Craig Callender Dept of Philosophy University of California, San Diego The Subjectivity of the Present
1. Introduction • Objects are booming and buzzing by, vivid present perceptions are replaced, and we feel ourselves inexorably slipping into the future. • By contrast, the time of fundamental physics doesn’t speed up or slow down, distinguish the past from future, or single out a time as now. • To echo another debate, we have an ‘explanatory gap’ between time in experience and time in science.
The set of temporal events in physics has lots of structure, e.g., ordering relations, topology, metric. But it does not have… Is the time of natural science incomplete or inaccurate? Has physics missed the properties of time that cause the above? Or is the time of physics all the time that is needed? Can the rest be explained with psychology, environmental features and complicated relations between them?
“Tenseless” Past, present and future ‘equally’ exist. Fundamental temporal properties are relations of earlier than, later than and simultaneous with. No distinguished present B. Russell, J.J.C. Smart, A. Gruenbaum “Tensed” Many varieties, e.g., presentism, becoming, primitive tenses, branching, etc. All of these distinguish the present in some way A.N. Prior, C.D. Broad, Two Different Answers
Time Your death Today’s lecture Past Space Your birth
Presentism NOW Mom’s memories of your birth
“Nuclear” Arguments Against Tenses McTaggart Smart/Broad “How fast…?” Relativity No-go theorems Arguments for Tenses Semantics of now Headache argument Temporal “Knowledge” argument Experience Dialectical Situation Detensers typically concede that tenses do better with experience, but claim that nuclear objections overwhelm these arguments. However, when the debate goes conventional…
Fight back on the experiential front, too! Oddly, given the centrality of temporal experience to the arguments in the field, empirical work on the topic is virtually absent from the field. Focus on the present and experience Bracket “nuclear” objections and also bracket knowledge argument. I’ll put the mind into the mind-dependent present. On the basis of recent work in cognitive neuroscience and psychophysics, I’ll develop a tenseless rival to the tensed metaphysics hypothesis. By using essentially Mill’s methods, I argue this rival hypothesis is better supported by the evidence than the tensed theory is. Plan for Today
2. Experiencing the Present Pig experiences bacon Pig calendars etc Experience of the present The Now
Do We Experience an Objective Present? • Like Hume searching in vain for his self, I don’t perceive any stamp of present on my experiences… • Whether something is past, present or future doesn’t change the way it looks. The light from a lighthouse 1 mile away and from Jupiter look the same, even though one image is of an hour in the past and the other is of 0.000005 seconds past. • We cannot, as Mellor writes, “refute someone who claims to see the future in a crystal ball by pointing to the visible pastness of the image: there is no such thing” (1998, 16).
What is this Experience? • Tensers seem to read the theory into the data--or not mention the data explicitly. • Craig 2000: we’re “appeared to presently” • Schlesinger 1991: the present is “palpably real” • Smith the presentness we sense “inheres” in every state of affairs; we have an “unreflexive awareness of events as present” • Balashov 2005: some events are “known to be present simpliciter” • Confinement? Our experience is confined to the present. • Mellor: if this means we only experience present events or objects, then this claim is false. • If we re-phrase to ‘the sensory experiences we have are present when we have them’, then contentious: my experience of a hospital when born is not present.
Problem with Token-Reflexive Theory? • Oaklander 1994: "There is nothing more, ontologically speaking, to the presence of experience than our being conscious of our experiences when they are happening.” • Detensers understand ‘e is present’ as e is roughly simultaneous with the judgment. • The token reflexive account explains a correlation between a propositional attitude about presentness and an experience. It doesn't account for or describe an experience itself. • Tensers steadfastly maintain that there is an experience of presentness.
Presentness Qualia? Perhaps it's impossible to describe the experience. Compare: if I try to describe the phenomenological character of redness then I can contrast this feature with other features also in my experience. I can contrast redness with greenness and employ lots of color vocabulary to describe the redness and its difference with greenness, e.g., its brightness, how saturated it is, and so on. But all aspects of my alleged experience of presentness are present.
