Download Unit 4A: Sensation

UNIT 4A: SENSATION
◦ 24 hours a day, all kinds of stimuli
from the outside world bombard
your body. Meanwhile, in a silent,
cushioned, inner world, our brain
floats in utter darkness. By itself, it
see nothing. It hears nothing. It feels
nothing.
◦ So.. How does the world get in
there?
◦ How do we construct our
representations of the external
world?
Difference Between Sensation and Perception
◦ Prosopagnosia – Face blindness
◦ Sensation: When they look at a face, sensation is normal. Detects the visual of a face.
◦ Perception: Cannot process who’s face it belongs to.
Sensing the World: Basic Principles
◦ Sensation and Perception are 1 continuous process.
◦ Sensation  the process by which our sensory receptors and
nervous system receive and represent stimulus energies
from our environment.
◦ Perception  the process of organizing and interpreting
sensory information, enabling us to recognize meaningful
objects and events.
◦ Always start with the sensory receptors and work to higher levels of
processing to understand how the 2 wok together.
◦ Sensory analysis at the entry level is called bottom – up processing 
analysis that begins with the sensory receptors and works up
to the brain’s integration of sensory information.
◦ Then your mind must INTERPRET what our senses
DETECT.
◦ This allows your brain to construct perceptions while drawing
on sensations (bottom-up processing) and combining them
with our experience and expectations, which are called topdown processing  information processing guided by higherlevel mental processes, as when we construct perceptions
drawing on our experience and expectations.
◦ Nature’s sensory gifts suit each recipients needs. They enable each
organism to obtain essential information.
◦ For example; A frog feeds on flying insects. Therefore it’s eyes have
receptor cells that fire only in response to small, dark moving objects.
A frog can starve to death if it was knee deep in motionless, black
flies.
◦ For example, in humans, we are
equipped to detect the important
features of our environment. These
cut across our entire sensory system.
Our ears are most sensitive to sound
frequencies that include human
voice constants and a baby’s cry.
Use Bottom-Down and Top-up Processing o
explain how you interpret the following
painting.
Selective Attention
◦ Your conscious awareness focuses, like an flashlight beam, on only a very limited aspect of all you
experience.
◦ Your 5 senses take in 11,000,000 bits of information per second, of which you process about 40.
◦ POP QUIZ: What part of the brain allows for this filtering of information?
◦ Selective Attention  the focusing of conscious awareness on a particular stimulus.
◦ Cocktail Party Effect: The ability to attend to only one voice among many. For example, at a party,
if another voice speaks your name at a party, your cognitive radar, operating on the mind’s other
track, will instantly bring that voice into consciousness. You may tune in long enough to decide to
join in or ignore the conversation.
Selective Attention
Selective Attention and Accidents
◦Cell phone use and car accidents
Selective Inattention
◦ At the level of conscious awareness, we are
‘blind’ to all but a tiny sliver of the immense
array of visual stimuli constantly before us.
◦ Inattentional Blindness  failing to see
visible objects when our attention is
directed elsewhere.
◦ https://www.youtube.com/watch?v=b7
LuvAM6XLg
◦ https://www.youtube.com/watch?v=v3iPrBrGSJM
◦ Change blindness  failing to notice changes in the environment
◦ Change deafness – experiment where 40% of people
focused on repeating a list of sometimes challenging words
failed to notice a change in the person speaking.
◦ Choice blindness – experiment where 120 people were
shown 2 female faces for 2 to 5 seconds and asked them to
name which face was more attractive. Then the
researchers put the photos face down and handed viewers
the one they had chosen and asked them why they thought
they were attractive. However, the researchers used slight
of hand and switched some of the photos. People seldom
noticed the switch (only 13%).
◦ Choice-choice blindness – Continuing from the pervious
experiment, they asked people if they think they would
notice a switch, 84 % said they would, even though only
13% noticed it.
◦ Pop-out- We don’t choose to attend to these stimuli; they draw our eye and demand out
attention.
Thresholds – What can we detect?
◦ Psychophysics  the study of relationships between the physical characteristics of
stimuli, such as their intensity, and our psychological experience of them.
◦ Absolute Thresholds  the minimum stimulation necessary to detect a particular
stimulus (light, sound, pressure, taste, odor) 50% of the time.
◦ For example, during a hearing test, your ears are exposed to different, varying sound
levels. For each tone, the test would define where half the time you correctly detect
the sound and half the time you do not. For each of you sense, the 50-50 recognition
defines you absolute threshold.
◦ Vary with age. Sensitivity to high pitched sounds decline with age.
◦ Convenience store pitches example.
Circle = fixations, # = # of milliseconds of
focus.
◦ Detecting a weak stimulus, depends on the strength of the signal, but also our psychological state
– alertness, experience, expectations, motivation.
