SOSC 2GENERAL PSYCHOLOGY

Chapter 3: Sensation, Perception and Conscious Experience

PART 1

SENSATIONSensation: the process of receiving sensory data from the environment and translating it to the brain.

Perception: The sorting out, interpretation, analysis, and integration of stimuli by the sense organs and brain.

Stimuli: Energy that produces a response in a sense organ.

Psychophysics: the study of the relationship between the physical aspects of stimuli and our psychological experience of them.

Receptor cell: a specialized cell that responds to a particular type of energy.

Absolute threshold: the least amount of energy that can be detected as a stimulation 50 percent of the time; the smallest intensity of a stimulus that must be present for the stimulus to be detected.

Noise: background stimulation that interferes with the perception of other stimuli.

The approximate absolute thresholds under ideal circumstances are as follows:Hearing The tick of a watch from 6 meters (20 feet).Vision A candle flame seen from 50 km (30 miles) on a clear, dark night.Taste 1 gram (.0356 ounce) of table salt in 500 liters (529 quarts) of

water.Smell One drop of perfume diffused throughout a three-room

apartment.Touch The wing of a bee falling on the cheek from a height of 1 cm (0.39

inch)

Difference threshold or just-noticeable difference (jnd): the smallest change in stimulation that can be detected 50 percent of the time; the smallest level of added or reduced stimulation required to sense that a change in stimulation has occurred.

Weber’s law: the principle that the jnd for any given sense is a constant fraction or proportion of the stimulation being judged.

Adaptation: an adjustment of the senses to the level of stimulation they are receiving.

THE SENSES: VISION

A cross section of the human eye. Light enters the eye through the cornea, passes through the pupil, and is focused by the lens onto the retina.

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The retina. A view of the retina through an ophthalmoscope, an instrument used to inspect blood vessels in the eye.

The small dark spot is the fovea. The yellow circle marks the blind spot, where the optic nerve leaves the eye.

o Cornea – the transparent protective coating over the front part of the eye

o Pupil – a small opening in the iris through which light enters the eye.

o Iris – the colored part of the eye that regulates the size of the pupil.

o Lens – the transparent part of the eye behind the pupil that focuses light onto the retina.

o Retina – the lining of the eye containing receptor cells that are sensitive to light.

o Fovea – the area of the retina that is the center of the visual field.

o Rods – receptor cells in the retina responsible for night vision and perception of brightness.

o Cones – receptor cells in the retina responsible for color vision.

Rods and Cones. As you can see, the rods and cones are

named for their shape.

The basic cells of the eye. Light entering the eye travels through the ganglion and bipolar cells and strikes the light-sensitive rods and cones located at the back of the eye. The rods and cones then transmit nerve impulses to the brain via the bipolar and ganglion cells.

o Bipolar cells – neurons that have only one axon and one dendrite; in the eye, these neurons connect the receptors on the retina to the ganglion cells.

o Visual acuity – the ability to distinguish fine details visually.

o Dark adaptation – increased sensitivity of rods and cones in darkness.

o Light adaptation – decreased sensitivity of rods and cones in bright light.

o Afterimage – sensory experience that occurs after a visual stimulus has been removed.

o Ganglion – neurons that connect the bipolar cells in the eyes to the brain.

o Optic nerve – the bundle of axons of ganglion cells that carries neural messages from each eye to the brain.

o Blind spot – the place on the retina where the axons of all the ganglion cells leave the eye and where there are no receptors.

o Optic chiasm – the point near the base of the brain where some fibers in the optic nerve from each eye cross to the other side of the brain.

o Feature detectors – specialized brain cells that only respond to particular elements in the visual field such as movement or lines of specific orientation.

o Additive color mixing – the process of mixing lights of different wavelengths to create new hues.

o Trichromatic theory – the theory of color vision that holds that all color perception derives from three different color receptors in the retina (usually red, green, and blue receptors).

o Color blindness – partial or total inability to perceive hues.

o Opponent-process theory – theory of color vision that holds that three sets of color receptors (yellow-blue, red-green, black-white) respond to determine the color you experience.

Stare at the dot on this flag for about a minute and then look at a piece of plain white paper. What do you see? Most people see an

afterimage that converts the colors in the figure into the traditional red, white, and blue U.S. flag.

