Sensation and Perception

• Sensation and perception are related processes

Sensation

• The stimulation of sense organs
• Picking up raw information from the eyes, ears, nose, tongue, and skin

Perception

• Selection, organization, and interpretation of sensory input
• Understanding what that information means

Visual Agnosia

• A condition where individuals with perfect vision are unable to recognize or identify objects

Psychophysics

• Study of how physical stimuli translate into psychological experience
• Gustav Fechner was an important contributor to the field

Sensation

• Begins with a stimulus, or any detectable input from the environment
• Detectability depends on the perceiver

Absolute Threshold

• The minimum stimulus intensity an organism can detect for a specific type of sensory input
• Defines the boundaries of an organism's sensory capabilities
• It is the Weakest amount of a stimulus that can be distinguished from no stimulus at all
  • Detected 50% of the time

Difference Threshold

• Minimum difference in magnitude between two stimuli required to tell them apart
• Detected 50% of the time
• Weber’s constant is a standard of difference, where:
  • Light needs a 2% change in intensity
  • Weight needs a 2% change in weight
  • Sound needs a one-third of 1% change in pitch (frequency)
  • Taste needs a 20% difference in saltiness

Sensory Adaptation

• Gradual decline in sensitivity to prolonged stimulation
• Stimulus intensity remains stable, but sensitivity decreases with continued exposure

The Eye

• Light enters through the cornea, a transparent window
• The cornea and lens form an upside-down image on the retina
• The lens is a transparent structure made of soft tissue, allowing adjustment called accommodation -Accommodation allows the curvature of the lens to adjust and alter visual focus
• Cataract: clouding of the lens
• Pupil: opening in the center of the iris, regulating light amount
• Constricts to block too much light and dilates in low light conditions
• Retina: neural tissue lining the inside back surface
• Absorbs light, processes images, and sends information to the brain
• Images on the retina are upside down
• Nearsightedness: close objects are clear, distant ones blurry
• Farsightedness: distant objects are clear, close ones blurry
• Optic disk: axons leaving the retina converge, creating a blind spot in the retina
• The image when falls onto the hole cannot be seen
• It absorbs light, processes images and sends visual information to the brain

Visual Receptors

• Rods: specialized for night and peripheral vision
  • Rods are elongated and outnumber cones
• Cones: specialized for daylight vision and color
  • Cones are stubbier then rods
• Fovea: tiny spot in the center of the retina, containing only cones

Dark and Light Adaptations

• Dark adaptation: eyes become more sensitive to light in low illumination
• Occurs when entering a cinema from a bright environment
• Light adaptation: eyes become less sensitive to light in high illumination
• Occurs when returning outdoors from a dark cinema

Gestalt Principles of Visual Perception

• Phi Phenomenon: Illusion of movement shown by visual stimuli in quick succession
• Figure and Ground: Organizes visual perception; the figure is the focus and the ground is the background
• Proximity (Closeness): Elements near each other are grouped together
• Similarity: Grouping stimuli that are together.
• Continuity: Tendency to follow in whatever direction elements lead
• Simplicity: Forms are organized in the simplest way possible
• Closure: Missing pieces are added to complete familiar figures

Pictorial Depth Cues

• Cues about distance that can be given in a flat picture
• Linear perspective: Depth cue reflecting lines converging in the distance
• Texture gradient: Texture is coarse for near areas and finer for more distant areas
• Relative size: Closer objects appear larger
• Height in planes: Distant objects appear higher in an image
• Light and Shadow: Creates an impression of three-dimensional forms
• Interposition: Near objects overlap or mask more distant ones