The SI system of units (Système International d'Unités) should be used for measurements. The SI system is completely coherent, which means that all derived units are formed by simple multiplication or division of base units without the need for any numerical factors or powers of ten. This distinguishes the SI system from earlier metric systems such as the centimetre-gramme-second (CGS) system, which it superseded. The SI system comprises nine base units, each of which is independently defined, and various other units which are derived by combining two or more base units. The base units, together with some of the more common derived units, are listed in Table A2.1. Some common non-SI units and their SI equivalents are shown in Table A2.2.

Conventions. Each unit is represented by a standard unit symbol (e.g., m, s, A, kg), which may be multiplied or divided by other unit symbols or numbers (e.g., 3 m, 0.12 kg m, 16.5 m s-2). Unit symbols are algebraic symbols and follow the conventions of algebra. They are not abbreviations, and should never be followed by a full stop or an ‘s’ (to denote plural). The names of units (e.g., metre, second, ampere) are all spelt with a lower case initial letter. Symbols for units named after a person start with an upper case letter (e.g., A for ampere, K for kelvin, Pa for pascal). When a measurement is used as an adjective, the number and unit should be joined by a hyphen (e.g., three-metre tube, 5-m distance, 9-s delay, 6-m2 area, seventy-kilogram adult, 2-A current).

The beeper was designed by Chris Hereward of the Cambridge University Department of Zoology, who kindly gave permission for it to be reproduced here.

Circuit description

IC1 (a PXO 1000) is an integrated circuit crystal oscillator and divider unit. The interval between beeps (i.e., the sample interval) is determined by the settings of switches A–D, as shown in Fig. A4.1. The output of IC1 is inverted by a part of IC2 (a 4049UB) and used to turn on IC3 (a TLC 555CP) for about 0.1 s, timed by a 1 MΩ resistor and a 0.1 µF capacitor. IC3 is an astable multivibrator that produces the output tone. This is buffered and amplified by IC2 and fed into the positive battery line via a 390 Ω resistor. The battery is given a degree of isolation from the circuit supply by a silicon diode. This may seem a curious way of coupling the output, but it has the advantage that the circuit is turned off by unplugging the earphone. Plugging in the earphone switches on and resets the timer.

1. Formulate an initial question and make preliminary observations.

The question(s) asked may stem from previous knowledge or observations and may initially be rather broad or quite specific. A period of preliminary observations provides an essential opportunity to become familiar with the subjects and their behaviour and to develop hypotheses and methods of measurement (Chapter 4).

2. Formulate hypotheses and make predictions. On the basis of preliminary observations and existing knowledge, formulate hypotheses: the more the better. These should make specific predictions. Choose observations or experiments that will best distinguish between the competing hypotheses (Chapters 2 and 3). Formulating hypotheses is a creative process requiring imagination.

3. Choose behavioural measures and a research design. Be reasonably selective. Choose measures that are relevant to the question and which will help distinguish between different hypotheses. Hypotheses can be tested by observing natural variation as well as by performing experiments (Chapters 3 and 5).

4. Define each measure. Definitions should be clear, comprehensive and unambiguous. Write down the definitions before starting to collect data (Chapter 4).

5. Select the appropriate recording methods. These will depend on the nature of the behaviour to be recorded (Chapters 6 and 7). In practice, steps 3, 4 and 5 are inter-related, since the recording methods available often influence the choice and definition of categories.

6. Practise the recording methods. Assess the reliability and validity of each category. Drop categories that are clearly unreliable and irrelevant.

Rules for research

Formal prescriptions about the way in which scientific research should be conducted often fail to capture the flair, intuition and idiosyncrasies of the best scientists. Therefore, advice on how to organise thought and carry out research has to be given and taken with caution. Some people start studying a particular species simply because they find the animal interesting. Other scientists are initially more interested in a theoretical problem and, if they are wise, choose an animal that is especially suitable for studying that problem. It is not obvious that one approach is better than the other and, indeed, they are usually complementary.

Empirical data that distinguish between competing hypotheses can be obtained by observing natural variation as well as by performing controlled experiments. Thus, for many purposes, it is unnecessary to draw a rigid distinction between observational and experimental research. Many questions about behaviour are most appropriately answered by observational research. Moreover, in order to be effective, experimental research almost invariably needs to be preceded by observation. Knowledge of the normal behaviour of healthy animals, preferably in their natural environment, is an essential precursor to experimental research (see section 2.E on field studies). One of the distinguishing features of the ethological approach to studying behaviour has been its emphasis on combining observation with experiment.

Laboratory and field experiments

The point of doing an experiment is to distinguish between alternative explanations or hypotheses.

Sampling rules: ad libitum, focal, scan and behaviour sampling

When deciding on systematic rules for recording behaviour, two levels of decision must be made. The first, which we refer to as sampling rules, specifies which subjects to watch and when. This covers the distinction between ad libitum sampling, focal sampling, scan sampling and behaviour sampling. The second, which we refer to as recording rules, specifies how the behaviour is recorded. This covers the distinction between continuous recording and time sampling (which, in turn, is divided into instantaneous sampling and one-zero sampling; see Fig. 6.1). In this section, we consider the four different sampling rules.

