Transcript Mental activities

Mental activities
The Brain-Nerve Network
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Brain
◦ Control center for the body
◦ Requires a continuous flow of oxygen and blood,
20 % of CO
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Parts of the brain
◦ Cerebrum
 Left and right hemispheres
 Frontal lobe – skilled motor behavior; speech, mood, thought,
planning
 Parietal lobe – interprets sensory info controls body
movement
 Occipital lobe – vision
 Temporal lobe – memory and emotions, long term memories,
initiates communication and actions
The Brain-Nerve Network
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Nerve cells at the base of the cerebrum:
◦ Basal ganglia – smooth out movements
◦ Hypothalamus – coordinates automatic
functions of the body
 Sleep/wakefulness, body temp, water balance
◦ Thalamus – organizes sensory messages to and
from the cerebrum
The Brain-Nerve Network
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Parts of the brain
◦ Cerebellum
 Coordinates the body’s movements
◦ Brain stem
 Regulates body functions –body posture, breathing,
swallowing, heartbeat, increases alertness
 Damage causes death
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Spinal cord
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Pathways for nervous signals and reflexes
Protected by vertebral column
Afferent nerves = motor = ventral
Efferent nerves = sensory = dorsal
The Brain-Nerve Network
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Nerve impingements
◦ Displacements of vertebrae and material from
ruptured vertebrae can inhibit nervous signals
◦ Motor nerve damage consequences?
◦ Sensory nerve?
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Neurons – the basic functional unit of the
nervous system
◦ 1 billion within the NS
◦ 3 sections:
1. Cell body/ soma
2. Dendrites – receives signals
3. Axon – transmits signals
The Brain-Nerve Network
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Signal transmission
◦ Synapses as transmitters and filters/switches
◦ Signal amounts vary, 25-1000 impulses/ sec
◦ Transmission speed varies among neurons
depending on thickness and myelination
 0.5 – 150 m/s
 Velocity is constant for each individual fiber
 Slow transmission for pain fibers, fast for muscle
innervation
The Brain-Nerve Network
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Action potential
◦ Electrical spike generated when the stimulus
reaches threshold
The Brain – Nerve Network
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Motor unit – consists of a motor neuron
and the muscle fibers it innervates
◦ Muscles involved in precise movements have 1
MU per 3-6 muscle fibers, heavy work
muscles may have 1MU per 100 fibers
◦ Motor endplate – point where the motor
neuron ends and the NMJ is formed, impulse
leaps from the neuron to the muscle fiber
The Brain-Nerve Network
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EMGs
◦ Records the electrical activity in a muscle
◦ Electric current is picked up via electrodes
inserted into the muscle or attached to the
surface of the skin
◦ Observe strength and frequency of muscle
activation and status of fatigue
◦ Useful in studying individual muscle
contribution to maintaining posture
The Brain-Nerve Network
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Feedforward/feedback loop
◦ Stretch receptors—two types; muscle spindles and Golgi tendon receptors
operate to provide body with information concerning muscle length and
strength of muscle contraction
 Muscle spindle—composed of 5 to 10 intrafusal fibers lying between
and parallel to regular (extrafusal) muscle fibers
 If length of a muscle exceeds a certain limit, a stretch reflex is
initiated to shorten the muscle, thus helping to maintain posture
 Golgi tendon organs—located at junction between muscle tissue and
tendon
 Transmit sensory impulses to the cord whenever the tendon is
under tension
 Golgi tendon reflex protects muscle from tearing internally as a
result of excessive contractile force
 Reflex arc – system of an afferent sensory nerve and efferent motor
nerve of the same muscle to keep tension and length constant
 Muscle spindle and GTO = detectors within this system
The Brain-Nerve Network
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Design for simple movement control
◦ Muscle activities involving fine regulation
requires involvement of high brain centers
◦ Learning complex movements is difficult and
slow
◦ Human factors engineers need to design
activities in the simplest way
 Least decision making
 Using fastest path of info transmission
 Using smallest body mass
The Brain-Nerve Network
The brain is the control center which
communicates with the body via nerves
moving up and down the spinal cord
 Sensory nerves relay info about pressure,
pain, heat, cold, vibration, feel, body part
position (GTO and muscle spindles)
 The brain integrates the information and
makes decisions
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The Brain-Nerve Network
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Reflexes
◦ Spinal cord is also a source for coordination
of movements
◦ Sensory receptor stimulation
message
sent to SC
immediate response to the
appropriate muscles
◦ Reaction occurs in a few milliseconds because
there is no higher brain function necessary
The Brain-Nerve Network
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CNS and PNS
◦ CNS – brain and spinal cord
 Controls the body by gathering information, making
decisions and initiating actions
◦ PNS – sensory (afferent) and motor (efferent)
divisions
 Somatic nervous system – controls conscious
actions and mental activities; links organism to
environment
 Autonomic Nervous system – controls internal
organs and mechanisms essential for functioning
 Parasympathetic vs sympathetic
The Brain-Nerve Network
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Sensory receptors
◦ Nervous system monitors all sensations
◦ If the signal is strong enough, info is transmitted to
the CNS where it is integrated and an appropriate
