The aim of the present study was to examine whether a task-irrelevant visual action context could cause a time distortion in tactile duration judgments. Participants were asked to judge the duration of a vibrotactile stimulus while watching an irrelevant swinging ball. We hypothesized that real ball movements might automatically elicit an appropriate action schema, even when participants were instructed not to make any explicit response (such as grasping) to the ball. The results indicated that monitoring task-irrelevant real ball movements with strong S–R associations expanded tactile duration judgments relative to a static baseline condition, provided that the hands were not occupied. Participants markedly overestimated the tactile duration when the ball was approaching relative to when it was moving laterally or was static (Exp. 1). When the hand was placed at the middle path of the approaching and receding movements, providing comparable S–R associations, both conditions led to a comparable expansion of subjective tactile duration (Exp. 2). Most interestingly, the duration expansion engendered by observing an approaching ball was greatly reduced when participants held two lightweight objects in their hands (Exps. 3 and 4).
Previous studies had shown that a movement event is perceived as lasting longer than a static event of the same physical duration (Brown, 1995; Kanai, Paffen, Hogendoorn, & Verstraten, 2006; Kaneko & Murakami, 2009). It has been argued that a speeding up of the visual “internal clock” by moving objects provides an ecological advantage for the prevention of collisions, avoidance of predators, and so forth (Kaneko & Murakami, 2009). It should be noted that in those studies, duration expansion was directly related to the moving stimuli, and judgments were made within the same, visual modality. In our study, by contrast, the main task was to estimate duration in the tactile modality, and the ball movement was a task-irrelevant visual event that bore no causal relation to the tactile stimulation. Given this, our findings go beyond previous reports by indicating that not only the perceived duration of the movement event itself, but also those of other, action-irrelevant events such as tactile stimulation may be affected.
It might be argued that these effects were due to the ball movement inducing a general arousal effect, since previous studies had shown that high-contrast or high-arousal stimuli speed up the internal pacemaker, expanding the subjective durations of those stimuli (Droit-Volet, Brunot, & Niedenthal, 2004; Penton-Voak, Edwards, Percival, & Wearden, 1996). However, this is unlikely to account for our results, because we found no physiological indications of increased arousal in the movement conditions (Exp. 4); that is, the ball swing was not experienced as a highly arousing stimulus, capable of speeding up the internal pacemaker. Even though the SAM subjective rating values were slightly higher in the two approaching-movement conditions than in the static condition, this increased subjective arousal cannot explain the differential subjective durations between the two approaching-movement (i.e., hands-occupied vs. hands-free) conditions (Exp. 3) and the lack of a difference between the approaching-movement hands-occupied and baseline conditions (Exp. 4). In this regard, our findings are consistent with the conclusions from saccadic chronostasis studies—namely, that the arousal induced by an action or movement is not a critical factor per se for the expansion of subjective duration (Yarrow et al., 2001; Yarrow et al., 2004).
