PERSPECTIVE PERSPECTIVE A taxonomy of prospection: Introducing an organizational framework for future- oriented Karl K. Szpunara,b,1, R. Nathan Sprengc,d, and Daniel L. Schactera,b aDepartment of and bCenter for Brain Science, Harvard University, Cambridge, MA 02138; and cLaboratory of Brain and Cognition, Department of Human Development, and dHuman Neuroscience Institute, Cornell University, Ithaca, NY 14853

Edited by Larry R. Squire, Veterans Affairs San Diego Healthcare System, San Diego, CA, and approved October 30, 2014 (received for review September 11, 2014)

Prospection—the ability to represent what might happen in the future—is a broad concept that has been used to characterize a wide variety of future-oriented , including , prospective memory, temporal discounting, episodic simulation, and autobiograph- ical planning. In this article, we propose a taxonomy of prospection to initiate the important and necessary process of teasing apart the various forms of future thinking that constitute the landscape of prospective cognition. The organizational framework that we propose delineates episodic and semantic forms of four modes of future thinking: simulation, prediction, intention, and planning. We show how this framework can be used to draw attention to the ways in which various modes of future thinking interact with one another, generate new questions about prospective cognition, and illuminate our understanding of disorders of future thinking. We conclude by considering basic cognitive processes that give rise to prospective cognitions, cognitive operations and emotional/motivational states relevant to future-oriented cognition, and the possible role of procedural or motor systems in future-oriented behavior.

prospection | simulation | prediction | intention | planning

Over the past decade, the concept of pro- believed to support memory for personally to parse the concept of prospection and relate spection—the ability to represent what might experienced events (episodic), expression of these four modes of future thinking to two happeninthefuture—has been the subject of general knowledge about the world (seman- well-characterized types of memory or rapidly growing research interest within var- tic),andmotorbehavioraswellaslearningof knowledge that subserve distinct forms of ious subdisciplines of psychology and neuro- various kinds of skills (procedural) (13, 14), future thinking: episodic and semantic. In science (1, 2). One reason why the concept of give rise to corresponding types of future this context, the term episodic is meant to prospection has gained so much attention is thinking that vary in terms of the flexibility refer to simulations, predictions, intentions, that the term casts a wide net around a variety with which they enable the individual to or plans in relation to specific autobiograph- of future-oriented cognitions. Studies on think about the future. These initial steps to- ical events that may take place in the future topics as varied as episodic simulation (3, ward organizing future thinking have served (e.g., thinking about an upcoming event that 4), affective forecasting (5), intention forma- to highlight important questions in the liter- will take place over the weekend). The term tion (6), and autobiographical planning (7) ature (e.g., are episodic and semantic forms semantic is meant to refer to simulations, have all been described as instances of pro- of future thinking dissociable from one an- predictions, intentions, and plans that re- spection (1, 2, 8, 9). Although the practice of other?). However, this approach does not late to more general or abstract states of the clumping various forms of future thinking provide a means by which to draw connec- world that may arise in the future (e.g., together may be beneficial in terms of high- tions or distinctions between the various thinking about how to enhance company lighting the breadth of the concept of pro- future-oriented cognitions that constitute the profitability). Note, however, that not all spection, it also runs the risk of obscuring broad nature of prospection (e.g., what are instances of memory or future thinking can the manner in which various forms of future the relations between simulation and plan- be strictly classified as either episodic or thinking relate to one another. The purpose ning?; how might the episodic–semantic dis- semantic. For instance, personal semantic of this article is to directly address this issue tinction qualify these relations?). In this knowledge (15) is not associated with a spe- and begin the process of developing an orga- article, we propose a taxonomy that is intended cific episode (e.g., I am a good basketball nizational framework to draw connections to both organize and stimulate research and player) and may be projected forward into and distinctions between various forms of theory across various domains of future- the future (e.g., I want to play professional future thinking that serve different functions oriented cognition. basketball in the future). As with personal for adaptive behavior (10). Our approach will be to distinguish among semantic knowledge, such hybrid forms of Although various works have intimated four modes of future thinking that encapsu- episodic and semantic future thinking are the need for a taxonomy of prospection (11, late the bulk of the literature on prospective not strictly episodic, in that they do not refer 12), prior attempts to parse future-oriented cognition: simulation, prediction, intention, cognition have focused exclusively on relating and planning. These four modes of future Author contributions: K.K.S., R.N.S., and D.L.S. wrote the paper. taxonomies of human memory to future thinking support prospective cognition from The authors declare no conflict of interest. thinking. For instance, Suddendorf and the initial conception of a possible future This article is a PNAS Direct Submission. Corballis (12) proposed that episodic, semantic, event to the process of attaining a goal. 1To whom correspondence should be addressed. Email: and procedural memory systems, which are Importantly, we will build on past attempts [email protected].

