Process Dissociation Tutorial

The Problem

Memory researchers have discovered that sometimes past events influence our present behavior without our conscious awareness that this is occuring. Such memories are called implicit memories, because the existence of the memory for the event is implied by the subject's behavior even though the subject isn't consciously aware of having a memory. Explicit memory, on the other hand, refers to memories where the subject is consciously aware again of the past experience.

Explicit memory has typically been measured using direct memory tests such as recall or recognition. Implicit memory has typically been measured using indirect memory tests. For instance, in a stem completion task subjects are presented with word stems that can be completed in several ways (e.g. "BA--"). Subjects are asked to complete the word stem with the first word that comes to mind (e.g. bank, band, bang, bard, barb, etc.). Research has indicated that subjects who have been exposed to a word during study (e.g. bard) will complete the word stem with that word at higher than baseline levels.

Results of studies using indirect tests haveoften been attributed to implicit memory. But Larry Jacoby argued that indirect tests are not process pure. That is, indirect tests, although intended to measure implicit memory, may sometimes be influenced by explicit memory (e.g. "hmmm, BA--, hey that reminds me of the word bard that I saw"). Similarly, responses on direct tests, although designed to measure explicit memory, may be influenced by unconscious processes (e.g. guessing on a multiple choice test).

The process dissociation procedure was developed to provide better measures of conscious and unconscious processes by setting those processes in opposition to one another.

Theoretical Background

Process dissociation is a dual process model of memory. The two processes it posits are called Recollection and Familiarity.

Recollection: Consciously retrieving the item in terms of its original study context. Recollection is a relatively slow strategic process.
Familiarity: A fast, automatic process that does not include contextual information. Jacoby has argued that at least some familiarity occurs because of an inference based on increased perceptual fluency (i.e. your perceptual system processes the information more quickly than usual).

Example: Say you read in the Weekly World News (that supermarket tabloid) that Ross Perot is going to need to have his ears amputated. Initially, you would tend to discount this story, because its coming from the same source that says Elvis is alive and living on Pluto with Jimmy Hendrix. But after some time passes you might find yourself telling people, "Hey did you hear Ross Perot may need to have his ears amputated?" Social psychologists call this the sleeper effect. After the delay, recollection of the source of the information has disappeared, but familiarity is still retained. So you end up thinking the information is true.

The Process Dissociation Procedure

Let's use this example to explore process dissociation. Imagine we conduct an experiment in which we have subjects read newspaper articles from the New York Times (NYT) as well as from the Weekly World News (WWN). What we want to measure is the extent to which the WWN stories will be recollected vs. the extent to which they will be responded to based on familiarity. To assess this, subjects are given a recognition memory test for facts taken from the various stories. They are placed in one of two conditions:

Inclusion Instructions (I): Select any facts that were in any of the newspaper stories.
Exclusion Instructions (E): Select any facts that were any of the NY Times stories, but do not select any fact that you read in the Weekly World News.

The Venn diagrams below illustrate the probility of selecting a WWN item under the two types of instructions. The circle with the R in it depicts the probability of consciously recollecting the WWN item. The circle with the F in it depicts the probability that a WWN item will be familiar.

Figure 1. Selection of Items Under Inclusion and Exclusion Instructions.

Under the inclusion instructions you would select the WWN item whether you recollect it or whether it is merely familiar. In contrast, under the exclusion instructions, you would still select the item if its familiar, but you should reject the information if you consciously recollect its source.

Estimating Recollection and Familiarity

Recollection:

You can use the probability of selecting an item under the exclusion and inclusion instructions to estimate both Recollection and Familiarity. The following Venn diagrams show how you would estimate Recollection using the process dissociation procedure:

Figure 2. Estimating Recollection from Inclusion and Exclusion Responses.

