Abstract Two experiments investigate the effects of language comprehension on affordances. Participants read a sentence composed by either an observation or an action verb (Look at/Grasp) followed by ...an object name. They had to decide whether the visual object following the sentence was the same as the one mentioned in the sentence. Objects graspable with either a precision or a power grip were presented in an orientation affording action (canonical) or not. Action sentences were faster than observation sentences, and power grip objects were faster than precision grip objects. Moreover, faster RTs were obtained when orientation afforded action. Results indicate that the simulation activated during language comprehension leads to the formation of a “motor prototype” of the object. This motor prototype encodes information on temporary/canonical and stable affordances (e.g., orientation, size), which can be possibly referred to different cognitive and neural systems (dorsal, ventral systems).
According to the premotor theory of attention, the mechanisms responsible for spatial attention and the mechanisms involved in programming ocular saccades are basically the same. The aim of the ...present experiments was to test this claim. In experiment 1 subjects were presented with a visual display consisting of a fixation point and four boxes arranged horizontally and located above the fixation cross. Two of the boxes were in the left visual hemifield, two in the right. A fifth box was located on the vertical meridian below the fixation cross. Digit cues indicated in which of the upper boxes the imperative stimulus was most likely to appear. Subjects were instructed to direct attention to the cued box and to perform a saccadic eye movement to the lower box on presentation of the imperative stimulus. The trajectory of the saccades deviated contralateral to the hemifield in which the imperative stimulus was presented. This deviation was larger when the hemifield where the imperative stimulus was presented was the cued one. In experiment 2, the visual display consisted of five boxes forming a cross. The central box served as a fixation point. The cue was a small line, linked to the central box, pointing to different directions and indicating where the visual imperative stimulus would appear. In 50% of trials, the imperative stimulus was a visual stimulus presented either in one of the lateral boxes or in the central one. In the remaining 50% of trials, the imperative stimulus was a non-lateralised sound. Half the subjects were instructed to make a saccade to the upper box at the presentation of the visual imperative stimulus and to the lower box at the presentation of the acoustic stimulus. Half the subjects received the opposite instructions. The results confirmed that the saccades deviate contralateral to the hemifield of stimulus presentation in the case of visual imperative stimuli. Most importantly, they showed that the saccades deviate contralateral to the cued hemifield, also in the case of acoustic imperative stimuli. Experiment 3 was similar to experiment 2. It confirmed the results of that experiment and showed that slow ocular drifts, which are observed in the time interval between cue and imperative stimulus presentation, cannot explain the ocular deviations. Taken together, the experiments demonstrate that spatial attention allocation leads to an activation of oculomotor circuits, in spite of eye immobility.
We correct Table VII of original paper, where the order of the z-expansion parameters and the entries of the covariance matrix do not match. All the material of the paper, except for this misprint, ...remains valid and unchanged.
Mirror neurons, first described in the rostral part of monkey ventral premotor cortex (area F5), discharge both when the animal performs a goal-directed hand action and when it observes another ...individual performing the same or a similar action. More recently, in the same area mirror neurons responding to the observation of mouth actions have been also found. In humans, through an fMRI study, it has been shown that the observation of actions performed with the hand, the mouth and the foot leads to the activation of different sectors of Broca’s area and premotor cortex, according to the effector involved in the observed action, following a somatotopic pattern which resembles the classical motor cortex homunculus. These results strongly support the existence of an execution-observation matching system (mirror neuron system). It has been proposed that this system is involved in action recognition. Experimental evidence in favor of this hypothesis both in the monkey and humans are shortly reviewed.
We present the first lattice Nf=2+1+1 determination of the tensor form factor fTDπ(K)(q2) corresponding to the semileptonic D→π(K)ℓνℓ and rare D→π(K)ℓℓ decays as a function of the squared ...four-momentum transfer q2. Together with our recent determination of the vector f+Dπ(K)(q2) and scalar f0Dπ(K)(q2) form factors, we complete the set of hadronic matrix elements regulating the semileptonic D→π(K)ℓνℓ and rare D→π(K)ℓℓ transitions within and beyond the standard model, when a nonzero tensor coupling is possible. Our analysis is based on the gauge configurations produced by the European Twisted Mass Collaboration with Nf=2+1+1 flavors of dynamical quarks, which include in the sea, besides two light mass-degenerate quarks, also the strange and charm quarks with masses close to their physical values. We simulated at three different values of the lattice spacing and with pion masses as small as 220 MeV and with the valence heavy quark in the mass range from ≃0.7mcphys to ≃1.2mcphys. The matrix elements of the tensor current are determined for a plethora of kinematical conditions in which parent and child mesons are either moving or at rest. As in the case of the vector and scalar form factors, Lorentz symmetry breaking due to hypercubic effects is clearly observed also in the data for the tensor form factor and included in the decomposition of the current matrix elements in terms of additional form factors. After the extrapolations to the physical pion mass and to the continuum and infinite volume limits, we determine the tensor form factor in the whole kinematical region from q2=0 up to qmax2=(MD−Mπ(K))2 accessible in the experiments. A set of synthetic data points, representing our results for fTDπ(K)(q2) for several selected values of q2, is provided and the corresponding covariance matrix is also available. At zero four-momentum transfer, we get fTDπ(0)=0.506 (79) and fTDK(0)=0.687 (54), which correspond to fTDπ(0)/f+Dπ(0)=0.827 (114) and fTDK(0)/f+DK(0)=0.898 (50).
