Randomizing visual feedback in manual aiming: reminiscence of the previous trial condition and prior knowledge of feedback availability

A trial-by-trial analysis was used to systematically examine the influence of switching visual conditions on visual feedback utilization for a manual aiming movement. In experiment one, vision was randomly manipulated from trial to trial with no more than four consecutive trials in the same visual condition. In experiment two, participants were provided with certainty of visual feedback availability prior to every trial. Results of both studies revealed that movement endpoint variability was most associated with visual feedback availability on the previous trial. Furthermore, correlation analyses comparing movement trajectory at 25, 50 and 75% with movement end (i.e. 100%) revealed that the efficiency of online corrections also depends on the availability of visual feedback on the previous trial. These results suggest that the accuracy of an aiming movement is highly dependent on processing of offline visual information from the preceding trial. This study was supported by a grant from the Natural Sciences and Engineering Research Council of Canada (NSERC) awarded to Luc Tremblay.

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A Judd illusion in far-aiming: evidence of a contribution to action by vision for perception

The present study addresses the role of vision for perception in determining the location of a target in far-aiming. Participants (N = 12) slid a disk toward a distant target embedded in illusory Judd figures. Additionally, in a perception task, participants indicated when a moving pointer reached the midpoint of the Judd figures. The number of hits, the number of misses to the left and to the right of the target, the sliding error (in mm) and perceptual judgment error (in mm) served as dependent variables. Results showed an illusory bias in sliding, the magnitude of which was comparable to the bias in the perception of target location. The determination of target location in far-aiming is thus based on relative metrics. We argue that vision for perception sets the boundary constraints for action and that within these constraints vision for action autonomously controls movement execution, but alternative accounts are discussed as well.

Involuntary inhibition of movement initiation alters oculomotor competition resolution

Identifying a stimulus as the target for a goal-directed movement involves inhibiting competing responses. Separable inhibitory interconnections bias local competition to ensure only one stimulus is selected and to alter movement initiation. Behavioural evidence of these inhibitory processes comes from the effects of distracters on oculomotor landing positions and saccade latencies. Here, we investigate the relationship between these two sources of inhibition. Targets were presented with or without close and remote distracters. In separate experiments the possible position and identity of the target and distracters were manipulated. In all cases saccade landing position was found to be less affected by the presence of the close distracter when remote distracters were also present. The involuntary increase in the latency of saccade initiation caused by the presence of the remote distracters alters the state of competitive processes involved in selecting the saccade target thus changing its landing position.

The relationship between poor sleep and inhibitory functions indicated by event-related potentials

The present study focused on the relationship between normal variations of sleep and inhibitory functions as reflected in event-related potentials. For this reason one night of 21 healthy participants was analysed. After waking up all participants completed a visual Go/Nogo task. On the basis of a sleep disturbance index (SDI) the participants were separated into 8 SDI-good and 13 SDI-poor sleepers using a cluster analysis. The results showed that Nogo-N2 amplitude was smaller and Nogo-P3 latency longer in SDI-poor sleepers. Moreover, Go-P3 amplitude was smaller in SDI-poor sleepers. Performance parameters were not influenced by poor sleep. We concluded that poor sleep specifically affects the intensity of pre-motor inhibitory processes (Nogo-N2 amplitude), the speed to inhibit a motor response (Nogo-P3 latency) and the intensity of task-relevant information processing (Go-P3 amplitude). In further studies, it should be explored under which conditions such subliminal deficits also become relevant for overt behaviour.

Methodological problems undermine tests of the ideo-motor conjecture

Recent behavioural research has investigated whether viewing someone perform an action results in activation of that action by the observer. Postulated empirical support for this ‘ideo-motor (IM) conjecture’ typically rests upon two types of experimental paradigm (reaction time and movement tracking tasks). These paradigms purport to show movement facilitation when compatible movements are observed and vice versa, but only for biological stimuli. Unfortunately, these paradigms often contain confounding (and unavoidable) generic stimulus–response compatibility effects that are not restricted to observed human movement. The current study demonstrates in three experiments that equivalent compatibility effects can be produced by non-biological stimuli. These results suggest that existing empirical paradigms may not, and perhaps cannot, support the IM-conjecture.

