Surprise and change: Variations in the strength of present and absent cues in causal learning

16 Pages·2005·0.22 MB·English

Learning & Behavior
2005, 33 (2), 131-146
Surprise and change: Variations in the strength of
present and absent cues in causal learning
EDWARD A. WASSERMAN
University of Iowa, Iowa City, Iowa
and
LEYRE CASTRO
Universidad de Deusto, Bilbao, Spain
It is said that “absence makes the heart grow fonder.” But, when and why does an absent event be-
come salient to the heart or to the brain? An absent event may become salient when its nonoccurrence
is surprising. Van Hamme and Wasserman (1994) found that a nonpresented but expected stimulus can
actually change its associative status—and in the opposite direction from a presented stimulus. Asso-
ciative models like that of Rescorla and Wagner (1972) focus only on presented cues; so, they cannot
explain this result. However, absent cues can be permitted to change their value by assigning different
learning parameters to present and absent cues. Van Hamme and Wasserman revised the Rescorla–
Wagner model so that the αparameter is positive for present cues, but negative for absent cues; now,
changes in the associative strength of absent cues move in the opposite direction as presented ones.
This revised Rescorla–Wagner model can thus explain such otherwise vexing empirical findings as
backward blocking, recovery from overshadowing, and backward conditioned inhibition. Moreover,
the revised model predicts new effects. For example, explicit information about the absence of non-
presented cues should increase their salience (that is, their negative αvalue should be larger), leading
to stronger associative changes than when no explicit mention is made of cue absence. Support for this
prediction is detailed in a new causal judgment experiment in which participants rated the effective-
ness of different foods’ triggering a patient’s allergic reaction. Overall, these and other findings en-
courage us to view human causal learning from an associative perspective.
A dog was kept in the stables, and yet, though someone show us her infectious smile, then we are prompted to
had been in and had fetched out a horse, he had not barked give extra thought to these episodes. An absent event can
enough to arouse the two lads in the loft. Obviously the in fact be very informative. The nonoccurrence of an
midnight visitor was someone whom the dog knew well. event, like its occurrence, can be of very real psycholog-
Sherlock Holmes discovered the criminal in one of his ical significance (Hearst, 1991).
celebrated cases (Silver Blaze) thanks to his paying atten- Nevertheless, a vast number of events are not occurring
tion to the absence of an event: The dog had not barked. at any given moment. It might be intuitively surmised that
This event’s nonoccurrence provided the famous fictional the absence of an event will be salient only when the event
detective with relevant and important information. Al- is expected. In an experimental situation, if two stimuli,
though countless events are not occurring when something Cue A and Cue X, are always presented together, and
else is occurring, making it more economical to deploy our CueA later occurs, then it is reasonable also to expect the
cognitive resources to process the events that do occur, occurrence of CueX. More formally expressed, when two
there are occasions when event absences can be very sig- cues are conjointly presented, an associative link may be
nificant. If two close friends arrive separately at a party, if established between their central representations. Once
our plane does not take off after we have already stopped this linkage has been formed, the representation of one
on the runway, or if a normally happy person does not cue can be activated not only by the presentation of that
cue by itself, but also by associative links it has forged
with other cues. When CueA is presented alone, the rep-
L.C. is now at the University of Iowa. We would like to give special resentation of CueX will be activated by means of this as-
thanks to Linda Van Hamme for her exceptional creativity and ingenuity sociative link; because its representation is now activated,
in revising the Rescorla and Wagner model in order to accommodate ret-
the absent cue becomes salient.
rospective revaluation effects. We also thank Lorraine Allan, Mike Aitken,
an anonymous reviewer, and Miguel A. Vadillo for their helpful comments Learning and conditioning theories have not tradition-
on an earlier version of this paper. L.C. was supported by a fellowship ally paid much attention to how organisms learn about
from the Spanish Ministry of Education (AP99-14605555). Correspon- absent events nor even to whether organisms are sensi-
dence should be addressed to E.A. Wasserman or L. Castro, Department
tive to the nonoccurrence of events except, of course, in
of Psychology, E11 Seashore Hall, University of Iowa, Iowa City, IA
the case of the nonoccurrence of expected reinforcers
52242 (e-mail: [email protected] or leyre-castroruiz@uiowa.
edu). (e.g., Amsel, 1967). However, the modification of re-
131 Copyright 2005 Psychonomic Society, Inc.
132 WASSERMAN AND CASTRO
sponding to a cue—even when this cue is absent—was ity, but their responses reflect their knowledge of causal re-
actually observed in some of the earliest animal condi- lationships. If one assumes that, during a conditioning pro-
tioning experiments. Sensory preconditioning is one ex- cedure, even animals acquire information about the causal
ample. After presenting a bell and a light together several structure of their environment, then the correspondence
times, Brogden (1939) found that, when the bell alone between animal conditioning and human causality learn-
was later paired with shock, the light, although it was ing might not be at all far-fetched.
