Psychology: Sensation
Sensation:
1) Sensation vs. Perception a) Sense - System that translates information from outside the nervous system into neural information i) this info is necessary to help us to create our own personal reality b) Sensation - Messages from the senses c) Perception - Give meaning to the sensations
2) Sensory Systems a) Parts of the system: i) Energy input ii) Accessory structure - Modifies the energy created by something in the environment iii) Transduction - conversion of physical energy into a neural signal iv) Sensory receptors are what do transduction - detect certain forms of energy and are like neurons and fire an action potential in response to energy and release neurotransmitters
(1) Adaptation - A constant level of stimulation of the sensory receptors leads to adaptation.
(a) A gradual decline in responsiveness to the stimulus v) Sensory nerves transfer output of receptors to CNS vi) Thalamus (analyzes info) vii) Cerebral cortex (produces sensation & perception)
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b) The Problem of Coding i) The senses have to engage in coding - translate physical properties of a stimulus into a pattern of neural activity that specifically identifies it, and the senses do so by the: ii) Doctrine of specific nerve energies - Stimulation of a sensory nerve codes for only that sense, regardless of the source of stimulation iii) Temporal code - Attributes of a stimulus are coded in the temporal timing of neuron firing iv) Spatial code - Attributes of a stimulus are coded through the
location of the neurons that are firing
3) Hearing a) We hear sounds - repetitive fluctuation in the pressure of a medium
(e.g., air, water…) b) Vibrations of an object produce the fluctuations in pressure that create sound c) Fluctuations spread as waves d) A waveform represents a wave in two-dimensions: i) Characteristics of Waveforms:
(1) Amplitude - The difference between the peak and baseline
(2) Wavelength - The distance from one peak to the next
(3) Frequency - The # of complete waveforms/cycles that pass by a given point in space every second
(a) described in hertz (Hz)
(b) one full up and down from dotted line on the picture below is one frequency/one pure tone, represented by a sine wave
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e) Psychological Dimensions of Sound – the physical characteristics of the waves produce the following psychological dimension: i) Loudness - Amplitude of the sound wave
(1) Intensity of sound sources
(2) Measured in decibels (dB) ii) Pitch – Frequency of the sound wave
(1) How high/low a tone sounds
(2) Some people have perfect pitch in that they can identify specific frequencies and the notes they represent iii) Timbre – Complicated wave patterns added onto the lowest, or
fundamental, frequency of a sound
(1) Quality of sound (clarinet vs. tuba) f) Structures of the ear i) Outer ear:
(1) Pinna (“the ear”) funnels sound down through the ear canal
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ii) Middle ear:
(1) Sounds travels through the ear canal to strike the tympanic
membrane = eardrum
(2) The vibrations from the tympanic membrane are passed on through three tiny bones:
(a) Malleus (“hammer”)
(b) Incus (“anvil”)
(c) Stapes (“stirrup”)
(3) The three bones focus the vibrations onto the oval window iii) Inner ear:
(1) The cochlea (“snail”) is where (auditory) transduction occurs
(a) Wrapped into a coil
(b) Fluid-filled tube runs down its length
(c) Sound wave passes through the fluid and along the floor of this duct, called the basilar membrane bending the hair cells of the Organ of Corti
(d) The hair cells stimulate neurons in the auditory nerve to fire
(e) The firing of those neurons are a coded message about waves’ amplitude/frequency that get sent to brain iv) Conduction Deafness
(1) The three tiny bones of the middle ear are fused together
(2) Prevents accurate reproduction of vibrations
(3) Treated by surgery to break or replace the bones; hearing aids help too
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v) Nerve Deafness
(1) Results when the auditory nerve or the hair cells are damaged
(2) Can be caused by extended exposure to loud noise
(3) Hair cell regeneration is being studied now, but people also use
cochlear implants that stimulate the auditory nerve to help g) Auditory Pathways i) Auditory nerve  brainstem  thalamus  primary auditory
cortex ii) Various aspects of sound processed in different regions of auditory system
(1) Cells in cortex have similar preferred frequencies – respond most vigorously to sounds of a particular frequency. iii) Certain parts of auditory cortex process certain types of sounds h) Sensing Pitch i) Most sounds are made up of mixtures of frequencies ii) Pitch sensitivity is a result of both genetics and culture i) Locating Sounds i) Determined partly by the very slight difference in when sound arrives at each ear ii) The brain also uses information about the difference in sound intensity at each ear
