Sensory Systems & Perception: How We Experience the World
Understanding Sensory Processes and Perception
Key Sensory Processes
Sensation: The process by which sensory receptors capture, transduce, and transmit information to the brain.
Attention: The process by which an individual selects certain stimuli from their environment.
Perception: The cognitive process by which an individual organizes sensory information into meaningful objects or experiences.
Basic Sensory Mechanisms
Receptor Cells: Specialized cells that respond to a particular type of energy (e.g., auditory, touch, smell, taste).
Doctrine of Specific Nerve Energies: A one-to-one relationship between the stimulation of a specific nerve and its corresponding sensory outcome.
Sensory Thresholds
Absolute Threshold: The minimum intensity a stimulus must have to be detected.
Extrasensory Perception (ESP)
This refers to extraordinary perception, such as:
- Clairvoyance: Awareness of an event or unknown object without sensory input.
- Telepathy: Knowledge of the thoughts or feelings of someone else.
The Visual System
Anatomy of the Eye
- Cornea: A transparent membrane covering and protecting the front of the eye.
- Pupil: A small opening in the iris through which light enters.
- Iris: The colored part of the eye that contracts or relaxes to control pupil size.
- Lens: The transparent part of the eye behind the pupil that focuses light (becomes round for proximity, flattens for remoteness).
- Retina: The light-sensitive coating at the back of the eye containing receptor cells.
- Fovea: The central visual field where images are focused most sharply.
Retinal Receptor Cells
Cells in the retina that are sensitive to light. Visual receptors include rods and cones.
- Bipolar Cells: Relay information from receptor cells to ganglion cells.
- Ganglion Cells: Receive information from bipolar cells; their axons form the optic nerve.
Visual Adaptation
- Dark Adaptation: Increases the sensitivity of rods and cones in low light conditions.
- Light Adaptation: Decreases the sensitivity of rods and cones in bright light conditions.
Brain-Eye Connection
- Optic Nerve: A bundle of ganglion cell axons that carry nerve messages from each eye to the brain.
- Optic Chiasm: The point near the base of the brain where some fibers of the optic nerve from each eye cross to the opposite side of the brain.
The Auditory System (Hearing)
Hearing is the interpretation our brain makes of the ebb and flow of air molecules hitting our eardrum.
Properties of Sound
- Sound Waves: Changes in pressure caused when air or liquid molecules collide and then move apart.
- Frequency: The number of waves measured in cycles per second, expressed in Hertz (Hz). Frequency determines pitch.
- Amplitude: The magnitude (height) of a sound wave, which determines volume, measured in decibels (dB).
- Overtones: Tones resulting from sound waves that are multiples of the basic tone.
- Timbre: The quality or texture of sound, caused by overtones.
Anatomy of Hearing
- Eardrum: A membrane that vibrates when sound waves strike it.
- Middle Ear: Contains three tiny bones (the hammer, anvil, and stirrup) that are hit in sequence, transmitting vibrations to the inner ear.
- Basilar Membrane: A diaphragm in the cochlea containing receptor cells, also known as hair cells (located in the Organ of Corti).
- Auditory Nerve: Connects the ear to the brain, providing information to both sides of the brain.
Theories of Hearing
- Place Theory: The brain determines pitch based on where on the basilar membrane the message is strongest.
- Frequency Theory: The frequency at which hair cells in the cochlea discharge determines pitch.
- Volley Principle: The entire pattern of neural discharge corresponds to the frequency of the sound wave.
The Olfactory System (Smell)
The sense of smell detects common odors. It is triggered by olfactory binding proteins (OBP), which bind with airborne molecules. These molecules activate receptors in the olfactory epithelium, whose axons project directly to the olfactory bulb.
Women often have a better sense of smell than men.
Anosmia: The complete loss of the sense of smell.
The Gustatory System (Taste)
Taste receptor cells are located in taste buds, which are housed in the papillae of the tongue. Chemicals in the foods we eat dissolve in saliva and enter the cracks between the tongue’s papillae, where they contact taste receptors.
Laws of Perception (Gestalt Principles)
These principles describe how the mind organizes sensory information into meaningful wholes:
- Figure-Ground: The mind organizes stimuli so that some parts stand out against a background.
- Similarity: When there are several elements of different classes, there is a tendency to group those that are alike.
- Proximity: When parts of a whole receive the same stimulus, they coalesce into groups based on minimal distance.
- Prägnanz (Good Form, Simplicity): The tendency to perceive forms as regular, simple, symmetrical, orderly, and understandable, making them easier to remember.