Winfried Ilg

Spatiotemporal Tuning of the Facilitation of Biological Motion Perception by Concurrent Motor Execution

The execution of motor behavior influences concurrent visual action observation and especially the perception of biological motion. The neural mechanisms underlying this interaction between perception and motor execution are not exactly known. In addition, the available experimental evidence is partially inconsistent because previous studies have reported facilitation as well as impairments of action perception by concurrent execution. Exploiting a novel virtual reality paradigm, we investigated the spatiotemporal tuning of the influence of motor execution on the perception of biological motion within a signal-detection task. Human observers were presented with point-light stimuli that were controlled by their own movements. Participants had to detect a point-light arm in a scrambled mask, either while executing waving movements or without concurrent motor execution (baseline). The temporal and spatial coherence between the observed and executed movements was parametrically varied. We found a systematic tuning of the facilitatory versus inhibitory influences of motor execution on biological motion detection with respect to the temporal and the spatial congruency between observed and executed movements. Specifically, we found a gradual transition between facilitatory and inhibitory interactions for decreasing temporal synchrony and spatial congruency. This result provides evidence for a spatiotemporally highly selective coupling between dynamic motor representations and neural structures involved in the visual processing of biological motion. In addition, our study offers a unifying explanation that reconciles contradicting results about modulatory effects of motor execution on biological motion perception in previous studies.

On the representation, learning and transfer of spatio-temporal movement characteristics

In this paper we present a learning-based approach for the modeling of complex movement sequences. Based on the method of Spatio-Temporal Morphable Models (STMMs) we derive a hierarchical algorithm that, in a first step, identifies automatically movement elements in movement sequences based on a coarse spatio-temporal description, and in a second step models these movement primitives by approximation through linear combinations of learned example movement trajectories. We describe the different steps of the algorithm and show how it can be applied for modeling and synthesis of complex sequences of human movements that contain movement elements with a variable style. The proposed method is demonstrated on different applications of movement representation relevant for imitation learning of movement styles in humanoid robotics.

An Intact Action-Perception Coupling Depends on the Integrity of the Cerebellum

It is widely accepted that action and perception in humans functionally interact on multiple levels. Moreover, areas originally suggested to be predominantly motor-related, as the cerebellum, are also involved in action observation. However, as yet, few studies provided unequivocal evidence that the cerebellum is involved in the action perception coupling (APC), specifically in the integration of motor and multisensory information for perception. We addressed this question studying patients with focal cerebellar lesions in a virtual-reality paradigm measuring the effect of action execution on action perception presenting self-generated movements as point lights. We measured the visual sensitivity to the point light stimuli based on signal detection theory. Compared with healthy controls cerebellar patients showed no beneficial influence of action execution on perception indicating deficits in APC. Applying lesion symptom mapping, we identified distinct areas in the dentate nucleus and the lateral cerebellum of both hemispheres that are causally involved in APC. Lesions of the right ventral dentate, the ipsilateral motor representations (lobules V/VI), and most interestingly the contralateral posterior cerebellum (lobule VII) impede the benefits of motor execution on perception. We conclude that the cerebellum establishes time-dependent multisensory representations on different levels, relevant for motor control as well as supporting action perception. Ipsilateral cerebellar motor representations are thought to support the somatosensory state estimate of ongoing movements, whereas the ventral dentate and the contralateral posterior cerebellum likely support sensorimotor integration in the cerebellar-parietal loops. Both the correct somatosensory as well as the multisensory state representations are vital for an intact APC.

Motor Training in Degenerative Spinocerebellar Disease: Ataxia-Specific Improvements by Intensive Physiotherapy and Exergames

The cerebellum is essentially involved in movement control and plays a critical role in motor learning. It has remained controversial whether patients with degenerative cerebellar disease benefit from high-intensity coordinative training. Moreover, it remains unclear by which training methods and mechanisms these patients might improve their motor performance. Here, we review evidence from different high-intensity training studies in patients with degenerative spinocerebellar disease. These studies demonstrate that high-intensity coordinative training might lead to a significant benefit in patients with degenerative ataxia. This training might be based either on physiotherapy or on whole-body controlled videogames (“exergames”). The benefit shown in these studies is equal to regaining one or more years of natural disease progression. In addition, first case studies indicate that even subjects with advanced neurodegeneration might benefit from such training programs. For both types of training, the observed clinical improvements are paralleled by recoveries in ataxia-specific dysfunctions (e.g., multijoint coordination and dynamic stability). Importantly, for both types of training, the retention of the effects seems to depend on the frequency and continuity of training. Based on these studies, we here present preliminary recommendations for clinical practice, and articulate open questions that might guide future studies on neurorehabilitation in degenerative spinocerebellar disease.

Videogame-based coordinative training can improve advanced, multisystemic early-onset ataxia