www.pnas.org/cgi/doi/10.1073/pnas.1417144111 PNAS Early Edition | 1of8 Downloaded by guest on September 24, 2021 to a specific episode, and they are not strictly prospective cognition on the basis of relevant these modes of future thinking have been semantic. Although thinking about the desire modes of future thinking and types of mem- studied in relative isolation, and our goal is to to be a professional basketball player refers to ory or knowledge, (ii) provide a brief over- bring these largely disparate lines of research a more general future state, that future state is view of our resulting framework along with and theory into meaningful dialogue with autobiographical in nature. To accommodate discussion of its implications for understand- one another. such hybrid forms of future thinking, our ing relations between different modes of fu- Modes of future thinking are not neces- framework conceptualizes the episodic– ture thinking and deficits of future thinking, sarily orthogonal to one another. Rather, they semantic distinction as a continuous dimension and (iii) consider important caveats to our interact and build on one another at various as opposed to a categorical variable, and we framework. levels of abstraction and complexity (17). For instance, when planning, people may draw will identify various forms of simulation, pre- Modes of Future Thinking and Types of diction, intention, and planning that fall on simulations and predictions and formu- Memory or Knowledge within the purview of this episodic–semantic late and revise intentions. Given such possi- Modes of Future Thinking. Over the course continuum (Fig. 1). Finally, we do not in- bilities,itisallthemoresurprisingthat of each day, people devote considerable clude procedural forms of future thinking research on these various modes of future time to thinking about the future (16). in our taxonomy. The focus of this article is thinking has been subject to little cross-talk, People simulate and evaluate possible on future-oriented cognitions as opposed to although we will discuss important excep- encounters with friends, colleagues, romantic tions. We anticipate that an organizational future-oriented motor actions. Nonetheless, partners, and even their future selves; form framework will stimulate research programs we do not rule out the possibility that pro- intentions to deliver messages, take pre- to consider both connections and distinctions cedural or motor systems may play a role in scribed medications, and pick up mis- among the modes of future thinking. Of the future-oriented cognition and will revisit the cellaneous items at the grocery store; and four modes of future thinking that we have issue later in the article. Moreover, the trans- plan daily routines, vacations, and savings identified, only prediction, intention, and lation of future-oriented cognition into action strategies for retirement. Despite the seem- planning may be considered to be strictly represents an important aspect of prospec- ingly innumerable ways in which people future-oriented. Simulation is not necessarily tion, and we highlight relevant issues associ- think about the future, we propose that directed toward the future (3) but may be co- – ated with cognition action interactions as prospective cognition may be organized into opted in the service of generating mental they become pertinent to the various modes four modes of future thinking. These four representations of possible futures. Later, we of future thinking discussed below. modes of future thinking include simulation will highlight studies showing that detailed The result of our approach is a set of four (construction of a detailed mental represen- simulations of the future can also sub- basic modes of future-oriented cognition that tation of the future), prediction (estimation of stantially improve the effectiveness of other may vary in the extent to which they draw the likelihood of and/or one’s reaction to modes of future thinking, such as intention on episodic and semantic knowledge struc- a particular future outcome), intention (the formation. tures and represent key components of the mental act of setting a goal), and planning landscape of prospection. In what follows, (the identification and organization of steps Types of Memory or Knowledge. The we (i) provide rationales for decomposing toward achieving a goal state). Historically, distinction between and semantic memory or knowledge has a long history in the psychological literature (18), and it continues to be refined by various scholars (19). In relation to future thinking, cognitive neuroscientists and neuropsy- chologists have generated considerable ev- idence showing that the capacity to re- member past events and imagine future events is closely related, spurring the sug- gestion that event details can be flexibly extracted and recombined from memory in the service of simulating new events that may take place in the future (20). Here, we extend this proposed relation between memory and future thinking to highlight, as others have done as well (4, 11, 12, 21, 22), that general knowledge about the world (semantic knowledge) may also lay the groundwork for allowing us to reason about what the world may be like in the future. However, much work is needed to show these proposed relations between different types of knowl- edge and future thinking. For instance, whether episodic and semantic forms of simulation, prediction, intention, and plan- ning represent dissociable phenomena or Fig. 1. A taxonomy of prospective cognition. nominal distinctions regarding the content

