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  • NARRATOR: The name "Perkins" carved in stone.

  • Below a gothic tower a boy navigates with a cane.

  • A title: Visual Acuity Testing:

  • History of Preferential Looking and Early Testing

  • with D. Luisa Mayer, Ph.D.

  • - Preferential looking is something that a baby does

  • when they see something that's very interesting

  • next to something that isn't interesting.

  • So they prefer to look at something that's interesting.

  • I'll give you an example.

  • A three-month-old baby, if we show a three-month-old baby

  • a drawing of a face where all the features are regular--

  • the eyes are where they should be,

  • the nose is in the middle, the mouth is below--

  • and then you put next to that a drawing of the same features

  • of the face, but where everything's scrambled--

  • the eyes are over here, the nose is there,

  • the mouth is up here.

  • NARRATOR: We see the image of two faces side-by-side.

  • The image on the left is of a normal face.

  • And on the right the shapes depicting the eyes,

  • nose, hairline and eyebrows are randomly placed

  • within the same space.

  • - What's the baby going to look at?

  • The baby's going to look at that face that's regular

  • and not at the scrambled face.

  • We call that the baby's preference to look at a face.

  • So preferential looking has a really long history

  • as both, just natural observation of what babies do.

  • They naturally look at things.

  • Things they're interested in capture their attention

  • and they spend a lot of time looking at them.

  • And that observation started a whole field

  • of vision science,

  • studying the development of visual perception

  • and the development of sensory visual functions

  • in babies,

  • using modifications of this method now

  • that's called preferential looking.

  • The first person to do that formally was someone

  • named Robert Fantz,

  • who was an American developmental psychologist.

  • And he presented two stimuli like stripes and a bull's-eye

  • to babies and he looked at...

  • he measured which one they preferred

  • by having somebody just measure their looking time

  • to the stripes, to the bull's-eye.

  • He would change the position, measure their looking time,

  • say in a two-minute interval.

  • And cumulating their looking time

  • over that two-minute interval would tell you that the baby

  • preferred one or the other

  • if the time was sufficiently different.

  • NARRATOR: We see the two shapes as described,

  • on the left a bull's-eye of three concentric black rings

  • and on the right side,

  • six identical wide, black vertical stripes.

  • - And he did that starting with newborn babies,

  • babies shortly after birth.

  • To do that he had to create this funny-looking box

  • that he called a looking chamber,

  • but actually I call it the baby box.

  • And it's open on the bottom.

  • A baby is slid in lying on their back

  • underneath this box.

  • Someone is peeking over the top of the box,

  • looking through a little peephole.

  • And inside the box are either two objects or two images

  • that the baby's looking at.

  • So baby's down below looking up at these images

  • or these objects.

  • And the observer looking through that peephole

  • is measuring how much time the baby looks

  • at one or the other object.

  • NARRATOR: A black and white photograph

  • shows Fantz's apparatus.

  • An infant on its back gazes up at a balloon-like object

  • at the top of the box.

  • An observer stands to the left of the apparatus

  • on a small step stool and leans over the top of the box

  • to observe the baby through a small opening.

  • - When he did that with newborns, he found

  • that newborn babies actually have visual preferences.

  • They look at things, some things more than others.

  • And it turns out it's pretty complicated

  • and pretty interesting.

  • He also studied babies up to about six months of age,

  • sitting them upright in a little baby chair

  • and showing them also patterns and objects.

  • The bottom line of his findings with newborns

  • was that babies actually make visual discriminations.

  • They're not blind, they see differences between things.

  • It's fairly rudimentary, but nevertheless

  • they're making discriminations.

  • He considered that evidence for innate visual perception

  • in babies,

  • that babies are able to see forms right after birth.

  • They don't need experience.

  • Now, some would argue, well, they need some experience.

  • Well, yes, to refine their vision

  • certainly they need experience.

  • He also showed that babies had preferences

  • for certain things that changed over time.

  • They weren't always interested in looking at the bull's-eye

  • versus the stripes.

  • Later on they seemed to be more interested in stripes

  • than bull's-eyes.

  • But at all ages he found that babies preferred

  • to look at regular faces over scrambled faces.

  • So Fantz started doing these studies in the '50s.

