Time and Time Perception

Time and Time Perception Berit Brogaard, Dimitria Gatzia (Forthcoming in Topoi) Abstract There is little doubt that we perceive the world as tensed—that is, as consisting of a past, present and future each with a different ontological status—and transient—that is, as involving a passage of time. We also have the ability to execute precisely timed behaviors that appear to depend upon making correct temporal judgments about which changes are truly present and which are not. A common claim made by scientists and philosophers is that our experiences of entities enduring through transient changes are illusory and that our apparently accurately timed behaviors do not reflect dynamical time. We argue that our experiences of objects enduring through transient changes need not be thought of as illusory even if time is not dynamic at the fundamental level of reality. For, the dynamic properties we experience objects as having need not be fundamental properties. They could be weakly emergent from static, temporal properties. Temporal properties, on this view, are similar to ordinary properties like that of being solid, which are correctly experienced as properties of medium-sized material bodies even though they are not instantiated at the fundamental level of reality. Keywords: A-theory of time; brain’s internal clock; endurantism; four-dimensional spacetime; perdurantism; temporal illusion; temporal passage; time perception; emergence; responsedependence 1. The A-Theory Versus the B-theory of Time Two distinct theories of time (proposed by McTaggart, 1908) appear to fit current theories of physics (Monton, 2010), although it is generally accepted that only one of them is directly supported by empirical data from physics. On the A-theory, time differs from the dimensions of space in the sense that although there are only two-place spatial relations such as being south of, and hence no unary spatial properties such as being south, there are genuine A-theoretical properties such as being present, being one day out in the future, etc. (McTaggart, 1908). On this theory, time passes and there are genuine changes involving material bodies. On the Btheory, time does not differ from the dimensions of space since the only temporal relations that are instantiated are space-like B-relations such as being earlier than. On this theory, no genuine A-theoretical properties exist and the passage of time is only apparent (McTaggart, 1908) in the sense that it is the result of the way humans happen to perceive the world. One of the main challenges for B-theorists is to explain why time is experienced as passing, if it is not. The standard claim is that our experiences of the passage of time are illusory. However, as we shall argue, making this claim on the grounds that physics has no need for A-theoretical properties (e.g., temporally passing, enduring through genuine change) does not show that our experiences of these properties are illusory. After all, the B-theory does not rule out the 1 possibility that there are dynamic, temporal properties, as the properties of physical theories are not the only properties that are instantiated. We argue that it is plausible that A-theoretical properties of the kind we experience objects as having are emergent properties akin to properties such as being solid. On this view, A-theoretical properties exist but not as fundamental or irreducible properties. 2. The B-Theoretical Fallacy Philosophers have offered various explanations of the apparent passage of time (see e.g., Oaklander, 1993; Mellor, 1998; Skow, 2011; Prosser, 2012). What these explanations have in common is that they either implicitly or explicitly treat the ordering of experiences as forming a tenseless B-series but the phenomenology of the experiences as generating the appearance of passage and endurance through genuine change. To each time slice of a perceiver, it feels to him or her as if time is passing and that his or her present moment is present in an A-theoretical sense. The temporal properties presented in experience are thus fundamentally different from the temporal properties instantiated in the external world. One influential explanation is that of Mellor (1998), who proposes that our experiences of time as passing are generated as an effect of memory. Each time slice of a perceiver remembers the past but not the future, which generates an experienced asymmetry. On this view, our experiences of the passage of time are illusions generated by our experiencing some events as occurring simultaneously with us and others as having occurred only previously. As Prosser (2012) points out, however, this explanation seems implausible for two reasons. The first is that time perception does not seem to require reflection on the contents of our memories. The second is that while the accumulation of memories may explain our sense that time has a direction and that there is an asymmetry between the past and the future, it does not by itself explain why time perceptually seems to pass. Upon rejecting Mellor’s explanation, Prosser (2012) proposes another explanation of how we experience the passage of time, according to which, our sense of a passage of time originates in our experiences of persistence. On this view, our experiences represent objects as enduring through genuine dynamic changes, which gives rise to the illusion that time passes. This explanation, however, faces several difficulties. Firstly, it explains why we seem to experience time as passing only by raising another mystery, viz., why do we experience objects as enduring (that is, as being wholly present at each moment at which they exists), if they are in fact perduring (that is, they are spatiotemporal parts located at different spacetimes). It is hardly a satisfactory