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The experiment reported examined: (a) the role of the geometrical body scaled informational invariant for the transition of human grip configurations; (b) whether the same invariant can be scaled considering also the force applied during the grasp phase; and (c) how the temporal duration of the grasp and displacement phases of prehension are scaled to the object properties of size and mass. Adult subjects performed a series of trials in reaching, grasping, and displacing spheres that varied in size and mass. The grip transitions were described by the body scaled relation: [formula: see text] where L(s) and M(s) are, respectively, the diameter and the mass of the spheres grasped and L(h) and M(h) are the length and the mass of the hand. The impulse during the grasp phase was linearly related with the mass of the spheres within each density. The temporal durations of the grasp and displacement components were scaled coherently to the object properties. These findings provide support to the hypothesis that the grasp and displacement components of prehension are organized coherently within a single action. [ABSTRACT FROM AUTHOR]

In the tradition of Dharmakīrti (ca. 600-660), perception is, by definition, free from conceptual construction. Insofar as perception is thus, it lacks the nature of determining its object. Without identifying its object, how does perception lead one to a successful action? Perception in isolation would not be pramāṇa unless it is supplemented by perceptual judgement. This paper looks at how Dharamkīrti and his commentators offer solutions to the contradiction between perception's foundational role and its seeming dependence on conceptual construction. The key point in their proposed solutions is the argument that perception is understood in accordance with two distinct perspectives of the moment (kṣaṇa) and the continuum (santāna). Perception from the perspective of the moment has the activities of 'grasping' (grahaṇa) and 'ascertaining' (niścaya). The 'grasping' induces perceptual awareness to be possessed of the image (ākāra) of an object-moment; the 'ascertaining' identifies its object in the form of "this is something." Perception from the perspective of the continuum, on the other hand, consists of a series of the first moment of sense perception and its subsequent moments of mental perception. It is a continuous process allowing one to attain or avoid a thing that s/he sees. The fulfilment of a purpose is achieved not through a perception-moment but through a perception-continuum. It is worthy stressing, however, that in a very strict sense, the perception-moment alone is ultimately real. Perception from the perspective of the moment is purely epistemological while perception from the perspective of the continuum is pragmatic. [ABSTRACT FROM AUTHOR]

I will try to show that the process of making an aesthetic experience can be conceived as a process of understanding via re-enactment in which we structure the phenomenal qualities of perceptions (e.g. of a melody) at a fundamental level by means of the phenomenal qualities of other perceptions (e.g. of a gesture); and this in such a way that we grasp the object of this understanding as a unity. Thereby, it turns out that understanding is not restricted to conceptually grasping meanings, actions, or relations of cause and effect. Moreover, re-enactment shows itself as a form of understanding, which enables us to become aware of aspects of our subjective experience, to make others understand these aspects, and to articulate them conceptually. Philosophy of mind must therefore face the task of elucidating the relationship between phenomenal and intentional aspects of our mind in a more productive way than in the form of a mere disjunction. [ABSTRACT FROM AUTHOR]

Do illusory distortions of perceived object size influence how wide the hand is opened during a grasping movement? Many studies on this question have reported illusion-resistant grasping, but this finding has been contradicted by other studies showing that grasping movements and perceptual judgments are equally susceptible. One largely unexplored explanation for these contradictions is that illusion effects on grasping can be reduced with repeated movements. Using a visuomotor adaptation paradigm, we investigated whether an adaptation model could predict the time course of Ponzo illusion effects on grasping. Participants performed a series of trials in which they viewed a thin wooden target, manually reported an estimate of the target’s length, then reached to grasp the target. Manual size estimates (MSEs) were clearly biased by the illusion, but maximum grip apertures (MGAs) of grasping movements were consistently accurate. Illusion-resistant MGAs were observed immediately upon presentation of the illusion, so there was no decrement in susceptibility for the adaptation model to explain. To determine whether online corrections based on visual feedback could have produced illusion-resistant MGAs, we performed an exploratory post hoc analysis of movement trajectories. Early portions of the illusion effect profile evolved as if they were biased by the illusion to the same magnitude as the perceptual responses (MSEs), but this bias was attenuated prior to the MGA. Overall, this preregistered study demonstrated that visuomotor adaptation of grasping is not the primary source of illusion resistance in closed-loop grasping. [ABSTRACT FROM AUTHOR]

Linkenauger, Witt, and Proffitt ( Journal of Experimental Psychology: Human Perception and Performance, 37(5), 1432-1441, 2011, Experiment 2) reported that right-handers estimated objects as smaller if they intended to grasp them in their right rather than their left hand. Based on the action-specific account, they argued that this scaling effect occurred because participants believed their right hand could grasp larger objects. However, Collier and Lawson ( Journal of Experimental Psychology: Human Perception and Performance, 43(4), 749-769, 2017) failed to replicate this effect. Here, we investigated whether this discrepancy in results arose from demand characteristics. We investigated two forms of demand characteristics: altering responses following conscious hypothesis guessing (Experiments 1 and 2), and subtle influences of the experimental context (Experiment 3). We found no scaling effects when participants were given instructions which implied the expected outcome of the experiment (Experiment 1), but they were obtained when we used unrealistically explicit instructions which gave the exact prediction made by the action-specific account (Experiment 2). Scaling effects were also found using a context in which grasping capacity could seem relevant for size estimation (by asking participants about the perceived graspability of an object immediately before asking about its size on every trial, as was done in Linkenauger et al., 2011; Experiment 2). These results suggest that demand characteristics due to context effects could explain the scaling effects reported in Experiment 2 of Linkenauger et al. (2011), rather than either hypothesis guessing, or, as proposed by the action-specific account, a change in the perceived size of objects. [ABSTRACT FROM AUTHOR]

