The influence of visual feedback from the recent past on the programming of grip aperture is grasp-specific, shared between hands, and mediated by sensorimotor memory not task set

Revisiting the effect of visual illusions on grasping in left and right handers

Visual illusions have provided compelling evidence for a dissociation between perception and action. For example, when two different-sized objects are placed on opposite ends of the Ponzo illusion, people erroneously perceive the physically smaller object to be bigger than the physically larger one, but when they pick up the objects, their grip aperture reflects the real difference in size between the objects. This and similar findings have been demonstrated almost entirely for the right hand in right handers. The scarce research that has examined right and left-handed subjects in this context, has typically used only small samples. Here, we extended this research with a larger sample size (more than 50 in each group) in a version of the Ponzo illusion that allowed us to disentangle the effects of real and illusory size on action and perception in much more powerful way. We also collected a wide range of kinematic measures to assess possible differences in visuomotor control in left and right handers. The results showed that the dissociation between perception and action persisted for both hands in right handers, but only for the right hand in left handers. The left hand of left handers was sensitive to the illusion. Left handers also showed more variable and slower movements, as well as larger safety margins in both hands. These findings suggest that grasping in left handers may require more cognitive supervision, which could lead to greater sensitivity to visual context , particularly with their dominant left hand.

Sleep Deprivation Influences Trial-to-Trial Transfer but Not Task Performance

Previous research has shown that sleep deprivation can affect emotions and some cognitive functions. However, research on how sleep deprivation influences the visuomotor memory have rarely been reported. In the current study, a Fitts’ Law task was used to investigate how movement and the visuomotor memory are affected under the condition of sleep deprivation. Experiment 1 had 36 participants (15 males, mean age = 21.61 years) complete the same Fitts’ Law task 10 days apart under standard conditions. Experiment 2 had five participants (three males, mean age = 27.2 years) complete the task after 7 days of sleep deprivation, then complete it again after 10 days without sleep deprivation. Experiment 1 demonstrated the stability of the trial-to-trial effects. Experiment 2 showed that the previous trial (n) exerted no effect on the current trial (n + 1) under the conditions of sleep deprivation (p = 0.672). However, the effect was observed after 10 days without sleep deprivation (p = 0.013). This suggests that sleep deprivation did not affect task performance but influenced the transfer of the trial history. Future studies are required to investigate the effect of sleep deprivation with more participants.

The Influence of Induced Emotions on Distance and Size Perception and on the Grip Scaling During Grasping

Previous studies have shown that our perception of stimulus properties can be affected by the emotional nature of the stimulus. It is not clear, however, how emotions affect visually-guided actions toward objects. To address this question, we used toy rats, toy squirrels, and wooden blocks to induce negative, positive, and neutral emotions, respectively. Participants were asked to report the perceived distance and the perceived size of a target object resting on top of one of the three emotion-inducing objects; or to grasp the same target object either without visual feedback (open-loop) or with visual feedback (closed-loop) of both the target object and their grasping hand during the execution of grasping. We found that the target object was perceived closer and larger, but was grasped with a smaller grip aperture in the rat condition than in the squirrel and the wooden-block conditions when no visual feedback was available. With visual feedback present, this difference in grip aperture disappeared. These results showed that negative emotion influences both perceived size and grip aperture, but in opposite directions (larger perceived size but smaller grip aperture) and its influence on grip aperture could be corrected by visual feedback, which revealed different effects of emotion to perception and action. Our results have implications on the understanding of the relationship between perception and action in emotional condition, which showed the novel difference from previous theories.

Integration of haptics and vision in human multisensory grasping

Grasping actions are directed not only toward objects we see but also toward objects we both see and touch (multisensory grasping). In this latter case, the integration of visual and haptic inputs improves movement performance compared to each sense alone. This performance advantage could be due to the integration of all the redundant positional and size cues or to the integration of only a subset of these cues. Here we selectively provided specific cues to tease apart how these different sensory sources contribute to visuo-haptic multisensory grasping. We demonstrate that the availability of the haptic positional cue together with the visual cues is sufficient to achieve the same grasping performance as when all cues are available. These findings provide strong evidence that the human sensorimotor system relies on non-visual sensory inputs and open new perspectives on their role in supporting vision during both development and adulthood.

