UNIT 1:
SENSATION AND PERCEPTION
I. Overview: Reality Versus Perception
II. Sensation: activities at the level of a sensory receptors resulting in neural impulses
from the receptors to the brain
III. Perception: the organization and interpretation of sensory input.
Example: Illusions:
IV. Thresholds:
1. Threshold: when a physical change becomes strong enough to elicit a response
2. Absolute Threshold: the smallest amount of stimulation necessary to elicit a response 50% of the time.
3. Just Noticeable Difference (JND): When a change in a stimulus or the difference between two stimuli can be detected 50% of the time
4. Webers Law: the size of the Just Noticeable Difference (JND) is a constant proportion of the original stimulus value. The size of the difference threshold appears to be lawfully related to the initial stimulus magnitude. In more understandable terms, suppose you are 64 and weigh 225 pounds and you have a friend that is 52 and weighs 95 pounds. In a short period of time each of you gains five pounds. Others notice the weight change in your friend but not yours. Webers explanation is that the greater the weight of the original stimulus, the greater the magnitude of the change necessary for you to to detect a just noticeable difference (JND).
V. Signal Detection Theory: attempts to explain why persons can detect signals in some
situations but not in others. Signals always occur in the context of some type of environmental noise noise means irrelevant stimuli or background stimuli that might be confused with the stimuli that you are trying to detect. Noise refers to the stimuli that are irrelevant the noise could be in the form of visual stimuli, auditory stimuli, or tactile stimuli. Two key concepts explain how signals are detected or missed:
1. Sensitivity: if you have greater sensitivity, then you will have a lower threshold for detecting the signal a lower threshold for distinguishing between the signal from the background noise.
2. Bias: how willing you are to report noticing the signal. Your willingness to report seeing the signal may change depending on the circumstances. For example, if detecting the signal will allow you to avoid a painful shock you might report seeing it earlier than if the detection of the signal will allow you to receive a one cent reward. In these two situations, you might change your bias by adjusting your criterion for detection.
1. Amplitude: the height of a wave
2. Frequency: the rate at which the peaks of the wave move past a given point
3. Wavelength: how long or short of time between the arrivals of the peaks in the electromagnetic spectrum there is a narrow band of radiation perceived as visible light. All colors are conveyed in this light but the seven we can easily detect are: red, orange, yellow, green, blue, indigo, and violet. Lower frequencies and longer wavelengths are near the red end of the spectrum and higher frequencies and shorter wavelengths are near the violet end.
1. Pupil: an opening of the eye which permits light to enter that center portion of the eye that looks like a round black spot
2. Iris: a muscle which can change the size of the pupil to permit more or less light to enter various drugs can act on this muscle cause a change in pupil size dilation or constriction
3. Lens: permits the eye to help focus light. Muscles can adjust the lens to focus light from objects at different distances
4. cornea: the transparent covering over the eye which plays a significant role in focusing light. A corneal scratch can be quite irritating, but heals very rapidly if treated.
5. Retina: tissue at the back of the eye about the thickness of paper.
6. Fovea: the central part of the retina that is composed of densely packed cells which transforms light into nerve impulses images which strike the fovea are the sharpest
7. Optic Nerve: a moderately large nerve composed of a bundle of axons from retinal cells in each eye. The place where the optic nerve exits the retina is called the blind spot because there are no rods or cones at the point of exit
VIII. Rods and Cones (two kinds of cells in the retina that are important for converting
light into nerve impulses)
1. Rods: cells shaped like little rods which are highly sensitive to light, but only
register different shades of gray no color
2. Cones: cells in the retina shaped little cones which are less sensitive to light
than rods but are highly sensitive to different wavelengths of light this allows us to see colors
1. Transduction: the conversion process by which the eye converts the
electromagnetic energy that is light into nerve impulses (this allows
communication to the brain)
2. Accommodation: the automatic adjustment of the eye to different distances that
results when muscles change the shape of the lens so that it focuses light on the retina from near or far away objects
3. Dark Adaptation: Most of you have had the experience of going into a theatre and not being able to see rows or seats unless you wait awhile. When you are in darkness, your pupils will dilate which lets in much more light than in bright daylight (up to 16 times more light). During the adaptation to darkness, rods become more sensitive because your genes cause the production of a chemical called rhodopsin, which is critical for responding to light
1. Three ways in which color can vary:
(a) Hue: different wavelengths of light produce different colors (red or blue, etc.)