◦ Think of a text message… How would you detect it? Do you anticipate it? Are you waiting for it?
Do you ignore it?
◦ Signal Detection Theory  a theory predicting how and when we detect the presence of
a faint stimulus (signal) amid background stimulation (noise). Assumes there is no
absolute threshold and that detection depends partly on a person’s experience,
expectations, motivation, and alertness.
◦ Ratio of ‘hits’ to ‘false alarms’.
◦ Why do people respond differently to the same stimulus?
◦ Why the same person’s reactions vary as circumstances change? Ex. Soldiers in war time.
◦ Signal detection can diminish after 30 minutes of constant diligence. Ex. Airport scanner tricks.
Subliminal Messages
◦ Ex. Subliminal weight loss, quit smoking messages.
◦ Do they work? If they do, they assume we can:
◦ 1) Unconsciously, we can sense subliminal ( below one’s absolute threshold
for conscious awareness) signals.
◦ 2) We assume that without our awareness that these stimuli have extraordinary
suggestive powers.
◦ Backmasking songs!
◦ http://listverse.com/2011/08/28/top-10-famous-cases-of-backmasking/
◦ Can we be affected by stimuli so weak as to
be unnoticed?
◦ Kitten/Werewolf Face study
◦ Much of our information processing occurs
automatically, out of sight, off the radar
screen of our conscious thought.
◦ Priming  the activation, often
unconsciously, of certain associations,
thus predisposing one’s perception,
memory, or response.
◦ Masking stimulus
◦ Subliminal persuasion
Difference Thresholds
◦ To function effectively, we need absolute thresholds low enough to allow us to detect important sights,
sounds, textures, tastes and smells. We also need to detect small changes among stimuli.
◦ Ex) Detecing your friend’s ovice among all other in the hallway during class change.
◦ Difference Threshold  the minimum difference between two stimuli required for detection. We
experience the difference threshold as a just noticeable difference (jnd).
◦ Ex) Add 1 ounce to a 10 ounce weight, detect it. Add 1 ounce to 100 ounce weight, will not
detect it.
◦ Weber’s Law  the principle that, to be perceived as different, two stimuli must differ by a
constant percentage/proportion (rather than a constant amount).
◦ Ex) For a person to notice the difference between 2 weights, the object must differ by 2%.
Just noticeable difference
Sensory Adaptation
◦ Ex) The smell in different people’s houses.
◦ Sensory Adaptation  diminished sensitivity as a consequence of constant stimulation.
◦ Try moving your watch up your wrist by 1 inch. Switching your ring onto another finger. Feel it, but only for
a few moments.
◦ Informative changes and reality versus usefulness. What is actually important stimulation?
◦ Eye movment plays a big role.
◦ Eyes are always moving, just slightly. This allows our senses to change just slightly and to keep our
eye receptors on their toes.
◦ Fit eye with device that moves the image when the eye moves.
Senses Part 1: Vision
◦ Eyes take in light energy and transduce (
conversion of one form of energy into
another. In sensation, the transforming of
stimulus energies, such as sights, sounds,
and smells into neural impulses our brains
can interpret) it into neural messages that
our brain can understand to process into
what we are actually seeing.
◦ Pulses of electromagnetic light hit our eyes,
and we perceive the different colours.
◦ What we can see as visible light, is only a
small part of the electromagnetic spectrum.
◦ Different species see different light spectrums –
ex. Bees cannot see red but can see ultraviolet
light.
How light works for vision
◦ Wavelength  the distance from the peak of one light or sound wave to the peak
of the next. Electromagnetic wavelengths vary from the short blips of comic
rays to the long pulses of radio transmission.
◦ Wavelength determines the hue of the light.
◦ Hue  the dimension of color that is determined by the wavelength of light;
what we know as the color names blue, green, and so forth.
◦ The strength of the hue is determined by intensity of the light.
◦ Intensity  the amount of energy in a light or sound wave, which we perceive as
brightness or loudness, as determined by the wave’s amplitude.
Electromagnetic Energy Spectrum
The Physical Property of Waves
The Eye – A Crash Course in Vision
◦ Light enters the eye at the cornea (protects the eye and bends light to provide focus).
◦ Then to the pupil  the adjustable opening in the center of the eye through which lights enters.
◦ Pupil is surrounded by the iris  a ring of muscle tissue that forms the colored portion of the eye around
the pupil and controls the size of the pupil opening.
◦ Iris adjusts light intake by dilating or constricting. Also influenced by emotions. Act like fingerprints of your
eyes.
◦ Behind the pupil is the lens the transparent structure behind the pupil that changes shape to help focus the
images on the retina.
◦ Lens focuses the light rays by changing their curvature in a process called accommodation  the process by
which the eye’s lens changes shape to focus near or far objects on the retina.
