Parallel and distributed neural models of the ideomotor principle: An investigation of imitative cortical pathways

Neural and Computational Mechanisms of Action Processing: Interaction between Visual and Motor Representations

Action recognition has received enormous interest in the field of neuroscience over the last two decades. In spite of this interest, the knowledge in terms of fundamental neural mechanisms that provide constraints for underlying computations remains rather limited. This fact stands in contrast with a wide variety of speculative theories about how action recognition might work. This review focuses on new fundamental electrophysiological results in monkeys, which provide constraints for the detailed underlying computations. In addition, we review models for action recognition and processing that have concrete mathematical implementations, as opposed to conceptual models. We think that only such implemented models can be meaningfully linked quantitatively to physiological data and have a potential to narrow down the many possible computational explanations for action recognition. In addition, only concrete implementations allow judging whether postulated computational concepts have a feasible implementation in terms of realistic neural circuits.

Towards a Computational Comparative Neuroprimatology: Framing the language-ready brain

We make the case for developing a Computational Comparative Neuroprimatology to inform the analysis of the function and evolution of the human brain. First, we update the mirror system hypothesis on the evolution of the language-ready brain by (i) modeling action and action recognition and opportunistic scheduling of macaque brains to hypothesize the nature of the last common ancestor of macaque and human (LCA-m); and then we (ii) introduce dynamic brain modeling to show how apes could acquire gesture through ontogenetic ritualization, hypothesizing the nature of evolution from LCA-m to the last common ancestor of chimpanzee and human (LCA-c). We then (iii) hypothesize the role of imitation, pantomime, protosign and protospeech in biological and cultural evolution from LCA-c to Homo sapiens with a language-ready brain. Second, we suggest how cultural evolution in Homo sapiens led from protolanguages to full languages with grammar and compositional semantics. Third, we assess the similarities and differences between the dorsal and ventral streams in audition and vision as the basis for presenting and comparing two models of language processing in the human brain: A model of (i) the auditory dorsal and ventral streams in sentence comprehension; and (ii) the visual dorsal and ventral streams in defining "what language is about" in both production and perception of utterances related to visual scenes provide the basis for (iii) a first step towards a synthesis and a look at challenges for further research.

A Programmer–Interpreter Neural Network Architecture for Prefrontal Cognitive Control

There is wide consensus that the prefrontal cortex (PFC) is able to exert cognitive control on behavior by biasing processing toward task-relevant information and by modulating response selection. This idea is typically framed in terms of top-down influences within a cortical control hierarchy, where prefrontal-basal ganglia loops gate multiple input–output channels, which in turn can activate or sequence motor primitives expressed in (pre-)motor cortices. Here we advance a new hypothesis, based on the notion of programmability and an interpreter–programmer computational scheme, on how the PFC can flexibly bias the selection of sensorimotor patterns depending on internal goal and task contexts. In this approach, multiple elementary behaviors representing motor primitives are expressed by a single multi-purpose neural network, which is seen as a reusable area of "recycled" neurons (interpreter). The PFC thus acts as a "programmer" that, without modifying the network connectivity, feeds the interpreter networks with specific input parameters encoding the programs (corresponding to network structures) to be interpreted by the (pre-)motor areas. Our architecture is validated in a standard test for executive function: the 1-2-AX task. Our results show that this computational framework provides a robust, scalable and flexible scheme that can be iterated at different hierarchical layers, supporting the realization of multiple goals. We discuss the plausibility of the "programmer–interpreter" scheme to explain the functioning of prefrontal-(pre)motor cortical hierarchies.

Information processing in the mirror neuron system in primates and machines

The mirror neuron system in primates matches observations of actions with the motor representations used for their execution, and is a topic of intense research and debate in biological and computational disciplines. In robotics, models of this system have been used for enabling robots to imitate and learn how to perform tasks from human demonstrations. Yet, existing computational and robotic models of these systems are found in multiple levels of description, and although some models offer plausible explanations and testable predictions, the difference in the granularity of the experimental setups, methodologies, computational structures and selected modeled data make principled meta-analyses, common in other fields, difficult. In this paper, we adopt an interdisciplinary approach, using the BODB integrated environment in order to bring together several different but complementary computational models, by functionally decomposing them into brain operating principles (BOPs) which each capture a limited subset of the model's functionality. We then explore links from these BOPs to neuroimaging and neurophysiological data in order to pinpoint complementary and conflicting explanations and compare predictions against selected sets of neurobiological data. The results of this comparison are used to interpret mirror system neuroimaging results in terms of neural network activity, evaluate the biological plausibility of mirror system models, and suggest new experiments that can shed light on the neural basis of mirror systems.

