Memory: Storage of information for later retrieval • The process by which we encode (record), store (retain), and retrieve information i.e. a process of 3R • Process by which information is: • Acquired (process of recording information in a form usable to memory) • Encoding • Stored in the brain (the retention of encoded infor. over time) • Storage • Later retrieved (Material in memory storage has to be located and brought into awareness to be useful) • Retrieval • Eventually (possibly) forgotten Information processing approach • Computer as a model for our memory • A stimulus that registers on our senses can be remembered only if it • 1. Draws attention, which brings it into consciousness; • 2. Is encoded, or transferred to storage sites in the brain, and • 3. Is retrieved for use at a later time. • Three types of memory • Sensory memory • Short-term memory (STM) • Long-term memory (LTM) • Can hold vast quantities of information for many years • According to this three-system approach to memory there are different memory storage systems or stages through which information must travel if it is to be remembered (Atkinson & Shiffrin, 1968,1971) Information-Processing Model of Memory Retrieval Sensory Attention Short-term Encoding Long-term Stimulus memory memory memory Forgetting Forgetting Forgetting Atkinson and Shiffrin’s (1971) Modal Model Environmental Input Sensory Registers Detect sensory input from the various modalities Visual, auditory, haptic, etc. Memories are held for only a few hundred milliseconds Short-Term Store (STS) Lasts a few seconds and is made up of: Temporary working memory Control processes: Rehearsal Coding Decisions Retrieval strategies Long-Term Store Permanent memory store Atkinson and Shiffrin Model •12 items 7±2 •George Sperling (1960) Miller’s Magic Number •Partial Report Paradigm (1956) Sensory Memory • Stores all the stimuli that register on the senses • Lasts up to three seconds • Two types Sensory Sensory • Iconic memory Input Memory • Visual • Usually lasts about 0.3 seconds • George Sperling’s tests (1960s) • Echoic memory Sperling’s Experiment • Presented matrix of letters for 1/20 seconds • Report as many letters as possible • Subjects recalled only half of the letters • Was this because subjects didn’t have enough time to view entire matrix? • No • How did Sperling know this? Sperling’s Iconic Memory Experiment Sperling’s Iconic Memory Experiment Sperling’s Iconic Memory Experiment Sperling’s Iconic Memory Experiment Sperling’s Experiment • Sounded low, medium or high tone immediately after matrix disappeared High • Tone signaled 1 row to report Medium • Recall was almost perfect Low • Memory for images fades after 1/3 seconds or so, making report of entire display hard to do Sensory Memory • Echoic memory • Sensory memory for auditory input that lasts only 2 to 3 seconds • Christopher Darwin and others (1972) put headphones on subjects and all at once played three sets of spoken letters – in the right ear, in the left ear, and in both ears at once. • Subjects then received a visual signal indicating which set to report. • Using this study and others, researchers have found that echoic memory holds only a few items but lasts for two or three seconds, and perhaps even longer, before activation in the auditory cortex fades. • Why do we need sensory memory? Short-term Memory • Function • Conscious processing of information • Attention is the key • Limits what info comes under the spotlight of short-term memory at any given time • From the sensory register, the brain encodes information - converts it into a form that can be stored in short-term memory – visual, acoustic or semantic encoding. • Also known as working memory Sensory Attention Input Sensory Working or Memory Short-term Memory Memorize the following list of numbers: 1 8 1 2 1 9 4 1 1 7 7 6 1 4 9 2 2 0 0 1 Write down the numbers in order. Now, try again… 1812 1941 1776 1492 2001 Short-term Memory • Limited capacity • Can hold 7 ± 2 items for about 20 seconds • Maintenance rehearsal • The use of repetition to keep info in short-term memory • Memory span • The longest list of items that a person can repeat back immediately after presentation in correct order on 50% of trials • Miller observed this span to be approx 7 (Miller’s Magic Number) for adults • CHUNK • The largest meaningful unit in the presented material that the person recognizes • Without rehearsal, we remember 4 ± 2 chunks • With rehearsal, we remember 7 ± 2 chunks • Ericsson & Chase (1982) 8931944349250215784166850612094888856877273141861 0546297480129497496592280 Memory span not limited in terms of bits but rather in terms of chunks • Forgetting is due to decay of the trace • The capacity for storage is small • Trace is a phonetic code Baddeley and