We examined how action goals influence the distribution of visuospatial attention near the body (Experiment 1) and how the temporal relationship between distractors and targets modifies shifts in visuospatial attention (Experiment 2). Targets were light emitting diodes (LEDs) in the left and right hemispace of a visual display. Following left or right target illumination, participants reached to point-to or grasp target object in blocked trials. Coincident with target onset, a distractor LED illuminated in the same or opposite hemispace between the initiation point and target, or no distractor appeared. In Experiment 1, during grasping there was a larger temporal interference effect (slower reach initiation) than with pointing. When grasping versus pointing, participants deviated more towards same-side distractors and away from opposite-side distractors. In Experiment 2, distractors onset 200ms prior to (−200-ms), coincident with (0 ms), or 200ms following (+200 ms) the target. For both reach types, −200-ms distractors had greater onset temporal interference than 0 ms and +200-ms distractors. For grasping, +200 ms distractors had larger temporal interference than 0 ms distractors. For −200-ms, reach trajectories deviated more towards opposite-side distractors and away from same-side distractors, the reverse of the pattern for 0 ms and +200-ms distractors. [ABSTRACT FROM PUBLISHER]

Pantomime-grasps entail a response to an area adjacent to (i.e., spatially dissociated pantomime-grasp), or previously occupied by (i.e., no-target pantomime-grasp) a target. Previous work has reported that pantomime-grasps differ kinematically from naturalistic grasps (i.e., grasping a physical target object) - a result taken to evince that pantomime-grasps are perception-based and mediated via relative visual information. However, such actions differ not only in terms of their visual properties, but also because the former precludes haptic feedback related to a target's absolute size. The current study provides four experiments examining whether experimenter-induced haptic feedback influences the information mediating spatially dissociated and no-target pantomime-grasps. Just-noticeable-difference scores were computed to determine whether grasps adhered to, or violated, the relative psychophysical properties of Weber's law. Spatially dissociated pantomime-grasps performed with haptic feedback adhered to Weber's law (Experiments 1-3), whereas their no-target pantomime-grasp counterparts violated the law (Experiment 4). Accordingly, we propose that the top-down demands of decoupling stimulus-response relations in spatially dissociated pantomime-grasping renders aperture shaping via a visual percept that is not directly influenced by the integration of haptic feedback. In turn, the decreased top-down demands of no-target pantomime-grasps allows haptic feedback to serve as a reliable sensory resource supporting an absolute visuo-haptic calibration. [ABSTRACT FROM AUTHOR]

Experimental evidence is given that the perceptual system adapts to repetitive task execution in a perceptual two-choice judgment task. Participants were tested with respect to their perception of opportunities for plank grasping. Participants had to report whether planks were perceived as objects being graspable with either one hand or two hands. When the plank size was gradually increased and subsequently decreased, transitions from one hand judgments to two hands judgments and vice versa were observed. Analysis of the transition scores revealed that the perceptual judgments were body-scaled, as it is known in the literature. However, judgments were also found to be context dependent. Judgment transition scores were affected in a systematic way by the kind of and the number of previously made judgments. The latter quantitative impact was observed in three related experiments and suggests that perceptual judgments about opportunities for action adapt to task repetition. Overall, the experimental findings are consistent with the predictions of a dynamical systems model, which assumes that perceptual judgments are emergent properties of a self-organizing process that involves inhibitory top-down feedback. [ABSTRACT FROM AUTHOR]

Background/objective: Some of the behavioral disorders associated with Parkinson’s disease (PD), such as the reduced magnitude of actions (hypometria) may be related to an impairment in cognitive disengagement. A reduced ability to disengage attention from previous sensory stimuli will alter perception with a reduced range of estimated stimulus magnitudes (contraction to the mean). To test this disengagement hypothesis, participants with PD were tested to learn whether they had abnormal sensory perception with overestimation of the relative magnitude of weaker tactile stimuli and underestimation of the relative magnitude of stronger tactile stimuli in relation to a reference stimulus.Design/method: The participants were 12 people with PD and 12 healthy adults. Test stimuli were applied to the palm using Semmes–Weinstein monofilaments (SWM) of 6 magnitudes, 3 greater and 3 less than a standard stimulus. In each trial, after being stimulated with the reference (standard) stimulus, a test monofilament was applied, and the participant was asked to provide a numerical estimate of the magnitude of the second stimulus relative to the standard.Results: Compared to the control group, participants with PD overestimated the magnitudes of the tactile stimuli below the standard stimulus and underestimated the magnitudes of stimuli above the standard stimulus.Conclusions: These results demonstrate that people with PD likely have a reduced ability to estimate the relative magnitudes of tactile sensory stimuli. Whereas deafferentation would alter perception in one direction, the impairment of these participants with PD may result from a disorder of disengagement, and disorders of disengagement are often due to frontal-executive dysfunction. [ABSTRACT FROM PUBLISHER]

It has been shown that memorized information can influence real-time visuomotor control. For instance, a previously seen object (prime) influences grasping movements toward a target object. In this study, we examined how general the priming effect is: does it depend on the orientation of the target object and the similarity between the prime and the target? To do so, we examined whether priming effects occured for different orientations of the prime and the target objects and for primes that were either identical to the target object or only half of the target object. We found that for orientations of the target object that did not require an awkward grasp, the orientation of the prime could influence the initiation time and the final grip orientation. The priming effects on initiation time were only found when the whole target object was presented as prime, but not when only half of the target object was presented. The results suggest that a memory effect on real-time control is constrained by end-state comfort and by the relevance of the prime for the grasping movement, which might mean that the interactions between the ventral and dorsal pathways are task specific. [ABSTRACT FROM AUTHOR]

