1 Cognitive Interaction Technology Center of Excellence Why do we find hysteresis effects? Why do people persist to a former grasp type? Movement planning

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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]

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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.

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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.

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•Hysteresis effect is present before the increase.

•Effect size is significantly reduced after the increase. [F(1,22) = 11.320, 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.

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•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]

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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]

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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.

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Are hysteresis effects also found for other kinds of reaching movements?

•Ranges of motion differ between the grasping and pointing task.[F(8,304) = 89.390, 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]

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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]

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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.

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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]

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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).

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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.

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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.

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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) = 85.577, p < .001]

b) an incongruent gaze direction [F(1,20) = 126.714, p < .001]

•Pass and gaze direction do not interact.

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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?

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The task-irrelevant stimulus channel (the gaze) can be suppressed.

•The COM shift is still affected by pass direction [F(1,21) = 123.656, 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.

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1 Cognitive Interaction Technology Center of Excellence Why do we find hysteresis effects? Why do people persist to a former grasp type? Movement planning