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Biomedical subjects

A Dubrowski

Publications and source records attributed to A Dubrowski.

9 recordsLinked to original sources
PubMed2006

Quantification of process measures in laparoscopic suturing.

BACKGROUND: Process measures describing the generation of movement are useful for evaluation and performance feedback purposes. This study aimed to identify process measures that differ between novice and advanced laparoscopists while completing a suturing skill. METHODS: A group of junior and a group of senior residents and fellows in surgery (n = 6) placed 10 laparoscopic sutures in a synthetic model. Process measures were quantified using an opto-electric motion/force sensor assembly that recorded: instrument rotation, applied forces, time, and time delays between force application and instrument rotation. RESULTS: Advanced trainees showed increased instrument rotation, higher peak applied force, and faster performance compared to novices (alll p < .01). However, over trials, only novices showed adaptations for instrument rotation and total time (interactions at p < .01) with no adaptation for the force application. The difference between the moments of force application and instrument rotation was not sensitive to participant training. CONCLUSIONS: Movement process measures can enhance our understanding of early adaptation processes and how such factors might be used as feedback to facilitate skill acquisition.

Clinical Competence↗
PubMed2006

Structural flexibility of laparoscopic instruments: implication for the design of virtual reality simulators.

Laparoscopic training, under simulated settings, benefits from high fidelity models of the actual environment. This study was aimed at reducing uncertainty in the displacement and loads experienced by a laparoscopic instrument during surgical training. Infrared tracking of laparoscopic instruments is ineffective when real tissues attenuate the infrared signals. Incorporating the use of strain gauges for tip deflection measurements allows for online motion and load tracking during a procedure. Strain gauge voltages and infrared markers indicating displacement were both linear with respect to loads up to 700 grams. The resultant strain gauge voltage was equated to deflection values with a calibration constant. The results serve two purposes. First, it may enable the tracking and analysis of the skill level of novice surgeons using bench models. Second, the mechanical model of each instrument can be quantified and incorporated into virtual simulations, thus increasing model fidelity, effectively leading to better learning.

Computer Simulation↗
PubMed2005

Surface exploration using laparoscopic surgical instruments: the perception of surface roughness.

During laparoscopic surgery video images are used to guide the movements of the hand and instruments, and objects in the operating field often obscure these images. Thus, surgeons often rely heavily on tactile information (sense of touch) to help guide their movements. It is important to understand how tactile perception is affected when using laparoscopic instruments, since many surgical judgements are based on how a tissue 'feels' to the surgeon, particularly in situations where visual inputs are degraded. Twelve naïve participants used either their index finger or a laparoscopic instrument to explore sandpaper surfaces of various grits (60, 100, 150 and 220). These movements were generated with either vision or no vision. Participants were asked to estimate the roughness of the surfaces they explored. The normal and tangential forces of either the finger or instrument on the sandpaper surfaces were measured. Results showed that participants were able to judge the roughness of the sandpaper surfaces when using both the finger and the instrument. However, post hoc comparisons showed that perceptual judgements of surface texture were altered in the no vision condition compared to the vision condition. This was also the case when using the instrument, compared to the judgements provided when exploring with the finger. This highlights the importance of the completeness of the video images during laparoscopic surgery. More normal and tangential force was used when exploring the surfaces with the finger as opposed to the instrument. This was probably an attempt to increase the contact area of the fingertip to maximize tactile input. With the instrument, texture was probably sensed through vibrations of the instrument in the hand. Applications of the findings lie in the field of laparoscopic surgery simulation techniques and tactile perception.

Adult↗
PubMed2002

The coordination of hand transport and grasp formation during single- and double-perturbed human prehension movements.

We investigated the mechanisms underlying human prehension movements, by perturbing the size and position of virtual targets. Subjects grasped virtual target discs with thumb and index finger. In 25% of trials, target size or position (single perturbation), or both (double perturbation) were changed 300 ms after target appearance. The experiments were designed such that the kinematic profiles of grasp formation and hand transport had a similar shape, and were analysed by the same algorithm. We found that grasp kinematics were influenced by changes of target position, and transport kinematics by changes of target size; we also found that the kinematics of double-perturbation trials could not be explained as a linear combination of single-perturbation effects. These findings confirm and expand previous evidence against the view that grasp and transport are controlled by fully independent channels. Most importantly, we found that the time of correction onset was not the same for grasp and transport, neither in single- nor in double-perturbation trials. This outcome argues against a holistic (single-channel) model of prehension; instead, our data are consistent with the notion of two mutually coupled channels.

