Catch Trials Research Articles

Effect of robotic performance-based error-augmentation versus error-reduction training on the gait of healthy individuals

Effective locomotion training with robotic exoskeletons requires identification of optimal control algorithms to better facilitate motor learning. Two commonly employed training protocols emphasize use of training stimuli that either augment or reduce performance errors. The current study sought to identify which of these training strategies promote better short-term modification of a typical gait pattern in healthy individuals as a framework for future application to neurologically impaired individuals. Ten subjects were assigned to each of a performance-based error-augmentation or error-reduction training group. All subjects completed a 45-min session of treadmill walking at their preferred speed with a robotic exoskeleton. Target templates prescribed an ankle path for training that corresponded to an increased step height. When subjects’ instantaneous ankle positions fell below the inferior virtual wall of the target ankle path, robotic forces were applied that either decreased (error-reduction) or increased (error-augmentation) the deviation from the target path. When the force field was turned on, both groups walked with ankle paths better approximating the target template compared to baseline. When the force field was removed unexpectedly during catch and post-training trials, only the error-augmentation group maintained an ankle path close to the target ankle path. Further investigation is required to determine if a similar training advantage is provided for neurologically impaired individuals.

Limited interlimb transfer of locomotor adaptations to a velocity-dependent force field during unipedal walking

Several studies have demonstrated that motor adaptations to a novel task environment can be transferred between limbs. Such interlimb transfer of motor commands is consistent with the notion of centrally driven strategies that can be generalized across different frames of reference. So far, studies of interlimb transfer of locomotor adaptations have yielded disparate results. Here we sought to determine whether locomotor adaptations in one (trained) leg show transfer to the other (test) leg during a unipedal walking task. We hypothesized that adaptation in the test leg to a velocity-dependent force field previously experienced by the trained leg will be faster, as revealed by faster recovery of kinematic errors and earlier onset of aftereffects. Twenty able-bodied adults walked unipedally in the Lokomat robotic gait orthosis, which applied velocity-dependent resistance to the legs. The amount of resistance was scaled to 10% of each individual's maximum voluntary contraction of the hip flexors. Electromyography and kinematics of the lower limb were recorded. All subjects were right-leg dominant and were tested for transfer of motor adaptations from the right leg to the left leg. Catch trials, consisting of unexpected removal of resistance, were presented after the first step with resistance and after a period of adaptation to test for aftereffects. We found no significant differences in the sizes of the aftereffects between the two legs, except for peak hip flexion during swing, or in the rate at which peak hip flexion adapted during steps against resistance between the two legs. Our results indicate that interlimb transfer of these types of locomotor adaptation is not a robust phenomenon. These findings add to our current understanding of motor adaptations and provide further evidence that generalization of adaptations may be dependent on the movement task.

Cortical and brainstem differentiation of neural responses to hits versus misses

Near threshold, the same physical stimuli sometimes are perceived, but sometimes go unheard. Past visual studies have shown cortical evoked response potentials (ERPs) recorded via electroencephalography (EEG) are greater when an input is perceived than when it is not detected. Here, this approach was extended to ask whether there are detectable differences in neural activity in response to detected and undetected sounds, and whether these differences are present not only cortically, but also even earlier in the auditory system. Listeners are asked to detect the presence of a threshold-level tone complex presented in noise, presented amidst “no tone complex” catch trials. Tone-present trials are binned based on perceptual outcome (“hits” versus “misses”). Cortical ERPs from “hits” trials were found to be more robust than ERPs from “misses.” Moreover, post-stimulus alpha activity (8-12 Hz) differs; specifically, “misses” showed sustained alpha activity beginning 200 ms post-stimulus, while “hits” showed an amplitude decrease in alpha around 250-300 ms. FFRs from the same EEG data for “hits” and “misses” are being compared to determine whether perceptual differences are observable early in the auditory processing stream.

