To what extent, if any, does Universal Grammar (UG) constrain second language (L2) acquisition? This is not only an empirical question, but one which is currently investigable. In this context, L2 acquisition is emerging as an important new domain of psycholinguistic research. Three logical possibilities have been articulated regarding the role of UG in L2 acquisition: The first is the “no access” hypothesis that claims that no aspect of UG is available to the L2 learner. The second is the “partial access” hypothesis that claims that only LI instantiated principles and LI instantiated parameter-values of UG are available to the learner. The third, called the “full access” hypothesis, asserts that UG in its entirety constrains L2 acquisition.

In this paper we argue that there is no compelling evidence to support either of the first two hypotheses. Moreover, we provide evidence concerning functional categories in L2 acquisition consistent with the claim that UG is fully available to the L2 learner (see also Flynn 1987; Li 1993; Martohardjono 1992; Schwartz & Sprouse 1991; Thomas 1991; White 1989). In addition, we will attempt to clarify some of currently unclear theoretical issues that arise with respect to positing UG as an explanatory theory of L2 acquisition. We will also investigate in some detail certain crucial methodological questions involved in experimentally testing the role of UG in L2 acquisition and finally, we will present a set of experimental results of our own supporting the “Full Access” hypothesis.

Whereas Latash & Anson (L&A) have underscored the rearrangement or setting of new priorities, our primary focus is on preexisting central nervous system (CNS) priorities that become even more prevalent and intrusive under pathological conditions. The adaptations observed in the disordered motor system can often be understood against the backdrop of these primary CNS constraints. Even though this perspective has not been specifically addressed in the target article, we consider it complementary and not necessarily in opposition to L&A's primary thesis.

Although a number of further studies have now been published exploring possible roles for the NO-cGMP signal transduction system in various models of LTD, there still appears to be confusion regarding the physiological functions of these molecules in the cerebellar cortex. What seems clear is that NO can be produced in granule cells and basket cells, and can stimulate soluble guanylyl cyclase, thereby activating cGMP-dependent protein ldnase in Purkinje cells. However, substrates for this Idnase are still poorly defined, and its role in the modulation of synaptic transmission remains to be determined. The recent development of novel transgenic models and new pharmacological agents with which to dissect this signal transduction system, gives one confidence that our understanding of the cerebellar NO system will quickly advance. With its unique properties as a signaling molecule, it is clear that NO news has been good news for those studying synaptic plasticity in the cerebellum.

The male advantage in certain mathematical domains contributes to the difference in the numbers of males and females that enter math-intensive occupations, which in turn contributes to the sex difference in earnings. Understanding the nature and development of the sex difference in mathematical abilities is accordingly of social as well as scientific concern. A more complete understanding of the biological contributions to these differences can guide research on educational techniques that might someday produce more equal educational outcomes in mathematics and other academic domains.

There is some complementarity of models for the origin of the electroencephalogram (EEG) and neural network models for information storage in brainlike systems. From the EEG models of Freeman, of Nunez, and of the authors' group we argue that the wavelike processes revealed in the EEG exhibit linear and near-equilibrium dynamics at macroscopic scale, despite extremely nonlinear – probably chaotic – dynamics at microscopic scale. Simulations of cortical neuronal interactions at global and microscopic scales are then presented. The simulations depend on anatomical and physiological estimates of synaptic densities, coupling symmetries, synaptic gain, dendritic time constants, and axonal delays. It is shown that the frequency content, wave velocities, frequency/wavenumber spectra and response to cortical activation of the electrocorticogram (ECoG) can be reproduced by a “lumped” simulation treating small cortical areas as single-function units. The corresponding cellular neural network simulation has properties that include those of attractor neural networks proposed by Amit and by Parisi. Within the simulations at both scales, sharp transitions occur between low and high cell firing rates. These transitions may form a basis for neural interactions across scale. To maintain overall cortical dynamics in the normal low firing-rate range, interactions between the cortex and the subcortical systems are required to prevent runaway global excitation. Thus, the interaction of cortex and subcortex via corticostriatal and related pathways may partly regulate global dynamics by a principle analogous to adiabatic control of artificial neural networks.

Although the Full-access hypothesis accounts for a range of empirical generalizations of L2A, it underrepresents the role of language transfer in the construction of the L2 grammar. We suggest the possibility that linguistic principles which constrain the L2 grammar are available both directly from UG and via the L1, a logical hypothesis which Epstein et al. do not consider.

