Understanding Human Senses and Perception
The Feeling and Psychophysics
The feeling is the stimulation of sensory organs by a stimulus. Perception is the organization, interpretation, analysis, and integration of stimuli from our sense organs and brain.
Psychophysics studies the relationship between the physical nature of sensory stimuli and the responses they evoke.
Sensory Thresholds and Adaptation
The absolute threshold is the minimum amount of physical intensity needed to detect a stimulus.
The theory of signal detection predicts the accuracy of sensory judgments.
The threshold difference or JND (Just Noticeable Difference) refers to the minimum detectable difference between two stimuli. Weber’s law states that a JND is a constant ratio of the intensity of an initial stimulus.
Sensory adaptation occurs when people are exposed to a stimulus for an extended period.
Vision
- In dark adaptation, the rods are activated while the cones undergo chemical processes.
- With bright light, the pupil contracts to capture and distinguish details clearly.
Visual spectrum: The range of wavelengths sensitive to a person represents only a small part of the existing wavelengths in our environment.
- Lens: Directs light rays to focus properly on the back of the eye.
- Accommodation: Focuses light by modifying the lens’s thickness.
- Retina: Converts the electromagnetic energy of light into information for the brain.
- Rods: Located in the retina, operate in low light, used for peripheral vision and black/white perception.
- Cones: Sensitive to light, responsible for precise focus and color perception, especially in bright light.
There are fewer cone-rod cells in the cornea.
Dark adaptation: Increased light sensitivity resulting from exposure to low light.
- Bipolar cells: Receive information from the rods and cones.
- Ganglion cells: Gather visual information; their axons form the optic nerve.
- In the optic chiasm, axons are divided.
- The final visual information processing occurs in the visual cortex (occipital lobe).
- A person can see more than a million colors.
- Cones perceive colors by interacting with each other, meaning all cones are in constant operation.
Trichromatic theory suggests that there are three kinds of cones in the retina, each responding to a specific range of wavelengths.
Opponent-process theory of color vision suggests that receptor cells are linked in pairs and operate in opposition to each other.
Hearing
- Outer ear: Receives and amplifies sound to the eardrum.
- Eardrum: Part of the ear that vibrates when sound waves hit.
- Hair cells: Small cells lining the basilar membrane, which, when bent by vibrations entering the cochlea, transmit neural messages to the brain.
- Sound: Movement of air molecules produced by the vibration of an object.
Inner ear: Changes sound vibrations into a form that allows transfer to the brain.
Cochlea: Coiled tube filled with fluid that receives sound through the oval window or bone conduction.
Basilar membrane: Structure that passes through the center of the spiral chamber, dividing it into upper and lower sections.
Small hair cells lining the basilar membrane transmit neural messages to the brain when bent by vibrations.
- Middle ear (hammer, anvil, stirrup): Transmit vibrations to the oval window.
- Frequency theory of hearing: The entire basilar membrane vibrates as a whole in response to a sound, and hair cells encode the message according to the sound’s frequency.
- The visual and auditory senses reveal our environment.
- Place theory of hearing: Different areas of the basilar membrane respond to different frequencies.
Semicircular canals: Structures consisting of three fluid-filled tubes that detect head movement and angular/rotational motion.
Otoliths: Tiny crystals sensitive to movement within the semicircular canals that sense the body’s acceleration.
The senses of hearing, movement, and balance are located in the ear.
Other Senses
- Taste: Tip of the tongue (sweet), sides (sour), back (bitter). These areas correspond to different brain regions.
Skin senses include touch, pressure, temperature, and pain.
Gate-control theory of pain: Specific nerve receptors lead to specific brain areas related to pain.
Perceptual Organization
Gestalt laws of organization: Principles describing how we organize information into meaningful units.
- Closure: We tend to ignore discontinuities and focus on the overall form.
- Proximity: We group items closer to each other.
- Similarity: We group similar items together.
- Simplicity: We perceive patterns in the most basic and straightforward way possible.
Analysis of attributes: Studying how we perceive shapes, patterns, objects, or scenes through the initial relationship of their elements.
- Neurons are sensitive to specific spatial configurations like angles, curves, shapes, and edges.
- The brain’s perceptual processing system first responds to parts, comparing them with stored information.
- Top-down processing: Perception guided by knowledge, experience, expectations, and motivations.
- Bottom-up processing: Perception is the recognition and processing of individual stimulus components.
- Both processes occur simultaneously and interact.
Perceptual constancy: Physical objects are perceived as invariant and consistent despite changes.
Depth perception: The ability to see the world in three dimensions and perceive image depth.
- Monocular cues: Signals that allow depth perception with one eye.
- Optical illusions: Physical stimuli consistently produce errors in perception.