Hockenbury Discovering Psychology 5th txtbk

236 CHAPTER 6 Memorymaintenance rehearsalThe mental or verbal repetition of informationin order to maintain it beyond theusual 20-second duration of short-termmemory.chunkingIncreasing the amount of informationthat can be held in short-term memory bygrouping related items together into asingle unit, or chunk.Demonstration of Short-Term MemoryCapacityRow 1 — 8 7 4 6Row 2 — 3 4 9 6 2Row 3 — 4 2 7 7 1 6Row 4 — 5 1 4 0 8 1 3Row 5 — 1 8 3 9 5 5 2 1Row 6 — 2 1 4 9 7 5 2 4 8Row 7 — 9 3 7 1 0 4 2 8 9 7Row 8 — 7 1 9 0 4 2 6 0 4 1 8U A V F C I D B D S A IThe Duration of Short-Term MemoryGoing, Going, Gone!Information in short-term memory lasts longer than information in sensory memory,but its duration is still very short. Estimates vary, but generally you can holdmost types of information in short-term memory up to about 20 seconds before it’sforgotten (Peterson & Peterson, 1959). However, information can be maintainedin short-term memory if it is rehearsed, or repeated, over and over. Because consciouslyrehearsing information will maintain it in short-term memory, this processis called maintenance rehearsal. For example, suppose that you decide to order apizza for yourself and some friends. You look up the number in the phone book andmentally rehearse it until you can dial the phone.Information that is not actively rehearsed is rapidly lost. Why? One possible explanationis that information that is not maintained by rehearsal simply fades away, ordecays, with the passage of time. Another potential cause of forgetting in short-termmemory is interference from new or competing information (Baddeley, 2002;Nairne, 2002). For example, if you are distracted by one of your friends asking youa question before you dial the pizza place, your memory of the phone number willquickly evaporate. Interference may also explain the irritating experience of forgettingsomeone’s name just moments after you’re introduced to him or her. If youengage the new acquaintance in conversation without rehearsing his or her name, theconversation may “bump” the person’s name out of your short-term memory.The Capacity of Short-Term MemorySo That’s Why There Were Seven Dwarfs!Along with having a relatively short duration, short-term memory also has a relativelylimited capacity. This is easy to demonstrate. Take a look at the numbers inthe margin. If you’ve got a friend handy who’s willing to serve as your research subject,simply read the numbers out loud, one row at a time, and ask your friend torepeat them back to you in the same order. Try to read the numbers at a steady rate,about one per second. Note each row that he correctly remembers.How many numbers could your friend repeat accurately? Most likely, he couldcorrectly repeat between five and nine numbers. That’s what psychologist GeorgeMiller (1956) described as the limits of short-term memory in a classic paper titled“The Magical Number Seven, Plus or Minus Two.” Miller believed that the capacityof short-term memory is limited to about seven items, or bits of information, atone time. It’s no accident that local telephone numbers are seven digits long(Cowan & others, 2004).So what happens when your short-term memory store is filled to capacity? Newinformation displaces, or bumps out, currently held information. Maintenancerehearsal is one way to avoid the loss of information from short-term memory. Byconsciously repeating the information you want to remember, you keep it active inshort-term memory and prevent it from being displaced by new information.Although the capacity of your short-term memory is limited, there are ways toincrease the amount of information you can hold in short-term memory at anygiven moment. To illustrate this point, let’s try another short-term memory demonstration.Read the sequence of letters in the margin, then close your eyes and try torepeat the letters out loud in the same order.How many letters were you able to remember? Unless you have an exceptionalshort-term memory, you probably could not repeat the whole sequence correctly.Now try this sequence of letters: D V D F B I U S A C I A.You probably managed the second sequence with no trouble at all, even thoughit is made up of exactly the same letters as the first sequence. The ease with whichyou handled the second sequence demonstrates chunking—the grouping of relateditems together into a single unit. The first letter sequence was perceived as 12 separateitems and probably exceeded your short-term memory’s capacity. But the