WEBVTT

00:00:00.000 --> 00:00:02.300 align:middle line:90%
Hi, Werner.

00:00:02.300 --> 00:00:03.500 align:middle line:90%
Hello, Greta.

00:00:03.500 --> 00:00:09.030 align:middle line:84%
In pupillometry, people
often use baselines.

00:00:09.030 --> 00:00:11.150 align:middle line:90%
What are those?

00:00:11.150 --> 00:00:11.650 align:middle line:90%
Yeah.

00:00:11.650 --> 00:00:14.770 align:middle line:84%
So we use baselines
because there

00:00:14.770 --> 00:00:18.460 align:middle line:84%
are a lot of things
that we don't control

00:00:18.460 --> 00:00:20.290 align:middle line:90%
when we measure pupil sizes.

00:00:20.290 --> 00:00:21.950 align:middle line:90%
But we can control that.

00:00:21.950 --> 00:00:24.790 align:middle line:90%
So there are these things like--

00:00:24.790 --> 00:00:28.690 align:middle line:84%
for example, different people
have different pupil sizes.

00:00:28.690 --> 00:00:31.870 align:middle line:84%
You might have slightly
different default pupil size

00:00:31.870 --> 00:00:36.460 align:middle line:84%
than I do, or it can be reactive
in a slightly different way.

00:00:36.460 --> 00:00:40.600 align:middle line:84%
And then pictures or
videos, or any stimuli

00:00:40.600 --> 00:00:44.260 align:middle line:84%
that we might want to show
our study participants,

00:00:44.260 --> 00:00:47.920 align:middle line:84%
they also might have different
luminance or brightness,

00:00:47.920 --> 00:00:49.450 align:middle line:90%
different visual properties.

00:00:49.450 --> 00:00:51.230 align:middle line:90%
They change a lot.

00:00:51.230 --> 00:00:57.400 align:middle line:84%
So we use baselines to basically
control for all these factors

00:00:57.400 --> 00:00:59.140 align:middle line:90%
that might vary.

00:00:59.140 --> 00:01:02.980 align:middle line:84%
In our experiment, it became a
common practise to first take

00:01:02.980 --> 00:01:05.890 align:middle line:84%
the baseline measurement
of our pupil,

00:01:05.890 --> 00:01:11.000 align:middle line:84%
and then take the measurement
from our target stimulus.

00:01:11.000 --> 00:01:11.500 align:middle line:90%
OK.

00:01:11.500 --> 00:01:13.480 align:middle line:90%
So let me understand.

00:01:13.480 --> 00:01:16.430 align:middle line:90%
So the baseline is an image.

00:01:16.430 --> 00:01:21.170 align:middle line:84%
And is there an image that
works for all experiments,

00:01:21.170 --> 00:01:24.570 align:middle line:84%
or you have to adjust
to each situation?

00:01:24.570 --> 00:01:25.070 align:middle line:90%
Yeah.

00:01:25.070 --> 00:01:26.720 align:middle line:84%
So it depends on your
experiment, right?

00:01:26.720 --> 00:01:27.762 align:middle line:90%
It depends on your study.

00:01:27.762 --> 00:01:33.140 align:middle line:84%
If, in your study, you show
your study participants

00:01:33.140 --> 00:01:35.870 align:middle line:84%
static images,
then your baseline

00:01:35.870 --> 00:01:37.880 align:middle line:90%
can also be a static image--

00:01:37.880 --> 00:01:42.140 align:middle line:84%
that is, for example, a
blurred or pixelated version

00:01:42.140 --> 00:01:44.820 align:middle line:84%
of what you want to show
to your participants.

00:01:44.820 --> 00:01:48.560 align:middle line:84%
So in this way, you are
maintaining all the visual

00:01:48.560 --> 00:01:52.040 align:middle line:84%
properties-- all the luminance
and brightness, colours--

00:01:52.040 --> 00:01:55.760 align:middle line:84%
of your target stimulus
that you're showing,

00:01:55.760 --> 00:01:58.400 align:middle line:84%
but you're taking
away the meaning

00:01:58.400 --> 00:02:01.350 align:middle line:84%
or the content of what you're
showing to a participant.

00:02:01.350 --> 00:02:01.850 align:middle line:90%
OK.

00:02:01.850 --> 00:02:02.350 align:middle line:90%
I got that.

00:02:02.350 --> 00:02:08.669 align:middle line:84%
But then, when would you
show this baseline image?

00:02:08.669 --> 00:02:09.169 align:middle line:90%
Yeah.