Physical inactivity and cognitive functioning: results from bed rest studies

In addition to multiple health benefits, participation in physical activity can enhance cognitive functioning. Less clear is how reducing physical activity levels affects cognition, an issue potentially addressed by bed rest studies having included cognitive tests. Detailed and reviewed here are 17 such studies, featuring 251 subjects, bed rest for 7–70 days, and tests of cognition ranging from reaction time to executive functions. The reported effects of bed rest on cognitive performance vary considerably, from a generally expected worsening to an improvement. Practice effects could be implicated in the performance improvements, and reports of worsening are often of limited interpretability or the results were not replicated. Any cognitive effects of bed rest thus remain to be established. Detrimental effects could influence the in-progress plans for human spaceflights to Mars (simulated by bed rest), and have implications for medical conditions promoting inactivity and lifestyles that are largely sedentary.

Learning the visuomotor transformation of virtual and real sliding levers: simple approximations of complex transformations

Learning to operate a complex tool such as a sliding lever can be conceived as learning both a kinematic and a dynamic transformation. We investigated whether the presence of the dynamic transformation has an inhibitory or a facilitative effect on learning to control a sliding lever. Furthermore, we examined the characteristics of the internal model of the kinematic transformation of the lever in visual open-loop trials. In the experiment, one group of participants practiced with only the kinematic transformation of the lever (virtual lever), the other group practiced with both the kinematic and the dynamic transformation (physical lever). Visual feedback was continuously present during practice. Results showed only marginal differences between both groups in open-loop tests. This finding is likely to be related to the fact that in both groups a simplified approximation of the kinematic transformation was acquired, in particular a symmetry approximation. With such an approximation the target for the hand movement is derived from the visual target for the tip of the lever as the position which is symmetric around a sagittal axis.

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Does the semantic activation of quantity representations influence motor parameters?

In size and parity judgment tasks, we investigated whether the activation of numerical quantity exerts an influence on motor response parameters such as response force. Results showed typically strong effects on reaction time of numerical distance in the size judgment task (Experiments 1 and 2) and SNARC-compatibility (Experiment 1) in both tasks, indicating that semantic quantity representations were activated. Response force, however, varied at most weakly with the numerical magnitudes of the digits. Our results place limits on previously suggested interconnections of the magnitude and response systems. Activations within the magnitude system seem to have a strong influence on the initiation and selection of which action to produce, but only a little influence on the dynamics of response production (i.e., response execution).

A self-paced brain–computer interface for controlling a robot simulator: an online event labelling paradigm and an extended Kalman filter based algorithm for online training

Due to the non-stationarity of EEG signals, online training and adaptation are essential to EEG based brain–computer interface (BCI) systems. Self-paced BCIs offer more natural human–machine interaction than synchronous BCIs, but it is a great challenge to train and adapt a self-paced BCI online because the user’s control intention and timing are usually unknown. This paper proposes a novel motor imagery based self-paced BCI paradigm for controlling a simulated robot in a specifically designed environment which is able to provide user’s control intention and timing during online experiments, so that online training and adaptation of the motor imagery based self-paced BCI can be effectively investigated. We demonstrate the usefulness of the proposed paradigm with an extended Kalman filter based method to adapt the BCI classifier parameters, with experimental results of online self-paced BCI training with four subjects.

Misperceiving the speed-accuracy tradeoff: imagined movements and perceptual decisions

Research has suggested that prospective motor decisions are consistent with actual motor action. In a study that we recently published (Young et al. in Exp Brain Res 185:681–688, 2008), however, participants demonstrated a preference for closer targets that was inconsistent with the predictions of Fitts’s law. With a pair of experiments, the present paper investigates the underlying basis of this non-optimal behaviour. Participants showed a similar deviation from Fitts’s law when imagining movements—believing that movement duration increased with distance within the same index of difficulty. Participants did not behave similarly, however, in a perceptual version of the decision task. These results suggest that imagined movements and motor decisions are linked, as well as demonstrating one situation in which both show a similar deviation from the patterns of actual movement duration.