conclusion that virtually all of the experiences we take to be veridical are necessarily falsidical. Secondly, it does not explain why some illusions of passage seem to be less accurate than others, which as we shall see is an assumption made by dominant theories of time perception. Thirdly, Prosser’s explanation is too simplistic. It is unlikely that our sense of a passage of time simply comes from the experience of objects enduring through changes. Our perceptual experiences are limited to those particular times that we call ‘present moments’, moments during which we are simultaneously aware of the succession of several entities undergoing endurance or change. We never perceive events occurring at any moments other than those that we view as the present. Yesterday you were perceiving a different slice of the 2 universe than you are today, and the slices of the universe that you perceive appear to line up neatly in a temporal series. This very fact that perceptual experiences that mark some things as being present seems to be the main contributing factor to our sense of a passage of time. One urgent problem, then, is to explain why our experiences mark certain events as present in an Atheoretical sense. There are numerous other authors who have suggested that our experiences of dynamic temporal properties are illusory (see e.g. Oaklander, 1993; Mellor, 1998; Dyke, 2002; Skow, 2011; Prosser, 2012; Ingthorsson, 2013; see also Yehezkel, 2013). It is not clear why they think that this conclusion follows directly from the B-theory of time. A plausible explanation is that the following sort of argument is implicitly accepted:1 B-Theoretical Argument: 1. The A-theoretical temporal properties experienced in ordinary experience are not properties to which the theories of physics are committed. 2. If a property perceived in ordinary experience is not one to which the theories of physics are committed, then the experience is illusory. 3. Hence, when A-theoretical temporal properties are perceived in ordinary experience, the experience is illusory. However, this argument is problematic. Premise (2) assumes that in order for our experiences of time as passing to be veridical A-theoretical properties must be irreducible or ontologically primitive. This, however, is incorrect. For, our experiences would not be illusory if A-theoretical properties were akin to properties such as being solid. Physicists will tell us that the mediumsized material bodies that we become acquainted with through experience are not really solid but consist mostly of empty space. However, few theorists would deny the veridicality of all of our experiences of solid, medium-sized material bodies. Saying that some experiences are veridical does not require seeing into the deepest corners of reality. Our visual experiences of solid medium-sized material bodies and their colors, shapes, and textures can be characterized as veridical without us having to commit to the claim that these properties are irreducible or ontologically primitive. B-theorists generally agree with this characterization of the circumstances under which visual experience is veridical (see e.g., Oaklander, 1993; Mellor, 1998; Dyke, 2002; Skow, 2011; Prosser, 2012). They nevertheless appear to treat time differently from space, colors, shapes, texture, etc., in this regard. And although they do not deny the veridicality of our experiences of rocks as solid in spite of the fact that physicists say that they are mostly empty space, they do appear to regard our experiences of the passage of time as illusory. In the absence of a good argument, this difference in assessment seems unjustified since our experiences of A-theoretical properties can be veridical, even if the B-theory of time happens to be true at the fundamental level of reality. 1 Just to be clear, we are not arguing that the authors mentioned here are accepting this argument. We are merely suggesting a plausible argument that can be made in support of the claim that the passage of time is illusory if the B-theory is true. 3 The issue of veridicality bears on the question of truth. When we say that our experience of a rock as solid is veridical, this is normally taken to mean that it is true that the rock in question is solid (Siegel, 2010). Regardless of whether the veridicality of experience is cashed out in terms of true content or obtaining facts, veridicality is a function of truth. There can be different truths at different levels of organization and complexity, and only some of these truths are fundamental truths. For example, the medium-sized objects that we experience as solid or as having a smooth surface are neither solid nor have a smooth surface at the fundamental level of reality. Similarly, even if the B-theory is true at the fundamental level of reality, there is still room for Atheoretical facts, such as time is passing. Of course, in that case, these facts would not be irreducible or ontologically primitive but would be akin to facts such as the rock is solid. In what follows, we argue that A-theoretical properties are best construed as weakly emergent properties. 