never paired with shock, also elicited a conditioned re- One of the most representative and influential cases of
sponse; that is, the bell–shock pairings led animals to the application of a conditioning model to explain human
change their responding to an absent cue, the light. causal learning is the Rescorla and Wagner (1972) model
More recent evidence in the animal literature concern- (hereafter RW), which was not originally intended to ex-
ing the possibility of learning about absent cues comes plain learning about absent cues, but to explain the fail-
from Holland’s studies of mediated conditioning. In Hol- ure of learning about present cues. RW can explain, for
land’s (1981) experiments, a tone was paired with food. example, why when a compound of two cues is paired
The tone was later paired with a LiCl injection. When the with an outcome (AX(cid:2)) after one of the cues has previ-
food was presented again, it had become aversive (see ously been paired with the same outcome (A(cid:2)), a very
also Ward-Robinson & Hall, 1996). According to Hol- weak response to Cue X is observed, although Cue X
land, during tone–LiCl pairings, the tone activates a rep- was directly paired with the outcome. This is the well-
resentation of food, which becomes associated with the known blocking effect found by Kamin (1968) with rats,
illness produced by LiCl. The food becomes aversive and subsequently reported with human beings as well
through this mediated association and its consumption (e.g., Arcediano etal., 1997; Chapman, 1991; Chapman &
correspondingly decreases. The tone–LiCl pairings evi- Robbins, 1990; De Houwer etal., 2002; Dickinson etal.,
dently prompted the animals to revalue their response to 1984; Shanks, 1985). The RW model explains the blocking
the absent stimulus—food. effect as the result of a failure of CueX to acquire asso-
Despite these earlier animal studies, it was primarily ciative strength. According to the RW model, changes in
when associative theories were applied to how humans the associative strength of CueX should proceed accord-
learn causal relationships that event nonoccurrence be- ing to the following learning rule:
came a major challenge for these accounts. How did this ΔV (cid:3) αβ(λ(cid:4) ΣV)
story unfold? X i
Tasks as different as Pavlovian and instrumental con- so that the change in the associative strength of a CueX
ditioning and human causality judgment seem to require on a particular trial (ΔV ) is proportional to the differ-
X
organisms to combine information from multiple sources ence between the outcome that actually occurs (λ) and
in order to acquire new behavior. Several researchers the outcome that is predicted by the sum of all present
have noted that the same factors seem to affect behavior cues (ΣV), weighted by the learning parameters αand β,
i
in both paradigms: Both were sensitive to temporal con- corresponding to the salience of the cue and the out-
tiguity (Shanks & Dickinson, 1991; Shanks, Pearson, & come, respectively. When there is no discrepancy be-
Dickinson, 1989; Wasserman & Neunaber, 1986), to the tween what it is predicted and what actually occurs, there
contingency between events (e.g., Chatlosh, Neunaber, & is no disparity in the associative strength of the corre-
Wasserman, 1985; Dickinson, Shanks, & Evenden, 1984; sponding cue and, therefore, there is no learning. Ac-
Shanks & Dickinson, 1987; Shanks & Dickinson, 1991; cording to RW, in a blocking experiment, at the end of
Shanks, López, Darby, & Dickinson, 1996; Wasserman, the first phase, the organism has already learned that
Elek, Chatlosh, & Baker, 1993), and to cue competition; CueA perfectly predicts the occurrence of the outcome;
that is, learning depends not only on the relationship be- that is, the error term (λ(cid:4) ΣV) is equal to 0. When, in
i
tween the cue and the outcome, but also on the relation- the second phase, CueX is presented along with CueA,
ship of other cues with the outcome (e.g., Arcediano, because the occurrence of the outcome is already fully
Matute, & Miller, 1997; Chapman, 1991; Chapman & Rob- predicted, nothing is learned about Cue X. Thus, RW
bins, 1990; De Houwer, Beckers, & Glautier, 2002; Dick- predicts the blocking effect because changes in the asso-
inson etal., 1984; Shanks, 1985). ciative strength of CueX depend on the associative sta-
These empirical parallels encouraged the possibility tus of other cues presented along with it.
that the same underlying learning mechanisms might In the last decade, several human studies have consis-
also be operative in studies of associative learning in an- tently found weaker responding to CueX even when AX(cid:2)
imals and causal judgment in humans (Allan, 1993; Alloy trials precede A(cid:2)trials, relative to a condition when the
& Tabachnik, 1984; Dickinson et al., 1984; Gluck & AX(cid:2)trials precede A(cid:4) trials—a so-called retrospective
Bower, 1988; Shanks & Dickinson, 1987; Wasserman, revaluation effect (Chapman, 1991; De Houwer et al.,
1990b; Young, 1995). Indeed, some authors interpreted 2002; Dickinson & Burke, 1996; Wasserman & Berglan,
conditioning in animals as involving causal perception 1998; Williams, Sagness, & McPhee, 1994). This retro-
(i.e., Dickinson, 1980; Killeen, 1981; Mackintosh, 1977). spective revaluation effect poses a considerable problem
Other authors, such as Kaufman and Bolles (1981), sug- for RW. According to RW, when AX(cid:2)pairings are first
gested that animals learn about both contiguity and causal- given, the outcome is not predicted by either cue, A or X;
LEARNING ABOUT ABSENT CUES 133
so, participants should learn the A–outcome and X– Table1
outcome associations and respond strongly to CueX in Van Hamme and Wasserman’s (1994) Experimental Design
testing. A(cid:2)trials after AX(cid:2)trials should not influence re- Condition 1.00 Condition 0.50 Condition 0.00
sponding to CueX, because CueX is not presented dur- Outcome Outcome Outcome
ing those trials; but, they do. Retrospective revaluation AX 8 Yes 0 No 6 Yes 2 No 4 Yes 4 No
BX 0 Yes 8 No 2 Yes 6 No 4 Yes 4 No
studies indicate that the later pairing of CueA with the out-
come after AX(cid:2)pairings leads to weakened responding to Note—AX and BX are compounds of two cues that were paired with
the occurrence (Yes) or nonoccurrence (No) of the outcome.
CueX in testing. Thus retrospective revaluation is a par-
ticular problem for RW because this model only allows for
changes in the associative value of presented cues—absent
cues should not change their associative value. cue and the outcome, participants’ utilization of this in-
But, if the premises of the RW model are reconsid- formation has generally been found to reflect the follow-
ered, then the problem can be solved. Van Hamme and ing biased weighting of the four types of information: a(cid:5)
Wasserman (1994) observed that the RW model explic- b(cid:5)c(cid:5)d (Anderson & Sheu, 1995; Kao & Wasserman,
itly considers the occurrence and nonoccurrence of the 1993; Levin, Wasserman, & Kao, 1993; Mandel &
outcome in two different ways: (1) by adjusting the as- Lehman, 1998; Wasserman, Dorner, & Kao, 1990).
