Kind: captions
Language: en
[Applause]
at the 1939 World's Fair in New York the
exciting new tech was the live
television broadcast Roosevelt became
the first president to address the
nation live on TV but for years leading
up to this event Engineers had been
working on one particular technical
problem how to ensure the audio and
video remain perfectly synced during the
live broadcast without this words and
lip movements wouldn't match up which
would be annoying and distracting for
viewers so how did they do it
well actually they didn't instead they
discovered something pretty incredible
we are not very good at Discerning
whether audio and video are in sync for
example I intentionally delayed the
audio of this entire monologue nearly a
tenth of a second and did you notice
I'll clap to make it more
[Music]
obvious the engineers also found that
there's an asymmetry in our tolerance
for this misalignment we don't really
notice if the sound lags video by up to
125 milliseconds but we can tell
something is wrong if it's leading the
video by more than 45 milliseconds and
to understand why take a look at this
here I am bouncing a basketball as I
walk away from the camera the sight and
the sound of the bounces match up
perfectly but as I walk away you know
the sound will be increasingly delayed
due to the extra time it takes the sound
to reach the camera but the sound still
appears synced this is because your
brain is not reporting to you each
instant exactly as it happens but rather
a short interval of time reorganized to
make sense so in this case your brain
automatically aligns the sound with the
sight of the bounce at least up to a
point once I'm over 30 m away the sound
is now delayed by over 100 milliseconds
and your brain no longer integrates the
information from your eyes and ears here
let me play the actual sound of the
bounce together with the sound as
received by the
camera this explains why sound can lag
video by more than it can lead I mean
imagine you were at a basketball game
and because of how far away you're
sitting the sound is delayed your brain
can handle that but if the sound
precedes the site of an event that would
look really odd because that's something
that would never happen in nature this
is why the broadcast guidelines for
acceptable audio and video mismatches
are skewed in favor of audio lagging
behind the video our brains are good at
aligning audio with the vision that
preceded it we can actually exploit our
Autos syncing capabilities to produce
some strange results for example we
created this computer program where when
you press the space bar a light appears
on the screen but not immediately there
is an 80 millisecond delay between the
button push and the light coming on in a
study participants who familiarized
themselves with a similar program came
to believe that the light turned on
immediately after they push the button
just as our brains synchronize The Sight
and Sound of the the basketball bounce
press the space key wants to begin this
is just the section where you get the
idea of what it does so you push the
space bar now watch what happens when
you remove the delay that last one came
up without me even pressing anything you
didn't press anything and it just
flashed up there right some participants
were convinced that the light came on
before they pushed the button they
believed that something else caused the
light to come on even though it was
their action that made it happen this is
remarkable because causality the idea
that one thing leads to another is
fundamental to our understanding of the
world otherwise how would we know who
shot first babies as young as 8 months
can demonstrate an understanding of
causality when watching a caregiver wind
a music box if the Music Stops the
Babies touch the caregiver's hand to get
the music to start again causality is
something we're hardwired to recognize
but even this core part of our brains
can be fooled and the Flash lag effect
gives further insight into how this
happens stare at the red s Square in the
middle of the screen and remember what
you see when the flash
happens where was the ring when the
flash occurred if you're like most
people you probably saw the flash in the
top half of the ring but what actually
happened was the flash appeared in the
exact center of the ring so our
perception of The Flash seems to be
delayed to explain this result
scientists hypothesized that the brain
was anticipating motion you see the
flash behind the ring because your brain
is predicting where the the ring will be
not where it actually is when the flash
happens to test this hypothesis
neuroscientist David Eagleman and his
team modified the experiment so that the
ring reverses direction right at the
moment of the flash now what did you see
if the brain was predicting the motion
of the ring you should have seen exactly
the same thing as before with a flash on
the top side of the ring but most people
see it in the bottom half of the Ring
how is this possible considering all the
frames leading up to the flash were
exactly the same in both cases if our
brains were anticipating motion then we
would have had to somehow known in
advance that the ring was going to
reverse Direction and that seems
impossible so the alternative hypothesis
is that where we see the flash occur
depends on what happens after the flash
there is a delay between the flash
occurring and you perceiving it and the
stuff that happens during that delay is
actually incorporated into your
perception of the event this is
incredibly counterintuitive and it calls
into question are perceptions of
causality the underlying cause of all of
these Illusions is the same what we
perceive as the present is not just one
moment but a short interval of time
which is around a tenth of a second long
now during this period your brain can
perform manipulations that distort your
perception of time and rearrange
causality this interval has been called
the specious present a term coined by E
Robert Kelly all the way back in 1882 he
said all the notes of a bar of a song
seem to The Listener to be contained in
the present all the changes of place of
a meteor seem to the beholder to be
contained in the present the present is
really a part of the past a recent past
delusively given as being a time that
intervenes between the past and the
future Let It Be Named the specious
present why do we experience time in
this illusory way we feel like we're
living in each instant but what we're
actually experiencing is a short period
of of time I think it's not so that our
brains can syn up the Sight and Sound of
distant events or so we can watch TV and
movies without distractions but because
fundamentally our brains need to hold
multiple moments at once to make sense
of the world just as you can't read a
book letter by letter you can't make
sense of the world and form memories
Instant by instant so we live in the
specious present under the illusion that
we experience each moment exactly as it
happens hey a lot of the research in
this episode was performed by
neuroscientist David Eagleman and he's
actually written a book entitled The
Brain the story of you which includes a
lot of the details of his research so if
you want to know more about these topics
I highly recommend you check out his
book and in fact you can download it for
free by going to audible.com/veritasium
where this book is read by David
Eagleman himself but if you're not
interested in this one you can also pick
any other book of your choosing for a
one-month free trial audible is a great
audiobook website with hundreds of
thousands of titles in all areas of
literature including fiction non-fiction
and periodicals plus audible is a
longtime supporter of veritasium so I
really want to thank them for helping me
to keep doing what I'm doing and making
these videos and I want to thank you for
watching