, 2013; Raaijmakers & Jakab, 2013). After quantitatively reviewing the existing literature, Murayama, Miyatsu, Buchli, and Storm (2014) concluded that retrieval-induced forgetting is likely to be a multifarious phenomenon, resulting from multiple mechanisms with the particular role of any specific mechanism dependent on the nature of the paradigm employed to measure it, but that the preponderance of the evidence seems to suggest that inhibition plays at least some role in causing retrieval-induced forgetting. Storm (2011) has argued that the inhibitory process presumed to underlie retrieval-induced forgetting should facilitate performance on any type of task in which old and irrelevant information interferes with the task objective. In support of this conjecture, retrieval-induced forgetting has been found to correlate with measures of working memory capacity (Aslan & Bäuml, 2011), stop-signal reaction time (Schilling, Storm, & Anderson, 2014), and the ability to generate more positive than negative autobiographical memories (Storm & Jobe, 2012). Perhaps most germane to the present research, retrieval-induced forgetting has also been shown to predict one s capacity to overcome mental fixation. For example, individuals who exhibit greater levels of retrieval-induced forgetting are significantly better at overcoming the fixating effect of prior exposure to inappropriate word pairs while solving problems on the Remote Associates Test (Koppel & Storm, 2014; Storm & Angello, 2010). Moreover, providing further support for the role of inhibition in this problem-solving context, Storm et al. (2011) showed that inappropriate pairs are forgotten as a consequence of attempting to solve problems, a finding they referred to as problem-solving-induced forgetting. The role of inhibition and forgetting in overcoming fixation does not appear limited to solving problems on the Remote Associates Test. Even performance on divergent thinking tasks, such as the Alternative Uses Task (AUT; Guilford, 1957), may have the potential to benefit from the ability to set aside and forget inappropriate information. In the AUT, participants are asked to think of new (and sometimes unusual) uses for common household objects (e.g., a spoon). The task is believed to measure the creative ability to generate new ideas that are different from those that are most typical. One factor that would seem to limit performance on the AUT is the relative accessibility of typical uses. Generating new and unusual uses for a spoon, for example, may be difficult, at least in part, because standard uses for a spoon (e.g., eating something with a liquid component) are already so familiar. If these common and more familiar uses interfere with the ability to generate new uses, then an inhibitory mechanism, such as the one which has been argued to underlie retrieval-induced forgetting and problem-solving-induced forgetting, may also play a role in the AUT by providing a means by which to decrease the accessibility of such uses. Storm and Patel (2014) examined this idea with a modified version of the AUT in which participants were asked to study four example uses for an object before attempting to think of new uses for that object. The example uses were intended to cause fixation by making the generation of new uses more difficult than it would have been otherwise. Storm and Patel predicted that to overcome this fixation, participants would need to inhibit the example uses, thus causing them to be forgotten (i.e., thinking-induced forgetting). Across four experiments, that is precisely what was observed. Participants were significantly less likely to remember example uses after generating new uses for an object than they were when they did not generate new uses for that object. In other words, thinking of new uses caused the forgetting of old uses. Interestingly, the only condition in which participants failed to exhibit thinking-induced forgetting was when they were explicitly instructed to use example uses as hints to guide their generation of new uses, presumably because such instructions made the example uses function more as mediators than as competitors, thus helping participants to think of new uses instead of preventing them from being able to do so. Are our own ideas susceptible to thinking-induced forgetting? There has been a great deal of research on the ways in which people generate creative ideas, but there has been very little research on the ways in which people remember

3 680 Psychological Research (2017) 81: (and forget) their creative ideas. For example, a particularly frustrating experience shared by the present authors in particular is that of generating a new thought or important insight and then subsequently forgetting that thought or insight before being able to take advantage of it. This often occurs in the context of lab meetings. We might think of a new idea for an experiment, agree that it would be a great avenue for future research, and then proceed with our lab meeting assuming that we will be able to remember that idea. Much to our chagrin, however, as exciting and as important of an idea as it might have been, we later find ourselves at a loss to retrieve it. This form of forgetting may be attributable, at least in part, to the fact that we continued to think of new ideas and engage in lab discussions after generating the idea, thus providing an opportunity for the idea to be subject to thinking-induced forgetting. The work by Storm and Patel (2014) demonstrated that example ideas are forgotten as a result of attempting to think of new ideas, but are our own ideas susceptible to this type of forgetting? Moreover, does the importance or subjective value of an idea mitigate such effects? Are ideas that we believe to be particularly important, creative, or