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ABSTRACT: 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.
Experimental Brain Research 01/2013; · 2.39 Impact Factor
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ABSTRACT: Motor imagery may use the same mental representations as overt actions, or it may be performed using a nonmotoric cognitive estimation strategy. These competing hypotheses were tested by having participants perform either simple overt pointing tasks or analogous motor imagery tasks while manipulating the visual context and the availability of visual information. In three pairs of experiments, visual illusions, word labels, and numeric labels were all found to have comparable effects on overt pointing and motor imagery. In each case, effects of the contextual variables on overt performance and imagery were larger when vision was removed and a delay imposed before movement initiation. These findings support the hypothesis that a common mental representation is used in both motor imagery and overt actions. In contrast, the results were inconsistent with the view that motor imagery is performed using a cognitive estimation strategy. Limitations in the ability of motor imagery to faithfully simulate overt actions are discussed. (PsycINFO Database Record (c) 2013 APA, all rights reserved).
Journal of Experimental Psychology Human Perception & Performance 01/2013; · 3.06 Impact Factor
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ABSTRACT: In order to assess sequential effects in grasping a disc, grip aperture was measured as a function of whether the previous disc was smaller or larger than the current target. In Experiment 1, a biphasic sequential effect was found over the course of the reach: Early in the movement, a contrast effect was observed in which grip aperture was wider following a smaller target; later in the movement, a perseveration effect was observed in which grip aperture was smaller following a smaller target. In Experiment 2, the target was accompanied by context discs that were larger and smaller than the range of target sizes. In this case, there was no contrast effect, and a perseveration effect was observed over the course of the movement trajectory. In a third experiment, a sequential contrast effect was found when subjects did not grasp the disc but merely estimated its size. Our interpretation is that there are two mechanisms producing sequential effects: a perceptual contrast effect in which the target appears larger following a smaller disc, and a motor perseveration effect in which subjects tend to reuse similar motor control parameters from trial to trial. These effects were overlaid in Experiment 1, producing the observed biphasic response. However, in Experiment 2, the context eliminated sequential perceptual contrast, and grip aperture only showed an effect of perseveration. In Experiment 3, only the perceptual effect was found because subjects did not need to grasp the disc.
Neuropsychologia 02/2009; 47(6):1578-84. · 3.64 Impact Factor
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ABSTRACT: The aim of the present study is to elucidate the influence of context on the kinematics of the reach-to-grasp movement. In particular, we consider two basic modes of social cognition, namely cooperation and competition. In two experiments kinematics of the very same action - reaching-to-grasp a wooden block - were analyzed in two different contexts provided by a cooperative task and competitive task. For the 'cooperation' tasks two participants were required to reach and grasp their respective objects and to cooperate to join the two objects in specific configurations in the middle of the working surface. For the 'competition' tasks, the two participants had to compete to place their own object first in the middle of the working surface. Results revealed specific kinematic patterns for cooperation and competition which were distinct from similar actions performed by each participant in isolation. Further, during the cooperation tasks, a high level of correlation between key kinematical parameters of the two participants was found. In accordance with evidence from neuroimaging, developmental and social psychology our results suggest the existence of motor patterns which reflect the intention to act in a social context.
Cognition 04/2007; 102(3):415-33. · 3.16 Impact Factor
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ABSTRACT: People can adjust their reach-to-grasp movements online to sudden changes in the spatial properties of a target. We investigated whether they can also do this when a non-spatial property, weight, suddenly changes. Guiding your movement by using visual cues about an object's weight depends heavily on experience and is expected to be processed by the (slow) ventral stream rather than the (fast) 'online control' dorsal stream. In the first experiment, participants reached out and lifted an object with an expected or an unexpected weight. As predicted, there was an effect of expected weight on the time between the end of the reaching phase and the object's lift-off. In the second experiment, the object sometimes visibly changed weight after the participants had started their movement. The lifting time did not depend on whether the object had changed weight. Thus, participants can make online adjustments to a visually indicated change in weight. These results are interpreted as being contrary to existing theories of online control.
