00:01
Okay. Let’s talk about how we
sense the environment around us.
00:05
So there’s a lot of ways
that we can actually do this
and we’re going to walk
through a whole bunch of ways
we detect the things that
are interacting with us.
00:16
So one of the easiest ways to
determine whether or not there’s
something around us is
something called thresholds.
00:20
And this is a
different way to --
this is a way for us to measure
activation of, say, a receptor.
00:27
So if you have a threshold, you
can have two types of threshold.
00:31
One is called
absolute threshold.
00:33
And this is when we’ve
achieved a certain
level of activation so that we
know that something has happened.
00:40
So, you know, in simple English,
let’s say you’re in a dark room.
00:45
So you’re at your
desk right now.
00:47
Turn off all the lights in your
room and it’s pitch black.
00:50
Now if it’s completely
pitch black,
you see nothing.
00:55
Now what is it going to take for you
to say there’s a light on somewhere?
So if you were to
flick on your phone,
you would easily detect that and you can
say, “Yes, there’s light right there.”
But at what point,
how dim does that light have
to be for you to actually
say, “Oh yeah, there’s
a light on right now”?
So that’s called absolute threshold and
it can be things like sight in low light,
it can be hearing slightest noise,
it could be the taste of something.
01:20
So how much water
when you’re drinking water,
can you taste the sugar?
Is it sweet or is it
still tastes neutral?
And you know we figured out, “Okay.
We’ll, it’s roughly
about three sugar cubes and
a hundred liters of water.”
So
the other side is something
called difference threshold.
01:37
And so this is when one
receptor will have a measurable
absolute threshold value and a
measurable difference threshold.
01:43
So you can have a receptor
that says, “Yes, I’m on.”
And then you can have a receptor
that once it’s activated,
it can detect a difference.
01:52
Okay. So we’re going to walk through
each, giving examples of each.
01:54
We’re going to walk through an example
so this all make sense to you.
01:58
So absolute threshold is defined
as the minimum stimulus intensity
required to activate a sensory
receptor half of the time.
02:05
So if we’re back to
our light example,
I think the research has
shown that at roughly three
miles if you have a candle
in a dark and nighttime,
you could detect that
roughly 50% of the time.
02:21
And why do we say
50% of the time?
Because that’s basically
right at and above chance.
02:27
So if I have a candle lit or don’t have
it lit and I say, “Do you see a candle?”
If you were to guess,
you’d be 50/50.
02:33
So you have to be
just above that.
02:35
Okay. So we’re establishing
what is a signal detection.
02:40
We also know that for most individuals
there are some minor differences.
02:44
And that being said, you know, the
average human would have a value,
but then like with anything,
there’s going to be a range.
02:50
There’s going to be
some people whose
signal detection is extremely
great and they could find --
they could see a candle
at, say, four miles
and there are some people who
need, you know, two miles.
03:01
So they’re not as good.
03:02
We also know that
as you get older,
like everything, your machinery starts
to slow down and it’s not as great.
03:07
So age can be an
influencing factor.
03:09
So as you get older,
you’re hearing is not as good,
your eyes aren’t as good.
03:13
It’s harder for you
to see things, right?
And so your absolute
threshold can shift as well.
03:19
So now difference threshold is also
known as just noticeable difference.
03:25
And what this is, is this is
defined as the minimum noticeable
difference between any two sensory
stimulus half of the time.
03:33
And what we’re saying here is
detecting change.
03:38
And if you are activating a
sensory stimulus -- sorry,
sensory receptor
with the stimulus,
you need to detect a difference
at least half of the time.
03:49
So let’s go back to our candle example
in the darkness in the desert.
03:53
And at three miles,
I have a candle.
03:55
Now,
if I was to add a second candle,
would you be able to detect the fact
that I have now made it brighter
because there are two candles?
And you would have to
notice that difference of
that additional candle
at least half the time.
04:09
Okay?
So that would be that
value that you would get
would be your just
noticeable difference.
04:15
So the initial stimulus can
influence the difference threshold.
04:18
So what are you starting with?
And we’ll walkthrough examples.
04:20
This makes a lot more sense.
04:22
But let’s say if I ask you
to pick up a textbook,
your MCAT book that’s sitting
on your desk right now.
04:30
You put that in your hand
and you’re holding it
and you feel a certain
weight in your hand,
your muscles can feel that
and you know roughly
what it weighs.
04:36
and you know roughly
what it weighs.
04:38
Now you close your eyes
and I add one sheet of paper
from your printer and I put
that on top and say, “Okay. Can
you notice any difference?”
Chances are
you’re probably not going to
notice the fact that I’ve
added a piece of paper on
top of your heavy textbook.
04:54
Now what if I was to add,
say, another small book,
a study notes book
that went on top?
Now you’re noticing
there’s a difference.
05:03
And there’s a clear difference there
and you would be able to notice that.
05:07
So now you can back track and
say, “Okay, well, how little,
how little do I have to add before
you actually notice a difference?”
That would be your just
noticeable difference.
05:17
Now if you’re starting with a
textbook and I add a piece of paper,
that JND, just
noticeable difference,
is going to be a certain
value but not much.
05:28
You’re going to need to add a
little bit more than that.
05:30
Now what if you started
with a piece of paper
and now I’m adding
maybe another sheet of paper?
You might notice that difference because
you were starting with something so small
and you added something
relatively small.
05:45
But because of the initial
stimulus that you started with,
that difference is
going to be there.
05:49
So if you start, let’s say, the
phonebook or that study book,
you’re starting with something
large, you’re going to need a
larger proportional difference
in order detect that change.
05:59
So your JND is going to
be changed accordingly.