to-be-remembered less likely to suffer thinking-induced forgetting than ideas that we believe are unimportant or forgettable? There is some evidence that memory can be enhanced by the motivation to remember, but such effects generally arise when motivation is manipulated before encoding (e.g., Kassam, Gilbert, Swencionis, & Wilson, 2009; Loftus & Wickens, 1970; Naveh-Benjamin, Craik, Gavrilescu, & Anderson, 2000). Moreover, even if motivation to remember leads to an overall benefit for memory, it may not necessarily do so in a way that protects from thinkinginduced forgetting. Indeed, research on retrieval-induced forgetting has shown that information we want to remember can actually be more susceptible to forgetting than information we want to forget, presumably because it is the information we want to remember that is most likely to interfere with retrieval practice and thus prompt the need for inhibition to reduce the accessibility of items causing such interference (Bäuml & Samenieh, 2010; Storm, Bjork, & Bjork, 2007). In the context of generating and remembering our own ideas, therefore, the ideas we want to remember may be, if anything, more susceptible to thinking-induced forgetting than the ideas we do not want to remember. Of course, there are also reasons to think that our own ideas and particularly those ideas that we value most might be protected from thinking-induced forgetting. Information that is either highly distinctive or wellintegrated with a person s personal or general knowledge, for example, has been shown to suffer less retrieval-induced forgetting than information that is less distinctive and less well-integrated (e.g., Anderson & McCulloch, 1999; Carroll, Campbell-Ratcliffe, Murnane, & Perfect, 2007; Dunn & Spellman, 2003; Goodmon & Anderson, 2011; Macrae & Roseveare, 2002; Migueles & García- Bajos, 2007; Smith and Hunt, 2000). Moreover, people might be more likely to use their initially generated ideas to facilitate the generation of new ideas, a condition under which Storm and Patel failed to observe thinking-induced forgetting. We investigated these and other questions in the present research by adapting the paradigm employed by Storm and Patel (2014). Specifically, rather than having participants study examples of uses for objects and then generate new uses for half of those objects, we instructed participants to generate their own initial uses for objects and then to generate additional uses for half of those objects. If thinking-induced forgetting is observed in this context, then initially generated uses should become less recallable when participants attempt to think of new uses for an object than when they do not. To our knowledge, this study is the first to examine a potential mechanism by which we forget our own creative ideas. Experiment 1 The goals of Experiment 1 were twofold: first, to explore whether our own ideas are susceptible to thinking-induced forgetting; and second, if thinking-induced forgetting is observed, to explore whether ideas that are identified as being creative and to-be-remembered are protected from such forgetting. If certain uses are identified as creative standouts, for example, and deemed important to be remembered for a subsequent test, would those items be spared from the deleterious consequences of attempting to think of new ideas? In Experiment 1, participants completed eight experimental trials (four thinking and four baseline; presented in a randomized order) and a final cued-recall test. At the beginning of each trial, participants were shown a common household object (e.g., brick) and instructed to come up with four creative/unusual uses for that object, which they were told they would later be asked to recall. On thinking trials, participants were then given 90 s to think of additional uses for that object. They were specifically told to think of new uses that were unrelated to those they had previously generated. On baseline trials, after coming up with the initial four uses, participants simply moved on to the next trial. Upon completion of the eight trials, a cuedrecall test was administered to test participants memory for the initial uses they had generated. Half of the participants were given special instructions such that after they generated four uses for a given object, the researcher identified two of the generated uses as being

4 Psychological Research (2017) 81: very creative and specifically instructed the participants to remember those uses while indicating that it was not important to remember the other two, non-selected uses. Unbeknownst to participants, the two uses selected as being particularly creative were chosen at random, thus allowing us to ascertain whether uses identified as being creative and important to remember though identical otherwise might be differentially affected by thinkinginduced forgetting than uses not identified as such. The other half of the participants were not given any special instructions, and were, thus, expecting to be tested on all four of the uses they generated for each object. In line with the results of Storm and Patel (2014), we predicted that initial uses associated with thinking trials would be recalled less well than initial uses associated with baseline trials. Additionally, based on research showing that the intention to remember does not protect items from retrieval-induced forgetting (e.g., Bäuml & Samenieh, 2010; Storm et al., 2007), we predicted that selected uses would be just as susceptible to thinking-induced forgetting as non-selected uses. These results would provide further evidence of thinking-induced forgetting and suggest that such forgetting can extend to the ideas we generate ourselves. Method Participants A total of 96 undergraduate participants (M age = 19.5) were recruited from the University of