Sensory memory is the temporary storage of sensory information for reference, lasting in terms of seconds. If a person wants to convert a sensory memory into a permanently stored memory, he will need to pay attention to the sensory input so the brain knows to file it in a more permanent location. Numerous studies have explored sensory memory and the way it works. It plays an important role in cognition, perception, and performance of tasks.
Under normal conditions, an experience like a sight, sound, or touch will be held in the brain for a few seconds and then discarded. This can create strange sensory phenomena, like the sense that a train whistle is still blowing after it has stopped, or the appearance of visual blurring when a bright object is dragged against a dark background. Some displays rely on this aspect of sensory memory and have the brain fill in part of an image from its temporary memory while flashing the next segment.
Haptic, iconic, and echoic memory are all different types of sensory memory, covering touch, vision, and sound, respectively. For a memory to stick for more than a few seconds, it needs to stand out. Traumatic visuals, for example, often enter long term memory because the person is shocked or upset by the sight of a car accident or other traumatic event. Likewise, a waitress may be able to remember an order without having to write it down when she focuses on the customer as he speaks.
The fleeting nature of sensory memory also explains why people sometimes have poor memory for something they have just seen, heard, or touched. If a student is distracted while looking something up, for instance, she will read the relevant information, flip back to what she was doing, and realize that she cannot remember what she's just read. Likewise, when a family member shouts a phone number at someone running out the door, that person may not remember the number when he goes to call it several hours later.
The brain can store about seven units of information in its sensory memory before it has to make room for more by either discarding or storing the information. It can be important to be aware of this during study sessions, as chunking information can make it easier to remember. Numbers provided in sets, for example, are easier to remember than a long string. Many people can remember a phone number like 555-1212 but couldn't remember the string 5551212.