Performance of humans vs. exploration algorithms on the Tower of London Test.

The Tower of London Test (TOL) used to assess executive functions was inspired in Artificial Intelligence tasks used to test problem-solving algorithms. In this study, we compare the performance of humans and of exploration algorithms. Instead of absolute execution times, we focus on how the execution time varies with the tasks and/or the number of moves. This approach used in Algorithmic Complexity provides a fair comparison between humans and computers, although humans are several orders of magnitude slower. On easy tasks (1 to 5 moves), healthy elderly persons performed like exploration algorithms using bounded memory resources, i.e., the execution time grew exponentially with the number of moves. This result was replicated with a group of healthy young participants. However, for difficult tasks (5 to 8 moves) the execution time of young participants did not increase significantly, whereas for exploration algorithms, the execution time keeps on increasing exponentially. A pre-and post-test control task showed a 25% improvement of visuo-motor skills but this was insufficient to explain this result. The findings suggest that naive participants used systematic exploration to solve the problem but under the effect of practice, they developed markedly more efficient strategies using the information acquired during the test.

Certainty in categorical judgment of size.

The certainty of judgment (or self-confidence) has been traditionally studied in relation with the accuracy. However, from an observer's viewpoint, certainty may be more closely related to the consistency of judgment than to its accuracy: consistent judgments are objectively certain in the sense that any external observer can rely on these judgments to happen. The regions of certain vs. uncertain judgment were determined in a categorical rating experiment. The participants rated the size of visual objects on a 5-point scale. There was no feedback so that there were no constraints of accuracy. Individual data was examined, and the ratings were characterized by their frequency distributions (or categories). The main result was that the individual categories always presented a core of certainty where judgment was totally consistent, and large peripheries where judgment was inconsistent. In addition, the geometry of cores and boundaries exhibited several phenomena compatible with the literature on visual categorical judgment. The ubiquitous presence of cores in absence of accuracy constraints provided insights about objective certainty that may complement the literature on subjective certainty (self-confidence) and the accuracy of judgment.

Movement irregularities in atypical parkinsonian syndromes.

This study examined discrete motor irregularities in ballistic aiming movements in patients with atypical parkinsonian syndromes (APS). Nine patients with APS were compared to 9 patients with idiopathic Parkinson's disease (PD) and 9 controls on ballistic arm extension movements performed on a digitizing tablet without visual feedback and without accuracy constraints. Patients with APS showed a higher number of irregularities in the acceleration and jerk time series compared to PD patients and controls. No difference was found between PD patients and controls. These discrete irregularities were not associated with general motor impairment, tremor, akinesia, or rigidity. These results suggest that atypical parkinsonism is associated with movement irregularities in ballistic movements, which may help differentiate APS from PD.

Myocontrol in aging.

Myoelectric (EMG) signals are used in assistive technology for prostheses, computer and domestic control. An experimental study previously conducted with young participants was replicated with elderly persons in order to assess the effect of age on the ability to control myoelectric amplitude (or myocontrol). Participants performed pointing tasks as the myoelectric amplitude was captured by a surface electrode in two modalities (sustained: stabilize the amplitude after reaching the desired level; impulsion: return immediately to resting amplitude). There was a significant decrease of performance with Age. However, the patterns of performance of young and aged were noticeably similar. The Impulsion modality was difficult (high rates of failure) and the speed-accuracy trade-offs predicted by Fitts' law were absent (bow-shaped patterns as function of target amplitude instead of logarithmic increase). Conversely, the reach phase of the Sustained modality followed the predictions of Fitts' law. However, the slope of the regression line with Fitts' index of difficulty was quite steeper in aged than in young participants. These findings suggest that 1) all participants, young and aged, adapt their reaching strategies to the anticipated state (sustained amplitude or not) and/or to the difficulty of the task, 2) myocontrol in aged persons is more fragile, i.e., performance is markedly degraded as the difficulty of the task increases. However, when individual performance was examined, some aged individuals were found to perform as well as the young participants, congruently with the literature on good aging.

Speed-accuracy trade-offs in myocontrol.

Myoelectric (EMG) signals are used in assistive technology for prostheses, computer and domestic control. However, little is known about the capacity of controlling these signals. Specifically, it is unclear whether myocontrol, i.e., the control of myoelectric signals, obeys the same laws as motor control. Neurologically intact adult participants performed pointing tasks with EMG signals captured from the forehead or the hand in two modalities (sustained: stabilize the signal amplitude in the target; impulsion: produce an impulse and return to resting level). In the sustained modality, the time to reach the target (reach time) increased logarithmically with target amplitude, which is compatible with the predictions of Fitts' law. The rate of failure was not significantly affected by target amplitude. In the impulsion modality, the reach time and the rate of failure followed a bow-shaped pattern as a function of target amplitude. Stabilization time in the sustained modality followed a convex (bow-shaped) pattern for the forehead and a concave pattern for the hand. This was the only significant effect of electrode placement in this study. These findings suggest that myocontrol obeys laws that are distinct from those determining motor control, and that the muscular and intra-muscular synergies that produce EMG signals are specific of each pointing modality and target amplitude.

Automatic detection of movement disorders using recordings of rapid alternating movements.

The present work assesses the potential of rapid alternating movement analysis for detecting movement disorders like Parkinson's disease. Rapid alternating wrist movements were recorded by a diadochokinesimeter for patients with Parkinson's disease (n=10) and healthy controls (n=20). An index of irregularity was computed for each individual as the density of jerk singularities (i.e. zero-crossings) during the movements. Several scales of analysis (i.e. "coarseness") were used for detecting the jerk events and two methods were compared for all of these scales: (1) automatic classification by means of a threshold that optimally separates the indexes of irregularity of the patients from those of the controls, and (2) statistical decision (normal or abnormal) based upon a distribution of indexes of irregularity obtained from a large population of normal subjects. The results showed that (1) two scales of analysis were sufficient and that (2) both methods presented similar performances (e.g. sensitivity=1.00, specificity=0.85, efficiency=0.90). However, statistical decision should be preferred because of its simplicity. The possibility of automatic detection of movement disorders from alternating movements is discussed.

Event identification in movement recordings by means of qualitative patterns.

We present a pattern-matching technique for detecting events in movement recordings. The events are defined as sequences of qualitative changes in the speed and/or the higher order derivatives (e.g., in a speed peak, the acceleration changes from positive to negative). The technique uses qualitative patterns that are sequences of qualitative states (e.g., negative, infinitesimal, positive...) of the speed and the higher order derivatives. A fast pattern-matching algorithm is presented. Its sensitivity can be tuned by means of a filtering parameter, and a multiscale analysis method is proposed for detecting events of different amplitudes and durations. An application to the assessment of the irregularity of rapid movement in Parkinson's disease is presented.