![]() Your task is to determine whether the neural activity that you are experiencing is due to the background noise alone or is the result of a signal within the noise. Because our ears are constantly sending background information to the brain, you will sometimes think that you heard a sound when none was there, and you will sometimes fail to detect a sound that is there. The problem for you is that the very faint signals create uncertainty. The signals are purposefully made to be very faint, making accurate judgments difficult. On each of the trials your task is to indicate either “yes” if you heard a sound or “no” if you did not. Imagine, for instance, that you were asked to take a hearing test. In a typical psychophysics experiment, an individual is presented with a series of trials in which a signal is sometimes presented and sometimes not, or in which two stimuli are presented that are either the same or different. The absolute threshold of a sensation is defined as the intensity of a stimulus that allows an organism to just barely detect it. One important criterion is the ability to detect very faint stimuli. The measurement techniques developed by Fechner and his colleagues are designed in part to help determine the limits of human sensation. The field of psychophysics was founded by the German psychologist Gustav Fechner (1801-1887), who was the first to study the relationship between the strength of a stimulus and a person’s ability to detect the stimulus. Psychophysics is the branch of psychology that studies the effects of physical stimuli on sensory perceptions and mental states. What looks like a black bird to us is in colour for a bird. Birds can see ultraviolet light humans cannot. Figure 6.3 Ultraviolet Light and Bird Vision. Each species is adapted to sensing the things that are most important to them, while being blissfully unaware of the things that don’t matter. The fact that different organisms have different sensations is part of their evolutionary adaptation. ![]() Cats have an extremely sensitive and sophisticated sense of touch, and they are able to navigate in complete darkness using their whiskers. Birds are able to see the ultraviolet light that we cannot (see Figure 6.3, “Ultraviolet Light and Bird Vision”) and can also sense the pull of the earth’s magnetic field. Dogs (Figure 6.2), bats, whales, and some rodents all have much better hearing than we do, and many animals have a far richer sense of smell. The dog’s highly sensitive sense of smell is useful for searches of missing persons, explosives, foods, and drugs.Īlthough there is much that we do sense, there is even more that we do not. Video: How Old Are Your Ears? (Hearing Test) Figure 6.2 Smell. To get an idea of the range of sounds that the human ear can sense, test your hearing by watching the following video. We can feel the wing of a bee on our cheek dropped from one centimeter above (Galanter, 1962). We can taste a teaspoon of sugar dissolved in two gallons of water, and we are able to smell one drop of perfume diffused in a three-room apartment. The human ear can detect sounds as low as 20 hertz ( vibrations per second) and as high as 20,000 hertz, and it can hear the tick of a clock about 20 feet away in a quiet room. The human eye can detect the equivalent of a single candle flame burning 30 miles away and can distinguish among more than 300,000 different colours. In many ways our senses are quite remarkable. ![]() The human perceptual system is wired for accuracy, and people are exceedingly good at making use of the wide variety of information available to them (Stoffregen & Bardy, 2001). Our tongues react to the molecules of the foods we eat, and our noses detect scents in the air. Our skin senses touch, pressure, hot, and cold. Our eyes detect light energy and our ears pick up sound waves. Humans possess powerful sensory capacities that allow us to sense the kaleidoscope of sights, sounds, smells, and tastes that surround us. Sensory Thresholds: What Can We Experience? Explain the difference between sensation and perception and describe how psychologists measure sensory and difference thresholds.Review and summarize the capacities and limitations of human sensation.
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