SENSATION & PERCEPTION

PSYCHOPHYSICS

1. What is the difference between sensation and perception?

Sensation is the stimulus-detection process by which our sense organs respond to and translate environmental stimuli into nerve impulses that are sent to the brain.
Perception – making “sense” of what our senses are telling us – is the active process of organizing this stimulus input and giving it meaning (Banks & Krajicek, 1991)

2. What is the absolute threshold and how is it calculated?

Because we are often unsure of whether we have actually sensed very faint stimuli, researchers designate the absolute threshold as the lowest intensity at which a stimulus can be detected 50 percent of the time. The lower the absolute threshold the greater the sensitivity. Studies of absolute thresholds, the general limits of human sensitivity for the 5 major senses can be estimated. Some senses are very sensitive. Absolute thresholds vary among species. Thresholds are approximates and have been derived from several experiments are various species.

3. How do subliminal stimuli impact attitudes and behavior?

A subliminal stimulus is one that is so weak or brief that, although it is received by the senses, it cannot be perceived consciously. Can register in the nervous system and can affect attitudes and behavior without knowing it to a limited extent.
? i.e. Move theatre flashed “drink Coca-Cola” and “eat popcorn”. There was an increase of popcorn by 50% and coke 18%. As far as consumer behavior is concerned, the conclusion is that persuasive stimuli above the perceptual threshold are far more influential than subliminal attempts to sneak into our subconscious mind, perhaps because we are more certain to “get the message”
? subliminal materials are used by people who are trying to change themselves – apparently the power of belief is greater than the power of subliminal self improvement messages

4. What is the difference threshold?
The difference threshold is defined as the smallest difference between two stimuli that people can perceive 50 percent of the time. Sometimes call the “just noticeable difference” i.e. slight variation in taste might signal that food is tainted or spoiled.

The Weber law?

Weber’s law states that the difference threshold, or jnd, is directly proportional to the magnitude of the stimulus with which the comparison is being made and can be expressed as a Weber fraction. I.e. the jnd value for weights is a Weber fraction of approximately 1/50. This means that if you lift a weight of 50 grams, a comparison weight must weigh at least 51 grams in order for you to be able to judge it as heavier. If the weight were 500 grams, a second weight would have to weigh at least 510 grams for you to discriminate between them.

How is the Weber fraction calculated?

Breaks down at extremely high and low intensities of stimulation, it holds up reasonably well within the most frequently encountered range, therefore providing a reasonable barometer of our abilities to discern differences in the various sensory modalities. The smaller the fraction, the greater the sensitivity to differences. Web fractions show that humans are highly sensitive to difference in the pitch of sounds, but far less sensitive to loudness differences.

5. What processes are involved in sensory adaptation?

Sensory systems are finely attuned to changes in stimulation. Sensory neurons are engineered to respond to a constant stimulus by decreasing their activity and the diminishing sensitivity to an unchanging stimulus is called sensory adaptation – sometimes called habituation. i.e. if you dive into a pool, the water may fee cold at first because your body’s temperature sensors respond to the change in temperature. However with time you become used to the water temperature.

THE SENSORY SYSTEMS

VISION

1. What is the stimulus for each of our sense organs?

For vision?
Normal stimulus for vision is electromagnetic energy

For audition?

Stimuli for our sense of hearing are sound waves, a form of mechanical energy. What we call sound is actually pressure waves in air, water or some or conducting medium. These sounds have 2 characteristics frequency and amplitude. Frequency is number of sound waves or cycles per second. Amplitude refers to the vertical size of the sound wave.

For gustation (taste)
Chemical senses – Taste buds are receptors concentrated along the edges and back surface of the tongue. Humans have 9,000 taste buds each consisting of several receptor cells arranged like the segments of an orange. A small number of receptors also are found in the roof and back of the mouth, so that even people without a tongue can taste substances.

Olfaction (smell)
Both gustation and olfaction are chemical senses because their receptors are sensitive to chemical molecules rather than to some form of energy.