Dexterity and technique in termite fishing by chimpanzees (Pan troglodytes troglodytes) in the Goualougo Triangle, Republic of Congo

Although the phenomenon of termite fishing by chimpanzees (Pan troglodytes) has historical and theoretical importance for primatology, we still have a limited understanding of how chimpanzees accomplish this activity, and in particular, about details of skilled actions and the nature of individual variation in fishing techniques. We examined movements, hand positions, grips, and other details from remote video footage of seven adult and subadult female chimpanzees using plant probes to extract Macrotermes muelleri termites from epigeal nests. Six chimpanzees used exclusively one hand (left or right) to grip the probe during termite fishing. All chimpanzees used the same repertoire of actions to insert, adjust, and withdraw the probe but differed in the frequency of use of particular actions. Chimpanzees have been described as eating termites in two ways—directly from the probe or by sweeping them from the probe with one hand. We describe a third technique: sliding the probe between the digits of one stationary hand as the probe is extracted from the nest. The sliding technique requires complementary bimanual coordination (extracting with one hand and grasping lightly with the other, at the same time). We highlight the importance of actions with two hands—one gripping, one assisting—in termite fishing and discuss how probing techniques are correlated with performance. Additional research on digital function and on environmental, organismic, and task constraints will further reveal manual dexterity in termite fishing.

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Using remote video footage from camera traps in Goualougo Triangle, Republic of Congo, we describe chimpanzees' manual actions, postures, and positions, and movements of the probe while they fished for termites in epigeal termite nests.

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Chimpanzees used diverse grips, with and without the thumb, and two hands—one gripping, one assisting—to handle the probe delicately and to move it precisely.

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We describe a new technique for recovering termites: sliding the probe between the digits of one stationary hand as the probe is extracted from the nest with the other hand, and a new action: oscillatory movements of the probe while it was inserted in the nest.

Grip Constancy but Not Perceptual Size Constancy Survives Lesions of Early Visual Cortex

Object constancies are central constructs in theories of visual phenomenology. A powerful example is "size constancy," in which the perceived size of an object remains stable despite changes in viewing distance [1-4]. Evidence from neuropsychology [5], neuroimaging [6-11], transcranial magnetic stimulation [12, 13], single-unit and lesion studies in monkey [14-20], and computational modeling [21] suggests that re-entrant processes involving reciprocal interactions between primary visual cortex (V1) and extrastriate visual areas [22-26] play an essential role in mediating size constancy. It is seldom appreciated, however, that object constancies must also operate for the visual guidance of goal-directed action. For example, when reaching out to pick up an object, the hand's in-flight aperture scales with size of the goal object [27-30] and is refractory to the decrease in retinal-image size with increased viewing distance [31-41] (Figure 1), a phenomenon we call "grip constancy." Does grip constancy, like perceptual constancy, depend on V1 or can it be mediated by pathways that bypass it altogether? We tested these possibilities in an individual, M.C., who has bilateral lesions encompassing V1 and much of the ventral visual stream. We show that her perceptual estimates of object size co-vary with retinal-image size rather than real-world size as viewing distance varies. In contrast, M.C. shows near-normal scaling of in-flight grasp aperture to object size despite changes in viewing distance. Thus, although early visual cortex is necessary for perceptual object constancy, it is unnecessary for grip constancy, which is mediated instead by separate visual inputs to dorsal-stream visuomotor areas [42-48].