The Perception-Action Model (PAM) claims to provide a coherent interpretation of data from all areas of the visual neurosciences, most notably data from neuropsychological patients and from behavioral experiments in healthy people. Here, we tested two claims that are part of the core version of the PAM: (a) certain actions (natural, highly practiced, and right-handed) are controlled by the dorsal vision for action pathway, while other actions (awkward, unpracticed, or left-handed) are controlled by the ventral vision for perception pathway. (b) Only the dorsal pathway operates in an analytical fashion, being able to selectively focus on the task-relevant dimension of an object (Ganel and Goodale, Nature 426(6967):664-667, ). We show that one of these claims must be wrong: using the same test for analytical processing as Ganel and Goodale (), we found that even an action that should clearly be ventral (left-handed awkward grasping) shows analytical processing just as a dorsal task does (right-handed natural precision grasping). These results are at odds with the PAM and point to an inconsistency of the model. [ABSTRACT FROM AUTHOR]

The somatosensory processing model (SPM) asserts that dissociable cortical processing streams mediate tactile perceptions and actions via relative and absolute cues, respectively ( Dijkerman and de Haan, 2007 ). Accordingly, we sought to determine whether the introduction of a memory delay and/or physically touching a target object (i.e., haptic feedback) differentially influences the cues supporting tactile perceptions and actions. Participants used their right hand to manually estimate (i.e., perceptual task) or grasp (i.e., action task) differently sized objects placed on the palm of their left limb in conditions wherein the target object was available for the duration of the response (i.e., closed-loop condition), or was removed prior to response cuing (i.e., memory-guided condition). As well, trials were performed in conditions wherein the physical object was available (i.e., haptic feedback) or unavailable (i.e., no haptic feedback) to touch. Notably, we computed just-noticeable-difference (JND) scores to determine whether the aforementioned tasks and conditions adhered to – or violated - the relative properties of Weber's law. JNDs for manual estimations adhered to Weber's law across each condition – a finding supporting the SPM's contention that an immutable and relative percept supports tactile perceptions. In turn, JNDs for grasping violated Weber's law only when haptic feedback was available. Such a finding indicates that haptic feedback supports the absolute calibration between a tactile defined object and the required motor output. What is more, our study highlights that multiple somatosensory cues (i.e., tactile and haptic) support goal-directed grasping. [ABSTRACT FROM AUTHOR]

Preparation for an action, such as grasping an object, is accompanied by an enhanced perception of the object's action-relevant features, such as orientation and size. Cortical feedback from motor planning areas to early visual areas may drive this enhanced perception. To examine whether action preparation modulates activity in early human visual cortex, subjects grasped or pointed to oriented objects while high-resolution fMRI data were acquired. Using multivoxel pattern analysis techniques, we could decode with >70% accuracy whether a grasping or pointing action was prepared from signals in visual cortex as early asV1.Thesesignals in early visual cortex were observed even when actions were only prepared but not executed. Anterior parietal cortex, on the other hand, showed clearest modulation for actual movements. This demonstrates that preparation of actions, even without execution, modulates relevant neuronal populations in early visual areas. [ABSTRACT FROM AUTHOR]

From a very young age, infants perceive others’ actions as goal directed. Yet, the processes underlying this competence are still debated. In this study, we investigated whether (a) 4- and 6-month-old infants and adults discriminate the biomechanical properties of the human hand within an action context, (b) the manipulation of the biomechanics of hand movements has an impact on the ability to anticipate the goal of an action, and (c) the emergence of motor experience with grasping is related to infants’ ability to discriminate the biomechanics of hand movements and to anticipate the action goal. The 6-month-olds discriminated between biomechanically possible and impossible grasps, and in some (but not all) instances they made more anticipatory gaze shifts toward the goal of the possible action. Both the 4- and 6-month-olds’ processing of biomechanical properties of the hand were significantly related to their ability to anticipate the goal of a grasping action. Importantly, those 4-month-olds with higher precision grasping skills manifested faster anticipatory gazes toward the goal of the action. These findings suggest that multiple sources of information from an action scene are interdependent and that both perceptual information and motor experience with an action are relevant for on-line prediction of the final goal of the action. [ABSTRACT FROM AUTHOR]

The grounded cognition framework proposes that sensorimotor brain areas, which are typically involved in perception and action, also play a role in linguistic processing. We assessed oscillatory modulation during visual presentation of single verbs and localized cortical motor regions by means of isometric contraction of hand and foot muscles. Analogously to oscillatory activation patterns accompanying voluntary movements, we expected a somatotopically distributed suppression of beta and alpha frequencies in the motor cortex during processing of body-related action verbs. Magnetoencephalographic data were collected during presentation of verbs that express actions performed using the hands (H) or feet (F). Verbs denoting no bodily movement (N) were used as a control. Between 150 and 500 msec after visual word onset, beta rhythms were suppressed in H and F in comparison with N in the left hemisphere. Similarly, alpha oscillations showed left-lateralized power suppression in the H-N contrast, although at a later stage. The cortical oscillatory activity that typically occurs during voluntary movements is therefore found to somatotopically accompany the processing of body-related verbs. The combination of a localizer task with the oscillatory investigation applied to verb reading as in the present study provides further methodological possibilities of tracking language processing in the brain. [ABSTRACT FROM AUTHOR]