2of8 | www.pnas.org/cgi/doi/10.1073/pnas.1417144111 Szpunar et al. Downloaded by guest on September 24, 2021 on which these various modes of prospective that are likely to be near the ends of the last decade has shown a close relation PERSPECTIVE cognition operate remains to be adjudicated episodic–semantic continuum in Fig. 1 for between episodic memory and episodic in the literature. Moreover, it will be impor- each of four modes of future thinking. simulation (20). Episodic memory and epi- tant to assess the extent to which these types However, we stress that any given instance sodic simulation engage similar brain net- of knowledge may interact with one another of future-oriented cognition may ultimately works, and deficits of episodic memory are in the service of future-oriented cognition. evoke both episodic and semantic forms of typically accompanied by deficits of episodic For example, according to the semantic future thinking. Accordingly, we will con- simulation (recent reviews in refs. 3, 4, and scaffolding hypothesis (21), semantic knowl- clude our discussion of each mode of future 10). Considerable research has focused on edge provides a framework or scaffolding thinking by providing examples of how epi- the extent to which the hippocampus and that helps to organize event details that sodic and semantic forms of future thinking related medial structures, long comprise simulations of future experiences. may interact with one another. We will also associated with episodic memory (13), are also This kind of hypothesis implies strong in- briefly consider the manner in which hybrid important for episodic simulation: hippo- teraction and interdependence between forms of episodic and semantic future campal and medial temporal lobe regions are episodic and semantic knowledge during thinking (Fig. 1, Middle) fit into our frame- typically engaged during episodic simulation, prospective thought (23). work of prospective cognition. Wherever and some amnesic patients with damage to Characterizing the influence of episodic possible, we provide brief descriptions of the these regions exhibit impairments of episodic and semantic knowledge structures as part of typical methodological approaches used to simulation (discussion in refs. 29–31). It is our organizational framework is intended to study the four modes of future thinking. A important to note that episodic simulation stimulate novel questions about simulation, key step forward in the study of prospective neednotbedirectedtowardthefuture(3). prediction, intention, and planning that may psychology will involve the development of For instance, one could simulate how the past turn out to be important (e.g., can someone research programs that are able to bridge the could have turned out differently (i.e., coun- be a good semantic planner but a poor epi- gap in existing methodological approaches to terfactual simulation) (32, 33). Nonetheless, sodic planner?; to what extent are semantic the study of simulation, prediction, intention, episodic simulation is often directed at the plans supported by semantic and episodic and planning. future, and even past-oriented episodic sim- knowledge?). In what follows, we present our ulations are often carried out in service of the resulting framework. Extending beyond Simulation. The construct of simulation has future (34). Hence, episodic simulation rep- a simple summary of independent lines been used in multiple ways in psychology resents an important form of prospective of research, we propose a framework that and neuroscience. For example, Ingvar (24) cognition. highlights naturally occurring forms of characterized a “simulation of behavior” as Semantic simulation is the construction of future-oriented cognition with additional “an inner anticipatory programming of sev- a detailed mental representation of a general consideration for their interactions for the eral alternative behavioral modes prepared to or abstract state of the world. emergence of goal-directed behavior. be used depending upon what will happen” Example of semantic simulation. In antici- (ref. 24, p. 21). In a similar spirit, Taylor and pation of the upcoming discussion with her Varieties of Future Thinking Schneider (25) defined simulation as “the boss, Monika envisions the future direction To help facilitate discussion of our organi- imitative representation of the functioning or of the company. zational framework of prospection, we pres- process of some event or series of events ... Research on semantic simulation. Although ent the following hypothetical scenario to we will use the term to mean the cognitive semantic simulation has not received as highlight the manner in which various forms construction of hypothetical scenarios or the much research attention as episodic simula- of our four basic modes of future thinking reconstruction of real scenarios” (ref. 25, tion (11, 22), evidence suggests that the two arise in the context of everyday experience. p. 175). Others have used simulation strictly are, at least to some extent, dissociable from Monika,whohaslongsoughttoplayanin- to refer to processes involved in “mentalizing” oneanother.Onestudyfoundthatanepi- fluential role in business, works as a midlevel or making attributions about another sodicamnesicpatientwhowasunableto executive at a Fortune 500 company. The person’s mental state (26). Conceiving simu- reliably express what he might do in the fu- Chief Executive Officer (CEO) of the com- lation in a much broader sense, Barsalou (27) ture was nonetheless able to think about pany asks Monika if she would join him for contended that “conceptual processing uses problems that might face the world in the a game of tennis over the upcoming week- reenactments of sensory-motor states— future (e.g., global warming) (35). Although end. Although Monika is flattered by the simulations—to represent categories” (ref. 27, the results of this important study suggest offer, she is also anxious about the invitation, p. 521; 28). Our use of the concept of simu- that episodic and semantic simulations differ because she has not played tennis in over lation shares most in common with the ideas in some fundamental way, a subsequent a year and would need to purchase new of Ingvar (24) and Taylor and Schneider (25), study that used additional measures of se- athletic gear before the weekend. Monika also focusing