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3) Vision a) Light is a form of energy called electromagnetic radiation i) We can only see visible light – wavelength from 400-750
nanometers (one-billionth of a meter!) b) Light doesn’t need a medium to pass through; can be wave or particlelike, so we call them light waves or light rays c) Sensation of light depends on 2 things: i) Light intensity (amount of energy) ii) Light Wavelength - the distance of one wave peak to another
(1) Determines color of light
(1) Determines brightness of light d) Path of light waves is that they reflect off an object, pass through eyes where it is transduced, then goes to brain
(1) Cornea  pupil  lens  retina
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ii) Cornea: helps gather and direct incoming light iii) Pupil: black opening; changes size to let in light iv) Iris: colored part of the eye; muscle that controls the size of the pupil v) Lens: transparent structure behind the pupil
(1) Accommodation: thins/thickens to bend or focus light vi) Retina: surface at the back of the eye onto which the lens focuses light rays
(1) visual transduction occurs on the retina e) Before transduction can occur, light rays must pass through several layers of the retina to reach photoreceptor cells i) Photoreceptors are cells in the retina that convert light energy into neural activity
(1) Contain photopigments, chemicals that respond to light
(a) When light hits a photopigment, it breaks apart changing the membrane potential of the cell and that is transferred to the brain
(b) Dark adaptation – after the photopigmnets break down they rebuild, increasing ability to see in dark as time in dark increases ii) Types of Photoreceptors (cones and rods):
(1) Cones
(a) Have three varieties of iodopsin (photopigment)
(b) Responsible for color vision
(c) Best to see in bright light
(d) In center of retina (fovea)
(e) For fine detail/acuity
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(2) Rods
(a) Have one variety of rhodopsin (photopigment)
(b) No color vision / see in B&W
(c) Sensitive to light / good for dim light
(d) Reason for dark adaptation
(e) In periphery
(f) Cannot see fine detail
(g) The fovea (region with the most cones and point of highest acuity) contains no rods
4) Synesthesia a) Synesthesia is the blending of sensory experience b) Causes people to “see” sounds or “taste” colors, for example i) May be due to combined activation of brain regions processing different sensory info
5) The Chemical Senses a) Olfaction (smell) i) detects airborne chemicals ii) Accessory structures = nose, mouth, upper part of throat
(1) Funnel odor molecules to the receptors
(2) Can enter through nostrils or palate at back of mouth iii) Olfactory receptors are in the mucous membrane in the nose
(1) Molecules bind to the receptors = transduction
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iv) Only sense that does not send its messages through the thalamus
(1) Axons from neurons in nose go straight to the olfactory bulb v) Olfactory bulb sends info to several brain regions including frontal lobe and amygdala
(1) Therefore, strong relationship between olfaction and emotional memory vi) Pheromones are chemicals released by one animal, and when detected by another, can shape the second animal’s behavior or physiology
(1) in animals, the pheromones are licked and passed into the
vomeronasal organ
(a) this further triggers sexual response
(2) in humans, pheromones and the vomeronasal organ is probably less important but it can definitely change the menstrual cycle of other women nearby to match = menstrual synchrony b) Gustation (taste) i) detects chemicals in solution that come into contact with receptors inside the mouth ii) Receptors are in the taste buds = papillae iii) Taste system detects only a few elementary sensations
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(1) Bitter, sour, sweet, salty, Umami = some proteins and MSG, &
Astringent = tannins (in tea) iv) Taste results from responses of the particular taste bud activation, and some people (supertasters) have more papillae than others (nontasters) c) Smell, taste, and flavor i) People with anosmia can’t distinguish different smells; they also have trouble distinguishing taste because smell and taste act together to form system known as flavor. ii) Olfactory and gustatory pathways converge in the orbitofrontal
cortex iii) Tastes and odors can prompt strong emotional responses iv) Nutritional needs, texture, and temperature also affect taste
(1) for example, hot food has more flavor and spicy foods with capsaicin can actually stimulate pain fibers in the mouth, so they physiologically feel hot