Effects of model orientation on the visuomotor imitation of arm movements: the role of mental rotation

An experiment was conducted to examine whether visual perspective has an effect on visuomotor imitation. The experiment presented varied visual perspectives in terms of spatial disparity between a model and an observer (model-observer-disparity) on six levels. Female participants were asked to imitate different arm movements presented in videos by animated models. These arm movements were elbow-extension-flexion movements with one (lower complexity) or three (higher complexity) reversals of movement direction. The results showed that model-observer-disparity affects spatial trajectories and velocities in the performance of motor imitations. The movements' complexity did not affect orientation dependence. Due to the non-linearity of the data, it is questionable if orientation dependence can be at least partially explained by mental rotation processes or differential ideomotor effects. According to these results, high model-observer-disparity should be avoided when using visual instructions in visuomotor imitation.

In praise of a model but not its conclusions: commentary on Cooper, Catmur, and Heyes (2012)

Cooper et al. (this issue) develop an interactive activation model of spatial and imitative compatibilities that simulates the key results from Catmur and Heyes (2011) and thus conclude that both compatibilities are mediated by the same processes since their single model can predict all the results. Although the model is impressive, the conclusions are premature because they are based on an incomplete review of the relevant literature and because the model includes some questionable assumptions. Moreover, a competing model (Scheutz & Bertenthal, 2012) is introduced that suggests the two compatibilities are not mediated by the same processes. We propose that more research is necessary before concluding that spatial and imitative compatibilities are mediated by the same processes.

The case of Watson vs. James: effect-priming studies do not support ideomotor theory

In this paper we show that response facilitation in choice reaction tasks achieved by priming the (previously perceived) effect is based on stimulus-response associations rather than on response-effect associations. The reduced key-press response time is not accounted for by earlier established couplings between the key-press movement and its subsequent effect, but instead results from couplings between this effect and the contingent key-release movement. This key-release movement is an intrinsic part of the entire performed response action in each trial of a reaction-time task, and always spontaneously follows the key-press movement. Eliminating the key-release movement from the task leads to the disappearance of the response facilitation, which raises the question whether response-effect associations actually play a role in studies that use the effect-priming paradigm. Together the three experiments presented in the paper cast serious doubts on the claim that action-effect couplings are acquired and utilized by the cognitive system in the service of action selection, and that the priming paradigm by itself can provide convincing evidence for this claim. As a corollary, we question whether the related two-step model for the ideomotor principle holds a satisfying explanation for how anticipation of future states guides action planning. The results presented here may have profound implications for priming studies in other disciplines of psychology as well.

Automatic imitation and spatial compatibility in a key-pressing task

Automatic imitation has been often confounded with spatial compatibility effects. Heyes (2011) called attention to this confound, and proposed some criteria which must be satisfied before these effects could be unequivocally taken to be an index of the functioning of the human mirror system. Evidence satisfying such criteria has been reported by Catmur and Heyes (2011), using a relatively unfamiliar finger abduction movement. However, because many previous studies relied on more familiar actions, we aimed at testing whether analogous effects could be obtained with a more practiced key-pressing task. In Experiment 1, we used anatomical controls (i.e., views of right vs. left hands) under conditions affording mirror imitation, and showed that spatial compatibility masked the effects of automatic imitation. Experiment 2 used rotated conditions to control for this spatial-anatomical confound, and it showed unequivocal effects of automatic imitation, which were obtained regardless of its relation to the spatial stimulus-response mapping. These results cast some doubts on the interpretation of previous reports relying exclusively on scenes presented from a mirror perspective, and suggest the convenience of using both rotated scenes and anatomical controls in order to assess automatic imitation.

Are automatic imitation and spatial compatibility mediated by different processes?

