Short-term memory, sometimes referred to as "primary", "working" or "active" memory, is said to hold a small amount of information for about 20 seconds. Estimates of short-term memory capacity vary -- from about 3 or 4 elements (i.e., words, digits, or letters) to about 9 elements: a commonly cited capacity is 7±2 elements. In contrast, long-term memory indefinitely stores a seemingly unlimited amount of information. Short-term memory can be described as the capacity (or capacities) for holding in mind, in an active, highly available state, a small amount of information. The information held in short-term memory may be: recently processed sensory input; items recently retrieved from long-term memory; or the result of recent mental processing, although that is more generally related to the concept of working memory. This book presents the latest research in the field from around the world.