High genetic diversity of Sappinia-like strains (Amoebozoa, Thecamoebidae) revealed by SSU rRNA investigations

Sappinia diploidea is known as a free-living amoeba of worldwide distribution and has also been reported as causative agent of a brain infection in an immunocompetent young man. In the current study, we were able to isolate eight strains of S. diploidea-like amoebae identified by light microscopy from different habitats. Cultures of all strains were established successfully for molecular characterization. The small subunit ribosomal RNA genes of all strains were sequenced and compared to one another, to the neotype of S. diploidea, and to strains of Sappinia pedata, the only other Sappinia species known to date, from GenBank by multiple sequence alignment and cluster analysis. Altogether, the phylogenetic position of the genus Sappinia within the Thecamoebidae was corroborated; however, it was shown that the genus splits into several well-separated clusters making the establishment of new species within this genus inevitable. Furthermore, two of the S. diploidea-like strains were actually more closely related to S. pedata than to S. diploidea, although the diagnostically relevant standing form which seems to be characteristic for S. pedata was not observed in either of the two strains. Claudia Wylezich and Julia Walochnik have contributed equally to this work.

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Working memory capacity,intelligence, and the magnitude of the attentional blink revisited

The attentional blink (AB) is a well-established phenomenon in the study of attention. This deficit in reporting the second of two targets presented in rapid serial visual presentation when it occurs 200–500 ms after the first is considered to reflect a fundamental limitation in attentional processing. However, we recently reported that some individuals do not show an AB, and presented psychophysiological evidence that target processing differs between blinkers and non-blinkers. One possibility is that non-blinkers may have a larger WM capacity, allowing better attentional control. Here we explore the relation between the magnitude of the AB, general intelligence, and different measures of working memory (WM) and short-term memory (STM) capacity. Surprisingly, no correlation was found between memory capacity measures and AB magnitude, raising doubts about the generalizability of earlier findings of such a relationship.

Preparation and inhibition of interceptive actions

Two experiments aimed to provide an estimate of the last moment at which visual information needs to be obtained in order for it to be used to initiate execution of an interceptive movement or to withhold execution of such a movement. In experiment 1, we sought to estimate the minimum time required to suppress the movement when the participants were first asked to intercept a moving target. In experiment 2, we sought to determine the minimum time required to initiate an interceptive movement when the participants were initially asked to keep stationary. Participants were trained to hit moving targets using movements of a pre-specified duration. This permitted an estimate of movement onset (MO) time. In both experiments the requirement to switch from one prepared course of action to the other was indicated by changing the colour of the moving target at times prior to the estimated MO. The results of the experiments showed that the decision to execute or suppress the interception must be made no less than about 200 ms before MO.

Local motion inside an object affects pointing less than smooth pursuit

During smooth pursuit eye movements, briefly presented objects are mislocalized in the direction of motion. It has been proposed that the localization error is the sum of the pursuit signal and the retinal motion signal in a ~200 ms interval after flash onset. To evaluate contributions of retinal motion signals produced by the entire object (global motion) and elements within the object (local motion), we asked observers to reach to flashed Gabor patches (Gaussian-windowed sine-wave gratings). Global motion was manipulated by varying the duration of a stationary flash, and local motion was manipulated by varying the motion of the sine-wave. Our results confirm that global retinal motion reduces the localization error. The effect of local retinal motion on object localization was far smaller, even though local and global motion had equal effects on eye velocity. Thus, local retinal motion has differential access to manual and oculomotor control circuits. Further, we observed moderate correlations between smooth pursuit gain and localization error.

Postural costs of performing cognitive tasks in non-coincident reference frames

Dual-task interactions in posture and cognitive tasks have been explained as a competition for spatial processing structures or as interference in the online sensorimotor adjustments required for sensory integration. Going beyond these general terms accounts, we propose that interference between spatial and temporal operations in posture–cognition arises at least partly from the need to share a common behavioral context, such as a spatial frame of reference. Using immersive visualization and motion-tracking techniques, we manipulated the spatial reference frames for a standing task and a conjunction visual search task into or out of coincidence. Aside from performance trade-offs due to task-load manipulations, performing visual search in a non-coincident reference frame led to cognitive task and postural task performance decrements (Experiment 1). Postural dual-task decrements were also observed when visual search was split between coincident and non-coincident frames and both frame conditions rendered identical in visual information relevant to posture control (Experiment 2). We concluded that the postural control costs observed for posture–cognition dual-tasking may in part reflect costs of keeping tasks’ reference frames in register.

