Psychologists originally used the term short-term memory to refer to the ability to hold information in mind over a brief period of time. As conceptions of short-terra memory expanded to include more than just the brief storage of information, psychologists created new terminology. The term working memory is now commonly used to refer to a broader system that both stores information briefly and allows manipulation and use of the stored information. Psychologists often study working memory storage by examining how well people remember a list of items. In a typical experiment, people are presented with a series of words, one every few seconds. Then they are instructed to recall as many of the words as they can, in any order. Most people remember the words at the beginning and end of the series better than those in the middle. This phenomenon is called the serial position effect because the chance of recalling an item is related to its position in the series. In this experiment, recall was tested either immediately after presentation of the list items or after 30 seconds. Subjects in both conditions demonstrated what is known as the primacy effect, which is better recall of the first few list items. Psychologists believe this effect occurs because people tend to process the first few items more than later items. Subjects in the immediate-recall condition also showed the recency effect, or better recall of the last items on the list. Working memory has a basic limitation: It can hold only a limited amount of information at one time. Early research on short-term storage of information focused on memory span--bow many items people can correctly recall in order. More recent studies have attempted to separate true storage capacity from processing capacity by using tests more complex than memory span. These studies have estimated a somewhat lower short-term storage capacity than did the earlier experiments. People can overcome such storage limitations by grouping information into chunks, or meaningful units. Working memory is critical for mental work, or thinking. The ability to carry out these kinds of calculations depends on working memory capacity, which varies individually. Studies have also shown that working memory changes with age. As children grow older, their working memory capacity increases. Working memory declines in old age and in some types of brain diseases, such as Alzheimer's disease. Working memory capacity is correlated with intelligence (as measured by intelligence tests). This correlation has led some psychologists to argue that working memory abilities are essentially those that underlie general intelligence. In addition, research suggests that there are different types of working memory. For example, the ability to hold visual images in mind seems independent from the ability to retain verbal information. The concept of working memory is ______ that of short memory.