In general, conditioned attention theory, CAT (Lubow, Schnur, & Rifkin, 1976; Lubow, Weiner, & Schnur, 1981), states that nonreinforced preexposure to a stimulus retards subsequent conditioning to that stimulus because during such preexposure the animal learns not to attend to it. The theory is based on the use of attention as a hypothetical construct, with the characteristics of a Pavlovian response, and on the specification of reinforcement conditions that modify attention.

The assumption that changes in attention to stimuli are a function of reinforcement conditions may be traced to Lashley (1929) and Krechevsky (1932). Likewise, Lawrence (1949) suggested that the “acquired distinctiveness of cues” might be a gradual learning process subject to traditional analysis. In more recent theorizing, changes in attention as a function of reinforcement conditions have been emphasized by Mackintosh (1975), Frey and Sears (1978), and Pearce and Hall (1980), as well as in the “selective attention” theories of Lovejoy (1968), Sutherland and Mackintosh (1971), Trabasso and Bower (1968), and Zeaman and House (1963).

In similarity to selective attention theories, CAT treats attention as a response, occurring on stimulus presentation, the probability of which is increased when it is followed by reinforcement and decreased when it is not reinforced. However, CAT differs from those theories in a number of important respects: the conditions specified for the changes in the attentional response; the mechanism postulated to govern such changes; and the course of these changes with repeated stimulus presentation.

Originally, this book was to have been organized such that a separate chapter would be devoted to each of the major paradigms within which latent inhibition had been demonstrated. Although such a categorization proved to be convenient for the initial organizing of the hundreds of published reports, it soon became clear that there was an absence of major differences in the latent inhibition phenomena that could be attributed to the type of testing procedure employed. Therefore, it was decided to present the empirical evidence for latent inhibition on the basis of manipulated variables, organismic variables, and variations across experiments. It is, of course, in this latter category that testing procedures are to be found. Procedures are placed at the head of the list, for two reasons: first, to present evidence that latent inhibition is indeed a ubiquitous phenomenon, found across a very wide range of testing procedures; second, by accomplishing the preceding, to avoid, in subsequent sections, the necessity of repetitiously labeling the experimental procedures for each point that is made.

Before identifying those paradigms in which latent inhibition has been investigated, two general comments are in order, one concerning the number of stages in the procedure, and the second concerning the problem of differentiating the conditioned response (CR) to the target stimulus in the test from the unconditioned response (UR) to that stimulus.

Although conditioned attention theory was developed specifically to account for latent inhibition effects, it is also relevant to other phenomena in the area of learning, particularly to those situations where the target stimulus is presented under conditions in which attention is diverted from it by competing stimuli, such as in blocking and overshadowing, or in which stimuli are presented repeatedly, as S1 in the preexposure phase of the learned helplessness paradigm, or S1–S2 in the first phase of sensory preconditioning. In regard to the first of these areas, Lubow, Weiner, and Schnur (1981) have already commented on the implications of conditioned attention theory for understanding blocking and overshadowing, as well as the feature positive effect. Similarly, in the second area, the relationships among CAT, learned helplessness, habituation, and sensory preconditioning have been explored. With the exception of learned helplessness, there is little to be added to the already published analysis, and the interested reader is referred to the original source (Lubow, Weiner, & Schnur, 1981). However, in regard to learned helplessness, new and important materials are available, enough to warrant a reconsideration of the relationship between latent inhibition and learned helplessness. In addition, a literature has recently developed on the relationship between latent inhibition, as it reflects normal attentional processes, and schizophrenia, often regarded as characterized by attentional dysfunction. These two topics, learned helplessness and schizophrenia, will be explored in the following two sections.

In the past, the extensive efforts to understand latent inhibition were directed at behavioral analyses of the phenomenon, the data from which we have discussed at some length in the previous chapters. More recently, however, a keen interest has developed in the neural substrates of latent inhibition. Although this certainly reflects a general trend in the experimental psychology of learning, the additional focus also can be partially explained by the relatively new interest in the area of attention among psychologists, as well as by the consensual opinion that latent inhibition reflects some aspect of attention (e.g., Lubow, Weiner, & Feldon, 1982). More specific manifestations of this direction can be seen in various attempts to evaluate the attentional deficits of schizophrenia by assessing impairments of latent inhibition (Baruch et al., 1988a,b; Lubow et al., 1987) and, at the same time, to explore the animal amphetamines model of schizophrenia by examining the effects of amphetamines as well as neuroleptics on latent inhibition in animals (e.g., Solomon et al., 1981; Solomon & Staton, 1982; Weiner et al., 1984; Weiner & Feldon, 1987; Weiner, Feldon, & Katz, 1987; Weiner, Lubow, & Feldon, 1981). In addition to these efforts, which will be described in the section on the effects of dopaminergic manipulations on latent inhibition, other brain systems have also been studied in this regard. These will be reviewed and discussed separately in sections on noradrenergic, serotonergic, cholinergic, septo-hippocampal, and opiate manipulations.

