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How We Sense Objects and Energy

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Title: How We Sense Objects and Energy


1
How We Sense Objects and Energy
2
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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4
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

9
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

10
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

11
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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13
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

14
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

15
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

16
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

17
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

18
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

19
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

20
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

21
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

22
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

23
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

24
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

25
Designing for Tactile Sensation
  • Complex reactions
  • Uncertainty of signal appearance
  • Choice reaction
  • Differentiation between stimuli creating the
    response increases reaction time

26
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

27
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
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