Theories of forgetting

Theories of forgetting

According to Munn (1967) “Forgetting is the loss, temporary or Permanent, of the ability to recall or recognize something learnt Earlier.

“According to Drever (1952) “Forgetting means failure at any time. To recall an experience, when attempting to do so, or to perform an Action previously learnt .

Schacter’s “Seven Sins of Memory”

•         Memories are transient (fade with time)

•         We do not remember what we do not pay attention to

•         Our memories can be temporarily blocked

•         We can misattribute the source of memory

•         We are suggestible in our memories

•         We can show memory distortion (bias)

•         We often fail to forget the things we would like not to recall (persistence of memory)

Decay theories

n  Memories fade away or decay gradually if unused

n  Time plays critical role

n  Ability to retrieve info declines with time after original encoding

Decay Theory = gradual fading of the physical memory trace (when new memory forms, there is a change in brain structure or chemistry.    If unused, normal brain metabolic processes erode memory trace. 

The term decay theory was first coined by Edward Thorndike in his book “The Psychology of Learning” in 1914. This simply states that if a person does not access and use the memory representation they have formed the memory trace will fade or decay over time. This theory was based on the early memory work by Hermann Ebbinghaus in the late 19th century. The decay theory proposed by Thorndike was heavily criticized by McGeoch and his interference theory.

Trace Decay Theory of Forgetting

This explanation of forgetting in short term memory assumes that memories leave a trace in the brain. A trace is some form of physical and/or chemical change in the nervous system. Trace decay theory states that forgetting occurs as a result of the automatic decay or fading of the memory trace. Trace decay theory focuses on time and the limited duration of short term memory. This theory suggests short term memory can only hold information for between 15 and 30 seconds unless it is rehearsed. After this time the information / trace decays and fades away.

Decay theory proposes that memory fades due to the mere passage of time. Information is therefore less available for later retrieval as time passes and memory, as well as memory strength, wears away. When we learn something new, a neurochemical “memory trace” is

created. However, over time this trace slowly disintegrates. Actively rehearsing information is  believed to be a major factor counteracting this temporal decline.

It is widely believed that neurons die off gradually as we age, yet some older memories can be stronger than most recent memories. Thus, decay theory mostly affects the short-term memory system, meaning that older memories (in long-term memory) are often more resistant to shocks or physical attacks on the  brain. It is also thought that the passage of time alone cannot cause forgetting, and that Decay Theory must also take into account some processes that occur as more time passes.

Trace decay refers to apparent loss of information already encoded and stored in an individual's long term memory. It is often a gradual process in which old memories are unable to be recalled from memory storage.

Decay theory

Decay is the simplest explanation of forgetting. Decay is what supposedly occur when the  passage of time causes us to forget. The memory trace (or engram) fades and the memory is no longer available. This theory is popular because it appears to fit with common-sense views of the way memory works. One of the most influential attempts to explain forgetting in terms of decay was by Hebb (1949). However, it is very difficult to prove experimentally that decay actually occurs. For example, Peterson & Peterson’s results can be explained in terms of decay of the memory trace over the retention interval, but they can also be explained by interference by the distracter task (counting  backwards in threes).

However, one observation to support decay is that STM can hold fewer words when the words are long (harpoon or cyclone) than if words are short (bishop & pewter). Note that we are referring here to how long the word takes to say (try it). According to Baddeley et al (1975) this effect occurs because as the words are presented, they are encoded acoustically. This takes longer for the long sounding words resulting in an increased possibility that the trace will have decayed for some of the words.

Ebbinghaus also employed a savings method to test his memory retention. He first counted the number of times needed to rehearse a list of nonsense syllables in order to commit it to memory. Then he counted the number of times it took to relearn the list after a period of time had elapsed. If it look ten repetitions to learn the list the first time and five the second, the savings would be 50 percent.

