– Paulson cmf

Types of Human Memory

  1. Short Term Memory
  2. Working Memory
  3. Long Term Memory

Short Term Memory

While Ebbinghaus studied retention over long intervals, later experiments studied memory loss over periods of seconds to minutes. Short term memory was postulated to explain temporary retention of information as distinct from long term retention of information . Short term memory acts to also store current sensory information and to rehearse new information from sensory buffers. It has limited capacity (Miller’s 7 plus or minus 2). The probability of encoding in Long term memory has been directly related to time in short term memory.

It is now believed that the loss of information stored in short term memory has the same characteristics as loss of information stored in long term memory. It happens quicker because it involves information that is not learned as well. What we call the learning process is transferring information from short term to long term memory and is a physiological process. The shape of the memory loss curves are the same. Hence we don’t need to postulate a special type of memory. Instead, we need a theory of: 

  • Why we can rehearse only a limited amount of information at a time.
  • How different memories get different strengths (and so are forgotten at different rates).

Working Memory

Here we address why we can rehearse only limited information at a time.

Articulatory Loop Rehearsal limitations are due to limits in how long it takes verbal material to decay, not how many items we can store. Hence, the faster we can rehearse, the more we can store (Baddeley, 1986). Experimental support: word length effect. How long it takes to read words predicts how many words will be remembered. Articulatory loop is called the phonological loop due to evidence that it involves speech. We can rehearse about 1.5 seconds of verbal material before it decays. Time in the loop is not related to probability of coding in long term memory. Baddeley’s model  proposes that we have a visual/spatial sketchpad as well as the phonological loop. These hold information for use by a central executive. There is evidence that a particular area of the frontal cortex is involved in working memory.

Long Term Memory

A simple observation: we often need to recall information that we learned long ago.How quickly and reliably we recall it depends on:

  • Activation: How long since we last used the information.
  • Strength: How well we have practiced it.

Experimental Evidence: (Anderson 1976) – Subjects learn some sentences. Some sentences are studied twice as long as others. Subjects must discriminate sentences they learned from distracters. They are tested for each sentence more than once, with varying intervening sentences. Results: Both amount of study and how recently the information was accessed affect speed of response. However amount of study matters only if the information was not recently accessed (an interaction effect).

Some basic facts about long term memory

Sometimes we fail to retrieve info that we know we have – retrieval failure

One common type of retrieval failure is the Tip-of-the-tongue phenomena – you know you know the meaning of a word, or the answer to a question, but you can’t retrieve it.

But sometimes, we simply don’t encode well. Even a highly familiar item may not have a detailed representation in memory.

Accessing one category can lead to retrieval of others that are linked to it (remembering in clusters; spreading activation from one concept to another, as in Collins & Quillian’s model)

Other times, activating one category member that is active can inhibit retrieval of another – Brown’s (1968) state name experiment. (Fixating on an already active concept….)

Delay (number of intervening items)

Degree of Study

Less Study

More Study

Short (0-2)

1.11 seconds

1.10 seconds

Long (3 or more)

1.53 seconds

1.38 seconds

 Other facts about memory

  1. Practice and Strength
  2. Depth of Processing
  3. Elaborative Processing and Text
  4. Forgetting: Gone or Inaccessible?
  5. Forgetting: Decay or Interference?

 Practice and Strength

We’ve seen that speed of recall of information from long term memory depends in part on how recently that information has been activated. However, what about the fact that speed of recall also depends on amount of practice? Activation changes quickly over time. The effect of practice decays much more slowly over time (witness Ebbinghaus, the alphabet). Thus these are believed to be distinct processes.

Power Law of Learning

A very robust result: the effect of practice in a wide range of different tasks fits a power law 

Reaction Time equals C * Practice Time K where C and K are constants that depend on the task. 

Practice helps a lot at first, then provides decreasing gains as you reach the limits of your performance ability.

Long-Term Potentiation – There appears to be a neural basis for this law of learning. Neural pathways in the hippocampus (known to be involved in learning) become increasingly sensitive when stimulated. The change in sensitivity follows a power law relationship.

Depth of Processing

Craik and Lockhart (1972) proposed that strength of memory depends on how deeply information is processed, not on how long it is processed

Experimental support:  Memory for words not improved by merely repeating them for a longer period of time (Glenberg et al. 1977). A large number of studies support the depth of processing conclusion. It applies to subject matter learning as well as laboratory situations. Subsequent work focused on what constitutes deep processing.

Processing Meaning:

Some lab studies compare tasks that require processing meaning of words versus form (e.g., what letters do they have).

Elaborative Processing and Text

Studies show benefits of connecting the items to be remembered to other related information (e.g., elaborating on sentences to be remembered, or rhyming). Intention does not matter. Subjects in deeper processing conditions do better regardless of whether they know they will need to remember the processed items.

Implications for study habits and method.

  1. Preview the material
  2. Make up questions
  3. Read, trying to answer the questions
  4. Reflect while you read. think of examples, relate it to what you know.
  5. Recite the information in each section after you’ve read it. Re-read what
  6. you can’t recall.
  7. Review the major points and the answers to your questions at the end.
  • Question generation is at least as beneficial as question answering.
  • Questions generated before the material rather than after may be more beneficial

Forgetting: Gone, or Inaccessible

Do we forget because the information is gone, or do we forget because we can’t access information that is still there? It is difficult to distinguish the two. However, there is evidence that we retain more than we can retrieve.

Experiment: (Nelson 1971) – Learn paired associates (numbers to nouns). Tested 2 weeks later to see which were remembered. Then given new material to learn that had some of the forgotten numbers, both with and without their original nouns.

Results: Subjects relearned the original associations faster (in spite of the fact that they could not recall them). Subjects relearned the original associations faster (in spite of the fact that they could not recall them). This suggests that some associative information was retained. One possible interpretation: strength of memories decay gradually. If these strengths fall below a certain threshold, we can’t recall the information, but the remaining memory trace is still there to facilitate relearning.

Forgetting: Decay or Interference?

Is forgetting due to decay of unused information, or to interference of new information with old information? Different kinds of evidence are offered for each position.

A survey of forgetting research concluded that the rate at which we forget information usually conforms to a power law: we forget a lot at first, but over time the rate of forgetting diminishes. 

Decrease in long-term potentiation follows a similar power law. These facts are interpreted by some as evidence for a physiologically determined decay rate.

Recognition vs. Recall

Two main ways we access memory: recognition and recall.


  • when provided with the information in memory,
  • just double check that we’ve seen it before.
  • includes: feeling of familiarity, matching, multiple. choice, True/False on exams, recognizing someone you know…


  • coming up with the information from memory yourself.
  • Includes: coming up with the name for person you recognized, recalling where you were when Kennedy assassinated, fill-in-the-blank on exams.

Recognition involves a process of comparison of info with memory. Recall involves a search of memory and then the comparison process once something is found.

Not just different amounts of the same memory – not just a diff. in strength. Qualit. different. Example: rare words are almost always better recognized than common ones, but usually less well recalled.

Recognition has 2 mechanisms: familiarity and retrieval. We can recognize. an uncommon item just because it seems familiar. For a more common item, will need to retrieve additional information, such as where the item was encountered.