Spatial attention and eye movements Sheliga, B M; Riggio, L; Rizzolatti, G
Experimental brain research,
08/1995, Letnik:
105, Številka:
2
Journal Article
Recenzirano
We previously showed that when attention is allocated to the right or left of the fixation point, saccades directed to targets located above or below the fixation point deviate contralateral to the ...attention locus. In the present study, we examined how general this phenomenon is and whether the amount of saccade deviation depends on the location of attention with respect to that of the saccade target. Three experiments were carried out. In experiment 1 the location of the imperative stimulus was uncued. Its presentation exogenously directed attention to its location. In experiment 2 the location of the imperative stimulus was cued by a central cognitive cue. In this experiment attention was endogenously directed to the imperative stimulus location before its presentation (expectancy paradigm). In experiment 3 all stimulus boxes contained a possible imperative stimulus at the display presentation. A central cue, presented subsequently, indicated which of them had to be used for the saccade. In this experiment attention was endogenously directed to the imperative stimulus, but after its presentation (no-expectancy paradigm). The results showed that, regardless of how attention was directed to the imperative stimulus, the vertical saccades deviated contralateral to the attention location. The deviation was larger when attention was in the upper field and the saccade was directed upward ("same hemifield" condition) than when attention was in the upper field and the saccade was directed downward ("opposite hemifield" condition). The same relationship between the "same hemifield" condition and "opposite hemifield" condition was found when attention was in the lower field. Saccadic reaction times (SRTs) were shortest in experiment 2 and longest in experiment 3. In experiment 2, SRTs of the "same hemifield" condition were significantly longer than those of the "opposite hemifield" condition. Taken altogether, these results strongly support the notion that attention allocation in space leads to an activation of oculomotor circuits, in spite of eye immobility. The possible mechanisms responsible for saccade deviations and for greater saccade deviations when attention is in the same hemifield as the programmed ocular saccade are discussed.
We present a lattice determination of the vector and scalar form factors of the D→πℓν and D→Kℓν semileptonic decays, which are relevant for the extraction of the CKM matrix elements |Vcd| and |Vcs| ...from experimental data. Our analysis is based on the gauge configurations produced by the European Twisted Mass Collaboration with Nf=2+1+1 flavors of dynamical quarks, at three different values of the lattice spacing (a≃0.062,0.082,0.089 fm) and with pion masses as small as 210 MeV. Quark momenta are injected on the lattice using nonperiodic boundary conditions. The matrix elements of both vector and scalar currents are determined for plenty of kinematical conditions in which parent and child mesons are either moving or at rest. Lorentz symmetry breaking due to hypercubic effects is clearly observed in the data and included in the decomposition of the current matrix elements in terms of additional form factors. After the extrapolations to the physical pion mass and to the continuum limit, we determine the vector and scalar form factors in the whole kinematical region from q2=0 up to qmax2=(MD−Mπ(K))2 accessible in the experiments, obtaining a good overall agreement with experiments, except in the region at high values of q2 where some deviations are visible. A set of synthetic data points, representing our results for f+Dπ(K)(q2) and f0Dπ(K)(q2) for several selected values of q2, is provided and also the corresponding covariance matrix is available. At zero four-momentum transfer, we get f+D→π(0)=0.612(35) and f+D→K(0)=0.765(31). Using the experimental averages for |Vcd|f+D→π(0) and |Vcs|f+D→K(0), we extract |Vcd|=0.2330(137) and |Vcs|=0.945(38), respectively. The second row of the CKM matrix is found to be in agreement with unitarity within the current uncertainties: |Vcd|2+|Vcs|2+|Vcb|2=0.949(78).
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