Sensory Organs & Transducers

• Sensory organs enable the appreciation of the external world.
• The main function of a sensory organ is to act as a biological transducer.

Transducers

• Transducers convert one type of energy into another, like a microphone changes sound into electricity.
• Brain processes electrical energy in action potentials.
• Sense organs act as transducers, converting energy forms into electrical signals the brain can understand.
• Sensation is the process of converting energy from the environment into a response pattern in the nervous system.
• Damaged sensory organs prevent the interpretation of sensory information, modern tech can help restore capabilities around damaged organs.
• Psychophysics studies how the mind interprets physical stimuli properties.
• Absolute threshold is the minimum physical energy for sensory impression occurs 50% of the time.
• Difference threshold measures the minimum energy difference between two stimuli for a noticeable difference half the time.
• Sensory transduction involves selection to focus on the most relevant information.
• The brain narrows what can be observed, acting as a data selection system.

Sensory Selection: Reducing Sensory Overload

• Human sensory receptors do not transduce all possible energies, indicating selective reception.
• Sense receptors transduce part of their target range for focused perception.
• Sensory adaptation is sensory receptors become less responsive to constant stimuli over time.
• Feature detectors in the brain prioritize important perceptual features, basic stimulus patterns.
• Feature detectors are specialized cells in the cerebral cortex that respond to specific object attributes.
• Visual pop-out demonstrates the visual system's sensitivity to perceptual features
• Sensitivity to perceptual features develops through experience.

Vision

• Eyes transduce a limited range of electromagnetic energies (the visible spectrum).

Characteristics of Light

• Visible spectrum is the range of electromagnetic energies eyes respond to, from 400 nm (purple/violet) to 700 nm (red).
• Hue (colors are determined by the wavelength of light.
• Saturation the purity of a color is determined by the narrow band of wavelengths.
• Brightness relates to light wave amplitude, affects the intensity of perceived colors.

How Eyes Work

• Similar to cameras, eyes use a lens to focus light onto a light-sensitive surface.
• Eyes focus light waves and transducing them into signals the brain can interpret.

Focus: Accommodation

• Focusing in the eye uses the cornea to bend light inward, with the lens making adjustments.
• Accommodation is when ciliary muscles alter lens shape to focus on objects at varying distances.
• Focus is compromised by eye shape and lens flexibility.
• Hyperopia (farsightedness is when the eye is too short, causes difficulty focusing on near objects.
• Myopia (nearsightedness) is when the eyeball is too long, causes difficulty focusing on distant objects.
• Astigmatism occurs when the cornea or lens is misshapen, results in parts of vision being out of focus.
• Presbyopia ("old vision") is a loss of lens flexibility with age, corrected with bifocals.

Transduction in the Eye

• The cornea and lens focus light onto photoreceptors in the retina.
• Retina area is similar to the size of a postage stamp
• Retina is an area lined with photoreceptors
• Rods and cones are two photoreceptor types that transduce light into electrical energy.

Photoreceptors: Nerve Cells in the Eye

• Cones work best in bright conditions, enabling color vision and detail.
• Fovea is a spot in the retina with lots of cones, produces sharp, detailed images.
• Normal acuity is 20/20 vision
• Color blindness is when one cannot perceive colors.
• Color weakness is a partial lack of color perception.
• Red-green color-blind individuals can still manage traffic lights due to light positioning and additional colors.
• Rods function in peripheral vision and are most numerous 20 degrees from the fovea center.
• Rods and cones contribute to visual acuity.
• Converting light to electrical energy, action potentials move along interneurons to the optic nerve, then brain.
• Rods are sensitive to movement in peripheral vision.
• People with tunnel vision have lost their peripheral vision.
• Rods are very sensitive to light
• With rods one can see in dim light but detects no colors.
• Dark adaptation is the eye's increased light sensitivity in low-light, takes 30-35 minutes.
• Rhodopsin is a light-sensitive pigment in rods for black and white vision.
• Red light does not stimulate rods, helping adaptation in submarines and airplane cockpits.
• The retina has a blind spot with no photoreceptors and where the optic nerve exits.
• The brain fills in retinal blind spots using surrounding patterns and disregards certain visual information.

Theories of Color Vision

• Trichromatic theory says three cones detect red, green, or blue, leading to various color combinations.
• One issue with trichromatic theory is that red, green, blue and yellow is the fact that colors are primary, another is the fact that reddish green or yellowish blue is not possible.
• Opponent-process theory says vision analyzes colors into opposing messages (red/green, yellow/blue, black/white).
• According to the opponent-process theory fatigue occurs by cones responding to one color.
• Afterimages are persistent visual sensations after a stimulus is removed.
• The three-color theory explains how things work in the retina, opposed to how the opponent process works with color.

