Elsevier

Cognition

Volume 210, May 2021, 104603
Cognition

The future is in front, to the right, or below: Development of spatial representations of time in three dimensions

https://doi.org/10.1016/j.cognition.2021.104603Get rights and content

Highlights

  • Investigated the development of two types of spatiotemporal mappings in children.

  • Both calendar orientation and writing direction influenced the mental timeline.

  • Proportion of children who mapped the future to the front increased with age.

  • Temporal focus predicted whether the future was mapped to the front or back.

  • Conventional orientations of both mapping types emerged in parallel.

Abstract

Across cultures, people frequently communicate about time in terms of space. English speakers in the United States, for example, might “look forward” to the future or gesture toward the left when talking about the past. As shown by these examples, different dimensions of space are used to represent different temporal concepts. Here, we explored how cultural factors and individual differences shape the development of two types of spatiotemporal representations in 6- to 15-year-old children: the horizontal/vertical mental timeline (in which past and future events are placed on a horizontal or vertical line that is external to the body) and the sagittal mental timeline (in which events are placed on a line that runs through the front-back axis of the body). We tested children in India because the prevalence of both horizontal and vertical calendars there provided a unique opportunity to investigate how calendar orientation and writing direction might each influence the development of the horizontal/vertical mental timeline. Our results suggest that the horizontal/vertical mental timeline and the sagittal mental timeline are constructed in parallel throughout childhood and become increasingly aligned with culturally-conventional orientations. Additionally, we show that experience with calendars may influence the orientation of children's horizontal/vertical mental timelines, and that individual differences in children's attitudes toward the past and future may influence the orientation of their sagittal mental timelines. Taken together, our results demonstrate that children are sensitive to both cultural and personal factors when building mental models of time.

Introduction

Although we cannot see or touch time, it is a fundamental component of our lives. But how do we think and reason about it? As evidenced by language, gesture, and cultural artifacts, people from cultures around the world use space to represent time. Spatial language is frequently used metaphorically to talk about time (e.g., many languages describe the future as being in front and the past behind; Clark, 1973; Lakoff & Johnson, 1980), co-speech gestures add a spatial component to temporal language (Núñez & Cooperrider, 2013; Núñez & Sweetser, 2006), and external tools that project time onto space, like clocks and calendars, are common (e.g., Barnett, 1999; Gell, 1992; Whitrow, 1989). Associations between space and time also run deeper than external cultural tools or linguistic metaphors, as decades of work have suggested that representations of time and space are also linked in the mind (e.g., Boroditsky, 2000; Casasanto & Boroditsky, 2008; Casasanto, 2009b; Casasanto, Fotakopoulou, & Boroditsky, 2010; Gibbs, 1994; Lakoff & Johnson, 1980). Using space to represent time is thought to be cognitively beneficial by facilitating our ability to reason about temporal order and intervals (Boroditsky, 2000; Casasanto, 2008; Casasanto et al., 2010; Gentner, 2001). Notably, however, spatial representations of time can take varied forms across cultures, and within a culture it is common to use different dimensions of space (e.g., the left-right and front-back axes) to represent different types of temporal concepts (Núñez & Cooperrider, 2013).

Two of the most prevalent mental mappings of time onto space across cultures take the form of a line. One form, commonly referred to as the mental timeline, is a mental model of time based on a linear reference frame oriented on the horizontal or vertical axis (for reviews, see Bender & Beller, 2014; Bonato, Zorzi, & Umiltà, 2012). With the mental timeline, an observer takes an external perspective, viewing events from outside of the timeline. In other words, the observer is mapping time onto a line that does not intersect with the body. A second type of linear spatiotemporal mapping reflects how individuals represent the future and past relative to themselves. This spatiotemporal mapping employs the sagittal axis, the axis running between the front and back of the body. Unlike the horizontal/vertical mental timeline, the sagittal mental timeline involves an internal perspective with the observer in the center of the axis (Núñez & Cooperrider, 2013). Here, we use the term ‘horizontal/vertical mental timeline’ to refer to what most prior work has referred to as the ‘mental timeline’ and we use the term ‘sagittal mental timeline’ to refer to mapping time onto space in the sagittal axis. As we will review below, the orientation of these mappings—such as whether the future is mapped to the right or left, or to the front or the back—can vary from culture to culture.

The present study explored the development of these two forms of spatiotemporal mappings across early and middle childhood, in a sample of 6- to 15-year-old children in Gujarat, India. We address two overarching questions. First, when—and through what trajectory—might children develop conventional horizontal/vertical and sagittal mappings? Do children initially map time onto space with idiosyncratic orientations that only later become aligned with cultural conventions, or are these mappings constructed in alignment with cultural conventions from the outset? Moreover, do horizontal/vertical and sagittal mappings follow independent developmental trajectories or are these mappings constructed in parallel? Second, what factors influence the orientation of children's mappings? Are these mappings guided solely by characteristics of the spoken and written languages that children learn, or might they also be influenced by exposure to cultural artifacts like calendars, and reflect individual differences in how much children value the past or future? Below, we review prior research on the horizontal/vertical and sagittal mental timelines before describing our study.