Saccadic inhibition underlies the remote distractor effect

The remote distractor effect is a robust finding whereby a saccade to a lateralised visual target is delayed by the simultaneous, or near simultaneous, onset of a distractor in the opposite hemifield. Saccadic inhibition is a more recently discovered phenomenon whereby a transient change to the scene during a visual task induces a depression in saccadic frequency beginning within 70 ms, and maximal around 90–100 ms. We assessed whether saccadic inhibition is responsible for the increase in saccadic latency induced by remote distractors. Participants performed a simple saccadic task in which the delay between target and distractor was varied between 0, 25, 50, 100 and 150 ms. Examination of the distributions of saccadic latencies showed that each distractor produced a discrete dip in saccadic frequency, time-locked to distractor onset, conforming closely to the character of saccadic inhibition. We conclude that saccadic inhibition underlies the remote distractor effect.

Primary immune surveillance: some like it hot

The thermal element of fever has been found to be beneficial in models of infectious disease. The contributions of fever-range temperatures to the efficacy of the adaptive immune response have only begun to be delineated. There is accumulating evidence that fever-range thermal stress bolsters primary immune surveillance of lymph nodes and Peyer patches by augmenting lymphocyte extravasation across specialized vessels termed high endothelial venules. Molecular mechanisms have recently come to light by which the thermal component of fever alone may promote lymphocyte trafficking, and thereby the probability of mounting a defense against microbial infection. Acquired knowledge of the molecular changes associated with thermal stress may allow for the development of novel therapies for a variety of disease processes.

RNAi-dependent and -independent antiviral phenotypes of chromosomally integrated shRNA clones: Role of VASP in respiratory syncytial virus growth

Stable RNA interference (RNAi) is commonly achieved by recombinant expression of short hairpin RNA (shRNA). To generate virus-resistant cell lines, we cloned a shRNA cassette against the phosphoprotein gene of respiratory syncytial virus (RSV) into a polIII-driven plasmid vector. Analysis of individual stable transfectants showed a spectrum of RSV resistance correlating with the levels of shRNA expressed from different chromosomal locations. Interestingly, resistance in a minority of clones was due to mono-allelic disruption of the cellular gene for vasodilator-stimulated phosphoprotein (VASP). Thus, pure clones of chromosomally integrated DNA-directed RNAi can exhibit gene disruption phenotypes resembling but unrelated to RNAi.

Computational Modeling and Real-Time Control of Patient-Specific Laser Treatment of Cancer

An adaptive feedback control system is presented which employs a computational model of bioheat transfer in living tissue to guide, in real-time, laser treatments of prostate cancer monitored by magnetic resonance thermal imaging. The system is built on what can be referred to as cyberinfrastructure—a complex structure of high-speed network, large-scale parallel computing devices, laser optics, imaging, visualizations, inverse-analysis algorithms, mesh generation, and control systems that guide laser therapy to optimally control the ablation of cancerous tissue. The computational system has been successfully tested on in vivo, canine prostate. Over the course of an 18 min laser-induced thermal therapy performed at M.D. Anderson Cancer Center (MDACC) in Houston, Texas, the computational models were calibrated to intra-operative real-time thermal imaging treatment data and the calibrated models controlled the bioheat transfer to within 5 °C of the predetermined treatment plan. The computational arena is in Austin, Texas and managed at the Institute for Computational Engineering and Sciences (ICES). The system is designed to control the bioheat transfer remotely while simultaneously providing real-time remote visualization of the on-going treatment. Post-operative histology of the canine prostate reveal that the damage region was within the targeted 1.2 cm diameter treatment objective.

Modelling the human pharyngeal airway: validation of numerical simulations using in vitro experiments

In the presented study, a numerical model which predicts the flow-induced collapse within the pharyngeal airway is validated using in vitro measurements. Theoretical simplifications were considered to limit the computation time. Systematic comparisons between simulations and measurements were performed on an in vitro replica, which reflects asymmetries of the geometry and of the tissue properties at the base of the tongue and in pathological conditions (strong initial obstruction). First, partial obstruction is observed and predicted. Moreover, the prediction accuracy of the numerical model is of 4.2% concerning the deformation (mean quadratic error on the constriction area). It shows the ability of the assumptions and method to predict accurately and quickly a fluid–structure interaction.