Binocular rivalry is a visual phenomenon in which perception alternates between two different monocular images presented to each of the two eyes. Here, we propose using this phenomenon as a method to study the relation between action execution and action perception. In our experiment, a simple background (a checkerboard) was contrasted with a video representing a hand continuously grasping and releasing a ball. In Experiment 1, our subjects were asked to reproduce the perceived movement with their right hand whenever they became aware of it and to stop doing this when the checkerboard dominated. Our results revealed that motor imitation of the perceived action significantly increased the time spent perceiving the hand. Three control experiments showed that these effects were not due to a generic involvement of focused attention (Experiment 2 and 3), to a verbal description of the performed action (Experiment 3) or to the execution of an unrelated movement of the hand (Experiment 4). Although an intrinsic connection between action execution and attention cannot be excluded with certainty, and the boundary between action imitation and unrelated action execution may vary along various degrees of similarity, on the whole, the present results seem to suggest, at least on a preliminary basis, that action imitation do play a relevant role in the perception of action. We discuss these findings in the frame of current theories concerning the relation between perception and action. [ABSTRACT FROM AUTHOR]

Spatial features of an object can be specified using two different response types: either by use of symbols or motorically by directly acting upon the object. Is this response dichotomy reflected in a dual representation of the visual world: one for perception and one for action? Previously, symbolic and motoric responses, specifying location, has been shown to rely on a common representation. What about more elaborate features such as length and orientation? Here we show that when motoric and symbolic responses are made within the same trial, the probability of making the same symbolic and motoric response is well above chance for both length and orientation. This suggests that motoric and symbolic responses to length and orientation are driven by a common representation. We also show that, for both response types, the spatial features of an object are processed independently. This finding of matching object-processing characteristics is also in agreement with the idea of a common representation driving both response types. [ABSTRACT FROM AUTHOR]

The perception of objects does not rely only on visual brain areas, but also involves cortical motor regions. In particular, different parietal and premotor areas host neurons discharging during both object observation and grasping. Most of these cells often show similar visual and motor selectivity for a specific object (or set of objects), suggesting that they might play a crucial role in representing the ?potential motor act? afforded by the object. The existence of such a mechanism for the visuomotor transformation of object physical properties in the most appropriate motor plan for interacting with them has been convincingly demonstrated in humans as well. Interestingly, human studies have shown that visually presented objects can automatically trigger the representation of an action provided that they are located within the observer?s reaching space (peripersonal space). The ?affordance effect? also occurs when the presented object is outside the observer?s peripersonal space, but inside the peripersonal space of an observed agent. These findings recently received direct support by single neuron studies in monkey, indicating that space-constrained processing of objects in the ventral premotor cortex might be relevant to represent objects as potential targets for one?s own or others' action. [ABSTRACT FROM AUTHOR]

A goal of research on human perception and performance is to explore the relative importance of constraints shaping action selection. The present study concerned the relative importance of two constraints that have not been directly contrasted: ( 1 ) the tendency to grasp objects in ways that afford comfortable or easy-to-control final postures; and (2) the tendency to grasp objects with the dominant rather than the nondominant hand. We asked participants to reach out and grasp a horizontal rod whose left or right end was to be placed into a target after a 90° rotation. In one condition, we told participants which hand to use and let them choose an overhand or underhand initial grasp. In another condition, we told participants which grasp to use and let them choose either hand. Participants sacrificed hand preference to perform the task in a way that ensured a comfortable or easy to control thumb-up posture at the time of object placement, indicating that comfort trumped handedness. A second experiment confirmed that comfort was indeed higher for thumb-down postures than thumb-up postures. A third experiment confirmed that the choice data could be linked to objective performance differences. The results point to the importance of identifying constraint weightings for action selection and support an account of hand selection that ascribes hand preference to sensitivity to performance differences. The results do not support the hypothesis that hand preference simply reflects a bias to use the dominant hand. [ABSTRACT FROM AUTHOR]

Previous studies have shown that viewing others in pain activates cortical somatosensory processing areas and facilitates the detection of tactile targets. It has been suggested that such shared representations have evolved to enable us to better understand the actions and intentions of others. If this is the case, the effects of observing others in pain should be obtained from a range of viewing perspectives. Therefore, the current study examined the behavioral effects of observed grasps of painful and nonpainful objects from both a first- and third-person perspective. In the first-person perspective, a participant was faster to detect a tactile target delivered to their own hand when viewing painful grasping actions, compared with all nonpainful actions. However, this effect was not revealed in the third-person perspective. The combination of action and object information to predict the painful consequences of another person's actions when viewed from the first-person perspective, but not the third-person perspective, argues against a mechanism ostensibly evolved to understand the actions of others. [ABSTRACT FROM AUTHOR]

Anticipatory force planning during grasping is based on visual cues about the object’s physical properties and sensorimotor memories of previous actions with grasped objects. Vision can be used to estimate object mass based on the object size to identify and recall sensorimotor memories of previously manipulated objects. It is not known whether subjects can use density cues to identify the object’s center of mass (CM) and create compensatory moments in an anticipatory fashion during initial object lifts to prevent tilt. We asked subjects (n = 8) to estimate CM location of visually symmetric objects of uniform densities (plastic or brass, symmetric CM) and non-uniform densities (mixture of plastic and brass, asymmetric CM). We then asked whether subjects can use density cues to scale fingertip forces when lifting the visually symmetric objects of uniform and non-uniform densities. Subjects were able to accurately estimate an object’s center of mass based on visual density cues. When the mass distribution was uniform, subjects could scale their fingertip forces in an anticipatory fashion based on the estimation. However, despite their ability to explicitly estimate CM location when object density was non-uniform, subjects were unable to scale their fingertip forces to create a compensatory moment and prevent tilt on initial lifts. Hefting object parts in the hand before the experiment did not affect this ability. This suggests a dichotomy between the ability to accurately identify the object’s CM location for objects with non-uniform density cues and the ability to utilize this information to correctly scale their fingertip forces. These results are discussed in the context of possible neural mechanisms underlying sensorimotor integration linking visual cues and anticipatory control of grasping. [ABSTRACT FROM AUTHOR]