One key factor that can influence subjective time perception is attentional modulation (Block & Zakay, 1997; Zakay & Block, 1997). A classic phenomenon—namely, that “time flies when you are having fun, and time drags when you are having trouble” (e.g., Droit-Volet & Meck, 2007; Gable & Poole, 2012)—is partly due to attentional and arousal modulations. According to attentional-gate theory (Block & Zakay, 1997; Zakay & Block, 1997), attentional resources are divided between timing and nontiming processes. When attention is engaged by some nontiming event, such as the context of a fun story you are reading, the timing process for estimating the reading time is temporally halted, leading to a subjective time contraction. An irrelevant stimulus, such as the ball movement in our study, might give rise to an analogous diversion (or disengagement) of attention from the tactile temporal process. If this were the case, we should have observed a subjective duration contraction for tactile temporal judgments. However, in the present experiments (hands-free conditions), we did not find duration contraction but observed the opposite: a subjective duration expansion. In terms of the attentional-gate theory, this would mean that the visual movement did not draw attention away from the tactile modality, at least not for tactile temporal processing. Additional evidence against attentional capture by the visual event is provided by the fact that the sensitivity of temporal bisection was unreduced in the movement as compared to the static conditions in any of four experiments.Footnote 2
Thus, instead, we propose that the real ball swing may spontaneously induce action preparation (e.g., preparation for manual grasping or collision avoidance), even though no explicit action is (to be) made (Fotowat & Gabbiani, 2011), in that motor activation is likely to alter subjective time estimates. Consistent with our suggestion of an implicit reaction induced by the automatic activation of an S–R association, previous studies have confirmed that viewing objects with action meanings can prime manual responses related to those objects (Tucker & Ellis, 2004); such priming effects have been observed in premotor and motor cortex, parietal visuomotor cortex, and the supplementary motor area (Bensmaïa, Killebrew, & Craig, 2006; Grezes & Decety, 2002; Kiefer, Sim, Helbig, & Graf, 2011; Sim, Helbig, Graf, & Kiefer, 2014). The intrinsic perception–action links revealed by these studies constitute a core notion of embodied cognition, which posits that perception and cognition can be appropriately understood only in terms of sensorimotor interaction (Engel et al., 2013; Varela, Thompson, & Rosch, 1991). The embodiment view has recently also been introduced in time perception (for reviews, see Droit-Volet et al., 2013; Effron et al., 2006; Gable & Poole, 2012), providing a theoretical framework for our proposal of a functional linkage between action context and time perception. According to embodied timing (Craig, 2009; Droit-Volet et al., 2013; Effron et al., 2006; Niedenthal, 2007), subjective duration is based on both the sensory encoding of external events and the internal sensorimotor and bodily states during the judgment process. Indeed, a recent functional magnetic resonance imaging (fMRI) study has shown that insular cortex, a region typically involved in the awareness of emotional and bodily states (Craig, 2009), is activated during the duration-encoding phase of a temporal reproduction task (Wittmann, Simmons, Aron, & Paulus, 2010). The findings of the present study favor and extend the embodiment view of time perception: They show that temporal processing in one modality (here, touch) can be influenced by task-irrelevant motor activation through the operation of S–R associations (even though no explicit action is being made), with the influence depending on the urgency and possibility of interaction. For instance, the urgency of a reaction was, arguably, higher for the approaching ball swing than for the lateral swing, and was similar for the approaching and receding swings in the present study. As a consequence, the tactile duration was perceived as being longer in the approaching- than in the lateral-movement condition, but the same as in the receding-movement condition (both approaching and receding movements provided equal opportunities for interaction). In addition, the weak S–R association with the lateral ball may be a cause for its marginal effect relative to the static conditions. Furthermore, when participants held two lightweight objects in their hands under conditions of approaching movement, the possibility of manually reacting to the ball was limited, and the motor activation (using the hands) might have been inhibited. As a result, the tactile expansion was greatly reduced in the approaching-movement hands-occupied condition (Exps. 3 and 4). Note that in Experiment 4, participants’ fingers were tied to SCR sensors, which might have acted as an inhibitor that reduced the subjective duration expansion (relative to simply holding objects in Exp. 3) in the approaching-movement hands-free condition. Importantly, however, we found no difference in tactile duration judgments between the static hands-free and hands-occupied conditions (Exp. 3). These findings have several implications: First, both the differential effects on subjective duration between the approaching-movement conditions (hands-free vs. hands-occupied) and between the approaching- and lateral-movement conditions may be indicative of the roles of action preparation and its possibility, rather than merely reflecting the (abstract) representation of objects with action meanings (Barsalou, 2008; Kiefer & Barsalou, 2013; Kiefer & Pulvermüller, 2012). Second, the reduced effect in the approaching-movement hands-occupied condition also suggests that visual looming and/or a distance effect seems not to be the main factor for tactile-duration expansion, given that the movement settings (visual size and travelling distance) were exactly the same in the two approaching-movement (hands-free and hands-occupied) conditions. Third, the null difference in tactile-duration estimates between the static hands-free and hands-occupied conditions indicates that the subjective duration expansion observed in the ball movement conditions requires strong action context, rather than merely the presence of an affordance (Helbig, Graf, & Kiefer, 2006).
