SENSATION AND PERCEPTION

Sensation and Perception Overview

  • Sensation: Activation of sense organs by physical energy, transforming environmental information into brain signals.
  • Perception: Psychological interpretation and integration of sensory inputs; influenced by past experiences, context, and cognitive processes.

Sensory System Components

  • External Sensation: Knowing physical stimuli through:
    • Stimulus: Any form of energy causing a sensory response.
    • Receptors: Specialized cells in sense organs detecting stimuli.
    • Transmissors: Nerve fiber bundles conveying sensory information to the brain.
    • Brain Center: Areas in the brain that process sensory signals.

Understanding Stimuli

Absolute Thresholds
  • Definition: Minimum intensity of a stimulus detectable by senses.
    • Examples:
    • Sight: Candle flame 30 miles away on a clear night.
    • Hearing: Watch ticking from 20 feet away.
    • Touch: Bee wing falling on cheek from 1 cm.
    • Smell: One drop of perfume in a three-volume house.
    • Taste: One teaspoon sugar in two gallons of water.
  • Implication: Lower absolute threshold indicates higher sensitivity.
Difference Thresholds
  • Also known as just noticeable differences (JND): Minimal change in stimulation detectable 50% of the time.
  • Weber’s Law: JND is proportional to the intensity of the original stimulus.

Adaptation and Noise

  • Adaptation: Adjustment of sensory capacity after prolonged exposure to constant stimuli.
  • Noise: Background stimulation interfering with perception, leading to overload or distraction.

Types of Receptors

  • Exteroceptors: Detect external stimuli (e.g., skin receptors).
  • Proprioceptors: Provide information on body position and movement (found in muscles/joints).
  • Interoceptors: Respond to internal environment changes (located in organs).

Visual System

Light and Visual Stimuli
  • Light: Electromagnetic radiation; visual spectrum detectable by the human eye (380 nm to 750 nm).
  • Visual Receptors: Rods (for low light) and cones (for color and detail).
Structure of the Eye
  • Cornea and Lens: Focus light on the retina; process is called accommodation.
  • Retina: Contains rods and cones; converts light to electrical impulses.
  • Optic Nerve: Transmits visual information to brain's visual cortex.
    • Bipolar Cells: Connect rods and cones to ganglion cells.
    • Ganglion Cells: Collect and transmit visual data to the brain.
Visual Phenomena
  • Color Vision: Normal vision can distinguish up to 7 million colors.
  • Color Blindness Types:
    • Trichromats: Normal color perception.
    • Dichromats: Limited in one color spectrum.
    • Monochromats: Only perceive black and white.
Color Vision Theories
  • Trichromatic Theory: Three types of cones (red, blue, green) allow full color perception.
  • Opponent-Process Theory: Color perception based on opposing pairs (red vs green, blue vs yellow).
  • Afterimage Effect: Persistent visual sensation post-exposure due to retinal activity.
Abnormalities in Vision
  • Scotomas: Blind spots due to primary visual cortex damage; completion phenomenon.
  • Blindsight: Ability to respond to visual stimuli without conscious perception.
  • Prosopagnosia: Inability to recognize familiar faces despite visual capability.
  • Akinetopsia: Inability to perceive movement smoothly.

Hearing and Other Senses

Sound Structure
  • Sound: Movement of air molecules from vibrating objects.
  • Parts of Ear:
    • Outer Ear: Collects and channels sound waves.
    • Middle Ear: Transmits vibrations via ossicles.
    • Inner Ear: Converts vibrations into neural signals; includes cochlea and organ of Corti.
Auditory Processing
  • Cochlea: Fluid-filled structure that vibrates in response to sound.
  • Auditory Nerve: Carries sound signals to the brain.
Hearing Theories
  • Different areas of basilar membrane respond to different frequencies.
  • Frequency: Number of wave cycles per second.
  • Intensity/Loudness: Amplitude of sound waves.

Somatosensation

  • Skin Senses: Able to detect touch, pressure, pain, temperature.
  • Kinesthesia: Ability to sense body movement and position.

Gustatory and Olfactory Senses

  • Taste (Gustatory): Five primary tastes (sweet, sour, salty, bitter, umami).
  • Smell (Olfactory): Detects chemical substances; olfactory system vital for flavor perception.
  • Supertaster vs. Nontaster: Genetic differences in taste receptor sensitivity.

Perception and Interpretation

Gestalt Laws
  • Organizing sensory input into meaningful wholes:
    • Figure-Ground: Distinguishing foreground from background.
    • Similarity: Grouping similar items.
    • Closure: Filling in gaps for completeness.
    • Proximity: Grouping closely located objects.
    • Continuity: Perceiving smooth, continuous patterns.
Processing Types
  • Top-Down Processing: Guided by prior knowledge and expectations; filling in gaps.
  • Bottom-Up Processing: Starts with raw sensory data; step-by-step processing.
Perceptual Constancy
  • Objects perceived consistently despite changes in appearance due to distance, angle, illumination.
Depth Perception
  • Ability to perceive three-dimensionality using monocular and binocular cues.
  • Monocular Cues: Depth perception using one eye (e.g., texture gradient, relative size).
  • Binocular Cues: Depth perception using both eyes (e.g., convergence, binocular disparity).