3. Weakly Emergent A-Theoretical Properties Emergent properties ‘arise’ out of more fundamental properties at a certain level of complexity or organization. When people say that a property emerges at a certain level of complexity, they typically mean that a property that is absent at a lower level appears, or comes into being, at a higher level. The emergent property is novel and unexpected compared to the properties of the emergence base. There are, however, two very different versions of emergence. On a weak version, truths about emergent properties are deducible, at least in principle (or by simulation), from the low-level phenomenon. The apparent novelty of a weakly emergent property is an artifact of the limited reasoning skills of mortal human beings. As David Chalmers (2006) puts it, weakly emergent properties are interesting, non-obvious features that are interesting and non-obvious to us relative to the perceived simplicity of the underlying principles governing the system. Weak emergence is uncontroversial. The property of being liquid water, for example, weakly emerges from the low-level properties characterizing hydrogen and oxygen molecules. Weakly emergent properties can be derived, at least in principle, from complete knowledge of micro-level information (Bedau, 1997). On a strong version, truths about emergent properties are not deducible, even in principle, from the low-level phenomenon. According to C.D. Broad, in the case of strong emergence, “the characteristic behavior of the whole could not, even in theory, be deduced from the most complete knowledge of the behavior of its components, taken separately or in other combinations, and of their proportions and arrangements in this whole” (1925: 59). Strongly emergent properties are not deducible from the low-level phenomenon because they are fundamental properties in their own right but unlike the fundamental properties of physics, strongly emergent properties appear at a certain level of complexity. The view that there are strongly emergent properties is controversial and requires a special argument. The view that there are weakly emergent properties, by contrast, is widely accepted by scientists and philosophers alike (Chalmers, 2006; Green, 2003). The suggestion that A-theoretical properties are weakly emergent from the properties of microphysics make it plausible that our experiences of time passing are sometimes veridical. 4 Emergent properties are instantiated by systems that have the relevant organizational complexity and are typically thought to exert a causal influence on the system’s behavior. The relevant systems that instantiate A-theoretical properties appear to be events and objects that undergo changes. It remains to be seen how A-theoretical properties could weakly emerge from B-theoretical properties and relations. The least controversial idea is that A-theoretical properties arise from static temporal properties in the sense of being response-dependent properties, viz., dispositions to cause experiences of passage and genuine change in normal perceivers in normal circumstance.2 If this is correct, then A-theoretical properties are similar to colors, on the traditional account of colors as secondary qualities. There are, of course, familiar problems with specifying what ‘normal’ means in this context, but we can set this problem aside here. On this view, external objects literally possess A-theoretical properties. So, statements about passage and dynamic change can literally be true. It is literally true that time is passing, that the present moment is special and that there are dynamic changes. The suggestion that A-theoretical properties are response-dependent is compatible with the tenet underlying weak emergence— that is, response-dependent A-theoretical properties are deducible at least in principle from Btheoretical properties. Whether their appearance is novel or surprising, as the criteria for weak emergence state, is debatable. The suggestion that A-theoretical properties are responsedependent, however, is plausible only if there is a credible account of how the brain generates A-theoretical properties on the basis of a reality in which there is only static time. In what follows, we will show that current theories about time perception, at least at first glance, appear to be able to account for how the appearance of passage and genuine change is generated on the basis of B-theoretical properties. 4. The Brain’s Internal Clock Michel Treisman, one of the pioneers in the psychology of time perception, rejected the commonly accepted naive realist view about time perception in the same fashion that Galileo, and his contemporaries, had rejected naive realism about color and taste. On this view, we do not experience temporal properties directly but perceive them by experiencing objects as enduring through transient changes. Treisman held that the dimensions of space and time relate to the physical world in a way similar to the way the colors we experience objects as having relate to the external world. Both time and color perception is constrained by the needs it must serve. In the case of time perception, it is constrained by the need for accurate predictions. Treisman’s work on time perception led to the dominant view that the brain keeps track of time in virtue of high-level cognitive processes involving scalar-timing properties (SET). SET theories posit the existence of an internal clock in the brain, which generates subjective temporal values that are typically correctly related to real time (François 1927; Treisman, 1963; Gibbon et al. 1984). Although SET theories were originally developed as theories of the striking regularities in 2 Of course, an account of how these properties emerge from microphysics would be needed. However, due to space constraints, here we can only make some plausible suggestions. 