California, Santa Cruz (UCSC) subject pool and compensated with partial credit in a psychology course. Materials The materials were adapted from the AUT in which participants are asked to think of uses for common household objects. We selected the same eight objects used by Storm and Patel (2014): brick, spoon, newspaper, bucket, coat hanger, rubber band, paperclip, and screwdriver. Procedure The experiment was conducted in two phases: a generation phase, and then a final recall phase. In the generation phase, participants were shown each of the eight objects one at a time on a computer screen and were asked to come up with four uses for those objects, which they wrote down on a sheet of paper. They were given as much time as needed to accomplish this task, but most finished each object within 1 2 min. If a participant struggled to come up with four uses, they were encouraged to write anything that came to mind. Half of the participants were instructed to remember all four of the uses they came up with during this generation phase (hereafter referred to as the remember-all condition), while the other half were told to remember a subset of the four uses (hereafter referred to as the selection condition). Specifically, in this latter condition, after participants generated their four uses, the experimenter looked over the uses and placed checkmarks next to two of them, indicating that those two uses were very creative and that it was very important for the participant to remember those uses (hereafter referred to as selected uses ) for the final recall test. The experimenter also noted that it was not important that they remember the other two uses ( non-selected uses ). The two selected uses were chosen randomly to ensure that all uses were equally likely to serve as selected and non-selected uses. Participants were given a few seconds to look over the selected uses before they moved on to either the 90-s additional thinking portion of the same trial or to a new object in the next trial. To examine whether the four initially generated uses would be susceptible to thinking-induced forgetting, all participants were allotted an additional 90 s to think of new uses for half of the objects, which they wrote down on a separate sheet of paper. Participants were instructed to think of new uses that were unrelated to those they had generated before, and they were told that they would not be asked to recall these new uses later in the experiment. For the other half of the objects, participants simply moved on to the next object without thinking of additional uses. The eight objects were presented in the same order for all participants, while the particular subset of objects associated with 90 s of additional thinking was counterbalanced across participants. The order of the trials was set such that participants would not be able to predict whether they would be asked to think of additional uses for a given object. After completing the generation phase, participants entered the final recall phase in which they were cued with the eight objects for 16 s each and asked to recall out loud all of the first four uses they had generated for those objects. Participants in the selection condition were told to try to remember all four of the uses, and not just the two that had been selected by the experimenter. The objects were presented in the same order as in the generation phase. Uses for objects associated with additional thinking are referred to as items in the thinking condition, whereas uses for objects not associated with additional thinking are referred to as items in the baseline condition. Owing to counterbalancing, all uses were equally likely to serve in the thinking and baseline conditions. Results and discussion Initial uses generated Participants generated four uses per object on 99 % of the trials. The remaining trials were removed. For this and all subsequent experiments, the same three independent raters scored the creativity of all of the uses on a 1 9 scale, where 1 was uncreative and 9 was highly creative (inter-rater reliability, a = 0.69). A

5 682 Psychological Research (2017) 81: Table 1 Average creativity ratings for all experiments Experiment Initial four uses Additional uses Condition (# of uses) Selected Non-selected Experiment 1 Remember-all (4) 3.8 (0.1) N/A 4.5 (0.1) Experimenter-selected (2) 3.9 (0.1) 3.9 (0.1) 4.4 (0.1) Experiment 2a Self-selected (2) 4.5 (0.1) 3.7 (0.2) 4.6 (0.1) Experiment 2b Self-selected (1) 4.5 (0.1) 3.7 (0.1) 4.4 (0.1) Experiment 3 Self-selected (1) hint 4.5 (0.2) 3.8 (0.1) 4.7 (0.1) Average creativity ratings for all experiments. Standard errors are shown in parentheses. Experiment 1 is split into the Remember-all condition, in which participants were told to remember all of their initial four uses, and the Experimenter-Selected condition, in which participants were told that two of their ideas were very creative, and it was very important to remember them. For all other experiments, the initial four uses are Self-Selected, with the number of uses selected shown in parentheses. For Experiment 3, they self-selected their single use and used it as a hint. For all experiments, Selected refers to the chosen uses, Non-selected refers to the non-chosen uses, and Additional refers to the uses that participants generated during the additional 90 seconds of thinking composite score was created for each use by averaging across the three ratings. Creativity was defined by asking the raters how creative the use was compared to other uses. Creativity ratings as a function of experimental condition can be seen in Table 1. Notably, for participants in the selection condition, a paired-samples t test failed to find evidence of a significant difference between selected and non-selected uses, t(88) = 0.30, p = 0.77, d = 0.03, which is to be expected given that the selected uses were randomly determined. Additional uses generated Participants in the rememberall and selection conditions generated 4.36 (SE = 0.22) and 4.01 (SE = 0.25) new uses per object during the 90 s of additional thinking, respectively a non-significant difference, t(94) = 1.04, p = 0.30, d = The average creativity rating of these uses can be seen in Table 1. Final recall performance Recall performance was analyzed using a 2 (trial type: thinking vs. baseline) x 3 (condition: selected vs. non-selected vs. remember-all) mixed design ANOVA. Two main effects were observed. First, a main effect of trial type was observed such that participants recalled fewer uses in the thinking condition (M = 0.52, SE = 0.01) than in the baseline condition (M = 0.70, SE = 0.01), F(1, 141) = , MSE = 0.02, p \ 0.001, g p 2 = Second, a main effect of condition, F(2, 141) = 9.62, MSE = 0.04, p \ 0.001, g p 2 = 0.12, with participants recalling 0.55 (SE = 0.02), 0.67 (SE = 0.02), and 0.60 (SE = 0.02) uses in the nonselected, selected, and remember-all conditions, respectively. Most importantly, we failed to find evidence of a significant interaction, F(2, 141) = 1.58, MSE = 0.02, p = 0.21, g p 2 = As can be seen in Fig. 1, and as confirmed by three separate paired-samples t tests, regardless of condition, participants recalled significantly fewer items in each of the thinking conditions than they did in each of the baseline conditions (all p values \0.001). 1 Thinking-induced forgetting for creative and less creative uses One might expect creative uses to be less susceptible to thinking-induced forgetting than non-creative uses because such uses are particularly interesting or distinctive. Given the logic put forth in the introduction, however, we expected creative and non-creative uses to be equally susceptible to forgetting. To explore this possibility, we compared thinking-induced forgetting effects for creative and less creative uses in the remember-all condition. Creative uses were operationalized as the two initial uses for an object that received the highest average creativity ratings from the three independent raters, whereas the less creative uses were operationalized as the two initial uses for an object that received the lowest average creativity scores. If there was a tie in the ratings, 1 Although not a goal of the present research, it is interesting to note that the results of Experiment 1 do provide some evidence of selective directed forgetting (see e.g., Delaney, Nghiem, and Waldum, 2009; Storm, Koppel, & Wilson, 2013). Specifically, looking at baseline items alone, selected uses in the selection condition (M = 0.77, SE = 0.02) were recalled significantly better than were uses in the remember-all condition (M = 0.70, SE = 0.02), t(94) = 2.49, p = 0.01, d = 0.51, whereas non-selected uses in the selection condition (M = 0.62, SE = 0.02) were recalled significantly worse than uses in the remember-all condition, t(94) = 2.14, p = 0.04, d = This result suggests that participants were able to selectively forget the subset of uses that were deemed non-creative/ not-to-be-remembered while maintaining (and even increasing) the accessibility of the subset of uses that were deemed creative/to-beremembered.

6 Psychological Research (2017) 81: Propor on of Ini al Uses Recalled Thinking Baseline Non-selected Selected Remember-all Fig. 1 Final recall performance as a function of trial type and remember instruction in Experiment 1. Remember-all refers to the condition in which participants were told to remember all four of their initial uses. The two leftmost pairs of bars make up the selection condition, in which participants were told to remember the two uses that the experimenter deemed very creative ( selected ), and not remember the other two uses ( non-selected ). Error bars represent standard error of the mean the use that received the highest individual creativity rating was classified as more creative. If there was still a tie, an independent rater selected one use as more creative than the other. A 2 (trial type: thinking vs. baseline) 9 2 (creativity: creative vs. less creative) repeated measures ANOVA revealed a main effect such that less creative uses were recalled at a higher rate (M = 0.69, SE = 0.02) than creative uses (M = 0.55, SE = 0.02), F(1, 47) = 17.82, MSE = 0.025, p \ 0.001, g p 2 = This finding may seem unexpected, but can likely be attributed to the fact that it is easier to remember typical, non-creative uses in two different contexts (initial generation and final recall) than it is to remember atypical, creative uses. Most importantly, we failed to find evidence of a difference between the amount of thinking-induced forgetting for creative uses (think: M = 0.46, SE = 0.03; baseline: M = 0.64, SE = 0.03) and less creative uses (think: M = 0.55, SE = 0.03; baseline: M = 0.75, SE = 0.02), F(1, 47) = 0.091, MSE = 0.025, p = 0.76, g p 2 = 0.00, suggesting that the creative uses were just as susceptible to thinking-induced forgetting as the less creative uses. Experiments 2a and 2b In Experiment 1, we demonstrated that thinking-induced forgetting occurs for people s own ideas, and even for ideas that people are motivated to remember per the instructions of the experimenter. Moreover, creative uses were just as susceptible to thinking-induced forgetting as were less creative uses. In Experiments 2a and 2b, we sought to replicate and extend these findings by having participants self-select either two uses (Experiment 2a) or one use (Experiment 2b) of the initial four uses that they felt were most creative and thus, most important to be remembered. Although we failed to observe a reduction in forgetting for uses selected by the experimenter as being creative and to-be-remembered, there