Practice makes perfect, but only with the right hand: Sensitivity to perceptual illusions with awkward grasps decreases with practice in the right but not the left hand
ABSTRACT It has been proposed that the visual mechanisms that control well-calibrated actions, such as picking up a small object with a precision grip, are neurally distinct from those that mediate our perception of the object. Thus, grip aperture in such situations has been shown to be remarkably insensitive to many size-contrast illusions. But most of us have practiced such movements hundreds, if not thousands of times. What about less familiar and unpracticed movements? Perhaps they would be less likely to be controlled by specialized visuomotor mechanisms and would therefore be more sensitive to size-contrast illusions. To test this idea, we asked right-handed subjects to pick up small objects using either a normal precision grasp (thumb and index finger) or an awkward grasp (thumb and ring finger), in the context of the Ponzo illusion. Even though this size-contrast illusion had no effect on the scaling of the precision grasp, it did have a significant effect on the scaling of the awkward grasp. Nevertheless, after three consecutive days of practice, even the awkward grasp became resistant to the illusion. In a follow-up experiment, we found that awkward grasps with the left hand (in right handers) did not benefit from practice and remained sensitive to the illusion. We conclude that the skilled target-directed movements are controlled by visual mechanisms that are quite distinct from those controlling unskilled movements, and that these specialized visuomotor mechanisms may be lateralized to the left hemisphere.
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ABSTRACT: I argue that the neural realizers of experiences of trying (that is, experiences of directing effort towards the satisfaction of an intention) are not distinct from the neural realizers of actual trying (that is, actual effort directed towards the satisfaction of an intention). I then ask how experiences of trying might relate to the perceptual experiences one has while acting. First, I assess recent zombie action arguments regarding conscious visual experience, and I argue that contrary to what some have claimed, conscious visual experience plays a causal role for action control in some circumstances. Second, I propose a multimodal account of the experience of acting. According to this account, the experience of acting is (at the very least) a temporally extended, co-conscious collection of agentive and perceptual experiences, functionally integrated and structured both by multimodal perceptual processing as well as by what an agent is, at the time, trying to do.Nous 01/2015; DOI:10.1111/nous.12086
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ABSTRACT: When we grasp an object using one hand, the opposite hemisphere predominantly guides the motor control of grasp movements (Davare et al. 2007; Rice et al. 2007). However, it is unclear whether visual object analysis for grasp control relies more on inputs (a) from the contralateral than the ipsilateral visual field, (b) from one dominant visual field regardless of the grasping hand, or (c) from both visual fields equally. For bimanual grasping of a single object we have recently demonstrated a visual field preference for the left visual field (Le and Niemeier 2013a, 2013b), consistent with a general right-hemisphere dominance for sensorimotor control of bimanual grasps (Le et al., 2013). But visual field differences have never been tested for unimanual grasping. Therefore, here we asked right-handed participants to fixate to the left or right of an object and then grasp the object either with their right or left hand using a precision grip. We found that participants grasping with their right hand performed better with objects in the right visual field: maximum grip apertures (MGAs) were more closely matched to the object width and were smaller than for objects in the left visual field. In contrast, when people grasped with their left hand, preferences switched to the left visual field. What is more, MGA scaling showed greater visual field differences compared to right-hand grasping. Our data suggest that, visual object analysis for unimanual grasping shows a preference for visual information from the ipsilateral visual field, and that the left hemisphere is better equipped to control grasps in both visual fields.Frontiers in Human Neuroscience 10/2014; 8. DOI:10.3389/fnhum.2014.00782 · 2.90 Impact Factor
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ABSTRACT: Twenty-two experienced action video-game players (AVGPs) and 18 non-VGPs were tested on a pen-and-paper line bisection task that was untimed. Typically, right-handers bisect lines 2 % to the left of true centre, a bias thought to reflect the dominance of the right-hemisphere for visuospatial attention. Expertise may affect this bias, with expert musicians showing no bias in line bisection performance. Our results show that experienced-AVGPs also bisect lines with no bias with their right hand and a significantly reduced bias with their left hand compared to non-AVGPs. Bisections by experienced-AVGPs were also more precise than those of non-AVGPs. These findings show the cognitive proficiencies of experienced-AVGPs can generalize beyond computer based tasks, which resemble their training environment.Attention Perception & Psychophysics 10/2014; DOI:10.3758/s13414-014-0789-x · 2.15 Impact Factor