5 the performance of non-human subjects (e.g., rats and pigeons) on temporally-constrained reinforcement schedules, they were subsequently repurposed as theories of how humans keep track of time (Wearden and McShane 1988; Wearden 2001; Allan 1998). This framework is consistent with our proposal that A-theoretical properties are response-dependent properties since the internal clock in the brain provides the mechanism by which events and objects are disposed to cause experiences of passage and genuine change to perceivers like us. Unlike Treisman’s theory, which postulates that the brain’s internal clock is not self-sustaining but needs to be initiated regularly by external stimuli, contemporary SET theories speculate that the brain’s internal clock is continuously running and self-sustaining. SET models consist of several modules, including a pacemaker, a switch, an accumulator, working and reference memory, and a comparator (Block, 2003; Grondin, 2010; Klink et al., 2011). The linear function of physical time is thought to involve both a pacemaker that produces pulses at a fairly constant rate and the accumulation of these pulses in working and reference memory. During an event, a mode switch allows the accumulator to collect emitted pulses. At the end of the timed event, the number of pulses in the accumulator is compared with a reference time from memory (known as reference memory). This comparison is necessary because although the content (i.e., the pulse rate) of the accumulator is reflected in working memory, the representations of times, which are necessary for temporal tasks (e.g., comparing interval durations for similarity), and which are the source of the scalar properties observed in time estimates, are stored in reference memory (Gibbon et al., 1984; Wearden 2003). Longer perceptual durations require more accumulated pulses than shorter perceptual durations (Klink et al., 2011). SET theories thus predict that the experience of succession can reflect the succession of experiences. However, various factors can affect the pace of experienced succession and the brain’s ability to keep track of time. For example, if subjects are exposed to a series of repetitive clicks prior to the duration signal that they are supposed to estimate, the speed of the internal clock increases, probably due to an arousal effect. This results in the time interval being perceived as longer compared to an interval preceded by silence (Treisman et al., 1990; Penton-Voak et al., 1996; Droit-Volet and Wearden, 2002). The perception of time is also greatly affected by conditions that direct attention to the passage or flow of time (Wearden, 2003: Block, 2003). For example, time appears to pass more slowly than normally when one attends to it. Most SET theories view attention as the factor that controls the on/off switch, where simple delays in closing the switch are supposed to explain its effects in time perception. The attentional-gate model is a variation on traditional SET theories, which incorporates a cognitive module in the form of an attentional gate, i.e., a cognitive mechanism controlled by the allocation of attention to time (Zakay and Block, 1995; Block, 1990; Block, 2003). On this view, attention to time is necessary for the cognitive counter to be switched on. The more attention is allocated to time, the wider the gate opens, and more pulses emitted by the pacemaker are transferred to the cognitive counter. The attentional-gate model provides a better explanation of 6 complex human timing behavior. Timing behavior in animals depends on learned intervals represented in reference memory. Humans, however, are more flexible in the sense that although in some temporal tasks such as the reproduction of an interval’s duration the count of pulses can be compared to reference memory until a match is achieved, in other temporal tasks reference memory might not be used (Zakay and Block, 1995). The brain’s time-tracking mechanisms result in successive events being experienced together in what is sometimes called the ‘specious present’ (James, 1890/1981; Treisman, 1963; Phillips, 2008). The specious present is a short time span (consisting of a few seconds) during which we are simultaneously aware of several successive entities constituting endurance. The succession of events being experienced together gives rise to a sense of endurance through transient change. But, as far as SET theories go, there need not be any fundamental endurance through transient change in order for us to have such experiences. It follows that SET theories can explain A-theoretical properties as a function of B-theoretical properties. This explanation, if correct, gives credence to our claim that A-theoretical properties are emergent properties, for example response-dependent properties, though the model is compatible with many other ways of accounting for A-theoretical properties as weakly emergent. The view that A-theoretical properties are weakly emergent is superior to competing explanations, i.e., Mellor (1998) and Prosser (2012), for two related reasons. Firstly, Mellor’s and Prosser’s explanations assume that our experiences of the passing of time are illusory. As such they are inconsistent with the SET theories, which aim to explain that our subjective experiences track real time. Secondly, by assuming that all experiences of time passing are illusory, neither Mellor nor Prosser’s proposals can explain why the brain sometimes tracks the passing of time correctly and other times incorrectly. Their views entail that all of our experiences are non-veridical, and if theories of time are necessary, they entail that all of our experiences are necessarily non-veridical. This is inconsistent with the theories of perception, which treat some experiences as veridical and others as falsidical. The proposed view is consistent with both the aims and assumptions made by SET theories and other theories of perception. In addition to being consistent with SET theories, our proposal also plays an important explanatory role: it explains what sorts of properties our brain clock posited by such theories may in fact be tracking. By positing that the brain tracks weakly emergent A-theoretical properties, the proposed account adds an important piece to an otherwise puzzling brain behavior. 