Understanding Perception

• Perception is the subjective experience of sensory information after cognitive processing.
• It acts as the interface between the physical world and our interpretation of it.
• Perception relies on cognitive functions like memory to recognize stimuli.
• The process allows us to identify and respond to environmental stimuli.

Definition by APA

• The American Psychological Association defines perception as becoming aware of objects, relationships, and events through the senses.
• This includes recognizing, observing, and discriminating.

Sensation vs. Perception

• Sensation is a physical process.
• Perception is psychological.
• For example, sensation is scent receptors detecting cinnamon fragrance.
• Perception: "Mmm, this smells like Grandma's holiday bread."

Stages of Perception

• Stage I: Selection occurs because the brain has limited capacity; it selects and ignores stimuli.
• Stage II: Organization involves mentally arranging stimuli into meaningful patterns, depending on Gestalt principles.
• Stage III: Interpretation is assigning meaning to organized stimuli based on experiences, needs, beliefs, and expectations.
• Interpretation is subjective; the same stimuli are interpreted differently.

Types of Perceptual Processing

• Bottom-up processing builds on sensory input and is driven by data.
• It is direct and does not rely on experience.
• Top-down processing involves interpreting sensations using available knowledge, experience, and thoughts.
• It is indirect and driven by experience.

Perceptual Constancy

• Perceptual constancy is the ability to perceive constant object characteristics despite varying stimuli.
• Shape constancy is when an object maintains its shape despite retinal image changes.
• Size constancy is when an object's size remains consistent despite changes in distance.
• Color constancy is when familiar objects appear the same color under varied conditions.

Size Constancy & Illusions

• Illusions occur when sensory and perceptual systems are misled by cues that usually help achieve size constancy.
• The Ponzo illusion shows two objects the same size that appear different due to depth cues of converging lines.
• The Müller-Lyer illusion shows two same-length line segments as different lengths.

Depth & Distance Perception

• Depth perception is the ability to perceive distance.
• It is vital for judging distances between oneself, other people, and moving objects.
• It is also known as third dimension.

Cues for Depth Perception

• Depth perception relies on cues to understand distances.
• These cues are monocular or binocular.

Monocular Cues

• Monocular cues can be observed with one eye.
  • Linear perspective: Parallel lines converge at an angle.
  • Relative size: An object's size helps determine distances; closer objects appear larger.
  • Motion parallax: Farther moving objects appear slower.
  • Interposition: When one object blocks another.
  • Texture gradients: Closer regions have rough textures with details; texture gets finer with distance.
• Pattern of light and shadow creates 3D

Binocular Cues

• Binocular cues are perceived using both eyes.
  • Retinal disparity: The image falling on both retinas differs.
  • Information from both eyes is integrated.
• Convergence/divergence of eyeballs: Eyeballs converge as objects get closer and diverge as they move away.

Perception of Movement

• This is a process where humans and other animals orient themselves.
• It is the ability to perceive their own or others' physical movements.
• It is gained naturally from birth.

Types of Perception Movement

• Physical movement is movement that creates the perception of movement when the object is physically moving.
• Apparent motion is the appearance of real motion from a sequence of still images in succession.
  • In apparent motion, the objects are stationary, but may appear to be moving, hence the illusion.

Phi Phenomenon

• Phi phenomenon produces the perception of movement when separate stimuli are presented together with rapid stimului.
• It causes an illusion of movement from rapidly illuminated stationary objects.

Theories of Perception

• Schemas and template matching are theories of perception.
  • The schema theory analyzes new perceptual input and compares them to schemas, items stored in memory, such as shapes and sounds.
  • The template theory uses information from past experiences to make sense of new stimuli.
  • Templates are stored object representations that enable object recognition.
• Gestalt group thought we add more to what we perceive.
  • This group said the perception of a whole object will always be greater than the sum of its parts.
  • If recognizing objects, separate them from everything else.

Principles of Perceptual Organization

• There are five principles of perceptual organization.
  • The principle of proximity: Objects near each other are grouped.
  • The principle of similarity: Similar objects are grouped regardless of their proximity.
  • The principle of continuation: Grouping together objects with continuous patterns or direction.
  • The principle of closure: People fill in blanks to perceive complete objects.
  • The principle of common fate: Visual elements moving in the same speed/direction are seen as parts of a single stimulus.

Disorders of Perception

• Agnosia is the inability to process sensory information and there is typically a lack of ability to recognize objects, persons, sounds, shapes, or smells with no memory loss.
• Typically results from occipital or parietal damage in the brain.
• Visual agnosia is impaired recognition of visually presented objects and intact visual field, acuity, color vision, etc.
• Auditory agnosia is the inability to recognize certain sounds; it typically causes damage to the temporal lobe.
• Ataxia means without coordination.
  • People with ataxia lose muscle control in their arms and legs.
  • This may lead to a lack of balance, coordination, and trouble walking.
  • Ataxia may affect the fingers, hands, arms, legs, the body, speech, and eye movements.
  • It is caused by damage to the cerebellum or related connections.
• Akinetopsia is Motion Bindness or selective loss of motion perception where one is unable to perceive motion.
  • Instead, motion occurs as a series of snapshots.
• Achromatopsia is a hereditary disorder resulting in the absence of cones in the retina.
• Those with Achromatopsia rely on rods, lack color vision, and have trouble seeing details.
  • The incidence of Achromatopsia is estimated to be roughly 1 in 33,000 people.