Inference to Tensed Metaphysics • Tensers believe an experience (that we haven’t been able to cleanly identify) warrants belief in a global objective present. • For Craig the belief in such a present “enjoys such powerful positive epistemic status for us that not only can we be said to know that tense and temporal becoming are real, but also that this belief constitutes an intrinsic defeater-defeater which overwhelms the objections brought against it.” • But of course, even our experience of red doesn’t guarantee objective red things in the world. We have reason to believe that there are red things in the world (and tables, chairs and pigs) just in case the evidence best confirms these hypotheses.
3. The Framework • Butterfield 1984 seeks to explain some of our intuitions about the objectivity of the present. • Typically macro-objects in our local environment change much more slowly than the rate at which light and sound travels to us, plus time to form beliefs. • Consider looking at a chair nearby: visual lag of roughly 0.5s. At t* I form a belief about an object at t. Thanks to rapidity of light/processing and the above fact, the result of this process is a belief at t* that is typically accurate. The lag t-t* typically does not make the belief about local macroscopic objects false. t*: Object is chair-shaped 300,000,000m/s t t-t* doesn’t affect truth value!
Same goes for communication, say, by signing; same goes for some other sensory modalities. None of these types of information require a time stamp for reliable information transfer. (By contrast, consider mail and smell). • All of this makes good sense from an evolutionary perspective. Evol pressure to make t-t* small… And it makes sense to update rapidly… • These circumstances allow for great inter-subjective agreement about what happens “now”, agreement that can be used to explain why we’re tempted to restrict existence to the present and say that we share a now but not a here. • Call a region over which a ‘time stamp’ is not needed for reliable information transfer a Now Patch. Now Patches can be “glued” together to form a “global” Present. This explains why we think there is an objective global Present.
Now’s as Local Patches Now Now Now Now Now Now Now Now Patches as local patches that we ‘glue’ together to form a global Now—explains alleged objectivity of the Present…
Mechanisms of Simultaneity Constancy • Although I think Butterfield has it more or less right, the main character in the mind-dependence story is left out…yet it seems important. • E.g. multisensory integration • There are temporal integration mechanisms in the brain that weld together inputs as present. • Instead of defining Now Patches via time stamps, define them via these temporal integration mechanisms. This offers a deeper and more accurate explanation than the time stamp theory. • What psychologists call simultaneity constancy explains the apparent objectivity of the present.
4. Evidence of the Constructed Present: A. Sim Windows Subjective Simultaneity Put headphones on a subject and let her listen to tones lasting for 1ms. If the left and right ears are stimulated simultaneously, then the subject hears not two tones but one fused tone. Hirsh and Sherrick 1961, Poppell 1988; Euler 1997
Subjective Simultaneity Compensation of Subjective Simultaneity Subjective Time Now delay one of the tones. Up to a certain threshold, the two tones will still be fused as one.
If If <20ms >20ms t t Visual Simultaneity + Not Simultaneous Simultaneous
Different sensory modalities Different resolutions: • Vision: > 20 ms • Tactile: > 10 ms • Audition: > 2 ms Event Fusion Thresholds
If If 20-40ms >40ms t t Temporal order + Not Simultaneous but no reliable temporal order Reliable Temporal Order
Simultaneity Windows In all the sensory modalities, the simultaneity window varies from person to person. (In hearing, for instance, from 2ms to 5 ms.) It also varies with age, older people fusing more events than younger people, and many other factors. In each person the minimum threshold of simultaneity cannot be shrunk. Whose simultaneity window coincides with the Present?
