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PubMed2003

Multimodal feedback: an assessment of performance and mental workload.

Multimodal interfaces offer great potential to humanize interactions with computers by employing a multitude of perceptual channels. This paper reports on a novel multimodal interface using auditory, haptic and visual feedback in a direct manipulation task to establish new recommendations for multimodal feedback, in particular uni-, bi- and trimodal feedback. A close examination of combinations of uni-, bi- and trimodal feedback is necessary to determine which enhances performance without increasing workload. Thirty-two participants were asked to complete a task consisting of a series of 'drag-and-drops' while the type of feedback was manipulated. Each participant was exposed to three unimodal feedback conditions, three bimodal feedback conditions and one trimodal feedback condition that used auditory, visual and haptic feedback alone, and in combination. Performance under the different conditions was assessed with measures of trial completion time, target highlight time and a self-reported workload assessment captured by the NASA Task Load Index (NASA-TLX). The findings suggest that certain types of bimodal feedback can enhance performance while lowering self-perceived mental demand.

Adult↗

PubMed1994

Feature-linked synchronization of thalamic relay cell firing induced by feedback from the visual cortex.

The function of the massive feedback projection from visual cortex to its thalamic relay nucleus has so far eluded any clear overview. This feedback exerts a range of effects, including an increase in the inhibition elicited by moving contours, but the functional logic of the direct connections to the thalamic cells that relay the retinal input to the cortex remains largely unknown. In contrast to its thalamic nucleus, the visual cortex is characterized by cells that are strongly sensitive to the orientation of moving contours. Here we report that when driven by moving oriented visual stimuli the cortical feedback induces correlated firing in relay cells. This cortically induced correlation of relay cell activity produces coherent firing in those groups of relay cells with receptive field alignments appropriate to signalling the particular orientation of the moving contour to the cortex. Synchronization of relay cell firing means that they will elicit temporally overlapping excitatory postsynaptic potentials in their cortical target cells, thus increasing the chance that the cortical cells will fire. Effectively this increases the gain of the input for feature-linked events detected by the cortex. We propose that this feedback loop serves to lock or focus the appropriate circuitry onto the stimulus feature.

Action Potentials↗

PubMed2001

Experimental and computational analysis of monkey smooth pursuit eye movements.

Smooth pursuit eye movements are guided by visual feedback and are surprisingly accurate despite the time delay between visual input and motor output. Previous models have reproduced the accuracy of pursuit either by using elaborate visual signals or by adding sources of motor feedback. Our goal was to constrain what types of signals drive pursuit by obtaining data that would discriminate between these two modeling approaches, represented by the "image motion model" and the "tachometer feedback" model. Our first set of experiments probed the visual properties of pursuit with brief square-pulse and sine-wave perturbations of target velocity. Responses to pulse perturbations increased almost linearly with pulse amplitude, while responses to sine wave perturbations showed strong saturation with increasing stimulus amplitude. The response to sine wave perturbations was strongly dependent on the baseline image velocity at the time of the perturbation. Responses were much smaller if baseline image velocity was naturally large, or was artificially increased by superimposing sine waves on pulse perturbations. The image motion model, but not the tachometer feedback model, could reproduce these features of pursuit. We used a revision of the image motion model that was, like the original, sensitive to both image velocity and image acceleration. Due to a saturating nonlinearity, the sensitivity to image acceleration declined with increasing image velocity. Inclusion of this nonlinearity was motivated by our experimental results, was critical in accounting for the responses to perturbations, and provided an explanation for the unexpected stability of pursuit in the presence of perturbations near the resonant frequency. As an emergent property, the revised image motion model was able to reproduce the frequency and damping of oscillations recorded during artificial feedback delays. Our second set of experiments replicated prior recordings of pursuit responses to multiple-cycle sine wave perturbations, presented over a range of frequencies. The image motion model was able to reproduce the responses to sine wave perturbations across all frequencies, while the tachometer feedback model failed at high frequencies. These failures resulted from the absence of image acceleration signals in the tachometer model. We conclude that visual signals related to image acceleration are important in driving pursuit eye movements and that the nonlinearity of these signals provides stability. Smooth pursuit thus illustrates that a plausible neural strategy for combating natural delays in sensory feedback is to employ information about the derivative of the sensory input.

