Size Perception and Motion Chapter 8

Size perception

The ability to perceive the actual size of distal stimuli regardless of variations in the size of the proximal stimulus.

Size-distance Invariance

The principle stating that the visual system perceives an object’s size by considering both retinal size and perceived distance.

Emmert’s Law

A formula describing size-distance invariance: Sp = K (Sr x Dp), where Sp is perceived size, Sr is retinal size, and Dp is perceived distance.

Size Constancy

The visual system's ability to maintain a constant perception of an object's size despite variations in retinal size.

The Moon Illusion

The phenomenon where the horizon moon appears larger than the zenith moon due to perceived distance.

Flat-dome hypothesis

The idea that the sky appears flattened, which contributes to the Moon Illusion.

Illusory motion

Perceived motion with no actual motion, often demonstrated through various types.

Apparent Motion

An illusion of motion created by the rapid sequential presentation of two separate stimuli.

Induced Motion

The perception of motion in a stationary object caused by the motion of a background.

Autokinetic Motion

An illusion where a stable point of light appears to move in darkness due to microsaccades.

Motion after-effects

An illusion where prolonged exposure to motion in one direction leads to the perception of motion in the opposite direction upon viewing a stationary object.

Real motion

The perception of actual motion in the environment.

Factors Affecting Real Motion Perception

Influences include background texture and the size of the object observed.

Background impact on motion perception

Motion is easier to detect against a heterogeneous (textured) background than a homogeneous one.

Corollary Discharge Theory

A signal that helps the brain compare active motor signals with sensory information to manage motion perception.

Perceptual Vector Analysis

Method by which the visual system analyzes motion into vectors influenced by nearby objects.

Testing Theory with Curare

When eye muscles are paralyzed, the brain can still perceive motion due to the lack of corresponding motor signals that would normally indicate movement, leading to a dissociation between perception and actual physical motion.

Common Vectors

These vectors cancel

Relative Vectors

These vectors are constituted (part of something) vectors.