ymptotic level of associative strength that is supportable The key purpose of the Van Hamme and Wasserman
from λto 0 (presence vs. absence of the outcome) and (1994) project was to see whether participants would up-
(2)by applying different learning-rate parameters on tri- date on every trial the associative value of not only the
als with the outcome (β) and without the outcome (β). present cues but also the absent cues. During the exper-
1 2
However, the RW model does not explicitly consider both imental task (Wasserman, 1990a), participants rated the
the occurrence and nonoccurrence of the antecedent plausibility of three different foods’ (e.g., shrimp, straw-
event, the cue. Only a cue that is actually presented is as- berries, and peanuts) being the source of a hypothetical
signed a learning-rate parameter (α); a nonpresented cue patient’s allergic reaction (0(cid:3)definitely not; 4(cid:3)possi-
is not entered into any associative process and therefore bly; 8 (cid:3) definitely the cause of the reaction). On any
is assigned a zero value. given trial, two of three different foods (A, B, or X) were
Van Hamme and Wasserman (1994) suggested that, just given as possible causes of the allergic reaction, as shown
as in the case of presented and nonpresented outcomes (the in Table 1. Both AX and BX trials were randomly pre-
terms β and β, respectively), one can assign different sented, half of which were paired with the occurrence of
1 2
learning-rate parameters with nonzero values to presented the allergic reaction and half with the nonoccurrence of
and nonpresented cues (the terms α and α, respectively). the allergic reaction. The precise compound cue–outcome
1 2
As we will see, this theoretical maneuver allows the RW pairings differed in each of three experimental condi-
model to explain many otherwise problematic findings. tions. In Condition 1.00, each AX trial was paired with
the occurrence of the allergic reaction and each BX trial
Updating the Strength of Both Present was paired with the nonoccurrence of the allergic reac-
and Absent Cues: Van Hamme and tion; the score of 1.00 represents the difference in the
Wasserman (1994) probability of the allergic reaction given AX (1.00) minus
Until recently, researchers had not seriously considered the probability of the allergic reaction given BX (0.00). In
the possibility that people who are engaged in evaluating Condition0.50, AX was assigned a probability of the al-
a causal relationship might not only change their ratings lergic reaction of 0.75 and BX was assigned a probability
of the cues that are presentedon an informational trial, but of the allergic reaction of 0.25, a difference of 0.50. And,
they might also change their ratings of cues that are not in Condition0.00, AX was assigned a probability of the
presented. Nevertheless, it seems reasonable to believe allergic reaction of 0.50 and BX was assigned a probabil-
that, if the presented cue were to gain strength in light of ity of the allergic reaction of 0.50, a difference of 0.00.
evidence, then nonpresented cues might immediately and This experimental design was inspired by the classical
correspondingly lose strength; conversely, if the presented and instrumental conditioning work developed by Wagner,
cue were to lose strength in light of evidence, then non- Logan, Haberlandt, and Price (1968) and later extended by
presented cues might immediately and correspondingly Wasserman (1974), who showed that, although CueX had
gain strength. been paired with reinforcement equally often in these ex-
In fact, work on contingency learning has shown that perimental conditions, rats’, rabbits’, and pigeons’ condi-
participants’ judgments reflect the use of information tioned responding to Cue X systematically decreased as
about boththe occurrence and the nonoccurrence of both the differential predictiveness of AX and BX increased.
the cue and the outcome. Specifically, when participants Presumably, as the A and B cues came to better signal the
are provided with: (a) the frequency of occurrence of occurrence and nonoccurrence of reinforcement, Cue X
both a cue and an outcome together, (b)the frequency of more poorly competed with A and B for the control of con-
occurrence of the cue without the outcome, (c) the fre- ditioned responding.
quency of occurrence of the outcome when the cue is ab- Indeed, in this human judgment experiment, we found
sent, and (d)the frequency of nonoccurrence of both the that participants’ final ratings of the causal efficacy of
134 WASSERMAN AND CASTRO
common CueX systematically fell as the AX(cid:4)BX dif- zero values to presented and nonpresented signalingcues
ference increased from 0.00 to 0.50 to 1.00. Although (the terms α1 and α2, respectively). This theoretical ma-
the actual relation of Cue X to the allergic reaction did neuver not only introduces symmetry into the treatment of
not change across the three conditions, the causal ratings cues and outcomes, but it also allows the RW model to em-
of Cue X decreased as Cue A became a more reliable brace the very results on causal judgment change scores
cause of the occurrence of the allergic reaction and that at first had appeared to be so embarrassing.
CueB became a more reliable predictor of its nonoccur- In order to see how the revised RW model accom-
rence. This parallel between humans’ causal ratings and plishes this theoretical feat, consider both the original
animals’ conditioned responses was certainly important and the revised models. As shown in Table 2, there are
and it greatly increased our confidence that similar psy- only two equations in the original model, corresponding
chological processes may be at work in these two very to cases in which a cue is given and the outcome follows
different situations. But, the central interest in this ex- and to cases in which a cue is given and the outcome
periment was to see whether participants lawfully changed does not follow. The revised model adds two equations,
their ratings of both the presented and nonpresented cues. corresponding to cases in which a signaling stimulus is
In order to do so, we had participants rate all threefoods not presented and the reinforcing stimulus is, and to
(A, B, and X) on everytrial, meaning that one of the two cases in which neither the signaling stimulus nor the re-
distinctive cues (either A or B) was notpresented. We then inforcing stimulus is presented. If the α2parameter is 0,
compared participants’ ratings on trialn(cid:4)1 and on trialn then the revised model reduces to the original model;
to determine the momentary impact of outcome occur- however, if the α2parameter takes on a negativevalue,
rence and nonoccurrence on causal ratings. then changes in the associative strength of nonpresented
The resultsfor the distinctive A and B cues were clear. stimuli will move in the oppositedirection as changes in
When a cue was given on trialn(cid:4)1, reinforcement on the associative strength of presented stimuli. If the ab-
that trial increased ratings of that stimulus on trialnby solute value of α2is less than that of α1—amounting to
a mean of 1.23; when a cue was given on trialn(cid:4)1, non- the plausible assumption that presented stimuli are more
reinforcement on that trial decreased ratings of that stim- salient than are nonpresented stimuli—then, after rein-
ulus on trial n by a mean of 0.57. These results were forcement, presented stimuli will increase in strength
completely unproblematic and were expected by asso- and nonpresented stimuli will decrease in strength, but to
ciative learning models like that of Rescorla and Wagner a smaller degree. Oppositely, after nonreinforcement,
(1972). However, when a cue was not given on trial n(cid:4) presented stimuli will decrease in strength and nonpre-
1, reinforcement on that trial decreased ratings of that sented stimuli will increase in strength, again to a smaller
stimulus on trialnby a mean of 0.86; when a cue was not degree. The data from the Van Hamme and Wasserman
given on trial n (cid:4) 1, nonreinforcement on that trial in- (1994) experiment perfectly correspond to these predic-
creased ratings of that cue on trialnby a mean of 0.22. tions. What else can the revised model do?
