You can see that in this case making a false alarm by alerting the other soldiers to the sound might not be as costly as a miss (a failure to report the sound), which could be deadly. Imagine, for instance, that rather than taking a hearing test, you are a soldier on guard duty, and your job is to detect the very faint sound of the breaking of a branch that indicates that an enemy is nearby. The other measure, response bias, refers to a behavioural tendency to respond “yes” to the trials, which is independent of sensitivity. People who have better hearing will have higher sensitivity than will those with poorer hearing. One measure, known as sensitivity, refers to the true ability of the individual to detect the presence or absence of signals. The analysis of the data from a psychophysics experiment creates two measures. Two of the possible decisions (hits and correct rejections) are accurate the other two (misses and false alarms) are errors. Our ability to accurately detect stimuli is measured using a signal detection analysis. In the other two cases you respond “no” - either a miss (saying “no” when there was a signal) or a correct rejection (saying “no” when there was in fact no signal).įigure SAP.2 Outcomes of a Signal Detection Analysis. A false alarm occurs when you respond “yes” to no signal. As you can see in Figure SAP.2, “Outcomes of a Signal Detection Analysis,” each judgment trial creates four possible outcomes: A hit occurs when you, as the listener, correctly say “yes” when there was a sound. Signal detection analysis is a technique used to determine the ability of the perceiver to separate true signals from background noise (Macmillan & Creelman, 2005 Wickens, 2002). The responses that you give on the hearing test can be analyzed using signal detection analysis. 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. We also have sensory systems that provide information about balance (the vestibular sense), body position and movement (proprioception and kinesthesia), pain (nociception), and temperature (thermoception). It turns out that this notion of five senses is oversimplified. You have probably known since elementary school that we have five senses: vision, hearing (audition), smell (olfaction), taste (gustation), and touch (somatosensation). The conversion from sensory stimulus energy to action potential is known as transduction. These cells relay messages, in the form of action potentials (as you learned when studying biopsychology), to the central nervous system. For example, light that enters the eye causes chemical changes in cells that line the back of the eye. When sensory information is detected by a sensory receptor, sensation has occurred. What does it mean to sense something? Sensory receptors are specialized neurones that respond to specific types of stimuli. Discuss the roles attention, motivation, and sensory adaptation play in perception.Describe the concepts of absolute threshold and difference threshold.Distinguish between sensation and perception.By the end of this section, you will be able to:
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