The Implications of Arousal Effects for the Study of Affect and Memory


We started this chapter with the claim that the study of arousal is important when studying the effect of affect upon memory. We have reviewed the reasons suggesting that arousal is a useful theoretical construct, discussed some of the problems in the measurement of arousal, and summarized the striking and reliable individual differences in either phasic or tonic arousal level. We have suggested that various manipulations of affect probably are also manipulations of arousal. We now consider evidence that arousal has at least four different effects upon the detection, storage and utilization of information. (Table 1) Two of these effects are beneficial: high arousal facilitates the detection and encoding for long term retention of information. However the third effect does not seem as beneficial: high arousal at input may be associated with an inability to retrieve information for a short period of time (up to about 30 minutes) following the original encoding. Finally, the fourth effect of arousal on information processing exists in those situations where the task demands combine beneficial and detrimental effects. On such (complex) tasks, increases of arousal from low to moderate are associated with improved performance, increases from moderate to high are associated with decrements in performance. This inverted-U relationship between arousal and performance is a function of the relative task demands of detection versus immediate versus delayed memory. We also raise the question of a fifth potential effect of arousal upon information processing: arousal effects upon retrieval.

That arousal facilitates detection and long term retrieval is not particularly surprising, for most scientific and folk models of memory would suggest that being more alert is a good thing for most cognitive tasks. What is surprising, however, is that increased arousal at storage seems to inhibit immediate retrieval processes. (That it must be a retrieval effect can be understood when the beneficial effects of arousal on long term retrieval are considered.) Finally, most theories of cognitive performance find it difficult to explain the inverted-U relationship between arousal and performance (Hebb, 1955; Humphreys and Revelle, 1984).

Insert Table 1 about here (NOTE--This table is available in the original publication or from W. Revelle. It is not reprinted here).

Beneficial effects of arousal upon detection

High levels of arousal facilitate the sustained detection of and rapid responding to simple stimuli (Hamilton, Fowler, & Porlier, 1989). Although ignored by most memory researchers, from the subject's point of view many memory studies are rather dull. Being exposed to one or more lists of words and then eventually being asked to recall words from the list is not a particularly exciting task. Indeed, Bowyer, Humphreys, and Revelle (1983) found that the performance of subjects thought to be susceptible to decrements in arousal (high impulsives) deteriorated rapidly over four blocks of a forced choice recognition study. This was not true for low impulsives. Increased arousal as induced by moderate doses of caffeine (4 mg/kg body weight) inhibited this decay in performance. Bowyer et al. interpreted this result as consistent with the general decrement in vigilance performance for extraverts (Bakan, Belton & Toth, 1963) or other subjects thought to be in a low aroused state (c.f. Mackie, 1977).

Detrimental effects upon shorter term retention

Perhaps the most intriguing effect of arousal lies in the finding of a deficit in immediate or shorter term recall. Walker and Tarte (1963) and Kleinsmith and Kaplan (1963, 1964) reported evidence that high arousal led to deficits for shorter term recall but facilitated longer term recall. Their studies served to instigate numerous attempts to replicate such an effect. These early studies relied on GSR responses to arousing and nonarousing word-number pairs (Kleinsmith & Kaplan, 1963; Walker & Tarte, 1963) or to nonsense syllable-number pairs (Kleinsmith & Kaplan, 1964) as indicators of the arousal present for implicit learning. Moreover, the deficits were found anywhere from immediate recall (2 minutes post-learning; Kleinsmith & Kaplan, 1963; Walker & Tarte, 1963) to some 20 minutes later (Kleinsmith & Kaplan, 1964). Kaplan and Kaplan (1969) and Butter (1970, Expt. 1) later replicated these detriments upon shorter term recall using the arousing and nonarousing word-number pairs and GSR responses in implicit learning designs. Butter (1970, Expt. 2) also replicated the effect using word-number pairs in which the words differed in concreteness-imagery. The effect was found both when analyzed from the perspective of GSRs to the paired associates upon learning and concreteness-imagery of the stimulus word (low concreteness-imagery was associated with a shorter-term detriment) as the independent variable.

