Previous RT studies have shown that people code time from right to left (e.g., Ouellet, Santiago, Funes, & Lupiáñez, 2010a; Ouellet Santiago, Israeli, & Gabay, 2010b; Santiago et al., 2007; Torralbo et al., 2006; Ulrich & Maienborn, 2010; Vallesi et al., 2008; Weger & Pratt, 2008), at least in cultures with a left-to-right writing system (Fuhrman & Boroditsky, 2010; Ouellet, Santiago, Israeli, & Gabay, 2010b). These studies have demonstrated that responses to past- and future-related linguistic information are generally faster when the response direction is compatible with the left-to-right mental timeline than when it is not. Strangely enough, this left-to-right coding has no counterpart in the inventory of temporal expressions in the languages all over the world. Instead, we quite frequently encounter an association of time with the back–front axis. Future is commonly associated with the front, and past with the back (see Haspelmath, 1997; Radden, 2004; Traugott, 1978; see also Núñez & Sweetser, 2006, for a discussion of the prominent exception Aymara). The present study investigated the linguistic relevance of this back–front mental timeline for the processing of past- and future-related sentences.
More precisely, the present study had two goals. First, it examined whether this conjectured back-to-front mental timeline is involved when people process complete sentences. Second and theoretically most crucially, the study assessed whether processing sentences automatically activates this back-to-front mental timeline. Such a result would provide strong evidence for the hypothesis that activation of a back–front timeline is involved in sentence processing and, thus, in the comprehension of a sentence’s content.
Experiment 1 was analogous to the first experiment reported in Ulrich and Maienborn (2010). Participants were asked to move a slider forward or backward in response to past- or future-related sensible sentences. A clear front–back congruency effect on RT was obtained, supporting the assumption that processing of temporal sentence information activates spatial schemata even for manual push and pull responses (cf. Torralbo et al., 2006). In contrast to RT, the time required to move the slider from its middle starting position to its proximal or distal goal was not significantly influenced by the spatial mapping of future and past to the front and to the back.Footnote 3 This indicates that the relevant spatial schema operates entirely on cognitive processes that precede the initiation of the response, rather than on late motor processes that are involved in guiding the overt response (cf. Ulrich, Giray, & Schäffer, 1990).
Experiment 2 examined whether understanding a temporally located sentence would automatically activate the back–front timeline. If spatial schemata are involved in the processing of temporal sentence information, the space–time congruency effect on RT should also emerge in a task when time–space association is task irrelevant, similar to the SNARC effect (Dehaene et al., 1993) or to the Simon effect (Kornblum et al., 1990). As in Ulrich and Maienborn’s (2010) study, however, the effect disappeared when participants classified the displayed sentences according to their meaning (sensible vs. nonsensical), rather than their temporal content (past or future related). It seems difficult to attribute this outcome to not paying attention to temporal sentence information, since participants had to process this information for the secondary task. It is also unlikely that the secondary task inferred with the primary one, because an additional experiment without the secondary task produced virtually identical results. Hence, this pattern of results suggests that a congruency effect does not emerge when the temporal reference of the sentence is not task relevant (see note 3).
The results of Experiment 2 are consistent with a nonautomatic account of the space–time congruency effect. This conclusion also fits in with the weak view of the metaphoric mapping hypothesis that was originally suggested by Boroditsky (2000, p. 4). This view holds that spatial schemata are needed only to establish temporal representations. Once these representations are available within the cognitive system, the spatial domain is no longer required to think about time, and thus the mental representation of time may be entirely separated from sensory and motor information (cf. Mahon & Caramazza, 2008). By contrast, the strong version of the metaphoric mapping hypothesis maintains that thinking about time always requires the activation of spatial schemata. Therefore, it seems possible that participants in the more implicit task of Experiment 2 did not need to activate spatial schemata in order to perform this task, whereas in Experiment 1, the activation of spatial metaphors or preexperimental time–space linkages may have helped to increase task performance.
For example, according to the memory account of Ulrich and Maienborn (2010), response selection in Experiment 1 is particularly efficient when salient features of the stimulus (i.e., past and future) and of the response (i.e., back and front) correspond to each other (Proctor & Cho, 2006). Thus, participants could employ the preexperimental cognitive linkage between space and time to memorize and, thus, enhance the mapping of temporal sentence information (past vs. future) onto the spatially arranged responses (left vs. right). Memorizing the S–R mapping would be more efficient and, thus, would involve especially fast responses when participants can build on the preexperimental linkage between space and time, as in the congruent condition in Experiment 1.
Although this memory account is consistent with the results of the present study, it is at variance with results reported by Torralbo et al. (2006, Experiment 1). As was reviewed in the introduction, participants responded vocally with the words “past” and “future” to the temporal meaning of words, instead of with spatially arranged responses, as in most other RT studies investigating this topic. Therefore, participants in the study of Torralbo et al. did not need to memorize any S–R mapping that involved a spatial S–R relation. Nevertheless, participants’ responses were faster when future (past) words were presented in front (back) of the silhouette than when this mapping was reversed. This result argues against a memory account of the space–time congruency effect on RT. One must bear in mind that several experimental differences exist between the study of Torralbo et al., the present one, and the study of Ulrich and Maienborn (2010). For example, the vocal responses “past” and “future” may activate spatial schemata rather than the temporal reference of the target word. Therefore, the front–back congruency effect obtained in their first experiment might be attributed to the temporal content of the vocal responses (similar to a Stroop effect), rather than to the temporal reference of the target words. Consistent with this view, the front–back congruency effect disappeared in their second experiment, when participants made manual rather than vocal responses.
