scholarly journals Prehension and Perception of Size in Left Visual Neglect

2002 ◽  
Vol 13 (1-2) ◽  
pp. 3-15 ◽  
Author(s):  
R. D. McIntosh ◽  
C. L. Pritchard ◽  
H. C. Dijkerman ◽  
A. D. Milner ◽  
R. C. Roberts
Keyword(s):  
Right Hemisphere ◽  
Visual Neglect ◽  
Grip Aperture ◽  
Estimation Task ◽  
Deceleration Phase ◽  
Maximum Grip Aperture ◽  
Patient Groups ◽  
Visual Size ◽  
Null Finding ◽  
Maximum Grip

Right hemisphere damaged patients with and without left visual neglect, and age-matched controls had objects of various sizes presented within left or right body hemispace. Subjects were asked to estimate the objects’ sizes or to reach out and grasp them, in order to assess visual size processing in perceptual-experiential and action-based contexts respectively. No impairments of size processing were detected in the prehension performance of the neglect patients but a generalised slowing of movement was observed, associated with an extended deceleration phase. Additionally both patient groups reached maximum grip aperture relatively later in the movement than did controls. For the estimation task it was predicted that the left visual neglect group would systematically underestimate the sizes of objects presented within left hemispace but no such abnormalities were observed. Possible reasons for this unexpected null finding are discussed.

scholarly journals Are reaching and grasping effector-independent? Similarities and differences in reaching and grasping kinematics between the hand and foot

2021 ◽  
Author(s):  
Yuqi Liu ◽  
James Caracoglia ◽  
Sriparna Sen ◽  
Ella Striem-Amit
Keyword(s):  
Peak Velocity ◽  
Object Size ◽  
Body Parts ◽  
Acceleration Phase ◽  
Grip Aperture ◽  
Deceleration Phase ◽  
Neural Representations ◽  
Maximum Grip Aperture ◽  
Similarities And Differences ◽  
Maximum Grip

While reaching and grasping are highly prevalent manual actions, neuroimaging studies provide evidence that their neural representations may be shared between different body parts, i.e. effectors. If these actions are guided by effector-independent mechanisms, similar kinematics should be observed when the action is performed by the hand or by a cortically remote and less experienced effector, such as the foot. We tested this hypothesis with two characteristic components of action: the initial ballistic stage of reaching, and the preshaping of the digits during grasping based on object size. We examined if these kinematic features reflect effector-independent mechanisms by asking participants to reach toward and to grasp objects of different widths with their hand and foot. First, during both reaching and grasping, the velocity profile up to peak velocity matched between the hand and the foot, indicating a shared ballistic acceleration phase. Secondly, maximum grip aperture and time of maximum grip aperture of grasping increased with object size for both effectors, indicating encoding of object size during transport. Differences between the hand and foot were found in the deceleration phase and time of maximum grip aperture, likely due to biomechanical differences and the participants' inexperience with foot actions. These findings provide evidence for effector-independent visuomotor mechanisms of reaching and grasping that generalize across body parts.

scholarly journals Is Grasping Impaired in Hemispatial Neglect?

2002 ◽  
Vol 13 (1-2) ◽  
pp. 17-28 ◽  
Author(s):  
Monika Harvey ◽  
Stephen R. Jackson ◽  
Roger Newport ◽  
Tanja Krämer ◽  
D. Llewlyn Morris ◽  
...  
Keyword(s):  
Right Hemisphere ◽  
Target Object ◽  
Cerebral Stroke ◽  
Hemispatial Neglect ◽  
Grip Aperture ◽  
Maximum Grip Aperture ◽  
Path Curvature ◽  
The Right ◽  
Path Deviation ◽  
Maximum Grip

Patients with right unilateral cerebral stroke, four of which showed acute hemispatial neglect, and healthy aged-matched controls were tested for their ability to grasp objects located in either right or left space at near or far distances. Reaches were performed either in free vision or without visual feedback from the hand or target object. It was found that the patient group showed normal grasp kinematics with respect to maximum grip aperture, grip orientation, and the time taken to reach the maximum grip aperture. Analysis of hand path curvature showed that control subjects produced straighter right hand reaches when vision was available compared to when it was not. The right hemisphere lesioned patients, however, showed similar levels of curvature in each of these conditions. No behavioural differences, though, could be found between right hemisphere lesioned patients with or without hemispatial neglect on either grasp parameters, path deviation or temporal kinematics.