Impaired Motor Recycling during Action Selection in Parkinson's Disease

Behavioral studies have shown that the human motor system recycles motor parameters of previous actions, such as movement amplitude, when programming new actions. Shifting motor plans toward a new action forms a particularly severe problem for patients with Parkinson’s disease (PD), a disorder that, in its early stage, is dominated by basal ganglia dysfunction. Here, we test whether this action selection deficit in Parkinson’s patients arises from an impaired ability to recycle motor parameters shared across subsequent actions. Parkinson’s patients off dopaminergic medication (n = 16) and matched healthy controls (n = 16) performed a task that involved moving a handheld dowel over an obstacle in the context of a sequence of aiming movements. Consistent with previous research, healthy participants continued making unnecessarily large hand movements after clearing the obstacle (defined as “hand path priming effect”), even after switching movements between hands. In contrast, Parkinson’s patients showed a reduced hand path priming effect, i.e., they performed biomechanically more efficient movements than controls, but only when switching movements between hands. This effect correlated with disease severity, such that patients with more severe motor symptoms had a smaller hand path priming effect. We propose that the basal ganglia mediate recycling of movement parameters across subsequent actions.

Why some size illusions affect grip aperture

There is extensive literature debating whether perceived size is used to guide grasping. A possible reason for not using judged size is that using judged positions might lead to more precise movements. As this argument does not hold for small objects and all studies showing an effect of the Ebbinghaus illusion on grasping used small objects, we hypothesized that size information is used for small objects but not for large ones. Using a modified diagonal illusion, we obtained an effect of about 10% on perceptual judgements, without an effect on grasping, irrespective of object size. We therefore reject our precision hypothesis. We discuss the results in the framework of grasping as moving digits to positions on an object. We conclude that the reported disagreement on the effect of illusions is because the Ebbinghaus illusion not only affects size, but—unlike most size illusions—also affects perceived positions.

How long is the interval over which trial-to-trial effects on Fitts' Law task can operate?

Fitts' Law is a well-studied principle in psychology which holds that movement time (MT) varies with the size and distance of a target across a wide range of tasks. In a recent study, the authors demonstrated that performance on a current trial in a Fitts' Law paradigm is affected by what happens during the previous trial (Tang et al. in Psychon Bull Rev 25(5):1833-1839, 2018). The aim of the present study was to explore how long this trial-to-trial transfer might last and whether or not the transfer would occur between the left and right hands. A series of experiments was carried out using discrete trials, a paradigm in which the current authors and others have previously established that Fitts' Law operates (Fitts and Peterson in J Exp Psychol 67(2):103-112, 1964; Tang et al. 2018). Three inter-trial intervals (3 s, 4 s, and 5 s) were used in separate testing sessions, the order of which was counterbalanced across participants. In addition, trial-to-trial transfer was tested within a single hand and between hands. The results demonstrate that transfer from one trial to the next could bridge 4 s when either the right or the left hand was used and would disappear by 5 s. Moreover, the effect transferred between the two hands. The endpoint accuracy of the current trial was not affected by the previous trial. These findings suggest that the trial-to-trial effect reduces over time and that the transfer of sensorimotor memory or the task set is independent of the particular hand used.

Older Adolescents and Young Adults With Autism Spectrum Disorder Have Difficulty Chaining Motor Acts When Performing Prehension Movements Compared to Typically Developing Peers

It is known that motor actions performed by individuals with autism spectrum disorders (ASD) are clumsy and a previous study revealed that children with ASD of around 8 years old showed less smooth movement and dysfunction of appropriate usage of online vision for grip aperture control. The present study investigates whether and how the kinematic properties of reach-to-grasp movements in older adolescents and adults with ASD [mean (±SD) age: 18.3 ± 2.1] differ from those in typically developing (TD) peers [mean (±SD) age: 19.1 ± 2.2]. Revealing the kinematic properties of reach-to-grasp movements in older adolescents and adults with ASD is indispensable in determining the developmental trajectory of this motor behavior in individuals with ASD. While wearing liquid crystal shutter goggles, participants reached for and grasped a cylinder with a diameter of either 4 or 6 cm. Two visual conditions were tested: a full vision (FV) condition (the goggles remained transparent during the movement) and a no vision (NV) condition (the goggles were closed immediately after the movement was initiated). These two visual conditions were either alternated with each trial in a single experimental session (alternated condition) or blocked within the session (blocked condition). We found that the reaching movement smoothness calculated as a normalized jerk score (i.e., index of skilled, coordinated human movements) of ASD participants did not differ significantly from that of TD peers although ASD participants showed smoother reaching in the alternated condition than in the blocked condition. The influence of online vision and its visual condition schedule on grip aperture during the in-flight phase was remarkably similar between the ASD and TD groups. Furthermore, we found that ASD group experienced a significant longer transition period from grasping end (i.e., stable holding when touching the surface of the object) to uplift initiation than the TD group. The results suggest that (1) deficits in movement smoothness and the use of online vision for motor control are rectified by the time individuals with ASD reach late adolescence and (2) older adolescents and adults with ASD still have difficulties chaining motor acts.