One might ask why the implicit motor activation induced by the real ball swing (i.e., approaching and receding movements) could expand, rather than contract, the subjective tactile duration. Overestimation of target durations caused by action or action context has been demonstrated in various paradigms, such as during saccadic or manual movements (Yarrow et al., 2001; Yarrow & Rothwell, 2003), simple duration reproduction (Ganzenmüller, Shi, & Müller, 2012; Shi, Ganzenmüller, & Müller, 2013), or manual preparation (Hagura et al., 2012). The idea that the various paradigms tap into different underlying mechanisms might explain why the accounts proposed for duration expansion are divergent. Duration expansion of an event that immediately follows an action has been interpreted in terms of a compensatory mechanism, in which the onset of the event is captured by the onset of the action (Yarrow et al., 2001); by contrast, expansion of the reproduced duration of an auditory event has been attributed to modality-specific “internal clocks,” with the auditory clock ticking faster than other modality-specific clocks (Ganzenmüller et al., 2012; Shi, Ganzenmüller, & Müller, 2013). It has also been suggested that activity induced by movement preparation in the motor cortices is linked to the initiation of dynamic movement activity (Churchland, Cunningham, Kaufman, Ryu, & Shenoy, 2010), as well as to the facilitation of perceptual processing (Hagura et al., 2012). Similarly, implicit motor activation induced by nearby moving stimuli with strong interactions with the body may increase the speed of somatosensory processing, such that the real action, if it becomes necessary, can be targeted more precisely—thus yielding a greater benefit for survival. The duration expansion of tactile events observed in the present study may reflect such facilitated sensory processing induced by motor activation. This view favors the notion of embodied time perception (Craig, 2009), which proposes that altering bodily states (e.g., here, motor activation) changes the temporal resolution of the “moment” representation of the sentient self, a building block of time perception. It is worth noting that action does not always expand perceived duration. For example, when an action has a causal effect, the gap between the action and its consequent effects is shortened, which is attributed to “intentional (action–effect) binding” (Haggard & Clark, 2003; Haggard, Clark, & Kalogeras, 2002). However, this type of shortening effect is specific to causal events and is induced by the anticipatory awareness of action effects (Haggard & Clark, 2003; Moore & Haggard, 2008) or by general causal binding (Buehner, 2012; Buehner & Humphreys, 2009).
Finally, note that the present study is potentially limited, in that activation of S–R associations was only manipulated using ball movements within reachable space (though Ball & Tronick, 1971, showed an automatic avoiding reaction to a real approaching object in infants), and the strength of the associations, rather than being assessed directly, was only inferred from their (differential) effects on duration judgments. However, when compared to alternative accounts framed in terms of visual-looming, attention, and/or arousal effects, the embodiment framework arguably provides the better predictive power for our overall pattern of our results. Nevertheless, in order to corroborate our conclusions, future, complementary work should attempt to examine automatic S–R effects using physiological measures (e.g., electrocardio- or electroencephalography), so as to establish a more direct link between implicit reactions and time perception, and to examine different degrees of “interaction”—for instance, by comparing “near-body” with “far-body” movements. Further research should also examine whether crossmodal duration expansion by action context is specific to the tactile modality, or whether it can be generalized to other modalities, such as audition.
In conclusion, our results provide new evidence that task-irrelevant action contexts induced by seeing a real moving (approaching or receding) object expand tactile duration judgments. When induction of this context is physically inhibited, subjective expansion of tactile durations is greatly reduced. These findings favor an embodiment view of time perception (Craig, 2009; Droit-Volet et al., 2013; Effron et al., 2006; Niedenthal, 2007), according to which action preparation is likely to increase the speed of sensory processing (Hagura et al., 2012) and, consequently, to expand subjective time in the sensorimotor loop. Our findings suggest that subjective duration expansion by action contexts is not limited to the action itself or to events relating to action goals, but is also found for task-irrelevant motor activation occurring in the sensorimotor loop.