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A Systematic Comparison of Identification Techniques Used in Industrial Systems of Autotuning
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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
Visual cortex projections to thalamic intralaminar nuclei in the cat. An autoradiographic stud
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'Real-motion' cells in visual area V2 of behaving macaque monkeys.
No full textExtracellular recordings were made in area V2 of behaving macaque monkeys. Neurons were classified into three groups: non-oriented cells, oriented cells with antagonistic areas and oriented cells without antagonistic areas in their receptive field. All neurons were tested with standard visual stimulations in order to assess whether they gave different responses to the movement of a stimulus and to the movement of its retinal image alone, when the stimulus was motionless and the animal voluntarily moved its eyes. To do this, 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 movements), were compared. 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. Out of a total of 263 neurons isolated in the central 10 deg representation of area V2, 101 were fully studied with the visual stimulation described above. Most of these (83/101; 82%) gave about the same response to the two situations. About 14% (14/101) gave a good response to stimulus movements during steady fixation and a very weak one to retinal image displacements of stationary stimuli during visual tracking. We have called neurons of this type "real-motion cells" (cf. Galletti et al. 1984). None of the non-oriented cells was a real-motion one, while about an equal percentage of real-motion cells was found among the oriented cells with and without antagonistic areas. Finally, we found only 4 neurons which showed behaviour opposite to that of real-motion cells, i.e. they showed a better response to displacement of the retinal image of stationary stimuli than to actual movement of stimuli. We suggest that real-motion cells might contribute to correctly evaluating movement in the visual field in spite of eye movements and that they might allow recognition of the movement of an object even if it moves across a non-patterned visual background. Present data on area V2, together with similar results observed in area V1 (Galletti et al. 1984; Battaglini et al. 1986), support the view that these two cortical areas analyse the movement in a parallel fashion along with many other characteristics of the visual stimulus
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
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