module 8 - sensation and absolute threshold,

sensation

The activation of the sense organs by a source of physical energy.

psychophysics

The study of the relationship between the physical aspects of stimuli and our psychological experience of them. Questions of stimulus type and intensity are considered in a branch of psychology known as psychophysics. Psychophysics played a central role in the development of the field of psychology. Many of the first psychologists studied issues related to psychophysics, and there is still an active group of psychophysics researchers.

Weber's law (Weber is pronounced "VAY-ber")

A basic law of psychophysics stating that a just noticeable difference is a constant proportion to the intensity of an initial stimulus (rather than a constant amount). The size of a stimulus that constitutes a just noticeable difference depends on the initial intensity of the stimulus. The relationship between changes in the original size of a stimulus and the degree to which a change will be noticed forms one of the basic laws of psychophysics: Weber's law. Weber's law holds for every type of sensory stimuli: vision, sound, taste, and so on. For example, Weber found that the just noticeable difference for weight is 1:50. Consequently, it takes a 1-ounce increase in a 50-ounce weight to produce a noticeable difference, and it would take a 10-ounce increase to produce a noticeable difference if the initial weight were 500 ounces. In both cases, the same proportional increase is necessary to produce a just noticeable difference (1:50 = 10:500). Similarly, the just noticeable difference distinguishing changes in loudness between sounds is larger for sounds that are initially loud than it is for sounds that are initially soft, but the proportional increase remains the same.

senses

Although perhaps you were taught, as I was, that there are just five senses—sight, sound, taste, smell, and touch—that enumeration is too modest. Human sensory capabilities go well beyond the basic five senses. For example, we are sensitive not merely to touch but to a considerably wider set of stimuli—pain, pressure, temperature, and vibration, to name a few. In addition, vision has two subsystems—relating to day and night vision—and the ear is responsive to information that allows us not only to hear but also to keep our balance.

absolute threshold

The smallest intensity of a stimulus that must be present for the stimulus to be detected. Despite the "absolute" in absolute threshold, things are not so cut and dried. As the strength of a stimulus increases, the likelihood that it will be detected increases gradually. Technically, then, an absolute threshold is the stimulus intensity that is detected 50% of the time. It often takes a very small stimulus to produce a response in our senses. For example, the sense of touch is so sensitive that we can feel a bee's wing falling on our cheeks when it is dropped from a distance of 1 centimeter. In fact, our senses are so fine-tuned that we might have problems if they were any more sensitive. For instance, if our ears were slightly more acute, we would be able to hear the sound of air molecules in our ears knocking into the eardrum—a phenomenon that would surely prove distracting and might even prevent us from hearing sounds outside our bodies.

perception

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

adaptation

An adjustment in sensory capacity after prolonged exposure to unchanging stimuli. for example, You enter a movie theater, and the smell of popcorn is everywhere. A few minutes later, though, you barely notice the smell. The reason you become accustomed to the odor is sensory adaptation. Adaptation occurs as people become accustomed to a stimulus and change their frame of reference. In a sense, our brain mentally turns down the volume of the stimulation that it's experiencing. Although initially difficult to tolerate, exposure to cold temperatures eventually becomes less unpleasant due to the phenomenon of adaptation.

stimulus

Energy that produces a response in a sense organ. Stimuli vary in both type and intensity. Different types of stimuli activate different sense organs. For instance, we can differentiate light stimuli (which activate the sense of sight and allow us to see the colors of a tree in autumn) from sound stimuli (which, through the sense of hearing, permit us to hear the sounds of an orchestra). In addition, stimuli differ in intensity, relating to how strong a stimulus needs to be before it can be detected.

noise

Of course, the absolute thresholds we have been discussing are measured under ideal conditions. Normally our senses cannot detect stimulation quite as well because of the presence of noise. Noise, as defined by psychophysicists, is background stimulation that interferes with the perception of other stimuli. Hence, noise refers not just to auditory stimuli, as the word suggests, but also to unwanted stimuli that interfere with other senses. For example, picture a talkative group of people crammed into a small, crowded room at a party. The din of the crowd makes it hard to hear individual voices. In this case, the crowded conditions would be considered "noise," because they are preventing sensation at more discriminating levels. Similarly, we have limited ability to concentrate on several stimuli simultaneously.

More about adaptation

One example of adaptation is the decrease in sensitivity that occurs after repeated exposure to a strong stimulus. If you were to hear a loud tone over and over, eventually it would begin to sound softer. Similarly, although jumping into a cold lake may be temporarily unpleasant, eventually you probably will get used to the temperature. This apparent decline in sensitivity to sensory stimuli is due to the inability of the sensory nerve receptors to fire off messages to the brain indefinitely. Because these receptor cells are most responsive to changes in stimulation, constant stimulation is not effective in producing a sustained reaction. Judgments of sensory stimuli are also affected by the context in which the judgments are made. This is the case because judgments are made not in isolation from other stimuli but in terms of preceding sensory experience.

difference threshold (just noticeable difference)

The smallest level of added or reduced stimulation required to sense that a change in stimulation has occurred. the difference threshold is the minimum change in stimulation required to detect the difference between two stimuli, and so it also is called a just noticeable difference.

more about Weber's law

Weber's law helps explain why a person in a quiet room is more startled by the ringing of a cellphone than is a person in an already noisy room. To produce the same amount of reaction in a noisy room, a cellphone ring would have to be set to a much higher level. Similarly, when the moon is visible during the late afternoon, it appears relatively dim. On the other hand, the moon appears much brighter when it is in the dark night sky. (more examples of Weber's law) If you are buying drinks with your friends at $5 each and there is a nicer drink that costs $10, you might hesitate to buy it because $5 extra seems like too much, but if you're buying a piece of furniture for $500 and see something you like better for $505, you'll probably take it, because $5 doesn't seem like that much of a difference. You'd notice if the better piece of furniture was $1000, and would probably be hesitant to buy it. If you have 20 glass beads and someone steals ten, you'll definitely notice the difference. If you have 200 glass beads and someone steals ten, you probably won't.