And it's amazing that that
enormously short period of time can be accurately measured.
But this is what's done here, it tells you what the distance and direction of every
point in theses scenes that I'll talk about a little more in detail in a second.
It tells you what that physical reality is, and
allows you to relate it to the frequency of occurrence
of line lengths that are projected onto the retina.
Now, where did this machine come from?
Well, it's obviously not made for neuroscience, it's made for
architects and construction companies in the course of building whatever it is
that the architect wants, if it's a major building, you won't use it for
your house but you use it for building a skyscraper and the light.
The architect and the construction engineers need to know,
well, is this proceeding is the building proceeding according to plan
by using the laser scanner to scan the building as it goes up, you can tell
within fractions of a centimeter within a few millimeters whether
the blueprint is being acurately executed in the construction of the building.
We are using it for a completely different purpose.
But the idea is the same.
Let's talk a little bit more about the scenes that it's scanning and
how it really represents information that we can use.
So here's a natural scene.
It happens to be a scene on the Duke campus that we transported the laser range
scanner to, to many sites of naturally constructed scenes of the Duke campus,
to ask what's the frequency of occurrence of lines that are existing in space?
And what's that frequency of occurrence translate into when you talk about
perceptual experience of line lengths.
Well, this is just a digital photograph taken with a digital camera
of one of those scenes as an example.
And here is what the laser range scanner returns to you from the same scene.
So this is a color code and it's in meters.
And the heat map here is showing you that when the distance
is very short when the object is closed to the laser range scanner,
it's shown in red, and this is now laser scanned image.
And when it is blue, that means that the object are greenish that means
the object is further away, when it's sometimes black as this little instances.
It mean that the beam never hit any object at all but
the distance was infinite and that's just returned as black.
So, what this is allowing you to do is as I said to know exactly the distance and
direction within a few millimeters of every point it is seen like this.
Then use that information to find out what the frequency of occurrence is of our
experience with lines of different lengths as they project onto our retinas.
Well, how do you do that?
Well, here is another scene from the Do campus,
just again to show how this is done technically.
And here is a blow up of the pixels that would be in any position on the scene and
lines at different orientations that are going to be applied to the scene.
A vertical line, horizontal line, and oblique line.
And by applying lines of different lengths repeatedly to the scene,
you are going to find out how often was that the case that
align of a certain orientation and length return from the scene
a valid line that was actually out there in the scene.
That's equivalent to asking what's the frequency of occurrence
of projections onto your retina of lines of different lengths and orientations
with respect to the real world that the laser scanner is telling you about.
