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Sensation and Perception
Sensation: The process of detecting physical energy (stimuli) from the environment and converting it into neural signals.
Perception: How we organize, interpret, and make sense of these sensory signals.
How We Process Sensory Information
Bottom-Up Processing: Building perception from the smallest sensory details and working up to a complete picture. Example: Seeing individual dots and then recognizing them as a picture.
Top-Down Processing: Using our existing knowledge, expectations, and context to interpret sensory information. Example: Reading a misspelled word but still understanding its meaning.
Thresholds: Limits of Sensation
Absolute Threshold: The minimum amount of stimulation needed to detect a stimulus half the time.
Difference Threshold (Just Noticeable Difference - JND): The smallest change in stimulation that can be detected half the time.
Weber's Law: The JND is proportional to the intensity of the original stimulus. Example: It's easier to notice a small change in weight if you're lifting a light object than a heavy one.
Subliminal Threshold: A stimulus below our conscious awareness but still detectable by some people or instruments.
Other Key Concepts
Signal Detection Theory: How we detect a faint stimulus (signal) in the presence of background noise. It depends on factors like expectations, motivation, and alertness.
Sensory Adaptation: Our senses become less sensitive to a constant stimulus over time. Example: Getting used to the smell of your own perfume.
Habituation: A decrease in response to a repeated stimulus due to conscious or unconscious learning. Example: Not noticing the ticking of a clock after a while.
Structure of the Eye
Cornea: The clear, curved front of the eye. Bends light to begin focusing it.
Iris: The colored part of the eye, a muscle that controls the size of the pupil.
Pupil: The opening in the iris that lets light into the eye. Dilates (opens wider) in dim light and constricts (gets smaller) in bright light.
Lens: A transparent, flexible structure that further focuses light onto the retina. Changes shape to focus on objects at different distances (accommodation).
Aqueous Humor: A watery fluid that fills the space between the cornea and lens.
Vitreous Humor: A jelly-like substance that fills the main chamber of the eye.
Retina: The light-sensitive inner surface of the eye, containing photoreceptor cells (rods and cones).
Fovea: The central point of the retina, where vision is sharpest and most cones are located.
Optic Disc (Blind Spot): Where the optic nerve leaves the eye, creating an area with no photoreceptors.
Photoreceptors: Rods and Cones
Rods:
Detect black, white, and gray.
Responsible for peripheral and night vision (work in low light).
Cones:
Detect color (red, green, blue).
Responsible for sharp, detailed vision and require bright light.
How We See:
Light enters the eye through the cornea and pupil.
The lens focuses the light onto the retina.
Rods and cones in the retina convert light into electrical signals.
These signals are sent through bipolar cells to ganglion cells.
Ganglion cells form the optic nerve, which carries the signals to the brain for processing.
Vision: Color and Perception
Color Vision: How We Perceive Colors
Hue: The dimension of color we experience (e.g., red, blue, green). Determined by the wavelength of light.
Short Wavelength: Bluish colors
Long Wavelength: Reddish colors
Intensity: The brightness of a color. Determined by the amplitude (height) of the light wave.
High Amplitude: Bright colors
Low Amplitude: Dull colors
Vision Problems
Nearsightedness (Myopia): Difficulty seeing distant objects clearly. The eyeball is too long, causing light to focus in front of the retina.
Farsightedness (Hyperopia): Difficulty seeing close objects clearly. The eyeball is too short, causing light to focus behind the retina.
The Brain's Role in Vision
Feature Detectors: Specialized neurons in the visual cortex that respond to specific aspects of a visual scene (edges, angles, movement, faces).
Parallel Processing: The brain processes different aspects of a visual scene simultaneously (color, depth, movement, etc.).
Theories of Color Vision
Trichromatic Theory (Young-Helmholtz): The retina has three types of cones sensitive to red, green, and blue light. These cones work together to produce our perception of all colors.
Color Deficiency: A genetic condition where one or more types of cones are missing or impaired, causing difficulty distinguishing certain colors.
