Errors and episodes of “freezing” seen during mirror writing by adults can be incorporated into the model suggested in Thelen et al.'s target article This requires assigning an important role to internal inverse models stored in memory. The strongly anti-dualism position of Thelen et al.'s leaves little room for the Bernsteinian notion of activity.

Scripts and deception are alternative means, both imperfect, to the goal of simulating an environment that cannot be created readily. Under scripts, participants pretend they are in that environment, while deception convinces participants they are in that environment although they are not. With repeated trials, they ought to be unnecessary. But they are not, which poses challenges to behavioral sciences.

A slight modification of Webb's diagrammatic representation of the dimensions for describing models is proposed which extends it to cover a range of theoretical models as well as material models. It is also argued that beyond a certain level robotic simulations could offer a number of real advantages over computer simulations of organisms interacting with their environment.

The limitations of the concept of internalised kinematic geometry have been recognised by Barlow, Hecht, Kubovy & Epstein, and Todorovič. I am in agreement but I still find the perception of curvature in two frames of apparent motion fascinating and I suggest some new directions. [Barlow; Hecht; Kubovy & Epstein; Shepard; Todorovič]

Memory dynamics need both stable and unstable properties simultaneously. Hence memory dynamics cannot be simulated by chaotic itinerant dynamics alone, with no real world correspondence. Memory dynamics are constrained by both semantics and causalities in the embodied cognition.

Claims made in the target article that information-that-specifies is contained in relations among structured energy arrays, considered as wholes, may well be true, but claims that information-that-specifies is only contained in irreducible relations among structured energy arrays, considered as wholes, fail to persuade, at least in the case of the blind.

There is an old joke about a theoretical physicist who was charged with figuring out how to increase the milk production of cows. Although many farmers, biologists, and psychologists had tried and failed to solve the problem before him, the physicist had no trouble coming up with a solution on the spot. “First,” he began, “we assume a spherical cow ... ” [Tenenbaum & Griffiths]

When theoreticians talk about noise, they frequently forget about the idealization coupled with this term. Another implicit and rarely mentioned assumption is that the tools of mathematics used are idealizations, too. Though some of Tsuda's ideas are similar to mine (e.g., we both believe that nonlinearity is one of the main reasons why the brain works the way it does; Kowalik et al. 1996), some critical remarks are in order.

We believe that the task goal in voluntary movements provides meaning to existing information sources in the environment and determines, in a dynamic way, the use and relative importance of these different sources. This task-centered meaning bridges the apparent controversy between what information is available in principle (i.e., specification), and what information is perceived.

There is no best scientific model of anything; there are only models more or less good for different purposes. Thus, there is no general answer to the question of whether one should model biological behavior using computer simulations or robots. It all depends on what one wants to learn. This is not a question about models, but about scientific goals.

Methodological practices differ between economics and psychology because economists use game theory as the basis for the design and interpretation of experiments, while psychologists do not. This methodological choice explains the “four key variables” stressed by Hert-wig and Ortmann. Game theory is currently the most rigorous basis for modeling strategic choice.

Some dynamic systems approaches posit discontinuous changes, even universal stages, in development. Conversely, Thelen and colleagues see development as gradual because it relies on real-time interactions among many components. Yet their new model hinges on one parameter, neural cooperativity, that should change discontinuously because it engenders new skills that catalyze neural connectivity. In fact, research on cortical connectivity finds development to be discontinuous, and possibly stage-like, based on experience-dependent and experience-independent factors.

No. Animals' primary problem is the shaping of movements, guided by and adapting to sensory signals. This requires a narrower class of biorobotic models than that spanned by Webb's dimensions and examples. We claim that all model variables and mechanisms must have real counterparts, input vectors must model known sensor fields, internal state vectors and transformations must model neurophysiological processes, and output vectors must model coordinated muscle signals.

Stoffregen & Bardy suggest that the senses are not separable. However, they have a philosophical approach rather than using direct evidence that the nervous system analyzes sensory information in a highly flexible manner.

Clear-cut designs have a number of methodological virtues, with respect to internal and external validity, which I illustrate by means of informal causal analysis. In contrast, a more uniform experimental practice across disciplines may not lead to progress if causal relations in the human sciences are highly dependent on the details of the context.

Thelen et al. not only offer an important new theoretical account of the Stage 4 object permanence error but provide the foundation of a new theory of cognitive development that is grounded in action. The success of dynamic field theory as a more general account of cognitive functioning, however, will depend on the degree to which it can model more generative capacities that are not limited to simple choice situations. Imitation and problem solving are suggested as two capacities that might be productively modeled within their approach.

Shepard claims that color constancy needs linear basis-function spectra, and infers the illuminant before removing its dependency. However, of the models of color constancy that have exact (and reasonable) spectral regimes, some do not need linear basis-function expansions of reflectance and illuminant spectra, some do not solve for the illuminant, and some estimate only partial object-reflectance information for single or multiple objects. [Shepard]

Chaotic itinerancy is useful for illustrating transitions in attractor dynamics seen in the olfactory system. Cantor coding is a good model for information processing, but so far it lacks perceptual proof. The theories presented provide a large step toward bridging the use of chaos as an interpretive tool and hard examination of chaotic neural activity during perception.

Psychologists can learn from the procedural conventions of experimental economics. But the rationale for those conventions must be examined and understood lest they become constraints. Field referents and the choice of heuristic, matter for behavior. This theme unites the fields of experimental psychology and experimental economics by the simple fact that the object of study in both cases is the same.

Spatio-temporal neuro-dynamics is a quickly developing field of brain research and Tsuda's work is a significant contribution toward establishing theoretical foundations in this area. It is conceivable that the fragmented attractor landscapes and dynamical memory patterns identified earlier in various K-sets are biologically plausible manifestations of attractor ruins, chaotic itinerancy, and Cantor encoding as applied to sensory information processing.