![]() ![]() If a person participates in an experiment and receives one dollar for each Hit and there is no penalty for a False Alarm, then it is in the person's best interest to say that the stimulus was present whenever there is uncertainty. Psychologists have established that when stimuli are difficult to detect, cognitive factors are critical in the decision an observer makes. The table refers to a task with an auditory stimulus, but it could be modified to involve stimuli for any sense. The accompanying table describes the combination of an observer's response and whether the stimulus is actually there. There are two possible responses, "Yes" and "No." There are also two different possibilities for the stimulus, either present or absent. The person responds positively (i.e., there is a stimulus) or negatively (i.e., there is no stimulus). In a typical sensory experiment that involves a large number of trials, an observer must try to detect a very faint sound or light that varies in intensity from clearly below normal detection levels to clearly above. This person is "detecting" a stimulus, or signal, that is not there because it would be worse to miss the person than to check to see if the individual is there, only to find that the visitor has not yet arrived. As time goes on, the person begins to "hear" the visitor and may open the door, only to find that nobody is there. ![]() Suppose a person is expecting an important visitor, someone that it would be unfortunate to miss. Finally, when a person is quite uncertain as to whether the stimulus was present, the individual will decide based on what kind of mistake in judgment is worse: to say that no stimulus was present when there actually was one or to say that there was a stimulus when, in reality, there was none.Īn example from everyday life illustrates this point. Further, a more sensitive person requires less stimulus intensity than a less sensitive person would. In other words, a person will be able to detect more intense sounds or lights more easily than less intense stimuli. Instead, the theory involves treating detection of the stimulus as a decision-making process, part of which is determined by the nature of the stimulus, by how sensitive a person is to the stimulus, and by cognitive factors. This approach abandons the idea of a threshold. In general, psychologists typically define threshold as that intensity of stimulation that a person can detect some percentage of the time, for example, 50 percent of the time.Īn approach to resolving this dilemma is provided by signal detection theory. ![]() There is no single, fixed value below which a person never detects the stimulus and above which the person always detects it. Factors other than the sensitivity of sense receptors influence the signal detection process. Unfortunately, one of the problems with this concept was that even though the level of stimulation remained constant, people were inconsistent in detecting the stimulus. This activity led to the development of the idea of a threshold, the least intense amount of stimulation needed for a person to be able to see, hear, feel, or detect the stimulus. One of the early goals of psychologists was to measure the sensitivity of our sensory systems. A psychological theory regarding a threshold of sensory detection. ![]()
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