Grasping the past

Abstract

"Optic ataxia" is caused by damage to the human posterior parietal cortex (PPC). It disrupts all components of a visually guided prehension movement, not only the transport of the hand toward an object's location, but also the in-flight finger movements pretailored to the metric properties of the object. Like previous cases, our patient (I.G.) was quite unable to open her handgrip appropriately when directly reaching out to pick up objects of different sizes. When first tested, she failed to do this even when she had previewed the target object 5 s earlier. Yet despite this deficit in "real" grasping, we found, counterintuitively, that I.G. showed good grip scaling when "pantomiming" a grasp for an object seen earlier but no longer present. We then found that, after practice, I.G. became able to scale her handgrip when grasping a real target object that she had previewed earlier. By interposing catch trials in which a different object was covertly substituted for the original object during the delay between preview and grasp, we found that I.G. was now using memorized visual information to calibrate her real grasping movements. These results provide new evidence that "off-line" visuomotor guidance can be provided by networks independent of the PPC.

Right-hemispheric dominance for visual remapping in humans

“…Note that the use of alternative spatial representations, operating on longer time scales, has been demonstrated for simple actions in patients with OA. Indeed, OA is a deficit of immediate and automatic visuo-motor guidance, and motor performance of these patients paradoxically improves with a memorization delay ( [64,65]; reviews in [62,66]). …”

Two action systems in the human brain

“…The cardinal deficit associated with lesions in the dorso-dorsal stream is optic ataxia (OA), as characterized by misreaching to visual targets that is most flagrant in the peripheral visual field (Balint, 1909; Garcin et al, 1967; Ratcliff, 1990). Indeed, deficits in on-line motor control demonstrated for reaching (Buxbaum & Coslett, 1997; Buxbaum & Coslett, 1998; Grea et al, 2002; Milner et al, 2001; Pisella et al, 2000; Rossetti, Goldenberg, & Rode, 2005; Rossetti, Revol et al, 2005) and more recently for grasping (Tunik, Frey, & Grafton, 2005) in patients with OA highlights the specificity of the superior parietal region and the parieto-occipital junction for direct goal-directed visuo-motor transformations involving short-lived processes (Milner & Goodale, 1995; but see Kroliczak, McAdam, Quinlan, & Culham, 2007). The usual lesion causing OA includes the superior parietal lobule (SPL), the intraparietal sulcus (IPS) and the parieto-occipital sulcus (POS) (Karnath & Perenin, 2005; Perenin & Vighetto, 1988).…”

Human electrophysiological reflections of the recruitment of perceptual processing during actions that engage memory

“…Converging neuropsychological, neuroimaging, and kinematic findings support this theory. For example, visual-form agnosia patient D.F., who has bilateral damage to her lateral occipital cortex (LOC) in the ventral stream, is perceptually compromised (James, Culham, Humphrey, Milner, & Goodale, 2003) but can guide her actions appropriately when the target object is in full view, presumably due to her intact dorsal stream (Milner et al, 2001;. These authors argue that D.F.…”