Analyzing visual illusions (perspective drawing, depth cues, shape relationships, tessellations, ambiguous images)

“About 30% of the brain is devoted to vision so the brain implicitly trusts eyes and makes mistakes”

Optical Illusions

Exploit the mismatch between the appearance and physical reality of a visual stimulus. They illustrate the perceptual system’s tendency to fill in missing components to perceive whole patterns.

Illusion #0 - Are the horizontal lines parallel or do they slope? (A: parallel)
Colors: black and white
Shape: squares

Activity: Squares within squares, see image

Term - Patterning: “a design formed by the arrangement of patterns”. ex. tessellations is a kind of patterning (repetition of a single shape without space in-between)
Term - Directional Lines: Used to guide a viewer’s eye through an image (lines/line segments are 1D)

Illusion #1 - Squares
Colors: primary colors (red, yellow, blue)
Shape/Dimension: squares, 3D (depth, width, height) and 2 point perspective
Light: mimics light and shadow (lightest on top, darkest on side)

Activity: Necker Cube - Perceived as a 3D object but the front and back depends on your perception. Draw Cubes and color different sides

Old Term - Parallax: Is when an object’s position appears to change when viewed at a different angle.

Illusion #2 - Lines
Colors: black and white
Shape: lines, straight becomes curved
Light: light and dark in its simplest form

Term - Contrast: The arrangement opposite elements (such as light and dark) in an image, high contrast = more extreme

Activity: Traced hand
Term - Curvilinear: Pattern-work or designs characterized by curved lines.
Term -  Curvilinear Perspective (5 point perspective)

Illusion #3 - Purple Ovals on Green
Colors: secondary colors (green and purple), black and white
Shape: ovals (ellipses)
Light: edges are half black and half white, 3D (depth, width, height)

Term: Motion Illusion: When an image looks as if it’s moving due to the position of shapes and contrasting colors

Term: Optical Flow: The pattern of apparent motion in objects and images
Term: Affordance Perception: The awareness of action possibilities on an object or environment.

Activity: Draw arrows in the directions the eye looks, turn that into a pattern

Illusion #4 - Orange Ovals on Blue
Colors: complimentary colors (blue and orange), black and white
Shape: ovals (ellipses), cylinder, motion illusion and optical flow, 
Light: edges are half black and half white, 3D

Old Term - Interposition): Objects that are in front of other objects may partially block our view of the rearmost object. Because we know what the object should look like, and because we see only part of it, we interpret the obstructed object as being farther away.

Activity: _________________________________

Illusion #5 - Yellow Black White and Blue Curved Lines
Colors: yellow, blue, black, and white (high contrast)
Shape: curved lines, center circle (focal point) creates a for optic flow
Light: dark center, varies among the lines

Old Term - Vanishing Point: Point in space where receding parallel lines appear to meet.
Term - Focal Point: The a specific place of visual emphasis
Term - Scale: The relative size of an object compared to other objects or space.
Term - Size Constancy: the perception of an object being the same size no matter how close or how far away it is. ex. linear perspective (1, 2, and 3 point perspective drawing), monocular depth cue - relative size

Activity: __________________________________

Show “Optical Illusions Show How We See” - Beau Lotto TED Talk (16:27)

From previous lessons:

Monocular Cues
Clues about distance based on the image of one eye. Motion parallax and accommodation require active use of the eye in viewing, while the others are pictorial depth cues that can be given in a flat picture.

1 Linear Perspective: The convergence of lines toward a single point of the horizon. 
Ex. railroad tracks

2 Relative Hight (Elevation): Objects closer to the horizon are perceived as being farther away; objects far away from the horizon are seen as being closer. 
Ex. Wildebeest migration pic

3 Relative Size: When two the closer of two same sized objects appears bigger than the farther one. Only applies to familiar objects. 
Ex. leaning tower of pisa, bell tower in Italy

5 Relative Brightness: Can be seen when the closer of two identical objects reflects light.
Ex. Field of flowers

6 Aerial Perspective (Haze): Objects that are a great distance away have less contrast and less color saturation, due to light scattering by the atmosphere, making them seem hazy.
Ex. Mountains

7 Texture Gradient: The closer the proximity to an object, the more detail or texture one can see.
Ex. Cracked sand

9 Motion Parallax: Objects closer are viewed as moving faster than objects that are further away.
Ex. Speeding car

Horizon Line: Is the axis around which a perspective drawing is constructed.
Orthogonal Lines: Lines parallel to the ground plane and move back from the picture plane. They set the varying heights or widths of a rectangular plane as it recedes from view and always appear to meet at a vanishing point on the eye level.
Transversal Lines: Lines at right angles to the orthogonal lines. They are parallel to the picture plane and to one another. They establish a fixed height or width between two orthogonal lines and they form the nearest and furthest edges of a rectangle as it recedes from view.

1 Dimensional (1D): Has length. Is the connection between two points - ex. a line segment.
2 Dimensional (2D): Has width and height - ex. a piece of paper.
3 Dimensional (3D): Has depth, width, and height - ex. a cube.