Midterm 2 is March 11th and 12th

Read Land article for March 5th

Illusions related to depth perception

• Misperceptions of size• Misperceptions of location

Muller - Lyer Illusion

Muller-Lyer Illusion

• What theory does Gregory take up?

Muller-Lyer Illusion

• What theory does Gregory take up?– Thiery / Woodworth : Muller-Lyer figure

“suggests perspective”

Muller-Lyer Illusion

• What theory does Gregory take up?– Thiery / Woodworth : Muller-Lyer figure

“suggests perspective”

– Is there something about the presence of pictorial depth cues in an image that distorts size?

Depth Cues and Size Distortion

The Ponzo Illusion:

Depth Cues and Size Distortion

The Ponzo Illusion:

Depth Cues and Size Distortion

• The illusion of depth in an image seems to distort the perception of size in the image

• This is due to misapplication of Size - Constancy

Pictures are Weird

• What does Gregory find paradoxical about pictures?

Pictures are Weird

• What does Gregory find paradoxical about pictures?

Pictures convey depth yet also appear flat

Why?

The Apparatus

• When you view a picture there are some depth cues telling you to perceive depth, but other cues telling you that the image is on a flat surface

• …the surface matters!

• Retinal image size

Pictorial Depth Cues

• Retinal image size

Pictorial Depth Cues

The Apparatus

• What does he do to remove the paradox so that the Muller-Lyer figure no longer looks flat?

• Remove the background surface

The Apparatus

Removing the Background

• With background removed, Muller-Lyer figure actually looks 3D

• What prediction can you make about how the perceived size and the perceived distance of the center line are related?

Removing the Background

• With background removed, Muller-Lyer figure actually looks 3D

• What prediction can you make about how the perceived size and the perceived distance of the center line are related?

When the centre line appears close,it should also appear smallWhen the centre line appears far, it should also appear large

Removing the Background

• How did Gregory test that?

The Apparatus

Removing the Background

• Perceived size and perceived distance are tightly related

• inward arrowheads make line look closer/ outward arrowheads make line look farther

Misperception of Depth Drives Other Illusions

• Ames Room view from above

Now on to Magic Eye Stereograms

Stereograms

Left Eye Right EyeDivider

•Right eye sees face to the left; left eye sees face to the right therefore:faces present crossed disparity to the brain

•Face appears in front of square

Autostereograms

• Optically separate images aren’t needed

Autostereograms

• Optically separate images aren’t needed

• WARNING! Tricky stuff coming in the next slides

Autostereograms

• Optically separate images aren’t needed

• WARNING! Tricky stuff coming in the next slides

• Keep the definitions of convergence and disparity separate.

Autostereograms

•Convergence is on a point at the same distance as the images

•Boxes and faces are on the horopter

•How many boxes would you see?

boxes and faces are on the horopter

What would happen if you remove the divider of a stereoscope?

Autostereograms

•right-eye line of sight crosses left-eye line of sight in front of image (crossed convergence)

•each retina is now pointed at the opposite box

•How many boxes would you see?

•What would happen to the face?crossed convergence

Now cross your eyes:

Autostereograms

•There would be three boxes

•middle box: right eye sees face shifted to right; left eye sees face shifted to left therefore:uncrossed disparity

•Face in the middle box appears behind square

crossed convergence

Autostereograms

• What would happen if you moved the faces within the box?

• What would happen if you viewed this with uncrossed convergence?