Animals↗

PubMed1997

Real-time direct volume rendering in functional magnetic resonance imaging.

Direct volume rendering is a visualization method that allows display of all information hidden in three-dimensional data sets of, for example, computed tomography or magnetic resonance imaging (MRI). In contrast to commonly used surface rendering methods, these algorithms need no preprocessing but suffer from a high computational complexity. A real-time rendering system, VIRIM (Vitec: Visualization Technology GmbH, Mannheim, Germany), cuts down rendering times of minutes on normal workstations to an interactive rate of 1 second or less. The immediate visual feedback allows interactive steering of the visualization process to achieve insight into the internal three-dimensional structure of objects. Additional information is obtained by using an interactive gray-value segmentation tool that both allows segmentation of the data set according to bone, tissue, and liquor and display of multifunctional data sets (e.g., functional MRI [fMRI] data sets). Thus, real-time direct volume rendering allows segmentation and volume data processing of functional and anatomical MR data sets simultaneously. As this method can be integrated in the clinical routine, it is of great importance for real-time motion artifact detection and the interpretation of fMRI data acquired during cognitive experiments with normal subjects and psychiatric patients. Because of the free programmability of VIRIM, more complex matching procedures are currently being investigated for future implementation.

Brain↗

PubMed2001

Visual and non-visual control of landing movements in humans.

1. The role of vision in controlling leg muscle activation in landing from a drop was investigated. Subjects (n = 8) performed 10 drops from four heights (0.2, 0.4, 0.6 and 0.8 m) with and without vision. Drop height was maintained constant throughout each block of trials to allow adaptation. The aim of the study was to assess the extent to which proprioceptive and vestibular information could substitute for the lack of vision in adapting landing movements to different heights. 2. At the final stages of the movement, subjects experienced similar peak centre of body mass (CM) displacements and joint rotations, regardless of the availability of vision. This implies that subjects were able to adapt the control of landing to different heights. The amplitude and timing of electromyographic signals from the leg muscles scaled to drop height in a similar fashion with and without vision. 3. However, variables measured throughout the execution of the movement indicated important differences. Without vision, landings were characterised by 10 % larger ground reaction forces, 10 % smaller knee joint rotations, different time lags between peak joint rotations, and more variable ground reaction forces and times to peak CM displacement. 4. We conclude that non-visual sensory information (a) could not fully compensate for the lack of continuous visual feedback and (b) this non-visual information was used to reorganise the motor output. These results suggest that vision is important for the very accurate timing of muscle activity onset and the kinematics of landing.

Adult↗

PubMed1997

Feedback strategies for visual search in airframe structural inspection.

Feedback of information has consistently shown positive results in human inspection, provided it is given in a timely and appropriate manner. Feedback serves as the basis of most training schemes; traditionally this has been performance feedback. Other forms of feedback which provide strategy information rather than performance information may have a role in improving inspection. This study compared performance feedback and cognitive feedback in a realistic simulation of an aircraft structural inspection task. Performance (time, errors) feedback showed the greatest improvements in performance measures. Cognitive feedback enhanced efficiency measures of search strategy. When cognitive feedback consisted of visual representations of the path and the coverage of the search sequence, subjects also were able to use this task information to improve their search performance.

Adult↗

PubMed2002

The effect of a fast bowling harness in cricket: an intervention study.