These results confirmed our hypothesis that nonpre-
sented cues are reevaluated in a way that contrasts with Trial-by-Trial Backward Blocking and
the changes in ratings of presented cues. As well, the Backward Conditioned Inhibition: Wasserman,
changes in ratings for presented cues were of greater ab- Kao, Van Hamme, Katagiri, and Young (1996)
solute value than those for nonpresented cues: 1.23 ver- We suspected that the revised model might be able to
sus 0.86 and 0.57 versus 0.22. Because associative learn- explain at least two other empirical findings that have
ing models like RW focus only on the signaling cues that challenged the original model: backward blocking and
are actually presented, these results were quite problem- backward conditioned inhibition. Each of these effects
atic and required serious theoretical consideration. entails the apparent retrospective revaluation of a cue,
something that is unpredicted by the original model.
Revised Rescorla–Wagner Model: Van Hamme In backward blocking, a first phase of training in-
and Wasserman (1994) volves AX being followed by the outcome. Then, a sec-
One way to deal with this empirical embarrassment is
to reconsider the premises of associative learning theory
Table2
and to modify it in light of the evidence. As explained Original and Revised Rescorla–Wagner Models
above, the RW model does not explicitly consider both
Original Rescorla–Wagner Model
the occurrence and nonoccurrence of a signaling cue. Cue present–outcome present (cellA): ΔV (cid:3) αβ(λ(cid:4) ΣV)
Only a signaling cue that is actually presented is as- Cue present–outcome absent (cellB): ΔVX(cid:3) α1β1(0(cid:4) ΣV)i
X 1 2 i
signed a learning-rate parameter (α); a nonpresented sig- Revised Rescorla–Wagner Model
naling cue is not entered into any associative equations, Cue present–outcome present (cellA): ΔV (cid:3) αβ(λ(cid:4) ΣV)
presumably because nonpresented stimuli have no psy- CCuuee apbresseennt-to–uotuctocmome ep raebsseenntt ((cceellllCB)):: ΔΔVVXX(cid:3)(cid:3) αα1ββ12((1λ0(cid:4)(cid:4) ΣΣVVi))i
chological significance. But, what if nonpresented stim- Cue absent–outcome absent (cellD): ΔVX(cid:3) α2β1(0(cid:4) ΣVi)
uli do have psychological significance? We suggested X 2 2 i
Note—α (cid:3)learning rate parameter for CueX present, α (cid:3)learning-
that, just as in the case of presented and nonpresented re- 1 2
rate parameter for CueX absent, β(cid:3)learning-rate parameter for out-
inforcingstimuli (the terms β1and β2, respectively), one come present, and β2(cid:3)learning-1rate parameter for outcome absent.
could assign different learning-rate parameters with non- Vs are summed only for the cues that are present on a given trial.
i
LEARNING ABOUT ABSENT CUES 135
ond phase of training is given involving Cue A alone, (1.93), indicating backward conditioned inhibition. These
also followed by the outcome. If causal ratings of CueX results are not predicted by the original RW model, but
are lower at the end of Phase2 than at the end of Phase1, they are predicted by the revised model.
then backward blocking can be said to have occurred. Also noteworthy are the trial-by-trial ratings in the back-
But, this effect cannot be predicted by the original model; ward blocking and backward conditioned inhibition con-
associative strength to Cue X cannot change during ditions. Figure1 shows participants’ ratings of CueX dur-
Phase2 because it is not given. The revised model does ing the whole set of trials in both the backward blocking
predict backward blocking, because A(cid:2)trials are trials in and backward conditioned inhibition conditions along with
which the representation of CueX will be activated; be- the ratings that were predicted by the original and revised
cause CueX is absent, these trials will effectively reduce RW models. The values chosen for the predictions of the
associative strength to CueX. revised RW model were based on independent research by
In backward conditioned inhibition, a first phase of Kao (1993): α, α, β, and β were 0.70, (cid:4)0.40, 0.50, and
1 2 1 2
training involves AX followed by no outcome. Then, a 0.40, respectively. In the backward blocking condition, the
second phase of training is given involving CueA alone original RW model predicts that ratings of CueX should
now followed by the outcome. If causal ratings of CueX increase during Phase 1, but remain constant throughout
are lower at the end of Phase2 than at the end of Phase1, the second phase, because it is not presented during that
then backward conditioned inhibition can be said to have
occurred. This effect cannot be predicted by the original
model either; associative strength to CueX cannot change
during Phase2 because it is not given. The revised model
does predict backward conditioned inhibition, again be-
cause A(cid:2)trials are trials in which the representation of
Cue X will be activated; because Cue X is absent, these
trials will effectively reduce associative strength to CueX.
Chapman (1991) had previously reported both back-
ward blocking and backward conditioned inhibition in a
stock market prediction task. Wasserman et al. (1996)
sought to both extend the generality of Chapman’s results
to a different judgment task and to document changes in
participants’ ratings on a trial-by-trial basis. We therefore
examined both forward and backward blocking as well as
both forward and backward conditioned inhibition within
a clinical setting. We also provided participants with in-
formation from all four cells of the contingency table in
each type of problem. In order to allow trial-by-trial rat-
ings of all relevant stimuli on every trial, after each piece
of information, participants were asked to rate the effect
of each of three foods on a person’s allergic reaction
from (cid:4)100 (makes very unlikely) to 0 (doesn’t affect the
likelihood) to (cid:2)100 (makes very likely) the allergic re-
action. Only one or two of these foods were actually
given on each trial, again allowing us to see whether both
presented and nonpresented cues would be affected by
the presentation or nonpresentation of outcomes.
Ratings at the end of Phase1 and Phase2 of training
showed that both forward blocking and forward condi-
tioned inhibition had occurred. Ratings of Cue X were
lower after A(cid:2)/AX(cid:2)training (21.76) than after AX(cid:2)train-
ing only (68.54), indicating forward blocking; ratings of
CueX were lower after A(cid:2)/AX(cid:4)training ((cid:4)33.98) than
after AX(cid:4)training only (1.93), indicating forward condi-
tioned inhibition. These results are consistent with the
original RW model. More interestingly, both backward
blocking and backward conditioned inhibition were also
obtained. Ratings of Cue X were lower after AX(cid:2)/A(cid:2) Figure1. Trial-by-trial ratings of participants in the backward
training (15.09) than after AX(cid:2)training only (68.54), in- blocking and backward conditioned inhibition conditions of Van
Hamme and Wasserman (1994) along with those predicted by
dicating backward blocking; ratings of X were lower after
Rescorla and Wagner’s model and by the revision of their model
AX(cid:4)/A(cid:2)training ((cid:4)27.22) than after AX(cid:4)training only by Van Hamme and Wasserman.