In further extensions of this work using stimulus materials to induce differential arousal and GSR as a reflection of the arousal, Kaplan, Kaplan & Sampson (1968) replicated the shorter-term recall deficit using two alterations in the design: explicit learning instructions and word-picture pairs as learning materials. Levonian (1966) employed GSR during the screening of a traffic safety film to derive the same type of effect. Jones and colleagues found inferior recall of 9 digit strings for those subjects who evidenced higher baseline EEG activation and higher EEG activation during the first part of the explicit learning trials (Jones, Gale & Smallbone, 1979, Expt. 1).

In an interesting varation of this work, Geen (1973) found that the presence of an observing experimenter led to short-term decrements in recall of nonsense syllable-number pairs learned under explicit instructions. Deffenbacher and colleagues also found that the presence of an observer was sufficiently arousing to produce a highly significant deficit in recall 2 minutes after explicit learning (Deffenbacher, Platt & Williams, 1974). In a later refinement of this work, Geen (1974) found that the presence of an evaluating observer led to a short-term decrement rather than simply an observer per se. Other novel manipulations of arousal that led to successful replication of shorter term deficits include white noise (Berlyne, Borsa, Craw, Gelman & Mandell, 1965, Expt. 3; McLean, 1969, Expt. 1 & Expt. 2); caffeine in humans (Terry & Phifer, 1986) and rats (Terry & Anthony, 1980); exercise (Loftus, 1990, Expt. 1); time of day (Gates, 1916; Folkard & Monk, 1980, Expt. 1; Folkard, Monk, Bradbury & Rosenthall, 1977; Jones et al., 1979, Expt. 3); individual differences (Howarth & Eysenck, 1968; McLaughlin, 1968) and the interaction between time of day and individual differences (Puchalski, 1988).

Attempts to replicate this effect are not without failure, however. Saufley and LaCava's (1977) attempt to replicate using 3-letter trigram-number paired associates and explicit learning instructions failed to find any significant arousal based effects on memory. Schmitt and Forrester (1973) utilized the same experimental materials and paradigm as Butter (1970, Expt. 2). They found a similar decrement in the shorter-term recall of low concreteness-imagery words but garnered no evidence of a matching decrement as a result of GSR to the paired associates. Other failed attempts include Fuller's (1978) use of differences in Introversion/Extraversion and Oakhill (1986) using time of day.

Beneficial effects upon long term retention

Many of the studies that found shorter-term deficits in retention evidenced a reminiscence effect. Arousal at learning led to enhancement of longer-term recall such that the high arousal subjects remembered better after some sort of longer term delay than they had shortly after learning. This pattern of results exhibits a cross-over interaction between arousal at learning and retention interval. For instance, Kleinsmith and Kaplan (1963, 1964) and Walker and Tarte (1963) both found that arousing words were better remembered after one week than they had been 2 minutes after learning. Those studies that evidenced this dramatic pattern of results are classified as having shown a reminiscence effect in Table 1.

Still other studies that evidenced shorter-term deficits in retention exhibited enhancement of longer-term recall such that the high arousal conditions led to a lesser degree of forgetting than the low arousal conditions. Thus, although Loftus (1990, Expt. 1) found that high self-rated arousal produced by exercise led to inferior shorter term recall, it also led to a greater retention of the initially-recalled word pairs as compared to the low arousal group.

A few researchers have found that high arousal led to benefits both in shorter and longer term retention. Corteen (1969) garnered results that suggested high arousal learning (as measured by GSR) of aurally presented words led to superior shorter- and longer-term recall across testings at immediate, 20 minute and 2 week delays. Similarly, Maltzman, Kantor, and Langdon (1966) found that high arousal learning led to better recall immediately and 30 minutes after learning (This finding represents more of a shorter-term finding given that many studies find the reversal occurs somewhere between 20 and 40 minutes post-learning). Noteworthy here is that these materials were also presented aurally and the materials were once again single words of arousing and nonarousing quality.

Arousal effects upon retrieval

The potential confounding of differential effects of a variable upon learning and retrieval processes often represents an inevitable aspect of memory research. Research of arousal effects upon memory is no different. The presence of state- and/or trait-based arousal differences in shorter-term learning is invariably confounded with the question of the influence of that same arousal on the recall that occurs. When a retrieval task follows closely upon learning, however, it seems likely that the state of arousal would be the same for both processes. "Potentially, therefore, the changes in immediate memory performance..may be due as much to the influence of arousal upon retrieval as upon learning or, indeed, a subtle interaction between the two processes (pg. 408)," (Millar, Styles & Wastall, 1980).