The influence of a bowling harness, as a training aid, was assessed as a means of modifying bowling technique. Thirty-three 13-year-old bowlers received a standardized 15 min of bowling coaching twice a week for 8 weeks. They were randomly assigned to one of two groups. The 13 participants in the intervention group used the bowling harness throughout the coaching, while also receiving verbal and visual feedback. The 20 participants in the non-harness group received the same visual and verbal feedback. Three-dimensional videography (200 Hz) of each player's bowling action enabled the calculation of transverse plane shoulder alignment counter-rotation, separation angle, lateral flexion and hyperextension of the trunk before and after the intervention. The restriction applied by the harness produced a significant reduction (P= 0.006) in separation angle and forced the bowler to adopt a position at back-foot impact that reduced the 'twist' in the spine. However, it had no effect on restricting other aspects of trunk movement during the critical phases of the bowling action. No significant long-term modifications to technique were found after the coaching intervention when players were assessed without the harness.

Adolescent↗

PubMed2004

Oculomotor rehabilitation in acquired brain injury: a case series.

OBJECTIVE: To investigate the effects of systematic, oculomotor rehabilitation on basic versional ocular motility, as well as reading eye movements, in subjects with acquired brain injury, using objective eye movement recording and subjective rating of reading ability. DESIGN: Case series. SETTING: Clinical research laboratory. PARTICIPANTS: Two men with acquired brain injury: one with traumatic brain injury and one with stroke. INTERVENTIONS: Versional oculomotor training was performed for 1 hour, twice weekly for 8 weeks. There were 2 feedback modes of training: normal internal oculomotor visual feedback alone (4wk), or that feedback in conjunction with external oculomotor auditory feedback (4wk). Testing was conducted before and after training. Main outcome measures Objective outcome measures included both basic eye movement parameters (fixational accuracy, saccadic gain and latency, pursuit gain, mean saccade frequency ratio for simulated reading), and reading eye movement parameters (words per minute, grade level equivalent, fixations per 100 words, regressions per 100 words, percentage of reading comprehension, duration of fixation in seconds). Subjective outcome measures included the subject's ability to read based on the responses to the reading rating-scale questionnaire. RESULTS: Both subjects improved objectively in terms of basic versional oculomotor accuracy and reading ability. These findings concurred with their subjective impressions. CONCLUSIONS: This case series provides objective documentation of the positive effects of oculomotor rehabilitation on basic ocular motility and reading ability in selected cases with acquired brain injury, thus suggesting the need for a larger clinical trial in this area.

Adult↗

PubMed2006

Subjective somatosensory vertical during dynamic tilt is dependent on task, inertial condition, and multisensory concordance.

To investigate how visual and vestibular cues are integrated for the perception of gravity during passive self-motion, we measured the ability to maintain a handheld object vertical relative to gravity without visual feedback during sinusoidal roll-tilt stimulation. Visual input, either concordant or discordant with actual dynamic roll-tilt, was delivered by a head-mounted display showing the laboratory. The four visual conditions were darkness, visual-vestibular concordance, stationary visual scene, and a visual scene 180 degrees phase-shifted relative to actual tilt. Tilt-indication performance using a solid, cylindrical joystick was better in the presence of concordant visual input relative to the other visual conditions. In addition, we compared performance when indicating the vertical by the joystick or a full glass of water. Subjects indicated the direction of gravity significantly better when holding the full glass of water than the joystick. Matching the inertial characteristics, including fluid properties, of the handheld object to the glass of water did not improve performance. There was no effect of visual input on tilt performance when using the glass of water to indicate gravitational vertical. The gain of object tilt motion did not change with roll-tilt amplitude and frequency (+/-7.5 degrees at 0.25 Hz, +/-10 degrees at 0.16 Hz, and +/-20 degrees at 0.08 Hz), however, the phase of object tilt relative to subject tilt showed significant phase-leads at the highest frequency tested (0.25 Hz). Comparison of the object and visual effects observed suggest that the task-dependent behavior change may be due to an attentional shift and/or shift in strategy.

