Because of their evolutionary importance, threat-detection mechanisms are likely to exist at a variety of levels. A recent study of face recognition suggests that novel stimuli receive enhanced processing when presented as fear-related. This suggests the existence of a complex, context-dependent threat-detection mechanism that can adaptively respond to spatiotemporally varying and unique environmental features.

A review of data concerning the uneven distribution of phobias suggests that nonassociative, ethological models can account for most of tile important findings that cannot be attributed to expectancy biases. The origin of a variety of fears that appear in fixed developmental patterns across divergent cultures and species can best be explained by biological models.

Failure to find an obvious or linear relationship between a developmental experiential factor and a developmental outcome often leads investigators to posit concepts such as “biological preparedness” and “evolved predispositions” that allude to hypothetical geneticmechanisms that may not exist. However, experiential nonlinearities alone may explain the development of certain instinctive behaviors, as shown by studies on alarm call responsivity in mallard ducklings.

Davey reviews evidence purporting to distinguish between two accounts of selective associations – expectancy bias and evolved predispositions, although these hypotheses largely apply to different levels of causal analysis. Criticisms of primate studies in which subjects lack prior exposure to stimuli seem uncompelling. Expectancies may sometimes serve as proximal mediators in selective associations, but other factors, both proximate and ultimate, are clearly also involved.

Expectations can facilitate rapid fear conditioning and this may explain some phenomena that have been attributed to preparedness. However, preparedness remains the best explanation for some aspects of clinical phobias and the difficulty of creating fears of modern dangers. Rapid fear conditioning based on expectancy is not an alternative to an evolutionary explanation, but has, like preparedness, been shaped by natural selection.

The evolutionary origin of phobias is strongly supported by behavioral genetics and monkey vicarious conditioning data. Prepared Pavlovian conditioning may be only one of the mechanisms mediating the evolutionarily determined outcome in phobias, avoidance. Davey's alternative biased expectancy hypothesis has merit in accounting for some aspects of laboratory data, but it is insufficient to explain the unconscious origin of phobic fear.

According to Davey, generalized expectancy biases cause fearrelevant behavior and may complement Seligman's biological preparedness model. Expectancy biases do not explain the preparedness phenomenon, because such cognitive (or covert behavioral) processes are themselves controlled by social and other environmentally based contingencies. Davey's own examination of the importance of cross-cultural factors can show the relationship between FR stimuli and behavior without needing cognitive agency to explain the behavioral phenomenon.

Davey suggests that increased resistance to extinction of CRs conditioned to fear-relevant stimuli may be due to more persistent expectancies of the UCS following these stimuli. However, this viewpoint is contradicted by existing empirical evidence that fear-relevant CRs survive an extinction trials series producing extinction of expectancies whereas CRs conditioned to non-fear-relevant CSs do not.

Davey has failed to clarify the critical evidence that could corroborate the expectancy bias hypothesis and refute preparedness theory. Such a clarification is necessary because each theory could potentially allow for multiple distal and proximal influences on selective associations. Expectancies are not the only proximal mediators. Our recent findings indicate that affective response matching may be an additional factor promoting such associations.

Studies on associative learning in normals and patients need appropriate dependent measures which are sensitive enough to reflect stimulus-specific responses and also consider the context in which the conditioning takes place. Patient's fear responses, once acquired, seem to be maintained by specific cognitive biases such as individual belief systems and a tendency to stay consistent with their previous judgments.

This volume explores how functional brain imaging techniques like positron emission tomography have influenced cognitive studies. The first chapter outlines efforts to relate human thought and cognition in terms of great books from the late 1800s through the present. Chapter 2 describes mental operations as they are measured in cognitive science studies. It develops a framework for relating mental operations to activity in nerve cells. In Chapter 3, the PET method is reviewed and studies are presented that use PET to map the striate cortex and to activate extrastriate motion, color, and form areas. Chapter 4 shows how top down processes involving attention can lead to activation of these same areas in the detection of targets, visual search, and visual imagery. This chapter reveals complex networks of activations. Chapters 5 and 6 deal with the presentation of words. Chapter 5 illustrates PET studies of the anatomy of visual word processing and shows how the circuitry used for generating novel uses of words changes as the task becomes automated. Chapter 6 applies high density electrical recording to explore these activations in real time and to show how a constant anatomy can be reprogrammed by task instructions to produce and perform different cognitive tasks. Chapter 7 shows how studies of brain lesions and PET converge on common networks underlying attentional functions such as visual orienting, target detection, and maintenance of the alert state. Chapters 8 and 9 apply the network approach to examine normal development of attention in infants and pathological conditions resulting from brain damage, and psychiatric pathologies of depression, schizophrenia, and attention deficit disorder. In Chapter 10, new developments such as functional MRI are discussed in terms of future developments and integration of cognitive neuroscience.

Posner & Raichle's (1994) exciting, wonderfully illustrated book describes the past successes and future potential of the relatively noninvasive imaging of the nervous systems of living people. The focus has been on cognitive processes but there is no reason why emotional and motivational systems cannot also be tapped. Although the authors do not formally address such contentious issues as consciousness and the private experience of other species, imaging methods may hold promise for helping us to understand these phenomena, as well as to integrate psychological processes into ethological and phylogenetic research in general.

This book delivers much more than its title appears to promise; it is not merely a description of current methods for remotely monitoring brain activity. It primarily concentrates on just one such method: positron emission tomography, but it demonstrates beautifully how far that technique can now take us in the quest to discover the mechanisms underlying thought.

In interpreting measurements of brain processes it is necessary to make the model used explicit. A concept such as attention cannot be used in the description of brain activities without a model of the relation of mental and neural processes.

Images of mind marks a new era in human cognitive neuroscience. Despite the difficult conceptual problems associated with using group-averaged data and paired subtractions, human PET images converge well with existing data from other areas of cognitive neuroscience while opening up new theoretical and experimental possibilities. However, greater attention to individual differences might prove necessary in the study of culturally driven adaptations such as literacy.

A methodological problem may distort the implications derived from the metabolism scans of the brain, but Posner & Raichle may have found neural networks which underlie the analytical and synthetical hemispheric data processing mechanism. This methodological problem is that a large regional consumption of energy, detected by the PET technique, is not necessarily related to more data processing. It may be related to the inefficiency of the neural system at this region.

Encoding articulate speech is widely accepted as the principal (or sole) role of the frontal operculum. Clinical observations of speech apraxia have been confirmed by brain-imaging studies of speech production. We present evidence that the frontal operculum also programs limb movements. We argue that this area is a ventral counterpart of the dorsal premotor area. The two are functionally distinguished by specialization for somatic and visual space, respectively.

Posner & Raichle's book presents methods and data that increase support for mind-brain unity and provide a method for studying and verifying brain dysfunction objectively. Their incorporation into the assessment technology of neuropsychology should accordingly constitute a major advance. In addition, these techniques may help clarify longstanding controversies in cognitive psychology such as whether perception is multimodal or amodal.