Natale Stucchi

Cerebral dominance and asynchrony between bimanual two-dimensional movements.

The asynchrony of bimanual movements was investigated. Right- and left-handers traced simple geometrical patterns (ellipses) continuously with both hands. All combinations of the direction of rotation in each hand were executed at different rhythms. Geometrically, performances were largely independent of manual dominance. However, by comparing the passage times at homologous positions, the authors found that the dominant hand led the nondominant one by about 25 ms. The asynchrony was affected by neither movement type nor rhythm. The variability of the asynchrony varied along the trajectory, with well-defined maxima and minima. The variability profiles for movements that engaged homologous muscles differed markedly from those that engaged nonhomologous muscles. The authors discuss the hypothesis that bimanual periodic movements are timed by a lateralized functional module and asynchrony is due to the necessity of transmitting time-keeping information to the other hemisphere.

Disambiguating Information and Memory Resources in Children's Processing of Italian Relative Clauses.

We investigated the role of number agreement on verb and of animacy in the comprehension of subject and object relative clauses in 51 monolingual Italian-speaking children, mean age 9:33, tested through a self-paced listening experiment with a final comprehension question. A digit span test and a listening span test were also administered to examine the role of memory in comprehension. Subject relative clauses were easier to comprehend than object relative clauses; animacy of the relative clause head improved comprehension of object relative clauses; memory, as measured by the digit span test, modulates comprehension of object relative clauses, both with animate and inanimate heads, as shown in response accuracy. Although all children process number agreement morphology on the verb, only some perform a correct reanalysis, as shown by the accuracy measures. We argue that number agreement disambiguation is particularly taxing for children, as it provides a negative symptom in the sense of Fodor and Inoue (J Psycholinguist Res 29(1):25–36, 2000) and reanalysis requires them to hold two dependencies in memory.

Distorting the visual size of the hand affects hand pre-shaping during grasping

Vision of the body is known to affect somatosensory perception (e.g. proprioception or tactile discrimination). However, it is unknown whether visual information about one’s own body size can influence bodily action. We tested this by measuring the maximum grip aperture (MGA) parameter of grasping while eight subjects viewed a real size, enlarged or shrunken image of their hand reaching to grasp a cylinder. In the enlarged view condition, the MGA decreased relative to real size view, as if the grasping movement was actually executed with a physically larger hand, thus requiring a smaller grip aperture to grasp the cylinder. Interestingly, MGA remained smaller even after visual feedback was removed. In contrast, no effect was found for the reduced view condition. This asymmetry may reflect the fact that enlargement of body parts is experienced more frequently than shrinkage, notably during normal growth. In conclusion, vision of the body can significantly and persistently affect the internal model of the body used for motor programming.

Shifting the start: backward mislocation of the initial position of a motion.

Participants asked to judge the final position of a moving target typically indicate a position shifted forward. In the 6 experiments reported here, participants were asked to indicate both the starting position (SP) and the vanishing position (VP) at the onset and offset of a moving target. Results confirmed the forward displacement of the VP and showed a backward displacement of the SP. To test whether perceptual estimation was influenced by curvature of the trajectory, curvilinear motions were also used. Results showed that apparent displacements are along the geometrical tangents to the SP and VP. Relationships between the results and other findings such as the flash-lag effect the representational momentum, and the Fröhlich effect are discussed.

The relation between geometry and time in mental actions.

Mental imagery is a cognitive tool that helps humans take decisions by simulating past and future events. The hypothesis has been advanced that there is a functional equivalence between actual and mental movements. Yet, we do not know whether there are any limitations to its validity even in terms of some fundamental features of actual movements, such as the relationship between space and time. Although it is impossible to directly measure the spatiotemporal features of mental actions, an indirect investigation can be conducted by taking advantage of the constraints existing in planar drawing movements and described by the two-thirds power law (2/3PL). This kinematic law describes one of the most impressive regularities observed in biological movements: movement speed decreases when curvature increases. Here, we compared the duration of identical actual and mental arm movements by changing the constraints imposed by the 2/3PL. In the first two experiments, the length of the trajectory remained constant, while its curvature (Experiment 1) or its number of inflexions (Experiment 2) was manipulated. The results showed that curvature, but not the number of inflexions, proportionally and similarly affected actual and mental movement duration, as expected from the 2/3PL. Two other control experiments confirmed that the results of Experiment 1 were not attributable to eye movements (Experiment 3) or to the perceived length of the displayed trajectory (Experiment 4). Altogether, our findings suggest that mental movement simulation is tuned to the kinematic laws characterizing actions and that kinematics of actual and mental movements is completely specified by the representation of their geometry.

