Fundraiser Concert for Haiti

• U of L Students and Faculty Performing

– 9pm Blues Sen-sa-shun

– 10pm Shawna Romolliwa

– 11pm Dave Renter

• At The Slice, Friday Feb. 26th – $5 for students, $10 for everybody else

Extra Credit for Participating in Experiments

Go to www.tatalab.ca to sign up

We are recruiting for a variety of experiments including basic

perception and ADHD

Upcoming

• Gregory Article for today

• Read Pinker Article for help with stereo vision and stereo grams

• Read Land Article for March 2

Depth Cues

Pictorial Depth Cues: aspects of 2D images that imply depth Physiological Depth Cues: Proprioception in ocular muscles indicates

accommodation and convergence Motion Depth Cues: foreground and background move in opposite directions Stereoscopic Depth Cues: disparity between two retinal images indicates

distance

Illusions related to depth perception

• Misperceptions of size• Misperceptions of location

Muller - Lyer Illusion

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?

Pictures are Weird

• 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

Pictures are Weird

• Retinal image size

Pictures are Weird

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

• Ames Room Video

Autostereograms: The Magic Eye

Binocular Disparity

• points nearer than horopter have crossed disparity

• points farther than horopter have uncrossed disparity

The Horopter

Stereograms

• seeing depth requires “only” two different images on the retina

Stereograms

• seeing depth requires “only” two different images on the retina

• this could be accomplished by an optical device that projects separate images into the two eyes

Presenting Binocular Images

• Various ways to add depth:– 1. Stereoscope

Presenting Binocular Images

• Various ways to add depth:– glasses with different lenses

Presenting Binocular Images

• Various ways to add depth:– glasses with different lenses

Presenting Binocular Images

• Various ways to add depth:– glasses with different lenses

Stereograms

Left Eye Right EyeDivider

• Right eye sees face to the right; left eye sees face to the left therefore:

uncrossed disparity

• Face appears behind the square

Stereograms

Left Eye Right EyeDivider

What would you see?

Stereograms

Left Eye Right EyeDivider

• Right eye sees face to the left; left eye sees face to the right therefore:

crossed disparity

• Face appears in front of square