Dear Sirs,Treatment options are rare in neurodegenerative childhood-onset ataxias, especially if presenting in advanced diseasestages and with multisystemic disease load. Moreover,wheelchair-bound children and young adults with ataxiaare commonly excluded from current drug treatment trials[1, 2], thus leaving them without prospects of access tonovel treatments. Using a rater-blinded intraindividualcontrol design, we here provide first proof-of-principleevidence that videogame-based coordinative training mightserve as an effective treatment even for advanced, multi-systemic degenerative ataxia.A 10-year-old boy suffering from genetically confirmedAtaxia Telangiectasia (compound heterozygous ATMp.Glu2596Aspfs*4 and p.Asp1625_Ala2626delinsGluPro)since 3 years of age and wheelchair-bound with onlyresidual standing and walking capacities since 7 years ofage (clinical details, Supplement 1) was recruited for asequentially structured 12-week coordinative training pro-gram based on specifically selected, commercially avail-able Nintendo Wii games (for details, see Fig. 1a). Thesubject was examined four times: 5 weeks before theintervention (E1), immediately before the first trainingphase (E2), after the first home training phase (E3) andafter the second home training phase (E4). Delta E1–E2was taken as an intraindividual control period to control forchanges associated with a monthly intravenous applicationof 750 mg methylprednisolone per day for 3 days whichhad been initiated by the patient’s local physicians [8 months before the study. Dosis and interval were keptconstant before and throughout the study. The outcomemeasures were: (1) clinical degree of clinical ataxiaseverity, rated by means of videotaped Scale for theAssessment and Rating of Ataxia (SARA) [3] scores pre-sented in a random order to an ataxia specialist (J.W.)blinded to the number of the specific examination (E1–E4);(2) quantitative movement analysis of balance capacities insitting (methodological details, [4, 5] and Supplement 3);and (3) achievements in patient self-selected individuallyimportant goals with respect to standing and sitting,assessed by the goal attainment score (GAS) [6] (Supple-ment 4). This study has been approved by the appropriateethics committee and has been performed in accordancewith the ethical standards laid down in the 1964 Declara-tion of Helsinki and its later amendments.The SARA score of 26.5/40 points, indicating anadvanced disease stage, remained unchanged before train-ing (E1–E2), thus demonstrating no major effect of corti-costeroids or substantial fluctuations in the natural history

Cerebellar tDCS Does Not Improve Learning in a Complex Whole Body Dynamic Balance Task in Young Healthy Subjects

Transcranial direct current stimulation (tDCS) of the cerebellum is of increasing interest as a non-invasive technique to modulate motor performance and learning in health and disease. Previous studies have shown that cerebellar tDCS facilitates reach adaptation and associative motor learning in healthy subjects. In the present study it was tested whether cerebellar tDCS improves learning of a complex whole body motor skill. Because this task involves learning of posture and balance likely including learning of a new motor sequence and cognitive strategies, cerebellar tDCS was applied over midline cerebellar structures and the posterolateral cerebellar hemispheres. 30 young and healthy subjects performed two days of balance training on a Lafayette Instrument 16030 stability platform®. Participants received either anodal, cathodal or sham cerebellar tDCS during training on day 1. The cerebellar electrode (7 cm width by 5 cm height) was centered 2 cm below the inion. Mean platform angle deviation and mean balance time were assessed. All subjects showed significant effects of learning. Learning rate was not different between the three modes of stimulation neither on day 1 nor on day 2. Cerebellar tDCS did not facilitate learning of a complex whole body dynamic balance task in young and healthy subjects. tDCS effects, however, may have been missed because of the small group size. Furthermore, it cannot be excluded that young and healthy subjects learned and performed already at a near optimal level with little room for further improvement. Future work has to evaluate potential benefits of cerebellar tDCS in elderly subjects and subjects with cerebellar deficits, whose motor control and motor learning network is not optimally tuned.

Estimation of Skill Levels in Sports Based on Hierarchical Spatio-Temporal Correspondences

We present a learning-based method for the estimation of skill levels from sequences of complex movements in sports. Our method is based on a hierarchical algorithm for computing spatio-temporal correspondence between sequences of complex body movements. The algorithm establishes correspondence at two levels: whole action sequences and individual movement elements. Using Spatio-Temporal Morphable Models we represent individual movement elements by linear combinations of learned example patterns. The coefficients of these linear combinations define features that can be efficiently exploited for estimating continuous style parameters of human movements. We demonstrate by comparison with expert ratings that our method efficiently estimates the skill level from the individual techniques in a ”karate kata”.

Modeling of Movement Sequences Based on Hierarchical Spatial-Temporal Correspondence of Movement Primitives

In this paper we present an approach for the modeling complex movement sequences. Based on the method of Spatio-Temporal Morphable Models (STMMs) [11] we derive a new hierarchical algorithm that, in a first step, identifies movement elements in the complex movement sequence based on characteristic events, and in a second step quantifies these movement primitives by approximation through linear combinations of learned example movement trajectories. The proposed algorithm is used to segment and to morph sequences of karate movements of different people and different styles.

Validation of enhanced kinect sensor based motion capturing for gait assessment

Optical motion capturing systems are expensive and require substantial dedicated space to be set up. On the other hand, they provide unsurpassed accuracy and reliability. In many situations however flexibility is required and the motion capturing system can only temporarily be placed. The Microsoft Kinect v2 sensor is comparatively cheap and with respect to gait analysis promising results have been published. We here present a motion capturing system that is easy to set up, flexible with respect to the sensor locations and delivers high accuracy in gait parameters comparable to a gold standard motion capturing system (VICON). Further, we demonstrate that sensor setups which track the person only from one-side are less accurate and should be replaced by two-sided setups. With respect to commonly analyzed gait parameters, especially step width, our system shows higher agreement with the VICON system than previous reports.

Individual changes in preclinical spinocerebellar ataxia identified via increased motor complexity.

Movement changes in autosomal‐dominant spinocerebellar ataxias are suggested to occur many years before clinical manifestation. Detecting and quantifying these changes in the preclinical phase offers a window for future treatment interventions and allows the clinician to decipher the earliest dysfunctions starting the evolution of spinocerebellar ataxia. We hypothesized that quantitative movement analysis of complex stance and gait tasks allows to (i) reveal movement changes already at early stages of the preclinical phase when clinical ataxia signs are still absent and to (ii) quantify motor progression in this phase.