On the Relation Between Object Shape and Grasping Kinematics

2004 ◽  
Vol 91 (6) ◽  
pp. 2598-2606 ◽  
Author(s):  
Raymond H. Cuijpers ◽  
Jeroen B. J. Smeets ◽  
Eli Brenner
Keyword(s):  
Principal Axis ◽  
Grip Aperture ◽  
Object Shape ◽  
Hand Orientation ◽  
Principal Axes ◽  
Movement Distance ◽  
Maximum Grip Aperture ◽  
The Many ◽  
Elliptical Cylinders ◽  
Maximum Grip

Despite the many studies on the visual control of grasping, little is known about how and when small variations in shape affect grasping kinematics. In the present study we asked subjects to grasp elliptical cylinders that were placed 30 and 60 cm in front of them. The cylinders' aspect ratio was varied systematically between 0.4 and 1.6, and their orientation was varied in steps of 30°. Subjects picked up all noncircular cylinders with a hand orientation that approximately coincided with one of the principal axes. The probability of selecting a given principal axis was the highest when its orientation was equal to the preferred orientation for picking up a circular cylinder at the same location. The maximum grip aperture was scaled to the length of the selected principal axis, but the maximum grip aperture was also larger when the length of the axis orthogonal to the grip axis was longer than that of the grip axis. The correlation between the grip aperture— or the hand orientation—at a given instant, and its final value, increased monotonically with the traversed distance. The final hand orientation could already be inferred from its value after 30% of the movement distance with a reliability that explains 50% of the variance. For the final grip aperture, this was only so after 80% of the movement distance. The results indicate that the perceived shape of the cylinder is used for selecting appropriate grasping locations before or early in the movement and that the grip aperture and orientation are gradually attuned to these locations during the movement.

The influence of object height on maximum grip aperture in empirical and modeled data.

2014 ◽  
Vol 40 (2) ◽  
pp. 889-896 ◽  
Author(s):  
Svenja Borchers ◽  
Rebekka Verheij ◽  
Jeroen B. J. Smeets ◽  
Marc Himmelbach
Keyword(s):  
Grip Aperture ◽  
Maximum Grip Aperture ◽  
Maximum Grip

The influence of target object shape on maximum grip aperture in human grasping movements

2014 ◽  
Vol 232 (11) ◽  
pp. 3569-3578 ◽  
Author(s):  
Rebekka Verheij ◽  
Eli Brenner ◽  
Jeroen B. J. Smeets
Keyword(s):  
Target Object ◽  
Grip Aperture ◽  
Object Shape ◽  
Maximum Grip Aperture ◽  
Maximum Grip

scholarly journals Some illusions are more inconsistent than others

2019 ◽  
Author(s):  
Jeroen B. J. Smeets ◽  
Eli Brenner
Keyword(s):  
Motion Aftereffect ◽  
Apparent Size ◽  
Ebbinghaus Illusion ◽  
Reach To Grasp ◽  
Grip Aperture ◽  
Maximum Grip Aperture ◽  
Pencil And Paper ◽  
Maximum Grip

Illusions are characterized by inconsistencies. For instance, in the motion aftereffect, we see motion without an equivalent change in position. We used a simple pencil-and-paper experiment to determine whether illusions that influence an object’s apparent size give rise to equivalent changes in apparent positions along the object’s outline. We found different results for two equally strong size illusions. The Ebbinghaus illusion affected perceived positions in a way that was consistent with its influence on perceived size, but a modified diagonal illusion did not affect perceived positions. This difference between the illusions might explain why there are so many conflicting reports about the effects of size illusions on the maximum grip aperture during reach-to-grasp movements.

scholarly journals Occurrence and Recovery of Different Neglect-Related Symptoms in Right Hemisphere Infarct Patients during a 1-Year Follow-Up

2018 ◽  
Vol 24 (6) ◽  
pp. 617-628 ◽  
Author(s):  
Laura Nurmi ◽  
Eija-Inkeri Ruuskanen ◽  
Mari Nurmi ◽  
Anna-Maija Koivisto ◽  
Anna-Kaisa Parkkila ◽  
...  
Keyword(s):  
Acute Phase ◽  
Processing Speed ◽  
Right Hemisphere ◽  
Clinical Work ◽  
First Year ◽  
Healthy Controls ◽  
Visual Neglect ◽  
Attentional Deficit ◽  
Patient Groups