1 Ad libitum sampling means that no systematic constraints are placed on what is recorded or when. The observer simply notes down whatever is visible and seems relevant at the time.

Clearly, the problem with this method is that observations will be biased towards those behaviour patterns and individuals which happen to be most conspicuous. For example, in a study of agonistic behaviour in rhesus monkeys, Bernstein (1991) found that ad libitum sampling tended to miss brief responses and under-estimated the involvement of younger individuals in social interactions. Provided this important limitation is borne in mind, however, ad libitum sampling can be useful during preliminary observations, or for recording rare but important events.

2 Focal sampling (or ‘focal animal sampling’) means observing one individual (or one dyad, one litter or some other unit) for a specified amount of time and recording all instances of its behaviour – usually for several different categories of behaviour.

Some of the more common statistical tests are listed here, according to the purposes for which they are used. Tests marked with an asterisk (*) are parametric and make more rigorous assumptions about the character of the data than do the non-parametric tests.

• Does the sample come from a specified population?

e.g. Chi square test for goodness of fit for a single sample Binomial test

• Are the scores of two unrelated samples different?

e.g. Chi square test for two independent samples Mann–Whitney U test

Student's t test for unmatched samples*

• Are the scores of two related samples different?

e.g. Wilcoxon matched-pairs test

Student's t test for matched samples*

• Are the scores of several unrelated samples different from each other?

e.g. Chi square test for more than two independent samples

Kruskal–Wallis one-way analysis of variance

Analysis of variance* (particularly when one variable may depend on two or more conditions)

• Are the scores of several related samples different from each other?

e.g. Friedman two-way analysis of variance

Repeated measures analysis of variance*

• Are two sets of scores associated?

e.g. Spearman correlation

Pearson correlation*

Simple regression* (when one variable may depend on another)

• Are several sets of scores associated?

e.g. Kendall coefficient of concordance

Multiple correlation*

Multiple regression* (when one variable may depend on others)

• Do more than one set of scores depend on more than one condition?

e.g. Multivariate analysis of variance*

How well does one remember the emotional events in one's life? Many studies indicate a strong correlation between the vividness with which an event is recalled, and the emotionality of the event, at the time it occurred (Bohannon, 1988; Brown & Kulik, 1977; Christianson & Loftus, 1990; Conway & Bekerian, 1988; Pillemer, 1984; Rubin & Kozin, 1984). Interestingly, this correlation seems independent of the type of emotion at stake (Reisberg, Heuer, McLean, & O'Shaughnessy, 1988; Robinson, 1980; White, 1989). Thus, in general, the stronger the emotion, the greater the vividness of subsequent recall. In this regard at least, “flashbulb” memories are continuous with remembering in general; that is, flashbulb memories simply represent the extreme of this affect–vividness relationship.

But how accurate are these vivid and detailed memories? If emotional events are recalled with great detail, is this evidence for some encoding or retrieval advantage associated with emotionality? Or, alternatively, is this evidence for high levels of construction and confabulation associated with emotion? In the former case, emotional memories would be both vivid and also veridical; in the latter case, emotional memories might be filled with errors and intrusions.

This question about accuracy is fueled by several concerns. As we describe below, several studies have documented conspicuous errors in the recall of emotional events. At the least, this implies that neither emotionality nor memory vividness provides any guarantee of memory accuracy.

In the classic paper on “flashbulb” memories, Brown and Kulik (1977) identified an aspect of autobiographical memory that had received scant attention from cognitive psychologists – memory for one's own personal circumstances (such as location, ongoing activities, and feelings) when receiving an important and shocking piece of news (such as first learning that President Kennedy had been shot), as opposed to memory for the newsworthy event itself. A second contribution of Brown and Kulik's original papers, and Neisser's (1982b) subsequent commentary, was a focus on memory function. What is the psychological value or adaptive significance of remembering personal details at such times?

In this chapter I examine memories of personal circumstances from a functional perspective. First, I argue that memories of personal circumstances are essential components of a fully functioning autobiographical memory system. Second, I critically examine the emphasis on memory accuracy in recent studies of flashbulb memories, and I conclude that the research agenda should be expanded to include memory functions that have heretofore fallen outside the realm of cognitive psychology. Third, I identify and describe three broad categories of memory function, none of which depends on absolute veridicality in recall:

1. Communicative functions: The act of recounting a detailed personal memory to others communicates meaning that transcends the surface content of the particular recollection, and this specialized form of communication appears to be rule governed.

2. Psychodynamic functions: Remembering personal circumstances in vivid detail can have a profound emotional and psychological impact on the rememberer, and on others with whom the memories are shared. Detailed recollection of specific episodes is frequently identified by clinicians as an essential component of psychotherapeutic process.

