Resultados y discusión 1. Mediciones de contadores

There are eight arguments against acceptance of the conditioning theory as a comprehensive explanation (Rachman, 1978, 1990, 1991).

People fail to acquire fears in what should be fear-conditioning situ-ations, such as air raids. It is dif®cult to produce stable conditioned fear reactions in human subjects, even under controlled laboratory conditions. The conditioning theory rests on the untenable equipoten-tiality premise. The distribution of fears in normal and neurotic populations is dif®cult to reconcile with the conditioning theory. A signi®cant number of people with phobias recount histories that cannot be accommodated by the theory. Fears can be acquired indirectly or vicariously. Fears can be acquired even when the causal critical events are temporally separated.

Failures to acquire fear

It would seem that few experiences could be more frightening than undergoing an air raid but the great majority of people endured air raids extraordinarily well during World War II, contrary to the uni-versal expectation of mass panic (Janis, 1951). Exposure to repeated bombing did not produce signi®cant increases in psychiatric dis-orders. Short-lived fear reactions were common but surprisingly few persistent phobic reactions developed. Few of the civilians who were injured or wounded developed a fear of the situation in which they received the injury (Rachman, 1990).

The observations of comparative fearlessness despite repeated exposures to intense trauma, uncontrollability, uncertainty, and even injury are contrary to the conditioning theory of fear acquisition.

People subjected to repeated air raids should acquire multiple, intense, conditioned fear reactions and these should be strengthened by repeated exposures. Civilian reactions to the warlike conditions in Northern Ireland (Cairns & Wilson, 1984) and the Middle East (Saigh, 1984, 1988) are consistent with the ®ndings from World War II. These

®ndings run contrary to prediction.

As stated, the phenomenon of PTSD provides convincing evidence of conditioning onsets of fear but a majority of the people who experience these trauma do not develop PTSD. Lesser examples of the failure to acquire fear include people who fail to develop a fear of dogs despite having unpleasant experiences with them, and even

having been bitten (di Nardo et al., 1988). Dental fears are fairly common but large numbers of people fail to develop a fear of dental treatment even though they have undergone uncomfortable and even painful experiences when con®ned in the dentist's chair (e.g. Davey, 1988; Lautch, 1971).

The absence of a direct relationship between injury and subse-quent fear runs contrary to conditioning theory. There should be a direct connection between injury and fear, but there is not (Rachman, 1990).

The conditioning of human fears

Deliberate attempts to generate conditioned fears in humans, as in the original attempts to treat alcoholism by establishing a conditioned aversion to alcohol, have had little success.

The equipotentiality premise

The theory assumes that any stimulus can be transformed into a fear signal; the choice of stimulus is a matter of indifference. Seligman (1970, 1971) argued convincingly that this premise is untenable, and hence its incorporation in the theory is a weakness.

The distribution of fears

The corollary of the equipotentiality premise is that all stimuli have an equal chance of being transformed into fear signals. However, this is not borne out by surveys of the distribution of fears, either in a general population or in psychiatric samples (Rachman, 1990).

Subject only to their prominence in the environment, many objects and situations should have an equal probability of provoking fear.

What we ®nd instead is that some fears are exceedingly common and certainly far too common for the theory; other fears are far too rare.

The fear of snakes is common and the fear of lambs is rare; moreover, a genuine fear of snakes is often reported by people who have not had contact with the reptiles. (Even more surprising is the absence of fears of motor cars and the small incidence of fears of motor travel.) Consequently, one is forced to conclude that the fear of snakes can be acquired even in the absence of direct contact, and this signi®cant concession opens three possibilities: (i) the fear of snakes is innate; (ii) the fear of snakes can be transmitted indirectly; or (iii) the fear of

snakes is ``lurking'' and will appear with only slight provocation. The last two of these three possibilities are compatible.

Patient reports of fear onset

It can be dif®cult to determine the origin of a patient's phobia and there are phobias in which there was ``no apparent trauma to initiate the phobia'' (Marks, 1969, p. 42). The absence of a plausible con-ditioning precipitant in a signi®cant number of phobic patients was demonstrated in the analysis by Ost (1985); 65% of the 183 patients acquired their fears by conditioning, 21% reportedly acquired their phobia indirectly and the remaining 14% were unable to recall the onset. In an expansion of this study, Ost (1987) found an association between the manner in which the phobia was acquired and the age of onset. The indirectly acquired phobias developed at an earlier age than the phobias with a conditioning origin.

The vicarious acquisition of fear

Advances in our understanding of the processes of observational learning and modelling have made it plain that we acquire much of our behaviour, including emotional responses, by vicarious experi-ences (Bandura, 1969, 1977). It is virtually certain that fears can be acquired either directly or vicariously and that stimuli are likely to develop fearful qualities if they are associated, directly or vicariously, with painful or frightening experiences (Rachman, 1990). To over-come the limitations of retrospective reports by participants, supple-mentary experimental investigations are needed. Mineka's (1985) research on monkeys showed conclusively that fears can be acquired by observational learning. More recently, Gerull and Rapee (2002) demonstrated the acquisition of a fear of snakes and spiders in 30 toddlers who were shown a rubber spider and snake in alternate pairings with positive, negative, or neutral facial expressions of their mothers. They found ``strong observational learning'' results, con-sistent with the view that early fears can be produced vicariously.