Attention↗

PubMed2005

Application of cross time-frequency analysis to postural sway behavior: the effects of aging and visual systems.

In this paper, the effects of visual feedback and aging on postural sway systems and signals are investigated by analyzing the transient phase difference between "input" and "output" which correspond to center of pressure (COP) and center of mass (COM), respectively. In order to analyze the transient phase difference characteristics of COP and COM, a relatively new cross time-frequency analysis technique that provides time- and frequency-localized phase difference information is utilized. The feedback control process in the postural sway is interpreted in terms of a feedback compensator which is characterized in terms of a phase difference. Using the experimental results of the transient phase difference obtained from the cross time-frequency distribution, it is demonstrated that the postural control of young persons are more stable and rely more on visual sensory feedback to stabilize postural control compared to that of the elderly persons.

Adaptation, Physiological↗

PubMed2000

Development of externally guided grip force modulation in man.

We examined the development of externally guided changes of grip force with respect to force rate and direction of force change. Sixty-nine children, 3-6 years of age, and 17 adults produced increasing or decreasing isometric forces on a small cylindrical sensor using a pinch grip with visual feedback. Force changes were instructed with a visual tracking task. Ramp-like paradigms with both force increase and force decrease and two different target force rates were used (0.5 N/s, 1.25 N/s). Precision of force tracking showed clear age effects and was influenced by the required force rates and directions of force change. In adults, tracking errors were much more dependent on target force rate and direction than in children. Up to four years of age, the children tended to overshoot the target force change in a 'jump and wait' manner in all conditions except for fast target force decreases. Older children tended to overshoot only in the condition with slow target force decrease. Adults showed close undershooting in all conditions when following the target. Adults used either a continuous 'following' strategy or a 'see and catch-up' strategy. The distinct effects on tracking errors suggest an age-related change of strategies from a feedforward strategy with intermittent use of sensorimotor feedback towards a fairly parallel and well-integrated feedback and feedforward processing. A critical age appears to be around five to six years. We suggest that these age effects may reflect distinct developmental velocities of neuronal subpopulations of the cortex and of the cerebello-cortical connections.

Adult↗

PubMed2003

A step and a hop on the Müller-Lyer: illusion effects on lower-limb movements.

Past studies have shown that the effects of visual illusions on upper-limb movements can be modulated by the availability of current or recent visual information. The generality of this finding across body movements was examined by measuring the impact of the Müller-Lyer illusion on two types of lower limb actions. Subjects stood at one end of a Müller-Lyer figure, then either stepped or hopped to the other end. Visual feedback was manipulated through the use of visual closed-loop, open-loop, and open-loop three second delay conditions. For both stepping and hopping, effects of the illusion on movement accuracy were small in the closed-loop, moderate in the open-loop, and large in the three-second open-loop delay condition. These results were similar to those found in studies involving the Müller-Lyer illusion and upper-limb movements. The similar effects across different body movements suggests that a common visuomotor system subserves both upper and lower-limb movements, and that egocentric and allocentric reference frames make similar contributions for the two types of movements.

Humans↗

PubMed2000

Prism exposure aftereffects and direct effects for different movement and feedback times.

The effects of movement time and time to visual feedback (feedback time) on prism exposure aftereffects and direct effects were studied. In Experiment 1, the participants' (N = 60) pointing limb became visible early in the movement (.2-s feedback time), and eye-head aftereffects increased with increasing movement time (.5 to 3.0 s), but larger hand-head aftereffects showed little change. Direct effects (terminal error during exposure) showed near-perfect compensation for the prismatic displacement (11.4 diopters) when movement time was short but decreasing compensation with longer movement times. In Experiment 2, participants' (N = 48) eye-head aftereffects increased and their larger hand-head aftereffects decreased with increasing movement time (2.0 and 3.0 s), especially when feedback time increased (.25 and 1.5 s). Direct effects showed increasing overcompensation for longer movement and feedback times. Those results suggest that aftereffects and direct effects measure distinct adaptive processes, namely, spatial realignment and strategic control, respectively. Differences in movement and feedback times evoke different eye-hand coordination strategies and consequent direct effects. Realignment aftereffects also depend upon the coordination strategy deployed, but not all strategies support realignment. Moreover, realignment is transparent to strategic control and, when added to strategic correction, may produce nonadaptive performance.

