*Video Transcription*

Editors Note: This is my first video transcription, I may have made mistakes.

(0:00)

*[There is a high pitched, introduction noise. ]*

*[There is a woman talking]*

This video is brought to you by CuriosityStream. Ok, take a look at this optical illusion, are the lines parallel or not?

*[A picture appears of alternating vertical and horizontal diagonals crossing through the parallel lines, the crossing lines give the appearance that the parallel lines are not parallel.]*

What about this one? Is the black line a continuation of the red line, or the blue line? Or if its misaligned, which direction does it have to move to be in line with the red one?

*[There is a photo of a black line at the top, with a rectangle in the middle, there are two lines, pretty close together, one is red, and one is blue. Your eyes attempt to throw you off, by overestimating where the line will drop off.]*

(0:29)

These are examples of Geometrical Optical Illusions. Mainly the Zöllner and Poggendorff illusions. The Zöllner illusion is made up of diagonal lines, they are parallel, but they are crossed with shorter lines that alternate between horizontal and vertical. The angles of these shorter lines, give the impression that the diagonal lines are not parallel. In the poggendorff illusion we have a tendency to misestimate the unknown angles hidden by the rectangle, the acute angle have an effect of us over predicting the position of the line. Many of us are tricked by looking at these images, and for centuries we thought that perceptual illusions just involved the visuals system, but people who have been blind since birth can be tricked by these illusions too.

(1:13)

In a classic 1938 study, an experimental psychologist mounted raised version of the Poggendorff, Zöllner, and Muller-Lyer illusions on the near ply board.

*[Photos of the illusions from earlier appear]*

When participants who were blind since Birth, touched the illusions and explored them haptically, almost all experienced the Poggendorff and Muller-Lyer illusions, and about half were tricked by the Zöllner illusion.

*[A hand is shown feeling around the illusions]*

*[A photo of a face, with a blind fold appears]*

When sighted participants only touched the illusions, there was no effect, but when the sighted participants looked at the illusions,

*[The blindfold on the face comes off]*

they were tricked by them too. For people who were blind, they could feel the illusions, that other see, and still be tricked by them.

(1:52)

And over time, with more participants, and more accurate ways of running these experiments, researchers found that many visual illusions exist with a tactile mode.

(2:02)

Take the Muller-Lyer illusion, do you think the lines are the same length, or are they different?

*[A photo of 3 lines appear, The arrows are pointed in different ways, which tends to throw people off, The lines, when measured away from the arrows, are the exact same size]*

For sighted people, some suggest this illusion prompts perceptual differences in depth, and in people who are blind, many have difficulty in separating where the straight line ends, and where the arrows begin. Leading to a over estimate, or under estimate of the straight line.

(2:25)

In many studies, this illusion has tricked participants who were both blind, and sighted. There are perceptual processes common in both vision and touch. But there are some differences too.

(2:38)

Take a look at this image, are the yellow lines the same length or difference?

*[There is a train track, one yellow line is placed in the background, and one is placed right in the middle of the photo. The difference in linear perspective makes it seem as if the line in front of the viewer is smaller than the one in the background]*

Mario Ponzo an Italian psychologist suggested that our minds judge an object size based on its background. That is when you can see an object. In numerous studies, the Ponzo illusion has not been found in touch, in those who are blind. Which means a different perceptual process is underlying the illusion. It's thought that the Ponzo illusion is dependent on our perception of linear perspective. Which isn't universally present in those blind since birth. Of course, people who are blind can learn about these principles of perspective just as sighted people do. But research suggests, they may not spontaneously use these ques in interpreting raised line drawings.

(3:26)

Studying haptic perception in blind, vision impaired, and sighted people, can help us better understand the sense of touch, and improve the design of things like raised maps, and accessible money, and even haptic feedback on our phones. And in addition to that, you can see there's more to the humble illusion than first meets the eye.

(4:16)

There was one interesting thing, that I couldn't fit in, because it was going to be too long, but when people touching the illusion, and experiencing the haptic illusions, and the magnitude of the effect changes depending on how much of their hands they use, if you just use the face of your finger, your index finder, it's greater, and if you use your whole hands, or you are feeling everywhere, it's not as great, I couldn't find a way to include that without this being really long, but now it's just really long anyway, and I'm monologuing, thanks for watching.

*[End of Video]*



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^^I'm a volunteer content transcriber for Reddit. $1