حافظه اپیزودیک و دوراندیشی اپیزودیک در کودکان 3- و 5 ساله

In the present study, we examined the development of episodic memory and episodic foresight. Three- and 5-year-olds were interviewed individually using a personalised timeline that included photographs of them at different points in their life. After constructing the timeline with the experimenter, each child was asked to discuss a number of different events: an event that happened yesterday, an event that happened earlier today, an event that would happen later today, and an event that would happen tomorrow. As judged by their parents, children's accounts were highly accurate. After controlling for age and language scores, there was a strong relation between amount of information reported about past and future events. Overall, 5-year-olds reported more total information than 3-year-olds; however, reports by 3-year-olds included a similar proportion of first-person reference as did reports by 5-year-olds. No age difference appeared in proportion of future-oriented talk. We conclude that the present task provides a promising method of exploring the emergence of mental time travel during early childhood.

“It's funny how memory erodes. If all I had to work from were my childhood memories, my knowledge of my mother would be faded and soft, with a few sharp moments standing out.” Audrey Niffenegger, The Time Traveler's Wife (2003), pp. 107–108 In Audrey Niffenegger's highly acclaimed novel, The Time Traveler's Wife, the main character, Henry, suffers from a fictional genetic disorder that transports him forward and backward in time. As the story unfolds, we watch as Henry experiences his life in both directions, encountering both younger and older versions of himself and other important people in his life. He travels back in time to meet his wife when she was only a child and returns again and again to the scene of the car accident that killed his mother. Henry also travels forward in time to meet his daughter before she is born and to learn the circumstances that will ultimately lead to his own death. In the present study, we explore the psychological equivalent of Henry's condition—mental time travel ( Suddendorf and Corballis, 1997 and Tulving, 2002)—the ability to travel forward and backward in mental, rather than physical, time. As adults, this ability allows us to remember our past and make predictions about our future. Here, we explore the developmental emergence of mental time travel in preschool age children. Memory is a fundamental aspect of human cognition that emerges very early in development. Even newborns exhibit memory for their mother's face (Pascalis, de Schonen, Morton, Deruelle, & Fabre-Grenet, 1995) and voice (DeCasper and Fifer, 1980 and DeCasper and Spence, 1986). In fact, depending on their age, human infants exhibit memory when tested after hours, days, weeks, or even months (Bauer, 2007 and Hayne, 2004). Despite a large body of research on memory development, a number of key questions remain. For example, what kind of memory do infants and young children exhibit? Although it is now generally accepted that by 6 months of age, infants succeed on memory tasks that are thought to measure explicit or declarative memory ( Hayne, 2004, Hayne, 2007 and Rovee-Collier et al., 2001), there is no evidence that these early memory skills are episodic in nature, and they may instead reflect semantic memory skill ( Colombo & Hayne, 2010). Although episodic and semantic memory are both considered part of the explicit or declarative memory system, episodic memory refers to memory for events, while semantic memory refers to memory for facts. Tulving originally coined the term episodic memory almost 40 years ago ( Tulving, 1972). Although some of the specific details of the theory have changed since then, the underlying assumption has always been that episodic memory involves a highly specialised set of neural structures that support autobiographical memory. More recently, Tulving has also argued that episodic memory is characterised by two other important features: (1) it involves a form of mental time travel in which the rememberer travels backward or forward in mental time to relive a past experience or to consider possible future scenarios, and (2) it is accompanied by conscious awareness that the event happened to “me” or will happen to “me” that does not accompany retrieval of other kinds of memories ( Conway, 2009, Tulving, 2002 and Tulving, 2005). The bulk of research on episodic memory development has focused on the retrospective quality of memory—that is, the ability to remember events from the past. By comparison, the prospective nature of episodic memory, or the ability to predict what might happen in the future based on what has happened before, has received much less attention. The relative lack of research on the development of mental time travel into the future is somewhat surprising given the importance of episodic foresight in accomplishing a wide range of tasks central to everyday life (Atance and Jackson, 2009, Hudson, 2002, Nelson, 1996, Suddendorf, 2006 and Suddendorf and Corballis, 1997). Recent interest in the phenomenon of episodic foresight has been fuelled, at least in part, by growing interest in Tulving's general theory of episodic memory. Much of the contemporary research on the development of episodic foresight has involved planning tasks in which children are required to anticipate their needs (or the needs of others) under a set of hypothetical circumstances. In some of these experiments, children are asked to imagine possible future events and to then make choices about items that might be necessary for those particular events. For example, Atance and O’Neill (2005) asked 3-year-olds to imagine that they were going on a trip with their parents. They were shown a group of eight items and were asked to choose which of them they would like to take on the trip and to provide a reason for their choice. These reasons were coded to determine how often they referred to the future in general (e.g., using words like will, going to, etc.) and how often they referred to an uncertain future (e.g., using words like maybe, might, etc.). Overall, 3-year-olds used these future-related terms approximately 37% of the time. Using a similar task, Atance and Meltzoff (2005) examined age-related changes in children's ability to talk about hypothetical future events. They showed 3-, 4-, and 5-year-olds a book containing photographs of different landscapes (e.g., a desert). For each photograph, children were given a choice of three items and asked which