5. Concluding Remarks We have argued that even if there is no need for A-theoretical properties at the fundamental level of reality, since the standard theory to time is not committed to any such properties, it does not follow that our experiences of A-theoretical properties are illusory and that A-theoretical properties are not real. A-theoretical properties were likened to properties such as being solid to illustrate that there is no need to deny that our experience of the passing of time is veridical. Properties such as being solid are weakly emergent properties that arise at a particular level of organization and complexity. Similarly, A-theoretical properties can be weakly emergent even if 7 the B-theory of time is true. Models of how the brain tracks time support the claim that Atheoretical properties are at least weakly emergent properties, more so than the claim that Atheoretical properties have no real existence. Although the story we painted thus far is very plausible, a stronger conclusion might be tenable. For it might turn out that A-theoretical properties must be treated as fundamental properties after all. This is because the explanation of how the brain tracks time is gappy. SET theories do not explain how it is possible for perceptual experience to present enduring objects, if Atheoretical properties are not primitive, irreducible properties. A closer look at what it is for endurance to be presented in experience seems to suggest that endurance requires treating Atheoretical properties as primitive, irreducible properties. The argument that endurance entails that there are primitive A-theoretical properties begins with David Lewis’ problem of temporary intrinsics, which is supposed to establish that objects perdure. As is familiar from the literature on persistence, there are two potential ways that material bodies may persist through time (Lewis, 1986; Sider, 1994, 2001; Rea, 1998; Hawley, 2010). On the endurance view, material bodies persist through time by enduring. To a first approximation, an object endures just in case it is wholly present at each time at which it exists. On this view, material objects do not have temporal parts. On the perdurance view, objects persist through time by perduring. An object perdures by having different temporal parts at different times. The problem of temporary intrinsics runs as follows: John sometimes has a straight shape and sometimes a bent shape. So, John has both a straight and a bent shape, which is contradictory. Lewis argues that presentism, a special version of the A-theory that states that only present things exist, avoids this problem because there is no existing time at which John is both bent and straight. Although Lewis only mentions that presentism blocks the argument, it is plausible that any version the A-theory would block it. For example, the passage view that states that only present things are concrete would have the same effect. So, we can take Lewis’s argument, if sound, to establish the following entailment: If the B-theory is true, then perdurantism is true A common response to the argument, which Lewis himself entertained, is to treat all apparently intrinsic properties as relations to times (Lewis, 1986). ‘John is straight-relative-to-t1 and bentrelative-to-t2’ is not a contradiction. Lewis dismissed this reply on the grounds that it is implausible to think that all properties are extrinsic. Lewis has a good point. Although the relational view formally solves the problem, it does so only by making times constituents of all properties, which is highly unsatisfying. An alternative reply is to argue that apparently intrinsic properties are instantiated only relative to a time (Brogaard, 2012). The view follows from the doctrine that the content of utterances must be evaluated for truth relative to particular times rather than just relative to the world as a whole. Since there is no time at which John is both straight and bent, there is no contradiction. A particular version of this view is adverbialism, according to which John has the property being-straight in a t1-way at t1, but he fails to have that same property in a t2-way at t2. However we spell out the details, this solution formally blocks Lewis’ argument without assuming that all properties are extrinsic. 8 There is, however, a variation of the argument that does not seem as easily dismissed. The argument runs as follows: If x is F at t1, and y is not F at t2, then x and y are discernible. However, if x = y, then x and y are indiscernible. So, if x is F at t1, and y is not F in t2, then x is not identical to y. But if x is not identical to y, then identity through time is not strict identity but some mereological relation that binds together the temporal parts of objects (Lewis, 1986; Kitcher, 1990: 123; Sider, 2001). It follows that perdurantism is true. Notice that, in this case, treating properties as instantiated only relative to times does not block the argument’s first premise if the B-theory is true. This is because a B-theoretical framework does not prevent us from comparing x and y with respect to the world as a whole. But with respect to the world as a whole, if x is F at t1 and y is not F at t2, then x and y are discernible. It’s only within a metaphysics that prevents cross-time comparisons, viz. a world in which every time is not equally respectable ontologically, that the argument can be blocked by taking properties to be instantiated only relative to times. So, it is only if the B-theory is true, that we can infer that perdurantism is true. In other words, if each time is equally ontologically respectable, then objects are spread out across time and hence are not enduring. It follows that if there are any enduring entities, then there are ontologically primitive or irreducible, A-theoretical properties. 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