are reasons to think that we would observe a reduction in forgetting for uses selected by the participants themselves. For example, the best and most creative uses generated by participants might be highly distinctive to them personally (and not necessarily to the independent raters), and in the retrieval-induced forgetting literature, distinctiveness has been shown to protect items from forgetting (Smith & Hunt, 2000; Anderson, Green, & McColloch, 2000). Second, by identifying one or two uses as being important to remember, participants might be more likely to employ preventative measures to protect those uses from forgetting while engaged in additional thinking than they would have been in Experiment 1 when the to-be-remembered uses were selected by the experimenter. Indeed, participants might rehearse the selected uses covertly while trying to think of new uses, thereby not only preventing the uses from suffering thinking-induced forgetting, but perhaps owing to such covert rehearsal, making them more recallable in the future than they would have been otherwise. Such dynamics would seem to be particularly likely when subjects are asked to personally select and try to remember a single highly creative idea (as was the case in Experiment 2b). Given the above considerations, it would seem reasonable to predict that the uses selected by participants as being most creative would be protected from thinking-induced forgetting. Based on the retrieval-induced forgetting literature (Bäuml & Samenieh, 2010; Storm et al., 2007), however, even intrinsic motivation to hold on to specific uses may not in itself afford protection from forgetting. If forgetting is observed for self-selected uses as a consequence of additional thinking it would suggest that thinking-induced forgetting has the potential to be a far more pervasive of a phenomenon than we perhaps realize, causing us to forget our own ideas despite their relative creativeness and despite the intention to hold on to them. Method In total, 72 (36 in Experiment 2a, M age = 21.0; and 36 in Experiment 2b, M age = 19.9) undergraduates were recruited from the UCSC subject pool and compensated with partial credit in a psychology course. The materials used were identical to those used in Experiment 1. The procedure was identical to that of the selection condition in Experiment 1, except that the participants themselves were

7 684 Psychological Research (2017) 81: instructed to place checkmarks next to either the two uses (Experiment 2a) or the one use (Experiment 2b) that they felt were/was particularly creative and thus to-be-remembered for the final recall test. They were again told that it was not important to remember the non-selected uses. Because participants self-selected uses as being creative, it would be problematic to compare levels of thinking-induced forgetting for such uses with other uses that were not selected as being creative. The problem is that the uses selected by participants would likely differ from those not selected in important ways, thus making any differences in thinking-induced forgetting potentially attributable to differences in the uses themselves and not to the actual judgment of the uses or the motivation to remember. As such, we planned to focus our analysis primarily on whether the self-selected items suffered thinking-induced forgetting, and not on whether rates of forgetting differed between selected and non-selected uses. Results and discussion Initial uses generated Participants generated four uses per object on all but two trials, which were removed. A pairedsamples t test determined that there was a significant difference between the average creativity ratings (see Table 1) for the selected uses and the non-selected uses in both Experiment 2a, t(64) = 8.11, p \ 0.001, d = 0.90, and 2b, t(70) = 8.58, p \ 0.001, d = 0.97, indicating that the uses identified as being creative by the participants were also identified as being creative by the raters. Additional uses generated During the 90 s of additional thinking, participants generated 4.2 (SE = 0.32) uses per object in Experiment 2a and 3.9 (SE = 0.18) uses per object in Experiment 2b. The average creativity rating of these uses can be seen in Table 1. Final recall performance AscanbeseeninFig.2, substantial thinking-induced forgetting was observed in both experiments. Specifically, in Experiment 2a, for selected uses, fewer uses were recalled in the thinking condition (M = 0.50, SE = 0.03) than in the baseline condition (M = 0.61, SE = 0.03), t(35) = 3.24, p = 0.003, d = Thus, even uses that participants selected as being their most creative ideas failed to be protected from thinking-induced forgetting. Non-selected uses also exhibited thinking-induced forgetting, with significantly fewer uses being recalled in the thinking condition than in the baseline condition, t(35) = 2.53, p = 0.016, d = For Experiment 2b, the story was similar. Specifically, for the selected uses, fewer uses were recalled in the thinking condition (M = 0.72, SE = 0.04) than in the baseline condition (M = 0.81, SE = 0.03), t(35) = 2.07, p = 0.045, d = Non-selected uses also exhibited thinking-induced forgetting, with significantly fewer uses being recalled in the thinking condition (M = 0.48, SE = 0.02) than in the baseline condition (M = 0.66, SE = 0.02), t(35) = 7.19, p \ 0.001, d = These results suggest that even ideas that participants identify themselves as being particularly creative and to-be-remembered are susceptible to thinking-induced forgetting. Experiment 3 Despite the evidence presented thus far that even our more creative ideas are susceptible to thinking-induced forgetting, and that such forgetting occurs even when participants are motivated to remember such ideas, there is a situation in which we would expect