In the preceding chapter we developed and applied CAT to the data from latent inhibition studies with animals, but we ignored the data from experiments with human subjects. It will be recalled that these human studies present a pattern of results not entirely consistent with that obtained from lower organisms. To review, the major findings, presented in chapter 5, are as follows:

1. There are standard stimulus preexposure procedures that will produce latent inhibition in young children, but not in older children or adults.

2. If these same procedures are coupled with a masking task, then latent inhibition can be produced in older children and adults.

3. Nevertheless, there are some procedures (i.e., electrodermal conditioning, conditioned tasted aversion, and Ivanov-Smolensky conditioning) that may not require masking for the production of latent inhibition.

The last point will be dismissed, perhaps somewhat cavalierly, because of the difficulty in separating the unconditioned response to the CS (orienting or otherwise) from the conditioned response to the CS in the test phase. As a result, one cannot determine whether stimulus preexposure produces an artifactual reduction in the conditioned response or a reduction in the associability of the CS. This, it will be recalled, is similar to the problem encountered in a number of animal conditioning paradigms. In addition, these studies with humans may have included unplanned masking procedures – either by the very nature of the procedure or by instruction.

Let us now consider the effects of age and masking on latent inhibition in humans.

It is difficult to determine exactly when I began this book, as such. However, the research on latent inhibition was initiated in the late 1950s while I was still a graduate student at Cornell University. The next memorable date for measurement was the publication of an article reviewing the latent inhibition literature in the Psychological Bulletin (1973), which appeared in about half of its original length. The conditioned attention theory of latent inhibition was developed later in a series of articles in the Journal of Experimental Psychology: Animal Behavior Processes in the mid-1970s, and then presented more fully in a chapter in Progress in Learning and Motivation edited by G.H. Bower (1981). The idea of developing this material into a book emerged during a sabbatical year at Yale University, 1977–1978, while much of the writing itself was postponed until another sabbatical, 1981–1982, as an Israel-Canada Fellow at Concordia Unversity. To all of these institutions, and to the individuals who were responsible for inviting me, I express my sincerest gratitude, particularly to Allan Wagner and Eugene Rothman.

In addition, throughout the years I have been fortunate to have my research supported by a number of organizations: The National Institutes of Health were particularly encouraging, especially at the early stages of my career with a Career Development Award. Other support has come from the Scottish Rite Schizophrenia Research Program and, in Israel, from the Charles Smith Psychobiology Fund, the Israel National Academy of Science, Israel Research Trustees Foundation (Ford), and Tel-Aviv Unversity.

Similarity of preexposed stimulus and test stimulus

Studies of the influence of stimulus preexposure on subsequent learning usually assume that these effects are stimulus-specific. That is, preexposure to stimulus A should not retard the subsequent acquisition of an association between stimulus B and another event. This assumption is particularly critical if one maintains the idea that the subsequent decrement in the acquisition of the association between A and another event is a result of some previous associative learning during the preexposure phase. Associative learning, by definition, presumes some degree of stimulus specificity. Indeed, the apparent absence of such specificity in the learned helplessness effect, at least in rats (Maier & Seligman, 1976) in which preexposures of a motivationally significant stimulus is administered, by itself, might raise the question whether or not one is dealing with an associative learning phenomenon. For latent inhibition, across different paradigms, the results are quite clear. The decremental effects of preexposure of the to-be-conditioned stimulus on subsequent acquisition of a new association are, without doubt, stimulus-specific.

Such stimulus specificity may be demonstrated in several ways. (1) A within-subject experimental design may be employed whereby the animal is preexposed to stimulus A and tested on both stimulus A and stimulus B. When appropriately counterbalanced, slower learning to the familiar stimulus compared with the novel stimulus serves as evidence for the stimulus specificity of latent inhibition. Such a design was employed by Lubow and Moore (1959), Reiss and Wagner (1972), and Wickens et al. (1983).

Concepts

Risk

Risk is associated with the undesired outcomes of an action or absence of an action. Every choice involves risk because the consequences are never certain and inevitably some consequences are less desirable than others. Statistically, risk can be defined as the sum of the probabilities of the separate undesirable consequences of an activity. As Rowe (1986) put it, risk is the downside of a gamble. Alternatively the pursuit of any objective can be assessed in cost: value terms and risks are associated with the costs. Risk is often defined as a compound measure of probability and magnitude of adverse effect, e.g. Lowrance (1980), but this complicates even further an already complex concept because the magnitudes of adverse effects involve value judgments which are idiosyncratic. With this kind of definition there can be no agreed measure of a specific risk.