Adaptation, Physiological↗

PubMed2006

The effect of visual biofeedback on the propulsion effectiveness of experienced wheelchair users.

OBJECTIVE: To determine the effect of visual feedback on the propulsion effectiveness of experienced manual wheelchair users. DESIGN: Controlled trial. SETTING: A motion analysis laboratory. PARTICIPANTS: A convenience sample of 16 healthy men and 2 healthy women with T4-L2 traumatic paraplegia, a mean age of 38+/-9 years, and a mean duration of manual wheelchair-based mobility of 14+/-8 years. INTERVENTION: Propulsion was assessed as the subjects propelled an instrumented wheelchair (with and without visual biofeedback) on a custom-built dynamometer at propulsion intensities of .15 and .25W/kg for 10 minutes. MAIN OUTCOME MEASURES: The primary outcome variable was the fraction of effective force (FEF) (ie, the ratio of effective to total force) applied by the subject to the wheelchair's pushrim. Secondary variables included velocity, stroke frequency, and stroke angle. RESULTS: A 2-factor analysis of variance with repeated measurements was used to detect significant differences between the outcome variables. The FEF ratio was 73.9% without feedback and 72.5% with feedback at the lower-intensity level. Propulsion during the higher intensity condition both with and without feedback resulted in a statistically significant improvement in the FEF (73.9%-78.7% with no feedback, 72.5%-80.2% with feedback), compared with the lower-intensity level. Stroke angle increased from 84.3 degrees to 98.7 degrees and frequency decreased from 66 to 57.8 strokes/min with feedback. CONCLUSIONS: Visual biofeedback may have little utility in improving the force effectiveness of manual wheelchair propulsion in experienced wheelchair users. Experienced wheelchair users may have already optimized their stroke in a manner that balances energy expenditure with stroke efficiency. Other variables such as stroke length and frequency may be more amenable to visual biofeedback.

Adult↗

PubMed2002

Visuomotor transformations affect bimanual coupling.

Interactions between bimanual movements may occur at two different levels: at a visually based level, where movement trajectories are programmed within the visually perceived external space, and at the executional level, through crosstalk of sensorimotor signals arising during movement execution. In order to distinguish between these sources of interactions, we investigated bimanual reversal movements under different conditions of visual feedback. A visuomotor transformation dissociated movement execution from visual appearance on a computer screen. The transformation we used made movements of the same amplitude evoke different excursions, and made movements of different amplitudes entail matched excursions on the screen. The transformed conditions allowed us to study which parameters of bimanual coupling were related to the way movements were executed and which correlated with the visual movement display. We found a clear dissociation between execution-related and visually related bimanual interactions. The assimilation of movement amplitudes was completely execution-related. Whenever movements of different amplitudes were generated, the shorter movement was lengthened, irrespective of how the movements appeared on the feedback screen. In contrast, temporal coordination at the point of movement reversal, as well as trial-by-trial correlations of movement amplitudes, also showed significant effects of the visuomotor transformation, suggesting that these parameters are influenced by visually perceived effects of movements. This dissociation confirms the idea of separate pathways for bimanual interactions and shows that a specific set of bimanual interactions occur at least partly within a visually based external reference frame.

Acculturation↗

PubMed1986

Scalp topography of ERP source-densities during visually guided target practice.