Obviously, paradigms involving Sustained Information Transfer (SIT) resource tasks only such as discrimination of degraded digits (Matthews et al., 1990) are less vulnerable to such confounding. In addition, studies that focus on more short-lived state manipulations of arousal and recall intervals that take place safely beyond the range of such a manipulation are also less vulnerable. When the strong influence of individual differences and circadian aspects of arousal on memory are considered, however, it would seem that even longer term retrieval paradigms are placed at risk for this type of confounding.

Some researchers have combined arousal manipulations at learning with arousal manipulations at recall in order to assess potential arousal effects on retrieval probability. Folkard and colleagues (Folkard et al., 1977; Folkard & Monk, 1980) have consistently failed to find any effect of circadian arousal at retrieval upon both longer term recall and recognition tasks. Still others have examined the more direct effect of arousal on retrieval latency and/or probability unconfounded by learning state. M. W. Eysenck (1975a) found that high levels of arousal (a measurement of energetic arousal) as measured before retrieval increased the number of words recalled by extraverts and decreased the number of words recalled by introverts. Moreover, Pascal (1949) found superior recall performance when a relaxation manipulation was given immediately prior to recall. M. W. Eysenck (1975b) also found that moderate levels of arousal (high state arousal extraverts and low state arousal introverts) increased the speed of retrieval when contrasted to low levels (low state arousal extraverts) and high levels (high state arousal introverts) of arousal. Millar et al. (1980) found that retrieval efficiency as measured by retrieval latencies increased during the afternoon when compared to both morning and evening.

A recent study within our own lab (Loftus, 1990, Expt 2) crossed state and trait arousal at learning and immediate recall with that at longer term recall (1 week later). A highly similar pattern was found in both the shorter and longer-term recall performances: high state arousal (measured either by self-report or exercise/relaxation manipulation) tended to increase recall for the high impulsive subjects (low trait arousal) and decrease recall for the low impulsive subjects (high trait arousal). The arousal present at learning was not found to affect recall one week later. The similarity between the two patterns of results is striking and raises the possibility that some sort of retrieval effect was operating at both recall sessions. This pattern of results is reminiscent of an inverted-U relationship (Hebb, 1955) between arousal at retrieval and recall performance.

Theoretical explanations

Several different theoretical explanations of the effect of arousal on memory have been reviewed by M. W. Eysenck (1976, 1977, 1981, 1983). These include Walker's (1958) theory of the action decrement, Easterbrook's (1959) hypothesis that arousal narrows the range of cue utilization, and Schwartz' (1975) arousal based generalization of Craik and Lockhart's (1972) level of processing theory. Walker (1958) proposed that arousal increases temporary inhibition of retrieval during the formation of long term memory traces. Easterbrook's (1959) cue utilization theory provides a partial account of the arousal effects if it is assumed that immediate memory relies more on peripheral cues (and thus is hindered by an arousal induced narrowing of cue utilization) but that delayed memory relies more on central cues (which thus become more prominent if arousal narrows the range of cues utilized). Applying arousal to a levels of processing explanation (Craik and Lockhart, 1972) follows if low arousal is associated with less elaborative encoding than is high arousal. That is, less aroused subjects would use shallow, maintenance rehersal while more aroused subjects would tend to use more elaborative encoding. Although this explanation can predict the cross over interaction of arousal and delay interval, it does not predict the reminiscence effect observed in some studies.

Another explanation for the effects of arousal on memory is the "tick rate hypothesis" (Humphreys and Revelle, 1984; Revelle, 1989; Revelle & Loftus, 1990) which proposes that arousal increases the rate at which the environment is sampled. In direct analogy to the clock speed of a computer, this hypothesis predicts that increased arousal should lead to a faster rate of response to environmental cues, but to a decrement in availability in immediate memory due to the increased interference associated with a more rapid sampling rate. Finally, by increasing the rate at which the to be learned material is associated with the internal and external context, the model also predicts that high arousal should facilitate long term retrieval.[7]