Rachlin overlooks that free will determines when and in what direction acts that appear impulsive will occur. Because behavioral patterns continuously evolve, animals are not guaranteed when they will, or how to, maximize larger-later reinforcements. An animal therefore uses self-control to emit free acts to vary behavioral patterns to optimize larger-later rewards.

The approach adopted by Posner & Raichle in this book, with its strong emphasis on the cognitive level of description, is ideally suited to the study of psychotic illnesses. However, their discussion of depression and schizophrenia is based on a very small number of studies and involves ad hoc arguments derived largely from neuroanatomy. Their conclusions are almost certainly wrong.

Behavioral biologists have long sought to link behavioral units (e.g., aggression, depression, sociopathy) with biological units (e.g., genes, neurotransmitters, hormones, neuroanatomical loci). These units, originally contrived for descriptive purposes, often lead to misunderstandings when they are reified for purposes of causal analysis. This genetic and biochemical explanation for sociopathy reflects such problems.

The concept of a conservative control strategy minimizing the number of degrees of freedom used is criticised with reference to 3-D simple reaching and grasping experiments. The vector error in a redundant system would not be the prime controlled variable, but rather the posture for reaching, as exemplified by nearly straight displacements in joint space as opposed to curved ones in task space.

The costliness of disrupting a pattern may not be a useful criterion for distinguishing between acts and patterns; there are instances in which omitted components of patterns are hard to detect (e.g., typographical errors), or in which distortions are easily introduced (e.g., slurred words in a trite phrase). Are there behavioral criteria for distinguishing between acts and patterns?

Images of mind is an exciting book, well-written and wellorganized, but many of the connections the authors draw between PET scan results and more general psychological issues are somewhat strained.

Mealey proposes two categorical classes of sociopath, primary and secondary. I criticize this distinction on the basis that “type” constructs of this kind have proved unrealistic in personality taxonomy and that dimensional systems capture reality much more successfully. I suggest how such a system could work in this particular context.

The lambda model of Feldman & Levin for intentional hand movement is compared with a hemispheric motor model (IIMM). Both models imply similar conclusions independently. This increases the validity of both models.

Research reported by Posner & Raichle may be usefully applied to the rehabilitation of persons with brain damage. Their findings are related to the “dual premotorsystems hypothesis” that reciprocally interactive medial and lateral brain systems are involved in attention and learning. Recent studies show that “brain healing” occurs through dynamic reorganization involving attentional networks postulated by Posner & Raichle.

Mealey distinguishes two types of sociopathy: (1) “primary,” or obligate, and (2) “secondary,” or facultative. Either sociopathy evolved twice, or one form is derived from the other, e.g., through: (1) genetic assimilation generating polymorphism in the relative strength of biases favoring the development of otherwise facultative strategies, or (2) independently heritable but strategically relevant characteristics biasing the optimal selection of facultative strategies.

We affirm the dynamical systems approach taken by Feldman and Levin, but argue that a more mathematically rigorous and standard exposition of the model according to dynamical systems theory would greatly increase readability and testability. Such an explication would also have heuristic value, suggesting new variations of the model. We present one such variant, a new solution to the redundancy problem.

The Aristotelian position on causality advocates explaining biological events by the configuration of outcomes they normally achieve. Rachlin's analysis follows this strategy as an alternative to explanation via hypothetical “inner” events, though he omits considering one definition of “inner” explanation (historical definition) as being complementary to teleological explanation. He also fails to provide a detailed teleological analysis of the role of bridging responses in allowing animals to select larger-outcome alternatives.

Sociobiological explanation requires both a reliable and a valid definition of the sociopathy phenotype. Mealey assumes that such reliable and valid definition of sociopathy exists in her “Integrated Evolutionary Model.” A review of psychiatric literature on the diagnosis of antisocial personality disorder clearly demonstrates that this assumption is faulty. There is substantial disagreement among diagnostic systems (e.g., RDC, DSM-III) over what constitutes the antisocial phenotype, different systems identify different individuals as sociopathic. Without a valid definition of sociopathy, sociobiological theories like Mealey's should be viewed as entirely speculative.

On the basis of neuroiinaging studies, Posner & Raichle summarily report that the prefrontal cortex is involved in executive functioning and attention. In contrast to that superficial view, we briefly describe a testable model of the kinds of representations that are stored in prefrontal cortex, which, when activated, are expressed via plans, actions, thematic knowledge, and schemas.

The λ model suggests that detailed kinematics arise from changes in control variables and need not be explicitly planned. However, we have shown that when moving a grasped object, grip force is precisely modulated in phase with acceleration-dependent inertial load. This suggests that the motor system can predict detailed kinematics. This prediction may be based on a forward model of the dynamics of the loaded limb.

Operant psychologists are looking for alternatives to radical behaviorism. Rachlin offers teleological behaviorism, but it may pose as many difficulties as radical behaviorism. There is, however, a less drastic way to defend Rachlin's thesis of “order in the relationship between organisms and environment.” It portrays operant principles as relating distal efficient causes to behavioral effects.

The willingness to trade off large but ill-defined future consequences for immediate work characterizes social problems such as environmental sustainability. This commentary argues that important applications of behavioral models of self-control are being overlooked in the experimental literature. Tying the experimental literature to longterm health, environmental, and other risks makes the experimental work more germane, and raises new research questions for experimental modeling.

Recent results have shown that the relative activation of muscles is different for isometric contractions and for movements. These results exclude an explanation of muscle activation patterns by a combination ofreciprocal and coactivation commands. These results also indicate that joint stiffness is not uniquely determined and that it may be different for isometric contractions and movements.

In this brief commentary the author concentrates on the treatment perspectives of Mealey's model. The main weakness of the model is that it does not provide a satisfactory theoretical connection between treatment and different types of target behavior. Even within the primary-secondary distinction, there are large individual differences that should not be overlooked in the planning of treatment.

PET detects changes in metabolism between task periods and is thus insensitive to areas that are activated during all or most of cognition. Depth-recorded, evokedpotentials indicate that many multimodal and limbic cortical areas may be activated during most cognitive tasks. Thus, PET may be insensitive to some core processes of awareness that are difficult to eliminate from the control periods.