thinking-induced forgetting to not occur specifically, when initial ideas are used to facilitate the thinking of new ideas (Storm & Patel, 2014). Presumably, when initial ideas are used in this way they are more likely to mediate, rather than hinder the generation of new ideas, thus protecting them from forgetting. Additionally, if an initial idea does mediate the generation of new ideas, then that idea is likely to be (or become) highly integrated with the new ideas; and because integration has been shown to be an important boundary condition for retrieval-induced forgetting (e.g., Anderson and McCulloch, 1999; Anderson et al., 2000; Chan, 2009; Bäuml & Hartinger, 2002), it may serve as an important boundary condition in the present context as well. To examine this hypothesis, as in Experiment 2b, we instructed participants to identify their single, most creative use, except this time we also instructed participants to use the self-selected use as the basis for generating new uses in the additional thinking phase. Method A total of 36 undergraduate participants (M age = 20.1) were recruited from the UCSC subject pool and compensated with partial credit in a psychology course. The materials and procedure were identical to that of Experiment 2b except that participants were instructed to use their single identified creative use as a hint to help them think of new uses during the 90 s thinking phase. Results and discussion Initial uses generated Participants generated four uses per object on 100 % of the trials. A paired-samples t test determined that there was a significant difference between the average creativity ratings (see Table 1) of the selected and non-selected uses, t(67) = 5.37, p \ 0.001, d = Additional uses generated On average, participants generated 4.0 (SE = 0.31) uses per object during the 90 s

8 Psychological Research (2017) 81: A 1 B Propor on of Ini al Uses Recalled Non-selected Selected Non-selected Selected Thinking Baseline Fig. 2 Final recall performance as a function of trial type and remember instruction in Experiments 2a (a) and 2b (b). The lower recall on the thinking trials compared to the baseline trials indicates very similar forgetting effects for both selected and non-selected uses when uses are self-identified as the most creative. Error bars represent standard error of the mean of additional thinking. The average creativity rating of these uses can be seen in Table 1. Final recall performance In line with our predictions, and as shown in Fig. 3, protection from thinking-induced forgetting was observed such that the recall of selected uses in the thinking condition (M = 0.70, SE = 0.04) and the baseline condition (M = 0.70, SE = 0.04) did not significantly differ, t(35) = 0.22, p = 0.83, d = These findings, which mirror those of Storm and Patel (2014), suggest that the susceptibility of our own ideas to thinking-induced forgetting can be modulated by how we use those ideas to continue to think of new ideas. As in the previous experiments, non-selected uses exhibited thinking-induced forgetting, with significantly fewer uses being recalled in the thinking condition (M = 0.48, SE = 0.03) than in the baseline condition (M = 0.62, SE = 0.03), t(35) = 3.57, p = 0.001, d = It is interesting to note, therefore, that Propor on of Ini al Uses Recalled Thinking Baseline Non-selected Selected Fig. 3 Final recall performance as a function of trial type and remember instruction in Experiment 3. The reduction in the forgetting effect in the selected condition demonstrates that using one s ideas as hints to generate future ideas may protect those ideas from forgetting. Error bars represent standard error of the mean using one idea as a mediator to facilitate the generation of new ideas did not protect non-selected ideas from forgetting. Analysis of the correlation between thinkinginduced forgetting and creativity Storm and Patel (2014) speculated that individuals who experience more thinking-induced forgetting of old ideas should be better able to think of new creative ideas than individuals who experience less thinking-induced forgetting, presumably because such individuals would be less hindered by mental fixation. To test this conjecture, Storm and Patel counted the number of uses that participants generated above and below the average creativity rating (observed across all objects and participants) and examined the relationship between those measures and thinking-induced forgetting. A significant correlation was observed with regard to creative uses, but not with regard to noncreative uses. They concluded that forgetting example uses allowed participants to come up with more creative uses because they were then less constrained by those uses. We conducted the same analysis reported by Storm and Patel (2014). On one hand, we might expect a similar pattern of results as they observed. Forgetting our own initial ideas might facilitate the generation of new creative ideas. On the other hand, it is possible that retaining access to one s initial ideas is beneficial for building on them and for generating new creative ideas. Said differently, our initial ideas may serve as a useful starting point for generating new ideas, and so forgetting them may not necessarily facilitate creativity. First, we calculated the average creativity rating of all uses generated in the additional thinking phase (not the initial four uses) across all four experiments. We then counted the number of additional uses that each participant generated above and below that average rating, thus

