Transcript The Subjectivity of the Present

The Subjectivity of the Present
Craig Callender
Dept of Philosophy
University of
California, San
Diego
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…
Time in Physics
No present
No asymmetry
No flow
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?
Two Different Answers

“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,
Time
Your death
Today’s
lecture
Space
Past
Your birth
Presentism
NOW
Mom’s memories
of your birth
Dialectical Situation

“Nuclear” Arguments  Arguments for Tenses
Against Tenses
– McTaggart
– Smart/Broad “How
fast…?”
– Relativity No-go
theorems
– Semantics of now
– Headache argument
– Temporal “Knowledge”
argument
– Experience
Detensers typically concede that tenses do better
with experience, but claim that nuclear objections
overwhelm these arguments. However, when the
debate goes conventional…
Plan for Today

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.
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).
Divide in Tensed Camp
Craig (2000, 143) writes:
as a resu lt of physics and neur ology, we now real ize tha t nothing w e sense i s
instanta neously sim ulta neous with ou r experien ce of it as prese nt. But in mos t
cases, th e things and events we observ e are con taine d withi n a brief tempo ral
interv al which is present Éand our basic belief m akes no referen ce to instants ,
so that s uch a basi c belie f re m ains properly bas ic even fo r sc ienti fic all y
educa ted persons lik e ourselves.
The fa ct that un der extraor dinar y
circums tan ces our basic bel ief in t he presentness of som e event /thing shoul d
turn out to be false is no proof at all either that we h ave no bas ic be lief s
concerning the prese ntness of events/t hings in the exter nal world or th at such
beliefs are not properl y basic . Me llor is therefo re sim ply wrong when he
asserts that we do not obser
ve (de feasibly ) the tense of events.
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.
t*: Object
is chairshaped
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.
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.
Visual Simultaneity
If
+
<20ms
If
>20ms
t
Simultaneous
t
Not Simultaneous
Different sensory modalities
Different resolutions:
•Vision: > 20 ms
• Tactile: > 10 ms
• Audition: > 2 ms
Event Fusion Thresholds
Temporal order
If
+
20-40ms
If
>40ms
t
Not Simultaneous but no
reliable temporal order
t
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.
B. Flash Lag Effect
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
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.”
C. Recalibration

Consider again binding
together auditory and
visual inputs from a
common target.
 We know two features
help sound “catch up”
a. Mechanical transduction
is faster than chemical
transduction
b. 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).
Multisensory Simultaneity
Input
Neural Processing
Time Course of
Neural Events

Subjective Time
Subjective Simultaneity
Compensation of
Subjective Simultaneity

Subjective Time
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 SoundArrival 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:
1.
2.
3.

Many open questions:
–
–
–

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
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).
Temporal Integration
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)