In many Western cultures, the horizontal/vertical mental timeline maps time onto a horizontal spatial axis, frequently with a left-to-right orientation such that earlier events occur on the left and later events occur on the right. However, this orientation is not universal: in some cultures, it is oriented right-to-left, while in others it is oriented top-to-bottom (e.g., Bergen & Lau, 2012; Fuhrman & Boroditsky, 2010; Ouellet, Santiago, Israeli, & Gabay, 2010; Tversky, Kugelmass, & Winter, 1991). One hypothesis for why these differences exist is that the orientation of the horizontal/vertical mental timeline is influenced by the orientation of written language within a culture (Bergen & Lau, 2012). Consistent with this hypothesis, the left-to-right orientation found in many Western cultures parallels the way texts in English and other European languages are read. Conversely, the horizontal/vertical mental timeline in Hebrew speakers is oriented with earlier events occurring on the right and later events occurring on the left, consistent with the right-to-left direction in which Hebrew is read (Fuhrman & Boroditsky, 2010). Similarly, Taiwanese speakers of Mandarin, who read top-to-bottom, orient their horizontal/vertical mental timelines consistent with this vertical orientation (Bergen & Lau, 2012).

An alternate hypothesis, however, is that it is not writing direction, per se, that influences the orientation of the horizontal/vertical mental timeline, but specifically the way that external representations of time, like calendars, are oriented (Pitt & Casasanto, 2020). In the United States, for example, the canonical wall calendar is oriented with the days of the week going from left-to-right (Fig. 1A). In other countries, vertical calendars, in which the days of the week are oriented from top-to-bottom, are also common (Fig. 1B). Although both of these calendar types each involve the horizontal and vertical axes (whether through the progression of days in the week or weeks in the month), here we classify calendar orientation based on the axis that represents the days of the week. Because many cultures orient this axis of their calendars in the same direction as their written language (e.g., in Arabic-speaking countries, written language is right-to-left and calendars are also oriented with the days of the week going from right-to-left), it is difficult to determine whether it is visual scanning patterns associated with written language versus the way that time is spatialized specifically that influences the orientation of the horizontal/vertical mental timeline. To tease apart these explanations, it is necessary to assess the orientation of the horizontal/vertical mental timeline in a culture in which writing direction is not confounded with calendar orientation.

In thinking about how oneself moves through time, many languages and cultures describe the future as being in front of the observer and the past as behind (Boroditsky, 2000; Clark, 1973; Lakoff & Johnson, 1980; Torralbo, Santiago, & Lupiáñez, 2006; Ulrich et al., 2011). This front-future orientation may arise from experience with moving through space. As one moves forward physically, the locations to be reached are in front, whereas the locations already passed are behind. However, despite this universal pattern of locomotor experience, there is variation in the way languages map time onto the sagittal axis. Some languages, including Vietnamese and the Andean language Aymara, use spatiotemporal metaphors that refer to the past, which is known, as being in front of the body where it can be seen, whereas the future, which is unknowable, is represented behind the body where it cannot be seen. These linguistic metaphors appear to have cognitive underpinnings – speakers of these languages also conceptualize time with a front-past orientation in the sagittal axis, as evidenced by co-speech gestures (Núñez & Sweetser, 2006; Sullivan & Bui, 2016).

Interestingly, recent work suggests that both cultural attitudes and individual differences can influence the orientation of the sagittal mental timeline, independent of the spatiotemporal metaphors present in a language (Callizo-Romero et al., 2020; de la Fuente, Santiago, Roman, Dumitrache, & Casasanto, 2014; Gu et al., 2019; Li & Cao, 2017; Sullivan & Bui, 2016). These studies measured participants' sagittal mental timelines using a temporal diagram task (Casasanto, 2009a), which presents participants with a top-down view of a cartoon character with one box in front of the character and one box behind (Fig. 2). Participants are told a story that involves one activity the character did in the past and another activity the character is planning to do in the future, and participants are asked to indicate using the boxes when each activity occurred. In the first study involving this task, de la Fuente et al. (2014) compared how Spanish and Moroccan Arabic-speaking participants completed the diagrams. Consistent with the front-future encoding of spatiotemporal metaphors in both Spanish and Arabic, Spanish speakers were more likely to place the future activity in the box in front of the character and the past activity in the box behind the character. However, Moroccan participants were more likely to put the past activity in the front box and the future activity in the box behind the character.

