Perceptual processing time differences owing to visual field asymmetries

Recent experiments have reported increased endpoint accuracy for movements performed in the lower vs. the upper visual field, suggesting that there is superior feedback-based processing in the lower visual field owing to a visuomotor subsystem processing advantage. Differences, however, in the perceptual subsystem may also play a role in the lower visual field advantage. In this study, participants performed an inspection time task, a measure of perceptual processing time, requiring the identification of an asymmetrical 'pi' stimulus presented in the central, upper, or the lower visual field for a brief period. Significant differences between the percentage of correct identifications between visual fields indicated a lower visual field advantage over upper visual field for perceptual identification.

On-line control of pointing is modified by unseen visual shapes

Shapes that are rendered invisible through backward masking are still able to influence motor responses: this is called masked priming. Yet it is unknown whether this influence is on the control of ongoing action, or whether it merely influences the initiation of an already-programmed action. We modified a masked priming procedure (Schmidt, 2002) such that the critical prime-mask sequence was displayed during the execution of an already-initiated goal-directed pointing movement. Psychophysical tests of prime visibility indicated that the identity of the prime shapes were not accessible to participants for conscious report. Yet detailed kinematic analysis of the finger in motion revealed that masked primes had an influence on the pointing trajectories within 277ms of their appearance, 56ms earlier than the trajectory deviations observed in response to the visible masks. These results indicate that subliminal shapes can indeed influence the control of ongoing motor activity.

Dual-target interference for the 'automatic pilot' in the dorsal stream

When a target moves to a new location during a rapid aiming movement, the hand follows it, even when the participant intends not to. Pisella et al. (Nat Neurosci 3:729-736, 2000) claim that the posterior parietal cortex, in the dorsal visual stream, is responsible for this 'automatic pilot'. Here we study the limits of automaticity in the dorsal stream through analysis of aiming movements to two targets in sequence. Participants were given a goal of moving rapidly to two targets, with the first movement being completed within approximately 200 ms. On 30% of trials, the first or the second target jumped unpredictably to a new location at movement onset, allowing us to measure the automatic capture of the hand. The results showed that hand movements were less responsive to target jumps in a 2-target condition than in a 1-target control condition. This indicates that the 'automatic pilot' is susceptible to interference from multiple visual inputs, implying that the dorsal stream is less effective at guiding actions online when multiple targets are attended.

Compatibility effects in stopping and response initiation in a continuous tracking task

Two experiments explored stopping performance using a new stimulus-response compatibility effect spanning action initiation and stopping. Participants tracked a sometimes-moving, sometimes-stationary target by controlling the speed of a response marker via a force sensor. In the compatible condition, participants pressed the sensor in response to the target moving and stopped pressing in response to the target stopping. In the incompatible condition, participants stopped pressing in response to the target moving and initiated pressing in response to the target stopping. Response initiation and stopping were found to be faster under compatible than under incompatible conditions, regardless of whether compatible and incompatible trials were blocked or mixed. These findings indicate that stopping, like response initiation, is influenced by stimulus-response properties such as compatibility. This in turn suggests that stopping is governed by constraints similar to those of other behaviours.

Predictability influences stopping and response control

Using a continuous tracking task, the authors examined whether stopping is resistant to expectancies as well as whether it is a representative measure of response control. Participants controlled the speed of a moving marker by continuously adjusting their response force. Participants stopped their ongoing tracking in response to auditory signals on 25%, 50%, 75%, or 100% of trials. Stopping was contrasted with accelerating, in which participants accelerated the marker in response to the signals. In Experiment 1, on each trial participants either stopped or accelerated, allowing a trade-off between the two. In Experiments 2 and 3, participants only stopped or only accelerated, thus decreasing the likelihood of a trade-off. When a trade-off was possible, stopping was resistant to expectancies. However, with little or no trade-off, expectancies influenced stopping and accelerating similarly. These findings contrast with the established view that stopping is insensitive to expectancies. In addition, when trade-offs are prevented, these results confirm that stopping is representative of other response adjustment measures.

Updating of an internal model without proprioception: a deafferentation study

This study sought to determine whether intact proprioception is required to adapt to a novel kinematic environment. We compared adaptation with a rotated visual feedback between a deafferented patient and healthy participants. They performed reaching movements towards visible targets while vision of the cursor was rotated by 30 degrees with respect to hand position. The patient adapted at the same rate and to the same extent as the controls when exposed to the rotated visual feedback. She also presented large aftereffects following removal of the perturbation. This suggests that proprioception is not an absolute requirement to update a kinematic internal model. Adaptation was likely mediated by a comparison between the sensory consequences of a movement as predicted by a forward model and the visual feedback from that movement.