Opponent-Process Theory (Hering): We have three pairs of opponent color receptors (red-green, blue-yellow, black-white). When one color in a pair is stimulated, the other is inhibited. This theory explains afterimages.
Color Constancy: The ability to perceive an object's color as relatively constant even under varying lighting conditions.
Hearing: How We Perceive Sound
Sound Properties
Frequency (Pitch):
Determined by the wavelength of the sound wave.
Measured in Hertz (Hz).
Long Wavelength: Low frequency (low-pitched sound)
Short Wavelength: High frequency (high-pitched sound)
Intensity (Loudness):
Determined by the amplitude (height) of the sound wave.
Measured in decibels (dB).
High Amplitude: Loud sound
Low Amplitude: Soft sound
The Ear: Structure and Function
Outer Ear:
Pinna: The visible part of the ear, funnels sound waves into the ear canal.
Ear Canal: Carries sound waves to the eardrum.
Middle Ear:
Eardrum (Tympanic Membrane): Vibrates in response to sound waves.
Ossicles (Hammer, Anvil, Stirrup): Tiny bones that amplify the vibrations and transmit them to the inner ear.
Inner Ear:
Cochlea: A snail-shaped, fluid-filled tube containing hair cells that convert vibrations into neural signals.
Semicircular Canals: Not involved in hearing; responsible for balance and equilibrium.
Auditory Nerve: Carries neural signals from the cochlea to the brain.
Theories of Hearing
Frequency Theory: The rate of nerve impulses traveling up the auditory nerve matches the frequency of the sound, allowing us to perceive pitch.
Important Note: Damage to the hair cells in the cochlea is the most common cause of sensorineural hearing loss (nerve deafness), which is often permanent.
Hearing: Theories and Beyond
Place Theory: Different pitches (frequencies) activate specific areas on the cochlea basilar membrane.
Localization of Sound: We determine the location of a sound based on the slight timing and intensity differences between our two ears.
Hearing Loss
Noise-Induced Hearing Loss: Damage to hair cells in the cochlea due to loud noises, often affecting high-frequency sounds first.
Conduction Deafness: Hearing loss due to damage to the middle ear (eardrum, ossicles), often treatable with hearing aids or surgery.
Sensorineural Deafness (Nerve Deafness): Damage to the cochlea's hair cells or the auditory nerve, usually permanent.
Cochlear Implants: Electronic devices that bypass damaged hair cells and directly stimulate the auditory nerve, providing a sense of sound.
Touch: The Somatic Senses
Four Basic Sensations: Pressure, warmth, cold, pain.
Pain:
A vital warning signal that something is wrong.
Congenital Insensitivity to Pain: A rare condition where individuals cannot feel pain.
Factors Influencing Pain Perception
Biological: Activity in the spinal cord, genetics (endorphin production), brain interpretation.
Social-Cultural: Presence of others, empathy, cultural expectations.
Psychological: Attention to pain, past experiences, expectations of relief.
Gate Control Theory: Pain signals can be blocked ("gated") in the spinal cord by competing signals from other senses or by brain signals.
Other Sensory Systems and Perception
Phantom Limb Pain:
Sensation of pain in a limb that has been amputated.
Likely caused by "cross-wiring" in the brain's somatosensory cortex where areas responsible for the missing limb are taken over by nearby areas.
Taste (Gustation):
Taste Buds (Papillae): Tiny bumps on the tongue that contain taste receptors.
Five Basic Tastes: Sweet, salty, sour, bitter, umami.
Chemical Sense: Taste receptors detect chemicals in food.
Smell (Olfaction):
Process: Odor molecules enter the nasal cavity, bind to receptors, and send signals to the olfactory bulb in the brain.
Olfactory Bulb: Located near the limbic system (emotion) and hippocampus (memory), explaining why smells can trigger strong emotions and memories.
Sensory Interaction: Taste and smell work together to create flavor.