One commonly perceives whether a visible object will afford grasping with one hand or with both hands. In experiments in which differently sized objects of a fixed type are presented, the transition from using one of these manual modes to the other depends on the ratio of object size to hand span and on the presentation sequence, with size increasing versus decreasing. Conventional positive hysteresis (i.e., a larger transition ratio for the increasing sequence) can be accommodated by the order parameter dynamics that typify self-organizing systems (Lopresti-Goodman, Turvey, and Frank, Attention, Perception, & Psychophysics 73:1948-1965, ). Here we identified and addressed conditions of unconventional negative hysteresis (i.e., a larger transition ratio for the decreasing sequence). They suggest a second control parameter in the self-organization of affordance perception, one that is seemingly regulated by inhibitory dynamics occurring in the agent-task-environment system. Our experimental results and modeling extend the investigation of affordance perception within dynamical systems theory. [ABSTRACT FROM AUTHOR]

Perseveration effects in grasping were examined in two experiments. In both experiments, participants reached and grasped different versions of a novel object with their thumb and forefinger using either a horizontal or vertical pincer grasp. The dependent variable was the choice of grasp. In Experiment 1, trials were performed either with or without visual feedback. In Experiment 2, trials were performed either physically or using motor imagery. In both experiments, participants tended to perseverate in their choice of grip. Further, there was no evidence that either the availability of visual feedback during the preceding or current action modulated this effect; mode of responding was similarly inconsequential. The results were interpreted as evidence for a motor priming explanation of perseveration and against an account that relies on perceptual priming. [ABSTRACT FROM AUTHOR]

The Dual Visuomotor Channel theory proposes that skilled reaching is composed of a Reach that directs the hand in relation to the extrinsic properties of an object (e.g., location) and a Grasp that opens and closes the hand in relation to the intrinsic properties of an object (e.g., size). While Reach and Grasp movements are often guided by vision, they can also be performed without vision when reaching for a body part or an object on one's own body. Memory of a recently touched but unseen object can also be used to guide Reach and Grasp movements although the touch-response memory durations described are extremely brief (Karl et al. in Exp Brain Res 219:59-74, ). The purpose of the present study was to determine whether repeated nonvisual reaching for a consistent object could calibrate Reach and Grasp movements in a way similar to those guided by vision. The nonvision group wore vision-occluding goggles and reached for fifty consecutive trials for a round donut ball placed on a pedestal. The control group performed the same task with vision. Frame-by-frame video analysis and linear kinematics revealed that nonvision participants consistently used an elevated Reach trajectory, in which the hand, rather than being directed toward the target in the horizontal plane, was first elevated above the target before being lowered to touch and locate it. First contact was established with the dorsal surface of the target, and thus, adjustments in contact locations were often required for purchase. Although nonvision participants initially used an open and extended hand during transport, with practice they began to scale digit aperture to object size with an accuracy and temporal relation similar to vision participants. The different ways in which the Reach and Grasp movements respond to nonvisual learning are discussed in relation to support for the dual channel theory of reaching and to the idea that the Reach and Grasp channels may be differentially dependent on online visual guidance. [ABSTRACT FROM AUTHOR]

Abstract: Two experiments, one on school-aged children and one on adults, explored the mechanisms underlying responses to an image prime (hand vs. control object) followed by graspable objects that were, in certain cases, dangerous. Participants were presented with different primes (a male, a female and a robotic grasping-hand; a male and a female static-hand; a control stimulus) and objects representing two risk levels (neutral and dangerous). The task required that a natural/artifact categorization task be performed by pressing different keys. In both adults and children graspable objects activated a facilitating motor response, while dangerous objects evoked aversive affordances, generating an interference-effect. Both children and adults were sensitive to the distinction between biological and non-biological hands, however detailed resonant mechanisms related to the hand-prime gender emerged only in adults. Implications for how the concept of “dangerous object” develops and the relationship between resonant mechanisms and perception of danger are discussed. [Copyright &y& Elsevier]

Abstract: Studies claiming a differential processing of visual illusions for perception and action have been subjected to many challenges. One criticism is that attentional demands were mismatched between the perception and action tasks. Dewar and Carey (2006) reexamined this argument by comparing bimanual grasping to bimanual size estimation and concluded that manual size estimation (ManEst) was affected by the illusion to a greater extent than grasping, supporting the case for two functionally distinct streams of visual processing. We tested whether this result may be due to their use of closed loop visual conditions by replicating their study under both closed and open loop conditions. We found that the difference in illusion effects between grasping and ManEst disappeared under open loop conditions, indicating that Dewar and Carey''s findings can be explained by the availability of visual feedback and not a perception/action dissociation. We also discuss potential shortcomings of bimanual designs. [Copyright &y& Elsevier]

Goodale et al. (1991) reported a striking dissociation between vision for perception and action. They examined DF, a human patient who had damage to her ventral visual stream and suffered from visual form agnosia. She was unable to perceive an object's size but could match the opening of her hand to the object's size during grasping. It was concluded that grasping relied on a separate representation of visual size in the dorsal stream and required no visual input from the ventral stream. This observation inspired the influential perception- action model, which claimed separate visual streams for perception and action. However, in grasping (but not in corresponding perceptual tasks), participants receive haptic feedback after each trial. Using this feedback, DF might compensate for her impaired size-vision. I reexamined DF's grasping behavior using a mirror apparatus to dissociate the image of an object from its physical presence. DF's grasping was only normal when she received haptic feedback. Thus, in grasping, DF can rely on haptic feedback to compensate for her deficit in size-perception. This can explain why her grasping is significantly better than her perceptual performance. The findings emphasize the extent of early interstream interactions and highlight the multimodal nature of sensory processing in the dorsal stream. [ABSTRACT FROM AUTHOR]