de La Fuente and colleagues additionally found that these opposing temporal diagram response patterns were related to cultural differences in the way Spaniards and Moroccans value and focus on the future versus the past. They developed a temporal focus questionnaire to assess individual differences in the value one places on past events and traditional values versus future events and technological progress. The results of this questionnaire indicated that Spanish participants were more future focused, whereas Moroccan participants were more past focused, consistent with their responses on the temporal diagram task. In other words, participants typically mapped the time period (i.e., future or past) that they valued most to the front, and the other time period to the back. A similar relation between participants' temporal focus and the type of mapping they produce on the temporal diagram task has also been found when comparing younger versus older adults, history and archeology students versus computer science and engineering students, and even museum goers visiting exhibits related to ancient versus contemporary art (de la Fuente et al., 2014; Gu et al., 2019; Li & Cao, 2017; Sullivan & Bui, 2016). A recent study that analyzed all existing data from these measures, as well as new data from additional cultural groups, indicates that this relation is robust: across more than 2000 participants from more than 10 cultural and subcultural groups, an individual's temporal focus score predicted significant variance in how likely that individual was to map the future to the front versus the back (Callizo-Romero et al., 2020). Taken together, these findings suggest that both individual and group-level differences in temporal focus influence how people map time onto the sagittal axis.

Given these well-documented effects of culture and individual differences on the orientation of the horizontal/vertical and sagittal mental timelines, a key open question concerns the development of these mappings. Relatively few studies have investigated the developmental origins of spatiotemporal mappings, and these past studies have focused primarily on the origins of the horizontal/vertical mental timeline (Busby Grant & Suddendorf, 2009; Tillman, Marghetis, Barner, & Srinivasan, 2017; Tillman, Tulagan, Fukuda, & Barner, 2018; Tversky et al., 1991; but see Marghetis, Tillman, Srinivasan, & Barner, 2014; Burns, McCormack, Jaroslawska, O'Connor, & Caruso, 2019 for investigations of children's temporal gestures). One open-ended method that has been used to assess the development of the horizontal/vertical mental timeline is to ask children to place stickers on a sheet of paper to represent the relative order of multiple events (Tillman et al., 2018; Tversky et al., 1991). For example, Tillman et al. (2018) used a variant of this open-ended timeline task to assess the development of linear horizontal or vertical representations of time in English-speaking preschoolers, kindergarteners, and adults. They found that the likelihood of spontaneously producing linear arrangements, and particularly left-to-right-arrangements, increased dramatically between preschool and kindergarten and continued to increase into adulthood. This pattern suggests that children may initially be flexible in how they orient their horizontal/vertical mental timelines; but with age and increasing exposure to cultural artifacts, this orientation may become more conventional.

Here, we aimed to build on prior work by investigating factors that contribute to the orientation and development of the horizontal/vertical mental timeline and the sagittal mental timeline in order to gain a holistic picture of how children construct their mental models of time. We collected data from 6- to 15-year-old children in Gujarat Province, India. All participants were enrolled in English-language schools and most spoke Hindi and Gujarati, in addition to English. Both Hindi and Gujarati are written left-to-right and use spatiotemporal metaphors that place the future in the front and the past in the back, similar to English language metaphors. Because previous studies on the development of spatiotemporal associations have focused on English-, Hebrew-, and Arabic-speaking children (Burns et al., 2019; Tillman et al., 2018; Tversky et al., 1991), the present study provides an additional datapoint for identifying how the organization and development of mental models of time may vary across cultures. As we describe below, studying children in India also provided a unique opportunity to investigate the influence of both writing direction and calendar orientation on the orientation of the horizontal/vertical mental timeline. We had two primary goals centered around understanding the development of spatial representations of time in three dimensions.

Our first goal was to investigate the trajectory with which children develop conventional horizontal/vertical and sagittal mappings. To assess the orientation of children's horizontal/vertical mental timelines, we used the open-ended timeline task adapted from Tillman et al. (2018). We assessed 1) the age at which children first began to spontaneously produce linear timelines on the open-ended timeline task, as well as 2) when a particular orientation (e.g., left-to-right or top-to-bottom) might become conventional, such that children within an age group respond similarly to each other (e.g., organizing events left-to-right or top-to-bottom), and 3) whether the conventional response changes with age. Similarly, to assess the orientation of children's sagittal mental timelines, we used a temporal diagram task (Casasanto, 2009a; de la Fuente et al., 2014). We focused on three aspects of children's responses: 1) children's consistency of responding across trials (an index of whether children exhibit an internally consistent sagittal mapping), 2) the conventionality of children's responses, (i.e., whether children within an age group respond similarly), and 3) whether the conventional response changes with age.