Hitch (1974) • Attempted to simulate an STM deficit to see how STM influenced reasoning, comprehension, and learning tasks. • The Technique: • Require participants to repeat a sequence of digits out loud while concurrently performing a variety of cognitive tasks. The digits should fill up STM and interfere with doing the tasks. • The Test: • Increasing the STM load by adding more digits should cause more interference in reasoning. However … • The Results: • Participants were able to reason without difficulty, even when repeating sequences of up to eight digits. • Reaction times did slightly increase with digit load but the number of errors did not increase. Baddeley and Hitch (1974): Implications • Since the error rate of the reasoning task remained constant across digit loads (around 5%), working memory does not appear to depend entirely on the same underlying memory system as digit span. • There does, however, appear to be some interaction between these systems, as the processing time did increase with increasing number of digits to be recalled. • To address these difficulties, Baddeley and Hitch (1974) proposed a model of working memory (WM) -- a system that supports complex cognitive activities like reasoning instead of just storage (like STM). Baddeley and Hitch’s (1974): Multi-Component Model • Central executive: an attentionally-limited system that selects and manipulates material in two slave systems: • Phonological loop: holds sequences of acoustic or speech-based items • Visuo-spatial sketchpad: holds visually and/or spatially encoded items and arrays Short-Term Memory as “Working Memory” • Holds only the most recently activated, or conscious, portion of long-term memory, and it moves these activated elements into and out of brief, temporary memory storage • STM not limited to phonemic encoding • Loss of information not only due to decay • Baddeley and Hitch model (1974) – 3 components of working memory • Phonological rehearsal loop • Visuospatial sketchpad • Executive control system • WM is a term used to describe short-term memory as an active workspace where information is accessible for current use. • Baddeley’s model of working memory contains three elements: • A “central executive” • Auditory working memory • Visuo-spatial working memory • Material can enter conscious workspace from senses or from long-term memory Evidence for Phonological Loop • Phonological similarity effect: • BBGTCD is harder to memorize than FKYWMR • Wordlength effect: • Pay,wit,bar,hop,sum vs. helicopter, university, television, alligator,opportunity • Subvocal articulation, auditory noise, interferes with verbal memory Visuospatial sketchpad • Closely related to visual imagery • Used to encode nonverbal visual and spatial information. • Disrupted by performing additional visuospatial tasks, eye movement, or irrelevant visual material (Baddley 1992) Central executive • Attentional control • Making changes to practiced routine. (Example: Altering driving to work routine when there is a traffic accident) • Dividing attention • Multitasking • Switching attention from one task to another Problems with the Three-Component Model of WM Chunking • The three-component model of WM cannot explain why memory span can sometimes exceed the capacity of the subsystems (as much as 15 words in a sentence) for words in a sentence • Aspects of LTM (e.g. grammar) help to chunk the items; yet, we lack an explanation of how LTM and WM interact for digit span (6 or 7 items) • If the phonological loop can store only about three items, where are the rest stored? If they are stored in visual STM, how does this interact with phonological STM? • Word span length vs. sentence span (Baddlely, Vallar, and Wilson 1987) • Some anterograde amnestics have excellent prose passage immediate recall, despite very poor delayed recall. Too much information for the phonological loop. Where is it stored? • LTM modulating factors! • Number of words stored in memory is susceptible to variables such as word frequency and imageability (Hulme, Roodenrys, Brown, and Mercer 1995) • Multimodal integration • Where and how is information from the two subsidiary systems combined? The Episodic Buffer • Episodic Buffer -- A newly proposed fourth component of the WM system. • Originally assumed to be controlled by the central executive. • Holds integrated episodes or scenes • Multimodal store integrating information from visual and auditory modalities • Integrates information from long and short term stores • Can explain “chunking” to improve STM capacity • A storage system with a capacity of around 4 chunks of information in a multidimensional code. • Information is retrieved through conscious awareness – consciousness pulls info together. • Allows for the binding of previously