Kristina A. Neely

Goal-directed reaching: movement strategies influence the weighting of allocentric and egocentric visual cues

The location of an object in peripersonal space can be represented with respect to our body (i.e., egocentric frame of reference) or relative to contextual features and other objects (i.e., allocentric frame of reference). In the current study, we sought to determine whether the frame, or frames, of visual reference supporting motor output is influenced by reach trajectories structured to maximize visual feedback utilization (i.e., controlled online) or structured largely in advance of movement onset via central planning mechanisms (i.e., controlled offline). Reaches were directed to a target embedded in a pictorial illusion (the induced Roelofs effect: IRE) and advanced knowledge of visual feedback was manipulated to influence the nature of reaching control as reported by Zelaznik et al. (J Mot Behav 15:217–236, 1983). When vision could not be predicted in advance of movement onset, trajectories showed primary evidence of an offline mode of control (even when vision was provided) and endpoints demonstrated amplified sensitivity to the illusory (i.e., allocentric) features of the IRE. In contrast, reaches performed with reliable visual feedback evidenced a primarily online mode of control and showed increased visuomotor resistance to the IRE. These findings suggest that the manner a reaching response is structured differentially influences the weighting of allocentric and egocentric visual information. More specifically, when visual feedback is unavailable or unpredictable, the weighting of allocentric visual information for the advanced planning of a reach trajectory is increased.

Visual feedback schedules influence visuomotor resistance to the Müller-Lyer figures

We examined whether blocked or random visual feedback schedules influence visuomotor resistance to the Müller-Lyer (ML) illusion. Participants completed closed-loop (CL) and open-loop (OL) grasping movements to an object embedded within fins-in and fins-out ML configurations. In the blocked feedback schedule, CL and OL trials were completed in separate blocks of trials, whereas visual conditions were randomly interleaved in the random feedback schedule. The results of the blocked feedback schedule showed that OL, but not CL, trials were influenced in a direction consistent with the perceptual effects of the ML illusion. For the random feedback schedule, however, both CL and OL trials were influenced by the illusion. We have interpreted these results to reflect the fact that participants evoked distinct control strategies based on the predicted availability of visual feedback. Specifically, the refractory nature of CL trials in the blocked feedback schedule suggests that advance knowledge that visual feedback would be available during a response encouraged an online control strategy wherein metrical visual information supported grasping. When visual feedback was unavailable (i.e., blocked OL trials), or could not be predicted in advance of a response (i.e., random CL and OL trials), it is proposed that movements were structured offline via perception-based visual information that was “tricked” by the cognitive properties of the ML illusion.

Time course analysis of closed- and open-loop grasping of the Müller-Lyer illusion.

The authors investigated whether the early or later stages of closed-loop (CL) and open-loop (OL) grasping movements were differentially influenced by the Müller-Lyer (ML) illusion. Participants (N = 21) reached out and grasped small (5 cm) and large (7 cm) objects embedded within fins-in and fins-out ML configurations. Grasping time (GT) was normalized, and absolute grip aperture (GA) as well as scaled illusion effects were computed at 20%, 40%, 60%, and 80% of GT. The results indicated that CL trials were refractory to the illusory array (i.e., from 20% to 80% of GT), whereas OL trials were influenced by the ML figure during that same time. Those findings suggest that CL trials were supported by unitary and metrical visual information, whereas OL trials were entirely supported by perception-based visual information.

Functional Brain Activity Relates to 0–3 and 3–8 Hz Force Oscillations in Essential Tremor

It is well-established that during goal-directed motor tasks, patients with essential tremor have increased oscillations in the 0-3 and 3-8 Hz bands. It remains unclear if these increased oscillations relate to activity in specific brain regions. This study used task-based functional magnetic resonance imaging to compare the brain activity associated with oscillations in grip force output between patients with essential tremor, patients with Parkinsons disease who had clinically evident tremor, and healthy controls. The findings demonstrate that patients with essential tremor have increased brain activity in the motor cortex and supplementary motor area compared with controls, and this activity correlated positively with 3-8 Hz force oscillations. Brain activity in cerebellar lobules I-V was reduced in essential tremor compared with controls and correlated negatively with 0-3 Hz force oscillations. Widespread differences in brain activity were observed between essential tremor and Parkinsons disease. Using functional connectivity analyses during the task evidenced reduced cerebellar-cortical functional connectivity in patients with essential tremor compared with controls and Parkinsons disease. This study provides new evidence that in essential tremor 3-8 Hz force oscillations relate to hyperactivity in motor cortex, 0-3 Hz force oscillations relate to the hypoactivity in the cerebellum, and cerebellar-cortical functional connectivity is impaired.