136 WASSERMAN AND CASTRO
period; however, participants’ ratings of Cue X progres- Table3
sively decreased during Phase 2, as predicted by the re- Wasserman and Berglan’s (1998) Experimental Design
vised model. In the backward conditioned inhibition, the Training
original RW model predicts that ratings of CueX should Phase 1 Phase 2 Test
also remain constant throughout the second phase, in AW(cid:2) A(cid:2)
W
which this cue is not presented; however, participants’ rat- BX(cid:2) –
X
ings of Cue X progressively decreased during Phase 2, CY(cid:2) C(cid:4) Y
DZ(cid:4) D(cid:4)
again confirming the prediction of the revised model.
Note—A, B, and C refer to the competing cues and W, X, and Y refer
to the target cues; D and Z are the filler cues. The(cid:2)denotes reinforce-
The Role of Within-Compound Associations: ment, the (cid:4)denotes nonreinforcement, and the – indicates that none of
Wasserman and Berglan (1998) the individual cues in the compound BX was presented in that training
As we have just seen, human research participants at- phase.
tend to and evaluate both present and absent cues. But, on
any given trial, very few events are actually presented,
whereas countless other events are not. To which nonpre- compound associations. These two design shortcomings
sented cues do participants attend? It is reasonable to sug- prompted us to conduct our next study.
gest that participants attend only to those cues whose mem- First, we aimed to clarify the nature of the retrospective
ories or representations are active on a particular trial. Van revaluation that was reported by Dickinson and Burke
Hamme and Wasserman (1994) suggested how those rep- (1996). We hoped to see whether backward blocking, re-
resentations might be activated. First, people can be given covery from overshadowing, or both effects were involved
instructions to consider particular cues, even though they in their reported results. As shown in Table 3, a control
may not have been presented on a given trial. Second, con- condition, BX, was included, without training of any of
textual or discrete cues that had been presented along with the cues in the compound during Phase 2, so that the
the target cues can also trigger representations of those causal ratings of CueX could serve as a baseline for other
now-absent cues. So, when two cues are paired, a within- critical comparisons. If ratings of CueW were lower than
compound association will be formed between them, ratings of Cue X at the end of Phase 2, then this result
which will then allow the presentation of one of the cues to would define backward blocking. If ratings of CueY were
activate the representation of the other cue. higher than ratings of CueX at the end of Phase2, then
Dickinson and Burke (1996) explored the possibility this result would define recovery from overshadowing.
that, for retrospective revaluation to occur, participants Cues D and Z were included in order to force participants
must form within-compound associations. It should be to discriminate among the compound stimuli in Phase1.
noted that the formation of a within-compound associa- To independently assess the formation and retention
tion is necessary to explain backward blocking (where of within-compound associations after the experimental
AW(cid:2)trials precede A(cid:2)trials) or recovery from over- task had been learned, at the end of the experiment, we
shadowing (where CY(cid:2)trials precede C(cid:4)trials), but it is asked participants to report which cues had been pre-
not required to explain forward blocking (where A(cid:2)tri- sented with one another during the first phase of train-
als precede AW(cid:2)trials) or superconditioning (where C(cid:4) ing. We hypothesized that those participants who had
trials precede CY(cid:2)trials) (for further discussion of this learned and remembered the compounds would show
issue, see Aitken, Larkin, & Dickinson, 2001; Larkin, backward blocking and recovery from overshadowing,
Aitken, & Dickinson, 1998; Melchers, Lachnit, & Shanks, whereas those participants who had not learned and re-
2004). Dickinson and Burke found that retrospective re- membered the compounds would not show these retro-
valuation occurred when it was possible for participants to spective revaluation effects.
form within-compound associations, but not when it was As predicted by the revised RW model, both backward
impossible for them to do so. blocking and recovery from overshadowing occurred.
Unfortunately, the retrospective revaluation effect that Final ratings of Cue W were lower than final ratings of
Dickinson and Burke (1996) reported could have in- CueX (4.75 and 5.63, respectively)—backward blocking.
volved not only backward blocking but also recovery In addition, final ratings of CueY were higher than final
from overshadowing. When two compound cues are first ratings of CueX (6.81 and 5.63, respectively)—recovery
presented, both followed by the outcome (e.g., AW(cid:2), from overshadowing. Because final ratings were ordered
CY(cid:2)) and then in a second training phase only one cue W(cid:6)X(cid:6)Y, it is likely that both backward blocking and
of each compound is presented—one followed by the recovery from overshadowing contributed to Dickinson
outcome (e.g., A(cid:2)), but not the other (e.g., C(cid:4))—lower and Burke’s (1996) reported results.
ratings of Cue W than Cue Y could be due to a decre- Furthermore, those participants who correctly identi-
ment in the strength of Cue W (backward blocking), to fied the stimulus compounds reliably exhibited the W(cid:6)
an increment in the strength of Cue Y (recovery from X(cid:6)Y pattern of results (W(cid:3)4.42, X(cid:3)5.63, and Y(cid:3)
overshadowing), or to the sum of both effects. In addi- 6.92); but, those participants who did not correctly iden-
tion, Dickinson and Burke did not independently assess tify the stimulus compounds did not respond differen-
participants’ learning and memory of the putative within- tially to the target cues (W(cid:3)6.00, X(cid:3)5.60, and Y(cid:3)
LEARNING ABOUT ABSENT CUES 137
6.40). These data thus are consistent with the notion that Materials
within-compound associations mediate the retrospective The experiment was programmed using PsyScope Version1.0.2
revaluation of causal judgments. More recently, the stud- (Cohen, MacWhinney, Flatt, & Provost, 1993) on four iMac comput-
ers. Eight different foods (yogurt, mushrooms, carrots, grapes, wal-
ies of Aitken et al. (2001) and Melchers et al. (2004)
nuts, noodles, oranges,and chicken) served as cues. As in Wasserman
have further demonstrated that the formation and preser-
and Berglan (1998), the cues were counterbalanced following a between-
vation of within-compound associations between the
participants Latin square design, which ensured that every food was
cues that were presented in compound are necessary for equally often assigned to each cue role and that each competing cue
retrospective revaluation effects to occur. was equally often paired with each target cue. The cues were written
In summary, the revised RW model correctly predicts in black type at the top of the screen. During training, the uninformed
trial-by-trial changes in the strength of nonpresented group observed the names of one or two foods on each trial: the two
foods of each pair in Phase1 and one food of each pair in Phase2.
cues in the form of backward blocking, backward condi-
The informed group observed the names of both foods of each pair
tioned inhibition, and recovery from overshadowing.
in both Phases 1 and 2: Below the name of each food, the word yes
The revised RW model also correctly predicts the partic- or nowas written, indicating whether or not the particular food had
ipation of within-compound associations in the retro- been eaten by the hypothetical patient. We reasoned that telling par-
spective revaluation effects. In the present study, we ticipants that a particular food had not been eaten (Group Informed)
delved more deeply into the RW model. would make such information more prominent than when a partic-
ular food simply did not appear (Group Uninformed). In each
group, the outcomes were Allergic Reaction on reinforced trials and
The Present Experiment No Allergic Reaction on nonreinforced trials.