Acquisition by transmission of verbal information

It has also been suggested that fears might be acquired by the absorption of verbal information, especially information that conveys a threat (Rachman, 1978). The social transmission of intense fear, even panic, is well illustrated by recurrent epidemics of koro in South-east

Asia. Koro, derived from the Malay word for ``head of a turtle'', is a

``condition of psychiatric panic characterized by complaints of genital shrinkage coupled with fear of impending death'' (Tseng et al., 1988, p. 1538). Episodes of this intense fear, involving hundreds or thou-sands of people, have occurred in Singapore (1967), Thailand (1976), Assam (1982), and China (1984/1985 and 1987) and mainly affected isolated, poorly educated people who are strongly in¯uenced by folk beliefs. In a survey of 232 victims of the 1984/1985 epidemic in China, Tseng et al. (1988) found that the episodes of koro were characterized by panic (intense fear, palpitations, tremor, perspiration, fear of impending death or catastrophe). The Singapore epidemic appears to have been set off by a verbal report that the Viet Cong had poisoned Thai food to produce impotence.

Ollendick and King (1991) found that 89% of children attributed their various fears to negative information, 56% to modelling, and 36% to conditioning. These ®ndings have been replicated twice.

Moreover, a prospective study by Field, Argyris, and Knowles (2001) showed that the fears of 7±9-year-old children were signi®cantly increased by negative information. Muris, Bodden, Merckelbach, Ollendick, and King (2003) reported comparable ®ndings; 285 chil-dren, aged 4 to 12 years, were given negative or positive information about an imaginary doglike beast. The negative information steeply increased their fear of the beast; the fear was not transient and showed some generalization to dogs and predators. The children who received positive information showed a small reduction in fear.

Acquisition by remote events

At present, there is not suf®cient information to include the acqui-sition of fear by a temporally remote event as an additional argument against acceptance of the conditioning theory. However, convincing proof that fears can be acquired even when the stimulus and response events are separated in time would oppose the original conditioning theory.

In conclusion, the weaknesses of the classical theory are serious but not fatal. One can either search for an entirely new theory to replace it or adopt a reformist view and formulate modi®cations and exten-sions of the theory. At its best, the conditioning theory can provide a partial explanation for the genesis of some fears. However, it cannot explain how the common fears are acquired, nor can it explain the observed distribution of fears, the uncertain point of onset of many

phobias, the indirect transmission of fears, the ready acquisition of prepared phobias, and the failure of fears to arise in circumstances predicted by the theory. Fears acquired without direct contact with a fearful stimulus are an added problem for the theory and the acquisition of fears when the causal events are temporally separated was considered to be a serious problem until conditioning theory was

``liberalized'' (see p. 89).

A satisfactorily comprehensive theory of fear acquisition must accommodate all of the above plus the fact that fears can emerge gradually as well as suddenly, the fact that there are individual differences in susceptibility, and the probable acquisition of fears of objects/situations that the person has never encountered. It is also necessary to account for the acquisition of fears by events that are temporally separated. The status of theorizing on the three pathways to fear was reviewed by Merckelbach, de Jong, Muris and van den Hout (1996), and, since then, the additional evidence on vicarious acquisition and transmission by negative information has accumulated. There has also been renewed interest in the fact that many respondents are unable to recall when or how their fears arose.

In¯uenced by the ®ndings emerging from the remarkable Dunedin longitudinal cohort study, in which all children born between April 1972 and March 1973 were intensively and repeatedly tested over a 20+-year period, Poulton and Menzies (2002) proposed that a fourth pathway to fear should be recognized: ``Associative learning pro-ducing associations between the relevant stimulus and negative outcomes is not necessary for fears to arise'' (p.129). There are non-associative fears, that is, fears that are not acquired by learning processes. Many of the children's fears reported by the children or their parents had no learned onset but rather were present from early in life, notably the fears of water and heights. Moreover, the children with a fear of heights had experienced fewer falls from heights than the non-fearful children. The authors provide a good deal of infor-mation about such fears and make a plausible case for non-associative fears. These are reminiscent of the prepared fears discussed earlier (see p. 66), and are a reminder that people do learn certain fears but they also learn to not-fear: ``What we learn is how to overcome our existing predispositions . . . in large part we learn to stop responding fearfully to predisposed or prepared stimuli'' (Rachman, 1978, p. 255).

Poulton and Menzies take this one step further and suggest that we also have to learn to overcome innate fears, such as a fear of water or heights.