Abstract: The ‘just noticeable difference’ (JND) represents the minimum amount by which a stimulus must change to produce a noticeable variation in one’s perceptual experience and is related to initial stimulus magnitude (i.e., Weber’s law). The goal of the present study was to determine whether aperture shaping for visually derived and memory-guided grasping elicit a temporally dependent or temporally independent adherence to Weber’s law. Participants were instructed to grasp differently sized objects (20, 30, 40, 50 and 60mm) in conditions wherein vision of the grasping environment was available throughout the response (i.e., closed-loop), when occluded at movement onset (i.e., open-loop), and when occluded for a brief (i.e., 0ms) or longer (i.e., 2000ms) delay in advance of movement onset. Within-participant standard deviations of grip aperture (i.e., the JNDs) computed at decile increments of normalized grasping time were used to determine participant’s sensitivity to detecting changes in object size. Results showed that JNDs increased linearly with increasing object size from 10% to 40% of grasping time; that is, the trial-to-trial stability (i.e., visuomotor certainty) of grip aperture (i.e., the comparator) decreased with increasing object size (i.e., the initial stimulus). However, a null JND/object size scaling was observed during the middle and late stages of the response (i.e., >50% of grasping time). Most notably, the temporal relationship between JNDs and object size scaling was similar across the different visual conditions used here. Thus, our results provide evidence that aperture shaping elicits a time-dependent early, but not late, adherence to the psychophysical principles of Weber’s law. [Copyright &y& Elsevier]

Some experimental evidence suggests that grasping should be regarded as independent control of the thumb and the index finger (digit control hypothesis). To investigate this further, we compared how the tips of the thumb and the index finger moved in space when grasping spheres to how they moved when they were hitting the sphere using only one digit. In order to make the tasks comparable, we designed the experiment in such a way that subjects contacted the spheres in about the same way in the hitting task as when grasping it. According to the digit control hypothesis, the two tasks should yield similar digit trajectories in space. People hit and grasped stationary and moving spheres. We compared the similarity of the digits' trajectories across the two tasks by evaluating the time courses of the paths of the average of the thumb and the index finger. These paths were more similar across tasks than across sphere motion, supporting the notion that grasping is not controlled fundamentally differently than hitting. [ABSTRACT FROM AUTHOR]

On a daily basis, one perceives whether an object affords grasping with one hand or with both hands. In experiments in which differently sized objects of a fixed type have been presented, the transition from using one manual mode to the other has depended on both the ratio of object size to hand span and the presentation sequence-that is, size increasing versus decreasing. The transitions and their observed hysteresis (i.e., a transition ratio larger for the increasing sequence) can be accommodated by the order parameter dynamics typifying self-organizing systems. Here, we show that hysteresis magnitude depends on (a) the interaction between the attractors (one hand vs. two hands) and (b) the strength of the two-hands attractor. Through modeling and experimental results, we extend the investigation of affordance perception within dynamical-systems theory. [ABSTRACT FROM AUTHOR]

Abstract: Patients with optic ataxia, a deficit in visually guided action, paradoxically improve when pantomiming an action towards memorized stimuli. Visual form agnosic patient D.F. shows the exact opposite pattern of results: although being able to grasp objects in real-time she loses grip scaling when grasping an object from memory. Here we explored the dissociation between immediate and delayed grasping in a patient (F.S.) who after a parietal-occipital stroke presented with severe left visual neglect, a loss of awareness of the contralesional side of space. Although F.S. had preserved grip scaling even in his neglected field, he was markedly impaired when asked to pretend to grasp a leftward object from memory. Critically, his deficit cannot be simply explained by the absence of continuous on-line visual feedback, as F.S. was also able to grasp leftward objects in real-time when vision was removed. We suggest that regions surrounding the parietal-occipital sulcus, typically damaged in patients with optic ataxia but spared in F.S., seem to be essential for real-time actions. On the other hand, our data indicates that regions in the ventral visual stream, damaged in D.F but intact in F.S., would appear to be necessary but not sufficient for memory-guided action. [Copyright &y& Elsevier]

Abstract: The Grasping Affordance Model (GAM) introduced here provides a computational account of perceptual processes enabling one to identify grasping action possibilities from visual scenes. GAM identifies the core of affordance perception with visuo-motor transformations enabling one to associate features of visually presented objects to a collection of hand grasping configurations. This account is coherent with neuroscientific models of relevant visuo-motor functions and their localization in the monkey brain. GAM differs from other computational models of biological grasping affordances in the way of modeling focus, functional account, and tested abilities. Notably, by learning to associate object features to hand shapes, GAM generalizes its grasp identification abilities to a variety of previously unseen objects. Even though GAM information processing does not involve semantic memory access and full-fledged object recognition, perceptions of (grasping) affordances are mediated there by substantive computational mechanisms which include learning of object parts, selective analysis of visual scenes, and guessing from experience. [Copyright &y& Elsevier]

