How We Sense Objects and Energy

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How We Sense Objects and Energy
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Sensing Body Movement

• Combined signals
• CNS receives information from the various human
  senses simultaneously
• Vestibulum
• Part of the inner ear that provides information
  about posture, body movement and balance
• Three semicircular canals
• Each canal is at a right angle to the other
• Membranous semicircular ducts within the canals
  each contains endolymph and connects with the
  utricle
• Each canal enlarges into an ampulla near junction
  with utricle

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Sensing Body Movement

• Sense of balance
• Static equilibrium ability to sense head
  position relative to gravity or
  acceleration/deceleration
• Movements of the maculae, located in both the
  utricle and saccule, provide information related
  to head position or acceleration
• Otoliths are located within the matrix of the
  macula
• Changing head position produces a change of
  pressure on the otolith-weighted matrix,
  stimulating the hair cells that stimulate the
  receptors of the vestibular nerve
• Vestibular nerve fibers conduct impulses to the
  brain and sense head position and a change in the
  pull of gravity

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Sensing Body Movement

• Dynamic equilibrium needed to maintain balance
  when the head or body is rotated or suddenly
  moved able to detect changes in direction and
  rate at which movement occurs
• Depends on the functioning of the cristae
  ampullaris, located in the ampulla of each
  semicircular duct
• Cupula gelatinous cap where the hair cells of
  cristae are embedded
• Does not respond to gravity
• Moves with the flow of endolymph in the
  semicircular ducts
• Hair cells bend as cupula moves, producing a
  receptor potential followed by an action
  potential
• Action potential passes through the vestibular
  portion of the eighth cranial nerve to the
  medulla oblongata
• Sent next to other areas of the brain and spinal
  cord for interpretation, integration, and
  response

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Sensing Body Movement

• Sense of body balance
• Brain must take information received from the
  cristae ampullaris and macula as well as many
  other body sensors and integrate
• Several vestibular illusions
• Motion sickness
• When the body is aligned with the gravitational
  vector, it does not sense right/left movement
• Illusionary tilt is the interpretation of linear
  acceleration as body tilt
• Elevator illusions occur when a gravitational
  pull produces an apparent rise or fall of seen
  objects
• A person lying down may have the illusion of
  inversion

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The Feel of Objects, Energy and Pain

• 4 groups of sensory skin receptors
• Mechanoreceptors touch, tickle, pressure
• Thermoreceptors hot and cold
• Electroreceptors electrical stimulation
• Nociceptors sense pain
• Taction
• Sense relating to skin contact
• Tactile sensation solely skin sensation
• Haptic sensation information simultaneously
  from the skin and kinesthetic sensors

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The Feel of Objects, Energy and Pain

• Tactile sensors
• Free nerve endings
• Most widely distributed type of sensory receptor
• Sensations mediated include itching, tickling,
  touch, movement, and mechanical stretching
• Primary receptors for heat and cold
• Nociceptors
• are primary receptors for pain
• Root hair plexuses
• Weblike arrangements of free nerve endings around
  hair follicles
• Merkel discs
• Mediate sensations of discriminative touch

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The Feel of Objects, Energy and Pain

• Tactile sensors
• Meissners corpuscle (tactile corpuscle)relativel
  y large and superficial in placement mediate
  touch and low-frequency vibration large numbers
  in hairless skin areas such as nipples,
  fingertips, and lips
• Two anatomical variations of Meissners
  corpuscle
• Krauses end bulbssmall, very sensitive to cold
• Ruffinis corpuscles have a flattened capsule
  and are deeply located in the dermis mediate
  crude and persistent touch
• Pacinian corpuscleslarge mechanoreceptors that
  respond quickly to sensations of deep pressure,
  high-frequency vibration, and stretch found in
  deep dermis and in joint capsules, palms and
  fingertips

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The Feel of Objects, Energy and Pain

• Temperature
• Relative and adaptive
• Skin temperature physiological zero
• Slowly warming or cooling may not elicit a change
  in sensation
• Physiologic zero may differ among body parts
• Feeling cold or warm
• Some receptors respond to hot, others to cold
• The two scales may overlap, providing paradoxical
  information
• Sense temperature changes to warmth more easily
• Warm sensations adapt more easily except at very
  high temperatures
• Rapid cooling can cause an overshoot phenomenon

