1 Cognitive Interaction Technology Center of Excellence Why do we find hysteresis effects? Why do people persist to a former grasp type? Movement planning results in a cognitive cost. [Rosenbaum & Jorgensen, 1992] In sequential tasks, this cost can be reduced by the reuse of a former movement plan. [Rosenbaum et al., 2007]

2 Cognitive Interaction Technology Center of Excellence The cost-optimization hypothesis [Schütz & Schack, 2013a] The fraction of plan reuse depends on the cognitive and mechanical cost of a task. The total cost is minimized. The fraction of reuse decreases as mechanical cost increases.

3 Cognitive Interaction Technology Center of Excellence How can we test this prediction? Sequential drawer opening task. Hand pro/supination is measured. The mechanical cost is increased by a counterforce of 25 N applied for 10 sequences.

4 Cognitive Interaction Technology Center of Excellence Hysteresis effect is present before the increase. Effect size is significantly reduced after the increase. [F(1,22) = , p =.003] The fraction of plan reuse depends on the cognitive and mechanical costs of the task. [Schütz & Schack, 2013a] Increasing the mechanical cost should reduce hysteresis effect size.

5 Cognitive Interaction Technology Center of Excellence Sequential drawer task with a hand switch in each sequence. Hysteresis effect size is analyzed before and after the hand switch. Are former motor plans reused only within or also across hands? [Schütz & Schack, 2015]

6 Cognitive Interaction Technology Center of Excellence If movement plans transfer across hands, so should hysteresis effects. Hysteresis effects are present before the hand switch. [t(23) = 5.273, p <.001] Hysteresis effects are lost after the hand switch. [t(23) = 0.837, p =.411] Movement plans are reused within hands, but do not transfer across hands. [Schütz & Schack, 2015]

7 Cognitive Interaction Technology Center of Excellence Are hysteresis effects also found for other kinds of reaching movements? [Schütz, Weigelt, & Schack, submitted] Modified drawer handles suitable for a pointing and grasping task. Identical target positions, different motor tasks. Hand pro/supination is measured.

8 Cognitive Interaction Technology Center of Excellence Are hysteresis effects also found for other kinds of reaching movements? Ranges of motion differ between the grasping and pointing task. [F(8,304) = , p <.001] Hysteresis effect size is the same. [F(1,38) < 1, p =.351] Hysteresis effect size in pointing movements is similar to that of grasping movements. [Schütz, Weigelt, & Schack, submitted]

9 Cognitive Interaction Technology Center of Excellence How is the redundant degrees of freedom problem addressed in reaching movements? [Schütz & Schack, 2013b] The arm has more degrees of freedom than are required for a reaching task. A target position can be reached by more than one posture. Joint couplings can reduce the number of degrees of freedom. [Bernstein, 1967]

10 Cognitive Interaction Technology Center of Excellence How many joint couplings are used in a three-dimensional pointing task? [Schütz & Schack, 2013b] Pointing task to virtual targets uniformly spaced in a three- dimensional workspace. Measurement of joint couplings by principal component analysis.

11 Cognitive Interaction Technology Center of Excellence Three joint couplings are suffcient. Three joint couplings capture 89.7 ±2.8 % of the variance. Each coupling corresponds to a valid movement of the arm, i.e., a motor primitive. The reduced number of degrees of freedom solves the redundancy problem. [Schütz & Schack, 2013b]

12 Cognitive Interaction Technology Center of Excellence Subliminal stimuli pre-activate the motor cortex. Subliminal prime stimuli affect response times to the target stimulus. [Dehaene et al. 1998] Faster response times if prime and target require the same response (congruent primes). Slower response times otherwise (incongruent primes).

13 Cognitive Interaction Technology Center of Excellence Can subliminal stimuli elicit an overt, full body response? Target pictures show a basketball player passing the ball left or right. gaze direction = pass direction Choice-reaction task: „Block the ball as fast and accurately as possible by pushing the button.“ Measurement of center of mass (COM) shifts on a force plate.

14 Cognitive Interaction Technology Center of Excellence Subliminal stimuli elicit overt responses. If pass/gaze direction in the prime is congruent, a movement towards the correct button is initiated. If it is incongruent, a movement away from the button is initiated. The COM shift 335 ms after prime presentation is quantified.

15 Cognitive Interaction Technology Center of Excellence Different stimulus channels are processed independent of each other. The incorrect COM shift is more pronounced for a) an incongruent pass direction [F(1,20) = , p <.001] b) an incongruent gaze direction [F(1,20) = , p <.001] Pass and gaze direction do not interact.

16 Cognitive Interaction Technology Center of Excellence Can the task-irrelevant stimulus channel (the gaze) be suppressed consciously? Target pictures are exchanged for gaze feints: gaze direction ≠ pass direction Participants should suppress the gaze direction to execute the task. Will the processing of the subliminal gaze stimuli be suppressed as well?

17 Cognitive Interaction Technology Center of Excellence The task-irrelevant stimulus channel (the gaze) can be suppressed. The COM shift is still affected by pass direction [F(1,21) = , p <.001] The effect of gaze direction is lost. The conscious suppression of the gaze direction in the target also suppresses the processing in the subliminal prime.