Wednesday, January 23, 2013

Sensory Memory

Sensory memory refers to the initial, momentary recording of information in our sensory systems. When sensations strike our eyes, they linger briefly in the visual system. This kind of sensory memory is called iconic memory and refers to the usually brief visual persistence of information as it is being interpreted by the visual system. Echoic memory is the name applied to the same phenomenon in the auditory domain: the brief mental echo that persists after information has been heard. Similar systems are assumed to exist for other sensory systems (touch, taste, and smell), although researchers have studied these senses less thoroughly.

American psychologist George Sperling demonstrated the existence of sensory memory in an experiment in 1960. Sperling asked subjects in the experiment to look at a blank screen.

Subjects were then asked to recall as many letters from the image as they could. Most could only recall four or five letters accurately. Subjects knew they had seen more letters, but they were unable to name them. Sterling hypothesized that the entire letter-array image registered briefly in sensory memory, but the image faded too quickly for subjects to “see” all the letters. To test this idea, he conducted another experiment in which he sounded a tone immediately after flashing the image on the screen. A high tone directed subjects to report the letters in the top row, a medium tone cued subjects to report the middle row, and a low tone directed subjects to report letters in the bottom row. Sperling found that subjects could accurately recall the letters in each row most of the time, no matter which row the tone specified. Thus, all of the letters were momentarily available in sensory memory.

Sensory memory systems typically function outside of awareness and store information for only a very short time. Iconic memory seems to last less than a second. Echoic memory probably lasts a bit longer; estimates range up to three or four seconds. Usually sensory information coming in next replaces the old information. For example, when we move our eyes, new visual input masks or erases the first image. The information in sensory memory vanishes unless it captures our attention and enters working memory.

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