🧠Intro to Brain and Behavior Unit 4 – Sensory Systems

Key Concepts and Terminology

• Sensory systems enable organisms to detect and respond to stimuli in the environment
• Sensory receptors are specialized cells or structures that detect specific types of stimuli (light, sound, touch, chemicals)
• Transduction converts physical or chemical stimuli into electrical signals that can be processed by the nervous system
• Sensory adaptation occurs when sensory receptors become less responsive to a constant stimulus over time
• Sensory thresholds determine the minimum intensity of a stimulus required to elicit a response
  • Absolute threshold is the lowest intensity of a stimulus that can be detected 50% of the time
  • Difference threshold (just noticeable difference) is the smallest change in stimulus intensity that can be detected 50% of the time
• Sensory coding involves the representation and interpretation of sensory information in the nervous system
• Sensory modalities refer to the different types of sensory information (vision, audition, somatosensation, gustation, olfaction)

Sensory Receptors and Transduction

• Sensory receptors are specialized to detect specific types of stimuli
• Photoreceptors (rods and cones) in the retina detect light
• Hair cells in the inner ear detect sound waves and head movement
• Mechanoreceptors in the skin detect pressure, vibration, and texture
• Chemoreceptors detect chemicals in the environment (olfaction) and within the body (gustation)
• Transduction occurs when sensory receptors convert stimuli into electrical signals (receptor potentials)
  • Receptor potentials are graded potentials that vary in magnitude based on stimulus intensity
• Sensory receptors have specific receptive fields that determine the area of the body or environment they respond to
• Sensory adaptation allows organisms to maintain sensitivity to changes in stimuli while ignoring constant background stimuli

Types of Sensory Systems

• Visual system detects light and processes visual information
  • Photoreceptors (rods and cones) in the retina transduce light into electrical signals
  • Rods are sensitive to low light levels and provide black-and-white vision
  • Cones are sensitive to color and provide high-acuity vision in bright light
• Auditory system detects sound waves and processes auditory information
  • Hair cells in the cochlea of the inner ear transduce sound waves into electrical signals
  • Different regions of the cochlea are sensitive to different sound frequencies (tonotopic organization)
• Somatosensory system detects touch, pressure, temperature, and pain
  • Mechanoreceptors, thermoreceptors, and nociceptors in the skin and internal organs detect various somatosensory stimuli
• Gustatory system (taste) detects chemicals in food and drink
  • Taste receptors on the tongue and in the oral cavity detect sweet, salty, sour, bitter, and umami (savory) tastes
• Olfactory system (smell) detects airborne chemicals in the environment
  • Olfactory receptors in the nasal cavity detect a wide variety of odors
• Vestibular system detects head movement and orientation relative to gravity
  • Hair cells in the semicircular canals and otolith organs of the inner ear detect rotational and linear acceleration

Neural Pathways and Processing

• Sensory information is transmitted from receptors to the central nervous system via afferent neurons
• Sensory pathways consist of multiple neurons that relay information from the periphery to the brain
  • First-order neurons synapse with sensory receptors and transmit information to the central nervous system
  • Second-order neurons relay information from first-order neurons to higher-order processing areas in the brain
• Thalamus acts as a relay station for most sensory information before it reaches the cerebral cortex
• Sensory cortices in the brain process and interpret sensory information
  • Primary sensory cortices (visual, auditory, somatosensory) receive direct input from thalamic relay nuclei
  • Association cortices integrate information from multiple sensory modalities and contribute to perception
• Sensory information is processed in parallel and hierarchical pathways
  • Parallel processing allows different aspects of sensory information to be processed simultaneously
  • Hierarchical processing involves increasing complexity and abstraction of sensory information at higher levels of the nervous system