  • And this type of work is really called

  • the study of visual perception in babies.

  • And it's been ongoing, there are all kinds

  • of modifications of this procedure used to study

  • complex visual perception and cognition in babies.

  • NARRATOR: Fade to black.

  • A graphic of the Perkins logo swoops across the screen,

  • revealing a chapter heading:

  • Visual Perception vs. Visual Sensory Function.

  • - I want to differentiate between what I mean

  • by sensory versus perceptual.

  • So sensory qualities of an object are things

  • that make up that object, that form,

  • such as the angles or the edges of a form,

  • the lines, the width of the lines that create that form.

  • Light/dark differences that define where that form is

  • in space.

  • Color differences and so forth.

  • So those are the components that go up to make a form,

  • and perception is seeing the form as a form,

  • seeing all those components put together,

  • and that creates an object that we can discriminate.

  • Now, the sensory visual functions that I'm talking about

  • that have been studied over many years

  • since shortly after Fantz's work are visual acuity,

  • detail vision, contrast sensitivity--

  • the ability to see different contrasts between objects--

  • color vision, temporal vision, motion sensitivity,

  • stereo, vernier acuity and a number of other

  • really basic visual functions.

  • The research started on these things really with babies

  • in the '60s, so shortly after mid-century.

  • Actually, there are a number of different modifications

  • of preferential looking that were used to test

  • visual sensory function.

  • I'm going to focus on one in particular

  • because it's what I know.

  • It's from the person I worked with,

  • it's where I did my graduate studies

  • and so you'll hear all about that.

  • But there were a number of other researchers

  • who used modifications of preferential looking

  • to study behavioral visual function in babies.

  • And I'm just going to name a couple of them

  • because they're prominent people,

  • they're people in our community

  • and they're good friends as well.

  • At MIT, Massachusetts Institute of Technology,

  • some of the first studies were done by Richard Held

  • and Jane Gwiazda on babies' vision.

  • And they were also very interested in clinical aspects--

  • so astigmatism, an abnormality of the eye

  • that causes visual acuity to be reduced.

  • And also Eileen Birch who was working in their lab

  • as a post-doc, and then now is at the Retina Foundation

  • in the Southwest and does a lot of really good research

  • on clinical aspects of visual function in babies.

  • And then there's a pair of people-- a couple--

  • from England who have been working

  • as long as everyone else:

  • Jen Atkinson and Oliver Braddock

  • from the United Kingdom.

  • These are just some people.

  • I can't name all of them.

  • There's a list of maybe 40 or 50 people

  • doing research in this area.

  • But the person I'm going to talk the most about, who for me

  • has the greatest influence-- but of course I'm biased--

  • is Davida Teller,

  • who was a scientist of vision in adults,

  • who was at the University of Washington in Seattle

  • and had an insight about how you might approach

  • testing visual sensory function in babies

  • using a modification of Fantz's preferential looking technique.

  • NARRATOR: Fade to black.

  • Early Testing: Forced Choice Preferential Looking.

  • - Now if you remember, Fantz showed two stimuli

  • and measured whether... how much looking time

  • the baby spent looking at each of those stimuli.

  • Teller realized that you really can't test sensory function

  • as a perceptual task, at least not in this kind of way,

  • and that what you needed to do was to create a stimulus setting

  • where there's just one stimulus.

  • That is, that's the stimulus that's going to measure

  • your sensory function.

  • And I'm going to give as an example a technique,

  • stimulus that I've been intimately involved in

  • and was the first that was used,

  • and that's test of visual acuity using stripes,

  • black and white stripes in a patch.

  • It refers to a circular patch.

  • So that stimulus was going to be the test of visual acuity,

  • varying the size of the width of the stripes

  • from very coarse, very wide to very fine,

  • and then at some point finding out what's the threshold,

  • or what is the acuity of the child for that stripe stimulus.

  • Well, okay, you've got a stripe

  • and now what do you do with it?

  • Well, what she designed was to put the stripe

  • either on the right or the left of center,

  • and in the other part there would be a stimulus

  • that was a circle just like the stripes were in a circle,

  • but it was gray and matched in average brightness

  • to the stripes when you couldn't see them.

  • So you take a measuring instrument and you measure

  • what's the average brightness of that patch

  • and you match it to this gray.

