Filippo Barbieri

How symbolic gestures and words interact with each other.

Previous repetitive Transcranial Magnetic Stimulation and neuroimaging studies showed that Brocas area is involved in the interaction between gestures and words. However, in these studies the nature of this interaction was not fully investigated; consequently, we addressed this issue in three behavioral experiments. When compared to the expression of one signal at a time, arm kinematics slowed down and voice parameters were amplified when congruent words plus gestures were simultaneously produced (experiment 1). When word and gesture were incongruent, arm kinematics did not change regardless of word category, whereas the gesture induced variation in vocal parameters of communicative and action words only (experiments 2 and 3). Data are discussed according to the hypothesis that integration between gesture and word occurs by transferring the social intention to interact directly with the interlocutor from the gesture to the word.

Automatic grasp imitation following action observation affects estimation of intrinsic object properties

The present study aimed to determine whether the observation of different grasps of the same object elicits automatic imitation of the kinematics of those grasps and this process influences the estimation of intrinsic target properties. In experiments 1 and 2, participants reached and grasped differently sized spheres after observation of the same objects grasped using two different types of grasp (power and precision grasp) and hand kinematics. The observed grasp kinematics were imitated especially when the vision of the target and the acting hand were precluded. In experiments 3, 4 and 5 participants matched the diameter of the spheres, either perceived or imagined, by opening their thumb and index finger (i.e. the fingers used to grasp the objects) after observation of the two types of grasp. Finger opening was larger after observation of power grasp than precision grasp, consistently with the notion that power grasp and precision grasp are preferentially used to grasp large and small objects, respectively. However, the effect was poorly observed for the small object, this depending on the fact that the participants imitated also the final position of the thumb and index finger, which were closer to each other in the power grasp. Finally, those participants, for whom the effect was stronger, reported to have perceived more differently sized objects than those really presented. The results suggest that imitation evoked by a mirror system is involved in planning how to interact with an object and in the estimation of the properties extracted for sensory-motor integration.

On the relations between affordance and representation of the agent’s effector

The present study aimed to determine whether the representation of object affordances requires specification of the effector potentially interacting with the object: specifically, in this study, vision of the interacting hand. In Experiment 1 we used an apparatus by which a fruit to be reached and grasped was identified by word reading, whereas another (interfering) fruit was visually perceived at the same location as the target. The apparatus allowed visual presentation of the agent’s interacting hand or prevented it. When visually presented, the hand was perceived as still at the start position even when it moved to grasp the fruit. An interference effect on the grasp congruent with the distractor size was observed only when the hand was visible. In Experiment 2, interference was observed also when a hand different from the agent’s own was visually presented. In both Experiments 1 and 2 the visible fruit interfered with the arm’s reach, but the effect was independent of its size and less dependent on the visually-presented hand. A control experiment (Experiment 3) enabled comparison of the interference of visual stimuli on targets identified by word reading (Experiments 1 and 2) with that of objects identified by word reading on visually-presented targets (Experiment 3). The interference induced by visual stimuli was stronger than the interference induced by objects identified by words (i.e. affordances evoked by visual stimuli were stronger than affordances evoked by semantics). Taken together, the results of the present study suggest that the specification of the agent’s effector is necessary for the elicitation of affordances. However, the elicitation of these affordances was observed for interactions between object and hand (grasp), rather than for interactions between object and arm (reach). Finally, our data confirm the influence of semantics on the control of arm movements, though less strong than that due to visual input.

Muon spin rotation and SQUID investigation of superconductivity in (NH3)xNaK2C60 (x∼0.7)

The family of superconducting fullerides (NH_3)_xNaK_2C_60 shows an anomalous correlation between T_c and lattice parameter. To better understand the origin of this anomaly we have studied a representative x=0.75 compound using SQUID magnetometry and MuSR spectroscopy. The lower critical field H_c1, measured by the trapped magnetization method, is less than 1 G, a very small value as compared with that of other fullerides. Muon spin depolarization in the superconducting phase shows also quite small local field inhomogeneities, of the order of those arising from nuclear dipolar fields. On the other hand, the 40 T value for H_c2, as extracted from magnetometry data, is comparable to that of other fullerides. We show that these observations cannot be rationalized within the framework of the Ginzburg-Landau theory of superconductivity. Instead, the anomalous magnetic properties could be interpreted taking into account the role played by polaronic instabilities in this material.