Our second goal was to explore the factors that influence the orientation of the horizontal/vertical and sagittal mental timelines. Because Hindi and Gujarati are written left-to-right, but both horizontal calendars (i.e., days of the week ordered left-to-right) and vertical calendars (i.e., days of the week ordered top-to-bottom) are common in India, children in India are an ideal population for exploring how writing direction and calendar orientation each influence the orientation of the horizontal/vertical mental timeline. In particular, if some children orient their horizontal/vertical mental timelines from top-to-bottom, consistent with the orientation of vertical calendars, this would suggest that cultural artifacts that explicitly spatialize time, such as calendars, play a unique role in the organization of the horizontal/vertical timeline, independent of writing direction.

With respect to the orientation of the sagittal mental timeline, we investigated whether individual differences in children's temporal focus would have an effect on the orientation of their sagittal mental timelines, in line with what has been observed in adults (Callizo-Romero et al., 2020; de la Fuente et al., 2014; Gu et al., 2019; Li & Cao, 2017; Sullivan & Bui, 2016). Because younger adults tend to be more focused on the future than older adults and are correspondingly more likely to endorse a front-future mapping (de la Fuente et al., 2014), one might predict that children would be even more future-focused and likely to map the future to the front. Alternatively, children may exhibit individual differences in their focus on the future versus the past – regardless of their age – and these differences may influence the direction of their sagittal mental timelines. To test this, participants were given an adapted, child-friendly version of the temporal focus questionnaire (de la Fuente et al., 2014) to determine the degree to which individual children valued the future versus the past. We then assessed whether children who placed a greater value on the past were more likely to endorse a front-past mapping compared to children who placed a greater value on the future.

We were also interested in how the developmental trajectories of the horizontal/vertical mental timeline and sagittal mental timelines relate to one another. On the one hand, because these two types of mappings might rely on different types of experience (i.e., exposure to written language and calendars for the horizontal/vertical timeline and locomotor experience and exposure to spatial metaphors for the sagittal timeline), these two types of mappings might exhibit independent developmental trajectories. In addition, because the sagittal mental timeline may arise from locomotor experience and is encoded in language whereas horizontal/vertical mappings are not (e.g., English describes future events as being in front but not to the right), it is possible that children develop a sagittal mental timeline earlier than they construct a horizontal/vertical mental timeline, which may be more reliant on cultural artifacts that young children have limited experience with. These different trajectories could play out in terms of the emergence of consistent spatiotemporal mappings or with regards to the emergence of culturally conventional mapping orientations. On the other hand, if children are constructing a holistic three-dimensional model of how to map time onto space, perhaps as they gain increasing exposure to linguistic metaphors and cultural artifacts, they may show evidence of constructing or changing the orientation of both types of spatiotemporal mappings in parallel.

Section snippets

Participants

Data from 149 participants were included in the final analyses, including data from 36 first grade students (mean age = 6.7 years, range: 5.8–8.0, 11 female), 37 third grade students (mean age = 8.6 years, range: 7.9–10.0, 10 female), 40 sixth grade students (mean age = 11.4 years, range: 10.7–12.4, 23 female), and 36 ninth grade students (mean age = 14.3 years, range: 13.5–15.3, 23 female). All participants were recruited from and tested at two English-language K-12 schools in and around the

Timeline task

In our first series of analyses, we explored the emergence of a linear horizontal/vertical mental timeline, as well as which orientations were most common. First, we assessed the proportion of trials in which participants placed the stickers in a linear configuration. The proportion of linear arrangements increased across grades (χ2(1) = 26.78, p < 0.001). Although most first grade students did not spontaneously create linear arrangements, by the third grade, the majority of students produced

Discussion

Within a culture, different spatial axes are frequently used to represent different temporal concepts. One common representation is the horizontal/vertical mental timeline, a line external to the body that is often oriented horizontally with either earlier events occurring on the left and future events on the right or the reverse (Bergen & Lau, 2012; Casasanto & Bottini, 2014; Tversky et al., 1991). In addition, when thinking about moving through time, many cultures map time onto the sagittal

CRediT authorship contribution statement

Ariel Starr: Conceptualization, Methodology, Investigation, Formal analysis, Visualization, Writing - original draft, Writing - review & editing. Mahesh Srinivasan: Conceptualization, Methodology, Writing - review & editing, Funding acquisition.

Acknowledgements

The authors would like to thank Neha Singh for her invaluable assistance with translating the materials and data collection and the members of the Language and Cognitive Development Lab at Berkeley for their helpful feedback on the study design, manuscript, and visualizations. This work was supported by NICHD award F32HD085736 to AS and awards from the National Science Foundation (SBE-16302040) and the James S. McDonnell Foundation to MS.

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