Automatic imitation or "imitative compatibility" is thought to be mediated by the mirror neuron system and to be a laboratory model of the motor mimicry that occurs spontaneously in naturalistic social interaction. Imitative compatibility and spatial compatibility effects are known to depend on different stimulus dimensions-body movement topography and relative spatial position. However, it is not yet clear whether these two types of stimulus-response compatibility effect are mediated by the same or different cognitive processes. We present an interactive activation model of imitative and spatial compatibility, based on a dual-route architecture, which substantiates the view they are mediated by processes of the same kind. The model, which is in many ways a standard application of the interactive activation approach, simulates all key results of a recent study by Catmur and Heyes (2011). Specifically, it captures the difference in the relative size of imitative and spatial compatibility effects; the lack of interaction when the imperative and irrelevant stimuli are presented simultaneously; the relative speed of responses in a quintile analysis when the imperative and irrelevant stimuli are presented simultaneously; and the different time courses of the compatibility effects when the imperative and irrelevant stimuli are presented asynchronously.

Is automatic imitation a specialized form of stimulus-response compatibility? Dissociating imitative and spatial compatibilities

In recent years research on automatic imitation has received considerable attention because it represents an experimental platform for investigating a number of interrelated theories suggesting that the perception of action automatically activates corresponding motor programs. A key debate within this research centers on whether automatic imitation is any different than other long-term S-R associations, such as spatial stimulus-response compatibility. One approach to resolving this issue is to examine whether automatic imitation shows similar response characteristics as other classes of stimulus-response compatibility. This hypothesis was tested by comparing imitative and spatial compatibility effects with a two alternative forced-choice stimulus-response compatibility paradigm. The stimulus on each trial was a left or right hand with either the index or middle finger tapping down. Speeded responses were performed with the index or middle finger of the right hand in response to the identity or the left-right spatial position of the stimulus finger. Two different tasks were administered: one that involved responding to the stimulus (S-R) and one that involved responding to the opposite stimulus (OS-R; i.e., the one not presented on that trial). Based on previous research and a connectionist model, we predicted standard compatibility effects for both spatial and imitative compatibility in the S-R task, and a reverse compatibility effect for spatial compatibility, but not for imitative compatibility, in the OS-R task. The results from the mean response times, mean percentage of errors, and response time distributions all converged to support these predictions. A second noteworthy result was that the recoding of the finger identity in the OS-R task required significantly more time than the recoding of the left-right spatial position, but the encoding time for the two stimuli in the S-R task was equivalent. In sum, this evidence suggests that the processing of spatial and imitative compatibility is dissociable with regard to two different processes in dual processing models of stimulus-response compatibility.

Apraxia: a review

Praxic functions are frequently altered following brain lesion, giving rise to apraxia - a complex pattern of impairments that is difficult to assess or interpret. In this chapter, we review the current taxonomies of apraxia and related cognitive and neuropsychological models. We also address the questions of the neuroanatomical correlates of apraxia, the relation between apraxia and aphasia and the analysis of apraxic errors. We provide a possible explanation for the difficulties encountered in investigating apraxia and also several approaches to overcome them, such as systematic investigation and modeling studies. Finally, we argue for a multidisciplinary approach. For example, apraxia should be studied in consideration with and could contribute to other fields such as normal motor control, neuroimaging and neurophysiology.

Dynamic updating of distributed neural representations using forward models

In this paper, we present a continuous attractor network model that we hypothesize will give some suggestion of the mechanisms underlying several neural processes such as velocity tuning to visual stimulus, sensory discrimination, sensorimotor transformations, motor control, motor imagery, and imitation. All of these processes share the fundamental characteristic of having to deal with the dynamic integration of motor and sensory variables in order to achieve accurate sensory prediction and/or discrimination. Such principles have already been described in the literature by other high-level modeling studies (Decety and Sommerville in Trends Cogn Sci 7:527-533, 2003; Oztop et al. in Neural Netw 19(3):254-271, 2006; Wolpert et al. in Philos Trans R Soc 358:593-602, 2003). With respect to these studies, our work is more concerned with biologically plausible neural dynamics at a population level. Indeed, we show that a relatively simple extension of the classical neural field models can endow these networks with additional dynamic properties for updating their internal representation using external commands. Moreover, an analysis of the interactions between our model and external inputs also shows interesting properties, which we argue are relevant for a better understanding of the neural processes of the brain.