(c) Saturation: the amount of white mixed in with the color, e.g. deep blue
(d) Lightness or Brightness: How much light is present.
2. Trichromatic Theory: This theory proposes that the eye contains three kinds of color sensors, each sensitive to a particular range of wavelengths long, medium, and short. The brain registers color by combining responses to these three separate wavelengths.
Support for theory: we do, in fact have three kinds of cones, one responsive to light in the wavelength seen as yellow, another to green, and a third to violet. The brain responses to the mixture, not to the output of individual cones. There is a difference between responding to a TV, which emits different wavelengths that act directly on the cones, and to a painting. When you look at a painting, you see a reflected light. For example, when you see yellow in a painting, you are seeing only what is not absorbed by the paint yellow paint absorbs all wavelengths except wavelengths underlying our perception of yellow.
3. Opponent Process Theory: the presence of one color of a pair (red/green;
yellow/blue; and black/white) inhibits the perception of the other color. This was based on the observation that some colors cannot be mixed. For example, you cant make a yellowish blue by mixing blue and yellow. You will get green, not a yellowish blue.
4. Afterimage: an image left behind by a previous perception. An afterimage occurs when one member of a pair of opponent cells inhibits the other, then releases it. For example, if you stare at Green, green inhibits red (you cant mix the two colors and get a greenish red). If you look away from the color green after fixating on it for awhile, you will see a red afterimage
5. Opponent Cells: cells that pit the colors in each pair against each other. For example, blue against yellow when wavelengths that produce blue are registered by cells, they inhibit the perception of wavelengths that produce yellow.
6. Color Blindness: persons are unable to distinguish one hue from another, or, more rarely, unable to respond to hue at all. Color Blindness most frequently results from genes that produce similar pigments in their cones causing them to not respond accurately to wavelengths.
(a) Proximity: marks near each other tend to be grouped together
(b) Continuity: patterns which appear to be continuous such as a line of dashes will be seen as a straight line
(c) Similarity: marks that look alike will be grouped together
(d) Closure: in a figure with small gaps, we tend to perceptually close the gap
(e) Good form: Marks that form a single shape tend to be grouped together
(a) Size Constancy: we tend to see familiar objects as the same size regardless of how far they area away, even though there size on the retina is greatly reduced the farther the object is from the eye
(b) Shape Constancy: We tend to see objects such as a Frisbee as the same regardless of the angle at which it is turned
(c) Color Constancy: when looking at familiar scenes or objects under different conditions of lighting, we tend to see their colors as being constant
XII. Distance or Depth Perception
1. Binocular Cues: cues to depth which require both eyes
(a) Retinal Disparity: objects in front and objects behind fall on slightly different parts of the retina. This difference is called retinal or binocular disparity, the brain uses this cue to determine which object is in back and which is in front.
2. Monocular Cues: cues to depth which require only one eye
(a) texture gradient: progressive changes in texture that signal distance. For example, a gravel road where rocks in front are relatively large whereas rocks at a distance are small or appear to merge together
(b) Linear perspective: example, railroad ties that appear closer together in the distance
(c) Superposition: one object cuts off the view of another
(d) Relative size: smaller objects appear to be more distant
(e) Motion Parallax: the differential velocity between near and far objects produced by our own movements (Near objects also appear to move in the opposite direction)
1. Two visual pathways in the brain:
(a) The where pathway: pathway going from the occipital lobes up to the parietal lobes concerned with special properties, e.g. the location of an object
(b) The what pathway: pathway going from the occipital lobes down to the temporal lobes concerned with properties of objects such as their shape and color
2. Perceptual Processing: the progression from sensation to organization, to recognition, and identification
3. Bottom up Processing: bottom up processing is initiated by the stimulus for example, an image on the TV that you recognize but that you have never seen before
4. Top Down Processing: top down processing is guided by previous learning, or beliefs. For example, you anticipate what is to come on TV because your past experience in watching that program or a similar program.