00:02:09.169 --> 00:02:14.540 align:middle line:84%
So typically, you show it
right before the target image

00:02:14.540 --> 00:02:15.560 align:middle line:90%
that you want to show.

00:02:15.560 --> 00:02:18.560 align:middle line:84%
But you don't have to show
it for the exact same amount

00:02:18.560 --> 00:02:19.550 align:middle line:90%
of time.

00:02:19.550 --> 00:02:21.620 align:middle line:84%
You can show it for a
shorter time-- for example,

00:02:21.620 --> 00:02:24.920 align:middle line:90%
one second or slightly shorter.

00:02:24.920 --> 00:02:31.160 align:middle line:84%
That said, also remember
that pupillary responses

00:02:31.160 --> 00:02:32.370 align:middle line:90%
are pretty slow.

00:02:32.370 --> 00:02:32.870 align:middle line:90%
Right?

00:02:32.870 --> 00:02:37.620 align:middle line:84%
So we need to allow the
pupil some time to adjust.

00:02:37.620 --> 00:02:39.920 align:middle line:84%
So if you would like to
show the baseline for just

00:02:39.920 --> 00:02:42.590 align:middle line:84%
a few milliseconds,
that's probably too short.

00:02:42.590 --> 00:02:44.900 align:middle line:84%
So it should be for
around a second.

00:02:44.900 --> 00:02:45.500 align:middle line:90%
OK.

00:02:45.500 --> 00:02:48.890 align:middle line:84%
And then you get a
measurement of the pupil

00:02:48.890 --> 00:02:50.330 align:middle line:90%
during the baseline.

00:02:50.330 --> 00:02:50.900 align:middle line:90%
Mm-hmm.

00:02:50.900 --> 00:02:54.340 align:middle line:90%
So how do you use those data?

00:02:54.340 --> 00:02:54.840 align:middle line:90%
Yeah.

00:02:54.840 --> 00:03:00.050 align:middle line:84%
So what you get, what you
measure from the baseline

00:03:00.050 --> 00:03:03.620 align:middle line:84%
image, you would
usually subtract

00:03:03.620 --> 00:03:07.440 align:middle line:84%
that-- that average pupil size,
collected from the baseline

00:03:07.440 --> 00:03:07.940 align:middle line:90%
image.

00:03:07.940 --> 00:03:11.840 align:middle line:84%
You would subtract that
from the average pupil size

00:03:11.840 --> 00:03:14.270 align:middle line:84%
that you collected at
your target stimulus,

00:03:14.270 --> 00:03:17.600 align:middle line:84%
at the actual picture that
you want participants to see.

00:03:17.600 --> 00:03:21.860 align:middle line:84%
And in this way, you
can have that difference

00:03:21.860 --> 00:03:27.260 align:middle line:84%
of how the pupil changed
from the baseline

00:03:27.260 --> 00:03:30.590 align:middle line:84%
while you were looking
at the target image.

00:03:30.590 --> 00:03:35.270 align:middle line:84%
And this shows us that
magnitude of pupil response.

00:03:35.270 --> 00:03:39.380 align:middle line:84%
And it's normalised across
your research subjects.

00:03:39.380 --> 00:03:43.190 align:middle line:84%
And it's irrespective of
their individual pupil size,

00:03:43.190 --> 00:03:46.670 align:middle line:84%
or the individual
properties of the stimuli--

00:03:46.670 --> 00:03:48.510 align:middle line:90%
like their luminance, right?

00:03:48.510 --> 00:03:49.010 align:middle line:90%
OK.

00:03:49.010 --> 00:03:51.720 align:middle line:84%
So it's correcting
that information.

00:03:51.720 --> 00:03:52.220 align:middle line:90%
Exactly.

00:03:52.220 --> 00:03:53.678 align:middle line:84%
And this is basically
what we want.

00:03:53.678 --> 00:03:55.220 align:middle line:90%
That's an important thing to do.

00:03:55.220 --> 00:03:56.970 align:middle line:90%
Exactly.

00:03:56.970 --> 00:03:58.800 align:middle line:90%
Thank you, Greta.

00:03:58.800 --> 00:04:01.900 align:middle line:84%
Now we understand much
better what's our baseline.

00:04:01.900 --> 00:04:04.280 align:middle line:90%
So I hope everyone understands.

00:04:04.280 --> 00:04:06.070 align:middle line:90%
Thank you.

00:04:06.070 --> 00:04:17.000 align:middle line:90%