on the construction of hypothetical mantic prospection points toward deficits in suspects that her boss will be vetting her for future events both specific and general. amnesic patients (36). Interestingly, a recent a higher-level position within the company Episodic simulation is the construction of case study of temporal lobe epilepsy revealed and therefore, plans to brush up on her a detailed mental representation of a specific impaired semantic simulation in the face of knowledge of the company before the meet- autobiographical future event. preserved episodic simulation (37). Other ing. In what follows, we define, provide Example of episodic simulation. Before meet- research has pointed toward differences examples of, and briefly discuss relevant re- ing her boss over the weekend, Monika between episodic and semantic simulation search on episodic (Fig. 1, Top) and semantic might simulate possible events that are likely based on analysis of details that comprise (Fig. 1, Bottom) forms of simulation, pre- to take place (e.g., playing tennis and having future simulations using the Autobiograph- diction, intention, and planning. For ease of a discussion about the company). ical Interview (38). The Autobiographical exposition, we highlight specific aspects of Research on episodic simulation. As we al- Interview distinguishes between two major the aforementioned hypothetical scenario luded to earlier, considerable work over the types of details that people typically report

Szpunar et al. PNAS Early Edition | 3of8 Downloaded by guest on September 24, 2021 when they remember a past experience or focus is on longer-term predictions about future events can impede success in these imagine a future experience: internal or specific events and general or abstract states domains (review in ref. 50). Additional de- episodic details (i.e., details concerning of the world that may arise in the future and velopment in understanding the precise people, places, and actions that constitute the manner in which such predictions may relations between passive thinking about the an event) and external or semantic details interact with other modes of future thinking. future, repeated simulation, expectation, and (i.e., related facts, general knowledge, and Episodic prediction is the estimation of the action awaits future work. Later, we will commentary). Several studies have shown likelihood of and/or one’s reaction to a spe- consider the potentially important implica- internal and external details can be disso- cific autobiographical future event. tions that perceived plausibility of event oc- ciated. For example, when young and older Example of episodic prediction. In anticipa- currence might have on other modes of fu- adults construct future simulations, young tion of meeting with her boss, Monika may ture thinking (e.g., intention and planning). adults produce more internal details than vacillate in making a determination about Semantic prediction is the estimation of older adults, whereas the opposite pattern whether the meeting will go well and how the the likelihood of and/or one’sreactiontoa is observed for external details (39–41). outcome that she thinks is most likely will general or abstract future state of the world. More recent work has shown that an epi- make her feel. Example of semantic prediction. Monika sodic specificity induction—brief training Research on episodic prediction. The process predicts that the future of the company that involving a cognitive interview about a re- of engaging in episodic prediction is perhaps she works for would best be served by merg- cent experience that guides individuals to most clearly shown in the affective fore- ing with a partner company. focus on recollecting specific details of that casting literature in which researchers assess Research on semantic prediction. Semantic experience—selectively increases the num- how well people are able to predict their prediction represents an important type of ber of internal details that young and older emotional reactions to future events. These future thinking that is highly valued in dis- adults generate when they construct future predictions are typically captured by ratings ciplines such as politics (e.g., who will win the simulations while having no effect on ex- on numerical scales (e.g., on a scale of one to election?) and economics (e.g., what stocks ternal details (42). Nonetheless, more re- nine, how happy do you think you will be at should people invest in?). One important search is needed to help discriminate your child’s first soccer match?). This line of question that our framework raises is episodic and semantic simulation in terms work has shown that people are generally whether episodic and semantic predictions of their phenomenological characteristics, limited in this ability. Specifically, people are based on different or similar mechanisms. susceptibility to cognitive manipulations, commonly think that upcoming future events In one study, different patterns of neural and neural correlates. As with episodic will make them feel better or worse than they activity uniquely characterized episodic (e.g., simulation, semantic simulation also does actually do, because they tend to overlook is it likely that you will still go clubbing at the not need be but often is directed at the seemingly minor details that turn out to be age of 40?) and semantic (e.g., is it likely that future (e.g., imagining what the world important (e.g., a young couple anticipating Sydney will have a Disneyland in 50 y?) might be like in 10,000 y). the joys of parenthood fails to consider how predictions (51). However, these differing As emphasized earlier, some forms of it will feel to change diapers or go into work neural signatures may have more to do with simulation cannot be neatly classified as ei- not having slept the previous night; 5). It has underlying differences in the content of the ther episodic or semantic but rather, repre- been argued