Adult↗
PubMed2001

Control strategies when intercepting slowly moving targets.

In 3 experiments, the authors investigated and described how individuals control manual interceptive movements to slowly moving targets. Participants (N = 8 in each experiment) used a computer mouse and a graphics tablet assembly to manually intercept targets moving across a computer screen toward a marked target zone. They moved the cursor so that it would arrive in the target zone simultaneously with the target. In Experiment 1, there was a range of target velocities, including some very slow targets. In Experiment 2, there were 2 movement distance conditions. Participants moved the cursor either the same distance as the target or twice as far. For both experiments, hand speed was found to be related to target speed, even for the very slowly moving targets and when the target-to-cursor distance ratios were altered, suggesting that participants may have used a strategy similar to tracking. To test that notion, in Experiment 3, the authors added a tracking task in which the participants tracked the target cursor into the target zone. Longer time was spent planning the interception movements; however, there was a longer time in deceleration for the tracking movements, suggesting that more visually guided trajectory updates were made in that condition. Thus, although participants scaled their interception movements to the cursor speed, they were using a different strategy than they used in tracking. It is proposed that during target interception, anticipatory mechanisms are used rather than the visual feedback mechanism used when tracking and when pointing to stationary targets.

Adult↗
PubMed2000

The effect of illusory size on force production when grasping objects.

Milner and Goodale (1995) have proposed that visuomotor and perceptual processes are mediated by discrete visual systems that reflect the functional independence of action and perception. The visuomotor system is proposed to be insensitive to pictorial illusions of object size, whereas the perceptual system is reliably "tricked" by such figures. Brenner and Smeets (1996) and Jackson and Shaw (2000) demonstrated that grasp preshaping, but not grasping force, is immune to the Ponzo visual illusion, suggesting that not all visuomotor processes operate independently of the perceptual system. The present study investigated the effect of illusory object size on prehension kinematics and grasping dynamics (i.e., grip force and load force) as well as perceptual judgements of object size. Unlike previous investigations, object mass was held constant independent of changes in size. The Ponzo figure reliably affected perceptual estimates of object size, but this effect was restricted to one form of the illusion. Some aspects of the prehension movement were sensitive to veridical but not illusory object size (peak grip aperture, peak grip force, peak vertical wrist acceleration), whereas other movement parameters demonstrated illusory size effects (movement time, peak wrist velocity). Still other movement parameters were not sensitive to veridical or illusory object size (peak load force). Together the data suggest that certain prehension components are immune to pictorial illusions of object size, whereas others are not. Complex interactions between the perceptual and visuomotor systems appear to underlie the anticipatory scaling of grasping forces in prehension.

Acceleration↗
PubMed2000

Target velocity effects on manual interception kinematics.

Participants generated manual interception movements toward a target cursor that moved across a computer screen. The target reached its peak velocity either during the first third, at the midpoint, or during the last third of the movement. In Experiment 1 the view of the target was available for either the first 316, 633, 950, or 1267 ms, after which it disappeared. Results showed that for all viewing conditions, the timing of the interception velocity was related to the temporal properties of the target's trajectory. In Experiment 2, when the portion of the target trajectory that was viewed was reversed (such that participants did not see the first 316, 633, 950, or 1267 ms of the trajectory, but instead saw only the later portions of the trajectory), there was no clear relationship between the target trajectory and the timing of the aiming trajectory. These results suggest that participants use visual information early in the target's trajectory to form a representation of the target motion that is used to facilitate manual interception.

Adult↗
PubMedDate not supplied

Task dependent processing of visual information about target acceleration.

The objective of this study was to investigate the sensitivity of the perceptual and motor systems to target acceleration information using verbal magnitude estimations of target acceleration and manual interception of these targets. The results showed that in the perceptual task the participants were responding mainly to acceleration threshold values, which is acceleration as a function of initial, final, and average velocities, rather then to the absolute accelerations. When manually intercepting the targets the participants responded mainly to the absolute acceleration value and target initial velocity. Thus, these results suggest that target motion can be processed in the ventral (perception) and dorsal (action) visual streams however different motion characteristics are processed in these streams depending on the required output.

Adult↗