An Apparent-Motion Confound Causes the Negative Exogenous Cuing Effect at SOAs With Larger Numbers of Target Locations

Salient but irrelevant stimuli seem to cause an automatic orienting of covert attention, facilitating the detection of targets at the cued location for a brief period of time. However, this finding is highly dependent on the number of possible target locations, at least when the simple detection of targets is all that the task requires. Whereas small numbers of possible target locations (e.g., 2 or 3) produce the well-known advantage in response time for valid cue trials (i.e., a positive cuing effect), larger numbers of possible target locations (e.g., 6 or 8) produce a negative cuing effect. If not explained in terms of a nonattentional mechanism, this latter finding raises serious questions about the standard interpretation of positive cuing effects. The present experiment tested a particular nonattentional mechanism: that a confound between target presence and apparent motion, which occurs only on invalid cue trials, is responsible for negative cuing effect. We reduced or eliminated this confound by the use of a new type of catch trial and eliminated the negative cuing effect with large numbers of target locations.

Syllable Effects in a Fragment-Detection Task in Italian Listeners

In the line of the monitoring studies initiated by Mehler et al. (1981), a group of Italian listeners were asked to detect auditory CV and CVC targets in carrier words beginning with a CV, a CVC, or a CVG (G = geminate) syllable with variable initial syllable stress. By slowing participants reaction times (RTs), using both catch and foil trials, a syllable effect was found, partially modulated by participants’ speed and stress location. When catch trials were removed in a second experiment the syllable effect was not observed, even if RTs were similar to that of the first experiment. We discuss these data in relation to the language transparency hypothesis, the nature of the pivotal consonant, and the resonance-based ART model for speech perception (Grossberg, 2003).

Behavioral Effects of Electrical Microstimulation in FEF of the Macaque Monkey with chronically implanted wire electrodes

Behavioral Effects of Electrical Microstimulation in FEF of the Macaque Monkey with chronically implanted wire electrodes

Inertia Compensation Control of a One-Degree-of-Freedom Exoskeleton for Lower-Limb Assistance: Initial Experiments

A new method of lower-limb exoskeleton control aimed at improving the agility of leg-swing motion is presented. In the absence of control, an exoskeleton's mechanism usually hinders agility by adding mechanical impedance to the legs. The uncompensated inertia of the exoskeleton will reduce the natural frequency of leg swing, probably leading to lower step frequency during walking as well as increased metabolic energy consumption. The proposed controller emulates inertia compensation by adding a feedback loop consisting of low-pass filtered angular acceleration multiplied by a negative gain. This gain simulates negative inertia in the low-frequency range. The resulting controller combines two assistive effects: increasing the natural frequency of the lower limbs and performing net work per swing cycle. The controller was tested on a statically mounted exoskeleton that assists knee flexion and extension. Subjects performed movement sequences, first unassisted and then using the exoskeleton, in the context of a computer-based task resembling a race. In the exoskeleton's baseline state, the frequency of leg swing and the mean angular velocity were consistently reduced. The addition of inertia compensation enabled subjects to recover their normal frequency and increase their selected angular velocity. The work performed by the exoskeleton was evidenced by catch trials in the protocol.

Functional magnetic resonance study of deliberate deception

The goal of the study was analysis of the cerebral mechanisms of deliberate deception. The eventrelated functional magnetic resonance (ER fMRI) imaging technique was used to assess the changes in the functional brain activity by means of recording the blood oxygen level-dependent (BOLD) signal. Twelve right-handed healthy volunteers aged 19–44 years participated in the study. The BOLD images were obtained during three experimental trials: deliberate deception, manipulative honest and control truthful trials (catch trials). The deliberate deception and manipulative honest actions were characterized by a BOLD signal increase in the anterior cingulate (Brodmann’s area (BA) 32), frontal (BAs 9/10, 6), and parietal (BA 40) cortices as compared with a truthful response. Comparison of the ER fMRI data with the results of earlier studies where event-related potentials (ERPs) were recorded under similar conditions indicates the involvement of the brain mechanism of error detection in deliberate deception.

Beside the point: motor adaptation without feedback-based error correction in task-irrelevant conditions

Adaptation of movement may be driven by the difference between planned and actual motor performance, or the difference between expected and actual sensory consequences of movement. To identify how the nervous system differentially uses these signals, we asked: does motor adaptation occur when movement errors are irrelevant to the task goal? Participants reached on a digitizing tablet from a fixed start location to one of three targets: a point, an arc, or a ray. For the arc, reaches could be in any direction, but to a specific extent. For the ray, reaches could be to any distance, but in a targeted direction. After baseline reaching to the point, the direction or extent of continuous visual feedback was perturbed during training with either a cursor rotation or gain, respectively, while reaching to either the ray (goal = direction) or the arc (goal = extent). The perturbation, therefore, was either relevant or irrelevant to the task goal, depending on target type. During interspersed catch trials, the perturbation was removed and the target switched back to the point, identical to baseline. Although the goal of baseline and catch trials was the same, significant aftereffects in catch trials indicated behavioral adaptation in response to the perturbation. Adaptation occurred regardless of whether the perturbation was relevant to the task, and it was independent of feedback control. The presence of adaptation orthogonal to task demands supports the hypothesis that the nervous system can rely on sensory prediction to drive motor learning that can generalize across tasks.

