Donald Hebb (19041985) was the first to come up with a way to tell the difference between short-term and long-term memory. When the brain receives an input, like something that is seen or heard, a sensory memory keeps a copy of what is seen or heard, but this memory lasts for only about a few seconds. Anything that is kept in the brain longer depends on our selective attention. Things that we "notice" are kept in short-term memory for up to a few minutes. This memory is thought to be dependent on electrical activity in the brain and is easily destroyed by interruption or interference. Short-term memory includes iconic memory as well, which holds visual images; acoustic memory, to hold sounds; and working memory, which is an active process to keep a memory until it is put to use.