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Sensation and Perception
Transcript of Sensation and Perception
Perception is the method by which people take all the sensations they experience at any given moment and interpret them in some meaningful fashion
What are the Perceptual Constancies?
3.9 The Gestalt Principles
These principles are based on the idea that people have a natural tendency to force patterns onto whatever they see.
a property of perception in which there is a tendency to perceive objects, or figures, as existing on some background.
The tendency to perceive objects that are close to one another as part of the same grouping.
refers to the tendency to perceive things that look similar as being part of the same group.
These are rules for how people perceive the world around them
is the tendency to interpret an object as always being the same size, regardless of its distance from the viewer
is the tendency to interpret the shape of an object as being constant, even when it's shape changes on the retina.
the tendency to perceive the apparent brightness of an object as the same even when the light conditions change.
the tendency to perceive two things that happen close together in time as being related
the tendency is to perceive objects in a common area or region as being in a group.
3.10 Depth Perception
The ability to see the world in three dimensions.
3.15- Visual Cliff Experiment
Gibson & Walk (1960) tested babies for depth perception at ages 6 months plus. 81% refused to crawl to the deep side.
There are various cues for perceiving depth in the world
These require the use of only one eye and
are also called pictorial depth cues. Artists use
these to give illusion of depth to their work.
Different visual patterns that exist when the visual fields of both eyes are used.
the tendency for parallel lines to appear to converge on each other
When objects that a person expects to be of a certain size appear to be small and are therefore assumed to be much farther away.
the assumption that an object that appears to be blocking part of another object is in front of the other object and closer to the viewer.
the haziness that surrounds objects that are farther away from the viewer, causing the distance to be perceived as greater.
the tendency for textured surfaces to appear to become smaller and finer as distance from the viewer increases.
the perception of motion of objects in which close objects appear to move more quickly than objects that are farther away
a muscular not a pictorial cue. The brain's use of information about the changing thickness of the lens of the eye in response to looking at objects that are close or far away.
the rotation of the two eyes in their sockets to focus on a single object, resulting in greater convergence for closer objects and lesser convergence if objects are distant.
the difference in images between the two eyes, which is greater for objects that are close and smaller for distant objects.
3.11 Perceptual Illusions
An illusion is a distorted perception of something that is there but doesn't correspond to reality. People think they see something when the reality is quite different.
illusion of line length that is distorted by inward-turning or outward-turning corners on the ends of the lines, causing lines of equal length to appear to be different.
The Moon Illusion
The moon on the horizon appears to be much larger than the moon in the sky.
Illusions of Motion
Sometimes people perceive an object as moving when it is really still.
Autokinetic effect - a small, stationary light in a darkened room will appear to move or drift because there are no surrounding cues to indicate that the light is not moving.
Stroboscopic Motion- a rapid series of still pictures will seem to be in motion. ex. flipbooks
phi phenomenon- lights turned on in sequence appear to move. ex. theater marquee signs
Factors that affect perception
Human perception of the world is obviously influenced by things such as culture and misinterpretations of cues. The following are other factors that cause people to alter their perceptions.
Perceptual Sets and Expectancies
the tendency to perceive things a certain way because previous experiences or expectations influence those perceptions.
What if there is no existing information that relates to the new information?
The use of pre-existing knowledge to organize individual features into a unified whole. ex. using the picture on the box to put together a jigsaw puzzle.
The analysis of the smaller features to build up to a complete perception. In this case, there is no expectancy to help organize the perception, making this more difficult in some cases.
3.1 How does sensation travel through the central nervous system, and why are some sensations ignored?
occurs when special receptors in the sense organs are activated, allowing various forms of outside stimuli to become neural signals in the brain.
Sensory receptors are specialized neurons that are stimulated by various kinds of energy ex. the receptors in the eye are triggered by light.