Neural prediction of complex accelerations for object interception

To intercept or avoid moving objects successfully, we must compensate for the sensorimotor delays associated with visual processing and motor movement. Although straightforward in the case of constant velocity motion, it is unclear how humans compensate for accelerations, as our visual system is relatively poor at detecting changes in velocity. Work on free-falling objects suggests that we are able to predict the effects of gravity, but this represents the most simple, limiting case in which acceleration is constant and motion linear. Here, we show that an internal model also predicts the effects of complex, varying accelerations when they result from lawful interactions with the environment. Participants timed their responses with the arrival of a ball rolling within a tube of various shapes. The pattern of errors indicates that participants were able to compensate for most of the effects of the ball acceleration (∼85%) within a relatively short practice (∼300 trials). Errors on catch trials in which the ball velocity was unexpectedly maintained constant further confirmed that participants were expecting the effect of acceleration induced by the shape of the tube. A similar effect was obtained when the visual scene was projected upside down, indicating that the mechanism of this prediction is flexible and not confined to ecologically valid interactions. These findings demonstrate that the brain is able to predict motion on the basis of prior experience of complex interactions between an object and its environment.

Importance of binocular vision in foot placement accuracy when stepping onto a floor-based target during gait initiation

This study investigated the importance of binocular vision to foot placement accuracy when stepping onto a floor-based target during gait initiation. Starting from stationary, participants placed alternate feet onto targets sequentially positioned along a straight travel path with the added constraint that the initial target (target 1) could move in the medio-lateral (M-L) direction. Repeated trials when target 1 remained stationary or moved laterally at the instant of lead-limb toe-off (TO) or 200ms after TO (early swing) were undertaken under binocular and monocular viewing. Catch trials when target 1 shifted medially were also undertaken. Foot-reach kinematics, foot trajectory corrections and foot placement accuracy for the step onto target 1 were determined via 3D motion analyses. Peak foot-reach velocity and initial foot-reach duration were unaffected by vision condition but terminal foot-reach duration was prolonged under monocular conditions (p=0.002). Foot trajectory alteration onsets were unaffected by vision condition, but onsets occurred sooner when the target shifted in early swing compared to at TO (p=0.033). M-L foot placement accuracy decreased (p=0.025) and variability increased (p=0.05) under monocular conditions, particularly when stepping onto the moving target. There was no difference between vision conditions in A-P foot placement accuracy. Results indicate that monocular vision provides sufficient information to determine stepping distance and correctly transport the foot towards the target but binocular vision is required to attain a precise M-L foot placement; particularly so when stepping onto a moving target. These findings are in agreement with those found in the reaching and grasping literature, indicating that binocular vision is important for end-point precision.

Cooperative and Opposing Effects of Strategic and Involuntary Attention

To assess whether working memory contents can effectively bias visual selection even when they do not represent the current target in the attention task, we recorded the ERP activity from participants performing both a memory task and, in the retention period, a visual search task. In this task, a distracter matching the memory content could be presented on the same side (congruent trials) or on the opposite side (incongruent trials) relative to the target location (Experiment 1 and Experiment 2). On some trials, only the matching distracter (but no target) was presented (catch trials, Experiment 2). Results showed that the N2pc component was modulated by the presence and location of a matching distracter. We interpret these results as evidence that the involuntary control exerted by the irrelevant memory contents coexists with the strategic mechanism related to the search target, influencing attention selection with roughly equal power. In Experiment 3, we found that the modulation of the N2pc is not strictly related to the active maintenance of the memory-target features but can also be elicited by repetition priming. Overall, these findings suggest that, together with the physical properties of the stimuli presented in the visual field, irrelevant memory contents represent a powerful class of factors that lead to involuntary attentional control.