Risk has become a social and technical rather than a personal problem because technology at any level generates hazards which are not confined to one person pursuing his private affairs. Even when using a hand-tool a worker who suffers or causes suffering might readily imply that the risk was generated not by him but by the tool design, by lack of appropriate training or by inadequate instructions. With higher technology the situation becomes still more complicated. A passenger in any vehicle is subject to appreciable risks over which he has no control once he has entered the vehicle.

Concepts

One of the fundamental attributes of human behaviour is that it changes continuously along the time dimension. This fact is neglected by many experimental psychologists who are attempting to describe the behaviour of the human operator, the average man, the laboratory subject (actually labelled ‘S’ in some journals) or even the human organism (labelled ‘O’). This is only defensible provided that it is recognised that whatever properties are adduced they relate to a static abstraction. The properties of this abstraction are described in Chapter 5 but as a preliminary to such studies the set of concepts which express what is known about dynamic behaviour are needed.

The constructive changes in time are generally put into the category of learning already described in Chapter 2. The analogous negative changes which occur in parallel are described as fatigue (in the short term) and ageing (in the long term). Ageing is also dealt with in Chapter 2.

There are several concepts which centre on the facility to change level of activity either voluntarily or involuntarily. This is described as arousal. Within arousal studies two sets of phenomena have been identified and investigated in great detail, particularly over the past forty years. These are stress and vigilance. Stress was adopted as a popular behavioural research topic because it seemed to have possibilities of easier measurement than fatigue which had its heyday from 1920 to 1950.

Concepts

Social factors

Activity involving others

It is rare for a human being to do anything in isolation for very long. It is possible to think of examples such as the tractor driver who may be alone for a working day, and there are unusual tasks such as single-handed yachting where the person may be alone for several weeks. Nevertheless, the obvious rarity of these illustrations emphasises the point that people at work are usually interacting with other people.

This may involve the interdependence of tasks, in which case there is a team or crew involved or it may be that people happen to be working in the same location and the interaction is social rather than operational. Many, perhaps most, tasks are of an intermediate kind where there is some common purpose linking the tasks, but nevertheless individuals are working more or less independently and their interaction is mainly social. They may chat at intervals, they share rest periods and meals and they may travel to and from work together. This is the common situation in industry and commerce. The social interaction is very highly prized, it is often mentioned as the main reason for enjoying going to work. A different kind of interaction occurs when one person is providing a service for a second person, for example the shop assistant or the dentist.

Concepts

Information acceptance

The processes on the input side of the human operator are, in serial order: sensation, perception and cognition. These are functional terms not neatly separated and not unambiguously related to physiologically identifiable mechanisms. Even the order is complicated by interaction and feedback processes.

Sensation

The sense organs are separately identifiable in that they contain specialised transducers: cells which are particularly reactive to light, pressure, chemicals or temperature. This separation is not the same as the classical five senses in that it merges the auditory system with the somaesthetic system within pressure detectors, and taste and smell within chemical detectors. The somaesthetic system provides experience of pressure discontinuities at the surface and in the movement of the body, it detects movement about joints (the kinaesthetic system), angular and linear acceleration (the vestibular system) and skin pressure (the tactile system) (Fig. 5.1). Its importance is underestimated because, by contrast with the distant senses, it functions with minimal conscious awareness. Taste is not important at work except for specialised tasks related to catering. In addition to its close relationship with taste, smell is useful in fault detection of high temperatures and leaks. Essentially the work of the human operator is guided by three main sensing devices: vision, hearing and somaesthesia. Sensation implies a generalised awareness of changes in light, sound or bodily position and posture. Thus the brain is involved as well as the specialised sense organs.

Concepts

This is one of the shorter chapters because, with the exception of road vehicles, the research effort is considerable but the practical application is limited and shows no signs of expanding rapidly in the near future. Nevertheless it is worthwhile to introduce the topic because at least potentially there is a considerable Human Factors contribution to the issues.

The technology-based society

The issue in general terms is that, throughout the world, changes in the environment, work and leisure are now based on advances in technology. If these changes are left to the physical scientists and engineers the consequences are not entirely satisfactory to the customer, the ordinary citizen. In his role as the people's representative in technology design teams the Human Factors specialist ought to take some responsibility for improving this state of affairs. There are a number of difficulties:

–the ultimate responsibility is with the politicians elected to government, but in terms of intellect, education and training, politicians are not well equipped to assimilate and weight the conflicting advice they receive, and national constitutions were designed for a different era. For example, most countries have a governmental Department of Transport, but no country has an integrated transport policy. There are too many vested interests, the interactions are too complicated, the consequences of decisions extend well beyond the life cycle of any one government – in general the problem is too big. Some impact is possible at regional and district levels, but not on a national scale.