1,721,011 research outputs found
Object-centred neglect: Simulation with head-centred coding based on Gaussian gaze-dependent units
No full textRight brain damaged patients affected by contralesional object-centred neglect are able to process all objects around them but systematically omit the left part of these objects. We show that pure object-centred neglect can be simulated by a basis function neural network in which the activity of units allowing head-centred coding of space is based on the activity of gaze-dependent units with no lateral gradient of preferred eye positions along the horizontal space. This type of network simulates complete dissociation between object-centred and egocentric neglect, as observed in patients’ copies of multi-item drawings. Based on these results and available neurophysiological, clinical and brain imaging data, it is proposed that disruption of a cerebral network including dorsal occipital and parietal areas and the supplementary eye fields could be the main cause of object-centred neglect
Simulating object-centred neglect with head-centred coding of space based on non-linear gaze-dependent units
No full textThis contribution introduces a new neurocomputational model of neglect which allows to reproduce through computer simulations all observed features of subjects affected by neglec
Perceiving numerosity does not cause automatic shifts of spatial attention
Full text linkIt is debated whether the representation of numbers is endowed with a directional-spatial component so that perceiving small-magnitude numbers triggers leftward shifts of attention and perceiving large-magnitude numbers rightward shifts. Contrary to initial findings, recent investigations have demonstrated that centrally presented small-magnitude and large-magnitude Arabic numbers do not cause leftward and rightward shifts of attention, respectively. Here we verified whether perceiving small or large non-symbolic numerosities (i.e., clouds of dots) drives attention to the left or the right side of space, respectively. In experiment 1, participants were presented with central small (1, 2) vs large-numerosity (8, 9) clouds of dots followed by an imperative target in the left or right side of space. In experiment 2, a central cloud of dots (i.e., five dots) was followed by the simultaneous presentation of two identical dot-clouds, one on the left and one on the right side of space. Lateral clouds were both lower (1, 2) or higher in numerosity (8, 9) than the central cloud. After a variable delay, one of the two lateral clouds turned red and participants had to signal the colour change through a unimanual response. We found that (a) in Experiment 1, the small vs large numerosity of the central cloud of dots did not speed up the detection of left vs right targets, respectively, (b) in Experiment 2, the detection of colour change was not faster in the left side of space when lateral clouds were smaller in numerosity than the central reference and in the right side when clouds were larger in numerosity. These findings show that perceiving non-symbolic numerosity does not cause automatic shifts of spatial attention and suggests no inherent association between the representation of numerosity and that of directional space
A neural model of number interval position effect (Nipe) in children
No full textIn the present paper we describe an artificial neural model of the Number Interval Position Effect (NIPE;[5]) that has been observed in the mental bisection of number intervals both in adults and in children. In this task a systematic error bias in the mental setting of the subjective midpoint of number intervals is found, so that for intervals of equal size there is a shift of the subjective midpoint towards numbers higher than the true midpoint for intervals at the beginning of decades while for intervals at the end of decades the error bias is directionally reversed towards numbers lower than the true midpoint. This trend of the bisection error is recursively present across consecutive decades. Here we show that a neural-computational model based on information spread by energy gradients towards accumulation points based on the logarithimic compressed representation of numbermagnitudes that has been observed at the single cell level in rhesus monkeys [9] effectively simulates the performance of adults and children in the mental bisection of number intervals, in particular replicating the data observed in children
A scoping review of cognitive training in neurodegenerative diseases via computerized and virtual reality tools: What we know so far
Full text linkMost prevalent neurodegenerative diseases such as Alzheimer’s disease, frontotemporal dementia, Parkinson’s disease and multiple sclerosis are heterogeneous in their clinical profiles and underlying pathophysiology, although they typically share the presence of cognitive impairment that worsens significantly during the course of the disease. Viable pharmacological options for cognitive symptoms in these clinical conditions are currently lacking. In recent years, several studies have started to apply Computerized Cognitive Training (CCT) and Virtual Reality (VR) tools to try and contrast patients’ cognitive decay over time. However, no in-depth literature review of the contribution of these promising therapeutic options across main neurodegenerative diseases has been conducted yet. The present paper reports the state-of-the-art of CCT and VR studies targeting cognitive impairment in most common neurodegenerative conditions. Our twofold aim is to point out the scientific evidence available so far and to support health professionals to consider these promising therapeutic tools when planning rehabilitative interventions, especially when the access to regular and frequent hospital consultations is not easy to be provided