that people base their pre- mental representations that such predictions sent hybrids of episodic and semantic sim- dictions on episodic simulations of the future are based on as opposed to mechanisms that ulation. These hybrid forms of simulation and that episodic simulations of the future underlie the predictions themselves. Indeed, may take the form of personal semantic are often imperfect and hence, result in errors repeated simulation has a similar influence knowledge (e.g., Monika has always had an in prediction (e.g., essentialized simulations on the perceived plausibility of specific events interest in business) that is projected into the of parenthood that focus on the rewarding (see above) and general states of the world future (e.g., Monika envisions herself playing aspects of childrearing; 1). As noted earlier, (e.g., the more often people imagine a particu- a more important role in her company). Such recent studies have shown that people are lar candidate winning an election, the more simulations are autobiographical but not re- able to generate more detailed simulations of likely they are to think the candidate will be lated to specific future episodes. Finally, each thefuturewhentheyaretrainedtoreport elected) (52). Moreover, positive fantasies of the examples highlighted in this section those details in the context of a cognitive about an idealized future in the context of may potentially evoke episodic, semantic, and interview about a recent experience (42). newspaper reports and presidential addresses hybrid forms of future thinking. For instance, Whether specificity inductions could be used have been shown to predict negative eco- in the context of simulating the future di- to enhance predictive accuracy awaits future nomic downturns (53). At this point, con- rection of her company, Monika may not research. Finally, although less attention has siderable work remains to be carried out to only simulate general or abstract information been paid to the likelihood that people as- develop an understanding of the extent to associated with company growth but also, cribe to the potential occurrence of events, an which episodic and semantic predictions envision herself eventually taking over as independent line of research has shown that about the occurrence of future events and CEO of the company (hybrid) and per- repeated simulation of the future can boost states of the world differ beyond the content forming particular actions that she might judgments of perceived likelihood—the more onwhichtheyoperate(e.g.,arepeoplewho enactinthatrole(episodic). often an event is simulated, the more likely are good at predicting general states of the people think the event will take place (47, 48). world that may arise in the future also good Prediction. Prediction is a fundamental task Importantly, the expectation of positive fu- at predicting the likelihood of occurrence of the brain (43, 44). Predictions about the ture outcomes has been linked to the suc- of specific autobiographical events?). Studies future include short-term predictions about cessful attainment of significant personal that have assessed predictions of emotional what object may appear next in a scene (45) milestones (e.g., acquiring gainful employ- reactions to specific autobiographical events and prediction errors concerning expected ment and finding a romantic partner) (49), and general autobiographical or nonautobio- rewards that are crucial to (46). Our whereas passive fantasizing about positive graphical states of the world (e.g., how happy

4of8 | www.pnas.org/cgi/doi/10.1073/pnas.1417144111 Szpunar et al. Downloaded by guest on September 24, 2021 does Monika think that she will be once she Early research on implementation intentions semantic intention). The extent to which PERSPECTIVE achieves a particular level of vocational suc- found that explicitly stating when and where such hybrid intentions rely on similar or cess?) have shown similar errors in predictive an intention will be carried out (e.g., when different mechanisms compared with more accuracy (54), suggesting that similar mecha- x occurs, I will perform y) enhanced pro- clear-cut examples of episodic and semantic nisms may be at work. Finally, we note that spective memory performance (review in ref. intention awaits future work. For instance, to each of the examples of prediction highlighted 6). More recently, researchers have shown what extent might similar mechanisms un- in this section could potentially give rise that mentally simulating this contextual in- derlie the acts of forming intentions to pick to episodic, semantic, or hybrid forms of formationinanepisodicmannerprovides up milk from the grocery store and pursue prediction or simulation (or intention or a similar benefit (59, 60; further discussion in a career in business? planning). For instance, in the process of ref. 61). Hence, although simulation may not attempting to predict the possible success of necessarily be as closely tied to action as in- Planning. For intended behaviors to be a merger, Monika might imagine a specific tention, simulation may be used to facilitate carried out in an effective manner, plans are future meeting between members of her action in the context of achieving intentions. often necessary. Although various works have company and a partner company (episodic As we discuss later, these exciting lines of defined the concept of planning (65–67), simulation). Such examples highlight the work highlight the importance of studying most definitions commonly conform to the ways in which various modes of future interactions between different modes of fu- notion of a plan as “a predetermination of thinking may interact with one another to ture thinking. Note also that implementation a course of action aimed at achieving some support adaptive cognition. intentions may be effective in part, because goal” (65). Here, we focus on the nature of they involve formulating a plan of action. plans that are aimed