Abstract: An exemplar metric of goal-directed grasping (i.e., peak grip aperture) has been shown to be refractory to a psychophysical principle governing visuoperceptual estimations of object size (i.e., Weber''s law). This dissociation suggests that vision for action and vision for perception are mediated by absolute and relative visual information, respectively. The present investigation examined whether aperture shaping elicits a unitary or process-dependent violation of Weber''s law. Participants grasped differently sized objects (20, 30, 40, 50 and 60mm of width) and just noticeable difference (JND) scores related to grip aperture were computed at the time of peak grip aperture as well as at normalized deciles of the response (i.e., 10–90% of grasping time). JNDs during the early and middle stages of the trajectory scaled to object size whereas values late in the trajectory (>50% of grasping time and including the time of peak grip aperture) did not. Thus, results show an early, but not late, adherence to Weber''s law and indicate that movement planning and movement control are supported via relative and absolute visual information, respectively. [Copyright &y& Elsevier]

In the present study two separate stimulus-response compatibility effects (functional affordance and Simon-like effects) were investigated with centrally presented pictures of an object tool (a torch) characterized by a structural separation between the graspable portion and the goal-directed portion. In Experiment 1, participants were required to decide whether the torch was red or blue, while in Experiment 2 they were required to decide whether the torch was upright or inverted. Our results showed that with the same stimulus two types of compatibility effect emerged: one based on the direction signalled by the goal-directed portion of the tool (a Simon-like effect as observed in Experiment 1), and the other based on the actions associated with an object (a functional affordance effect as observed in Experiment 2). Both effects emerged independently of the person's intention to act on the stimulus, but depended on the stimulus properties that were processed in order to perform the task. [ABSTRACT FROM AUTHOR]

Abstract: The new concept of embodied cognition theories has been enthusiastically studied by the cognitive sciences, by as well as such disparate disciplines as philosophy, anthropology, neuroscience, and robotics. Embodiment theory provides the framework for ongoing discussions on the linkage between “low” cognitive processes as perception and “high” cognition as language processing and comprehension, respectively. This review gives an overview along the lines of argumentation in the ongoing debate on the embodiment of language and employs an ALE meta-analysis to illustrate and weigh previous findings.The collected evidence on the somatotopic activation of motor areas, abstract and concrete word processing, as well as from reported patient and timing studies emphasizes the important role of sensorimotor areas in language processing and supports the hypothesis that the motor system is activated during language comprehension. [ABSTRACT FROM AUTHOR]

Abstract: Both in the catching and grasping component of prehension, the hand opens and closes before hand–object contact is made. The initiation of hand closure has to be coordinated with the time course of the decrease of the distance between the hand and the target object, i.e., with the reaching component in prehension or the approach of the target in catching. The authors investigated if this initiation of hand closure could be explained by a common control. For this purpose, they fitted the dynamic timing model to data from the two tasks. In both tasks, participants were asked to get hold of an object approaching along the table top at a constant velocity. In the prehension task, participants could reach out to grasp the object; in the catching task, they were required to keep their hand stationary. In comparison with other accounts, the dynamic timing model performed best in explaining the data. The model proved adequate for the prehension task but not for the current catching task. [Copyright &y& Elsevier]

Abstract: Research on self-agency emphasizes the importance of a comparing mechanism, which scans for a match between anticipated and actual outcomes, in the subjective experience of doing. This study explored the “feeling of doing” in individuals with checking symptoms by examining the mechanism involved in the experienced agency for outcomes that matched expectations. This mechanism was explored using a task in which the subliminal priming of potential action-effects (emulating outcome anticipation) generally enhances people’s feeling of causing these effects when they occur, due to the unconscious perception of a match between primed and observed outcomes. The main result revealed a negative relationship between checking and self-agency for observed outcomes that were primed prior to actions. This suggests that checking individuals fail to grasp the correspondence between actual outcomes of their actions and expected ones. We discuss the possible role of undermined self-agency in checking phenomena and its relationship with cognitive dysfunction. [Copyright &y& Elsevier]

Abstract: It is well established that during the preparation and execution of goal-directed movements, perceptual processing is biased towards the goal. Most of the previous work on the relation between action and attention has focused on rather simple movements, such as single saccades or manual reaches towards a single target. Here we review recent behavioural and neurophysiological studies on manual actions that require to consider more than a single spatial location in the planning of the response, such as movement sequences, grasping, and movements around obstacles. The studies provide compelling evidence that the preparation of these actions establishes multiple foci of attention which reflect the spatial–temporal requirements of the future action. The findings help clarify how perceptual processing is bound by action preparation and also offer new perspectives for motor control research. [Copyright &y& Elsevier]

In 4 experiments, we investigated the effects of object affordance in reach-to-grasp actions. Participants indicated whether a depicted small or large object was natural or manmade by means of different object-grasping responses (i.e., with a power or a precision grip). We observed that the size of the depicted object affected the grasping kinematics (grip aperture) and the reach-onset times of compatible and incompatible actions. Additional experiments showed that the effect of perceived object size on motor response was modulated by contextual action information and the observation of others' actions with the object. Thus, beyond the observation of object affordance effects in natural grasping actions, this study suggests that the coupling between object perception and action is not static and obligatory. Behavioral effects of action-relevant object features seem rather to depend on contextual action information. [ABSTRACT FROM AUTHOR]

Abstract: Memory for objects helps us to determine how we can most effectively and appropriately interact with them. This suggests a tightly coupled interplay between action and background knowledge. Three experiments demonstrate that grasping circumference can be affected by the size of a visual stimulus (Experiment 1), whether that stimulus appears to be graspable (Experiment 2), and the presence of a label that renders that object ungraspable (Experiment 3). The results are taken to inform theories on conceptual representation and the functional distinction that has been drawn between the visual systems for perception and action. [Copyright &y& Elsevier]