Stone et al 2003 • Recent experiments by Stone et al 2003 bolster the earlier experiments. In 1000 trials Stone et al presented 23 subjects with light-sound pairs of stimuli separated from -250ms (sound first) to +250ms. In each trial subjects were asked to indicate if the pair occurred simultaneously or not. These responses picked out a time t between -250ms and 250ms as the point of subjective simultaneity. Stone et al found two items of particular interest about PSS. (1) PSS is observer specific. The points varied greatly, from -21ms to 150ms, among subjects. Remarkably, the difference between each subject was statistically significant. (2) But—revealed in another experiment—the PSS is remarkably stable for each individual. • Given the mind-dependence theory, we might expect (1). But the second item is also one we should expect. Navigating about the world is not merely a question of aligning the visual with the auditory; it is also a question of calibrating that alignment with motor control. However your PSS differs from that of your friends, it had better be the case that it remains stable over time if you are to play table tennis at all well.
Non-laboratory Example? • “64 matches, 337 offsides were analysed using digital video technology. The error percentage was 26.2%. During the first 15 min match period, there were significantly more errors (38.5%) than during any other 15 min interval. As predicted by the flash-lag effect, we observed many more flag errors (86.6%) than non-flag errors (13.4%).” • J Sports Sci. 2006 May;24(5):521-8
B. Flash Lag Effect • Explanations: motion extrapolation, positional averaging, latency difference • “Bouncing” flash lag: Eagleman and Sejnowski (2000): postdiction. What we see for t depends on next 80ms. • Temporal integration mechanism: what we see depends on the average difference between different position signals over a temporal integration window. (Lappe and Krekelberg 1999, 2000) • Gelard and Sherrick’s 1972 cutaneous rabbit… • What is interesting is that the present we experience is not just the present, nor even just the slightly recent past, but rather something constructed from sampling across past and “future” times. • There may not be an isomorphism between the temporal order of brain processes and the represented temporal order of events in the world. “Time is not its own representation.”
Consider again binding together auditory and visual inputs from a common target. We know two features help sound “catch up” Mechanical transduction is faster than chemical transduction Neural transmission time from visual cortex to cerebral cortex is longer than time from auditory cortex to cerebral cortex But if a and b were the sole explanation of our ability to bind together info as synchronous, we would only be able to bind together inputs over a very restricted range of target distances (10-12m). C. Recalibration
Subjective Time Compensation of Subjective Simultaneity Subjective Time Multisensory Simultaneity Time Course of Neural Events Input Neural Processing Subjective Simultaneity Slide borrowed from Fujisaki et al,VSS 3rd Annual Meeting 5/10/03 -2-
Synchronicity Plasticity • Recent experiments have suggested that one's experience of synchronicity--of two things happening at the same time--change when intentions are involved. • Cunningham et al 2001: subjects moved a mouse that caused a spot on a computer screen to move in a video game. Gradually a lag between the movement of the mouse and the resulting effect on the screen was introduced. Subjects informally reported that after a while their actions and effects were simultaneous again. • Haggard et al 2002 then set about testing directing whether this was so, whether, that is, a subject’s intentions affected the experience itself of what things happen simultaneously. They showed that it did. (See Eagleman and Holcombe 2002.)
Temporal Ventriloquism • A temporally proximate audible click “captures” a flash. Fendrich and Corbalis 2001; Vroomen et al 2004. • Fujisaki et al 2004: experiments “suggest that the brain attempts to adjust subjective simultaneity across different modalities by detecting and reducing time lags between inputs that likely arise from the same physical events" • Harris, forthcoming: "reconstructive process is involved that is able to resynchronize asynchronous signals by taking into account many factors, both internal and external, which would otherwise distort accurate knowledge of timing."