The endless visuomotor calibration of reach-to-grasp actions

It is reasonable to assume that when we grasp an object we carry out the movement based only on the currently available sensory information. Unfortunately, our senses are often prone to err. Here, we show that the visuomotor system exploits the mismatch between the predicted and sensory outcomes of the immediately preceding action (sensory prediction error) to attain a degree of robustness against the fallibility of our perceptual processes. Participants performed reach-to-grasp movements toward objects presented at eye level at various distances. Grip aperture was affected by the object distance, even though both visual feedback of the hand and haptic feedback were provided. Crucially, grip aperture as well as the trajectory of the hand were systematically influenced also by the immediately preceding action. These results are well predicted by a model that modifies an internal state of the visuomotor system by adjusting the visuomotor mapping based on the sensory prediction errors. In sum, the visuomotor system appears to be in a constant fine-tuning process which makes the generation and control of grasping movements more resistant to interferences caused by our perceptual errors.

The left hand disrupts subsequent right hand grasping when their actions overlap

Adaptive motor control is premised on the principle of movement minimization, which in turn is premised on a form of sensorimotor memory. But what is the nature of this memory and under what conditions does it operate? Here, we test the limits of sensorimotor memory in an intermanual context by testing the effect that the action performed by the left hand has on subsequent right hand grasps. Target feature-overlap predicts that sensorimotor memory is engaged when task-relevant sensory features of the target are similar across actions; partial effector-overlap predicts that sensorimotor memory is engaged when there is similarity in the task-relevant effectors used to perform an action; and the action-goal conjunction hypotheses predicts that sensorimotor memories are engaged when the action goal and the action type overlap. In three experiments, participants used their left hand to reach out and pick up an object, manually estimate its size, pinch it, look at it, or merely rest the left hand before reaching out to pick up a second object with their right hand. The in-flight anticipatory grip aperture of right-hand grasps was only influenced when it was preceded by grasps performed by the left-hand. Overlap in the sizes of the objects, partial overlap in the effectors used, and in the availability of haptic feedback bore no influence on this metric. These results support the hypothesis that intermanual transfer of sensorimotor memory on grasp execution is dependent on a conjunction of action type and goal.

Fitts' Law is modulated by movement history

Fitts' Law is one of the most robust and well-studied principles in psychology. It holds that movement time (MT) for target-directed aiming movements increases as a function of target distance and decreases as a function of target width. The purpose of this study was to determine whether Fitts' Law is affected not only by the demands of the target on the current trial but also by the requirements for performance on the previous trial. Experiments 1 and 2 examined trial-to-trial effects of varying target width; Experiment 3 examined trial-to-trial effects of varying target distance. The findings from Experiments 1 and 2 showed that moving a finger or cursor towards a large object on a previous trial shortened the movement time on the current trial, whereas the opposite occurred with a small object. In contrast, target distance on the previous trial had no effect on movement time on the current trial. These findings suggest that performance on trial n has a clear and predictable effect on trial n+1 (at least for target width) and that Fitts' Law as it is normally expressed does not accurately predict performance when the width of the target varies from trial to trial.

