have in their collection of neuroscience volumes, this would certainly be the one.
It's a remarkable book that collects their papers written over
a period of 25 years during which they collaborated beginning,
as I said, in the late 1950s and going on to the early 1980s.
And the title of the book is Brain and Visual Perception.
We'll say more about that in a minute, but what's so
remarkable about this book is that it's not just a collection of papers,
it's a collection of papers with commentaries.
And in forewords and afterwords they say why they did the work,
and they say it in a very straightforward way, without trying to
remove the warts that are involved in any scientific endeavor.
And then they have afterwords that say how the conclusions of the paper
fared over the years and
other comments about some of the problems they encountered along the way.
So this is a very unusual book in that it tells it like it is.
Most books, of course, gussy things up to make it seem all sort of scientifically
inevitable, but this is certainly not the case in this book, and that's,
I think, the main reason, or one of the main reasons it's so remarkable.
The other reason, of course, is that this work set the stage for
understanding vision that began in the late 1950s but persists to this day.
So what's the nature of what they did?
Why has this been such an impressive and
field-determining body of work?
Well, this takes us back to something I mentioned early on in the course but
we need to come back to it now and talk about it in detail,
which is the concept of receptive fields.
And this way of doing an experiment is really the standard way of thinking about
the generation of visual perceptions, and
I want to describe it to you in a little bit of detail.
They started with cats as an experimental animal in the late 1950s and
on through the 60s, and then turned to monkeys, rhesus monkeys in particular,
which is an animal that's much more like the human visual system, but
it's the same idea.
And their students and many of the students' students,
a whole line of progeny over the last 50 years, have carried on work like this,
defining the receptive fields of individual neurons, individual system.
The idea being that if you could identify the behavior of individual neurons and
how they connected to each other, you could understand not
only how the visual system worked but how perception would fall out of that.
So let's make sure we are all on the same page about what's going on here.
So the cat is anesthetized, of course.
It's looking at a screen that's placed in front of the animal, and
stimuli are shown in that screen.
That can be determined in any way the experimenters wanted to do.
In the example here, there are bars of light that
are oriented in one orientation or another.
And recording from an individual cell, cell by cell with a microelectrode
which doesn't go inside the cells but is an extracellular microelectrode
that records when you place it in the cortex, the primary visual cortex,
in this case, of the cat, records from one cell or another.
And you can ask, well, what does this particular cell that I've isolated with
a microelectrode in this way, what is it responding to?
And again, in the example here the question being asked is what is
the location on the screen that it's responding to?
And what's the nature of the stimulus that it responds to?
What are the characteristics of the stimulus that it likes to see,
that it likes to respond to?
And that's being judged in terms of the number of action
potentials that the cell fires.
So you can hear this on an audio amplifier.
And you can actually find this on the Internet.
And I suggest for those of you who register that you find the Hubel and
Wiesel video of their actual experiments and see how this was done and
how [LAUGH] different it was 50 years ago from the way it's done now,
more than 50 years ago now, than the way it's done now.
But the point has been the same over this period of decades, and
the first point is that there's a location
in visual space that any particular cell is going to respond to.
So in this case the cell doesn't respond, the cell that one's recording from here.
Remember, it's just a single cell being record from the primary visual cortex
of the animal that, although anesthetized, the visual system is still working
at a reduced but adequate level to make these kinds of experiments.
But there's only one place on the screen that the cell is going to respond to.
That's the location of the receptive field.
The receptive field is the locus in space that the cell responds to.
That's the sort of primary definition of a receptive field as a location.
You put the stimulus here, you put the stimulus here, you put the stimulus here,
you put the stimulus here, no response.
So there's a particular locus, a particular location of
the receptive field, for any cell that one wants to test in this way.
The second characteristic, and it's equally important,
is, as I said, what kind of stimuli, not just in the placement
of stimulus, but what kind of stimuli does the cell like?
And again, you hear this by an increase in the frequency of action potentials
that you listen to or
you see on your oscilloscope that I'll tell you about in a second.