Updating the programming of a precision grip is a function of recent history of available feedback

In a recent study (Whitwell et al. in Exp Brain Res 185:111-119, 2008), we showed that the visuomotor system is "cognitively impenetrable" to the extent that explicit predictive knowledge of the availability of visual feedback on an upcoming trial fails to optimize grasping. The results suggested that the effects of trial history, rather than the anticipatory knowledge of the nature of an upcoming trial, plays the most significant role in how the availability of visual feedback is exploited by the visuomotor system when programming grip aperture (e.g., opening the hand wider when visual feedback is unavailable). Here, we provide direct evidence that trial history indeed plays a critical role in the programming of grip aperture. Twelve individuals grasped objects of three different sizes placed at one of two distances either with or without visual feedback of the hand and object (closed- or open-loop trials, respectively). Runs of four consecutive closed- or open-loop trials were interleaved with sequences of closed and open-loop trials that alternated back and forth from trial to trial. Peak grip aperture (PGA) decreased linearly with successive closed-loop trials and increased linearly with successive open-loop trials. We also compared PGA for trials that were preceded by a run of four consecutive closed- (or open-loop) trials with trials that were preceded by only one closed- (or open-loop) trial. This analysis indicated that consistency in the runs of closed- or open-loop trials significantly reduced the effect of the availability of feedback on grasping in the trial following the run. We conclude that while the margin of error observed in precision grasping is largely a function of the availability of visual feedback on the current trial, it is evidently also a function of the recent history of the availability of visual feedback on previous trials.