Midpoint: A Tool to Build Artificial Models of Numerical Cognition
No full textThe present paper describes a tool developed to model and simulate tasks related to numerical cognition, a very important element of both animal and human cognition. In particular, we describe how this software has been used to study a bias that has been consistently observed in humans, both adults and children, about the calculation of the middle point between two numbers and related with the position of numbers in intervals, called NIPE (number interval position effect). Along with the description of the software and the experimental results about the NIPE effect, some results are reported which show the potential of this approac
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Expectancy modulates pupil size during endogenous orienting of spatial attention
No full textfMRI investigations in healthy humans have documented phasic changes in the level of activation of the right temporal-parietal junction (TPJ) during cued voluntary orienting of spatial attention. Cues that correctly predict the position of upcoming targets in the majority of trials, i.e., predictive cues, produce higher deactivation of the right TPJ as compared with non-predictive cues. Since the right TPJ is the recipient of noradrenergic (NE) innervation, it has been hypothesised that changes in the level of TPJ activity are matched with changes in the level of NE activity. Based on aforementioned fMRI findings, this might imply that orienting with predictive cues is matched with different levels of NE activity as compared with non-predictive cues. To test this hypothesis, we measured changes in pupil dilation, an indirect index of NE activity, during voluntary orienting of attention with highly predictive (80% validity) or non-predictive (50% validity) cues. In agreement with current interpretations of the tonic/phasic activity of the Locus Coeruleus-Norepinephrinic system (LC-NE), we found that the steady level of cue predictiveness that characterised both the predictive and non-predictive conditions caused, across consecutive blocks of trials, a progressive decrement in pupil dilation during the baseline-fixation period that anticipated the cue period. With predictive cues we observed increased pupil dilation as compared with non-predictive cues. In addition, the relative reduction in pupil size observed with non-predictive cues increased as a function of cue-duration. These results show that changes in the predictiveness of cues that guide voluntary orienting of spatial attention are matched with changes in pupil dilation and, putatively, with corresponding changes in LC-NE activit
Determining priority between attentional and referential-coding sources of the Simon effect through optokinetic stimulation
No full textThe “Simon effect” is the performance advantage for spatially corresponding target–response ensemblesthat is observed when coding of target position is irrelevant for the selection of motor responses. The“attentional-shift” account of the Simon effect holds that it arises from the congruency between responselocation and the direction of the last shift of attention toward the target. The “referential-coding” accounttraces the origin of the Simon effect back to the congruency between the response location and theposition of the target with respect to a spatial reference frame. We were able to contrast these twohypotheses using full-field horizontal optokinetic stimulation (OKS). It was shown that OKS moving inone horizontal direction drives covert orienting of attention toward the side of arrival of OKS, i.e. the “Incoming”side, which is opposed to the direction of OKS motion toward the “Out-going” side (Teramoto etal., 2004; Watanabe, 2001). We therefore asked healthy participants to discriminate between slow andfast velocities of leftward or rightward OKS. “Fast” and “slow” responses were associated to responsebuttons positioned in the left or right side of space. The “attentional-shift” account of the Simon effectpredicts that response compatibility should be related to the direction of the attentional shift induced byOKS, i.e. in the direction opposite to OKS motion. By contrast, the “referential-coding” hypothesis predictsthat response compatibility should be related to the direction of OKS displacement with respect to itsstarting position.Weobserved faster RTs when the response button was on the “In-coming” side of space,opposite to the direction ofOKSmotion. This result supports priority of attentional over referential-codingfactors in the genesis of the Simon effect
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