◦ Lens sends them to the retina  the light-sensitive inner surface of the eye, containing the receptor rods and
cones plus layers of neurons that begin the processing of visual information.
The Structure of the Eye
The Structure of the Eye
Cornea = outer covering of the eye.
The Structure of the Eye
Pupil = the adjustable opening in the center of the eye through
which light enters.
The Structure of the Eye
Iris = a ring of muscle tissue that forms the colored portion of the
eye around the pupil and controls the size of the pupil opening.
• The iris dilates/constricts in response to changing light intensity
The Structure of the Eye
Lens = the transparent structure behind the pupil that changes
shape to help focus images on the retina.
The Structure of the Eye
Retina = the light-sensitive inner surface of the eye, containing the
receptor rods and cones plus layers of neurons that begin the
processing of visual information.
The Retina
◦Made of Rods  retinal receptors that detect black, white,
and gray; necessary for peripheral and twilight vision, when
cones don’t respond. AND Cones  retinal receptor
cells that are concentrated near the center of the retina and
that function in daylight or in well-lit conditions. The cones
detect fine detail and give rise to color sensations.
◦Nocturnal animals have eyes made up almost entirely of
rods. Why is this an advantage? What is the disadvantage?
Rods versus Cones
The Retina’ s Reaction to Light
The Retina
◦ Optic Nerve  the nerve that carries neural impulses from the eye to the brain.
◦ Blind Spot  the point at which the optic nerve leaves the eye, creating a “blind” spot because no
receptor cells are located there. Page 127 in text.
◦ Fovea  the central focal point in the retina, around which the eye’s cones cluster.
The Structure of the Eye
Blind Spot = the point at which the optic nerve leaves the eye,
creating a “blind” spot because no receptor cells are located
there.
The Structure of the Eye
Fovea = the central focal point in the retina, around which the
eye’s cones cluster.
The Structure of the Eye
Optic Nerve = the nerve that carries neural impulses from the eye
to the brain.
How does the brain process visual
information?
◦ Your retina processes visual information even before it is sent to the thalamus.
◦ Retinal neural layers don’t just pass along electrical impulses. They also help to encode and analyze
sensory information. This is why they are made in the womb from brain tissue that migrates to
the eye area. COOL!
◦ After processing through you rods and cones, the information travels to your bipolar cells, then to
your ganglion cells, through the axons on the optic nerve, to your brain in the occipital lobe.
◦ Turn your eyes to the left. Close them. Then gently rub the right side of your right eyelid. What
happens?
Pathways from the eyes to the visual
cortex
◦ Feature detectors  nerve cells in the brain that respond to specific features of the stimulus, such as shape,
angle, or movement.
◦ Teams of super cells will receive information from to respond to more complex patterns.
◦ You can tell what a person is looking at by analyzing where on an MRI the brain is ‘lit up’.
◦ Parallel Processing  the processing of many aspects of a problem simultaneously; the brain’ s
natural mode of information processing for many functions, including vision. Contrasts with the
step-by-step (serial) processing of most computers and of conscious problem solving.
◦ Processing many parts of vision at once.
◦ Face recognition – takes 30% of your cortex power at once.
◦ Ex. Stroke victim, damaged areas near the rear of both sides of the brain. Can no longer
perceive movement. People seem ‘suddenly there’ as she has not seem them moving. Pouring
tea in a cup = challenge because tea seems frozen and cannot tell when the cup is getting full.
◦ Blind sight – localized area of blindness in part of their visual field.
Visual information processing
Colour Vision
◦ You may have heard the common saying ‘If a tree falls in a forest, and no on hears it, does it make a
sound?’. What about ‘If no one sees a tomato, is it still red?’.
◦ Nope, because it is anything but red. It reflects the long wavelengths of red. Also, the tomato’s colour is
a construct of our mental processes. Colour resides not in the object, but in the theatre of our brains
and how we interpret colours.
◦ So how do we see colour then?
◦ Young-Helmholtz trichromatic (three-colour) theory  the theory that the retina contains three
different color receptors – one most sensitive to red, one to green, one to blue – which, when
stimulated in combination can produce the perception of any color.
◦ Red – Green – Blue – Colourblindness is deficiency in seeing one or more of the colours.
◦ Monochromatic vision – one colour vision
◦ Dichromatic vision – two colour vision
◦ Opponent-process theory  the theory that opposing retinal
processes (red-green, yellow-blue, white-black) enable color vision.
For example, some cells are stimulated by green and inhibited by red;
others are stimulated by red and inhibited by green.
◦ Helps to explain after images.
◦ Colour processing occurs in 2 stages:
◦ 1) The retina’s red, gree and blue cones respond in varying degrees to
different colour stimuli.
◦ 2) Their signals are then processed by the nervous system opponentprocess cells, en route to the visual cortex.
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