As we have just seen, recent research suggests that ab-
sent cues are behaviorally relevant when they are expected Procedure
From 1 to 4 participants were studied concurrently on each of 4
to occur due to within-compound association with other
identically configured computer workstations. All the procedures, in-
cues that are actually presented. Presented cues activate
structions, and questionnaires were the same as in Wasserman and
the representations of nonpresented cues with which they Berglan (1998). Each participant sat in front of a workstation and was
have formed within-compound associations, allowing the instructed to fill in the first paper-and-pencil questionnaire, in which
nonpresented cues to be involved in the learning process. they were asked to provide an initial evaluation of the probability that
In human studies, one might more strongly activate the each of the foods could cause an allergic reaction in an ordinary in-
dividual. This first rating, as well as the subsequent ones, was made
representations of absent cues through verbal instruc-
on a scale of 1 to 9. Then, participants were introduced to a sce-
tions, as Van Hamme and Wasserman (1994) suggested.
nario in which they played the role of an allergist trying to discover
In the present experiment, we hypothesized that explicit in-
which foods would or would not cause an allergic reaction in a spe-
formation about the absence of nonpresented cues would cific individual, Mr.X (see Appendixfor instructions). In order to
increase their salience, leading to stronger retrospective perform that task, participants had to study different daily allergy
revaluation effects than when no explicit mention is made tests in which Mr.X had or had not suffered an allergic reaction
about the absence of nonpresented cues. This prediction after eating certain foods. The individual food or compound of
foods appeared at the top of the screen, and after 3sec, participants
emerges directly from the revised RW model. Increased
were required to predict whether Mr.X would develop an allergic
salience of absent cues translates into a larger negative α
reaction. Once the participants pressed “1” to indicate yesor “3” to
value; therefore, increases or decreases in the associative indicate no, the actual outcome appeared below. After 3sec, partic-
value of absent cues should also be larger, yielding stronger ipants could proceed to the next trial.
retrospective revaluation effects. In the first training phase, participants observed four compounds
Using the same design as in the prior study, in the that were presented 30 times each. Compounds AW, BX, and CY
were always paired with the allergic reaction; CompoundDZ was
present experiment, we tried to modify the salience of
never paired with the allergic reaction. The 120 trials in Phase1
absent cues through instructions: we explicitly told par-
were presented in a block-randomized order; each compound cue
ticipants which of the cues were or were not presented on was seen six times every 24 trials. After the first training phase,
a particular trial. Tassoni (1995) had earlier used this participants again had to evaluate the eight foods, except that they
strategy, but he was not interested in documenting retro- were now asked to use all of the information that they had received
spective revaluation effects, only in showing that the to evaluate the likelihood of each food causing an allergic reaction
in Mr.X. Participants had no access to their initial ratings.
quantity of information provided by giving notice about
During the second training phase, CueA was always paired with
the absence of a cue is greater than is the quantity of in-
the allergic reaction; Cues C and D were never paired with the aller-
formation arising from the mere nonoccurrence of a cue.
gic reaction. In this second phase, each of the cues in isolation was
Our clear expectation was that providing explicit informa- presented to the uninformed group. The informed group, however,
tion about absent cues would produce stronger retrospec- observed the competing cues along with the target cues that had been
tiverevaluation effects. presented in compound with them during Phase1. Below each of the
foods, the words yesor noappeared, indicating whether or not the pa-
tient had eaten it; that is, indicating its presence or absence on any
METHOD
given trial. For example, the two foods corresponding to the com-
pound AW had been presented during Phase1. Now, during Phase2,
Participants the names of both foods were shown to the informed group; the word
A total of 91 students at the University of Iowa received course yesappeared below CueA, indicating that CueA had been presented
credit for their voluntary participation. Random assignment re- on that trial and the word noappeared below CueW indicating that
sulted in 48 participants in the uninformed group and 43 in the in- the CueW had been absent on that trial. Each of the three types of
formed group. trials was presented 30 times in a block-randomized order for a total
138 WASSERMAN AND CASTRO
Table4 and Y. Participants rated the target cues differently al-
Mean Ratings for All Cues in Each Rating Period in Group though all three had been associated with the same rein-
Uninformed and Group Informed
forcement schedule throughout the experiment. More-
Rating Rating Rating over, the differences among the target cues were larger in
Period1 Period2 Period3
the informed group than in the uninformed group.
Cue M SE M SE M SE A 2 (group: informed vs. uninformed)(cid:7)3 (rating pe-
Group Uninformed riod: 1 vs. 2 vs. 3) (cid:7)3 (cue: W vs. X vs. Y) analysis of vari-
A 2.20 .20 6.84 .29 8.77 .17
ance (ANOVA) revealed a significant main effect of rating
W 2.31 .21 6.82 .31 5.31 .34
B 2.46 .19 6.77 .29 5.95 .29 period [F(2,162)(cid:3)279.45, MSe(cid:3)4.73], simply showing
X 2.48 .22 6.55 .33 6.24 .29 that ratings of the target cues, low at the beginning of the
C 2.35 .20 6.95 .30 1.08 .04 experiment, increased due to the reinforcement of the cues,
Y 2.53 .21 6.84 .32 6.97 .33
as expected. There was also a significant main effect of cue
D 2.91 .27 1.35 .15 1.08 .05 [F(2,162)(cid:3)15.70, MS (cid:3)3.56] and a significant rating
Z 2.37 .17 1.95 .31 2.31 .35 e
period(cid:7)cue interaction [F(4,324)(cid:3)25.52, MS (cid:3)2.07],
Group Informed e
showing that ratings of the target cues changed differently
A 2.23 .23 6.60 .37 8.52 .29 during the different rating periods. A significant Group(cid:7)
W 2.26 .22 7.36 .25 2.89 .38
B 2.21 .22 7.13 .29 5.02 .33 Rating Periodinteraction [F(2,162)(cid:3)10.86, MSe(cid:3)4.73]
X 2.36 .20 6.86 .33 4.71 .38 and a significant group(cid:7)rating period(cid:7)cue interaction
C 2.31 .21 7.21 .31 2.10 .36 [F(4,324)(cid:3)4.73, MS (cid:3)2.07] were also found, indicat-
Y 2.42 .23 7.10 .30 6.76 .45 e
ing that changes among the target cues in the three rating
D 2.39 .24 1.31 .18 1.84 .35
Z 2.18 .24 1.05 .03 1.89 .37 periods differed in the informed and uninformed groups.