In algebra the equation would be: R = I - E

Familiarity:

You can also estimate familiarity. However to do so you need to know a little probability theory. See that portion of the Venn diagrams where the R circle and the F circle overlap? That's called the joint probability of R and F. Simply put, its the probability of R and F both happening. When two events are independent (i.e. they don't influence each other) the joint probability of two events is equal to the product of their individual probabilities. In other words, P(A&B) = P(A)xP(B). Armed with this knowledge, the following Venn diagrams illustrate how you would estimate familiarity:

Figure 3. Estimating Familiarity from Exclusion and Recollection.

In algebra, the equation would be

F = E + RF

Now you notice that F is on both sides of the equation, which isn't all that helpful. So you need to do a little high school algebra to make the equation more useful.

    F = E + RF
    F - RF = E
    (1-R)F = E
    F = E/(1-R)

There you go. Pretty easy really. By using the process dissociation procedure you can obtain estimates of the probability of recollection and familiarity by relying on the proportion of responses made in the inclusion condition and in the exclusion condition.

Assumptions of the Process Dissociation Procedure

As Jacoby himself has pointed out the math only works out if you are willing to make some assumptions.

Independence Assumption: Recollection and familiarity are independent in the statistical sense.

Independence means that the probability of one event happening is not influenced by whether or not the other event happened. For instance, say you playing craps and you roll two die. The probability of one die coming up six and the other die coming up five are independent probabilities. Jacoby assumes that recollection and familiarity are independent, just like the two die are.

The independence assumption is necessary for the math to work because the joint probability of R and F will only equal R times F if they are independent. If you don't assume independence then the overlapping segment is no longer equal to RF and all bets are off..

Invariance Assumption: Recollection and familiarity are not influenced by which instructions (inclusion or exclusion) the subject is given.

Its not difficult to imagine circumstances where the invariance assumption would be violated. Assume for instance that under the inclusion instructions subjects are more willing to respond based on familiarity. If that were the case then familiarity would be higher in the inclusion condition than in the exclusion condition. This would be a violation of the invariance assumption. You'd now be left with the following situation.

I = R + (1-R)F_I
E = (1-R)F_E
Where F_I > F_E. If you pull the old simultaneous subtraction bit like you did above you now get something much messier!

R_estimated = I-E = R + (1-R)F_I - (1-R)F_E
Notice that because F_I> F_E you would tend to overestimate R under these conditions.
Obviously, you are also going to run into problems estimating the value for F. For one thing these is no F. There are two F's that depend on which instructions are given. Second the value of F is calculated by making use of your estimate of R. But that estimate would be off. So if the invariance assumption is violated it can cause major problems.

Indeed people have argued against both of these assumptions. If you'd like to learn more about process dissociation check out the references listed below.

Some PDP References:

Early Evidence:

Jacoby, L.L. (1992). A process dissociation framework: Separating automatic from intentional uses of memory. Journal of Memory and Language, 30, 513-541.

Jacoby, L.L., Lindsay, D.S. & Toth, J.P. (1992). Unconscious influences revealed: Attention, awareness, and control. American Psychologist, 47, 802-809.

Some Critics:

Curran, T. & Hintzman, D.L. (1995). Violations of the independence assumption in process dissociation. Journal of Experimental Psychology: Learning, Memory, & Cognition, 21, 531-547.

Dodson, C.S & Johnson, M.K. (1996). Some problems with the process-dissociation approach to memory. Journal of Experimental Psychology: General, 125, 181-194.

Graf, P. & Komatsu, I. (1995). The process dissociation procedure: Handle with caution. European Journal of Cognitive Psychology, 6, 113-129.

Some Responses:

Jacoby, L.L. (1997). Invariance in automatic influences of memory: Toward a user's guide for the process-dissociation procedure. Journal of Experimental Psychology: Learning, Memory and Cognition, 24, 3-26.

Jacoby, L.L., Yonelinas, A.P. & Jennings, J. (1997). The relation between conscious and unconscious (automatic) influences. A declaration of independence. In J. Cohen & J.W. Schooler (Eds.), Scientific Approaches to Consciousness (pp.13-47). Mahweh NJ: Erlbaum.

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