at achieving goals in Intention. Understanding the conscious However, as we will highlight below, most relation to specific autobiographical and more determinants of human action has repre- conceptualizations of planning ability ex- general or abstract contexts and the extent to sented a central fixture in psychological re- tend beyond the simple if–then statements which other modes of future-oriented cogni- search since the cognitive revolution (55); characteristic of implementation inten- tionmayfactorintotheplanningprocess. considerable research has been devoted to tions to include the organization of com- Episodic planning is the identification and illuminating the nature of the underlying plex action sequences. organization of steps needed to arrive at intentions that guide behavior of the in- Semantic intention is the mental act of a specific autobiographical future event dividual (56) and also, the more general a general or abstract goal, such as the or outcome. setting that is the driving force behind the goal of an organization. Example of episodic planning. Before meet- growth and development of organizations Example of semantic intention. Before meeting ing with her boss over the weekend, Monika (57). Next, we provide a brief and necessarily herbossovertheweekend,Monikacon- devises a meticulous plan about what steps selective overview of specific and more gen- templates the goals of her company over sheneedstotaketoprepareforthemeeting eral or abstract intentions and identify pos- thecomingfiscalyear. (e.g., finding time during the week to read up sible links to other modes of future-oriented Research on semantic intention. Research on on her company and related companies and cognition. goal setting in organizations has a long his- finding time to purchase new athletic gear Episodic intention is the mental act of tory in the psychological and business and practice her tennis game). setting a goal in relation to a specific auto- literature (57, 62). Much of this research, Research on episodic planning. Research on biographical future event. however, has focused on enhancing the pro- the concept of episodic planning has a long Example of episodic intention. Before meet- ductivity of individual members of an orga- history in cognitive psychology and neuro- ing her boss over the weekend, Monika nization as opposed to identifying the psychology (65). One notable aspect of this realizes that she needs a new pair of sneakers cognitive determinates that underlie the for- literature is that planning tasks vary consid- and sets the goal of purchasing new sneakers on mation of a general or abstract intention for erably in terms of how well they approximate her way home from work on Friday evening. a particular organization (63). Nonetheless, real-life planning, ranging from tasks that are Research on episodic intention. Perhaps the the ability to generate semantic or strategic completely removed from everyday experi- most common example of such goal setting intentions is considered to be an important ence (e.g., Tower of London) (68) to tasks occurs in the context of prospective memory, aspect of running a successful business (64). thatmimicepisodicplanninginthelabora- in which people form intentions to achieve Hence, the development of research pro- tory (e.g., Six Elements Task) (69) to tasks some outcome(s) in the context of specific grams aimed at identifying the possible that involve carrying out episodic plans in future events (e.g., I need to pick up bread on overlapping and nonoverlapping cognitive real-world settings (e.g., planning and pre- my way home from work) (a comprehensive and neural mechanisms that give rise to ep- paring a meal) (70). Much of the research on overview is in ref. 58, and a more general isodic and semantic intentions should have planning has been conducted in the context discussion surrounding intentions is in ref. considerable implications for various fields of of frontal lobe dysfunction. The fact that 57). Of course, the focus of the prospective study, including psychology, business, and patients with frontal lobe damage have memory literature is not simply on the for- economics. After a semantic intention is trouble with each of these tasks highlights mation of intentions but rather, on how well formed, the process of semantic planning that processes subserved by the frontal lobes those intentions are later accomplished (e.g., maythenbeengagedtodeterminethenec- (e.g., executive control) play an important remembering to make a follow-up appoint- essary steps to accomplish the goal. role in planning and future thinking more ment with an experimenter, colleague, As with simulation and prediction, not all generally. More recent neuroimaging studies or doctor). Indeed, studies of prospective instances of intention can be classified as ei- (7, 71) have examined the neural under- memory have long investigated the extent to ther episodic or semantic. For instance, it is pinnings of episodic or autobiographical which the quality of encoding of episodic likely that, at some point in her past, Monika planning using a task in which participants intentions predicts the success with which formed the intention to pursue a career in mentally construct plans containing specific those intentions are carried out in the future. business (a hybrid form of episodic and steps to achieve specific autobiographical