  • Now, that's because if this were brighter,

  • the baby might be just looking at it

  • because it's brighter, not because they saw the stripes.

  • NARRATOR: We see an example of how Teller's stripe stimuli

  • would be presented to a test subject.

  • Two circles have been cut out of a large gray field.

  • They are on opposite sides of and equidistant from

  • the midline of the large field.

  • In the center there is a small peephole,

  • which allows the observer to see the test subject.

  • In this example, the circle on the left displays a pattern

  • of vertical stripes,

  • and the circle on the right displays a solid gray color

  • that matches the large field.

  • - And she also put the stripes in the gray in a big surround

  • that was the same gray approximately as the gray patch,

  • as the blank, we call it.

  • And that was to reduce features that might be distracting

  • to the baby.

  • So instead of looking at stripes, they might look

  • at something off on the side.

  • Now they have only one thing to look at: stripes versus gray.

  • So that was probably the, you know, the first...

  • I want to say innovation she created.

  • Other people did the same thing, but her second innovation

  • is even more striking and a little bit more difficult

  • to describe.

  • And that is, there's a person observing,

  • just as in Fantz's technique, a person observing a baby

  • looking at these things.

  • And that person's job she changed.

  • She changed the observer's job

  • so there's no longer measuring looking time

  • but rather where are the stripes based upon what the baby does.

  • So are the stripes on the right or the left?

  • And the observer, looking at the baby,

  • doesn't know where the stripes are and they have to make

  • this judgment just on the basis of what the baby's doing.

  • NARRATOR: A photograph depicts an observer

  • behind the testing apparatus.

  • The woman is looking through the peephole

  • to observe the test subject.

  • The next photo we see shows a view of a baby's face

  • as seen through the peephole.

  • In this example, the face is turned to the baby's right,

  • suggesting that the baby is responding

  • to a stripe stimulus on that side.

  • - And she called it a forced choice judgment,

  • which is really quite important.

  • The observer had no other choice.

  • Where are the stripes: right or left?

  • On every single trial, discrete trials,

  • showing a whole range of stripes from very tiny to very large.

  • And with that procedure, she reconceived

  • preferential looking and she called it

  • forced choice preferential looking.

  • Pretty obvious, but pretty significant change.

  • And I'm going to abbreviate that as FPL.

  • So I'm going to say FPL and just remember

  • I'm talking about that technique.

  • NARRATOR: Fade to black.

  • Using the Forced Choice Method.

  • - Created out of this series of presentations of stripes

  • of varying widths is this,

  • what we call a psychometric function.

  • And "psycho" is psychology, response,

  • and "metric" is a metric--

  • that is, some measure of sensory function.

  • And in fact, psychometric functions are,

  • I would say, the building blocks or the grounding

  • for a field of visual psychophysics.

  • So there's another fancy word.

  • What is psychophysics?

  • It is the psychological responses to the physics

  • of the stimulus, to qualities of the physical stimulus.

  • So we have stripe width, that's the physical parameter.

  • It varies over a certain range.

  • We take the psychological responses of the observer to...

  • in the paradigm that we're talking about.

  • Where is the stimulus?

  • You can also say, what interval is the stimulus in?

  • Or you can say, yes or no, does the baby see them or not?

  • That's another way of formulating an experiment.

  • Any sensory function can be measured with psychophysics.

  • So it doesn't have to be just vision,

  • but it can be hearing, smell, touch, taste.

  • And lots of interesting experiments are done

  • using psychophysics for testing all kinds of sensory functions.

  • NARRATOR: A young girl is shown wearing a large pair

  • of headphones while taking a hearing test.

  • She gazes up at a woman in a white lab coat

  • who is administering the test.

  • - How do you measure acuity doing that?

  • I mean, you know, I've said stripes

  • and a range of widths and so forth.

  • The way the technique developed was

  • the observer's correct and incorrect judgments

  • on each stripe was cumulated,

  • and a percent correct for each stripe width was calculated.

  • So what you now have is you have a function

  • that shows the percent correct performance of the observer

  • as a function of stripe width.

  • NARRATOR: An example of a psychometric function plot

  • is displayed.

  • Along the X or horizontal axis are six examples

  • of the stripe stimuli presented.