3. […]

Following the appearance of the now classic paper on “flashbulb” memory by Brown and Kulik (1977), Winograd and Killinger (1983) conducted a retrospective developmental study of the phenomenon. In reviewing Brown and Kulik's (1977) data, they noted that 24 of the 80 informants had been between 7 and 11 years of age at the time (1963) of the Kennedy assassination, yet their reports of the circumstances under which they discovered the news were no different from those informants who were adults at the time. A similar pattern was noted by Yarmey and Bull (1978), who found that only 15% of their subjects who had been between 6 and 10 years old in 1963 responded that they could not remember what they had been doing at the time they heard of Kennedy's assassination. Apparently, age at the time of encoding had little relation to subsequent recollections of the event's discovery. Winograd and Killinger (1983) thus set out to determine whether there were any differences between the memories of those who had been 7 or older at the time of the event versus those who had been younger. If age differences emerged, perhaps they could shed some light on both the development of autobiographical memory in general and the factors that contribute to flashbulb memories.

Winograd and Killinger (1983) collected questionnaires from 338 college students who had been 1 to 7 years old at the time of John F. Kennedy's assassination.

The purpose of this chapter is to analyze the concept of “flashbulb” memory and contrast it with other forms of human memory. The construct of flashbulb memory was introduced in a seminal paper by Brown and Kulik (1977) to account for memories of events such as the assassination of John F. Kennedy. Brown and Kulik described flashbulb memories as memories for the circumstances of hearing about a highly surprising and consequential event. These memories were said to be like a photograph, to show very little forgetting, and to be produced by a special purpose biological mechanism. Most recent work on this topic derives from the Brown and Kulik paper, and this chapter will begin with a conceptual analysis of that paper. The analysis will examine, in turn, each of the major theoretical and empirical claims of the original Brown and Kulik paper.

Brown and Kulik – theory

Circumstances (news reception context)

The core phenomenon described by Brown and Kulik (1977) is that certain events give rise to memories that show little forgetting. These flashbulb memories include both the central event and the circumstances in which one learned of the event.

Mental imagery

It appears to me that Brown and Kulik believe that the recollection of flashbulb memories involves the occurrence of visual images. Brown and Kulik do not state this explicitly, but it is the only interpretation I can give to their statement that flashbulb memories have a “primary, ‘live’ quality that is almost perceptual” (p. 74).

Commenting on this conference is a hard task. Every clever slant I could think of, and many I could not, were covered by comments in the continuing open discussion. I reflected on what others might do in this situation, and chose Allen Newell as a model. What he did to organize his discussion, on at least one occasion like this, was to spend half of his space on an issue not directly related to the papers of the conference. He had something worth saying that is as appropriate to this conference as it was to his, so I will just use his talk again. After all, he first gave his discussion in 1972 and we have heard here how confused memories can get over time. Newell began as follows.

This is the fourth volume in the Emory Symposia in Cognition series. Like two of its predecessors, Remembering Reconsidered (edited by Ulric Neisser and Eugene Winograd, 1988) and Knowing and Remembering in Young Children (edited by Robyn Fivush and Judith A. Hudson, 1990), it deals with memory. But whereas those earlier volumes were overviews of broad fields, this book is devoted to a single problem and – in large part – a single research paradigm. That problem is the relation between affect and memory; it is studied here by examining recollections of unexpected and emotional events. Although such recollections have only been called “flashbulb memories” since 1977 (the phrase was coined by Roger Brown and James Kulik in a seminal paper), they have long been the subject of theoretical speculation. Recently they have also been the subject of empirical research, much of it focused on memories of one particular event: the explosion of the Space Shuttle Challenger on January 28, 1986. It is those studies that form the core of this book.

The Emory Cognition Project conference on flashbulb memories was held on February 2–3, 1990. Our primary goal was to bring together everyone who had done research on memories of the Challenger episode and to review each others' data and learn from each others' methods. We hoped that the conferees would reach at least a sense of the meeting on the status of such memories: How do they compare with other kinds of recollections?

Several years ago, the teacher of a preschool class in the Boston area held a morning meeting to announce a sad occurrence: The mother of one of the children had died following a long illness. As the teacher began to talk, several children anticipated the topic: “K's mom died”; “I know, K's momdied.” Some children also spontaneously described their own personal circumstances when they originally heard the news: “My mom told me at the hospital”; “My mom told me at breakfast”; “My mom was making orange juice”; “My mom and dad told me”; “My mom said, ‘You won't be able to realize this.’” The teacher explained that K was fine, that K's mother had been sick for a long time, that the event was very unusual, and that it made people feel very sad. The discussion then turned to the general topic of death and the children's fears and misconceptions.

Preschool personnel observed and recorded the emotionally charged discussion, but had they not been aware of the author's interest in memories of personal circumstances, they might well have overlooked the children's comments about how they had “heard the news.” The target event itself – the death of a parent of a young classmate – was terrifying, and needed to be presented and discussed in a supportive context. On the other hand, the children's memories of their own circumstances upon hearing the news evoke the same sense of “mystery” first identified by Brown and Kulik (1977) with respect to adults' “flashbulb” memories of public tragedies.