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SENSATION AND PERCEPTION 4 Sensation refers to the detection of physical energy by our sense organs, including our eyes, ears, skin, nose, and tongue, which then relay information to the brain. Perception is the brain’s interpretation of these raw sensory inputs. In other words, sensation first allows us to pick up the signals in our environments, and perception then allows us to assemble these signals into something meaningful. Most of the time, filling-in (perception) is adaptive, as it helps us make sense of our often confusing and chaotic perceptual worlds. But sometimes it can fool us, as in the case of visual illusions (naive realism). Sensation: Transduction The first step in sensation is converting external energies or substances into a “language” the nervous system understands (action potential). Transduction is thus, the process by which the nervous system converts an external stimulus, like light or sound, into electrical signals within neurons. A specific type of sense receptor , or specialized cell, transduces a specific stimulus: cells at the back of the eye transduce light, cells in a spiral-shaped organ in the ear transduce sound, odd looking endings attached to axons embedded in deep layers of the skin transduce pressure, receptor cells lining the inside of the nose transduce airborne odorants, and taste buds transduce chemicals containing flavor. For all of our senses, activation is greatest when we first detect a stimulus. After that, our response declines in strength, a process called sensory adaptation. This occurs to conserve energy and attentional resources. psychophysics , the study of how we perceive sensory stimuli based on their physical characteristics. o absolute threshold of a stimulus is the lowest level of a stimulus we can detect on 50 percent of the trials when no other stimuli of that type are present. For instance, how loud does something have to be until we can actually hear it. o just noticeable difference (JND) is the smallest change in the intensity of a stimulus that we can detect. Essentially, it is our ability to distinguish a stronger from a weaker stimulus (quiet voice vs. loud voice). It is the question of “how much of a difference in a stimulus makes a difference?” o Weber’s law states that there’s a constant proportional relationship between the JND and the original stimulus intensity. The stronger the stimulus, the bigger the change needed for a change in stimulus intensity to be noticeable. Example: the light we need to add to a brightly lit room to notice an increase in illumination >>>> the amount of light we need to add to a dark bedroom to notice a change in illumination Signal detection theory describes how we detect stimuli under uncertain conditions (condition in which it is hard to determine a signal) o Signal-to-noise ratio : It becomes harder to detect a signal as background noise increases o Response biases is the tendency to make one type of guess over another when we’re in doubt about whether a weak signal is present or absent under noisy conditions.
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