Adaptive Coordination and Alignment of Eye and Hand

Abstract

Under spatial misalignment of eye and hand induced by laterally displacing prisms (11.4 degrees in the rightward direction), subjects pointed 60 times (once every 3 s) at a visually implicit target (straight ahead of nose, Experiment 1) or a visually explicit target (an objectively straight-ahead target, Experiment 2). For different groups in each experiment, the hand became visible early in the sagittal pointing movement (early visual feedback). Adaptation to the optical misalignment during exposure (direct effects) was rapid, especially with early feedback; complete compensation for the misalignment was achieved within about 30 trials, and overcompensation occurred in later trials, especially with an explicit target. In contrast, adaptation measured with the misalignment removed and without visual feedback after blocks of 10 pointing trials (aftereffects) was slow to develop, especially with delayed feedback and an implicit target; at most, about 40% compensation for the misalignment occurred after 60 trials. This difference between direct effects and aftereffects is discussed in terms of separable adaptive mechanisms that are activated by different error signals. Adaptive coordination is activated by error feedback and involves centrally located, strategically flexible, short-latency processes to correct for sudden changes in operational precision that normally occur with short-term changes in coordination tasks. Adaptive alignment is activated automatically by spatial discordance between misaligned systems and involves distributed, long-latency processes to correct for slowly developing shifts in alignment among perceptual-motor components that normally occur with long-term drift. The sudden onset of misalignment in experimental situations activates both mechanisms in a complex and not always cooperative manner, which may produce overcompensatory behavior during exposure (i.e., direct effects) and which may limit long-term alignment (i.e., aftereffects).

Prism adaptation in left-handers

“…These realignment aftereffect results replicate many previous studies of right- handers (e.g., Redding & Wallace, 1993, 2000Uhlarik & Canon, 1971); aftereffects of prismatic displacement are localized in the proprioceptive hand-head system when visual feedback is available early in the exposure pointing movements. Importantly, adaptation was not affected by the manipulation of order of testing.…”

“…Therefore, left-handers showed the same kind of exposure adaptation that right-handers do under the same conditions: rapid target achievement, but developing overcompensation when exposure is continued beyond target achievement, especially when visual feedback is available early in the exposure target pointing (Redding & Wallace, 1993, 1997b, 2001, 2009. This overcompensation has been attributed to the persistence of error-corrective strategies in the face of developing realignment.…”

“…Direct effects of the prismatic distortion on performance during exposure are not directly commensurable with aftereffects of prism exposure (but see Redding & Wallace, 1993). For this reason, the two kinds of measures were analyzed separately, before considering their joint implications.…”

“…The fact that prism exposure evokes at least two very different and dissociable kinds of adaptive processes, ordinary error correction and extraordinary spatial realignment, has been repeatedly demonstrated for prismatic displacement (Bedford, 1989(Bedford, , 1993a(Bedford, , 1993b(Bedford, , 1999Redding & Wallace, 1993, 1996, 2001; see also Newport & Jackson, 2006;Redding, Clark, & Wallace, 1985;Redding, Rossetti, & Wallace, 2005;Redding & Wallace, 1997aWeiner, Hallett, & Funkenstein, 1983) and has recently been shown for virtual displacement (Simani, McGuire, & Sabes, 2007). The spatial misalignment between the origins of the visual eye-head and proprioceptive handhead spatial maps, for example, is normally removed by transformational constants applied to control signals between sensory-motor systems.…”

“…A significant feature of this exposure adaptation, the reduction of the direct effect of the prisms, is that if targetpointing exposure is continued beyond target achievement, pointing errors opposite to the initial direction appear (Redding & Wallace, 1993, 1997b, especially when visual feedback is given early in the pointing movement (Redding & Wallace, 1993). This overcompensation is one of several sources of converging evidence indicating that while ordinary error correction is responsible for rapid adaptation, exposure adaptation also involves another, slower adaptive process that produces antiadaptive behavior when increasingly nonadaptive error correction strategies continue to be applied.…”