Experimental Brain Research 10/2006; 173(4):629-36. · 2.39 Impact Factor
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ABSTRACT: Neglect patients often show deficits in responding to targets in the contra-lesional side of space. Past studies were able to ameliorate these deficits through manipulation of visual input. Here, the neural bases of the recovery of space following virtual reality (VR) training in neglect patients were investigated. Neglect patients were trained to respond to targets in the left side of space that appeared in the central or in the right side of space in a VR system. It was found that only patients with lesions that spared the inferior parietal/superior temporal regions were able to benefit from the VR training. It was concluded that these regions play a crucial role in the recovery of space that underlies the improvement of neglect patients when trained with VR. The implications of these results for determining the neural bases of a higher order attentional and/or spatial representation and for treating patients with unilateral neglect are discussed.
Journal of Cognitive Neuroscience 06/2006; 18(5):833-43. · 5.18 Impact Factor
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ABSTRACT: A core feature of autism is the abnormal use of gaze to attribute mental states to others, and thus to predict others' behaviour. An untested idea is whether this dysfunction is confined to mental states having a propositional content, such as beliefs and desire or extends to motor intentional states which allow one to make inferences about the actions of others. This study used kinematics to examine the ability to use gaze to inform one about the motor states of another in normal and autistic children. In each trial two participants, a model and an observer, were seated facing each other at a table. In three experimental blocks the model was requested to grasp a stimulus, to gaze towards the same stimulus, and to gaze away from the stimulus without performing any action. The task for the observer was to grasp the stimulus after having watched the model perform her task. We observed that normal children showed facilitation effects in terms of movement speed following the observation of the model grasping or simply gazing at the object. In contrast, autistic children did not show any evidence of facilitation in these conditions. Neither normal nor autistic children showed evidence of facilitation when the model's gaze was not directed towards the stimulus. These findings demonstrate that, in contrast to normal children, children with autism fail to use information from the model's action or gaze to plan their subsequent action, and that in autism the inability to use of another person's gaze produces a lack of understanding of the motor intention of others.
Neuropsychologia 02/2006; 44(8):1483-8. · 3.64 Impact Factor
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ABSTRACT: Although the effect of visual illusions on overt actions has been an area of keen interest in motor performance, no study has yet examined whether illusions have similar or different effects on overt and imagined movements. Two experiments were conducted that compared the effects of an orientation illusion on an overt posture selection task and an imagined posture selection task. In Experiment 1 subjects were given a choice of grasping a bar with the thumb on the left side or right side of the bar. In Experiment 2 subjects were instructed to only imagine grasping the bar while remaining motionless. Subjects then reported which side of the bar their thumb had been placed in imagined grasping. Both the overt selection and imagined selection tasks were found to be sensitive to the orientation illusion, suggesting that similar visual information is used for overt and imagined movements, with both being sensitive to an orientation illusion. The results are discussed in terms of the visual processing and representation of real and imagined actions.
Experimental Brain Research 10/2005; 166(1):17-22. · 2.39 Impact Factor
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ABSTRACT: The aim of the present study is to investigate interactions between vision and audition during a target acquisition task performed in a virtual environment. We measured the time taken to locate a visual target (acquisition time) signalled by auditory and/or visual cues in conditions of variable visual load. Visual load was increased by introducing a secondary visual task. The auditory cue was constructed using virtual three-dimensional (3D) sound techniques. The visual cue was constructed in the form of a 3D updating arrow. The results suggested that both auditory and visual cues reduced acquisition time as compared to an uncued condition. Whereas the visual cue elicited faster acquisition time than the auditory cue, the combination of the two cues produced the fastest acquisition time. The introduction of secondary visual task differentially affected acquisition time depending on cue modality. In conditions of high visual load, acquiring a target signalled by the auditory cue led to slower and more error-prone performance than acquiring a target signalled by either the visual cue alone or by both the visual and auditory cues.