Gustav Fechner studied the
or the smallest abount of energy needed for a person to consciously detect a stimulus 50% of the time it is present
Ernst Weber did studies to try to determine the smallest difference between two weights that could be detected 50% of the time known as
Weber's Law of just noticeable differences.
Stimuli that are below the level of conscious awareness are called
. Many people believe that these stimuli act upon the unconscious mind, influencing behaviour in a process called
Researchers have gathered evidence that subliminal perception does not work in advertising. Subliminal stimuli may influence us using the
is a rare condition in which some of the signals from the various sensory organs are processed in the wrong cortical areas, resulting in the sense information being interpreted as more than one sensation. Ex. the sight of green grass smells like coffee, or the sound of a note of music is grey.
is the tendency of the brain to stop attending to constant, unchanging information. Ex. We don't hear the noise in a classroom unless it suddenly gets very quiet. (Sense of Hearing Only.....)
the sensory receptor cells for taste, touch, smell and vision become less responsive to an unchanging stimulus. Ex. polar bear swim, garbage smell, etc.
Different for vision. Constant movement of the eyes, vibrations known as
, keep the eyes from adapting to what they see.
Science of Seeing
3.2- What is light and how does it travel
through the various parts of the eye?
Light behaves like particles and sometimes like waves. Einstein proposed tiny "packets" of waves called photons that have wavelengths associated with them.
Three psychological aspects to the experience of light: brightness, colour, and saturation.
is determined by the amplitude of the wave - how high or low the wave actually is. The bigger the wave, the brighter the light will be. Smaller amplitude waves are dimmer.
Colour, or hue
, is determined by the wavelength, or distance from one crest to another. Long wavelengths are found at the red end of the visible spectrum, whereas shorter wavelengths are found at the blue end.
refers to the purity of the colour people see: Highly saturated red contains only red wavelengths, less saturated red contains a mixture of wavelengths. Ex. mixing colours of paint.
The surface of the eye is covered in a clear membrane called the
. The cornea protects the eye but also focuses most of the light coming into the eye. The next layer is a clear, watery fluid called the
. This fluid is continually replenished and supplies nourishment to the eye. The light from the visual image then enters the interior of the eye through a hole called the
. The pupil is found in a round muscle called the
(the coloured part of the eye), that can change the size of the pupil letting in more or less light and helps focus the image. Behind the iris, suspended by muscles, is another clear structure called the
. The lens finishes the focusing process through a process called
by changing the thickness of the lens as the eye focuses on objects that are far away or close. Once through the lens, light passes through a large, open space filled with a clear jellylike fluid called the
, which provides shape and nourishment to the eye.
The final stop for light within the eye is the
, a light-sensitive area at the back of the eye. The retina contains three layers: ganglion cells, bipolar cells and photoreceptor cells, called
, which respond to the various light waves. The rods and cones receive the photons of light and transduces it into neural signals, sending it to the bipolar cells, then to the ganglion cells that form the optic nerve with their axons entering the brain.
is the area in the retina where the axons of the three layers of retinal cells exit the eye to form the optic nerve, insensitive to light.
How the eye works
3.3 How do the eyes see, and how do the eyes see different colours?
(120 million in each eye) are found all over the retina except in the very centre, which contains only cones. Rods are sensitive to changes in brightness, but not changes in wavelength, so they see only black and white and shades of grey. They are very sensitive because several rods can be hooked up to one bipolar cell. Rods are located on the periphery of the retina and are therefore responsible for peripheral vision. Rods work well in low levels of light, they are also the cells that allow the eyes to adapt to low light.
(6 million in each eye), 50,000 cones have a private line to the optic nerve. These cones found in the very centre of the retina (fovea) are the receptors for visual acuity (sharpness). Cones need bright light to function and are sensative to different wavelengths of light, so they are responsible for colour vision.
- the recovery of the eye's sensitivity to visual stimuli in darkness after exposure to bright lights. The brighter the light, the longer the adaptation. (30 mins total) Ex. deer in the headlights, night blindness.
