Motor imagery of tool use: relationship to actual use and adherence to Fitts’ law across tasks

Abstract

A Fitts’ task was used to investigate how tools are incorporated into the internal representations that underlie pointing movements, and whether such knowledge can be generalized across tasks. We measured the speed-accuracy trade-offs that occurred as target width was varied for both real and imagined movements. The dynamics of the pointing tool used in the task were manipulated—regular pen, top-heavy tool, and bottom-heavy tool—to test the fidelity of internal representations of movements involving the use of novel tools. To test if such representations can be generalized, the orientation of the pointing task was also manipulated (horizontal vs. vertical). In all conditions, both real and imagined performances conformed to the speed-accuracy relationship described by Fitts’ law. We found significant differences in imagined MTs for the two weighted tools compared to the regular pen, but not between the weighted tools. By contrast, real movement durations differed between all tools. These results indicate that even relatively brief experience using novel tools is sufficient to influence the internal representation of the dynamics of the tool-limb system. However, in the absence of feedback, these representations do not make explicit differences in performances resulting from the unique dynamics of these weighted tools.

Differential contributions of the superior and inferior parietal cortex to feedback versus feedforward control of tools

“…This was true regardless of whether participants used a stick that extended their reach or a laser pointer that did not. However, consistent with our earlier results (Macuga et al, 2012), the complete absence of feedback and physical movement during motor imagery dampened the effect of the ID. This suggests that motor imagery may involve partially distinct cognitive mechanisms from execution for certain types of behaviors (Rodriguez et al, 2008), including those involving tools (Macuga et al, 2012).…”

“…However, consistent with our earlier results (Macuga et al, 2012), the complete absence of feedback and physical movement during motor imagery dampened the effect of the ID. This suggests that motor imagery may involve partially distinct cognitive mechanisms from execution for certain types of behaviors (Rodriguez et al, 2008), including those involving tools (Macuga et al, 2012). Second, the SPL and cerebellum showed greatest increases in activity during execution when vision was available for control, providing evidence for their involvement in feedback-based control.…”

“…These findings suggest that the left (or contralateral) SPL may code reachable space. The fact that a stick > laser difference did not arise in the SPL for imagery suggests that some type of sensorimotor feedback is required for this distinction, or that imagery of tool use is fairly coarse and does not distinguish between tool types (Macuga et al, 2012). …”

“…On the basis of previous behavioral findings (Macuga et al, 2012), we predicted that movement durations for all three conditions would conform to Fitts’ Law, but that slopes for participants’ estimates of movement times in the imagery condition would be smaller, reflecting a reduced influence of task difficulty (ID) on performance. As in earlier neuroimaging studies of visually-guided aiming, we expected that the closed-loop condition would involve the SPL, IPL, and cerebellum in addition to other regions associated with sensorimotor control (Seidler et al, 2004; Winstein et al, 1997).…”

The action-specific effect of execution on imagination of reciprocal aiming movements

“…Most interestingly, motor imagery was impaired for the same movements which the patient had difficulties executing overtly. In neurotypical adults, Fitts’ speed-accuracy trade-off has consistently been shown in imagined pointing movements (Cerritelli, Maruff, Wilson, & Currie, 2000; Macuga, Papailiou, & Frey, 2012; Papaxanthis, Schieppati, Gentili, & Pozzo, 2002; Young, Pratt, & Chau, 2009) and, more recently, researchers have revealed accuracy-dependent activation of the right cerebellum and superior parietal lobule when imagining a Fitts’-type task (Lorey et al, 2010). These results provide evidence that Fitts’ law is present in imagined movements.…”