Tactile Senses

Tactile sensations are also a source of many life’s pleasures, including sexual orgasm. A lack of tactual contact with a caretaking adult retards physical, social and emotional development and physically massaging newborn babies enhances their development (cigales et al., 1997; Fields et al., 1996)

There are 4 tactile sensations: pressure (touch), pain, warmth and cold. These sensations are conveyed by receptors in the skin and in our internal organs. Mixtures of these 4 sensations form the basis for all other common skin sensations, such as itch.

Describe the anatomy of the eye. What is the function of each of these?
Anatomical structures?

Light waves enter the eye thru the cornea, transparent protective structure

Behind the eye is the pupil, an adjustable opening that can dilate or constrict to control the amount of light that enters the eye. The pupil’s size is controlled by muscles in the colored iris that surrounds the pupil. Lower levels of illumination cause the pupil to dilate, letting more light into the eye to improve optical clarity, bright light triggers constriction of the pupil.

Lens – behind the pupil, an elastic structure that becomes thinner to focus on distant objects and thicker to focus on nearby objects i.e. lens of a camera

The lens of the eye focuses the visual image on the light-sensitive retina, a multi-layered tissue at the rear of the fluid-filled eyeball. The lens reverses the image from right to left and top to bottom when it is projected upon the retina, but the brain reconstructs the visual input into the image that that we perceive.

Describe the processes/deficits related to hyperopic and myopia.

The ability to see clearly depends on the lens’ ability to focus the image directly onto the retina.

Myopia if you have good vision for nearby objects but have difficulty seeing faraway objects you probably suffer from myopia (nearsightedness) In nearsighted people, the lens focuses the visual image in front of the retina (too near the lens) resulting in blurred image for faraway objects.

Some people have excellent distance vision but have difficulty seeing close-up objects clearly. Hyperopia (farsightness) occurs when the lens does not thicken enough and the image is therefore focused on a point behind the retina. (to far from the lens) Aging process typically causes the eyeball to become shorter over time, contributing to the development of hyperopia.

Describe the anatomy of the retina. Describe the different types of cells, and photoreceptors. How do neural signals pass through the retina?

The retina is a multi-layered screen that lines the back service of the eyeball and contains specialized sensory neurons; it is an extension of the brain. Contains 2 types of light-sensitive receptor cells, called the rods and cones because of their shapes. There are about 120 million rods and 6 million cones in the human eye.

What special function does each the photoreceptors (rods and cones) serve? How do the characteristics of the rods and cones affect our vision (i.e. acuity, color vision, brightness contrast?)

The rods, which function best in dim light, are primarily black and white brightness, receptors. They are 500 times more sensitive to light than are the cones; do not give rise to color sensations. i.e. night creatures such as the owl, contains only rods therefore having an exceptional vision in very dim light but no color vision during the day. Many rods are connected to the same bipolar cells. They funnel their individual electrical messages to the bipolar cell, where the additive effect of the many signals may be enough o fires it. This is why we can more easily detect a faint stimulus, such as a dim star, if we look slightly to one side so that its image falls not on the fovea but on the peripheral portion of the retina, where the rods are packed most densely.

The cones are color receptors, function best in bright illuminator. i.e. pigeon and chipmunk have only cones in their retinas, so they see the world in living color but have very poor night vision. Rods are found though the retina except in the fovea, a small area in the centre of the retina that contains only cones. Cones decrease in concentration as one moves from the centre of the retina and the periphery of the retina contains mainly rods.

Visual acuity Cones that lie in the periphery of the retina also share bipolar cells, In the fovea, however, the densely packed cones each have their their own “private line” to a single bipolar cells. Resulting in visual acuity or ability to see fine detail is greatest when the visual image projects directly onto the fovea.

Rods and cones send their messages to the brain via 2 additional layers of cells. Bipolar cells have synaptic connections with the rods and cones. The bipolar cells, in turn, synapse with a layer of about one million ganglion cells, whose axons are collected into a bundle to form the optic nerve. Input from more than 126 million rods and cones is eventually funneled into only a million traffic lanes leading out of the retina toward higher visual centres.