- the recovery of the eye's sensitivity to visual stimuli in light after exposure to darkness. Takes a few seconds as the cones have to adapt to increased levels of light faster than the rods adapt to darkness.
Theories of Colour Vision
Trichromatic ("Three Colours") Theory
proposed by Young in 1802 and modified by Hermann von Helmholtz in 1852.
This theory proposed three types of cones: red cones, blue cones and green cones, one for each of the three primary colours of light. Different shades of colours correspond to different amounts of light received by each of these three types of cones. These cones then fire their message to the brain's vision centres. It is the combination of cones and the rate at which they are firing that determine the colour that will be seen. Ex.red and green cones are firing the colour the person sees is yellow.
an image that occurs when a visual sensation persists for a brief time after the original stimulus is removed. This phenomenon cannot be explained by the trichromatic theory.
Explains the phenomenon of the colour afterimage. In this theory there are actually four primary colours: red, green, blue, and yellow. The cones are arranged in pairs, red with green and blue with yellow. If one member of a pair is stimulated, the other member cannot be working, so there are no reddish-greens or bluish-yellows.
Caused by defective cones in the retina of the eye. Normal colour vision (trichromats) can detect red-green, yellow-blue, and black-white.
Most colour blind individuals (dichromats) have a deficiency in the red-green system and see the world in blues, yellows and shades of grey.
This is a sex-linked disease where the defective genes are located on the X chromosome. Occurs in 1% of females and 7- 8% of males.
Much less common are yellow-blue dichromats. Blue cones don't work and their visual world consists of reds, greens, and shades of grey. Affects 1 in 10,000 people, men and women equally affected.
Monochromats are sensitive to only the black-white system and thus are totally colour blind and everything appears in shades of grey.
The Hearing Sense
Sound waves are the vibrations of the molecules of air that surround us. Sound waves have the same properties of light waves, wavelength, amplitude, and purity.
are interpreted by the brain as the frequency or pitch (high, medium, or low).
is interpreted as volume, how soft or loud a sound is.
is a richness in the tone of the sound.
A person is limited in the range of frequencies he or she can hear. Frequency is measured in cycles (waves) per second, or
Human limits are between 20 - 20000 Hz with the most accurate being around 1000 Hz. Dogs can hear between 50 and 60000 Hz, dolphins up to 200000Hz.
3.4 What is sound, and how does it travel through various parts of the ear.
The Structure of the Ear
The ear is a series of structures, each of which plays a part in the sense of hearing.
The Outer Ear
is the visible, external part of the ear that serves as a kind of concentrator, funnelling the sound waves from the outside into the structure of the ear.
The pinna is the entrance to the
, the short tunnel that runs down to the
, or eardrum. The eardrum is a thin section of skin that tightly covers the opening into the middle part of the ear. When sound waves hit the eardrum it vibrates and causes three tiny bones in the middle ear to vibrate.
The Middle Ear: Hammer, Anvil, and Stirrup
The hammer, anvil and stirrup are three tiny bones in the middle ear are known collectively as the auditory ossicles. When the eardrum vibrates, the hammer resting against the eardrum also vibrates, causing a chain reaction in the anvil and the stirrup. The stirrup rests against another membrane of tissue called the
, which in turn covers the entrance to the inner ear.
The Inner Ear
The oval window vibrates setting up another chain reaction within the inner ear.
The inner ear is a snail-shaped structure called the
, which is filled with fluid. When the oval window vibrates, it causes the fluid in the cochlea to vibrate. The fluid surrounds a membrane running through the middle of the cochlea called the
The basilar membrane is the resting place of the organ of Corti, which contains the receptor cells for the sense of hearing. When the basilar membrane vibrates, it vibrates the organ of Corti, causing it to brush against a membrane above it. On the organ of Corti are special cells called hair cells, which are the receptors for sound and transduce sound waves to neural messages. When these hair cells are bent up against the other membrane, it causes them to send a neural message through the auditory nerve and into the brain, where the auditory cortex will interpret the sounds. The louder the sound the stronger the vibrations.