The electromagnetic spectrum. The eye is sensitive to only a very small segment of the spectrum, known as visible light.

COMMON PROBLEMS OF VISIONCondition Description Treatment

Myopia (near-sightedness)

Difficulty seeing objects at a distance

Corrective lenses or corrective surgery

Presbyopia (far-sightedness)

Difficulty seeing close or highly detailed objects

Corrective lenses or corrective surgery

Astigmatism Blurred vision due to irregularities in the shape of the lens or retina

Corrective lenses or corrective surgery

Cataract A thin cloudy covering develops on the surface of the eye.

Surgery to remove the cataract

Glaucoma Build up of pressure within the eye that can lead to blindness

Diet and/or medication

Macular degeneration Degeneration of retinal cells, usually in and around the fovea; eventually causes blindness

No treatment at present

Retinitis pigmentosa Hereditary disorder that involves deterioration of cells in the retina; eventually causes blindness

No treatment at present

HEARINGo Sound: a psychological experience created by the brain

in response to changes in air pressure that are received by the auditory system.

o Eardrum: the part of the ear that vibrates when sound waves hit it.

o Sound waves: changes in pressure caused when molecules of air or fluid collide with one another and then move apart again.

o Frequency: the number of cycles per second in a wave; in sound, the primary determinant of pitch.

o Pitch: auditory experience corresponding primarily to frequency of sound vibrations, resulting in a higher or lower tone.

o Amplitude: the magnitude of a wave; in sound, the primary determinant of loudness.

Sound waves. As the tuning fork vibrates, it alternately compresses and expands the molecules of air, creating a sound wave.

o Timbre: the quality or texture of sound; caused by overtones.

o Oval window: membrane across the opening between the middle ear and inner ear that conducts vibrations to the cochlea.

o Cochlea: part of the inner ear containing fluid that can vibrate, which in turn causes the basilar membrane to vibrate.

o Basilar membrane: membrane in the cochlea of the inner ear that responds to vibrations; it contains sense receptors for sound.

o Organ of Corti: structure on the surface of the basilar membrane that contains the receptor cells for hearing.

o Auditory nerve: the bundle of axons that carries signals from each ear to the brain.

Prolonged exposure to sounds above 85 decibels can cause permanent damage to ears, as can even brief exposure to sounds near the pain threshold.

How we hear?1. Sound waves enter the outer ear and travel to the eardrum,

causing it to vibrate.2. The vibrating eardrum causes the bones of the middle ear (the

hammer, anvil, and stirrup) to strike each other, amplifying and carrying the vibrations to the oval window and on to the fluid in the coiled cochlea of the inner ear.

3. Now, the moving fluid sets the basilar membrane, inside the cochlea, moving.

4. The organ of Corti, on top of the basilar membrane, moves too. Inside the organ of Corti, thousands of tiny receptor cells are topped by a bundle of hair-like fibers. As the basilar membrane vibrates, the fibers bend, stimulating the receptor cells to send a signal through the afferent nerve endings, which join to form the auditory nerve.

5. The auditory nerve carries impulses to the brain.6. When the nerve impulses reach the temporal lobe, they are

interpreted as sounds.

At the top of each hair cell is a bundle of fibers. If the fibers bend as much as 100 trillionths of a meter, the receptor cells transmit a sensory message to the brain.

THE OTHER SENSESo SMELL (olfaction)

The human olfactory system. The sense of smell is triggered when odor molecules in the air reach the olfactory receptors located inside the top of the nose. Inhaling and exhaling odor molecules from food does much to give food its flavorful “taste.”

1. As we breathe, molecules from the flower reach the receptor cells high in each nasal cavity.

2. The axons from these millions of receptors carry nerve impulses to the olfactory bulb.

3. The olfactory bulb transmits these impulses to the temporal lobes of the brain where they are experienced as smell.

o Olfactory bulb: the small center in the brain.o Pheromones: chemicals that communicate information

to other organisms through smell.

o TASTE (gustatory) Taste buds: structures on the tongue that

contain the receptor cells for taste.