Will "no blood" kill Jehovah Witnesses?

A 46-year-old Indonesian woman presented with signs and symptoms suggestive of an ovarian tumour and was advised to have surgery with exploratory laparotomy and removal of the mass. She agreed but refused blood transfusion any time in the course of her treatment or procedure, as she was a Jehovah Witness. As there was a high risk of intraoperative haemorrhage, steps were taken to reduce any consequent complications due to the surgery. The ethical conflict is between respecting patient autonomy and compromising standards of care, arising from the refusal of a standard therapy. The latest developments in the blood transfusion doctrine policy for the Jehovah Witnesses are also discussed in this case study.

Reprogramming of Interceptive Actions: Time Course of Temporal Corrections for Unexpected Target Velocity Change

The authors investigated the time course of reprogramming of the temporal dimension of motor acts in a task requiring interception of a moving target. The target moved at a constant velocity on a monitor screen; in part of the trials, target velocity was unexpectedly increased or decreased. Those modifications were produced at different moments during target displacement, leaving periods of time from 100 to 800 ms for movement timing correction. The authors assessed the effects of probability of target velocity change (25% vs. 50%), uncertainty about direction of velocity change (unidirectional vs. bidirectional), and direction of velocity change (increase vs. decrease). Analysis of 24 participants' arm acceleration showed that fast adjustments took place between 100 and 200 ms after target velocity change similarly for all uncertainty conditions. Analysis of temporal error indicated that the combination of high probability of target velocity change and certainty on direction of target velocity change led to the most successful movement timing reprogramming. For the other experimental conditions, temporal accuracy was still poor when a period of 800 ms was available for correction. Movement reprogramming was a continuous process that was more efficient for target velocity increase than for target velocity decrease.

Measuring online volitional response control with a continuous tracking task

We present a new tracking task designed to measure elements of response control in particular types of response adjustments such as stopping. In this task, participants track a visual target by manually pressing on a force sensor to yield a trace of force over time. Hardware specifications are detailed, as is an algorithm for determining the latencies of response adjustments such as stopping. We illustrate the use of the task in two experiments. Experiment 1 explores the reliability of data produced by the task. Experiment 2 examines some of the issues that can be addressed using the new task. These results demonstrate the usefulness and potential of the task for gauging response control within the context of the stopping literature.

Use of visual information in the correction of interceptive actions

Use of visual information in interceptive actions requiring large-scale changes to movement timing was investigated. The task consisted of intercepting a moving target on a monitor screen through an angular arm movement. In half of the trials, the initial target velocity of 8 cm/s was unexpectedly decreased to 4 cm/s or increased to 12 cm/s, leaving 800 ms to target arrival after velocity change. Visual information about target displacement was manipulated by interpolating full vision with occlusion of the last 200, 400, or 600 ms before the due time of interception. The results revealed that reduction of visual exposure of target displacement affected movement variability, but not arm velocity or directional trend of temporal errors. This finding supports the concept that motor control in interception is based on an internal representation of target displacement, formed during the initial portion of visual exposure following velocity change, which is updated by further visual information of target displacement.

Determinants of offline processing of visual information for the control of reaching movements

The authors investigated the use of visual feedback as a form of knowledge of results (KR) for the control of rapid (200-250 ms) reaching movements in 40 participants. They compared endpoint accuracy and intraindividual variability of a full-vision group (FV) with those of no-vision groups provided with KR regarding (a) the endpoint in numerical form, (b) the endpoint in visual form, or (c) the endpoint and the trajectory in visual form (DEL). The FV group was more accurate and less variable than were the no-vision groups, and the analysis of limb trajectory variability indicated that their superior performance resulted primarily from better movement planning rather than from online visual processes. The FV group outperformed the DEL group even though both groups were obtaining the same amount of spatial visual information from every movement. That finding suggests that the effectiveness with which visual feedback is processed offline is not a simple function of the amount of visual information available, but depends on how that information is presented.

Comparison and validation of three measures of quality of life in patients with pulmonary hypertension

BACKGROUND

Pulmonary hypertension, when advanced, markedly limits exercise capacity, activities of daily living and quality of life (QoL). No measure of QoL has yet been validated for the assessment of pulmonary hypertension. The aim of the study was to compare the validity of the Minnesota Living with Heart Failure (MLwHF) questionnaire, the Short Form-36 (SF-36) questionnaire and the Australian Quality of Life (AQoL) measure for assessing pulmonary hypertension treatment.

