Transcript Signal Detection Theory

Bell Work
• When there is a conflict between bits of
information received by two or more senses,
which sense tends to dominate the others?
– hearing
– vision
– smell
– touch
– taste
Signal Detection Theory
• Signal detection theory is the theory which predicts how
and when we detect the presence of a faint stimulus amidst
background stimulation. Assuming that there is no single
absolute threshold and the detection depends partly on a
person’s experience, expectations, motivation and level of
fatigue.
• A person’s heightened attention decreases after 30
minutes.
– Ego Strength
– Age plus 7
• More false alarms are detected in heightened
responsiveness
• The Difference Threshold (just noticeable difference
or jnd) is the lowest difference you can detect between the
two stimuli 50% of the time. For example, you are just able
to notice the difference between 1kg and 1.02kg half the
time .
• Priming is an acuteness to stimuli because of
exposure to a certain event or experience. For
example, an individual who has just purchased a
new car may now start to notice with more
frequency other people driving her same make
and model. This person has been primed to
recognize more readily a car like hers because of
the experience she has driving and owning one.
• Sensory Adaptation- lowered sensitivity due to
constant exposure from stimulus. For example,
when you go into someone’s house you notice an
odor…but this only lasts for a little while
because sensory adaptation allows you to focus
your attention on changing environment.
– This adaptation allows the person to focus on
informative changes, leaving out uninformative,
constant stimulations.
Vision
• Transduction refers to Sensory energy being
convert (transformed) into Neural energy/impulses.
• Light is composed of electromagnetic waves with
Wavelengths (distance from one peak to another peak on a
wave)and Amplitudes (height of the wave)
• Wavelength determines hue and pitch determines the
frequency in sound.
• Amplitude determines intensity and loudness in sound.
• External Light entering the eye first travels through
the Cornea (protective layer)
• Pupil (an adjustable opening) is
controlled by Iris (muscle around the pupil)
• Lens (an oval transparency) that changes shape to focus
light by a process called accommodation
Retina
• Johannes Kepler revealed that the retinas did receive upside-down images.
• Researchers later revealed that the retina does not read the image as a
whole, receptor cells convert light energy into neural impulses
• The Retina has 2 types of receptor cells : Rods and Cones. Cells connecting
these detectors activate the bipolar cells that activate the ganglion cells and
then form the Optic Nerve that sends the impulses to brain.
– Rods are receptor cells in the retina responsible for night vision and perception
of darkness.
– Cones allow detail an color
– Cones allow one to perceive color. In the dark, the cone is ineffective. The rods
are not affected by the dim light and many rods will focus their energy into one
bipolar cell.
•
Everyone has a Blind Spot, a small region in the visual field where nothing
could be seen. This is because there are no receptor cells where the optic
nerve leaves the eye in the retina.
– Normally, we don’t witness this effect because we have two eyes
that compensate for each other’s blind spot, and the fact that our eyes are
constantly moving.
• Fovea is the region in the retina where light is centrally focused. The fovea
has no rods, only cones.
Visual Information Processing
• The retina is brain tissue that floats to the eye during
early fetal development
• There are three levels in which visual information is
received.
• First, the retina processes information before sending it
via the thalamus to the brain’s cortex.
• The retina also analyzes the sensory information
• Information from the retina is received and transmitted
ganglion cells.
• Nobel prize winners Hubel and Wiesel discovered
Feature Detectors in the brain cortex that are sensitive
to specific features in what we see ,like shape,
color, depth, movement, and form.
• Perret identified nerve cells that specialize in
responding to a specific gaze, head angle, posture.
Color Processing
• Young and von Helmholtz revealed that color can be
created by combining the light waves of blue, red and
green colors. They inferred that the eye must have
three types of color receptors.
• Color processing is described in 2 stages :
– 1) Young-Helmholtz trichromatic (three-color) theory –
Light is detected by 3 types of cones each specifically
sensitive to Red, Blue, or Green. Combinations of them
produce intermediate colors (yellow, cyan, purple)
– 2) Opponent-Process theory – Color is then processed by
their opponent colors (red-green, blue-yellow, blackwhite). Some cells are excited by blue and inhibited by
yellow, vice versa. Thus, you cannot see a bluish-yellow.
Hearing
• Hearing is highly adaptable
• Hearing Frequency (Pitch) is the number of waves
travelling through a point in one second, relates to
how fast a wave travels.
• Sound travels through the 3 sections of the ear to the
brain :
– Outer ear : Auditory Canal
– Middle ear: Ear drum (tight membrane) . Concentrates the
vibrations of the eardrum on the cochlea’s oval window
– Inner ear : contains the Cochlea (coiled, fluid-filled tube)
that contains the Basilar Membrane, which is lined with
hair cells that vibrates to excite nerve fibers. The
fibers form the Auditory Canal connecting to the brain.
– Loudness is determined by number of activated hair cells.
• Harder to hear sounds are amplified more than loud
sounds
Hearing Loss
• Conduction Deafness – loss of hearing due
to damage of eardrum, and/or the tiny bones in
middle ear. (Could be fixed by hearing aid)
• Sensorineural hearing loss- damage to the
cochlea’s receptors. Destroys the receptors
– Cochlear Implants are the only way to restore hearing
for people with nerve deafness
– These implants are wired to many sites on the
auditory nerve, which allows them to transmit
electrical impulses to the brain
– Most effective when the child is very young
Touch
• Touch is composed of 4 senses : Warmth, Pain,
Cold, and Pressure
• Only pressure has specific receptors
• Pressure and Cold = wet
• Cold and warm = hot
• Pressure and Pain = tickling itch
Pain
• The Gate-Control Theory
states that the spinal cord has “gates” that
opens/closes to transmit pain impulses.
– Small fibers open Gate = pain.
– Large fibers close Gate = no pain
•
Pain is merely a physical and
psychological interpretation. Distraction methods,
where attention is focused elsewhere, can ease the felt
pain.
• Acupuncture (may affect gate-control),
electrical stimulation, exercise can also relieve pain.
Taste
• Taste is a Chemical Sense composed of 4 basic
senses : Sweet, Sour, Salty, and Bitter
• Taste receptors (taste buds) regenerate every 1 or
2 weeks, but age, smoking, and alcohol will lower
taste bud number and sensitivity.
• Taste buds on top and sides of the tongue and in
the back and on the roof of the mouth contain
taste receptor cells.
• The taste receptor cells send information to an
area of the temporal lobe
Smell
•
Smell or Olfaction is also a Chemical
Sense that directly transmits information
from nose to the temporal lobe.
• The only sense that doesn’t first
relay impulses to the Thalamus.
Body Position and Movement
• Kinesthesis (using sensors in muscles,
tendons, and joints)
• Vestibular sense (using fluids in semicircular
canal, cochlea, and vestibular sacs
in inner ear)
• Both sense our position, movement,
and balance.