9 686 Psychological Research (2017) 81: providing measures of the number of creative and noncreative uses that each participant generated, respectively. To control for variability between conditions and counterbalancing, we Z-normalized the forgetting scores and number of creative/non-creative uses generated for all participants relative to the means and standard deviations of all other participants in the matched experimental and counterbalancing conditions. In a pattern of results that failed to replicate Storm and Patel (2014), neither the number of creative (r =-0.02, p = 0.75) or non-creative (r = 0.08, p = 0.28) uses generated by participants was related to thinking-induced forgetting. Thus, participants who exhibited greater levels of thinking-induced forgetting did not generate more creative uses than participants who exhibited reduced levels of thinking-induced forgetting. One important difference between our study and that of Storm and Patel (2014), however, is that participants in our study selected uses that they thought were particularly creative and were instructed to hold on to those uses for a later memory test. Perhaps it was this selection/focused remembering aspect of our design that eliminated the correlation between forgetting and creativity. To explore this possibility, we focused our analysis on Experiments 2 and 3, examining the correlation between the number of creative uses generated and the effects of thinking-induced forgetting observed for both selected and non-selected uses separately. Interestingly, when focusing on the forgetting of non-selected uses, the correlation approached significance, r = 0.15, p = When focusing on the forgetting of selected uses, however, the correlation numerically reversed, r =-0.12, p = To analyze these data further, we estimated Bayes factors to assess the relative probability of the data fitting the alternative and null hypotheses (Dienes, 2014; Wagenmakers, 2007) with the alternative hypothesis stating that there is a positive correlation between thinking-induced forgetting and the number of creative uses generated by participants (assuming a correlation of 0.26, as was observed by Storm & Patel, 2014), and the null hypothesis stating that there is not a positive correlation (assuming a correlation of 0.00). With regard to the forgetting of non-selected uses, a Bayes factor of 1.75 was estimated, suggesting that the data were marginally more likely to have occurred under the alternative hypothesis than under the null hypothesis. This result suggests that it would be inappropriate to conclude that thinking-induced forgetting of non-selected self-generated uses does not correlate with the generation of creative uses to the same extent as thinking-induced forgetting of example uses. Said differently, we cannot conclude that the correlation we observed (for non-selected uses) was different from the correlation observed overall by Storm and Patel. A very different finding was observed with regard to thinking-induced forgetting of selected uses. Specifically, a Bayes factor of 0.17 was estimated, suggesting that the data were 5.96 times more likely to have occurred under the null hypothesis than under the alternative hypothesis, a finding which can be interpreted as providing positive evidence in favor of the null hypothesis (e.g., Jeffreys, 1961; Raftery, 1995). This result suggests that thinkinginduced forgetting of one s own ideas that were selected as being creative and worth remembering does not correlate with the ability to generate additional creative ideas (at least to the same extent as was observed by Storm & Patel). General discussion Humans are inherently creative beings, as they are able to invent new objects, think up solutions to previously unsolved problems, and even imagine things that do not, and could not, exist. Understanding the cognitive processes underlying creativity is important not only for theoretical reasons but also for practical reasons in that it may allow us to harness and expand upon our creativity abilities. The results of the present study suggest that thinking of new ideas causes the forgetting of our old ideas, providing a new demonstration of thinking-induced forgetting (see Storm and Patel, 2014). This new demonstration is important because it shows that even our own ideas are susceptible to thinking-induced forgetting, and that even a desire to remember a given idea can fail to confer protection. In Experiment 1, initial uses for objects were forgotten as a consequence of thinking of new uses regardless of how creative the initial uses were judged to be, and regardless of whether participants were instructed to remember them for an upcoming test. In Experiment 2, participants were asked to identify the two uses (Experiment 2a) or one use (Experiment 2b) that were most creative and to focus efforts on remembering those two uses or that one use for the final test. Despite these instructions, the self-selected uses were still susceptible to thinking-induced forgetting. The finding that intentions to remember fail to protect items from forgetting is consistent with prior work in the retrieval-induced forgetting literature showing that items in memory that people want to remember are just as susceptible (if not more susceptible) to forgetting as items in memory that people want to forget (Bäuml & Samenieh, 2010; Storm et al., 2007). There are several reasons to be surprised by our results. At the most basic level, some might argue that our own ideas are special, and that they should be better remembered than ideas that are simply studied. Indeed, generation effects have been observed across a variety of paradigms (e.g., Bertsch, Pesta, Wiscott, & McDaniel, 2007;