NMR studies of Li15C60 fulleride

The intercalation compound Li15C60 has been studied with 13C, 7Li NMR and X-ray diffraction in the low temperature phase (T<520 K). XRD data suggest the presence of two different stable structures: a tetragonal monomeric and an orthorhombic polymerised phase. Detailed 13C MAS NMR experiments in the latter phase, evidence sp3 bondings among the carbon atoms, whereas the relative (sp2/sp3) intensities, together with X-ray data, suggest a C60 polymerization as [2+2] cycloaddition. Multiple quantum NMR experiments on 7Li confirm the presence of lithium clusters, previously shown by X-ray diffraction in the high temperature phase (T<520 K), also at lower temperatures. Nevertheless, the inferred cluster size is significantly smaller than that suggested by the stoichiometry, probably because of cluster fragmentation in the low-T phase. Further evidence about this scenario is obtained also from preliminary measurements of line shapes and Tt relaxation times, which exhibit a multi-exponential recovery with very di...

Clustering and polymerization of Li15C60

The structural and electronic properties of lithium intercalated fullerides (of which Li15C60 is the most representative) are still puzzling and unclear. Above 520 K, x-ray/neutron diffraction shows an fcc phase in which the 15 Li atoms clusterize in the octahedral interstices. However, at lower temperatures, a change in the crystalline symmetry and also in the electronic properties takes place as observed from 13C, 7Li/6Li NMR and x-ray diffraction measurements. X-ray diffraction data suggest the presence of two different stable structures: a tetragonal monomeric and an orthorhombic polymerised phase. Detailed 13C magic angle spinning NMR experiments in the latter phase indicate sp3 bondings among the carbon atoms, whereas the relative (sp2/sp3) intensities, together with x-ray data, suggest the C60 polymerization to be a [2+2] cycloaddition. Multiple quantum NMR experiments on 7Li confirm the presence of lithium clusters, as observed by x-ray diffraction in the high temperature phase, also at lower temperatures. However, the inferred cluster size is significantly smaller than that suggested by the stoichiometry. The distortion in the low-T structure of L15C60 is supposed to induce the migration of Li atoms from octahedral to tetrahedral voids, thus accounting for the lower number of Li atoms in the clusters. Further evidence of this scenario is obtained also from preliminary measurements of line shapes and T1 relaxation times, which exhibit a multiexponential recovery with very different constants that are hardly compatible with a single family of Li atom sites.

Raman investigation of charge-doped C60 polymer formed in heavily intercalated Li15C60 fulleride

Li15C60 can be obtained either as a monomeric or a polymeric phase depending on the preparation conditions. A series of Raman spectra of polymer Li15C60 have been acquired in the temperature range 293-565 K. The polymer starts to transform to a monomer phase at ∼420 K and the phase transition completes itself at a temperature ⩽470 K. When the monomer is formed, the Raman spectrum exhibits a charge state of C60−n, where 5<n<6. By lowering the temperature, the polymer phase is recovered accompanied by a considerable hysteresis. Raman results from Li15C60 samples prepared through other preparation routes that favor the stabilization of different monomer/polymer C60 phases are also presented, correlated with their corresponding X-ray diffraction structural data and discussed. Comparison with Li27C60 results is also discussed.

Anomalous superconductivity in (NH3)xNaK2C60

Contrary to what is observed in many fullerides, the transition temperature of the superconducting (NH3)xNaK2C60 decreases as its cubic lattice parameter increases, when more ammonia is intercalated in the system. To understand the origin of this anomaly we measure the electronic spin susceptibility with SQUID magnetometry and NMR in two differently doped samples. The relation between Tc and the density of states at the Fermi level is found to be opposite to the Migdal-Eliashberg prediction. CP-MAS measurements of the isotropic part of the 13C Knight shift qualitatively confirms this result. 13C NMR relaxation measurements validate the interpretation of the spin susceptibility in terms of density of states, ruling therefore out the presence of strong antiferromagnetic correlations in the Fermi liquid. A possible explanation of the anomaly should take into account the non adiabatic nature of the superconductivity in this compound.