of the items they would take with them if they were walking across the landscape depicted in the photograph. Each landscape was associated with a particular physiological state; for example, the desert scene was associated with sun getting in the child's eyes. The three items presented with each landscape included one item that would deal with the physiological state (e.g., sunglasses) and two irrelevant distracters. Atance and Meltzoff argued that if children were able to think about the future, they would choose the item that would remedy the physiological condition that was likely to occur in that landscape. The child was asked to explain the choice. The proportion of future talk contained in that explanation was coded. Overall, 4- to 5-year-olds chose the correct item significantly more often than 3- to 4-year-olds; they also provided more future-state information when asked to explain their choice. When a semantically-related distractor was included among the choice items (e.g., a shell was an item presented following a desert landscape that included sand), the performance of 3- to 4-year-olds suffered, whereas that of the older group did not. Thus, although children of all ages demonstrated some degree of future thinking, the ability of the youngest participants was inferior to that of the older children and was also more easily disrupted. Although research by Atance and her colleagues has been extremely valuable to our understanding of the emergence of children's future thinking more generally, the tasks in these experiments may tap skills that are different from the kinds of episodic memory skills Tulving describes. For example, a key feature of episodic memory is the notion of autonoetic consciousness, or the feeling that the experience has happened (or will happen) to “me.” Given this, children's expectations about which items would be useful in a desert or near a stream might reflect their prior personal experience with or their future predictions about their own experience with these environments (thus potentially reflecting episodic foresight), but they might also reflect more general semantic knowledge about the basic characteristics of hot sunny places or potentially dangerous ones. These tasks would therefore reflect children's semantic memory skill rather than episodic thinking about the future. Using a task that more clearly meets the definition of episodic memory, Busby and Suddendorf (2005) asked 3-, 4-, and 5-year-olds to “tell me something that you did yesterday” and to “tell me something that you are going to do tomorrow.” In two experiments, only about 30% of 3-year-olds responded accurately, while 4- and 5-year-olds provided accurate answers more than half the time. In both experiments, there was no difference in children's accuracy on the retrospective or prospective questions. On the surface, these data suggest there is a clear, step-wise improvement in both retrospective and prospective episodic memory between the ages of 3 and 4 (see also Suddendorf, 2010a). The data reported by Busby and Suddendorf (2005) and by Suddendorf, 2010a and Suddendorf, 2010b are highly consistent with the prediction that episodic memory emerges between ages 3 and 4 (Perner and Ruffman, 1995, Suddendorf and Corballis, 1997 and Tulving, 2002). Before drawing this developmental line in the sand, however, it would be important to rule out two alternative explanations. First, as Busby and Suddendorf (2005) suggest, it is possible their data reflect very young children's difficulty in understanding time words like “yesterday” and “tomorrow” (Friedman, 2002 and Friedman, 2003) rather than in episodic memory and episodic foresight per se. That is, 3-year-olds may have been more likely to fail the task simply because they did not understand the question. Second, it is possible the task was unnecessarily difficult because children were required to generate the events themselves. For preschoolers, parents have primary control over events that will take place in the future; young children are rarely given the opportunity to make decisions when it comes to future activity. It is therefore perhaps not surprising that the youngest children experienced difficulty when asked to generate future events. It is possible, however, that if children were asked to describe possible future events that were nominated by someone else, they might be able to use mental time travel to provide an account of both what happened in the past and what might happen in the future. With these issues in mind, we compared 3- and 5-year-olds’ mental time travel skills using a different version of the task originally developed by Busby and Suddendorf (2005). To do this, we provided each child with a personalised timeline similar to the one we have used in prior research on children's and adults’ earliest personal memories (Jack and Hayne, 2010, Jack et al., 2009 and Tustin and Hayne, 2010). The task involves the construction of a timeline on a large piece of construction paper that depicts the participant's life to date. Essentially, the timeline reinforces the linear notion of time and allows us to interview participants about things that happened at different points in their lives without relying exclusively on terms like “later,” “earlier,” “before,” and “after” that young children may struggle to understand. In addition, rather than asking children to generate events that had happened in the past or that would happen in the future, we asked their parents to nominate the events and we then interviewed the children about them. Two features of episodic memory have recently captured the attention of many developmental psychologists (including us) and provided the theoretical basis for the research we describe here. First, it has been hypothesized that episodic memory (i.e., mental time travel to the past) and episodic foresight (i.e., mental time travel to the future) involve many of the same neural and cognitive processes (Addis et al., 2007, Klein et al., 2002, Suddendorf, 2010a, Suddendorf and Corballis, 1997, Tulving, 1985 and Tulving et al., 1991). That is, the same skills underpin our ability to remember where we left our keys last night and our ability to plan what we will need to pack for our trip to the beach next week. If this is true, we might predict that these skills develop at the same rate. Second, it has been hypothesized that, in contrast to other forms of memory, episodic memory emerges substantially later in development, potentially around age 3½ to 4 (Perner and Ruffman, 1995 and Tulving, 2002). We set out to test these two hypotheses.