Describe how light is translated into neural impulses by our visual system.

Stimulus are converted into nerve impulses is called transduction. Rods and cones translate light waves into nerve impulses through the action of protein molecules called photopigments. Chemical reaction that changes the rate of neurotransmitter release at the receptors synapses with the bipolar cells. If nerve responses are triggered at each of the 3 levels (rod or cone, bipolar and gangilion cell) the message is instantaneously on its way to the visual relay station in the thalamus and then on to the visual cortex of the brain.

How is brightness coded by our sensory system? What occurs during the process of dark adaptation? How do rods and cones differ in this process?

Rods are far more sensitive than cones under conditions of low illumination. The brightness sensitivity of both the rods and the cones depends in part on the wavelength of the light. Research has shown that rods have greater brightness sensitivity than cones throughout the color spectrum except at the red end, where rods are relatively insensitive. i.e. airport landing lights are often blue because this wavelength is picked up particularly well by the rods during night vision, when the cones are relatively inoperative. Although rods are by nature sensitive to low illumination, they are not always ready to fulfill their function i.e. going into a dark theatre from sunlight, groping around in darkness; some people prefer to wait until their eyes have adjusted. Rods are important in night vision and relatively insensitive to red wavelengths, they suggested that fighter pilots either wear goggles with red lenses or work in rooms lit only by red lights while waiting to be called for a mission.

Dark adaptation is the progressive improvement in brightness sensitivity that occurs over time under conditions of low illumination. After absorbing light, a photoreceptor is depleted of its pigment molecules for a period of time. If the eye has been exposed to conditions of high illumination, such as bright sunlight, a substantial amount of photopigments will be depleted.

Describe each of the main theories of color vision.

Human vision is finely attuned to color our difference thresholds for light wavelengths are so small that we are able to distinguish an estimated 7.5 million hue variations.

Trichromatic theory

There are three types of color receptors in the retina. Individual cones are most sensitive to wavelengths that correspond to blue, green or red. Each of receptor classes sends messages to the brain, based on the extent to which they are activated by the light energy’s wavelength. The visual system then combines the signals to recreate the original blue. If all three cones are equally activated, a pure white color is produced. According to the theory, yellow is produced by activity of red and green receptors; however certain people with red-green color blindness are able to experience yellow. This finding suggested there must be a different means of perceiving yellow.

2nd phenomenon that posed problems for the Trichromatic theory was the color afterimage, in which an image in a different color appears after a color stimulus has been viewed steadily and then withdrawn. Trichromatic the theory cannot account for what you’ll see.

Opponent process theory

Proposed that each of the three cone types responds to 2 different wavelengths. One type responds to red or green, another to blue or yellow and a third to black or white. i.e. red-green cone respond with one chemical reaction to a green stimulus and with its other chemical reaction (opponent process) According to opponent theory as you stare at black and green colors, the natural process that register these colors became fatigued, then when you cast your gaze on the white surface, which reflects all wavelengths a “rebound” opponent reaction occurred as each receptor responded with its opposing white or red reactions.

Dual process theory

Dual process theory combines the Trichromatic and opponent-process theories to account for the color transduction process.

Trichromatic theorist Young and Helmholtz were correct in that cones do indeed contain one of three different protein photopigments that are most sensitive to wavelengths roughly corresponding to the colors blue, red and green. BUT different ratios of activity in the red-, blue-, green sensitive cones can produce a patter of neural activity that corresponds to any hue in the spectrum.