1. Different areas on the tongue are slightly more sensitive to different tastes.

2. When we eat, chemicals in the food dissolve in saliva and come into contact with the taste cells (receptors) within the taste buds.

3. Now, adjacent neurons fire, sending nerve impulses to the brain’s parietal lobe, where the messages are perceived as taste.

There are 10,000 taste buds on the tongue and other parts of the mouth. Taste buds wear out and are replaced every ten days.

o SKIN SENSES - the senses of touch, pressure, temperature, and pain.

o Gate-control theory of pain: the theory that particular nerve receptors in the spinal cord lead to specific areas of the brain related to pain.

Biopsychosocial theory: the theory that the interaction of biological, psychological, and cultural factors influences the intensity and duration of pain.

PERCEPTION

Perception: the brain’s interpretation of sensory information so as to give it meaning.

Gestalt laws of organization: a series of principles that describe how we organize bits and pieces of information into meaningful wholes.

An illusory triangle. When sensory information is incomplete, we tend to create a complete perception by supplying the missing details. In this figure we will fill in the lines that let us perceive a white triangle in the center of the pattern.

Perceiving a pattern. Knowing beforehand that the block blotches in this figure represent a person riding a horse changes our perception of it.

An optical illusion. In the case of the trident we go beyond what is sensed (black

lines on flat white paper) to perceive a three-dimensional object that isn’t really there.

Figure-ground relationship. Do you see a vase or the silhouettes of a man and a woman? Both interpretations are possible, but not at the same time. Reversible figures like this work

because it is unclear which part of the stimulus is the figure and which is the neutral ground against which the figure is perceived.

Although at first it is difficult to distinguish anything in this drawing, keep looking, and eventually you’ll probably be able to see the figure of a dog. The dog represents a gestalt, or perceptual whole, which is something greater than the sum of the individual elements.

Gestalt principles of perceptual organizations1. Proximity – When objects are close to one another, we tend to

perceive them together rather than separately.2. Similarity – Objects that are of a similar color, size, or shape are

usually perceived as part of a pattern.3. Closure – we are inclined to overlook incompleteness in sensory

information and to perceive a whole object even where none really exists.

4. Continuity – items that continue a pattern or direction tend to be grouped together as part of the pattern.

PERCEPTUAL CONSTANCY: a tendency to perceive objects as stable and unchanging despite changes in sensory stimulation.

o Shape constancy: the tendency to see an object the same shape no matter what angle it is viewed from.

Shape constancy. Even though the image of the door on the retina changes greatly as the door opens, we still perceive the door as being rectangular.

o Size constancy: the perception of an object as the same size regardless of the distance from which it is viewed.

DEPTH PERCEPTION: The ability to view the world in three dimensions and to perceive distance.

o Monocular cues: visual cues requiring the use of one eye.

o Binocular cues: visual cues requiring the use of both eyes.

o Interposition: monocular distance cue in which one object, by partly blocking a second object, is perceived as being closer.

Because the king of clubs appears to have been interposed on the king of spades, we

perceive it to be closer to us.

Because of the higher elevation and the suggestion of depth provided by the road, the tree on the right is perceived as being more distant and about the same size as the tree at lower left. Actually, it is appreciably smaller, as you can see if you

measure the heights of the two drawings.

Railroad tracks that seem to join together in the distance are an example of linear perspective.

o Perspective: monocular distance and depth cues that involve the convergence of lines, the haziness of images, and the relative elevation objects.

o Texture gradient: monocular cue to distance and depth based on the fact that objects seen at greater distances appear to be smoother and less textured.

o Shadowing: monocular cue to distance and depth based on the fact that shadows

often appear on the parts of objects that are more distant.

VISUAL ILLUSIONS: physical stimuli that consistently produce errors in perception.

REFLECTION:1. Do you think it is possible to have sensation without perception?

Is it possible to have perception without sensation? Explain why.2. Describe the basic mechanisms involved in vision, hearing, and

the other major senses.

Reference: Feldman, R. S. (2010). Understanding Psychology. 9th Edition. McGraw Hill Companies, Inc. Morris, C.G.,et al. (2007). Psychology Concepts and Applications. Pearson Education, Inc. New Jersey.

Prepared by:Mrs. Maria Angela L. Diopol

Instructor