It was (not) me: Causal Inference of Agency in goal-directed actions

Summary: 
The perception of one’s own actions depends on both sensory information and predictions derived from internal forward models [1]. The integration of these information sources depends critically on whether perceptual consequences are associated with one’s own action (sense of agency) or with changes in the external world that are not related to the action. The perceived effects of actions should thus critically depend on the consistency between the predicted and the actual sensory consequences of actions. To test this idea, we used a virtual-reality setup to manipulate the consistency between pointing movements and their visual consequences and investigated the influence of this manipulation on self-action perception. We then asked whether a Bayesian causal inference model, which assumes a latent agency variable controlling the attributed influence of the own action on perceptual consequences [2,3], would account for the empirical data: if the percept was attributed to the own action, visual and internal information should fuse in a Bayesian optimal manner, while this should not be the case if the visual stimulus was attributed to external influences. The model correctly fits the data, showing that small deviations between predicted and actual sensory information were still attributed to one’s own action, while this was not the case for large deviations when subjects relied more on internal information. We discuss the performance of this causal inference model in comparison to alternative biologically feasible statistical models applying methods for Bayesian model comparison.

Experiment: 
Participants were seated in front of a horizontal board on which their right hand was placed with the index finger on a haptic marker, representing the starting point for each trial. Participants were instructed to execute straight, fast (quasi-ballistic) pointing movements of fixed amplitude, but without an explicit visual target. The hand was obstructed from the view of the participants, and visual feedback about the peripheral part of the movement was provided by a cursor. Feedback was either veridical or rotated against the true direction of the hand movement by predefined angles. After each trial participants were asked to report the subjectively experienced direction of the executed hand movement by placing a mouse-cursor into that direction.

Model: 
We compared two probabilistic models: Both include a binary random gating variable (agency) that models the sense of ‘agency’; that is the belief that the visual feedback is influenced by the subject’s motor action. The first model assumes that both the visual feedback xv and the internal motor state estimate xe are directly caused by the (unobserved) real motor state xt (Fig. 1). The second model assumes instead that the expected visual feedback depends on the perceived direction of the own motor action xe (Fig. 2). 
Results: Both models are in good agreement with the data. Fig. A shows the model fit for Model 1 superpositioned to the data from a single subject. Fig. B shows the belief that the visual stimulus was influenced by the own action, which decreases for large deviations between predicted and real visual feedback. Bayesian model comparison shows a better fit for model 1.
Citations
[1] Wolpert D.M, Ghahramani, Z, Jordan, M. (1995) Science, 269, 1880-1882.
[2] Körding KP, Beierholm E, Ma WJ, Quartz S, Tenenbaum JB, et al (2007) PLoS ONE 2(9): e943.
[3] Shams, L., Beierholm, U. (2010) TiCS, 14: 425-432.
Acknowledgements
This work was supported by the BCCN Tübingen (FKZ: 01GQ1002), the CIN Tübingen, the European Union (FP7-ICT-215866 project SEARISE), the DFG and the Hermann and Lilly Schilling Foundation

The magic triangle goes MAD: experimental phasing with a bromine derivative

5-Amino-2,4,6-tribromoisophthalic acid is used as a phasing tool for protein structure determination by MAD phasing. It is the second representative of a novel class of compounds for heavy-atom derivatization that combine heavy atoms with amino and carboxyl groups for binding to proteins

Occurrence of tympanic bone spicules and bone crests in domestic cats

Small and hyperostotic tympanic bone spicules (STBS and HTBS) extending from the tympanic wall or from the septum bullae into the tympanic cavity have been described in large feline species such as Siberian tigers or African lions and in canids such as dogs, red foxes and wolves. Detailed descriptions of prevalence, location and orientation were performed for dogs and African lions by means of necropsy and conventional computed tomography (cCT). Aims of the current study were to describe same characteristics for domestic cats by means of microcomputed tomography (µCT) and cCT. A total of 15 cats or rather 30 ears were examined. Furthermore, new bone formations extending into the tympanic cavity shaped like small lamellae were found and named “tympanic bone crests” (TBCs). The registered phenomenon of a thickened tympanic wall in some cats was named “tympanic wall thickening” (TWT). STBS appeared in 43% of the ears being bilateral in 44% of the cases, whereas HTBS appeared in one ear. TBC was present in 33% of the ears with a bilateral prevalence of 67%, and TWT could be detected in 13% of the ears. The mentioned structures are just barely or not at all detectable with cCT; therefore, µCT is necessary for an identification and detailed description. The origin and the factors inducing the development of examined phenomena are unknown, and it is hypothesized that the occurrence can be assessed as anatomical norm variations