5. Perceptual Set: expectations and beliefs lead you to expect to perceive certain objects or characteristics in a particular context. For example in Slide 20, you expect to see the word beer - a perceptual set
1. Selective Attention: allows you to pick out a particular characteristic, object, or
event from an array of stimuli.
2. Popout: when a particular stimulus is salient because it differs substantially from
surrounding stimuli
3. Repetition blindness: for example, if you are watching a man and standing at a
Distance, then notice that the the man is falling from a ladder. You might miss the fact that the has been repeated twice in this sentence. This is Repetition blindness.
4. Attentional blink: attention is lost for a certain time immediately following
attention a stimulus to which attention is paid. For example, a proofreader that is attending to a large error, may miss smaller errors that occur shortly after they have attended to the larger one.
I. Sound Waves:
1. Sound waves have both Frequency and amplitude
(a) Pitch: results from hearing variations in frequency of sound waves
(b) Loudness: results from hearing variations in amplitude of sound waves
II. Structure of the Ear (Three major parts: the Outer Ear, the Middle Ear, and the Inner
Ear)
1. Eardrum (Tympanic Membrane): the eardrum is composed of the Tympanic Membrane which stretches
across the inside end of the auditory canal. Sound waves move the Tympanic
Membrane
2. Hammer, Anvil, and Stirrup: the three smallest bones of the human body. Sound
waves move the eardrum (Tympanic Membrane) which in turn moves the three little bones in the inner ear which amplify the vibrations and cause the Basilar Membrane to vibrate
3. Cochlea: a snail shaped structure in the inner ear which contains the Basilar
Membrane
4. Basilar Membrane: lines the inner portion of the Cochlea and contains Hair Cells
5. Hair Cells: hairs along the Basilar Membrane which trigger nerve impulses that are conveyed to the brain
III. Two Theories about the way the Basilar Membrane converts pressure waves to
perceived sound:
1. Frequency Theory: basically contends that higher frequencies produce greater
neural firing. However, neurons can fire only about 1,000 times per second, but we can hear sounds produced by much higher frequencies. Therefore, Frequency Theory cannot fully explain our ability to hear.
2. Place Theory: contends that different frequencies activate different places along
the Basilar Membrane (see Figure 3.14 in your text on page 111). Low frequencies cause maximal vibrations of the basilar membrane at one end, medium frequencies cause maximal vibrations in the middle,, and high frequencies cause maximal vibrations at the other end
IV. Deafness: Two forms
1. Nerve Deafness: usually occurs when Hair Cells in the Basilar Membrane are
destroyed by loud sounds. It may affect only certain frequencies. For this reason, persons on a rifle range usually wear some type of ear protectors to limit the noise
2. Conduction Deafness: usually results from an accident or other causes that impairs
the functioning of the external or middle ear. A ruptured tympanic membrane or
eardrum can be one cause of conduction deafness
V. Organizing Sounds and Perception:
1. Auditory Scene Analysis the process of making sense out of what we hear
2. Gestalt laws similar to vision. For example, we may group sounds with the same pitch
3. Speech Segmentation Problem: often, speech is continuous if we did not know the meaning of words, it is unlikely that we could tell when individual words in a sentence begin or end. This is referred to as the Speech Segmentation Problem.
4. Categorical Perception: we tend to hear speech as distinct categories. Categorical perception also occurs in human infants. It is not even unique to humans - it has been demonstrated in several other species (for example, monkeys)
For example, a difference in loudness may be one cue to the distance of the sound. The fact that sound is louder in one ear than another can serve as a cue to the sounds location.