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The Feel of Objects, Energy and Pain

• Sensing electricity
• there are no known receptors in our skin
• Electricity can arouse almost any sensory channel
  of the PNS
• Threshold depends on individual as well as
  location, rate, intensity and type of electrode
  used
• Usually 0.5-2 mA if pulse lasts 1ms

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The Feel of Objects, Energy and Pain

• Pain
• Nociceptors sense pain because they possess
  special molecules for detecting pain-causing
  stimuli
• Sharp pain surface, head, toothache
• Dull pain deep in the body
• Pain threshold
• Variable because hard to separate from sensory
  and emotions
• Pain adaptation
• Secondary pain
• Referred pain
• Phantom pain

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Designing for Tactile Perception

• Research Needs
• Stimuli are not well defined in older research
• Sensors are located all over the body in
  different densities
• Functioning is not understood
• Signal conduction to the CNS is complex
• How the CNS interprets the information is unknown
• ..basically we still have a lot to learn

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Designing for Tactile Perception

• Taction Sensitivity
• Mechanoreceptors differentiate touch information
  based on
• Strength of the stimulus
• Temporal rate of change
• Size of skin area stimulated
• Location of skin stimulated
• Sensitivity is greatest on the face and
  fingertips fair on the forearm and lower leg
  also depends on temperature

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Designing for Tactile Perception

• Using temperature signals
• Slow response time
• Poor in location identification
• Adapts to stimuli over time
• Integrates into one large signal from several
  different stimuli
• Mechanical and temperature signals interact

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Designing for Tactile Perception

• Strength of thermal stimulation depends on
  location and size of the detecting body surface
• Sensation can be made stronger by increasing
• The absolute temperature of the stimulus and its
  difference from physiologic zero
• The rate of change in temperature
• The exposed surface

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Designing for Tactile Perception

• Rules of thumb for skin
• Neutral temperature is 33?C
• 10 ?C is painful 18 ?C is cold 30 ?C is cool
• The highest sensitivities to changes in coolness
  are between18-30 ?C
• Heat sensors respond well throughout the range of
  20 - 47?C
• Thermal adaptation can occur between 18-42 ?C
• Very cold and very hot temperatures provoke
  sensations of pain
• Cold is sensed more quickly
• Warmth is felt best in hairy regions, around the
  kneecaps, fingers and elbows

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Designing for Tactile Perception

• Using the smell sense
• Seldom used by engineers because
• People react differently to olfactory stimuli
• Smells are easily masked
• Stimuli to test olfaction are hard to set up
• Common olfactory uses
• Adding methylmercaptan to natural gas
• Adding pyridin to argon

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Designing for Tactile Perception

• Using Electric signals
• Seldom used for information carrier, but has
  great potential for transmitting signals
• Electrode energies range between 30 microwatts
  300 milliwatts
• Signal variation based on placement, intensity,
  duration and pulsation
• Advantages provides a clear, attention demanding
  signal that is resistant to masking
• Disadvantages weak stimuli create long response
  latencies, many misses and false alarms

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Designing for Tactile Perception

• Do not use pain as a signal stimulus
• Cannot use for ethical reasons
• Reaction and response
• Reaction time is the period from the appearance
  of a stimulus to the beginning of a responding
  effector action
• Reaction time motion time response time

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Designing for Tactile Perception

• Simple reactions
• Shortest possible simplest reaction times
  (Table7.1)
• Small differences between electrical, tactile and
  sound stimuli
• Sight and temperature within the range of
  measuring accuracy and individuality
• Smell, taste and pain are the longest

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Designing for Tactile Sensation

• Complex reactions
• Uncertainty of signal appearance
• Choice reaction
• Differentiation between stimuli creating the
  response increases reaction time

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Designing for Tactile Sensation

• Reaction time motion time response time
• Minimizing response time is the goal
• Need to consider
• The most appropriate stimulus
• Body part best suited for the task
• The equipment that allows the fastest execution

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Summary

• Daily life relies on integrating information
  received by the senses
• Research can explain the basics of sensory
  processes, however many details are still unknown
• Challenges for future investigation