Behavioral audiogram of the giant panda (Ailuropoda melanoleuca): Preliminary results

We used behavioral techniques to assess the hearing sensitivity of four, critically endangered, giant pandas at the San Diego Zoo. Study subjects included one adult male (age 19), two adult females (ages 5 and 19), and one sub-adult female (age 3). We used a down-up staircase presentation order and a go/no-go response paradigm and thus far have measured hearing thresholds between 250 Hz and 31.5 kHz. Test stimuli were 500 ms shaped tones, and catch trials represented 30% of presentations. All subjects were trained using positive reinforcement. Preliminary results suggest that giant pandas have good hearing sensitivity between 8 and 14 kHz, and best sensitivity was centered at 12.5 kHz. Low frequency hearing sensitivity declined at 250 Hz for all subjects. All bears retained functional hearing at 31.5 kHz: the younger females could hear tones as low as 15 dB, and the adults could hear to 25 dB. Preliminary results suggest that panda hearing sensitivity is similar to that of other terrestrial carnivores studied to date. Hearing sensitivity data will enhance the understanding of how anthropogenic noise may impact both free-ranging and captive giant pandas.

Force Field Adaptation Can Be Learned Using Vision in the Absence of Proprioceptive Error

It has been shown that people can learn to perform a variety of motor tasks in novel dynamic environments without visual feedback, highlighting the importance of proprioceptive feedback in motor learning. However, our results show that it is possible to learn a viscous curl force field without proprioceptive error to drive adaptation, by providing visual information about the position error. Subjects performed reaching movements in a constraining channel created by a robotic interface. The force that subjects applied against the haptic channel was used to predict the unconstrained hand trajectory under a viscous curl force field. This trajectory was provided as visual feedback to the subjects during movement (virtual dynamics). Subjects were able to use this visual information (discrepant with proprioception) and gradually learned to compensate for the virtual dynamics. Unconstrained catch trials, performed without the haptic channel after learning the virtual dynamics, exhibited similar trajectories to those of subjects who learned to move in the force field in the unconstrained environment. Our results demonstrate that the internal model of the external dynamics that was formed through learning without proprioceptive error was accurate enough to allow compensation for the force field in the unconstrained environment. They suggest a method to overcome limitations in learning resulting from mechanical constraints of robotic trainers by providing suitable visual feedback, potentially enabling efficient physical training and rehabilitation using simple robotic devices with few degrees-of-freedom.

Sequence effects by non-predictive arrow cues.

Previous studies have found that attention orienting is influenced by the orienting processes of previous trials in a spatial cueing paradigm. This study mainly investigated whether this sequence effect could happen for a non-predictive arrow cue and whether it was influenced by the cue-target SOAs in previous and current trials. A significant sequence effect was observed for arrow cues even when voluntary control was not required, and it was significantly influenced by the SOAs of previous trials. The present results support the automatic memory check hypothesis and may reflect some temporal characteristics of the memory mechanism in sequential processes. In addition, contrary to the previous findings, we found an overall response facilitation following a catch trial, suggesting that the influence of preceding catch trials may be sensitive to experimental contexts.

Grip force regulates hand impedance to optimize object stability in high impact loads

Anticipatory grip force adjustments are a prime example of the predictive nature of motor control. An object held in precision grip is stabilized by fine adjustments of the grip force against changes in tangential load force arising from inertia during acceleration and deceleration. When an object is subject to sudden impact loads, prediction becomes critical as the time available for sensory feedback is very short. Here, we investigated the control of grip force when participants performed a targeted tapping task with a hand-held object. During the initial transport phase of the movement, load force varied smoothly with acceleration. In contrast, in the collision, load forces sharply increased to very large values. In the transport phase, grip force and load force were coupled in phase, as expected. However, in the collision, grip force did not parallel load force. Rather, it exhibited a stereotyped profile with maximum ∼65 ms after peak load at contact. By using catch trials and a virtual environment, we demonstrate that this peak of grip force is pre-programmed. This observation is validated across experimental manipulations involving different target stiffness and directions of movement. We suggest that the central nervous system optimizes stability in object manipulation-as in catching-by regulating mechanical parameters including stiffness and damping through grip force. This study provides novel insights about how the brain coordinates grip force in manipulation involving an object interacting with the environment.