Szpunar et al. PNAS Early Edition | 5of8 Downloaded by guest on September 24, 2021 goals (e.g., academic success). Results indicate (79), and research along these lines has the understand the extent to which such patients that episodic planning is associated with ac- potential to answer novel questions regarding areabletoengageinsemanticpredictionand tivity in the same core network of brain individual differences in planning ability. For semantic planning. Similarly, although it is regions that has been linked previously to example, are people generally good planners, well-known that patients with frontal lobe episodic simulation (the default network) (72, or can someone be a good semantic planner damage exhibit considerable deficits in epi- 73). Moreover, activity in the default network but a poor episodic planner and vice versa? sodic and semantic planning, less is known during episodic planning was closely coupled Finally, we highlight that some forms of about the extent to which such patients are with activity in a distinct frontoparietal con- planning represent hybrid instances of epi- able to generate useful simulations and pre- trol network (74) that has been linked to sodic and semantic planning, such as plan- dictions of episodic and semantic future executive control and goal-directed cognition ning for one’s own retirement. Such instances events (81). Finally, studies of mood and and also supports planning performance on of planning are neither strictly episodic (i.e., -related disorders have historically the Tower of London task (7). Finally, real- they do not refer to specific episodes) nor focused on the fluency with which individu- world episodic planning tasks have further strictly semantic (i.e., the general state of the als with and anxiety think about illuminated the extent to which episodic future being planned for is autobiographical positive and negative events that may occur planning draws on other modes of future in nature). inthefuture(82).Althoughthisworkhas thinking. One study showed that participant provided important insights into future descriptions of strategies for completing a Interactions Between Modes of Future thinking in these populations, relatively little pseudoshopping/planning task included sim- Thinking. Episodic, semantic, and hybrid is known about the extent to which these ulation, prediction, and intention formation forms of simulation, prediction, intention, individuals are able to engage in episodic, (75). We address this point in additional and planning flexibly interact with one an- semantic, and hybrid forms of simulation, detail below. other to support prospective cognition. The prediction, intention, and planning. De- Semantic planning is the identification and extent to which such interactions serve to velopment of research programs that con- organization of steps needed for some general support/hinder adaptive behavior will repre- sider the role of these various modes of future or abstract state in the world to arise in sent an important avenue for future research. thinking could enhance our understanding of the future. Simulated representations of the future can the ability of individuals afflicted with various Example of semantic planning. Monika be used in the context of prediction, in- mood and anxiety disorders to engage in explains to her boss what steps, in her tention, and planning. However, the extent to adaptive behavior (e.g., how well are indi- opinion, would need to be taken for the which the level of detail associated with viduals with depression or anxiety able to company to successfully merge with a partner a simulation influences performance in other predict their reactions to future events?; how company and maximize profitability in domains remains to be investigated, particu- well are they able to formulate episodic or the future. larly in relation to prediction and planning. semantic plans for the future?). Research on semantic planning. Semantic Could specificity inductions (42) be used to planning is perhaps best represented in the improve the quality of plans? In a similar Caveats context of strategic (76) and urban planning vein, relatively little is currently known about The purpose of our organizational frame- (77). Although there exists a paucity of re- the extent to which the perceived likelihood work for future-oriented cognition is to search related to the cognitive determinants of the occurrence of a future event might provide an impetus toward delineating the of semantic planning, research concerning influence the formation and retention of multidimensional ways in which the various patients with frontal lobe damage has pro- intentions or the quality of plans. Is an in- modes of future thinking interact with one vided some initial data. Patients with frontal tention less likely to influence behavior if the another in the service of adaptive behavior. lobe damage exhibit difficulty in formulating perceived probability of occurrence is less Nonetheless, additional cognitive, emotional, both episodic plans (see above) and financial than certain? Studies examining the fre- and motor processes may contribute to and plans for others (78). It is important to point quency of occurrence of prospective memory support future-oriented behavior. In future out that financial planning for others may probes suggest that perceived probability of discussions of fractionating prospective cog- incorporate both episodic and semantic fea- occurrence may not play an appreciable role nition into its constituent parts, these addi- tures of planning (e.g., people may use their in determining prospective memory perfor- tional factors may require a revised taxonomy own experiences to formulate plans for mance (80). Additional work, however, is pending future research. Although a compre- others) (ref. 78, p. 1,882). Nonetheless, the needed to test the context of prospective hensive discussion of these factors is beyond results of this study suggest that cognitive memory tasks (e.g., laboratory vs. daily life) the scope of this article, we briefly draw at- functions subserved by the frontal lobes may and the manner that perceived plausibility of tention to each of these issues below. be important for both episodic and semantic occurrence is manipulated (e.g., frequency of planning. To our knowledge, however, no occurrence vs. explicit instruction). Cognitive Processes That Give Rise to study has directly compared episodic and Prospective Cognitions. An important av- semantic planning deficits in frontal lobe Applications. This organizational frame- enue