On the Portability of Computer-Generated Presentations: The Effect of Text-Background Color Combinations on Text Legibility

Objective: The aim of our study was to investigate which text-background (TB) color combinations improve legibility and pleasantness of texts either presented on a computer screen or projected on a wider surface. Background: Our work stems from the observation that multimedia presentations, even those by professionals in visual disciplines, are often spoiled by illegibility, which affects readability and the pleasantness of attending to such presentations. Methods: We investigated this problem through three experiments. Experiment 1 assessed the best TB color combinations in slides presented on a laptop. Experiment 2 verified the correlation between legibility and pleasantness for TB presentations. Experiment 3 investigated the legibility of a slide projected on a wide screen in different room lighting conditions. In all experiments participants expressed a rating score for stimulus legibility or pleasantness. Results: Experiments 1 and 3 showed that it is best to have a dark text on a light background for both displayed and projected texts. Experiment 2 showed that pleasantness is tightly correlated with legibility, though legibility depends on contrast between text and background. Conclusions: Our findings are not in complete agreement with the literature concerning legibility of text displayed on a computer screen, and they are in contrast with the common belief that for projection purposes it is best to have a light text on a dark background. Applications: Some practical rules on combining TB colors are given to enhance the legibility of presentations, especially important for the legibility of projected texts.

Dyslexic children fail to comply with the rhythmic constraints of handwriting

In this study, we sought to demonstrate that deficits in a specific motor activity, handwriting, are associated to Developmental Dyslexia. The linguistic and writing performance of children with Developmental Dyslexia, with and without handwriting problems (dysgraphia), were compared to that of children with Typical Development. The quantitative kinematic variables of handwriting were collected by means of a digitizing tablet. The results showed that all children with Developmental Dyslexia wrote more slowly than those with Typical Development. Contrary to typically developing children, they also varied more in the time taken to write the individual letters of a word and failed to comply with the principles of isochrony and homothety. Moreover, a series of correlations was found among reading, language measures and writing measures suggesting that the two abilities may be linked. We propose that the link between handwriting and reading/language deficits is mediated by rhythm, as both reading (which is grounded on language) and handwriting are ruled by principles of rhythmic organization.

The influence of facing direction on the haptic identification of two-dimensional raised pictures.

It has been hypothesized (Lederman et al, 1990 Perception & Psychophysics 47 54–64) that sighted people adopt a visual translation process when attempting to identify 2-D raised images by touch—they employ a visual image as a mediator between haptic sensory information and the object representation. If this hypothesis is correct, the performance in identifying pictures by touch (with eyes closed) ought to be better when the head is facing the picture than when facing in a very different direction. In this study, thirty-six blindfolded participants were required to identify raised pictures of common objects with their head facing either in the same direction as the raised picture or in an orthogonal direction. Identification performance was measured in terms of accuracy and response latencies. Overall, participants were more accurate and faster when their heads faced in the same direction as the picture. This finding is discussed in terms of spatial congruency between haptic representations of pictures and visual (or spatial) imagery created during exploration of haptic pictures.

Forward to the past

Our daily experience shows that the CNS is a highly efficient machine to predict the effect of actions into the future; are we so efficient also in reconstructing the past of an action? Previous studies demonstrated we are more effective in extrapolating the final position of a stimulus moving according to biological kinematic laws. Here we address the complementary question: are we more effective in extrapolating the starting position (SP) of a motion following a biological velocity profile? We presented a dot moving upward and corresponding to vertical arm movements that were masked in the first part of the trajectory. The stimulus could either move according to biological or non-biological kinematic laws of motion. Results show a better efficacy in reconstructing the SP of a natural motion: participants demonstrate to reconstruct coherently only the SP of the biological condition. When the motion violates the biological kinematic law, responses are scattered and show a tendency toward larger errors. Instead, in a control experiment where the full motions were displayed, no-difference between biological and non-biological motions is found. Results are discussed in light of potential mechanisms involved in visual inference. We propose that as soon as the target appears the cortical motor area would generate an internal representation of reaching movement. When the visual input and the stored kinematic template match, the SP is traced back on the basis of this memory template, making more effective the SP reconstruction.

Observer's control of the moving stimulus increases the flash-lag effect

The flash-lag effect (FLE) consists in perceiving a briefly presented stationary stimulus to lag behind an aligned moving stimulus. This study investigates the effects of actively controlling the moving stimulus. By means of a robotic arm, observers continuously moved a dot along a circular trajectory, and a flash was displayed closely at unpredictable times. In two experiments, we found that the FLE was larger when participants controlled the moving stimulus, compared to a computer-controlled condition. Two control conditions tested the possibility that the observed modulation of the FLE was due to visuo-spatial attention or dual-task factors. This study provides evidence that the motor system interacts with and possibly speeds up the processing of a moving visual stimulus when the observer controls its movement.