response is elicited
External receptors
◦ 5 senses
◦ Different kinds of nerve sensors are embedded in the
skin in varying concentrations
◦ Dermatome: region of skin surface area supplied by
efferent (sensory) fibers of a given spinal nerve
◦ Certain areas have less dense concentrations of
receptors than others
Taking up Information
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Processing Information
◦ Sense info, process it, act on it
◦ Figure 9.9 Linear processing of signals
◦ Sensory feedback loop compares the output
of the system to the desired performance and
makes the appropriate adjustments
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Sensors inside the body
◦ Interoreceptors – GTO, semicircular canals,
aortic arch pressure receptors
Taking up Information
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Sensors near the surface
◦ Exteroreceptors – involved in sight, sound,
taste, smell, touch; also control body activities
by providing feedback regarding the intensity
and direction of muscle activities
◦ Sensors are located in different densities
throughout our body
◦ Most common are free nerve endings,
Meissner’s and Pacinian corpuscles
Taking up Information
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Adaptation and speed
◦ Sensors respond quickly to stimulus, but
report less info when the load remains
constant
◦ Adaptation allows us to filter out unimportant
stimuli
◦ Speed of adaptation and velocity of signal
transmission varies with sensors
Taking up Information
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Modifying input signals
◦ Humans cannot perceive certain signals
◦ An ergonomic task is to modify external
signals which we are not able to sense but are
important to us
◦ In some cases we need to adjust the signal or
change the environment so the signal can
penetrate a cluttered environment
Making Decisions
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Models of information processing
◦ Model of mental work
 Evaluation
 Execution
 Resulting new environment is reevaluated
◦ Multiple sources of info are present and being
evaluated simultaneously
 Our mind filters and transforms info from previous
stages, integrates it and compares it to previous
memories
 Cognitive ability depends on: the number of stages
required and the efficiency of operations at each
stage
Making Decisions
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Perception of sensory signals
◦ First stage is to select the info to be further
processed
◦ The brain compares new inputs to memory,
searching for familiar features
◦ We use past experiences to generate future
expectations
◦ New sensory input can either be rejected, or
we just may not know what to do with it
Making Decisions
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Short term memory
◦ AKA working memory
◦ Registers information for a brief moment
(1sec)
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Long term memory
◦ No duration constraints
◦ General knowledge = semantic memory;
specific events = events memory
◦ Forgetting is due to never having the info
successfully stored or lacking the proper
queues
Making Decisions
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Long term memory (cont.)
◦ Recalling information stored in long term
memory may occur by associations with
similar situations in the past
◦ 2 things influence if the info is available:
1. The strength of the information trace depending on the initial importance, number of
times activated and how recently it occurred
2. Association with related items or events
Making Decisions
AKA central processing
 Must understand outcomes of several
different responses and recognize which
activities are needed to execute the
responses
 Shrinking the IP requirements, using
limited inputs and integration makes tasks
easier
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Making Decisions
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Fitting the human to the job
◦ People need experiences to compare
information coming into the CNS
◦ Comes with aging, teaching an training
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New models of IP
◦ Current concept is based on the computer
metaphor
◦ Advanced concepts base models on
neurophysiology
Actions and Reactions
Direct task – hammer, screw driver
 Transduced task – a piece of machinery is
used to modify the action of the body
 The design of the transducers and their
feedback is a challenge to human factors
engineers
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Actions and Reactions
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Response time
◦ Time from the appearance of a stimulus to
the beginning of an effector action
◦ Response time = reaction time + motion time
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Reaction time
◦ Time delays from the appearance of the signal
to action:
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receptor 1-38 ms
Afferent path 2-100 ms
CNS processing 70 – 100 ms
Efferent path 10 – 20 ms
Muscle latency and contraction 30 -70 ms
Actions and Reactions
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Simple reaction times
◦ Occurs when a person is prepared for a
particular stimulus
◦ Duration depends on kind of stimulus and
intensity
◦ Change little between 15 – 60 years, but are
slower at younger ages and decline with age
Actions and Reactions
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Choosing between reactions
◦ Choice reaction time – longer than a simple
reaction time and increases if multiple similar
stimuli are available to choose from
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Motion time
◦ Simple or complex
◦ Depends on distance of movement and
required precision
Actions and Reactions
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Human factors concerns
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Minimize response time
Optimizing the stimulus
Selecting the most appropriate body part
Careful task selection
Assessment of individual capabilities