6) Somatic Senses - those that are not located in a specific organ; also called somatosensory systems (e.g., touch, temperature, & pain) a) Touch & Temperature i) Energy detected = pressure ii) Free nerve endings: receptor involved with the sense of touch iii) Converts stimulation to neural message iv) Constant pressure => adaptation
(1) So, we react to changes in touch
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v) Intensity (heaviness) coded by firing rate and number of neurons stimulated vi) Location of touch coded by location of neurons in skin vii) Many fibers that respond to touch also respond to temp, but there are also:
(1) Warm fibers - Increase firing rate when temp change (95-
115°F), but not to simple contact
(2) Cold fibers - Respond to a broad range of cool temperatures b) Pain - Increase the intensity of pressure/stimulation i) Pain as an Information Sense:
(1) Involves free nerve endings
(a) E.g., capsaicin stimulates these pain nerve endings in the mouth
(2) Chemicals fit into specialized pain neuron receptors
(3) Neurotransmitters are released to spinal cord and near skin
(4) A-delta fibers
(a) Carry sharp, pricking sensations
(b) Axons coated in myelin
(5) C fibers
(a) Carry long-lasting, dull aches, & burning sensations
(b) Unmyelinated
(6) travels to the anterior cingulate cortex (important in emotions)
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ii) Pain has a direct emotional component too:
(1) This is direct – the emotional component of the pain stimulus goes along specific pathways to areas of the hindbrain and reticular formation, and to the cingulated cortex by the thalamus
(2) Overall emotional response depends on how we think about it iii) The Gate-Control Theory
(1) Gate-control theory suggests that sensation of pain is controlled by a series of “gates” that open and close along the spinal cord
(a) Gate open = pain
(b) Gate closed = no pain
(2) The brain may send signals to open or close spinal cord gates, either intensifying or dulling the sensation
(3) Analgesia: absence of sensation of pain in presence of normally painful stimuli
(a) Natural analgesics: endorphins & serotonin
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ENERGY DETECTED: Repeating pressure changes (“sound waves”) of a medium
ACCESSORY STRUCTURES: Pinna, ear canal, tympanic membrane (eardrum), malleus (hammer), incus (anvil), stapes (stirrup), oval window, fluid in cochlea.
TRANSDUCTION: Hair cells on basilar membrane of the cochlea bend as fluid moves.
INFORMATION CODING: Sound wave amplitude is coded as loudness, frequency is coded as pitch.
PERIPHERAL PROCESSING: Hair cells -- auditory nerve -->
CENTRAL PROCESSING: Auditory nerve --> contralateral thalamus --> primary auditory cortex
RELATED IDEAS: Pure tones, fundamental frequency, and noise; deafness; frequency matching (volley) and place theories.
ENERGY DETECTED: Photons.
ACCESSORY STRUCTURES: Cornea, iris (adjusts pupil), lens, fluid in eye.
TRANSDUCTION: Photopigment of photoreceptors (rods, cones) in the retina “absorbs” photon energy.
INFORMATION CODING: Light “wave” intensity is coded as brightness, wavelength is coded as color.
PERIPHERAL PROCESSING: Photoreceptors ---> bipolar cells ---> ganglion cells -- optic nerve -->; convergence; blind spot; interneurons give lateral inhibition.
CENTRAL PROCESSING: Optic nerve --> thalamus (lateral geniculate nucleus) --> primary visual cortex, topographical mapping; 50% of optic nerve axons cross at the optic chiasm, so each side of the thalamus receives input from the opposite-sided visual world.
RELATED IDEAS: Color vision; dark adaptation; parallel processing, feature detection, & spatial frequency filter models; receptive fields.
ENERGY DETECTED: Volatile (in olfaction) and nonvolatile (in gustation) chemicals.
ACCESSORY STRUCTURES: Nose, mouth, respiratory tract, tongue.
TRANSDUCTION: OLFACTION--receptors on cells in upper nose bind specific volatile chemicals.
GUSTATION--taste buds, grouped as papillae in the tongue and throat, bind chemicals in food.
INFORMATION CODING: OLFACTION--
GUSTATION--salty, bitter, sweet, sour, umami, more)
PERIPHERAL PROCESSING:
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CENTRAL PROCESSING: OLFACTION-- axons from nose ---> olfactory bulbs ---> many brain areas, especially amygdale
GUSTATION-- involves thalamus
RELATED IDEAS: Pheromones, flavor.
ENERGY DETECTED: Mechanical deformation or thermal state of skin.
ACCESSORY STRUCTURES: Skin, hair, attachments to free nerve endings.
TRANSDUCTION: TOUCH--skin deformation or hair movement physically stimulates free nerve endings.
PAIN--skin deformation, heat, cold, or chemical release stimulates A-delta or C fibers.
INFORMATION CODING: Stimulus changes; intensity, location.
PERIPHERAL PROCESSING: Peripheral nerves ---> spinal cord.
CENTRAL PROCESSING: Spinal cord ---> contralateral thalamus ---> primary somatosensory cortex
PAIN--also involves cingulate cortex, reticular formation
RELATED IDEAS: Adaptation, endorphins, analgesia, gate control theory.
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