1,721,113 research outputs found
The superior parietal lobule of primates: A sensory-motor hub for interaction with the environment
Full text linkThe superior parietal lobule of the macaque monkey occupies the postero-medial part of the parietal lobe and plays a crucial role in the integration of different sources of information (from visual, motor and somatosensory brain regions) for the purpose of high-level cognitive functions, as perception for action. This region encompasses the intraparietal sulcus and the parieto-occipital sulcus and includes also the precuneate cortex in the mesial surface of the hemisphere. It hosts several areas extensively studied in the macaque: PE, PEip, PEci anteriorly and PEc, MIP, PGm and V6A posteriorly. Recently studies based on functional MRI have suggested putative human homologue of some of the areas of the macaque superior parietal lobule. Here we review the anatomical subdivision, the cortico-cortical and thalamocortical connections of the macaque superior parietal lobule compared with their functional properties and the homology with human organization in physiological and lesioned situations. The knowledge of this part of the macaque brain could help in understanding pathological conditions that in humans affect the normal behaviour of arm-reaching actions and can inspire brain computer interfaces performing in more accurate ways the sensorimotor transformations needed to interact with the surrounding environment
Real-motion' cells in area V3A of macaque visual cortex.
No full textThe stability of visual perception despite eye movements suggests the existence, in the visual system, of neural elements able to recognize whether a movement of an image occurring in a particular part of the retina is the consequence of an actual movement that occurred in the visual field, or self-induced by an ocular movement while the object was still in the field of view. Recordings from single neurons in area V3A of awake macaque monkeys were made to check the existence of such a type of neurons (called 'real-motion' cells; see Galletti et al. 1984, 1988) in this prestriate area of the visual cortex. A total of 119 neurons were recorded from area V3A. They were highly sensitive to the orientation of the visual stimuli, being on average more sensitive than V1 and V2 neurons. Almost all of them were sensitive to a large range of velocities of stimulus movement and about one half to the direction of it. In order to assess whether they gave different responses to the movement of a stimulus and to that of its retinal image alone (self-induced by an eye movement while the stimulus was still), a comparison was made between neuronal responses obtained when a moving stimulus swept a stationary receptive field (during steady fixation) and when a moving receptive field swept a stationary stimulus (during tracking eye movement). The receptive field stimulation at retinal level was physically the same in both cases, but only in the first was there actual movement of the visual stimulus. Control trials, where the monkeys performed tracking eye movements without any intentional receptive field stimulation, were also carried out. For a number of neurons, the test was repeated in darkness and against a textured visual background. Eighty-seven neurons were fully studied to assess whether they were real-motion cells. About 48% of them (42/87) showed significant differences between responses to stimulus versus eye movement. The great majority of these cells (36/42) were real-motion cells, in that they showed a weaker response to visual stimulation during tracking than to the actual stimulus movement during steady fixation
Functional properties of neurons in area V1 of awake macaque monkeys: peripheral versus central visual field representation
No full textThe region of the striate cortex where the visual field is represented up to 52 degrees from the fovea was explored in awake, behaving monkeys. Extracellular recordings were made from 241 neurons. On the basis of their receptive field position in the visual field, they were subdivided into a central (within 10 degrees from the fovea) and a peripheral (beyond 10 degrees) group. Sensitivity to orientation, length, direction and velocity of movement of conventional light stimuli was tested and compared in the two samples. Besides the well-known increase of receptive field size with eccentricity, gross differences were found only for the sensitivity to the velocity of stimulus movement. The great majority of neurons in the central sample preferred slow velocities and showed no sensitivity to velocities above 100 degrees/sec. In contrast, many peripheral neurons were poorly sensitive to slow speeds of movement and well responsive to high velocities, above 100 degrees/sec. Cells that showed a better response to an actual stimulus movement in the visual field than to a retinal image movement self-induced by an eye-movement ("real-motion" cells) were also searched for in the two samples. They were found in the 13% of the central neurons and in the 25% of the peripheral neurons. Present data extend to the awake, behaving animal what already known from paralysed animal, indicating that in physiological conditions central and peripheral vision have a different functional role in the analysis of motion within the visual field
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
Caratteristiche socio-demografiche e «trading» degli investitori individuali: nuove evidenze sul caso italiano
No full textIl presente lavoro si inserisce nella letteratura riguardante gli effetti dell’overconfidence sul trading, uno degli aspetti più investigati dalla finanza comportamentale (Shefrin, 2007) per quanto riguarda le decisioni degli investitori
individuali. In particolare, utilizziamo alcune caratteristiche socio-demografighe per capire come esse possano influenzare l’overconfidence e, di conseguenza, le scelte di trading. Queste caratteristiche sono importanti nel determinare il comportamento in termini di trading degli individui. Tuttavia,
nonostante la loro rilevanza, vi sono ancora pochi studi che mettono in relazione queste caratteristiche alle distorsioni psicologiche degli individui
Individual Investor Behavior: Evidence from the Clients of a Small Credit Cooperative Bank
No full textIndividual characteristics are important in explaining investor
trading behaviour. The clients of a small cooperative bank are analysed over the three-year period 2005–2007 to measure the effect that age, gender, income, job position and status of online trader has on the number of stock trades completed. A negative binomial regression is used since our dependent variable, the number of trades, can only assume non-negative discrete values.
This paper shows that the number of transactions increases if the client is: man vs. women; self-employed vs. employee, retiree or housewife; online vs. traditional trader; higher vs. low income. Our findings are not clear cut with respect to age. In conclusion, individual characteristics are important in explaining an individual’s trading behaviour since they affect an investor’s attitude towards risk and overconfidence
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