We investigated the development of the Ebbinghaus illusion in children’s perception and grasping. A previous study (Hanisch et al. ) had reported negative illusion effects on 5- to 12-year-olds’ grasping as compared to their perception. We attempted to replicate this finding and to test different hypotheses based on a direct influence of the context elements on the trajectories of the fingers which could explain this reversal of the illusion effects. For 5- to 7- and 9- to 11-year-olds we observed the classical illusion effects in perception. Illusion effects were perfectly similar for perception and grasping in 9- to 11-year-olds, while there was a non-significant trend toward smaller illusion effects in grasping for the 5- to 7-year-olds. This could be due to a slightly different effect of the illusion on younger children’s grasping. However, it seems clear that there are no qualitative changes, as a reversal of the illusion effects in grasping of younger children. Finally, we show that our grasping data conform well to the motor literature for children’s grasping, thereby strengthening our conclusions. [ABSTRACT FROM AUTHOR]

Three experiments assessed the influence of the Ebbinghaus illusion on size judgments that preceded verbal, grasp, or touch responses. Prior studies have found reduced effects of the illusion for the grip-scaling component of grasping, and these findings are commonly interpreted as evidence that different visual systems are employed for perceptual judgment and visually guided action. In the current experiments, the magnitude of the illusion was reduced by comparable amounts for grasping and for judgments that preceded grasping ( Experiment 1 ). A similar effect was obtained prior to reaching to touch the targets ( Experiment 2 ). The effect on verbal responses was apparent even when participants were simply instructed that a target touch task would follow the verbal task. After participants had completed a grasping task, the reduction in the magnitude of the illusion remained for a subsequent verbal-response judgment task ( Experiment 3 ). Overall, the studies demonstrate strong connections between action planning and perception. [ABSTRACT FROM AUTHOR]

A decade ago, S. Aglioti, J. F. X. DeSouza, and M. A. Goodale (1995) published an experiment that has had a big influence on the way that visual information is thought to control human behavior. Their findings have often been simplified as suggesting that action is immune to perceptual illusions. The current authors critically analyze the 4 steps involved in this simplification and argue that research during the last 10 years has shown that the validity of 3 of the 4 steps is doubtful. They conclude that this experiment cannot be regarded as firm support for the 2-visual-systems hypothesis (i.e., that the ventral stream is for perception and the dorsal stream is for visually guided actions). [ABSTRACT FROM AUTHOR]

It is now well established that the visual brain is divided into two visual streams, the ventral and the dorsal stream. Milner and Goodale have suggested that the ventral stream is dedicated for processing vision for perception and the dorsal stream vision for action [A.D. Milner & M.A. Goodale (1995) The Visual Brain in Action, Oxford University Press, Oxford]. However, it is possible that ongoing processes in the visuomotor stream will nevertheless have an effect on perceptual processes. This possibility was examined in the present study. We have examined the visual form-discrimination performance of the form-agnosic patient D.F. with and without a concurrent visuomotor task, and found that her performance was significantly improved in the former condition. This suggests that the visuomotor behaviour provides cues that enhance her ability to recognize the form of the target object. In control experiments we have ruled out proprioceptive and efferent cues, and therefore propose that D.F. can, to a significant degree, access the object's visuomotor representation in the dorsal stream. Moreover, we show that the grasping-induced perceptual improvement disappears if the target objects only differ with respect to their shape but not their width. This suggests that shape information per se is not used for this grasping task. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The semantic meaning of a word label printed on an object can have significant effects on the kinematics of reaching and grasping movements directed towards that object. Here, we examined how the semantics of word labels might differentially affect the planning and control stages of grasping. Subjects were presented with objects on which were printed either the word "LARGE" or "SMALL." When the grip aperture in the two conditions was compared, an effect of the words was found early in the reach, but this effect declined continuously as the hand approached the target. This continuously decreasing effect is consistent with a planning/control model of action, in which cognitive and perceptual variables affect how actions are planned but not how they are monitored and controlled on-line. The functional and neurological bases of semantic effects on planning and control are discussed. [ABSTRACT FROM AUTHOR]

Recent work has shown that pictorial illusions have a greater effect on perceptual judgements than they do on the visual control of actions, such as object-directed grasping. This dissociation between vision for perception and vision for action is thought to reflect the operation of two separate streams of visual processing in the brain. Glover and Dixon claim, however, that perceptual illusions can influence the control of grasping but that these effects are evident only at early stages of the movement. By the time the action nears its completion any effect of illusions disappears. Glover and Dixon suggest that these results are consistent with what they call a 'planning and control' model of action, in which actions are planned using a context-dependent visual representation but are monitored and corrected online using a context-independent representation. We reanalysed data from an earlier experiment on grasping in the Ebbinghaus illusion in which we showed that maximum grip aperture was unaffected by this size-contrast illusion. When we looked at these data more closely, we found no evidence for an effect of the illusion even at the earliest stages of the movement. These findings support the suggestion that the initial planning of a simple object-directed grasping movement in this illusory context is indeed refractory to the effects of the illusion. This is not to suggest that more deliberate and/or complex movements could not be influenced by contextual information. [ABSTRACT FROM AUTHOR]

An experimental procedure that evaluates the quality of a grasp is developed. In this procedure human subjects grasp a rigid object that is subjected to an external load. Three formulations that capture the sense of grasping quality through the energy level stored in the gripper, maximum value of the applied finger forces, and through the distribution of the grasping forces are considered. The applied finger forces are measured and the quality values of the grasp based on these three different formulations are computed. These grasping quality values are compared with numerical human assessments, that are obtained via a psychophysical magnitude estimation method. We derive an augmented weighted functional that combines these three formulations, and show that it exhibits a high correlation with human quality assessment. Our results demonstrate that the most dominant mechanism that characterizes the quality of a rigid body grasp is the uniformity level of the contact forces. [ABSTRACT FROM AUTHOR]