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Zago M.,Laboratory of Neuromotor Physiology
Journal of vision | Year: 2011

Dealing with upside-down objects is difficult and takes time. Among the cues that are critical for defining object orientation, the visible influence of gravity on the object's motion has received limited attention. Here, we manipulated the alignment of visible gravity and structural visual cues between each other and relative to the orientation of the observer and physical gravity. Participants pressed a button triggering a hitter to intercept a target accelerated by a virtual gravity. A factorial design assessed the effects of scene orientation (normal or inverted) and target gravity (normal or inverted). We found that interception was significantly more successful when scene direction was concordant with target gravity direction, irrespective of whether both were upright or inverted. This was so independent of the hitter type and when performance feedback to the participants was either available (Experiment 1) or unavailable (Experiment 2). These results show that the combined influence of visible gravity and structural visual cues can outweigh both physical gravity and viewer-centered cues, leading to rely instead on the congruence of the apparent physical forces acting on people and objects in the scene. Source

Fiorentini C.,University College London | Viviani P.,Laboratory of Neuromotor Physiology
Journal of Vision | Year: 2011

Some evidence suggests that it is easier to identify facial expressions (FEs) shown as dynamic displays than as photographs (dynamic advantage hypothesis). Previously, this has been tested by using dynamic FEs simulated either by morphing a neutral face into an emotional one or by computer animations. For the first time, we tested the dynamic advantage hypothesis by using high-speed recordings of actors' FEs. In the dynamic condition, stimuli were graded blends of two recordings (duration: 4.18 s), each describing the unfolding of an expression from neutral to apex. In the static condition, stimuli (duration: 3 s) were blends of just the apex of the same recordings. Stimuli for both conditions were generated by linearly morphing one expression into the other. Performance was estimated by a forced-choice task asking participants to identify which prototype the morphed stimulus was more similar to. Identification accuracy was not different between conditions. Response times (RTs) measured from stimulus onset were shorter for static than for dynamic stimuli. Yet, most responses to dynamic stimuli were given before expressions reached their apex. Thus, with a threshold model, we tested whether discriminative information is integrated more effectively in dynamic than in static conditions. We did not find any systematic difference. In short, neither identification accuracy nor RTs supported the dynamic advantage hypothesis. © ARVO. Source

Solopova I.A.,Russian Academy of Sciences | Selionov V.A.,Russian Academy of Sciences | Kazennikov O.V.,Russian Academy of Sciences | Ivanenko Y.P.,Laboratory of Neuromotor Physiology
Neuroscience Letters | Year: 2014

Here, we compared motor evoked potentials (MEP) in response to transcranial magnetic stimulation of the motor cortex and the H-reflex during voluntary and vibration-induced air-stepping movements in humans. Both the MEPs (in mm biceps femoris, rectus femoris and tibialis anterior) and H-reflex (in m soleus) were significantly smaller during vibration-induced cyclic leg movements at matched amplitudes of angular motion and muscle activity. These findings highlight differences between voluntary and non-voluntary activation of the spinal pattern generator circuitry in humans, presumably due to an extra facilitatory effect of voluntary control/triggering of stepping on spinal motoneurons and interneurons. The results support the idea of active engagement of supraspinal motor areas in developing central pattern generator-modulating therapies. © 2014 Elsevier Ireland Ltd. Source

Self-location refers to the experience of occupying a given position in the environment. Recent research has addressed the sense of self-location as one of the key components of self-consciousness, together with the experience of owning the physical body (ownership) (Blanke and Metzinger, Trends Cogn Sci 13:7–13 in 2009. doi:10.1016/j.tics.2008.10.003). Experimentally controlled full-body illusions proved to be valuable research tools to study these components and their interaction, and to explore their underlying neural underpinning. The focus of this manuscript is to provide a close look into the nuances of different illusory experiences affecting the sense of self-location and to examine their relation to the concurrent experienced sense of body ownership. On the basis of previous reviewed studies, it is proposed that the sense of self-location may be regarded as the blending of two paralllel representations: the abstract allocentric coding of the position occupied in the environment, mainly associated with visual-perspective, and the egocentric mapping of somatosensory sensations into the external space, mainly associated with peripersonal space. Open questions to be addressed by future research are further addressed. © 2015, Marta Olivetti Belardinelli and Springer-Verlag Berlin Heidelberg. Source

Moscatelli A.,University of Rome Tor Vergata | Moscatelli A.,Laboratory of Neuromotor Physiology | Moscatelli A.,Bielefeld University | Mezzetti M.,University of Rome Tor Vergata | And 2 more authors.
Journal of Vision | Year: 2012

In psychophysics, researchers usually apply a two-level model for the analysis of the behavior of the single subject and the population. This classical model has two main disadvantages. First, the second level of the analysis discards information on trial repetitions and subject-specific variability. Second, the model does not easily allow assessing the goodness of fit. As an alternative to this classical approach, here we propose the Generalized Linear Mixed Model (GLMM). The GLMM separately estimates the variability of fixed and random effects, it has a higher statistical power, and it allows an easier assessment of the goodness of fit compared with the classical two-level model. GLMMs have been frequently used in many disciplines since the 1990s; however, they have been rarely applied in psychophysics. Furthermore, to our knowledge, the issue of estimating the point-of-subjective-equivalence (PSE) within the GLMM framework has never been addressed. Therefore the article has two purposes: It provides a brief introduction to the usage of the GLMM in psychophysics, and it evaluates two different methods to estimate the PSE and its variability within the GLMM framework. We compare the performance of the GLMM and the classical two-level model on published experimental data and simulated data. We report that the estimated values of the parameters were similar between the two models and Type I errors were below the confidence level in both models. However, the GLMM has a higher statistical power than the two-level model. Moreover, one can easily compare the fit of different GLMMs according to different criteria. In conclusion, we argue that the GLMM can be a useful method in psychophysics. © 2012 ARVO. Source

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