of future work will be to identify the patients, and therefore, more work is needed work provides a benchmark against which manner in which basic cognitive processes to understand the extent to which these clinical populations with deficits in future arestrungtogetherintheserviceofvarious forms of planning are supported by similar thinking can be assessed to develop a profile modes of future thinking. We have already and different mechanisms. Indeed, the of their future-thinking abilities. For instance, highlighted the important role that extracting broader literature on planning does not some episodic amnesic patients are able to details from episodic memory plays in the generally distinguish between episodic and think about the future in more general terms context of episodic simulation. However, semantic planning (review in ref. 66) or the (35), although they may have difficulty gen- other cognitive processes, such as causal extent to which the two may work together in erating semantic details of future events (36). reasoning (83), manipulating extracted epi- particular contexts (e.g., retirement planning) Nonetheless, more work is needed to further sodic details through executive resources

6of8 | www.pnas.org/cgi/doi/10.1073/pnas.1417144111 Szpunar et al. Downloaded by guest on September 24, 2021 (84), and scene construction (85), have also in which emotional/motivational systems prospective cognition must inform immediate PERSPECTIVE been proposed to feature prominently in the interact with systems that support the various motor behavior at some junction to organize context of episodic simulation (additional representations of the future that we have immediate behavior and accomplish many of discussion in ref. 12). This approach could outlined here represents an important di- the future-oriented thoughts considered (12). provide additional clarity as to how various rection for future work (discussion in ref. 92). Understanding how future-oriented cognition modes of future thinking are ultimately re- is translated into action and how particular lated to one another and also, understanding Procedural System and Future Behavior. modes of future thinking, such as simulation, of patterns of deficits of future thinking. For Looking beyond episodic and semantic forms can be used to enhance the successful attain- instance, it will be important for future of prospection, we note that the procedural ment of desired future goals and states rep- work to identify the overlapping and non- or motor system may also play an important resents an important mission of the field of overlapping contributions of specific exec- role in certain kinds of prospection (6). In prospective psychology. utive resources to episodic simulation and our hypothetical scenario, Monika could en- planning. gage in mental practice or simulation of her Conclusion tennis serve and also generate procedural The purpose of this article is to provide an Cognitive Operations and Emotional/ predictions, intentions, and plans in the initial framework for organizing key com- Motivational States. Related to the above course of her actual match. Considerable re- ponents that fit under the general concept of point, it will also be necessary to consider search has shown that mental practice may prospection. We suggest that conceiving an cognitive operations that build on the core benefit later performance (93) and that pre- episodic–semantic gradient within which modes of future thinking that we have frontal and parietal regions of the brain seem simulation, prediction, intention, and plan- identified and emotional/motivational states to play an important role in representing ning operate provides a useful framework by that arise or perhaps, give rise to these core motor predictions, intentions, and plans which to discriminate and develop con- modes of future thinking. For instance, in the (relevant reviews in refs. 94–96). None- nections among various forms of future process of simulating a desired autobio- theless, we resist the temptation to in- thinking that constitute the landscape of re- graphical state (e.g., I want to be a good clude procedural forms of prospection in search on prospective cognition. It is our tennis player), one may compare and con- our framework, because it is not clear the hope that our organizational framework will trast the vision of the future self with the extent to which procedural predictions, provide insights into disorders of future current self in an effort to stir intentions, and plans contribute to fu- thinking in humans, encourage more in- (50). Although mental contrasting is not ture-oriented cognitions as opposed to depth considerations of the manner in which necessarily a future-oriented cognitive oper- impending motor actions. For instance, it future-thinking capacities in human and ation, it may, nonetheless, enhance future- has been shown that intentions to make nonhuman animals overlap and diverge (99), oriented behavior. As another example, a motor movement may be encoded in and encourage cross-fertilization of research mentally contrasting the short- and long- the brain up to 10 s before those inten- and theory across various domains of pro- term consequences to impending actions can tions enter conscious awareness (97). The spective psychology (100). serve to enhance far-sighted decision-making extent to which motor intentions con- (86, 87). Although a thorough treatment of tribute to higher-level or conceptual thoughts ACKNOWLEDGMENTS. We thank Roland Benoit and the vast decision-making literature is beyond about the future awaits additional in- two anonymous reviewers for helpful discussion and comments on a draft of the manuscript. This work was the scope of this article (recent reviews in refs. vestigation (discussion relevant to social supported by National Institute of Health Grants AG08441 88and89),weviewdecisionsasendpoints cognition is in ref. 98). 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