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Understanding Sensation: Definitions and Mechanisms of the Human Senses

This module explores the intricate processes of sensation involving our complex sensory organs: eyes, ears, nose, skin, and tongue. Key concepts include transduction, the transformation of physical energy into neural signals, and adaptation, which describes the decreased response of senses to constant stimulation. We differentiate sensation from perception, highlight the cocktail party phenomenon, and delve into visual and auditory mechanisms including the roles of rods and cones in vision, as well as sound wave characteristics in hearing. Discover how our senses interpret and respond to the environment.

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Understanding Sensation: Definitions and Mechanisms of the Human Senses

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  1. Module 5 Sensation

  2. THREE DEFINITONS • Eyes, ears, nose, skin, and tongue are complex, miniaturized, living sense organs that automatically gather information about your environment • Transduction • Process in which a sense organ changes, or transforms, physical energy into electrical signals that become neural impulses, which may be sent to the brain for processing • Adaptation • The decreasing response of the sense organs as they’re exposed to a continuous level of stimulation

  3. THREE DEFINITONS (CONT’D) • Sensation versus perception • Relatively meaningless bits of information that result when the brain processes electrical signals that come from the sense organs • Perceptions • Meaningful sensory experiences that result after the brain combines hundreds of sensations

  4. Cocktail-party phenomenon • The cocktail party effect describes the ability to focus one's listening attention on a single talker among a mixture of conversations and background noises, ignoring other conversations. • Form of selective attention.

  5. Energy v. Chemical senses Energy Senses Chemical Senses

  6. Vision • Our most dominating sense. • Visual Capture

  7. EYE: VISION (CONT’D)

  8. EYE: VISION (CONT’D) • Structure and function • Eyes perform two separate processes • first: gather and focus light into precise area in the back of eye • second: area absorbs and transforms light waves into electrical impulses • Process called transduction

  9. Phase Two: Getting the light in the eye

  10. EYE: VISION (CONT’D) • Retina • Three layers of cells • back layer contains two kinds of photoreceptors that begin the process of transduction • change light waves into electrical signals • rod located primarily in the periphery • cone located primarily in the center of the retina called the fovea

  11. EYE: VISION (CONT’D) • Rods • Photoreceptor that contain a single chemical, called rhodopsin • Activated by small amounts of light • Very light sensitive • Allow us to see in dim light • See only black, white, and shades of gray

  12. EYE: VISION (CONT’D) • Cones • Photoreceptors that contain three chemicals called opsins • Activated in bright light • Allow us to see color • Cones are wired individually to neighboring cells • Allow us to see fine detail

  13. Transduction Continued • Order is Rods/Cones to Bipolar to Ganglion to Optic Nerve. • Sends info to thalamus- area called lateral geniculate nucleus (LGN). • Then sent to cerebral cortexes. • Where the optic nerves cross is called the optic chiasm.

  14. EYE: VISION (CONT’D) • Making colors from wavelengths • Sunlight is called white light because it contains all the light waves • White light passes through a prism; separates light waves that vary in length • Visual system transforms light waves of various lengths into millions of different colors • Shorter wavelengths of violet, blue, green • Longer wavelengths of yellow, orange, and red • An apple is seen as red because reflection of longer light waves that brain interprets as red

  15. EYE: VISION (CONT’D)

  16. Trichromatic Theory Three types of cones: • Red • Blue • Green • These three types of cones can make millions of combinations of colors. • Does not explain afterimages or color blindness well.

  17. Opponent-Process theory The sensory receptors come in pairs. • Red/Green • Yellow/Blue • Black/White • If one color is stimulated, the other is inhibited.

  18. Afterimage

  19. EYE: VISION (CONT’D) • Color blindness • Inability to distinguish two or more shades in the color spectrum • Monochromatic • total color blindness; black and white • result of only rods and one kind of functioning cone • Dichromatic • inherited genetic defect; mostly in males • trouble distinguishing red from green • two kinds of cones • see mostly shades of green

  20. Hearing Our auditory sense

  21. The Ear

  22. EAR: AUDITION • Stimulus • Sound waves • stimuli for hearing (audition) • ripples of different sizes; sound waves travel through space with varying heights and frequency • Height • distance from the bottom to the top of a sound wave; amplitude • Frequency • number of sound waves occurring within a second

  23. EAR: AUDITION (CONT’D) • Loudness • Subjective experience of a sound’s intensity • Brain calculates loudness from specific physical energy (amplitude of sound waves) • Pitch • Subjective experience of a sound being high or low • Brain calculates from specific physical stimuli • Speed or frequency of sound waves • Measured in cycles (how many sound waves in a second)

  24. EAR: AUDITION (CONT’D) • Measuring sound waves • Decibel: unit to measure loudness • Threshold for hearing • 0 decibels (no sound) • 140 decibels (pain and permanent hearing loss)

  25. EAR: AUDITION (CONT’D)

  26. EAR: AUDITION (CONT’D) • Outer, middle, and inner ear • Outer ear • consists of three structures • external ear • auditory canal • tympanic membrane

