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Sensation
Sensation: The process of detecting physical energy (stimuli) from the environment and converting it into neural signals.
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’s needed to detect change half the time.
Weber's Law: The difference threshold 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 at a level at which the participant is not aware of the stimulus being presented.
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.
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