Herring’s opponent-process theory was also partly correct, but opponent processes do not occur at the level of the cones as he maintained. Certain ganglion cells in the retina, as well as some neurons in visual relay stations and the visual cortex, respond in an opponent-process fashion by altering their rate of firing i.e. a red light is shone on the retina, an opponent-process ganglion cell may respond with a high rate of firing, but a green light will cause the same cell to fire at a very low rate. Other neurons respond in a similar opponent fashion to blue and yellow stimuli. The red-green opponent processes are triggered directly by input from the red- or green-sensitive cones in the retina. The blue-yellow opponent process is more complex – activity of blue-sensitive cones directly stimulate the “blue” process farther along in the visual system – yellow opponent process is triggered not by a “yellow-sensitive” cone as Herring proposed, but rather by simultaneous input from the red- and green- sensitive cones

Have these theories been supported by research findings?

There have been 2 centuries of research that have yielded a win-win verdict for both sets of theorists Herring – opponent-process and Young/Helmholtz Trichromatic theory.

Which of these 3 theories (or combination of theories) best fits with our current understanding of color vision?

Dual process combines the Trichromatic and opponent-process theories to account for the color transduction process.

Describe the role of visual feature detectors. Where are these specialized cells located?

From the retina, the optic nerve sends nerve impulses to a visual relay station in the thalamus, the brain’s sensory switchboard. The input is routed to various parts of the cortex, particularly the primary visual cortex.

What higher areas in the brain are involved in vision, and what functions do these areas serve? Can’t find answer in textbook are they in your class notes Rudy?

AUDITION

Describe the anatomy of the ear. What is the function of each of these?
Anatomical structures?

The stimuli for our sense of hearing are sound waves, a form of mechanical energy. Sound is pressure waves in air, water or some other conducting medium. Sound waves have 2 characteristics frequency and amplitude. Frequency is the number of sound waves, or cycles per second. The hertz (Hz) is the technical measure of cycles per second.
Amplitude – refers to the vertical size of the sound waves. Differences in amplitude are expressed as decibels a measure of the physical pressures that occur at the eardrum.

The ear (transduction system) is made up of tiny bones, membranes and liquid-filled tubes designed to translate pressure waves into nerve impulses Sound waves travel into an auditory canal leading to the eardrum, a movable membrane that vibrates in response to the sound waves. The vibrating activity of these bones – the hammer (malleus) (attached to eardrum) anvil (incus) and stirrup (attached to another membrane) (stapes) which amplifies the sound waves more than 30 times.
The inner ear contains the cochlea, coiled, snail-shaped tube fill with fluid and contains the basilar membrane. Resting on the basilar membrane is the organ of Corti, contains thousands of tine hair cells that are the actual sound receptors. The hair cells synapse with the neurons of the auditory nerve which, in turn, sends impulses via an auditory relay station in the thalamus to the auditory cortex, which is located in the temporal lobe.

Describe how sound waves are transformed into neural impulses by our
Auditory system.

Soundwaves strike eardrum – pressure is created at the oval window by the hammer, anvil and stirrup of middle ear sets the fluid inside the cochlea into motion. Fluid waves the result vibrate the basilar membrane and the membrane above it, causing a bending of the hair cells in the organ of Corti. Bending of the hair cells triggers a release of neurotransmitter substance into the synaptic space between the hair cells and the neurons of the auditory nerve, resulting in nerve impulses that are sent to the brain.

Explain the 3 theories of pitch perception. Is there evidence to support?
of these theories?

Loudness is coded in terms of both the rate of firing in the axons of the auditory nerve and in terms of which specific hair cells are sending messages.

Frequency theory of pitch perception, nerve impulses sent to the brain match the frequency of the sound wave. Thus a 30 Hz (cycles per second) sound wave from a piano should send 30 volleys of nerve impulses per second to the brain.

Place theory of pitch perception, suggesting that the specific point in the cochlea where the fluid wave peaks and most strongly bends the hair cells serves as a frequency coding cue.

How is sound localized?

The two ears play an important role in sound localization. The nervous system uses information concerning the time and intensity differences of sound arriving at the two ears to locate the source of sounds in space. Sounds arrive first and loudest at the ear closest to the sound.

Discuss the different types of hearing loss. What causes each type of hearing loss?