Neural models are needed at many levels, ranging from the biophysically based to connectionist abstractions. The adjustable pattern generator (APG) model of the cerebellum discussed in the target article by Houk, Buckingham, and Barto operates at an intermediate level and is constrained by a large body of anatomical and physiological data. The associative memory model originally proposed by Marr (1969) and Albus (1971) on the basis of the microcircuitry of the cerebellar cortex is still relevant today, although it needs to be coupled to the problem of motor pattern generation. In considering the problem of cerebellar learning, one needs some source of training information to adjust network performance so that it performs fruitful interactions with the environment; however, it is not true that this “teacher” needs to be particularly smart. We address these and other important issues raised by the commentators.

Normal infants show a wide range of “atypical” movements. These, like the movements of atypical and normal adults, are best characterized as solutions to motor problems. Motor patterns alone may not be precise indicators of neurological status.

We show that left-handers can be considered as a “special” population. We indicate that the asymmetries in performance exhibited by left-handers are due to a basic asymmetry in the underlying coordination dynamics that constrains bimanual coordination. In contrast to the claims of Latash & Anson, we argue that considerable knowledge has been gained regarding the essential equations of motion that govern biological coordination.

This target article's handling of theory and data and the range of evidence surveyed for its main contention fall short of normal BBS standards. However, the contention itself is reasonable and can be supported if one rejects the “knowledge” metaphor for linguistic competence and accepts that “syntactic principles” are no more than the way the brain does language.

Some concepts relating to learned, structured functioning of local modules in neocortex are clarified in order to ensure that the integration from the small scale to the global attempted by Wright & Liley does not miss the target.

Several themes can be identified in the commentaries. The first is that the climbing fibers may have more than one function; the second is that the climbing fibers provide sensory rather than motor signals. We accept the possibility that climbing fibers may have more than one function – hence ‘consequence(s)’ in the title. Until we know more about the function of the inhibitory input to the inferior olive from the cerebellar nuclei, which are motor structures, we have to keep open the possibility that the climbing fiber signals can be a combination of sensory and motor signals.

Does the Wright & Liley model predict: (1) that subdural and hippocampal EEGs coherence tend to rise and fall in parallel for many frequencies, (2) that it is locally high or low within 10mm and falls steeply on average or, (3) that it is in constant flux, mostly rising and falling within 5–15 sec?

The argument that disordered or changed motor patterns can be adaptive or optimal given the constraints imposed is supported. Two major points of criticism are made, concerning the perceived superstates of the primary disorder and the absence of a systematic approach to identifying this adaptivity and optimality. We have tried to give the general outlines of such an approach to disordered movements from a dynamic systems perspective.

In response to several requests from commentators, an unambiguous definition of time-varying joint stiffness is provided. However, since a variety of different operations can be used to measure stiffness, a problem for quantification admittedly still exists. Several commentaries pointed out the advantage of controlling joint stiffness in optimizing the speed-accuracy trade-off known as Fittss law. The deficit in rapid reciprocal movements and the impact on joint stiffness inhibition caused by cerebellar lesions is clarified here, as the target article was apparently misinterpreted by some readers. In response to the challenge that there is little consensus among cerebellar physiologists, several areas of tacit agreement with other theories of cerebellar function are enumerated. An alternative interpretation of studies showing a transient activation of the cerebellum in motor learning is suggested. Finally, the relationship between the command signals generated by supraspinal centers such as the cerebellum and spinal interneuron networks controlling muscle synergies is discussed.

The Epstein, Flynn, and Martohardjorno full access hypothesis could be enhanced by inclusion of criteria for falsification.

The target article reviews studies of human cerebellar functional imaging and ablation in motor learning. This material is integrated with anatomical and physiological work in laboratory animals. A synthesis is presented as a working hypothesis on how the cerebellum might adapt, learn, and coordinate movement. An attempt is made to extend the motor role to certain mental operations, particularly those associated with mental movement. These notions met with varying enthusiasm. A few commentators seemed pleased with the overall result and offered supportive ideas. Some were critical of the proposed contributions to cognition and motor learning. A surprising number insisted that the cerebellum was more concerned with sensory processing than with movement management. Some thought we know too little to attempt such a synthesis.

Some dichotomies related to modeling electrocortical activities are analyzed. Attractor neural networks versus biologically motivated models, near-equilibrium versus nonequilibrium processes, linear and nonlinear dynamics, stochastic and chaotic patterns, local and global scale simulation of cortical activities are discussed.

The target article pays insufficient attention to (1) the difficulties that arise when the term “normal” is used to describe motor skill behavior, and (2) the need to resist ascribing motor control to an intelligent central nervous system. A complex systems perspective is proposed with attractor states and periodicity identified as markers of atypical coordination and control.

While child language development theory must explain invariant “success,” foreign language learning theory must explain variation and lack of success. The fundamental difference hypothesis (FDH) outlines such a theory. Epstein et al. ignore the explanatory burden, mischaracterize the FDH, and underestimate the resources of human cognition. The field of second language acquisition is not divided into camps by views on “access” to UG.