  27. EAR: AUDITION (CONT’D) • Outer, middle, and inner ear • Outer ear • external ear • oval-shaped structure that protrudes from the side of the head • function • pick up sound waves and then send them down the auditory canal

  28. EAR: AUDITION (CONT’D) • Outer, middle, and inner ear • Outer ear • auditory canal • long tube that funnels sound waves down its length so that the waves strike the tympanic membrane (ear drum)

  29. EAR: AUDITION (CONT’D) • Outer, middle, and inner ear • Outer ear • tympanic membrane • taut, thin structure commonly called the eardrum • sound waves strike the tympanic membrane and cause it to vibrate

  30. EAR: AUDITION (CONT’D) • Outer, middle, and inner ear • Middle ear • bony cavity sealed at each end by membranes that are connected by three tiny bones called ossicles • hammer, anvil, and stirrup • hammer is attached to the back of the tympanic membrane • anvil receives vibrations from the hammer • stirrup makes the connection to the oval window (end membrane)

  31. EAR: AUDITION (CONT’D) • Outer, middle, and inner ear • Inner ear • contains two structures sealed by bone • cochlea: involved in hearing • vestibular system: involved in balance

  32. EAR: AUDITION (CONT’D) • Cochlea • Bony coiled exterior that resembles a snail’s shell • Contains receptors for hearing • Function is transduction • Transforms vibrations into nerve impulses sent to the brain for processing into auditory information

  33. EAR: AUDITION (CONT’D)

  34. EAR: AUDITION (CONT’D) • Auditory cues • Direction of sound • determined by brain; calculates slight difference in time it takes sound waves to reach the two ears • Calculating pitch • frequency theory • applies only to low-pitched sounds • rate ate that nerve impulses reach the brain determines how low a sound’s pitch is • place theory • brain determines medium-to-higher-pitched sounds from the place on the basilar membrane where maximum vibration occurs

  35. EAR: AUDITION (CONT’D) • Auditory cues • Calculating loudness • brain calculates loudness primarily from the frequency or rate of how fast or how slow nerve impulses arrive from the auditory nerve

  36. Vestibular Sense • Tells us where our body is oriented in space. • Our sense of balance. • Located in our semicircular canals in our ears.

  37. VESTIBULAR SYSTEM: BALANCE (CONT’D) • Motion sickness (sensory mismatch between information from the vestibular system) • symptoms: feelings of discomfort, nausea, and dizziness in a moving vehicle • head bouncing, but distant objects look fairly steady • Meniere’s disease (malfunction of the semicircular canals of the vestibular system) • symptoms: dizziness, nausea, vomiting, spinning, and piercing buzzing sounds • Vertigo (malfunction of the semicircular canals of the vestibular system) • symptoms: dizziness and nausea

  38. CHEMICAL SENSES • Taste • Chemical sense because the stimuli are various chemicals • Tongue • Surface of the tongue • Taste buds

  39. CHEMICAL SENSES (CONT’D) • Tongue • Five basic tastes • sweet • salty • sour • bitter • umami: meaty-cheesy taste

  40. CHEMICAL SENSES (CONT’D) • Taste buds • Shaped like miniature onions • Receptors for taste • Chemicals dissolved in saliva activate taste buds • Produce nerve impulses that reach areas of the brain’s parietal lobe • Brain transforms impulses into sensations of taste • Flavor • Combination of taste and smell

  41. Taste • We have bumps on our tongue called papillae. • Taste buds are located on the papillae (they are actually all over the mouth). • Sweet, salty, sour and bitter.

  42. CHEMICAL SENSES (CONT’D) • Smell, or olfaction • Steps for olfaction • stimulus • olfactory cells • sensation and memories • functions of olfaction

  43. CHEMICAL SENSES (CONT’D)

  44. CHEMICAL SENSES (CONT’D) • Smell, or olfaction • Stimulus • we smell volatile substances • volatile substances are released molecules in the air at room temperature • examples: skunk spray, perfumes, warm brownies; not glass or steel

  45. CHEMICAL SENSES (CONT’D) • Smell, or olfaction • Olfactory cells • receptors for smell located in a one-inch-square patch of tissue in the uppermost part of the nasal passages • olfactory cells are covered in mucus that dissolves volatile molecules and stimulates the cells • the cells trigger nerve impulses that travel to the brain, which interprets the impulses as different smells

  46. CHEMICAL SENSES (CONT’D) • Smell, or olfaction • Sensations and memories • nerve impulses travel to the olfactory bulb • impulses are relayed to the primary olfactory cortex • cortex transforms nerve impulses into olfactory sensations • we can identify as many as 10,000 different odors • we stop smelling our deodorants or perfumes because of decreased responding (adaptation)

  47. CHEMICAL SENSES (CONT’D) • Smell, or olfaction • Functions of olfaction • one function: to intensify the taste of food • second function: to warn of potentially dangerous foods • third function: to elicit strong memories; emotional feelings

  48. CHEMICAL SENSES (CONT’D)

  49. TOUCH • Touch • Includes pressure, temperature, and pain • Beneath the outer layer of skin are a half-dozen miniature sensors that are receptors for the sense of touch • Change mechanical pressure or temperature variations into nerve impulses that are sent to the brain for processing

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