In addition, the results of Experiment 2 seem at variance with the results of Sell and Kaschak (2011). In their study, participants made categorical sensibility judgments about sentences that did not require participants attending explicitly to the temporal information of a sentence, as in Experiment 1. The task in Experiment 2 of the present study was less implicit, because participants had to process a sentence’s temporal information for performing the secondary task. These results are not contradictory but, rather, reflect task context. The results of Sell and Kaschak’s study indicate that the back–front axis becomes activated during text comprehension when a sentence like (2) is processed, which expresses a sufficiently large time shift in a narrative text such as in the following three-sentence story (adapted from Sell & Kaschak, 2011):
Jackie is taking a painting class.
Next month, she will learn about paintbrushes.
It is important to learn paintbrush techniques.
Spatial schemata may help to build up a discourse model, for example, by ordering the temporal events in this text along a mental timeline. By contrast, comprehending the content of a single, isolated sentence may not involve such excessive ordering of temporal events. Therefore, the results of Sell and Kaschak are not at variance with our major conclusion—namely, that the understanding of isolated sentences (i.e., the processing of grammatically and lexically supplied temporal information at sentence level) does not require the activation of spatial schemata. Future research is required to test this hypothesis—namely, that spatial schemata may be activated during the buildup of a discourse model, but not during the processing of a single sentence.
Furthermore, the present results rule out an alternative account of the left–right congruency effect observed in previous RT studies.Footnote 4 This alternative assumes that the space–time congruency effect on RT can be attributed to a mapping of space to emotional valence, instead of to a direct metaphoric mapping of space to time. For example, Casasanto (2009) found that right-handers tend to draw “good” animals on the right, whereas left-handers prefer to draw them on the left. Accordingly, the left (right) side tends to be associated with negative (positive) valence. Assume that participants link future with positive stimuli and the past with negative ones. In this case, the space–time congruency effect would be mediated by the mapping of space to emotional valence, rather than to space directly. A linkage between temporal connotation and emotional valence predicts, however, a front–back congruency effect of time that is opposite to the one observed in Experiment 1. Specifically, performance is usually better when positive stimuli are linked to a movement toward the body and negative stimuli are linked to a response away from the body (e.g., Chen & Bargh, 1999; Duckworth, Bargh, Garcia, & Chaiken, 2002). According to this alternative account, responses should be especially fast when future is linked to a movement toward the body and past away from it. This prediction was, however, disconfirmed by the results of Experiment 1, rendering it unlikely that the space–time congruency effect is mediated by emotional valence. In addition, this alternative account seems also to be at variance with RT results that show that the writing system of a culture determines direction of the mental time line (Fuhrman & Boroditsky, 2010; Ouellet, Santiago, Israeli, & Gabay, 2010b). This would imply that the writing direction of a culture modulates the association of future and past with positive and negative valence. This, however, seems unreasonable, because valence is not linked to body side for right- and left-handers alike (de la Vega, De Filippis, Lachmair, Dudschig, & Kaup, 2011).
In summary, our study demonstrated a clear space–time congruency effect during online processing of sentences. In contrast to previous studies (Ouellet, Santiago, Funes, & Lupiáñez, 2010a; Santiago et al., 2007; Weger & Pratt, 2008), a back–front response dimension was used, rather than a left–right dimension, for classifying temporal sentence information. From a psycholinguistic point of view, the back–front dimension is particularly relevant because almost all languages of the world associate future (past) with front (back). Therefore, if the association with a mental timeline were functional for the comprehension of temporal expressions, the back–front orientation of the mental timeline would be better suited than the left–right orientation to detect its activation during online sentence processing.Footnote 5 Consistent with the notion of a back–front mental timeline, faster responses occurred for the past–back and future–front mapping than for the reverse mapping. As in Ulrich and Maienborn’s (2010) study, this space–time congruency effect on RT disappeared when temporal sentence information was no longer task relevant for classifying the meaning of sentences. This particular result suggests that the back–front timeline may not be involved when people process the temporal meaning of a sentence.
In addition to this conclusion of the psycholinguistic relevance of the mental timeline, we strongly believe that null effects in experiments with high statistical power (i.e., small SEs, such as in Experiment 2) are of particular theoretical importance in the field of embodied cognition. Such effects help to demonstrate the limits of the tasks conforming to the predictions of the embodied cognition approach. This is especially true if experiments employ a design analogous to the one that has produced clear RT effects for a related issue (SNARC) in previous research. Not taking into account such null effects would bias research and create the exaggerated view that embodied effects are ubiquitous phenomena (see also Fiedler, 2011). Our research clearly casts doubt on such a view.