"Whole-head" maps of ERP source densities were recorded at 42 locations, spaced radially at 6 cm in hexagonal arrays, from two human subjects (S) during a visually-guided target-practice task with manual button-pressing and visual feedback, in a series of six or more 9 h recording sessions. From one S a finer-grained map (3 cm spacing) was also obtained at 13 occipital placements. Corresponding results at a smaller number of locations were obtained from nine other Ss. The topographical effects of changing the hand used, reversing the direction and hemifield of target approach, and changing the difficulty of the task were investigated in detail. Only locations near and just anterior to Cz were significantly affected by exchanging hands. Contralateral preparatory negativities, and ipsilateral negativities in anticipation of feedback, were enhanced. Changing the stimulus hemifield mainly affected occipito-parietal locations, with enhancement of contralateral preparatory-phase negativities, and of ipsilateral pre-feedback negativities, both there and near Cz. At certain parietal locations, however, the profiles were unaffected. Increase of task difficulty enhanced the difference between evaluation potentials for success and failure at a few locations, but left the general map largely unaltered. When comparing topographic features of the source-density maps in the two main Ss, the standard 10/20 topographic landmarks proved surprisingly unreliable. For each phase of the task, there were also hemispheric asymmetries not linked to the hand used or the hemifield stimulated; but their topography varied from S to S. Source densities during the preparatory phase were strongest around the vertex, with accompanying activity in parietal as well as occipital areas. No endogenous predictors of success and failure could be seen in the preparatory source-density profile. The source density map of the evaluation potential elicited by feedback suggests a relatively deep location for its generator. The ERP correlates of success and failure differ mainly in their form; amplitude differences vary from S to S. When S participates only imaginatively as a spectator of target practice by others or by machine, the general form of the ERP map is similar over the whole cycle, but amplitudes diminish from rear to front of the head. The cognitive significance of the main ERP features is confirmed by their virtual disappearance, except near the occipital poles, when S's attention is distracted from the significance of the visual input.

Attention↗

PubMed1977

The effect of visual guidance on the acquisition of a simple motor task.

Subjects were required to learn to depress a bar using concurrent visual feedback, which was removed for test. The overshooting found in test is attributed to visual dominance of the feedback traces; the way in which it occurs is not clear, since the reduction of the ratio of movement to display gain from 1:15 to 1:7.5 did not reduce overshooting. Performance improved after extended practice, but the direction of error remained positive. The results are discussed in terms of motor programming and feedback control of movement and are interpreted as evidence against Adams' (1971) two-trace theory.

Journal Article↗

PubMed1985

Properties of visual inputs that initiate horizontal smooth pursuit eye movements in monkeys.

Smooth pursuit eye movements allow primates to fixate and track small, slowly moving objects. Pursuit usually requires visual targets; our aim was to determine the properties of the visual signals transmitted to the pursuit motor system. Rhesus monkeys were rewarded for tracking spots of light that underwent discreet changes in velocity under a variety of visual conditions. We measured the resulting smooth eye acceleration in a 100-msec interval that began with the initiation of pursuit and ended before there had been time for visual feedback. This approach allowed us to vary the parameters of visual stimulation and measure eye movement responses in a way that provides estimates of the properties of signals transmitted by visual pathways. The initiation of pursuit showed different properties early and late in the interval we studied. In the first 20 msec of pursuit, eye acceleration was in the correct direction, but was independent of the initial position of the moving images, the velocity of the stimulus, or the presence or absence of background illumination. Thereafter, the initiation of pursuit depended strongly on all of the above parameters. Eye acceleration was highest when the moving images fell close to the fovea and decreased sharply as eccentricity was increased up to 21 degrees. When the background was diffusely illuminated, eye acceleration showed velocity selectivity; it was highest for a middle range of velocities (30 to 60 degrees/sec) and decreased for higher velocities. When the background was dark, eye acceleration increased as a function of target velocity up to 150 degrees/sec. We conclude that the initiation of pursuit has at least 2 visual components. The two components have different latencies and show quite different relationships to the visual properties of the stimulus, suggesting two cell populations that could provide the visual inputs for pursuit.

Animals↗