Body Position and Movement:
Kinesthesis: Sense of body position and movement of individual parts.
Vestibular Sense: Sense of balance and head position, located in the inner ear.
Perception: Making Sense of Sensations
Visual Capture: The tendency for vision to dominate other senses. Example: Movie sound seems to come from the screen, not the speakers.
Gestalt Psychology: The whole is greater than the sum of its parts. We organize sensory information into meaningful patterns and wholes.
Figure-Ground: Organizing the visual field into objects (figures) that stand out from their surroundings (ground).
Grouping: Our tendency to organize stimuli into groups based on:
Figure Ground
Gestalt Principles of Perceptual Organization
Proximity: We group nearby figures together.
Similarity: We group figures that are similar to each other.
Continuity: We perceive smooth, continuous patterns rather than discontinuous ones.
Connectedness: We see uniform and linked objects as a single unit.
Closure: We fill in gaps to create complete, whole objects.
Depth Perception: Seeing in 3D
Definition: The ability to judge distance and see objects in three dimensions, even though the images on our retinas are two-dimensional.
Visual Cliff Experiment (Gibson & Walk): Showed that infants (and young animals) have innate depth perception.
Types of Depth Cues
Monocular Cues: Cues that can be perceived with one eye alone.
Interposition (Overlap): Closer objects block the view of objects farther away.
Linear Perspective: Parallel lines appear to converge with distance.
Relative Size: If two objects are similar in size, the one that appears smaller is perceived as farther away.
Relative Height: Objects higher in the visual field are perceived as farther away.
Texture Gradient: Objects with finer, less detailed texture are perceived as farther away.
Binocular Cues: Cues that require both eyes.
Convergence: The eyes turn inward more to focus on closer objects.
Retinal Disparity: The brain compares slightly different images from each eye to calculate distance. The greater the disparity, the closer the object.
Perception: Movement, Constancy, and Interpretation
Movement Perception
Stroboscopic Motion: The illusion of movement created by a series of rapidly changing still images. Example: Flipbooks or animated films.
Phi Phenomenon: The illusion of movement created by flashing lights in a sequence. Example: Marquees or holiday lights.
Perceptual Constancy: We perceive objects as stable and unchanging even as sensory input (light, angle, distance) changes.
Size Constancy: We perceive an object's size as constant even when its distance changes.
Illusions:
Muller-Lyer Illusion: Two lines of the same length appear different due to the direction of arrows at their ends.
Ponzo Illusion: Two horizontal lines of the same length appear different because of converging lines around them.
Ames Room: A distorted room that makes people appear to shrink or grow as they move across it.
Perceptual Interpretation
Perceptual Adaptation: The ability to adjust to a changed sensory input, such as an inverted or distorted visual field.
Perceptual Sets: Our expectations and experiences influence how we perceive the world.
Schemas: Mental frameworks that organize our knowledge and influence how we interpret new information.
Context Effects: The surrounding environment or situation can alter our perception of a stimulus.
Cultural Context: Culture can also shape how we perceive things.
Factors Influencing Perception
Biological: Sensory processing, innate visual abilities, critical periods for development.
Psychological: Attention, learned schemas, emotions, expectations.
Social-Cultural: Cultural norms and beliefs, physical context.
Human Factors and Perception
Human Factors Psychology: A field that focuses on how people and machines interact. These psychologists use their understanding of perception and behavior to design user-friendly products and technology.
Extrasensory Perception (ESP): The controversial claim that some people can perceive information without using the normal senses.
Telepathy: Mind-to-mind communication.
Clairvoyance: Perceiving remote events (e.g., knowing a friend is in trouble).
Precognition: Predicting future events.
Psychokinesis: Moving objects with the mind.
Sensory Deprivation: Reducing sensory input to a minimum. Research has shown that this can lead to altered states of consciousness and even hallucinations.
Selective Attention: The ability to focus on specific sensory information while filtering out other stimuli. Example: Listening to your friend's voice in a noisy crowd.
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