Hearing

• Sound travels as compression (peaks) and rarefaction (valleys) waves.
• Sound waves' frequency relates to pitch, amplitude to loudness.
• Transduction in the ear converts mechanical (sound wave) energy to electrical energy.
• Hearing begins with the pinna channeling sounds into the ear canal, vibrating the eardrum.
• Eardrum vibrations move inward three ossicles of three small middle ear bones: malleus, incus, and stapes
• Stapes vibrates to the oval window on the cochlea.
• Oval window vibrates to makes waves in the cochlea's fluid.
• Fluid waves trigger basilar membrane (in the Organ of Corti) vibrations, which contains hair cells that translate sound waves into action potentials.
• Hair cells (receptor cells within the cochlea) bend against the tectorial membrane triggering action potentials.

Hearing Loss

• Conductive hearing loss when the transfer of vibrations from the outer ear to the inner ear weakens or poor transfer of sounds from the eardrum to the inner ear.
• Damaged eardrums or ossicles can be fixed with a hearing aid which amplify sound.
• Sensorineural hearing loss results from inner hair cell/auditory nerve damage.
• Noise-induced hearing loss is a sensorineural hearing loss subtype, caused by excessively loud sounds.
• Daily exposure to 85 decibels or more may cause permanent hearing loss.
• Cochlear implants bypass damaged hair cells, stimulating auditory nerves.

Theories of Hearing Pitch

• Pitch and loudness relates sound characteristics.
• The frequency theory of hearing (pitch is based on basilar membrane hair cells firing rate).
• Explains how sounds up to 4,000 hertz reach the brain.
• The place theory of hearing higher and lower tones excite specific places in the cochlea.
• Explains hearing above 4,000 hertz tones.
• Hunter's notch occurs from damaged hair cells from the pitch of gunfire.

Chemical Senses: Olfaction & Gustation

Olfaction (Smell)

• Olfaction is the sense of smell
• Smell receptors respond to airborne chemical molecules.

Transduction in the Nose

• Air enters the nose, then flows over 5 million nerve fibers sensitive to various airborne chemical molecules.

Odor Detection

• The way that different odors are determined is still an unfolding mystery
• Anosmia describes a persons "smell blindness" to a single odor.
• Theorized exists loss of sensitivity to specific odors in anosmia is receptors for specific odors

Theories of Olfaction

• Lock-and-key theory has airborne chemical molecules fit receptor shapes to create odors
• Receptor combinations create varied scents.
• At least 10,000 different human odors can be detected.

Gustation (Taste)

• Gustation is the sense of taste
• The five taste sensations are: sweet, salty sour, bitter, and umami.
• Most sensitive to bitter and sour
• Umami savory taste
• The receptors for umami are sensitive to glutamate, a substance found in monosodium glutamate (MSG).

Transduction on the Tongue

• Taste buds, which are the clusters of taste-receptor cells, are located mainly on the top side of the tongue, especially around the edges.
• As food is chewed, it dissolves and the chemical molecules enter the taste buds, where they set action potentials that travel to the brain.
• Saltiness and sourness are ions flowing into taste cells.
• Includes sensations of texture, temperature, pain, and smell in what is tasted.

Somesthetic Senses: Skin Senses, Kinesthetic, & Vestibular Senses

Skin Senses (Touch)

• Body-related senses include touch, pressure, pain, heat, and cold
• Anaphia loss of the sense of touch

Skin Transduction

• Five skin sensations are light touch, pressure, pain, cold, and warmth.
• The skin has about 200,000 nerve endings for temperature, 500,000 for touch and pressure, and 3 million for pain.
• Skin sensitivity relates to receptor density.
• High receptor areas: lips, tongue, face, hands, and genitals.
• The body has a warning pain system in large nerve fibers.
• Bodily damage warn by pain is sharp, bright, and fast.
• The body has a reminding pain system in small nerve fibers.
• Widespread, nagging, aching, slower.

Pain Gate

• Gate Control Theory holds that pain messages pass through a spinal cord "gate."
• Large nerve fiber pain closes the gate, preventing reminders.
• Slow fibers follow biasing system to close pain gates.
• Melzack holds that the gate control theory may explain painkilling acupuncture.
• The Kinesthetic and Vestibular Systems are body-related.

Kinesthetic Senses

• Defined as senses of body position & movement
• Kinesthetic transducers are the receptors special located in the muscles and joints. Send information to the brain.
• Kinesthetic senses helps one understand various body parts located in space.

Vestibular Senses

• Relates with gravity, balance, and acceleration
• The perception of balance and gravity.

Vestibular Transduction

• Inner ear transducers transduces the vestibular system are
• Otolith organs are fluid-filled movement, acceleration, and gravity.
• The otolith organs also contain tiny crystals in a soft, gelatinlike mass.
• Head movements/gravity cause mas shifts which stimulates receptor hair-like cells, for sensing gravity, acceleration, movement in space.
• Three fluid-filled tubes- also called semicircular canals- are the sensory organs for balance.

Sensation in Everyday Life: Motion Sickness

• Multimodal integration means the tendency to integrate (or combine) different senses (or “modalities”) sensory impression from different modalities. For instance: vestibular system vision and kinesthetic combines.
• Multimodal Integration is the process for the brain to combine information from multiple senses Vision and kinesthetic often integrates the give you a orientation in space.