Conduction deafness is caused by problems involving the mechanical system that transmits sound waves to the cochlea. i.e. a punctured eardrum or a loss of function in the tiny bones of the middle ear can reduce the ear’s capacity to transmit vibrations. Hearing aids may correct this.

Nerve deafness is caused by damaged receptors within the inner ear or damage to the auditory nerve itself and cannot be helped with a hearing aid. Aging and disease can produce nerve deafness; exposure to loud sounds is a leading cause of nerve deafness.

Explain how sensory prosthetics for both vision and hearing work.

These devices produce sensory input that can substitute, to some extent, for what can not be provided by the normal sensory receptors. Sonic guide provides new eyes by applying principles of auditory localization. (Used by bats to navigate in total darkness. i.e. sound pitch tells the person how far away the object is; a low pitch signals a nearby object and the pitch becomes higher with increasing distance. Tells the person where the object is located by means of differences in the intensity of the sounds that arrive at the 2 ears.

Another device was developed to stimulate the visual cortex differently. Stimulated electrically discrete flashes of light called phosphenes are experienced by both sighted and blind people. A specific patter of stimulation applied to individual neurons on the cortex can form a phosphene pattern that confirms to the shapes of letters or objects.

Cochlear implant a device that can restore hearing in people suffering from nerve deafness. The device sorts out useful sounds and converts them into electrical impulses, bypassing the disabled hair cells in the cochlea and stimulating the auditory nerve directly.

GUSTATION – The sense of Taste

What is the sensory stimulus for taste?

Taste buds

Describe the sensory receptors for taste.
When a substance is taken in by the mouth, it interacts with saliva to form a chemical solution that flows into the taste pore and stimulates the receptor cells resulting in a “taste” from complex patterns of neural activity produced by the 4 types of taste receptors.

How are these receptors distributed over the surface of the tongue?
are receptors concentrated along the edges and back surfaces of the tongue? There are 9,000 taste buds in humans, each consisting of several receptor cells arranged like segments of orange. A small number of receptors also are found in the roof and back of mouth.

OLFACTION

What is the sensory stimulus for our sense of smell?

Nose

Describe the sensory receptors for olfaction.

The receptors for smell are long cells that project through the lining of the upper part of the nasal cavity and into the mucous membrane. Humans have about 40 million olfactory receptors, dogs about 1 billion. Olfactory receptors recognize diverse odors individually rather than mixing the activity of a smaller number of basic receptors. These receptors resemble neurotransmitter binding sites on neurons. Any of the thousands of potential odor molecules can lock into sites that are tailored to fit them.

Discuss how pheromones are related to menstrual synchrony.

Chemical signals found in natural body scents, may affect human behavior in subtle ways. One observation known as menstrual synchrony is the tendency of women who live together or are close friends to become more similar in their menstrual cycles.

TACTILE & BODILY SENSES

What types of sensory stimuli encoded by our tactile senses?

A source of many of life’s pleasures, including sexual orgasm. A lack of tactual contact with a caretaking adult retards, physical, social and emotional development.

There are 4 tactile sensations: pressure (touch), pain, warmth and cold. These sensations are conveyed by receptors in the skin and in our internal organs. Mixtures of these 4 sensations form the basis for all other common skin sensations, such as itch.

What areas of the brain are especially important for our sense of touch?

The brain can locate sensations because skin receptors send their messages to the point in the somatosensory cortex that corresponds to the area of the body where the receptor is located. Sometimes the brain “locates” sensations that cannot possibly be present. This occurs in the puzzling phantom limb phenomenon, in which amputees experience vivid sensations coming from a missing limb.

Describe how the sensory homunculus is topically organized? Which areas of the body are associated with the greatest amount of cortical representation?

What is our vestibular sense?

We would be totally unable to coordinate our body movements were it not for the sense of kinesthesia, which provides us with feedback about our muscles and joints positions and movements. Cooperating with kinesthesia is the vestibular sense, the sense of body orientation or equilibrium. These receptors are located in the vestibular apparatus of the inner ear.

How does the anatomy of the ear contribute to our sense of balance?