1. Cocktail Party Phenomenon: you are talking to someone at a party and are ignoring the conversations of others around you, then you hear your name mentioned by one of the persons in the background. If you were not listening on one level, how would you have heard your name? In some way, you must have been processing the irrelevant conversations (using Bottom-up Processing which is initiated by the surrounding stimuli as opposed to Top-down Processing that would be guided by knowledge or expectations)
2. Dichotic Listening: based on experiments in the early 1960s by an undergraduate student named A. M. Treisman. When a person listens to stimuli presented separately to the two ears via headphones and are told to listen to the stimuli in only one ear, they still register some information from the other ear. For example, in the ear that they are not listening to, they are able to report afterwards whether it was a male or female speaking. Thus, they must have picked up some information from stimuli that they supposedly were igoring
OTHER SENSE MODALITIES
1. Olfaction relies on responding to the presence of specific chemicals
2. Some persons are 20 times more sensitive to odors than others
3. We think we are good at detecting particular smells, but we really arent. One study indicated that we can only identify about 50% of common odors even though we may recognize the familiar scent.
4. Lock and Key Theory of Olfaction: Olfactory receptors have different shapes and only molecules with particular shapes will fit. The receptors act as locks and the molecules that fit act as keys.
5. Detection of an odor involves a response to a pattern of stimuli
6. Odors and recall of memories particularly long term memories
7. Olfaction is an important sense for protecting us for example, detecting the smell of spoiled meat. But, we are also very sensitive to suggestion. Ask someone in the morning if the pork sausage smells right. Example of suggestion: the HyVee chicken phenomenon
8. Pheromones: chemical substances that serve as a means of communication. Pheromones are released outside the body by way of excretions such as perspiration or in the urine. We know that pheromones play a role in attracting sexual partners during mating in a number of species. There is some evidence that this also may be true in humans. For example, females who wear a perfume mixed with a clear, odorless pheromone tend to elicit more forms of sexual behavior such as petting and intercourse than women who wore a placebo mixed with perfume. Again, this is one study, and studies need to be replicated before definitive conclusions are drawn.
II. Taste
1. Taste Buds: microscopic structures on the sides of the tongue- there are also taste receptors in the back of the throat and inside the cheeks
2. Taste buds die and are replaced every ten days
3. Both adults and children are very sensitive to taste, but children are more so.
4. Sweet, Sour, Salty, and Bitter: receptors in the back of the mouth are most sensitive to Bitter substances. Nerve endings in the mouth are irritated by spicy foods, which helps in their detection. All kinds of taste buds are found in most locations of the tongue.
III. Somasthetic Senses: a collective term which includes a collection of five senses in
addition to the more common ones (sight, hearing, smell, and taste). There are really
nine senses not just five.
1. Kinesthetic Sense: registers movements of the limbs
2. Vestibular sense: involves the semicircular canals in the inner ear provides information about the body and its orientation to gravity. If disrupted by an infection or other causes of disruption, they can affect balance
3. Touch: the skin acts as a massive sensory organ. Receptors in the skin send messages to the somatosensory cortex. Women tend to be more sensitive to touch than men, particularly on their backs and stomachs.
4. Temperature: the skin has separate systems for registering hot and cold stimuli.
cold receptors will give rise to a cold sensation even if the receptor is triggered by heat. This is referred to as paradoxical cold
5. Pain: two kinds of nerves are stimulated, those for sharp pain and those for dull
Pain. Endorphins are substances in the brain that have pain killing effects similar to that of morphine. Parts of the brain that are activated when we anticipate pain are close to those that are active when we are experiencing pain. The areas involving anticipation may tend to exacerbate our reactions to actual pain producing stimuli
IV. Other Possible Senses?
1. Magnetic sense: response to magnetic fields. Birds apparently use this in migration. There is also evidence that some mammals (mole rats) may have this sense modality, It is uncertain whether humans may possess a weak magnetic sense
2. Extrasensory Perception: telepathy, clairvoyance, precognition, and psycho kinesis. In general, there is not impressive empirical evidence for any of these phenomena. It continues to be an area of debate within psychology.
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TEST 1 THURSDAY, SEPTEMBER 17, 2009
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