  • The stripe width varies progressively

  • from wide to very fine.

  • The Y or vertical axis

  • represents the observer's correct judgments

  • as a percentage.

  • The five points that are plotted show a diminishing percentage

  • of correct judgments from 100% to less than 60%,

  • which correlate to the diminishing widths

  • of the stripe stimuli presented.

  • - When the stripes are very large, the baby looks,

  • makes a really strong look at them.

  • The observer can tell easily where the stripes are.

  • When they get smaller and smaller,

  • it may be a little more subtle, and the baby may look like this,

  • may just glance a little bit at the stripes.

  • But the observer can still tell most of the time

  • where the stripes are.

  • But when they get so small the baby can't see them,

  • they're just two blanks for the baby,

  • the observer is just guessing

  • and most likely is just saying, "Oh, I think it's there,

  • I think it's there," and is wrong half the time,

  • correct half the time.

  • NARRATOR: We see an example of a stimuli

  • of very small stripes being presented,

  • along with a solid gray circle.

  • In the photo, the sensory qualities

  • of the stripes are too subtle to be distinguished.

  • A slight difference in the color of the circle to the left

  • of the midline is the only cue.

  • The next photo taken through the peephole

  • shows a baby looking down slightly,

  • exhibiting no preference for either side of the display.

  • Fade to black.

  • Early Testing: Operant Preferential Looking.

  • - Who are the babies that can be tested

  • with forced choice preferential looking, FPL?

  • In Davida's lab the babies that were being tested

  • were generally about two to three months of age.

  • Well, my colleague Jane Allen came along and the idea was

  • well, let's see if we can test really young babies

  • just like Fantz did with his preferential

  • and see how old... you know, when does acuity develop

  • and how does it develop normally?

  • And the person who did that was Jane Allen,

  • who in '78 finished her study of FPL acuity

  • tested in babies between two weeks and six months of age.

  • And she showed that acuity matured over that time,

  • it got better.

  • But it didn't get near adult levels.

  • So it wasn't over.

  • Well, what happened after six months?

  • Babies get bored, basically,

  • sitting for all the numbers of trials

  • that you have to present to do full psychometric functions.

  • At about six months they're no longer willing to do that.

  • And they need some kind of reinforcement

  • to keep looking, at least we realized that in those days.

  • And I was in Teller's lab at that time, and in fact,

  • working on Jane Allen's study.

  • There was another person in the lab

  • who was a research associate.

  • Her name was Velma Dobson,

  • a very important person in the field of infant vision.

  • And she and I conceived of a method to test babies,

  • or we wanted to try this method using a reinforcement procedure

  • to see if we could test older ages

  • and how far we could push this technique.

  • And what we did was we stole from audiologists

  • who use this technique to test hearing sensitivity in babies.

  • And basically it's a little bear, an animated bear

  • who is playing a drum in a box that is otherwise black,

  • but then when it gets turned on,

  • the box lights up and the baby plays the drum.

  • We placed a box on either side of the FPL screen

  • and when the observer said "Baby sees the stripes,"

  • pushed a button, stripes were on the left or the right,

  • the bear in the box on the left lit up

  • and the bear played his drum.

  • And so the baby was reinforced for looking at stripes.

  • NARRATOR: In a photograph, an infant sits

  • on his mother's lap in front of an OPL display.

  • There are dark black boxes on either side

  • of the flat gray display field.

  • The stripe stimulus has just been presented

  • to the baby's left.

  • The next photo depicts what happened.

  • Because the observer judged the stripes to be on the left

  • based on the baby's reaction, the observer then

  • pressed a button to record that choice.

  • As a result of making a correct judgment,

  • the box to the left of the display lights up

  • and the mechanical bear plays its drum.

  • - When the observer was wrong, nothing happened.

  • So it wasn't that it happened all the time,

  • it only happened

  • contingent on the baby's looking at the stripes.

  • Well, that worked pretty well and it worked for babies

  • up to the age of five years.

  • We could test now children from six months--

  • or actually earlier than that--

  • all the way up to five years of age, with one exception.

  • Toddlers were really tough.

  • And we gave up on 18-month-olds.

  • 18-month-olds are a terror.