In the uninformed group, simple effects analyses con-
Note—Cues W, X, and Y, in boldface, are target cues; Cues A, B, and
C are their associated competing cues; Cues D and Z are filler cues. firmed that significant differences existed among the
Rating Period1 provided initial ratings prior to training. Rating Period2 cues in Rating Period3 [F(2,162)(cid:3)7.04, MS (cid:3)4.45],
followed Phase1 training (AW(cid:2), BX(cid:2), CY(cid:2), DZ(cid:4)). Rating Period3 but not in Rating Period1 [F(2,162)(cid:6)1] or 2 [Fe(2,162)(cid:6)
followed Phase2 training (A(cid:2), C(cid:4), D(cid:4)).
1]. Figure2 shows that the final causal ratings of the three
cues in Group Uninformed were in the expected order:
W(cid:6)X(cid:6)Y. Planned comparisons revealed that ratings of
of 90 trials in the second training phase; each type of trial was seen
six times every 18 trials. Phase2 was followed by a third rating pe- Cue W were lower than ratings of Cue Y [F(1,81) (cid:3)
riod that was identical to the second. 11.27, MS (cid:3)5.54], replicating the typically reported ret-
e
Once participants had completed the third rating period, they were rospective revaluation effect. The significant difference
given a postexperimental questionnaire in which they were presented between ratings of Cue W and Cue X [F(1,81) (cid:3) 5.94,
with 16 pairs of foods; their task was to circle the four two-food com- MS (cid:3)3.29] indicated that backward blocking is involved
pounds that had actually been presented during the experiment. e
in this effect. The difference between ratings of Cue Y
Preanalysis of the Data and Cue X, which would indicate recovery from over-
To avoid the influence of possible preexperimental biases to the shadowing, was in the expected direction, but it fell just
foods, which might produce a ceiling effect prior to the experi- short of statistical significance in this analysis [F(1,81)(cid:3)
mental learning stages, we eliminated from the analysis data from 2.66, MS (cid:3)4.53, p(cid:3).10].
participants who gave extremely high initial ratings (a rating equal e
In the informed group, with explicit information about
to or greater than 7 to any of the cues in Rating Period1). With this
the absence of cues during Phase2, simple effects analy-
criterion, the data from 2 participants in each group were elimi-
nated. We also eliminated the data from 4 participants who invalidly ses also confirmed that significant differences existed
or incompletely marked their questionnaires: 3 participants in the among the cues in Rating Period 3 [F(2,162) (cid:3) 31.91,
informed group and 1 participant in the uninformed group. In total, MS (cid:3)4.46], but not in Rating Period1 [F(2,162)(cid:6)1]
e
the data from 8 participants were eliminated from the analysis. An or 2 [F(2,162)(cid:3)1.28, MS (cid:3)1.84]. Figure2 shows that
alpha level of .05 was adopted for all tests of statistical significance. e
the final causal ratings of the three cues in Group In-
When multiple comparisons were performed, Bonferroni correc-
formed were also in the expected order: W (cid:6) X (cid:6) Y.
tion was used to set the alpha level.
Planned comparisons revealed that ratings of Cue W
RESULTS were lower than ratings of Cue Y [F(1,81) (cid:3) 51.27,
MS (cid:3)5.54], replicating the retrospective revaluation ef-
e
Causal ratings of all eight cues in each of the three rat- fect in this group. The difference between ratings of
ing periods are provided in Table4. In both groups, ini- Cue W and Cue X was significant [F(1,81) (cid:3) 18.98,
tial ratings, prior to any experimental training, were low MS (cid:3)3.29], documenting backward blocking. Also sig-
e
and similar for all cues. After Phase1 training, the ratings nificant was the difference between ratings of CueY and
of reinforced cues increased, while the ratings of nonre- CueX [F(1,81)(cid:3)17.65, MS (cid:3)4.53], documenting re-
e
inforced cues remained low in both groups, confirming covery from overshadowing.
that training proceeded smoothly. More interesting re- Moreover, as shown in Figure2, these effects seemed
sults came after the crucial Phase2 training. Table4 and to be even stronger in the informed group than in the un-
Figure 2 display the final ratings of Target Cues W, X, informed group. To further analyze the difference in the
LEARNING ABOUT ABSENT CUES 139
Figure2. Mean final ratings of Target Cues W, X, and Y in the present ex-
periment for all participants in the uninformed and informed groups. Error
bars indicate the standard errors of the means.
magnitude of retrospective revaluation effects, we cal- rately (67% correct) than GroupInformed (80% correct),
culated difference scores among all three target cues: a which is reasonable given that participants in GroupIn-
backward blocking score, by subtracting the mean rating formed had been explicitly informed about the two cues
for Cue W from the mean rating for Cue X (1.82 and of the compound stimuli during Phase2 (those cues pres-
0.93, for Groups Informed and Uninformed, respec- ent, indicated with yes, or those cues absent, indicated
tively), and a recovery from overshadowing score, by with no), whereas participants in GroupUninformed had
subtracting the mean rating for CueY from the mean rat- only been explicitly informed about the presented cues.
ing for CueX (2.05 and 0.73, for Groups Informed and Because the enhanced retrospective revaluation effect in
Uninformed, respectively). A 2 (group: informed vs. un- the informed group might be due not only to enhanced
informed)(cid:7)2 (difference score: backward blocking vs. salience of the absent cues but also to enhanced memory
recovery from overshadowing) ANOVA yielded a main of the within-compound associations, we further ana-
effect of group [F(1,81)(cid:3)9.00, MS (cid:3)5.54], showing lyzed the final ratings of the target cues, segregating the
e
that the difference scores were significantly higher in data of participants who had correctly identified the four
Group Informed than in Group Uninformed. No inter- compounds from the data of participants who had not.