The effect of choice reaction task on impact of single-leg landing

This study aimed to investigate attentional demand during single-leg landing after a jump. The experiment was set up as dual-task test. Twelve healthy male participants were instructed to make a two-leg jump with right-leg landing as softly as possible. The flight time of the jump was set to 300ms through sufficient practice. As a cognitive task, the participants were asked to push the right or left custom-made button as soon as a go-signal was presented. The timing when the go-signal presented varied from 0 to 300ms from the take-off. Catch trials in which the go-signal was not presented were randomly inserted. The results showed that the maximum vertical ground reaction force after touchdown was greater under the dual-task condition than in the single-task condition. Increase in the maximum vertical ground reaction force was consistent regardless of the timing of presenting the go-signal, and the same effect was observed in the catch trials. These results indicate that the effect of dual tasking was caused by attentional allocation to the choice reaction time task. Athletes may be exposed a large ground reaction forces during landing while performing cognitive tasks.

A spatial explicit strategy reduces error but interferes with sensorimotor adaptation

Although sensorimotor adaptation is typically thought of as an implicit form of learning, it has been shown that participants who gain explicit awareness of the nature of the perturbation during adaptation exhibit more learning than those who do not. With rare exceptions, however, explicit awareness is typically polled at the end of the study. Here, we provided participants with either an explicit spatial strategy or no instructions before learning. Early in learning, explicit instructions greatly reduced movement errors but also resulted in increased trial-to-trial variability and longer reaction times. Late in adaptation, performance was indistinguishable between the explicit and implicit groups, but the mechanisms underlying performance improvements remained fundamentally different, as revealed by catch trials. The progression of implicit recalibration in the explicit group was modulated by the use of an explicit strategy: these participants showed a lower level of recalibration as well as decreased aftereffects. This phenomenon may be due to the reduced magnitude of errors made to the target during adaptation or inhibition of implicit learning mechanisms by explicit processing.

Does temporal preparation increase the rate of sensory information accumulation?

Recent studies showed that temporal preparation, i.e., the ability to prepare for an upcoming stimulus, improves perceptual processing. The mechanisms underlying this benefit are still controversial. Based upon the theoretical framework of accumulation models, it has been proposed that the accumulation of sensory stimulus information begins earlier when participants are temporally prepared than when they are unprepared. Alternatively, however, temporal preparation might also affect the accumulation rate of sensory information. In the present study, we examined these possibilities. Specifically, in three experiments, we manipulated participants' decision criterion. This manipulation should interact with any experimental manipulation affecting the rate of information processing, but produce additive effects with any manipulation affecting the onset of information accumulation rather than its rate. We obtained additive effects on RT, irrespective of whether the decision criterion was manipulated by increasing catch trial proportion or nogo trial proportion. These results suggest that temporal preparation improves perceptual processing by operating on the onset of sensory information accumulation rather than the rate of sensory information accumulation.

Corrigendum

CorrigendumCorrigendumPublished Online:01 Mar 2011https://doi.org/10.1152/jn.z9k-0544-corr.2010Original articleMoreSectionsPDF (46 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations Volume 104, November 2010 Heitz RP, Cohen JY, Woodman GF, Schall JD. Neural Correlates of Correct and Errant Attentional Selection Revealed Through N2pc and Frontal Eye Field Activity. J Neurophysiol 104: , 2010; doi:10.1152/jn.00604.2010; http://jn.physiology.org/cgi/content/full/104/5/2433.A notation is shown incorrectly in the fifth sentence of third paragraph of the “Catch trials” subsection of results as “RFcorrectDT,” but it should be “RFcorrectT.” The sentence is given correctly below.The spike rate was, though, elevated relative to that measured when a saccade was correctly made away from the receptive field (RFcorrectT) [t(15) = 4.99, P < 0.001].This article has no references to display. Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation Related ArticlesNeural Correlates of Correct and Errant Attentional Selection Revealed Through N2pc and Frontal Eye Field Activity 01 Nov 2010Journal of Neurophysiology More from this issue > Volume 105Issue 3March 2011Pages 1425-1425 Copyright & PermissionsCopyright © 2011 the American Physiological Societyhttps://doi.org/10.1152/jn.z9k-0544-corr.2010History Published online 1 March 2011 Published in print 1 March 2011 Metrics