Perception

Two types of processing functions

• Top-down- Filling the gaps, less accurate, uses schema

• Bottoms-up- Uses sensory input to create a perception.

Perceptual Organisations

Gestalt belief- Human brain perceives stimulus as a whole and not as the sum of its parts

Founder of the Gestalt Approach- 1912, Wertheimer, Koffka, Kohler

Gestalt- Organised whole

Law of Pragnanz (Good Figure, Simplicity)- People percieve and interpret ambiguous or complex images in the simplest form possible

Figure-Ground Relationships- Tendency to percieve objects or figures as existing on a background- Edgard Rubin

4 factors that contribute to change in figure-ground perception

• Blurriness- Sharpness/ Lack thereof of the edges between two objects. Blurry edges make the observer percieve an object or shape as the background

• Contrast- Contrast in colors between potential figure and potential background

• Size- Size of target object relative to the rest of the image

• Separation- Objects degree of separation from the background

Laws of Perceptual Organisation

• Similarity- Tendency to percieve things that look similar to one another as being part of the same group

• Proximity- Tendency to percieve objects that are close to each other as part of the same group

• Closure- Tendency to fill gaps and complete incomplete figures

• Continuity- Tendency to percieve patterns

• Common Region- Stephen Palmer1992, Objects in common area=Same Group

• Contiguity- Two things happening togethr= Seen as being related or part of the same group

Types of Perceptual Constancies- Allow us to recognise familiar stimuli under varying conditions

• Brightness- Occurs because the ratio of light intensity between the object and its surroundings is constant

• Shape- Allows us to percieve objects and people from all angles

• Size- Size of objects remains relatively constant even though images on our retina change in size with variations in distance.

Depth Perception- Defined as the ability to see in 3 dimensions

Depth Cues

• Monocular- Require use of one eye, pictorial depth cues

  • Linear perspective - Objects that are farther away appear smaller

  • Texture gradient - Surfaces appear to have more detail when closer

  • Interposition (overlapping) - Objects that partially block other objects are perceived as closer

  • Aerial perspective - Distant objects appear hazier or bluer

  • Relative size - When we know two objects are similar in size, the smaller one appears farther away

  • Relative height - Objects higher in our visual field appear farther away

  • Motion parallax - Closer objects appear to move faster than distant objects when we move

  • Shadows and shading - Help determine the shape and position of objects

• Binocular- Require use of both eyes to gather depth perception.

  • Stereopsis - Uses the slightly different images from each eye to judge distance

  • Convergence - Eyes move inward when looking at closer objects, providing a muscle cue for depth

  • Retinal disparity - Difference in image position on the retinas of the two eyes that helps calculate depth

Perceptual Illusions

• Hermann Grid

The Hermann Grid illusion is a visual illusion where dark spots appear at the intersections of a white grid on a black background. These dark spots disappear when you look directly at an intersection. The illusion occurs due to lateral inhibition in the visual system.

Key characteristics of the Hermann Grid illusion:

• First described by Ludimar Hermann in 1870

• The effect is strongest in peripheral vision

• Occurs due to lateral inhibition between light and dark receptive fields

• The illusory dark spots are called "scintillating" spots

• The effect diminishes when the grid lines are curved or distorted

• Muller-Lyer

  The Müller-Lyer illusion is a famous optical illusion where two lines of identical length appear to be different sizes due to the arrow-like fins attached to their ends.

  Key characteristics of the Müller-Lyer illusion:

  • First described by German psychiatrist Franz Müller-Lyer in 1889

  • Lines with outward-pointing fins appear longer than identical lines with inward-pointing fins

  • The effect persists even when we know the lines are actually the same length

  • The illusion is thought to occur because our visual system interprets the fins as depth cues

  • The effect is stronger in people from "carpentered" environments with many right angles

  • Demonstrates how our perceptual systems can be misled by contextual cues

• Moon Illusion

  The Moon Illusion is a well-known perceptual phenomenon where the Moon appears larger when it's near the horizon than when it's high in the sky.

  Key characteristics of the Moon Illusion:

  • First documented by ancient Greek astronomers, including Aristotle (384-322 BCE)

  • The Moon appears about 1.5 times larger on the horizon than when overhead

  • The illusion occurs despite no actual change in the Moon's angular size

  • Primarily explained by the "apparent distance theory" - we perceive the horizon as farther away than the zenith

  • Also influenced by the Ponzo illusion - foreground objects provide scale cues that make distant objects appear larger

  • Demonstrates how our perceptual systems integrate contextual information into size judgments

• Illusions of Motion

  Motion illusions are visual phenomena where static images appear to be moving or where actual motion is perceived incorrectly.

  Key characteristics of motion illusions:

  • Autokinetic effect - When staring at a static point of light in a dark environment, it appears to move

  • Phi phenomenon - Series of static images shown in sequence create the perception of movement (basis of animation and film)

  • Waterfall illusion (motion aftereffect) - After staring at moving stimulus then looking at stationary object, the stationary object appears to move in opposite direction

  • Rotating snakes illusion - Circular patterns appear to rotate continuously though the image is static

  • Wagon wheel illusion - A spinning wheel appears to rotate backward or stand still due to frame rate of observation

  • Perceived causality - When one object moves toward another and then the second begins moving, we perceive the first as causing the second's movement

  These illusions demonstrate how our visual system processes motion and highlight the constructive nature of perception.