Theories of Pitch
refers to how high or low a sound is. There are two theories about how the brain receives information about pitch.
Proposed by Hermann von Helmholtz. In this theory, the pitch a person hears depends on where the hair cells that are stimulated are located on the organ of Corti. High pitched sound stimulates all the hair cells near the oval window, while low pitched sound stimulates all the hair cells that are farther away on the organ of Corti.
Developed by Rutherford and states that pitch is related to how fast the basilar membrane vibrates. The faster the membrane vibrates, the higher the pitch; the slower it vibrates, the lower the pitch.
Both theories are correct to a certain point. For the place theory to be right, the basilar membrane has to vibrate unevenly, which it does when the frequency of the sound is above 1000Hz. For the frequency theory to be correct the hair cells would have to fire as fast as the basilar membrane vibrates. This only works up to 100 Hz.
works for pitches between 100 and 1000Hz. When frequencies are above 100Hz, the auditory neurons do not all fire at once. Instead they take turns in a process called volleying or the volley principle.
is the term used to refer to difficulties in hearing. A person can be partially hearing impaired or totally hearing impaired.
3.5 Why are some people unable to hear, and how can their hearing being improved?
The treatment for hearing loss varies according to the reason for the impairment.
Conduction Hearing Impairment
can result from either a damaged eardrum or damage to the bones of the middle ear. Middle ear damage is often from ear infections that are not treated quickly enough or from chronic ear infections. Hearing aids may be used to help restore hearing loss.
Nerve Hearing Impairment
the problem lies in the inner ear or in the auditory pathways and cortical areas of the brain. Normal aging causes loss of hair cells and loud noises can damage hair cells (Tinnitus).
An electronic device called a cochlear implant bypasses the outer and middle ears by sending signals from a microphone worn behind the ear to a sound processor which translates those signals into electrical stimuli that are sent to a series of electrodes implanted directly into the brain. With an implant people can hear some speech and their own speech to a degree.
The Chemical Senses
3.6 How do the senses of taste and smell work, and how are they alike?
Taste buds are the common name for the taste receptor cells found in the mouth. Most taste buds are located on the tongue, but there are a few on the roof of the mouth, the cheeks, and under the tongue. Sensitivity to taste depends on the number of taste buds which can range from 500 to 10000.
The bumps on the tongue are called papillae and the taste buds line the walls of these papillae. Each taste bud has about 20 receptors that are very similar to the receptor sites on receiving neurons at the synapse. Taste is considered a chemical sense as the molecules of food fit into the receptors, a signal is fired to the brain which then interprets the taste sensation. Receptors are replaced every 10 to 14 days.
There are five primary tastes described: sweet, sour, salty, bitter, and brothy (umami). These five sensations work together with the sense of smell and the texture, temperature and "heat" of foods to produce thousands of taste sensations.
Gustation: Sense of Taste
Olfaction: Sense of Smell
The ability to smell odours is called olfaction and is a chemical sense.
The outer part of the nose is a collection device that funnels odours to the top of the nasal passage where they are translated into neural signals the brain can understand.
The area of olfactory receptor cells is only 2.5 cm2 in each cavity and contains 10 million olfactory receptors.
The olfactory receptor cells have about a half-dozen little "hairs" (cilia) that project into the cavity. Like taste buds, there are receptor sites on these hair cells that send signals to the brain when stimulated by the molecules of substances that are in the air moving past them. Olfactory receptors are replaced every five to eight weeks and there are at least 1000 types of them.
The sense of smell has its own special place in the brain, the olfactory bulbs which are located right on top of the sinus cavity beneath the frontal lobes. The olfactory receptors send their neural signals directly up to these bulbs, bypassing the entire brain stem and the reticular formation.
are the body senses, consisting of the skin senses (touch, temperature, pressure and pain) the kinesthetic sense (the location of body parts in relation to the ground and to each other), and the vestibular senses (movement and body position).
