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Perception portrayed by the rainbow: height on plane, texture gradient, and relative brightness

The five senses portrayed by the cats: vision, hearing, taste, touch and smell.

What the College Board is asking for:

The study of sensation and perception often begins with the concept of threshold. Students learn about the measurement of absolute and difference thresholds and the physical, physiological, and psychological variables affecting those measurements. Understanding the concept of thrishold allows for a study of the functioning of the various sensory receptors that transduce energy for use in the nervous system. In covering the various sensory systems, the course gives greatest emphasis to vision and audition, with less attention to the sensory systems for taste, smell, touch, pain perception, and balance/equilibrium. Coverage includes anatomy and function of the eye and ear, theories of vision and audition, perceptual acuity, sensory adaptation, and sensory disorders such as deafness and color blindness.

Perception involves the interpretation of the raw materials provided by the senses. The study of perception focuses on the interplay between characteristics of the perceiver and those of the environment in the constructive processes of attending to and organizing experiential data. Students discover how a three-dimensional world is constructed from a two-dimensional retinal image, what conditions are required for the perception of motion, and how familiar and unfamiliar patterns are perceived. Of major importance is the role played by experience in perception and the way in which perception can be improved by learning.

The oldest field of psychology is psychophysics. The question of how does what's out there get in, predates even psychology. In 1950, Gustav Fechner provided the law that allowed to study the relationship between stimulus intensity and subjective experience. The first big contribution were absolute thresholds. This is the minimum necessary to detect a particular sensation 51% of the time. The human absolute thresholds are:

Vision: can see a candle 30 miles away on a dark clear night. Hearing: ticking of watch 20 feet away in a quiet room. Taste: one teaspoon of sugar in 2 gallons of water. Smell: one drop of perfume dissoved in small house. Touch: fly wing on cheek from .4 inches.

Difference threshold is the minimum difference a person can detect between any two stimuli 51% of the time. Weber's Law documents the relationship between the size of the stimulus and the amount that needs to be added or subtracted to that stimulus so that the observer notices a difference. Ernst Weber's law states the proportion varies depending on the stimulus.

Photographs courtesy of
Psychology Archives-University of Akron

Transduction is when physical energy stimulates our sensory neurons, which convert energy into electrochemical signals that the nervous system carries to the brain.

Vision: The visual stimulus is light. Objects are sources of light if they reflect some portion of the light and absorb the rest. Light comes in waves and like all waves they can vary in intensity and wavelength. The intensity measures brightness and wavelength determines the perceived color. Our vision is only sensitive to a small portion of the elecrtomagnetic spectrum. This visible spectrum is 360 (violet) to 750 (red) nanometers between successive crests of the waves. Shorter wavelengths, called ultraviolet and longer waves called infrared cannot be detected by the human eye.

The detection of light is done by the photoreceptors, located on the retina, a layer of tissue lining the back of the eyeball. The retina (fig. 1) contains two kinds of receptor cells: rods (dim light vision) and cones (color). The cones are most plentiful in the fovea, located at the center of the retina. The rods are abundant in the periphery of the retina. The receptor cells stimulate the bipolar cells, and these excite the ganglion cells. The ganglion cells converge to make a bundle of fibers called the optic nerve. Where the optic nerve leaves the eye is called the blind spot. It is important that you can identify and describe the function of the following eye structures: pupil, cornea, iris, lens, and scelera.

Color vision is dependent of three different kinds of cones; this is why our color vision is called trichromatic. These three primary colors are red, green and blue. These three colors in different combinations give use our perception of color. The Young-Helmholtz theory , simply states that when we stimulate any combination of these three cones, we see other colors. There is a Barney song that says, "When you mix red and green it makes yellow, when you mix...". Most

color deficient people are not actually "color blind." They simply lack functioning red-green sensitive cones (fig.2). Their vision is dichromatic, making it difficult to distinguish red and green. Soon Ewald Hering thought it strange that people red-green color blind still see yellow. So how is it that those blind to red and green can often still see yellow? His clue came in the form of afterimages (fig. 3). Hering's opponent-process theory states 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. Thus, the present solution to the mystery of color vision is therefore roughly this: Color processing occurs in two stages. The retina's red, green, and blue cones respond to different wavelengths of electro-magnetic energy, as the Young-Helmholtz trichromatic theory suggested. Their signals are then processed by the nervous system's opponent-process cells located in the thalamus en route to the visual cortex.

Myers, Sixth ed.