Integration of Sensory Information

• Multisensory integration combines information from different sensory modalities to create a unified perception
• Temporal and spatial congruence of sensory stimuli facilitate multisensory integration
  • Stimuli that occur at the same time and in the same location are more likely to be integrated
• Multisensory neurons in the superior colliculus and other brain regions respond to stimuli from multiple sensory modalities
• Multisensory integration enhances the salience and accuracy of sensory perception
  • Redundant information from multiple senses can improve detection and discrimination of stimuli
• Sensory conflicts can occur when information from different senses is inconsistent
  • Ventriloquism effect: visual information dominates auditory information in determining the perceived location of a sound source
  • McGurk effect: visual information from lip movements influences the perception of speech sounds

Perception and Interpretation

• Perception is the conscious experience and interpretation of sensory information
• Perceptual organization involves grouping and segregating sensory information into meaningful patterns
  • Gestalt principles (proximity, similarity, continuity, closure) describe how the brain organizes visual information
• Perceptual constancy allows the brain to maintain a stable perception of objects despite changes in sensory input
  • Size constancy: objects are perceived as having a constant size regardless of their distance from the observer
  • Color constancy: the perceived color of an object remains constant under different lighting conditions
• Perceptual learning and experience can influence how sensory information is interpreted
  • Expertise in a particular domain (face recognition, musical pitch perception) can enhance perceptual abilities
• Top-down processing involves the influence of prior knowledge, expectations, and attention on perception
  • Context and familiarity can influence the interpretation of ambiguous sensory stimuli
• Bottom-up processing involves the direct influence of sensory input on perception
  • Salient stimuli (bright colors, loud sounds) can automatically capture attention and influence perception

Sensory Disorders and Dysfunctions

• Sensory disorders involve impairments in the detection, processing, or interpretation of sensory information
• Visual disorders include blindness, color blindness, and visual agnosia (inability to recognize objects)
  • Retinitis pigmentosa is a genetic disorder that causes progressive loss of photoreceptors and leads to blindness
• Auditory disorders include deafness, tinnitus (ringing in the ears), and auditory processing disorders
  • Conductive hearing loss results from damage to the outer or middle ear and reduces the transmission of sound to the inner ear
  • Sensorineural hearing loss results from damage to the inner ear or auditory nerve and reduces the ability to detect and discriminate sounds
• Somatosensory disorders include neuropathic pain, phantom limb syndrome, and tactile agnosia (inability to recognize objects by touch)
  • Phantom limb syndrome involves the perception of sensations or pain in a limb that has been amputated
• Olfactory and gustatory disorders can result from head injuries, infections, or neurodegenerative diseases
  • Anosmia is the complete loss of the sense of smell
  • Ageusia is the complete loss of the sense of taste
• Sensory processing disorders involve difficulties with the regulation and interpretation of sensory information
  • Sensory overresponsivity (hypersensitivity) involves heightened sensitivity and aversive reactions to sensory stimuli
  • Sensory underresponsivity (hyposensitivity) involves reduced sensitivity and responsiveness to sensory stimuli

Real-World Applications and Research

• Sensory research has important applications in medicine, education, and technology
• Cochlear implants restore hearing in individuals with severe to profound sensorineural hearing loss
  • Cochlear implants bypass damaged hair cells and directly stimulate the auditory nerve with electrical signals
• Sensory substitution devices translate information from one sensory modality to another
  • Braille allows individuals with visual impairments to read by translating written text into tactile patterns
  • Tactile-visual substitution systems convert visual information into tactile patterns that can be felt on the skin
• Virtual reality and augmented reality technologies rely on the manipulation of sensory information to create immersive experiences
  • Head-mounted displays and haptic feedback devices provide visual and tactile stimuli to simulate realistic environments
• Sensory training and rehabilitation can help individuals with sensory disorders improve their functioning
  • Perceptual learning exercises can enhance visual and auditory discrimination abilities
  • Sensory integration therapy helps individuals with sensory processing disorders regulate their responses to sensory stimuli
• Animal studies and computational models provide insights into the neural mechanisms underlying sensory processing
  • Single-unit recordings in animals reveal the response properties of individual sensory neurons
  • Computational models simulate the processing of sensory information in neural networks and predict perceptual phenomena