Memory researchers recognize that when people attempt to memorize information, they generally retain more information when they space their study sessions than when they cram them together within a single day (Cepeda et al., 2006). One reason for this effect, called the massed vs. spaced practice effect, is that massed, or crammed, practice causes mental fatigue that interferes with learning and retention. A practical implication of this effect should be obvious: When studying for exams, don't cram. Rather, space out your study sessions. You'll learn more and remember more of what you learn. Also, spaced practice produces the same learning benefits for other animals, which is useful to keep in mind when trying to train your dog (Aamodt & Wang, 2008).

Decay theory helps account for memory kiss due to the passage of time. However, a major weakness of the theory is that it fails to account for the unevenness with which memory decays over time. Some memories remain well preserved over time, whereas others quickly fade. One reason for this unevenness is that more distinctive or unusual infor­mation tends to be remembered better over time. You're likely to remember your first date belter than your 14th. You're also more likely to later recall the name of a man you were introduced to at a party if the man’s name was Oscar than if it had been Bob or John.

Ebbinghaus studied retention of meaningless syllables. When we examine recall of more meaningful information, such as poetry or prose, we find a more gradual loss of memory over time. Then again, little if any forgetting may occur for important life events and knowledge we acquire about our work or career. Another factor that helps explain forgetting interference (Wixted, 2005).

Interference Theory: When Learning More Leads to Remembering Less

Chances are you have forgotten what you ate for dinner a week ago Wednesday. The reason for your forget fullness, according to interference theory, is interference from memories of dinners that preceded and followed that particular dinner. On the other hand, you are unlikely to forget your wedding day because it is so unlike any other day in your life (except for those, perhaps, who have taken many walks down the aisle). Interference theory helps explain why some events may be easily forgotten while others remain vivid for a lifetime. The greater the similarity between events, the greater the risk of interference. There are two general kinds of interference, retroactive interference and proactive interference.

Interference occurring after material is learned but before it is recalled is called retro­active interference. Perhaps you have found that material you learned in your9:0Q a.m. class, which seemed so clear when you left the classroom, quickly began to fade once you started soaking in information in the next class. In effect, new memories retroactively interfere with unstable earlier memories that are still undergoing the process of memory consolidation (Wixied, 2004).

■ Sleep on it. Want to improve your recall of newly learned material? Sleep on it. Investi­gators believe that sleep enhances learning and memory by helping to convert fragile new memories into lasting ones. Learning material and then sleeping on it may help you retain more of what you learn.

■ Rehearse fresh memories. New long-term memories are fragile. Practicing or rehearsing fresh memories aloud or silently can strengthen them, making them more resistant lo the effects of interference. Repeated practice beyond the point necessary to repro­duce material without error is called overlearning. Apply the principle of overlearning to reviewing the material in this text, such as by rehearsing your knowledge of the key concepts in each chapter two or more limes after you can demonstrate your knowledge without any errors.

■ Give yourself a break. Try not to schedule one class directly after another. Give your recent memories time lo consolidate in your brain.

■ Avoid sequential study of similar material. Try not to study material that is similar in content In back-to-back fashion—for example, avoid scheduling a French class right after a Spanish one.

Interference may help explain the serial position effect, the tendency lo recall the first and last items in a list, such as a shopping list, better than those in the middle of the list. The unfortunate items in the middle are often forgotten. In a study in which people were asked to name the last seven U-S. presidents in order, they were more likely lo make mistakes in the middle of the list than al either the beginning or the end. Serial position effects influence both short-term and long-term memory.

Interference is the likely culprit in serial position effects. Items compete with one another In memory, and interference is greatest in the middle of a list than at either end of the list. For example, in i list of seven items, the fourth item may interfere with the item that it follows and the item that it precedes. But interference is least for the first and last items in the list—the first, because no other item precedes it; the last, because no other item follows it. The tendency to recall items better when they arc learned first is called the primacy effect. The tendency to recall items better when they are learned last is called the recency effect. As the delay between a study period and a test period increases, primacy effects become stronger whereas recency effects become weaker. This recency-primacy shift means that as time passes after you have committed a list to memory, it becomes easier to remember the early items but more dif­ficult lo remember the later-appearing items in the list.

