@phdthesis {pub2738,
	title = {Cognitive Planning in Manual Action},
	author = {Christian Seegelke},
	year = {2014},
	month = {April},
	abstract = {Many of our daily activities require that we physically interact with one or more objects. Given that there is an infinite number of possible ways to achieve any given task, a core question in motor control is how particular actions for object manipulation are chosen. Previous research has demonstrated that the way people grasp objects is strongly influenced by future task demands or the intended action goal of the task. Anticipatory grasp posture planning has been extensively studies during object manipulation task composed of two action segments (i.e., grasp an object and one subsequent displacement), and a number of factors that consistently influence initial grasp choice (i.e., action selection constraints) have been identified. In contrast, surprisingly little work has considered action selection constraints during multi-segment object manipulation tasks.

The present thesis examined action selection constraints during grasp posture planning of multi-object manipulation tasks. Specifically, it focuses on the following action selection constraints and their interdependencies during multi-segment object manipulation tasks {\textendash} (1) the tendency to select grasp postures that allow for control at later stages (end-state comfort effect), (2) the tendency to minimize postural transitions between immediately forthcoming and subsequent postures, and (3) a cognitive planning gradient, which indicates that action segments which occur earlier in a sequence are considered stronger in an action plan.

Chapter 2 assessed to what extent biomechanical and cognitive factors contribute to grasp posture planning during multi-segment object manipulation tasks, and whether participants would adjust their initial grasp postures over time. To this end, participants performed a grasping and placing task consisting of one, two, or three movement segments. The position of the targets was manipulated such that the degree of required object orientation between the home and the first target positions, and between the first and the second target positions, varied. Participants selected initial grasp postures that were inversely related to both the first and second target positions, suggesting that the multi-segment action sequences were planned holistically in advance, and that each element was considered during grasp posture planning. In addition, initial grasp postures were differently adjusted to the target positions depending on the temporal order in which the object was to be placed to these targets. During the initial stages of the experimental session initial grasp postures were influenced to a larger extent by the demands of the temporally proximal segment.
However, over time, participants overcame these cognitive limitations and adjusted their initial grasp postures more strongly to the requirements of the temporally distal segment. Together, these results indicate that grasp posture planning is influenced by cognitive and biomechanical factors, and that participants learn to anticipate the task demands of temporally distal task demands, which reduces the burden on the central nervous system.

Chapter 3 examined the interplay between the tendency to select grasp postures that allow for comfortable or easy-to-control postures at later stages and the tendency to minimize differences between immediately forthcoming and subsequent postures during a three-segment object manipulation task. To this the experimental task introduced in Chapter 2 was modified such that the object orientation at the first (intermediate) target position was unconstrained, and participants were free to place the object in any desired orientation. On average, initial grasp postures were inversely related to final target orientation. In contrast, intermediate grasp postures were not influenced by final target orientation, but similar to the most comfortable postures obtained at this position indicating that participants selected initial grasp postures that afford control at the end of the movement sequence (end-state comfort) but also at the intermediate target position (intermediate-state comfort). Closer inspection of the data revealed the presence of inter-individual differences in initial grasp posture selection, ranging from very strong to virtually no adjustment. Strong adjustments in initial grasp postures led to more comfortable final grasp postures, whereas small adjustments led to less comfortable final postures. Interestingly, intermediate grasp postures were similar (and close to the most comfortable intermediate grasp postures) regardless of initial grasp posture adjustment. Consequently, it is proposed that participants who strongly adjusted their initial grasp postures to the final target positions planned the action sequence such that they adopted initial grasp posture that allow for more control at later stages. In contrast, participants who selected similar initial grips regardless of final target position might have aimed at minimizing postural differences between the initial and intermediate grasp postures as these were highly similar.

Chapter 4 examined whether participants would plan for comfort at later stages during a three-segment object manipulation tasks in which two objects are manipulated. In this task, participants opened a drawer, grasped an object from inside the drawer, and subsequently placed the object on a table in one of three different target orientations (0{\textdegree}, 90{\textdegree}, or 180{\textdegree} object rotation required). Results showed that initial grasp postures (i.e., when opening the drawer) were not influenced by the final target orientation, indicating that participants did not plan the entire movement sequence holistically in advance. In contrast, both the intermediate (i.e., when grasping the object) and the final grasp posture (i.e., when placing the object) were influenced by the final target orientation.

In addition, inter-individual differences in grasp selection emerged for the 180{\textdegree} target orientation condition. Specifically, 42 \% of the participants were able to successfully complete the action goal by adopting grasp postures that were comfortable at the intermediate but not the final position (intermediate-state comfort) and rotated the object counterclockwise. In contrast, 58 \% of the participants preferred clockwise rotations and adopted grasp postures that allow for comfort at the end of the movement but not at the intermediate position (end-state comfort). These findings indicate that that participants might prioritize comfort at different stages in an action sequence, especially when larger degrees of object rotation are required.

In sum, the findings presented in this thesis demonstrate that multiple action selection constraints are considered and interact during the planning and execution of multi-segment object manipulation tasks. It is conjectured that action selection might be best understood as a process of ranking or weighting of constraints which are ordered hierarchically according to their importance. This ranking is assumed to be not static, but rather flexible and depend and depend on contextual, conceptual, perceptual, environmental, cognitive, biomechanical, personal factors, forming task- and individual-specific constraint hierarchies. According to this view, inter-individual differences in task-performance are a result of variations in the relative order of action selection constraints between individuals. A challenge for future work is how individual-specific characteristics might predict participants{\textquoteright} motor behavior and how these factors might interact with other task- and environmental factors.},
	publisher = {HRI-EU},
	booktitle = {University of Bielefeld}
}