3.7 What allows people to experience the sense of touch, pain, motion, and balance?
is an organ about two square metres in size that keeps bodily fluids in, germs out, and also receives and transmits information from the outside world to the central nervous system. Information about light touch, deeper pressure, hot, cold, and even pain is collected by special receptors in the skin's layers.
There are half a dozen different receptors in the layers of the skin.
Pacinian corpuscles are just beneath the skin and respond to pressure only.
Nerve endings that wrap around hair follicles are sensitive to pain and touch. Free nerve endings just beneath the uppermost layer of the skin respond to changes in temperature, pressure and pain.
There are receptors called proprioceptive receptors that detect pain and pressure in the organs, a type of pain called
Pain sensations in the skin, muscles, tendons, and joints are carried on large nerve fibres and are called
. Somatic pain is the body's warning system that something is being, or is about to be, damaged and tends to be sharp and fast. Another type of somatic pain is carried on small nerve fibres and is slower and more of a general ache. Example- Hitting your thumb with a hammer causes the immediate sharp pain, whereas later the bruised tissue aches letting you know to take it easy on that thumb.
Gate- Control Theory
The best current explanation for how the sensation of pain works was first proposed by Melzack and Wall. In this theory, the pain signals must pass through a "gate" located in the spinal cord. The activity of the gate can be closed by non-pain signals coming into the spinal cord from the body and by signals coming from the brain. This explains why rubbing a sore spot can help to reduce the feeling of pain.
Stimulation of pain receptor cells releases a chemical called substance P. Substance P released into the spinal cord activates other neurons that send their messages through spinal gates. From the spinal cord, the message goes to the brain, activating cells in the thalamus, somatosensory cortex, areas of the frontal lobes, and the limbic system. The brain then interprets the pain information and sends signals that either open the spinal gates farther, causing a greater experience of pain, or close them, dampening the pain. This decision by the brain is influenced by the psychological aspects of the pain-causing stimulus. Anxiety, fear, negative thinking, and helplessness can intensify pain. Laughter, distraction, and a sense of control can diminish it.
Endorphins can inhibit the transmission of pain signals in the brain, and in the spinal cord they can inhibit the release of substance P.
The Kinesthetic Sense
The proprioceptors located in the skin, joints, muscles, and tendons, mentioned in the discussion of pain, are part of the body's sense of position in space, the location of the arms, legs in relation to one another and in relation to the ground. This sense is called kinesthesia. When you close your eyes and raise your hand above your head, you know where your hand is because the proprioceptors tell you about the changes in pressure within the muscles.
The Vestibular Sense
The vestibular sense, or sense of balance, is composed of the otolith organs and the semicircular canals both located in the innermost chamber of the ear.
organs are tiny sacs found just above the cochlea. These sacs contain a gelatinlike fluid within which tiny crystals are suspended. The head moves and the crystals cause the fluid to vibrate, setting off some tiny hairlike receptors on the inner surface of the sac, telling the person that he or she is moving forward, back, sideways, or up and down.
are three circular tubes that are also filled with fluid and will stimulate hairlike receptors when rotated. There are three tubes, one in each of the three planes of motion (x, y, z axes). Those are the three planes through which the body can rotate, and when it does, it sets off the receptors in these canals. Ex. Spinning in a circle
The disagreement between what the eyes say and what the body says is pretty much what causes motion sickness, the tendency to get nauseated when in a moving vehicle. Normally the vestibular sense coordinates with the other senses. But for some people, the information from the eyes may conflict a little too much with the vestibular organs, and dizziness, nausea, and disorientation are the result. One way to overcome this is to focus on a distant point or object.
Sensory Conflict Theory
is an explanation of motion sickness in which the information from the eyes conflicts with the information from the vestibular senses, resulting in dizziness, nausea and other physical discomforts.
Top - Down Processing
Bottom- up processing
The Hermann Grid Illusion