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Chapter 5

PSY270 Chapter 5.docx

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University of Toronto St. George
Kristie Dukewich

Chapter 5: Short-Term and Working Memory The Importance of Memory in Our Lives Memory: the processes involved in retaining, retrieving, and using information about stimuli, images, events, ideas, and skills after the original information is no longer present Just about everything we do depends on remembering what we have experienced in the past. The case of Clive Wearing: experienced brain damage to his temporal lobe (area responsible for making new memories) – now lives totally within the most recent one or two minutes of his life Because of Clive’s inability to form new memories, he constantly feels he has just become conscious for the first time. His loss of memory has robbed him of his ability to participate in life in any meaningful way, and he needs to be constantly cared for by others. Studying Memory Donald Broadbent’s filer model proposes how people can selectively attend to one message out of many: Messages  Sensory memory  Filter  Detector  To memory Attended Message Advantages of models: 1) Help organize what we know about an area 2) Help suggest questions to ask Modal model of memory (Atkinson and Shiffrin): includes many of the features of memory models that were being proposed in the 1960s Rehearsal: a control process Input  Sensory memory  Short-term memory Long-term memory Output Structural features of the modal model of memory: stages of the model 1) Sensory memory: an initial stage that holds all incoming information for seconds or fractions of a second 2) Short-term memory (STM): holds 5-7 items for about 15-30 seconds 3) Long-term memory (LTM): can hold a large amount of information for years or even decades Control processes: active processes that can be controlled by the person and may differ from one task to another e.g.  Rehearsal: repeating a stimulus over and over to hold it in your mind  Strategies you might use to help make a stimulus more memorable (like relating it to something you already know)  Strategies of attention that help you focus on information that is particularly important or interesting Encoding: the process of storing information in long-term memory Retrieval: the process of remembering information that is stored in long-term memory The components of memory do not act in isolation – long-term memory is essential for storing information, but before we can become aware of this stored information, it must be moved back into STM. Sensory Memory Sensory memory: the retention, for brief periods of time, of the effects of sensory stimulation The Sparkler’s Trail and the Projector’s Shutter Sweeping a sparkler through the air creates a trail of light, which appears to be the leftover light from the sparkler as it is being waved. However, in actuality, there is no light along this trail. The light trail is a creation of the mind, which retains a perception of the sparkler’s light for a fraction of a second. Persistence of vision: the retention of the perception of light in your mind Similar experience while watching a film: Sequence of events that occur as a film is projected: 1) A single film frame is positioned in front of the projector lens. 2) When the projector’s shutter first opens, the image on the film frame flashes into the screen. 3) The shutter then closes, so the film can move to the next frame without causing a blurred image, and during that time, the screen is dark. 4) When the next frame is positioned in front of the lens, the shutter reopens, flashing the next image onto the screen. This process is repeated rapidly, 24 times per second, so 24 images are flashed on the screen every second, which each image separated by a brief period of darkness. The person viewing the film doesn’t see the dark intervals between the images because the persistence of vision fills in the darkness by retaining the image of the previous frame. If the period between the images is too long, the mind can’t fill in the darkness completely, and the intensity of the image appears to flicker. Sperling’s Experiment: Measuring the Capacity and Duration of the Sensory Store George Sperling (1960) flashed an array of letters to a participant for 50 milliseconds. Whole report method: participants were asked to report as many letters as possible from the whole matrix (3 letters per row, 4 rows) Reported: 4.5/12 letters; ~37% Partial report method (developed to decide whether this percentage was due to how brief the exposure was or because the participants’ perception of the full array faded rapidly as they reported the letters): the matrix was flashed for 50 ms (again) and sounded one of the following cue tones to indicate which row of letters the participants were to report: High-pitched: Top row Medium-pitched: Middle row Low-pitched: Bottom row When the cue tones directed participant to focus their attention on one of the rows, they correctly reported an average of 3.3/4 letters (82%). He concluded that the latter was the explanation for low whole report percentage. Delayed partial report (developed to determine time course of fading): the presentation of cue tones was delayed for a fraction of a second after the letters were extinguished The result of the delayed partial report experiments was that when the cue tones were delayed for 1 second after the flash, participants were able to report only slightly more than 1 letter in a row, the equivalent to 4 letters in all three rows – the same number of letters they reported using the whole report method. Sperling concluded that a short-lived sensory memory registers all or most of the information that hits our visual receptors, but that this information decays within less than a second. Iconic memory (visual icon (“image”)): the brief sensory memory for visual stimuli; lasts less than 1 second Echoic memory: the brief sensory memory for auditory stimuli lasts for a few seconds (4 sec) after presentation Many cognitive psychologists believe that the sensory store is important for 1) Collecting information to be processed 2) Holding the information briefly while initial processing is going on 3) Filling in the blanks when stimulation is irregular/discontinuous Short-Term Memory Short-term memory (STM): the system involved in storing small amounts of information for a brief period of time; “whatever you are thinking about right now” Most of the information in STM is lost, and only some of it reaches the LTM. Everything we think about or know at a particular moment in time involves STM because short-term memory is our window to the present. What is the Duration of Short-Term Memory? Brown, Peterson, and Peterson used the method of recall to determine the duration of STM. Participants were read a triad of letters and then given a number from which they had to count down by threes. They were then told to recall the three letters. The Petersons did a similar experiment in which they varied the time between when they said the number and when the participant began recalling the letters. They found that participants were able to remember about 80% of letters after counting for 3 seconds but could remember an average of only 12% of letters after counting for 18 seconds. The above result demonstrates that a passage of time after hearing the letters caused the memory trace to decay Memory becomes even worse after a few trials due to proactive interference (PI) – interference that occurs when information that was learned previously interferes with learning new information. The outcome of this constant interference in our everyday life experiences is that the effective duration of STM, when rehearsal is prevented, is about 15-20 seconds. What is the Capacity of Short-Term Memory? There is a limit to how much information can be held in STM (range: 5 – 9) George Miller’s famous paper titled “The Magical Number Seven, Plus or Minus Two” summarizes evidence suggesting that STM can hold 5 – 9 items. More recent measures have set the capacity at about 4 items.  Chunking: small units (like words) can be combined into larger meaningful units, like phrases, or even larger units, like sentences, paragraphs, and stories  C
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