Applied Ergonomics 06/2005; 36(3):335-43. · 1.43 Impact Factor
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ABSTRACT: Previous studies have implicated the human parietal lobes in the on-line guidance of action. However, no study to date has examined at what stage in the on-line adjustment process do the parietal lobes play their most critical role. Repetitive transcranial magnetic stimulation (rTMS) was applied over the left intraparietal sulcus as participants reached to grasp a small or large illuminated cylinder. On some trials, the illumination could suddenly switch from the small to large cylinder, or vice-versa. Small-Large switches were associated with relatively early grip aperture adjustments, whereas Large-Small switches were associated with relatively late grip aperture adjustments. When rTMS was applied early in the movement, it disrupted on-line adjustments to Small-Large target switches, but not to Large-Small switches. Conversely, when rTMS was applied late in the movement, it disrupted adjustments to Large-Small target switches but not to Small-Large switches. The timing of the disruption by rTMS appeared linked to the initiation of the adjustment. It was concluded that the left parietal lobe plays a critical role in initiating an on-line adjustment to a change in target size, but not in executing that adjustment. The implications of these results for current views of on-line control are discussed.
Journal of Cognitive Neuroscience 02/2005; 17(1):124-36. · 5.18 Impact Factor
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Scott Glover
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ABSTRACT: A recent article by DeLoache et al. has documented an intriguing phenomenon in the development of action planning in young children. When children act on toy replicas of larger objects they make scale errors that are consistent with the full-sized object. Although the actions selected are inappropriate, their execution accurately takes into account the true size of the target. This phenomenon permits tests of the predictions of the perception-action and planning-control models of vision for action.
Trends in Cognitive Sciences 11/2004; 8(10):440-2. · 12.59 Impact Factor
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ABSTRACT: Empirical studies in psychology typically employ null hypothesis significance testing to draw statistical inferences. We propose that likelihood ratios are a more straightforward alternative to this approach. Likelihood ratios provide a measure of the fit of two competing models; the statistic represents a direct comparison of the relative likelihood of the data, given the best fit of the two models. Likelihood ratios offer an intuitive, easily interpretable statistic that allows the researcher great flexibility in framing empirical arguments. In support of this position, we report the results of a survey of empirical articles in psychology, in which the common uses of statistics by empirical psychologists is examined. From the results of this survey, we show that likelihood ratios are able to serve all the important statistical needs of researchers in empirical psychology in a format that is more straightforward and easier to interpret than traditional inferential statistics.
Psychonomic Bulletin & Review 11/2004; 11(5):791-806. · 2.61 Impact Factor
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Scott Glover
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ABSTRACT: Evidence for a dichotomy between the planning of an action and its on-line control in humans is reviewed. This evidence suggests that planning and control each serve a specialized purpose utilizing distinct visual representations. Evidence from behavioral studies suggests that planning is influenced by a large array of visual and cognitive information, whereas control is influenced solely by the spatial characteristics of the target, including such things as its size, shape, orientation, and so forth. Evidence from brain imaging and neuropsychology suggests that planning and control are subserved by separate visual centers in the posterior parietal lobes, each constituting part of a larger network for planning and control. Planning appears to rely on phylogenetically newer regions in the inferior parietal lobe, along with the frontal lobes and basal ganglia, whereas control appears to rely on older regions in the superior parietal lobe, along with the cerebellum.