action was found. Planned comparisons revealed that the These reformatted data are displayed in Figure3.
difference between groups in the backward blocking A 2 (condition: informed vs. uninformed) (cid:7) 2 (com-
score and in the recovery from overshadowing score, al- pound memory: incorrect vs. correct)(cid:7) 3 (cue: W vs. X
though numerically larger in Group Informed than in vs. Y) ANOVA confirmed reliable differences among the
GroupUninformed, fell short of statistical significance ratings of CuesW, X, and Y by participants who correctly
[F(1,81) (cid:3) 2.43, MS (cid:3) 6.59, p (cid:3) .12, and F(1,81) (cid:3) identified the compounds in the informed and uninformed
e
3.95, MS (cid:3) 9.07, p (cid:3) .05, for the backward blocking conditions, but yielded no differences for participants who
e
score and for the recovery from overshadowing score, re- failed to correctly identify the compounds. There was a
spectively]. Therefore, explicit information about absent significant main effect of condition [F(1,79) (cid:3) 16.25,
cues effectively increased the magnitude of the overall MS (cid:3) 7.07], a significant main effect of compound
e
retrospective revaluation effect, but not to the degree memory [F(1,79)(cid:3)6.95, MS (cid:3)7.07], and a significant
e
necessary to allow us to observe a reliable difference in main effect of cue [F(2,158)(cid:3)17.65, MS (cid:3)4.30]. No-
e
each of its two components: backward blocking and re- tably, there was also a significant compound memory(cid:7)
covery from overshadowing. cueinteraction [F(2,158)(cid:3)4.64, MS (cid:3)4.30], showing
e
In addition, we considered the results of the postex- that cue ratings were different in participants who cor-
perimental questionnaire, which allowed us to determine rectly identified the compounds and in participants who
which participants remembered the four compound cues did not correctly identify the compounds. Planned com-
that had been presented during the experiment. Eight parisons confirmed that participants who remembered
participants in the informed group and 15 participants in the compounds in the informed condition showed both
the uninformed group did not correctly identify the four backward blocking [F(1,79)(cid:3)23.30, MS (cid:3)3.20] and
e
compounds. Group Uninformed performed less accu- recovery from overshadowing [F(1,79)(cid:3)16.51, MS (cid:3)
e
140 WASSERMAN AND CASTRO
9 Correct
Incorrect
8
7
s
g 6
n
i
t
a
R 5
n
a
e 4
M
3
2
1
W X Y W X Y
Group Uninformed Group Informed
Figure3. Mean final ratings of Target Cues W, X, and Y in the present experiment for par-
ticipants in the uninformed and informed conditions separated according to whether or not
they correctly identified all four compounds presented during training. Error bars indicate
the standard errors of the means.
4.52]. Participants who remembered the compounds in (2.23 and 1.13, for the informed and uninformed condi-
the uninformed condition again showed backward block- tions, respectively). A 2 (condition: informed vs. unin-
ing [F(1,79)(cid:3)5.65, MS (cid:3)3.20]; recovery from over- formed) (cid:7) 2 (difference score: backward blocking vs.
e
shadowing, which had not reached significance in the recovery from overshadowing) ANOVA yielded a main
previous analysis, was now significant [F(1,79)(cid:3)4.25, effect of condition [F(1,58)(cid:3)6.44, MS (cid:3)5.80], show-
e
MS (cid:3)4.52]. ing that the difference scores were significantly higher in
e
Especially interesting was the fact that participants who the informed condition than in the uninformed condi-
did not correctly identify the compounds did not show any tion. No interaction was found. Planned comparisons re-
of the retrospective revaluation effects. There was no sig- vealed that the difference for the backward blocking score
nificant difference between ratings of CueW and CueX, and the recovery from overshadowing score, as before, al-
in either the informed condition [F(1,79)(cid:3)0.07, MS (cid:3) though numerically larger in the informed than in the un-
e
3.20] or in the uninformed condition [F(1,79) (cid:3) 0.84, informed condition, fell short of statistical significance
MS (cid:3)3.20]. Nor was there a significant difference be- [F(1,58) (cid:3) 3.13, MS (cid:3) 19.26, p (cid:3) .08, and F(1,58) (cid:3)
e e
tween ratings of CueY and CueX in the informed condi- 2.61, MS (cid:3) 18.15, p (cid:3) .11, for the backward blocking
e
tion [F(1,79)(cid:3)1.66, MS (cid:3)4.52] or in the uninformed score and for the recovery from overshadowing score, re-
e
condition [F(1,79) (cid:3) 0.01, MS (cid:3) 4.52]. There was not spectively]. Most important was the fact that the enhanced
e
even a significant difference between ratings of Cue W overall retrospective revaluation effect in the informed
and CueY [F(1,79)(cid:3)2.03, MS (cid:3)5.18, in the informed condition compared with the uninformed condition per-
e
condition, and F(1,79)(cid:3)0.41, MS (cid:3)5.18, in the unin- sisted, despite the removal from both conditions of par-
e
formed condition]. These results are consistent with the no- ticipants who had not correctly identified the compounds
tion that the formation and retention of within-compound (Figure 3). Thus, differential memory alone cannot ac-
associations in this task is necessary to produce retro- count for the difference in the magnitude of the overall ret-
spective revaluation effects (see also Aitken etal., 2001; rospective revaluation effect in the informed and unin-
Dickinson & Burke, 1996; Melchers etal., 2004; Wasser- formed groups.
man & Berglan, 1998; but see Matute & Pineño, 1998a, Finally, we should comment on the time course of par-
1998b, and Escobar, Pineño, & Matute, 2002). ticipants’ causal ratings. If we compare ratings after
We also analyzed the difference in the magnitude of Phase1 training to final ratings (Table4), we see that in
the retrospective revaluation effects, now without the both groups, causal ratings of CueW decreased from the
participants who did not remember the compounds. We end of Phase1 to the end of Phase2, consistent with back-
again calculated the difference scores among all three of ward blocking.
the target cues to yield a backward blocking score (2.23 Ratings of Control CueX—which should maintain a
and 1.10, for the informed and uninformed conditions, similar value from the second to the final rating because
respectively) and a recovery from overshadowing score neither it nor its associated Cue B were presented in