METHODS

Eighty-three patients were enrolled in three studies of pulmonary hypertension treatment (treprostinil, bosentan and sildenafil). They were assessed at baseline and 3 months with the MLwHF questionnaire. Treprostinil and bosentan groups also had 6 and 12 months' data. Twenty-one patients in the sildenafil trial completed concurrently, the SF-36 and AQoL measures at baseline and 3 months. QoL scores were correlated with the 6-min walk test distance, New York Heart Association functional class and right heart catheter-derived haemodynamic parameters of the disease for all matching time points and for changes in scores and clinical measurements over time.

RESULTS

The MLwHF and SF-36 scores correlated well with the 6-min walk test distance and New York Heart Association functional class, but did not correlate with haemodynamic measurements. MLwHF and SF-36 scores also correlated with the rate of change of the 6-min walk test distance and New York Heart Association functional class over time.

CONCLUSION

The MLwHF questionnaire and SF-36 are useful tools for the assessment of QoL in pulmonary hypertension and may be useful in the ongoing evaluation of QoL in the treatment and study of pulmonary hypertension.

Sensorimotor adaptation in response to proprioceptive bias

Studies investigating visuo-motor adaptation typically introduce sensory conflicts by manipulating visual information (prisms, cursor gains). The purpose of the present study was to determine whether similar adaptation would be observed when a conflict is created through distortion of the proprioceptive sense, rather than through visual distortion. We used a coordinated movement task that required participants to release thumb and index finger at a specific elbow angle during passive elbow extension. Participants could not see their arm, but were shown a cursor representing the forearm on a video screen. In the proprioceptive group, a sensory conflict was introduced by vibrating the biceps brachii muscle, introducing a discrepancy of approximately 7.5 degrees between the proprioceptively perceived and visually perceived elbow angle. In the visual group, a conflict of similar magnitude was obtained by introducing a gain of 7.5 degrees to the cursor with respect to forearm position. Adaptation was assessed by the presence of plastic changes in release elbow angles following a period of exposure to the sensory conflict (i.e., aftereffects). Both groups showed high accuracy during exposure despite the sensory conflicts. More importantly, the visual group presented large and persistent aftereffects, while the proprioceptive group presented none. We suggest that the proprioceptive group's lack of adaptation was due to the artificial muscle spindle activity resulting from vibration, which prevented visual and proprioceptive signals to be merged into a common frame of reference.

Startle produces early response latencies that are distinct from stimulus intensity effects

Recent experiments pairing a startling stimulus with a simple reaction time (RT) task have shown that when participants are startled, a prepared movement was initiated earlier in comparison to voluntary initiation. It has been argued that the startle acts to trigger the response involuntarily. However, an alternative explanation is that the decrease in RT may be due to stimulus intensity effects, not involuntary triggering. Thus the aim of the current investigation was to determine if RT simply declined in a linear fashion with increasing stimulus intensity, or if there was a point at which RT dramatically decreased. In the present experiment participants completed 50 active wrist extension trials to a target in response to an auditory stimulus of varying stimulus intensity (83-123 dB). The presented data show that RTs associated with a startle response are separate from stimulus intensity facilitated responses. Furthermore, this startle facilitation is more highly associated with sternocleidomastoid electromyographic (EMG) activity, rather than the EMG from the widely used startle response indicator muscle orbicularis oculi.

Gross motor skill acquisition in adolescents with Down syndrome

The purpose of this study was to assess whether verbal-motor performances deficits exhibited by individuals with Down syndrome limited their ability to acquire gross motor skills when given visual and verbal instruction together and then transferred to either a visual or verbal instructional mode to reproduce the movement. Nine individuals with Down syndrome (6 males, 3 females) performed 3 gross motor skills. Both visual and verbal instructional guidance was given to the participants over a 4-day period. Twenty-four hours later, the participants were video recorded as they produced the movements (used as baseline measures). On Day 6, they were randomly assigned into verbal and visual groups and required to reproduce the skills while the experimenter provided either visual demonstration or verbal instructions depending on the group. Based on skill performance scores, participants in the verbal-motor performance group demonstrated a lower level of proficiency and an increased number of performance errors when compared to participants in the visual-motor performance group. Moreover, while the visual group demonstrated an increase in performance levels compared to baseline measures, the opposite effect was seen for the verbal group.