In sum, evidence shows that both the passage of time and interference con­tribute to forgetting. But neither decay theory nor interference theory can deter­mine whether forgotten material becomes lost to memory or just more difficult to retrieve. Some forgotten material can be recovered if subjects are given retrieval cues to jog their memories, such as exposure to stimuli associated with the original situations in which the memories were formed. This brings us to a third model of forgetting, retrieval theory.

Tulving’s cue dependent theory of forgetting state dependent memory and forgetting

The cue-dependent theory of forgetting (Tulving, 1975)

 This theory of forgetting applies to long-term memory, not the short-term store. It states that forgetting occurs when the right cues are not available for memory retrieval. Tulving put forward this theory in 1975, stating that memory is dependent on the right cues being available, and forgetting occurs when they are absent.

Tulving’s theory states that there are two events necessary for recall:

 a memory trace (information is laid down and retained in a store as a result of the original perception of an event)

 a retrieval cue (information present in the individual’s cognitive environment at the time of retrieval that matches the environment at the time of recall)

For Tulving, forgetting is about the memory trace being intact, but memory failing because the cognitive environment has changed. There is no appropriate cue to activate the trace. The most noticeable experience of this cue-dependent forgetting is the Tip of the Tongue Phenomenon (Brown and McNeill, 1966). This refers to knowing a memory exists but being temporarily unable to recall it.

Cues have been differentiated into:

 context-dependent cues – the situation or context

 state-dependent cues – the person’s state or mood

Below are some brief outlines of studies which support the cue-dependency theory…

State (internal) Dependent Cues

The basic idea behind state-dependent retrieval is that memory will be best when a person's physical or psychological state is similar at encoding and retrieval.  For example, if someone tells you a joke on Saturday night after a few drinks, you'll be more likely to remember it when you're in a similar state - at a later date after a few more drinks.  Stone cold sober on Monday morning, you'll be more likely to forget the joke.

State Retrieval clues may be based on state-the physical or psychological state of the person when information is encoded and retrieved.  For example, a person may be alert, tired, happy, sad, drunk or sober when the information was encoded.  They will be more likely to retrieve the information when they are in a similar state.

Tulving and Pearlstone’s (1966) study involved external cues (e.g. presenting category names). However, cue-dependent forgetting has also been shown with internal cues (e.g. mood state). Information about current mood state is often stored in the memory trace, and there is more forgetting if the mood state at the time of retrieval is different. The notion that there should be less forgetting when the mood state at learning and at retrieval is the same is generally known as mood-state-dependent memory.

A study by Goodwin et al. (1969) investigated the effect of alcohol on state-dependent retrieval. They found that when people encoded information when drunk, they were more likely to recall it in the same state. For example, when they hid money and alcohol when drunk, they were unlikely to find them when sober.  However, when they were drunk again, they often discovered the hiding place. Other studies found similar state-dependent effects when participants were given drugs such as marijuana.

People tend to remember material better when there is a match between their mood at learning and at retrieval. The effects are stronger when the participants are in a positive mood than a negative mood. They are also greater when people try to remember events having personal relevance.

Retrieval inhibition as a theory of forgetting.

Retrieval inhibition refers to when some sort of cognitive event or environmental distractor reduces the probability of performance of a learning event. It may cause encoding inhibition.

Retrieval-induced forgetting (or RIF) is a memory phenomenon where remembering causes forgetting of other information in memory.