Lasersystem zur Kühlung relativistischer C3+-Ionenstrahlen in Speicherringen

Kalte Ionenstrahlen sind von essentieller Bedeutung für Präzisionsexperimente an Speicherringen. Nicht nur spektroskopische Experimente profitieren von der hohen Energieauflösung, sondern auch Kollisionsexperimente von der erhöhten Brillanz kalter Strahlen. Zusätzlich ist es vorstellbar, mit Hilfe kalter Ionenstrahlen exotischere Spezies sympathetisch zu kühlen. Neben der bereits lange etablierten Elektronenkühlung gewinnen gerade für hochenergetische Teilchen zunehmend auch alternative Methoden an Bedeutung. So gab es bereits in der Vergangenheit Experimente, gespeicherte Teilchen mit Hilfe von Lasern zu kühlen. Dabei kamen meist frequenzverdoppelte Argon-Ionenlaser bei 257 nm zur Anwendung, die sich wegen ihrer Ausgangsleistung im erforderlichen Wellenlängenbereich anbieten. Durch die stark eingeschränkte Abstimmbarkeit dieser Systeme war es jedoch nicht möglich, die gesamte Impulsbandbreite der Ionenstrahlen zu kühlen. Da bisher keine kommerziellen Alternativen erhältlich sind, die auch die notwendige Abstimmbarkeit bieten, wurde in dieser Arbeit ein eigenes Lasersystem entwickelt, charakterisiert und schlussendlich bei einer Strahlzeit am Experimentierspeicherring (ESR) der Gesellschaft für Schwerionenforschung (GSI) erprobt. Das vollständig festkörperbasierte System liefert bis zu 180 mW Ausgangsleistung bei 257 nm und ist bei dieser Wellenlänge bis zu 16 GHz in 10 ms modensprungfrei abstimmbar. Durch die Verwendung effizienter Diodenlaser ist das System zusätzlich deutlich energieeffizienter als vergleichbare Argon-Ionenlaser. Die Ausgangswellenlänge von 1028 nm wird mit Hilfe eines Yb-Faserverstärkers auf eine Leistung von bis zu 16 W gebracht. Anschließend wird in zwei konsekutiven Überhöhungsresonatoren die Zielwellenlänge von 257 nm realisiert. Als Frequenzreferenz dient ein zusätzlicher Diodenlaser, der auf ein Wellenlängenmessgerät stabilisiert ist. Dieses neue Lasersystem konnte im Rahmen einer Strahlzeit im August 2012 erstmals eingesetzt werden. Dabei wurden erfolgreich relativistische C3+ Ionen mit beta = 0,47 gekühlt. Erstmals war es hierbei möglich die gesamte Impulsbandbreite gebündelter Ionenstrahlen ausschließlich mit einem Laser ohne vorherige Elektronenkühlung anzusprechen. Dabei wurde im Vergleich zu vorherigen Experimenten lediglich die Frequenz des Lasers verstimmt und nicht die Bunchingfrequenz des Ionenstrahls. Die Ergebnisse für die verbleibende Impulsbandbreite waren mit Delta p/p = 10^-6 durch die Nachweismöglichkeiten des verwendeten Messsystems limitiert. Es konnte gezeigt werden, dass neue, abstimmbare Lasersysteme für die Kühlung relativistischer Ionenstrahlen geeignet sind und auch für zukünftige Anlagen wie SIS 100/FAIR eine bedeutende Rolle spielen können

5-Amino-2,4,6-triiodo­isophthalic acid monohydrate

The title compound, C8H4I3NO4·H2O, shows an extensive hydrogen-bond network; in the crystal structure, mol­ecules are linked by O—H⋯O, N—H⋯O and O—H⋯N hydrogen bonds involving all possible donors and also the water mol­ecule