  • When we measured full psychometric functions

  • in children over this whole age range and compared it

  • with Jane Allen's data, we found at overlapping ages

  • the results were the same.

  • So that said that operant preferential looking,

  • or OPL, wasn't biasing the results in any way.

  • It didn't make babies see better, it just made it

  • easier to test them.

  • So now we had techniques that would cover the whole age range,

  • and we could say we know now that acuity

  • is near adult levels at five years of age.

  • It's very poor at two weeks and it gradually increases

  • in a steady way between two weeks and five years.

  • NARRATOR: This graph depicts the development

  • of grating acuity from early infancy to preschool age.

  • Acuities obtained by forced choice preferential looking

  • between two weeks and six months are shown by open circles.

  • Acuities obtained by operant preferential looking

  • between five months and five years

  • are shown by filled circles.

  • Grating acuity improves from 20/600 at two weeks

  • to about 20/120 at five to 12 months,

  • and to 20/20 at five years.

  • Fade to black.

  • FPL and OPL Apparatuses.

  • - So we have this technique and we have apparatuses.

  • I call them apparatuses,

  • this FPL apparatus and OPL apparatus.

  • And those devices or pieces of equipment were fairly simple

  • and actually sort of primitive.

  • They were made out of gray cardboard,

  • mounted on wooden frames and held together with pushpins

  • and fishing wire and glue.

  • NARRATOR: In a photo, a graduate student

  • in Davida Teller's lab is holding a baby

  • in front of the FPL screen

  • with the black and white grating pattern on his right.

  • A close examination of the photo shows the many pushpins

  • holding the various pieces of gray cardboard together.

  • - Well, over the years...

  • I mean this work was done in the '80s, so it was...

  • Engineers say, "You know, you do a breadboard model

  • "and you get the proof of concept and then you go on

  • to do more sophisticated technological things,"

  • and so that's what happened.

  • NARRATOR: Now we see an OPL device

  • with some metal frames and glass panels

  • in front of the right and left display fields.

  • A young girl reaches out and touches the panel on the left.

  • Based on the toddler's reaction, the observer correctly judged

  • the striped stimuli to be on the left.

  • As a result, a reinforcement of Cheerios cereal

  • has been dropped from a plastic tube into a glass dish

  • that is within the child's reach.

  • - People started using equipment that was more advanced--

  • for example, they used cathode ray tubes,

  • and then eventually video displays and computers now.

  • And so some very interesting, important work that was done

  • and continues to be done using these more complicated

  • stimulus displays.

  • Still using preferential looking as the technique.

  • NARRATOR: We see in a photo a baby sitting up

  • in front of a box containing two video monitors side by side.

  • We can see that a display of stripes

  • is in one of the screens.

  • - Something we did do in Teller's lab

  • and in Children's Hospital, where I went,

  • was we replaced the observer and the holder as separate people,

  • but actually put that person into the same role.

  • So the observer and the holder were now the same person--

  • the person holding the baby, showing them the stripes

  • and the observer.

  • And how that worked was there was a video camera

  • behind a peephole that was showing the image of the baby

  • on a video monitor, that was then projected to a mirror

  • and the observer was able to watch the babies looking

  • and make judgments on the babies looking.

  • Now the observer, of course...

  • I mean the holder/observer couldn't see

  • where the stripes are, they shouldn't see them either.

  • NARRATOR: In this photo, Velma Dobson is seen

  • holding a baby, her three-month-old son.

  • He is looking at a grating on the FPL screen,

  • while Velma observes his face in the mirrored video image

  • projected by a camera behind the central peephole

  • in the screen.

  • We can see a black and white image of the baby's face

  • in a monitor that has been placed on a shelf.

  • - Over the many decades-- as I say, we're now

  • in the seventh decade of studies using preferential looking--

  • a number of different visual functions

  • have been tested using behavioral techniques,

  • using preferential looking types of techniques.

  • And that would include visual acuity is the most-studied,

  • and over the widest age range.

  • NARRATOR: Fade to black.

NARRATOR: The name "Perkins" carved in stone.

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視力検査(前編):優先視の歴史と初期検査について (Visual Acuity Testing (Part 1): History of Preferential Looking and Early Testing)

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    wei に公開 2021 年 01 月 14 日
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