Mechanisms Underlying List-Method Directed Forgetting

Retrieval Inhibition Hypothesis

n  Forget instructions inhibit List One items

n  Reduces the activation of unwanted memories

n  However, they remain available

n  Re-presenting forgotten items restores their activation levels

n  Explains why items can be recognized but not recalled

Context Shift Hypothesis

n  Forget instructions mentally separate List One from List Two items

n  The mental context (frame of mind) shifts between the lists

n  List Two context lingers into the final test

n  The new context is a poor retrieval cue for List One items

n  May involve inhibition of the unwanted context

Intentional Retrieval Suppression

n  Anderson et al. (2004)

n  Suppressing retrieval is related to:

n  Increased activity in control regions:

n  The left and right lateral prefrontal cortex and the anterior cingulate cortex

n  These regions are also involved in motor inhibition

n  Decreased activity in the episodic memory area:

n  The hippocampus

n  Suggests that people can intentionally regulate hippocampal activity to disengage recollection

n  Others have also found significant suppression for:

n  Negative memories
(Depue et al., 2006; 2007)

n  Faces paired with unpleasant scenes

n  Replicated previous neuroimaging results of Anderson et al. (2004)

n  Positive memories
(Joormann et al., 2005)

Motivated Forgetting encompasses 3 kinds of forgetting:

n  Intentional Forgetting:

n  Forgetting arising from processes initiated by a conscious goal to forget.

n  Conscious suppression

n  Intentional contextual shifts (avoidance of retrieval cues)

n  Psychogenic Amnesia:

n  Profound forgetting that is psychological in origin affecting major periods of one’s life or otherwise significant events.

n  Other Forgetting:  not accidental but also not consciously intended, such as simply attempting to think about something else when confronted with an unpleasant reminder, without necessarily trying to forget it.

Trace-dependent forgetting

According to the theory of trace-dependent forgetting, the memory trace fades with time and, once forgetting has occurred, material has been lost from the memory system. If this theory is correct then eyewitnesses should be interviewed as soon as possible after the crime. This theory does have some experimental support (Jenkins and Dallcnbach 1924), but research has also shown that it is not so much time, as what we do in this time, that is the crucial factor (Davies 1999).

According to Endel Tulving (1974), trace-dependent forgetting and cue-dependent forgetting are the only two major causes of forgetting. "Trace-dependent forgetting" occurs because the memory trace has deteriorated or decayed or required information or material has been lost from the memory system. Physiological traces in the brain are not available at the time of recall or retrieval.

"Cue-dependent forgetting" occurs when the memory trace still exists, but there is no suitable retrieval cue to trigger off the memory. The information is not accessible. It is a kind of forgetting in which the required information or material is in the long-term memory store, but cannot be retrieved without a suitable retrieval cue. The cues present at the time of learning are not present at the time of recall or interfering and competing cues are present and they block the memory. Cue-dependent or retrieval failure is the failure to recall a memory due to missing stimuli or cues that were present at the time the memory was encoded. It is one of the five cognitive psychology theories of forgetting. It states that memory is sometimes temporarily forgotten purely because it cannot be retrieved, but the proper cue can bring it to mind. The information still exists, but without these cues, retrieval is unlikely. Furthermore, a good retrieval cue must be consistent with the original encoding of the information. If the sound of the word is emphasized during the encoding process, the cue should also put emphasis on the phonetic quality of the word. Information is available, however, just not readily available without these cues.

Motivated forgetting theory

Motivated forgetting can be defined as the failure to retrieve unpleasant or threatening memories. Motivated forgetting can be either conscious, where you simply decide to think about other things, or unconscious. Conscious motivated forgetting has been referred to as suppression, while unconscious motivated forgetting has been referred to as repression.

The Motivated Forgetting theory suggests people forget because they push unpleasant thoughts and feelings deep into their unconscious. People may actively work to forget memories, especially those of traumatic or disturbing events or experiences.

The two basic forms of motivated forgetting are:

Suppression:	a conscious form of forgetting
Repression:	an unconscious form of forgetting

Physical Injury or Trauma

Anterograde amnesia is the inability to remember events that occur after an injury or traumatic event. Retrograde amnesia is the inability to remember events that occurred before an injury or traumatic event.

Organic Causes

Forgetting that occurs through physiological damage to the brain is referred to as organic causes of forgetting. These theories encompass the loss of information already retained in long term memory or the inability to encode new information. This is typically caused by the gradual slowing down of the central nervous system due to aging. Examples include Alzheimer's, Amnesia, and Dementia.