Fig. 2 Color deficient vision: people who suffer red-green deficiency have trouble perceiving the number within the design.

Hearing: Scientifically named audition. We hear a wide range of sounds, with normal human conversation being the most sensitive. It's just amazing how sensitive we are to all the different sounds and human voices we come in contact with throughout our lives. The stimulus that allows us to hear comes through sound waves, which are bouncing molecules of air. This compressed and expanded air creates a ripple that can then be detected by our ear. A sound wave varies in wavelength and amplitude. The amplitude determines loudness, while the wavelength determines its pitch (how high or low the sound is). Decibles are the measuring unit for sound energy. Normal conversation is 60 decibels and overexposure to 85 or more decibles can cause hearing loss.

To hear, we must somehow get the sound waves transduced into neural activity. This is accomplished by the ear. It is basically a tree step process. The first is the eardrum, a tight membrane that vibrates with the waves. The middle ear takes these vibrations and passes them through a piston made of three tiny bones called the Hammer, Anvil, and Stirrup. These bones compress the air so that the vibrations that strike the oval window can vibrate the fluid that fills the cochlea. Within the cochlea is the basilar membrane that is lined with hair cells. This rippling of the basilar membranebends these hairs cells, like wind in a wheat field. The movement of the hair cells triggers impulses in the adfacent nerve fibers, which converge to form the auditory nerve.

The delicate structure of the ear makes it vulnerable to hearing loss. One type of hearing loss is conduction hearing loss. This is when the eardrum is punctured or the three bones stop vibrating. Hearing aides are used to help amplify vibrations for frequencies that are the lowest (usually high). Damage to the cochlea's hair cells can cause sensorineural hearing loss. Disease, aging, or head-splitting noise are the culprits. Once the tissue is dead it stays dead. A hearing device can help to trigger surrounding live tissue.

Fig. 3 If you were to stare at this sort of picture for a minute and look at a white sheet of paper you would see a red, white, and blue flag. Tiring the neural responses to these colors would allow you to see their opponent colors.

Hammer

Anvil

Stirrup

Semicircular canals

Oval Window

Auditory Nerve

Nerve Fibers

Cochlea

Protruding cilia

Before we move onto perception let's discuss sensory adaptation (process of adjustment). Our senses have diminished sensitivity to constant stimulation. This continuous stimulation causes our nerve cells to fire less frequently. It enables us to focus our attention on informative changes without being distracted by uninformative stimulation.

Eardrum

Perception comes to us one perception at a time. In this sense, our attention is selective and allows us to only focus our awareness on one aspect at a time. There are three questions that our perceptual brain asks: where is it?, what is it?, and where is it going?.

The perception of depth (where is it?) leads researchers to understand depth cues. A depth cue is a stimulus situation that indicates how far an object is from the observer. There are two types: binocular and monocular cues. Binocular cues use both eyes and monocular cues can detect depth with only one eye.

Binocular: Retinal disparity comes from the fact that we have two eyes that look onto the world at slighly different angles; as a result sees a slightly different view.This difference induces the perception of depth.

Covergence: the second binocular cue uses the ossicles muscles surrounding the eye to detect depth. The closer an object, the greater the muscle strain to keep it in focus. This strain is a cue that the object is closer to us.

The monocular cues are discussed in the notes and examples can be seen in the slides.

The perception of depth can also be detected through motion. This is called motion parallax. For example, as a car moves forward, its position changes relative to stationary objects in its environment. Objects closer to the car move across our retina faster than objects in the distance.

Finally, we will discuss illusions of motion. The three illusions are autokinetic, stroboscopic, and Phi phenomenon. Autokinetic is the illusion of seeing light move in a dark room. Stroboscopic motion is provided by the presentation of a rapid progression of images of stationary objects. The Phi phenomenon is when a row of lights are swithched on and off to induce motion.

The perception of form (what is it?) leads researchers to the most important question of all: How do we recognize what an object is? One theory is that we have a memory checklist that we go through to determine what the object is. This seems too simple. Another theory is that we group perceive things by its whole and not sum parts. For example, a circle overlapping the corner of a square is still seen as a square and a circle even though the square is incomplete. This mental activity is called Gestalt Psychology, which we percieve things as intact or whole. Gestalt principles can be found in the notes link.

In the left eye's view, the image cast y A and that cast by B are close together; in the right-eye's view, the images are further apart. This disparity between the views serves as a powerful cue for depth. (Hochberg, 1978)

Sensation-Perception Review-Gleitman