Sound and Simultaneity • Sugita and Suzuki “Implicit Estimation of Sound-Arrival Time” Nature 27 Feb 2003 • Subjects were presented through headphones bursts of white noise (10ms duration) to simulate external sound from frontal direction. Brief light flashes were produced by an array of 5 green LEDs at different distances (1-50m). Intensity of light altered so as to produce consistent intensity at the eye. • Subjects were told to imagine that the LEDs were the source of the light and sound, while listening to sound directly from source. • To estimate subjective simultaneity, observers judged what came first, light or sound. • Subjective simultaneity increased by about 3 ms with each 1 m increase in distance up to about 40m. Sound travels 1m/3ms at sea level and room temp. • “Our results show that the brain probably takes sound velocity into account when judging simultaneity” (911)
Variations on Sugita and Suzuki’s experiment have often not replicated this result. Why? • Taking into account target distance would be a computationally complex task. Probably there are various “rules of thumb” and/or proxies used by the brain to do this. • It may be, as Fugisaki et al suggest, that the brain tries to reduce lags between inputs that likely arise from the same source. • Zambini et al 2005 show that subjects are more likely to report stimuli as simultaneous when they originate from the same spatial location than when not.
Explanations & Open Questions • Harris et al, forthcoming, suggest a 3-stage process: • Stimuli are fit into windows; these are candidates for recalibration • Unfamiliar stimuli delayed according to fixed rules (e.g., 40ms delay for sound to be bound w/ light plausibly from same source) • Familiar stimuli are delayed according to more fine-grained process • Many open questions: • One mechanism or more? • Bottom-up (i.e., neural transmission) or top-down (i.e., “decision point”)? • What is the neural basis? • And one closed question: the need for a temporal integration mechanism is “self-evident” (Stone et al).
5. Bearing on the Tense Debate? • None of the phenomena prove that our experience of presentness is of a subjective property rather than an objective metaphysical property. Revealing the operations of the mind in forming our impressions can only do so much… • But once the detensers have an alternative hypothesis, they can then compare this to the alternative tensed theory explanation of the phenomena, just as a materialist theory of (say) beliefs could be compared with the dualist alternative. We can compare P(E/H)’s. The evidence seems to be pointing one way. The phenomenology of the present bears the hallmarks of perceiving something mind-dependent, not mind-independent. The subjective present • is highly contingent on environmental variables, e.g., what you take yourself to causally affect, what you’re attending to, how loud stimuli are, where in field of vision, etc. • varies dramatically from person to person • varies intra-personally too, depending on your age, etc. • dependent on later information
Compare with Dualism Debate • Daily discoveries of the dependence of mental phenomena on neural dynamics do not falsify mind-body dualism. If the physical “receiver” is broken or at the wrong station, same tune won’t be played… • But dualism is still explanatorily inadequate: Why should caffeine and valium affect my non-material mind’s mood differently? Dualist answers are either ad hoc stipulations or ride piggyback on the explanation from natural science—but at the peril of leaving nonmaterial minds nothing left to explain. • Background: evolution, biology • Simplicity • Upshot: dualism looks really bad
Claim I submit that the tensed theory of time is in precisely the same situation as dualism. • We group various experienced inputs together as present; we are tempted to think this grouping is done by the world, not us. • But we have learned that our impression of subjective present-ness varies inter- and intra-subjectively and that it can be manipulated in a variety of ways. These changes and manipulations are not at all what one would expect if our impression of now-ness were the impression of a mind-independent global monadic present. Tensers must provide stipulative answers to questions such as why age but not weight affects the size of my simultaneity window; alternatively, they can adopt a detensed answer, but again, only at the risk of leaving tenses with nothing to explain. • Background: tenses aren’t needed and in fact aren’t wanted by the natural sciences. • Upshot: The tensed theory is in trouble.
“…our brain furnishes an integrative mechanism that shapes sequences of events to unitary forms…that which is integrated is the unique content of consciousness which seems to us present. The integration, which itself objectively extends over time, is thus the basis of our experiencing a thing as present. …The now, the subjective present, is nothing independently; rather it is an attribute of the content of consciousness. Every object of consciousness is necessarily always now—hence the feeling of nowness.” (Pöppell, 1987, 62-63)