Anchoring strategies for learning a bimanual coordination pattern

Anchoring has been defined as synchronizing a point in a movement cycle with an external stimulus (W. D. Byblow, R. G. Carson, & D. Goodman, 1994). Previously, investigators have examined anchoring during in-phase and antiphase movements. The present authors examined anchoring during acquisition of a novel bimanual coordination pattern. Participants performed a 90 degrees pattern at 1 Hz, with a 2- or 4-Hz metronome. No group differences were found in pattern performance; however, the 4-Hz group developed more consistent anchoring relative to the metronome. Mechanical anchor-point variability differed by hand, position (midpoint vs. endpoint), and direction (flexion vs. extension) but not by metronome frequency. Those results support and extend previous findings but leave unanswered questions regarding the benefits and effectiveness of anchoring during a 90 degrees pattern.

Decay in visuomotor representations during manual aiming

The time course of the decay of spatial representations used for planning and controlling manual aiming has not been established. The authors' purpose in the present investigation was to generate a psychometric function for memory-guided reaching movements. Eight university-aged students performed a reciprocal tapping task for 10 s. Participants could see the targets for 5 s; then, vision of the targets was occluded. The present findings provide mixed support for 2 prominent theories concerning memory representations. Variability increased concurrently with the removal of vision of the targets, supporting the real-time hypothesis. However, a brief plateau in the curve was apparent for approximately 2 s after vision was removed, consistent with the use of a highly accurate representation for action.

Temporal uncertainty does not affect response latencies of movements produced during startle reactions

Previous research has shown that a startle 'go' stimulus, presented at a constant latency with respect to a warning stimulus, is capable of eliciting an intended voluntary movement in a simple reaction time (RT) task at very short latencies without involvement of the cerebral cortex (Carlsen et al. in Exp Brain Res 152:510-518, 2003; J Motor Behav 36:253-264, 2004a; Exp Brain Res 159:301-309 2004b; Valls-Solé et al. in J Physiol 516:931-938, 1999). The purpose of the present experiment was to determine the effect of temporal uncertainty on response latency during an RT task that comprised a startle stimulus. Participants were required to perform an active 20 degrees wrist extension movement in response to an auditory tone that was presented 2,500 to 5,500 ms after a warning stimulus, in 1,000 ms increments. On certain trials the control auditory stimulus (80 dB) was unexpectedly replaced by the startle stimulus (124 dB). When participants were startled the intended voluntary movement was initiated at approximately 70 ms, regardless of foreperiod duration. The magnitude and invariance of response latencies to the startle stimulus suggest that the intended movement had indeed been prepared prior to the arrival of the imperative go stimulus, within 2.5 s of the warning stimulus. Furthermore, there was no evidence that the prepared movement decayed over a period of at least 3 s.

Inferring online and offline processing of visual feedback in target-directed movements from kinematic data

Vision plays an important role in the planning and execution of target-directed aiming movements. In this review, we highlight the limitations that exist in detecting visual regulation of limb trajectories from traditional kinematic analyses such as the identification of discontinuities in velocity and acceleration. Alternative kinematic analyses that involve examining variability in limb trajectories to infer visual control processes are evaluated. The basic assumption underlying these methods is that noise exists in the neuromotor system that subsequently leads to variability in motor output. This leads to systematic relations in limb trajectory variability at different stages of the movement that are altered when trajectories are modified during movement execution. Hence, by examining the variability in limb trajectories and correlations of kinematic variables throughout movement for vision and no vision conditions, the contribution of visual feedback in the planning and control of movement can be determined.

No automatic pilot for visually guided aiming based on colour

It has been claimed that visually guided limb movements are automatically corrected in response to a change in target location but not when the same change in target is cued through a colour switch (Pisella et al. 2000). These findings were based solely on limb endpoint data. Here we examine the kinematic trajectory of the hand during the entire movement. Participants pointed rapidly to a target object that could change position either by changing spatial location, or by switching colour with a second object. Participants performed in two instructional conditions: a "go" condition to index intentional movements and a "stop" condition in which failures to stop pointing indexed automatic limb guidance. Kinematic analysis indicated efficient intentional pointing in both location and colour change conditions. However, only targets that changed spatial location elicited involuntary limb modifications and these occurred within 150 ms of the change. This conclusion held even after baseline differences in the efficiency of processing colour-defined targets were taken into account, thereby strengthening the claim of a strongly automatic pilot for visually guided limb movements.