Chapter 8 Memory Memory is the process of maintain information over time. It is the most basic concept of human cognition. We use memory in our everyday life as remembering an incident from childhood or some event from the recent past. Memory helps us learn from our experiences. It is only when we remember what has happened in the past we do not repeat the behavior again, or indulge in it more if it was gratifying. Memory is internal record of some prior event or experience; a set of mental processes that receives, encodes stores, organizes, alters, and retrieves information over time. The basic processes of memory are encoding, storage and retrieval. Encoding is the process of translating information into neural codes that will be retained in memory. Information which is presented in the form of language is encoded in the form of mental representations. Storage is the process of retaining neural coded information over time. If any piece of information is stored properly it can be retrieved later. Retrieval is the process of recovering information from memory storage. Retrieval failure is possible if the information is not stored properly or is not accessed. Such retrieval failure is called forgetting. MULTI STORE MODEL OF MEMORY: Atkinson and Shiffrin proposed the modal model of memory. According to this model there are three different kinds of memory namely, sensory memory, short term memory and long term memory. This model assumes that each type of memory receives processes and stores information differently. The sensory memory receives information from the sensory registers namely eyes, ears, nose, skin. Vast amount of information is received from the sensory registers as it includes every object seen, heard or felt in the environment. The information which is paid attention to in this stage enters the short term memory. In short term memory or short term storage the information is stored for 20 to 30 seconds. Short term memory has limited capacity and can store 5 to 9 bits of information at a time. If the information is rehearsed and paid even more attention to enter the unlimited store of information called the Long term memory also known as Long term storage. Information which is required to be known for a longer period of time is stored in the long term storage. For example, spellings of words are stored in Long term memory which can be retrieved with ease at any point of time. SENSORY MEMORY: Sensory memory is the memory for events from the sensory inputs which we encounter every now and then in our surrounding. It is the raw material which forms the basis of any sort of memory stored by the human mind. The two main types of sensory memory studied widely are, Iconic memory i.e. memory for events or aspects which are visually encountered and Echoic Memory i.e. memory for auditory information. Iconic memory: Sperling suggested that when stimuli consisting of a number of items are shown briefly to an observer, only a limited number of the items can be correctly reported. The fact that observers assert they can see more than they can report suggests the memory sets a limit on a processes that is otherwise rich in information. He conducted the first experiment to understand the properties of iconic memory. He presented the participants with display of letters or numbers (figure 1). Letters were presented for a brief period of time, for 50 milliseconds. Sperling found that participants could recall 4 or 5 letters of the 12 letters presented. Figure 1: Display used by Sperling He further extended the display time to 500 milliseconds but it did not improve the performance. He then invented the partial report technique. After presenting the display the participants were presented with a low, medium, or a high pitched tone. Low pitched tone indicated recalling the letter in the bottom row, medium tone - middle row and high tone - upper row. Participants could recall 3 out of 4 items from any row when presented with the tone. Sperling explained that in the initial display of recalling all letters together, which he called the whole report technique, participants forgot the letter which came letter in the attempt to name the initial letters. Even when they were recalling the display, the information was fading from wherever it was being stored. This explains that information lasts only briefly in this memory system. Neisser gave the term ‘icon’ for the visual sensory memory. It holds the visual information for up to 1 second. Sperling presented participants with consonants and vowels and different tones for the recall for either vowels or consonants. However the participant’s performance was no different than the whole report technique. Sperling thus inferred that icon holds information that has not yet been categorized. Echoic memory: Neisser called the auditory sensory memory ‘echo’. Moray, Bates, and Barnett (1965) studied the echoic memory in a clever demonstration. Participants were made to listen to multiple messages simultaneously. In the whole report technique participants were made to recall all the letters they heard. In partial report technique participant was visually cued to report letters spoken on the specific speakers by presenting lights corresponding the speakers. Results of this study showed that a greater number of letters could be recalled through the partial report procedure than whole report technique. Thus, they concluded that one second after the auditory display, there is more information available than can be reported by the whole report procedure. Information was lost after about 4 seconds. Crowder (1982) studied the duration of the echo. He presented the participants with two vowels, one after the other. Sometimes the vowels were identical and other times they were different but similar. He used a Varied inter stimulus interval from 1/2 sec to 5 sec. The participants had to report whether the letters were the same or different than what was earlier presented. The results of the study showed that performance was most accurate where less than a second occurred between presentations reaching asymptote at about 3 sec. He thus concluded that the duration of the echo is 3 seconds. Cowan (1984) posited a short auditory store that decays in less than 1 sec and is pre categorical in nature. Echoic memory is similar to Iconic memory in that there is more information accessible than can be recalled. Echoic memory is different in that the trace lasts longer than a second SHORT TERM MEMORY: Short term memory Atkinson and Shiffrin proposed that information that had been attended to in the sensory stores went into a short-term store (also called short-term memory). There are three key aspects of short term memory: It has limited capacity .i.e., only about 5 to 9 items can be stored at a time It has limited duration i.e., storage is very fragile and information can be lost with distraction or passage of time Encoding in short term memory is primarily acoustic. It also translates visual information into sounds. Chunking is a phenomenon where participants group the information they are trying to remember. Participants demonstrate "chunking" in serialand free recall tasks. Test items may be formed of words, lists of letters ornumbers. Chunking is a process wherein responses based on the items' semantic relatedness or perceptual features are made. The chunks are often meaningful to the participant. Capacity: Miller’s (1956) Magic number 7 (plus or minus two) offersproof for the capacity of short term memory. Most adults can store between 5 and 9 items in their short-term memory. He thought that short term memory could hold 7 (plus or minus 2 items) because it only had a certain number of “slots” in which items could be stored. However, Miller didn’t specify the amount of information that can be held in each slot. Indeed, if we can “chunk” information together we can store a lot more information in our short term memory. Miller’s theory is provided evidence to by means of various studies, such as Jacobs (1887). He made use of the digit span test with every letter in the alphabet and numbers. However he did not use the alphabet “w” and the digit “7” because they had two syllables. The results of his study suggested that people can recall numbers better than letters. According to Atkinson and Shiffrin (1971), the duration of short term memory seems to be between 15 and 30 seconds. Items can be kept in short term memory by repeating them verbally (acoustic encoding), and by means of rehearsal. Peterson and Peterson (1959) showed that the longer the delay, the less information is recalled. They used a technique called the Brown-Peterson technique which prevents the possibility of retrieval by having participants count backwards from a digit for up to 3s. There was a rapid loss of information from memory when rehearsal was prevented which is as an indication of short term memory having a limited duration. WORKING MEMORY: Baddeley and Hitch (1974) developed an alternative model of short-term memory which they called working memory. They argue that the picture of short-term memory (STM) provided by the Multi-Store Model is far too simple. According to the Multi-Store Model, STM holds limited amounts of information for short periods of time with relatively little processing. It is a unitary system. This means it is a single system (or store) without any subsystems. Working Memory is not a unitary store. Working memory is STM. Instead of all information going into one single store, there are different systems for different types of information. In the diagram above, Short term memory is replaced with working memory as proposed by Baddeley and Hitch.