10 Psychological Research (2017) 81: Slamecka & Graf, 1978) and, in comparing our study with Storm and Patel (2014), we can see that participants in our study exhibited a far greater level of recall. The factors that make self-generated ideas more recallable than studied ideas do not appear to be sufficient, however, to protect self-generated ideas from thinking-induced forgetting. One factor that does appear to be capable of protecting initial ideas from forgetting is the extent to which participants use their initial ideas to help themselves think of new ideas. In Experiment 3, participants were asked to use their most creative use as a hint to help them think of new uses, and in this condition those initial uses failed to suffer thinkinginduced forgetting. It is interesting to note that participants in Experiments 1, 2a, and 2b did not seem to be doing this on their own when not explicitly instructed to do so. It would have been reasonable to assume that when participants attempted to generate new ideas they would have used their earlier uses to help them think of new uses, even if only implicitly; but to the extent that significant forgetting effects were observed in each of these experiments, this did not appear to be the case. Research has suggested that inhibition plays an important role in allowing people to overcome interference and mental fixation (for reviews, see Anderson, 2003; Storm, 2011; Storm et al., 2015; Storm & Levy, 2012). In trying to think of something new and creative, people are likely to experience interference from old ideas and thus need a way to get around those ideas. An inhibitory process may act during creative thinking to decrease the accessibility of old or inappropriate items in memory to reduce this interference. Such a mechanism would explain why old uses suffered forgetting as a result of thinking of new uses. The old uses may have caused interference and may have, thus, been inhibited to facilitate the generation of new uses, with this inhibition then rendering the old uses less recallable in the future than they would have been otherwise. The results of Experiment 3 are consistent with this explanation, as by using their initial selected uses as a hints to help themselves think of new uses, participants would have prevented those uses from causing interference and thus from being targeted by inhibition. It is also possible that the thinking-induced forgetting effects observed here can be explained by other mechanisms, such as associative interference, cue overload, or inappropriate contextual cuing (Jonker, Seli, & MacLeod, 2013; Raaijmakers & Jakab, 2013). Perhaps the initial uses suffered forgetting not because they were inhibited during creative thinking, but because they were occluded or blocked at the time of test. By generating additional uses for objects in the thinking condition, it may have become more difficult for participants to bypass such uses when searching their memory for the initial uses. In fact, despite being instructed to recall only the initial uses at the time of the final test, participants did on occasion recall the additionally generated uses as well. 2 Context dynamics may have made this sort of interference even more pronounced in the present study than would have been expected in the study by Storm and Patel (2014). In the study by Storm and Patel, participants would have been able to effectively target the initial study phase when attempting to recall the studied uses because the study phase and the generation phase would have been encoded as highly distinct events (i.e., one involved studying uses, the other involved generating uses). In the present study, however, participants may have had considerably more difficulty targeting the initial generation phase when attempting to recall the initially generated items because both the initial generation phase and the additional generation phase would have involved the same cognitive activity (i.e., generating new uses). Given this difference, it seems likely that interference would have played a relatively larger role in the present study than it did in the study by Storm and Patel, a possibility that future research should seek to explore. Another aspect of our results that deserves discussion is the relationship between thinking-induced forgetting and the extent to which participants generated creative uses. Although we failed to replicate the overall finding observed by Storm and Patel (2014) that participants who exhibit greater levels of thinking-induced forgetting generated more creative uses than participants who exhibited reduced levels of thinking-induced forgetting we did find a possible distinction in the results as a function of whether uses were selected by the participants as being creative. Specifically, for non-selected uses, a non-significant correlation was observed that went in the same direction as that observed by Storm and Patel. It is difficult to interpret this null result one way or the other. That is, it does not provide convincing evidence for or against the hypothesis that the thinking-induced forgetting of non-selected uses correlates with the creativity of subsequently generated uses. For selected uses, however, the correlation was numerically reversed, thus suggesting that the thinkinginduced forgetting of one s own selected uses does not correlate with the ability to think of new creative uses. In the context of creative cognition, it may be advantageous to hold onto previous ideas that one deems to be good or creative, possibly because such ideas can then 2 On average, when attempting to recall the initially generated uses related to a given object at the time of final test, participants recalled 0.15, 0.11, 0.18, and 0.12 of the uses they had generated during the additional thinking phases of Experiments 1, 2a, 2b, and 3, respectively. It is interesting to note that significant thinking-induced forgetting effects were observed in Experiments 1 and 2 (for selected and non-selected items) even when we limited our analysis to participants who, as determined by median split, made the fewest number of intrusions, all p values \0.05.