Prism Adaptation: Dependency on Motion Trajectory Christian Kaernbach Lutz Munka Institut für Allgemeine Psychologie Universität Leipzig Douglas Cunningham Max-Planck Institut für Biologische Kybernetik Tübingen

Perception and Action ؤ ت و ك ز ظ غ ن ه ى د ج Sign Theory Hermann von Helmholtz, 1879 ObjectPerception Perception as “Image” Perception Action Correlation theories Perception serves Action James J. Gibson, 1979

Experiments with prism goggles Fresnel prisms prism goggle set: 15 € Perception Action

Experiments with prism goggles ؤ ت و ك ز ظ غ ن ه ى د ج Action Perception Action Perception Action Perception ???  Adaptation  Problem: central representation of spatial knowledge spatial knowledge is distributed Suspicion: The exact motion sequence is relevant. Martin, T.A., et al. (1996). no transfer between underhand and overhand throwing Kitazawa et al. (1997): no transfer between fast and slow reaching Hypothesis: The Negative Aftereffect (NAE) is greater for the adapted as compared to an alternate trajectory.

Effect of motion trajectory –Touch screen –Horizontal bar as chin rest –72 participants, graded randomly in 4 groups –target position central (block 2&4) or horizontally randomized (Block 1&3) –prism goggles (Block 3) with 16.7° horizontal shift (left-hand base) Block 1 „Familiarization“ with full visual feedback, 20 trials (5 repetitions  4 trajectories) Block 2 „Pretest“ without feedback, 20 trials (5  4) Block 3 „Adaptation“ with prism goggles, with full visual feedback, 80 trials (80  1) a single trajectory is adapted, one per group Block 4 „Posttest“ without feedback, 20 trials (5  4)

Results passive hand: Block 4 vs. Block 2 Block 4 minus Block 2 µ = 3 ± 1.8 mm µ = 1 ± 1.7 mm temporal dynamics µ = -46 ± 2.2 mm µ = -26 ± 2.3 mm PH passive handST same trajectory AH active handAT alternate trajectory horizontal error [mm]

Results temporal dynamics PH passive handST same trajectory AH active handAT alternate trajectory handiness above/below familiar / unfamiliar motions non-pref

Discussion of first experiment no transfer of adaptation to unadapted hand only ca. 50% transfer to alternate trajectory of adapted hand passive decay of adaptation unfamiliar motions are affected more  adaptation seems not to depend on recalibration of proprioception otherwise 100% transfer to be expected.  relearning of motor scripts ?  Objection: same starting position, but slightly different end position, end position of unadapted trajectory was not adapted.

Some more experiments Interposing circular movementsVarying the starting position

Some more experiments With/without weighted wrist wrapVertical generalization

Some more experiments Temporal dynamics of adaptation in block 3 Alternate full/no feedback / Terminal feedback

Conclusions Adaptation does not transfer to the passive hand, nor fully to alternate trajectories of the adapted hand. Adaptation of pointing performance involves mainly relearning of motor scripts. Spatial motor knowledge is distributed. There is no central representation of spatial motor knowledge. Knowing where is knowing how to. But what about our phenomenal experience? It seems that it is not needed for direct motor actions like pointing, grasping etc. –blindsight patients catching balls –Stratton (1897) riding bicycle with inverting goggles with phenomenal experience still upside-down. What is phenomenal experience good for? It seems to be a late product of evolution, enabling us to plan alternative action schemes. Tolman, E.C. (1948). Cognitive maps in rats and men. Psychological Review, 55,

Illusion: Spatial knowledge is conscious uniform, central precise motor actions, planing Conclusions Does the proposed dissociation between two spatial representations answer the “illusion question” in the abstract of this symposium? Yes. Under ecological conditions perception and action work hand in hand without significant discrepancies, thus leading us safely through our daily activities. However, dissociations between space perception and spatial action are also well-known: Several figural illusions (e.g. the Müller-Lyer or the Titchener/Ebbinghaus illusions) deceive perceptual judgment but exert only a marginal influence on motor behavior like pointing and grasping. The aim of the symposium is to find the causes of these dissociations and to relate them to the contributions of motor processes to perceived visual space. Two spatial representations: III unconsciousconscious distributeduniform, central precisedistorted motor actionsaction planing