Behavioral and Brain Sciences 03/2004; 27(1):3-24; discussion 24-78. · 25.06 Impact Factor
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ABSTRACT: Past studies have shown that the effects of visual illusions on upper-limb movements can be modulated by the availability of current or recent visual information. The generality of this finding across body movements was examined by measuring the impact of the Müller-Lyer illusion on two types of lower limb actions. Subjects stood at one end of a Müller-Lyer figure, then either stepped or hopped to the other end. Visual feedback was manipulated through the use of visual closed-loop, open-loop, and open-loop three second delay conditions. For both stepping and hopping, effects of the illusion on movement accuracy were small in the closed-loop, moderate in the open-loop, and large in the three-second open-loop delay condition. These results were similar to those found in studies involving the Müller-Lyer illusion and upper-limb movements. The similar effects across different body movements suggests that a common visuomotor system subserves both upper and lower-limb movements, and that egocentric and allocentric reference frames make similar contributions for the two types of movements.
Experimental Brain Research 03/2004; 154(4):504-12. · 2.39 Impact Factor
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ABSTRACT: Action affordances can be activated by non-target objects in the visual field as well as by word labels attached to target objects. These activations have been manifested in interference effects of distractors and words on actions. We examined whether affordances could be activated implicitly by words representing graspable objects that were either large (e.g., APPLE) or small (e.g., GRAPE) relative to the target. Subjects first read a word and then grasped a wooden block. Interference effects of the words arose in the early portions of the grasping movements. Specifically, early in the movement, reading a word representing a large object led to a larger grip aperture than reading a word representing a small object. This difference diminished as the hand approached the target, suggesting on-line correction of the semantic effect. The semantic effect and its on-line correction are discussed in the context of ecological theories of visual perception, the distinction between movement planning and control, and the proximity of language and motor planning systems in the human brain.
Experimental Brain Research 01/2004; 154(1):103-8. · 2.39 Impact Factor
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Scott Glover
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ABSTRACT: Optic ataxia is characterized by inaccuracies in body movements under visual control, and is a common consequence of damage to the posterior parietal lobes in humans. It is argued here that optic ataxia can be characterized as a deficit in the visual on-line guidance of actions, with action planning remaining relatively intact. This contrasts with the common view of optic ataxia as representing a deficit in the transformations that take place between visual inputs and motor outputs. Evidence in support of the planning-control view comes from the pattern of spared and disrupted behaviors in patients with optic ataxia. It is shown that spared behaviors are those that emphasize planning, whereas disrupted behaviors are those that emphasize control. In particular, recent studies have highlighted the inability of a patient with optic ataxia to make on-line adjustments to targets that change position during the movement. Taken in sum, the data from patients with optic ataxia is more consistent with the planning-control interpretation of optic ataxia than with the visuomotor transformation interpretation.
Neuroscience & Biobehavioral Reviews 09/2003; 27(5):447-56. · 8.65 Impact Factor
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ABSTRACT: 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.
Experimental Brain Research 11/2002; 146(3):383-7. · 2.39 Impact Factor
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Scott Glover
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ABSTRACT: Much debate has arisen over how to account for the pattern of effects of visual illusions on action - that is, the findings that illusions affect actions in some circumstances but not others. I propose that this pattern can best be explained by postulating that visual illusions affect the planning of actions but do not affect the on-line control of actions. Strong evidence for this viewpoint comes from recent studies that show 'dynamic illusion effects': a large illusion effect early in a movement, but a decreasing effect as the hand approaches the target. These findings pose difficulties for other models of illusion effects on action.
Trends in Cognitive Sciences 08/2002; 6(7):288-292. · 12.59 Impact Factor
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ABSTRACT: A distinction between planning and control can be used to explain the effects of context-induced illusions on actions. The present study tested the effects of the Ebbinghaus illusion on the planning and control of the grip aperture in grasping a disk. In two experiments, the illusion had an effect on grip aperture that decreased as the hand approached the target, whether or not visual feedback was available. These results are taken as evidence in favor of a planning/control model, in which planning is susceptible to context-induced illusions, whereas control is not. It is argued that many dissociations between perception and action may better be explained as dissociations between perception and on-line control.
Perception & Psychophysics 03/2002; 64(2):266-78. · 1.37 Impact Factor
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