AbstractObjectives: To examine the occurrence of and recovery from visual neglect-related symptoms with the focus on neglect laterality, ipsilateral orienting bias, and slowed processing speed in right hemisphere (RH) infarct patients during a 1-year follow-up. Furthermore, to propose guidelines for assessing processing speed alongside the Behavioural Inattention Test (BIT). Methods: We studied three RH patient groups: neglect (N+), mild left inattention (MLI+), and non-neglect (N−) patients, and healthy controls. The BIT with some additional analyses was conducted at the acute phase and at 6 and 12 months. Results: The N+ group’s BIT score increased and originally lateralized omissions became more evenly distributed during the follow-up. The N+ and MLI+ groups’ starting points were more rightward located than the healthy group’s at the acute phase and at 6, and partly at 12 months. Patient groups were slower than the controls in performing cancellation tests at the acute phase. The N+ and MLI+ groups remained slower than the controls throughout the follow-up. Conclusions: During the first year after RH infarct, originally left-sided manifestation of neglect shifted toward milder non-lateralized attentional deficit. Ipsilateral orienting bias and slowed processing speed appeared to be rather persistent neglect-related symptoms both in neglect patients and patients with initially milder inattention. We propose some effortless, tentative ways of examining processing speed and ipsilateral orienting bias alongside the BIT to better recognize these neglect-related symptoms, and highlight the need to assess and treat patients with initially milder inattention, who have been under-recognized and under-treated in clinical work. (JINS, 2018, 24, 617–628)

scholarly journals The Presence of Visual Neglect after Thrombolytic Treatment in Patients with Right Hemisphere Stroke

2012 ◽  
Vol 2012 ◽  
pp. 1-5 ◽  
Author(s):  
J. E. Kettunen ◽  
M. Nurmi ◽  
A.-M. Koivisto ◽  
P. Dastidar ◽  
M. Jehkonen
Keyword(s):  
Right Hemisphere ◽  
Stroke Severity ◽  
Study Group ◽  
Thrombolytic Treatment ◽  
Visual Neglect ◽  
Stroke Patients ◽  
Neuropsychological Examination ◽  
The Difference ◽  
Right Hemisphere Stroke

Visual neglect (VN) is a common consequence of right hemisphere (RH) stroke. The aims of this study were to explore the presence of VN after RH stroke in the patients with (T+) or without (T−) thrombolytic treatment, and to determine whether thrombolysis is a predictor of VN. The study group consisted of 77 RH infarct patients. VN was evaluated with six conventional subtests of the Behavioural Inattention Test (BIT). Stroke severity was assessed using the National Institute of Health Stroke Scale (NIHSS). In the neuropsychological examination, 22% of all RH stroke patients had VN. VN was present in 15% of the patients in the T+ group and in 28% of the patients in the T− group, but the difference was not statistically significant. Despite that, patients in the T− group had a higher risk of VN than patients in the T+ group. Our results suggest that thrombolysis independently predicted absence of VN.

scholarly journals Grasping Discriminates between Object Sizes Less Not More Accurately than the Perceptual System

Vision ◽  
2019 ◽  
Vol 3 (3) ◽  
pp. 36
Author(s):  
Frederic Göhringer ◽  
Miriam Löhr-Limpens ◽  
Constanze Hesse ◽  
Thomas Schenk
Keyword(s):  
Continuous Variable ◽  
Perceptual System ◽  
Perceptual Task ◽  
Size Discrimination ◽  
Size Information ◽  
Visuomotor Task ◽  
System A ◽  
Dichotomous Variable ◽  
Visual Size ◽  
Maximum Grip

Ganel, Freud, Chajut, and Algom (2012) demonstrated that maximum grip apertures (MGAs) differ significantly when grasping perceptually identical objects. From this finding they concluded that the visual size information used by the motor system is more accurate than the visual size information available to the perceptual system. A direct comparison between the accuracy in the perception and the action system is, however, problematic, given that accuracy in the perceptual task is measured using a dichotomous variable, while accuracy in the visuomotor task is determined using a continuous variable. We addressed this problem by dichotomizing the visuomotor measures. Using this approach, our results show that size discrimination in grasping is in fact inferior to perceptual discrimination therefore contradicting the original suggestion put forward by Ganel and colleagues.

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