Segregated and overlapping neural circuits exist for the production of static and dynamic precision grip force

A central topic in sensorimotor neuroscience is the static‐dynamic dichotomy that exists throughout the nervous system. Previous work examining motor unit synchronization reports that the activation strategy and timing of motor units differ for static and dynamic tasks. However, it remains unclear whether segregated or overlapping blood‐oxygen‐level‐dependent (BOLD) activity exists in the brain for static and dynamic motor control. This study compared the neural circuits associated with the production of static force to those associated with the production of dynamic force pulses. To that end, healthy young adults (n = 17) completed static and dynamic precision grip force tasks during functional magnetic resonance imaging (fMRI). Both tasks activated core regions within the visuomotor network, including primary and sensory motor cortices, premotor cortices, multiple visual areas, putamen, and cerebellum. Static force was associated with unique activity in a right‐lateralized cortical network including inferior parietal lobe, ventral premotor cortex, and dorsolateral prefrontal cortex. In contrast, dynamic force was associated with unique activity in left‐lateralized and midline cortical regions, including supplementary motor area, superior parietal lobe, fusiform gyrus, and visual area V3. These findings provide the first neuroimaging evidence supporting a lateralized pattern of brain activity for the production of static and dynamic precision grip force. Hum Brain Mapp, 2013.

Muller-Lyer figures influence the online reorganization of visually guided grasping movements

In advance of grasping a visual object embedded within fins-in and fins-out Müller-Lyer (ML) configurations, participants formulated a premovement grip aperture (GA) based on the size of a neutral preview object. Preview objects were smaller, veridical, or larger than the size of the to-be-grasped target object. As a result, premovement GA associated with the small and large preview objects required significant online reorganization to appropriately grasp the target object. We reasoned that such a manipulation would provide an opportunity to examine the extent to which the visuomotor system engages egocentric and/or allocentric visual cues for the online, feedback-based control of action. It was found that the online reorganization of GA was reliably influenced by the ML figures (i.e., from 20 to 80% of movement time), regardless of the size of the preview object, albeit the small and large preview objects elicited more robust illusory effects than the veridical preview object. These results counter the view that online grasping control is mediated by absolute visual information computed with respect to the observer (e.g., Glover in Behav Brain Sci 27:3–78, 2004; Milner and Goodale in The visual brain in action 1995). Instead, the impact of the ML figures suggests a level of interaction between egocentric and allocentric visual cues in online action control.

Force control deficits in individuals with Parkinson's disease, multiple systems atrophy, and progressive supranuclear palsy.

Objective This study examined grip force and cognition in Parkinson’s disease (PD), Parkinsonian variant of multiple system atrophy (MSAp), progressive supranuclear palsy (PSP), and healthy controls. PD is characterized by a slower rate of force increase and decrease and the production of abnormally large grip forces. Early-stage PD has difficulty with the rapid contraction and relaxation of hand muscles required for precision gripping. The first goal was to determine which features of grip force are abnormal in MSAp and PSP. The second goal was to determine whether a single variable or a combination of motor and cognitive measures would distinguish patient groups. Since PSP is more cognitively impaired relative to PD and MSAp, we expected that combining motor and cognitive measures would further distinguish PSP from PD and MSAp. Methods We studied 44 participants: 12 PD, 12 MSAp, 8 PSP, and 12 controls. Patients were diagnosed by a movement disorders neurologist and were tested off anti-Parkinsonian medication. Participants completed a visually guided grip force task wherein force pulses were produced for 2 s, followed by 1 s of rest. We also conducted four cognitive tests. Results PD, MSAp, and PSP were slower at contracting and relaxing force and produced longer pulse durations compared to controls. PSP produced additional force pulses during the task and were more cognitively impaired relative to other groups. A receiver operator characteristic analysis revealed that the combination of number of pulses and Brief Test of Attention (BTA) discriminated PSP from PD, MSAp, and controls with a high degree of sensitivity and specificity. Conclusions Slowness in contracting and relaxing force represent general features of PD, MSAp, and PSP, whereas producing additional force pulses was specific to PSP. Combining motor and cognitive measures provides a robust method for characterizing behavioral features of PSP compared to MSAp and PD.