Dynamic modulation of illusory and physical target size on separate and coordinated eye and hand movements

In everyday behavior, two of the most common visually guided actions-eye and hand movements-can be performed independently, but are often synergistically coupled. In this study, we examine whether the same visual representation is used for different stages of saccades and pointing, namely movement preparation and execution, and whether this usage is consistent between independent and naturalistic coordinated eye and hand movements. To address these questions, we used the Ponzo illusion to dissociate the perceived and physical sizes of visual targets and measured the effects on movement preparation and execution for independent and coordinated saccades and pointing. During independent movements, we demonstrated that both physically and perceptually larger targets produced faster preparation for both effectors. Furthermore, participants who showed a greater influence of the illusion on saccade preparation also showed a greater influence on pointing preparation, suggesting that a shared mechanism involved in preparation across effectors is influenced by illusions. However, only physical but not perceptual target sizes influenced saccade and pointing execution. When pointing was coordinated with saccades, we observed different dynamics: pointing no longer showed modulation from illusory size, while saccades showed illusion modulation for both preparation and execution. Interestingly, in independent and coordinated movements, the illusion modulated saccade preparation more than pointing preparation, with this effect more pronounced during coordination. These results suggest a shared mechanism, dominated by the eyes, may underlie visually guided action preparation across effectors. Furthermore, the influence of illusions on action may operate within such a mechanism, leading to dynamic interactions between action modalities based on task demands.

Programming of left hand exploits task set but that of right hand depends on recent history

There are many differences between the left hand and the right hand. But it is not clear if there is a difference in programming between left hand and right hand when the hands perform the same movement. In current study, we carried out two experiments to investigate whether the programming of two hands was equivalent or they exploited different strategies. In the first experiment, participants were required to use one hand to grasp an object with visual feedback or to point to the center of one object without visual feedback on alternate trials, or to grasp an object without visual feedback and to point the center of one object with visual feedback on alternating trials. They then performed the tasks with the other hand. The result was that previous pointing task affected current grasping when it was performed by the left hand, but not the right hand. In experiment 2, we studied if the programming of the left (or right) hand would be affected by the pointing task performed on the previous trial not only by the same hand, but also by the right (or left) hand. Participants pointed and grasped the objects alternately with two hands. The result was similar with Experiment 1, i.e., left-hand grasping was affected by right-hand pointing, whereas right-hand grasping was immune from the interference from left hand. Taken together, the results suggest that when open- and closed-loop trials are interleaved, motor programming of grasping with the right hand was affected by the nature of the online feedback on the previous trial only if it was a grasping trial, suggesting that the trial-to-trial transfer depends on sensorimotor memory and not on task set. In contrast, motor programming of grasping with the left hand can use information about the nature of the online feedback on the previous trial to specify the parameters of the movement, even when the type of movement that occurred was quite different (i.e., pointing) and was performed with the right hand. This suggests that trial-to-trial transfer with the left hand depends on some sort of carry-over of task set for dealing with the availability of visual feedback.

Online repetitive transcranial magnetic stimulation (TMS) to the parietal operculum disrupts haptic memory for grasping

The parietal operculum (OP) contains haptic memory on the geometry of objects that is readily transferrable to the motor cortex but a causal role of OP in memory-guided grasping is only speculative. We explored this issue by using online high-frequency repetitive transcranial magnetic stimulation (rTMS). The experimental task was performed by blindfolded participants acting on objects of variable size. Trials consisted in three phases: haptic exploration of an object, delay, and reach-grasp movement onto the explored object. Motor performance was evaluated by the kinematics of finger aperture. Online rTMS was applied to the left OP region separately in each of the three phases of the task. The results showed that rTMS altered grip aperture only when applied in the delay phase to the OP. In a second experiment a haptic discriminative (match-to-sample) task was carried out on objects similar to those used in the first experiment. Online rTMS was applied to the left OP. No psychophysical effects were induced by rTMS on the detection of explicit haptic object size. We conclude that neural activity in the OP region is necessary for proficient memory-guided haptic grasping. The function of OP seems to be critical while maintaining the haptic memory trace and less so while encoding it or retrieving it.