Manual asymmetries in bimanual reaching: The influence of spatial compatibility and visuospatial attention

The goal of the present investigation was to explore the possible expression of hemispheric-specific processing during the planning and execution of a bimanual reaching task. Participants (N = 9) completed 80 bimanual reaching movements (requiring simultaneous, bilateral production of arm movements) to peripherally presented targets while selectively attending to either their left or right hand. Further, targets were presented in spatially compatible (ipsilateral to the aiming limb) and incompatible (contralateral to the aiming limb) response contexts. It was found that the left hand exhibited temporal superiority over the right hand in the response planning phase of bimanual reaching, indicating a left hand/right hemisphere advantage in the preparation of a bimanual response. During response execution, and consistent with the view that interhemispheric processing time (Barthelemy & Boulinguez, 2002) or biomechanical constraints (Carey, Hargreaves, & Goodale, 1996) generate temporal delays, longer movement times were observed in response to spatially incompatible target positions. However, no hemisphere-specific benefit was demonstrated for response execution. Based on these findings, we propose lateralized processing is present at the time of response planning (i.e., left hand/right hemisphere processing advantage); however, lateralized specialization appears to be annulled during dynamic execution of a bimanual reaching task.

Visuomotor mental rotation: reaction time is determined by the complexity of the sensorimotor transformations mediating the response.

In the visuomotor mental rotation (VMR) task, participants point to a location that deviates from a visual target by a predetermined angle. A seminal investigation of the VMR task reported a linear increase in reaction time (RT) as a function of increasing angle, for 5°, 10°, 15°, 35°, 70°, 105°, and 140° (Georgopoulos and Massey, 1987). This finding led to the development of the mental rotation model (MRM) and the assertion that response preparation is mediated via the imagined rotation of a movement vector. To determine if the MRM can be extrapolated to perceptually familiar angles (e.g., 90° and 180°) within a range of equally spaced angles, we evaluated two independent sets of angles: 5°, 10°, 15°, 35°, 70°, 105°, and 140° (experiment one) and 30°, 60°, 90°, 120°, 150°, 180°, and 210° (experiment two). Consistent with the MRM, experiment one revealed a linear increase in RT as a function of increasing angle; however, a non-linear relation was revealed for experiment two. RTs were fastest for 180°, followed by 30°, 90°, 60°, 150°, 210°, and 120°. Such results demonstrate that response preparation was not uniquely mediated via a mental rotation process. Instead, the present work provides evidence of a temporally demanding and cognitively mediated response substitution process, wherein the computational demands of response preparation are determined by the complexity of the sensorimotor transformations mediating the response.

Visuomotor mental rotation: Reaction time is not a function of the angle of rotation

The goal of the present investigation was to determine whether the anti-pointing task (i.e., pointing to a location 180 degrees from a visual cue [M. Heath, A. Maraj, A. Gradkowski, G. Binsted, Anti-pointing is mediated by a perceptual bias of target location in left and right visual space, Exp. Brain Res. 192 (2009) 275-286]) and a 90 degrees -rotated-pointing task are supported by a similar cognitive strategy. Previous work evaluating visuomotor mental rotation (MR) has reported a monotonic increase in reaction time (RT) as a function of the angle of rotation [A.P. Georgopoulos, G. Pellizzer, The mental and the neural: psychological and neural studies mental rotation and memory scanning, Neuropsychologia 33 (1995) 1531-1547]. Interestingly, however, anti-pointing movements have not been evaluated in concert with intermediary angles of rotation. We therefore examined RT for center-out pointing movements in four tasks: pro-pointing (PRO), anti-pointing (ANTI), and 90 degrees clockwise (CW90) and counter-clockwise (CCW90) pointing. We found that response latencies for PRO responses were faster than ANTI responses, which in turn were faster than CW90 and CCW90 responses. These findings counter the notion that the angle of rotation influences the speed of visuomotor MR. Instead, we posit that visuomotor MR is supported by a serial process requiring the suppression of a stimulus-driven response followed by voluntary response generation. Further, we suggest that preparation of the voluntary response is cognitively less demanding for the ANTI task because the sensorimotor transformations underlying such an action are completed within the same plane as the stimulus-driven response. In contrast, the cognitive demands associated with CW90 and CCW90 are more complex because the action requires the transformation of response parameters in a movement plane orthogonal to the original - and suppressed - stimulus-driven response.