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  • Motion perception  (2)
  • A. basilaris  (1)
  • Children  (1)
  • 1
    ISSN: 1432-1106
    Keywords: Motion perception ; Spatial frequency ; Aubert-Fleischl phenomenon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Apparent velocities of moving visual stimuli are known to be different depending on whether the subject pursues the stimulus (efferently controlled motion perception) or whether the eye is stationary and the image moves across the retina (afferent motion perception). Afferent motion perception of a periodic pattern or a moving single object causes overestimation of velocity (magnitude estimations) as compared to smooth pursuit. This socalled Aubert-Fleischl phenomenon is shown to depend on local temporal frequency stimulation on the retina caused by the repetitive passage of contrast borders of the moving periodic pattern. This is evidenced by the fact that for a given stimulus speed the amount of overestimation is a function of the spatial frequency of the pattern (or the angular subtend of a single moving object) and that the Aubert-Fleischl phenomenon is not observed if a single edge moves. Background characteristics seem not to influence the apparent velocity during smooth pursuit.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 16 (1973), S. 476-491 
    ISSN: 1432-1106
    Keywords: Optokinetic stimulation ; Motion perception ; Circularvection ; Spatial orientation ; Peripheral visual field
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Optokinetic stimuli allow for two perceptual interpretations. The observer may perceive himself as being stationary in a moving surround (egocentric motion perception) or he may experience an illusion of self-motion, so that the actually moving surroundings appear to be stable (exocentric motion perception). Results 1. Circular motion of the entire surroundings (rotating drum) invariably leads to an apparent self-rotation (circularvection: CV), which is indistinguishable from an actual chair rotation. 2. Following stimulus onset, CV begins after a few seconds latency and slowly increases its apparent velocity until its saturation. CV may outlast the visual stimulus by as much as 30 sec. Latencies are independent of stimulus velocity. 3. Even with drum accelerations up to 15°/sec2, stationary subjects cannot infer from the lack of vestibular input that only the drum is rotating. 4. With stimulation of the entire visual field or sufficiently large parts of the peripheral retina, the velocity of apparent self-rotation matches stimulus speed up to 90–120°/sec. At higher speeds, CV velocity lags behind stimulus speed and results in additional egocentric motion perception. 5. Masking the central visual field by black disks up to 120° in diameter scarcely diminishes CV. Conversely, if peripheral vision is precluded, stimulation of the central field up to 30° in diameter results in exclusive egocentric motion perception of the surround. With a central and peripheral stimulus equivalent in area, the peripheral stimulus predominates CV. 6. Simultaneous presentation of conflicting central and peripheral optokinetic stimuli (i.e., stimuli rotating in opposite directions) has shown that exocentric orientation depends on the peripheral stimulus whereas optokinetic nystagmus and egocentric motion perception rely on the center of the visual field.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1433-8491
    Keywords: Vertebral Angiography ; Basilar Artery ; Distance to Clivus ; Variations ; Adults ; Children ; Arteriosclerosis ; Infratentorial Tumors ; Vertebralisangiographie ; A. basilaris ; Clivusabstand ; Variationen ; Erwachsene ; Kinder ; Atherosklerose ; Infratentorielle Tumoren
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Die topographischen Beziehungen der A. basilaris zu Schädelbasisstrukturen sowie Abgangsvarianzen und Kalibrigkeitsvergleiche der basisnahen Hirnarterien wurden an 63 Brachialis- und 60 Vertebralisangiogrammen quantitativ untersucht. Normbereich und Grenzwerte wurden an normalen Angiogrammen von Erwachsenen und Kindern sowie bei cerebralen Gefäßprozessen und infratentoriellen Tumoren definiert. Im normalen Angiogramm (Erwachsene) betrug der mittlere Clivus-Basilaris-Abstand vom Apex dorsi sellae 7,2 mm, vom Fußpunkt des Dorsum sellae 4,9 mm und 2 cm unterhalb des Apex 2,9 mm. Eine Basilarisanpressung ist bei 2 mm und weniger eine -abhebung bei mehr als 12 mm anzunehmen. Bei 67,6% verlief die A. basilaris in der Frontalebene mit Seitauslenkungen von weniger als 2 mm. Bei cerebraler Atherosklerose fand sich eine deutliche Elongation der A. basilaris (48,5 mm) gegenüber dem mittleren Normwert (38,5 mm) mit ausgeprägtem Basilarisüberstand oberhalb des Apex (6,6 mm) und Seitauslenkungen der Arterie bis zu 12 mm. Kinder bis zu 10 Jahren hatten weitere Basalcisternen mit einem Basilarisabstand von 7,96 mm vom Apex, vom Fußpunkt des Dorsum sellae 6,0 mm und 2 cm unterhalb des Apex von 3,8 mm. Die mittlere Basilarislänge betrug 41,5 mm. Kinder haben mit 7,8 mm den höchsten Basilarisüberstand infolge des relativen Entwicklungsrückstandes der knöchernen Schädelbasis gegenüber den Hirnstammstrukturen und Gefäßen. Bei infratentoriellen Tumoren ist eine Basilarisanpressung (weniger als 2 mm) und -abhebung (mehr als 12 mm) diagnostisch verwertbar.
    Notes: Summary Topographical correlations of the basilar artery to skull base structures as well as variations of branching and of diameter of the arteries near the base were studied by evaluating 63 brachial and 60 vertebral angiographies. Normal values were established by computing normal angiograms of adults and children. Abnormal values were found in angiograms of patients with arteriosclerosis and with infratentorial tumors. In normal angiograms (adults) the average distance between clivus and basilar artery was 7.2 mm at the apex dorsi sellae, 4.9 mm at the lower edge of the dorsum sellae and 2.9 mm at a point 2 cm below the apex. At a distance of 2 mm and less the basilar artery is pressed toward the clivus. At a distance of 12 mm and more, the basilar artery is ablated from the clivus. In 67.6% of the cases the lateral deviation of the basilar artery was less than 2 mm. Patients with cerebral arteriosclerosis showed a significant elongation of the basilar artery (48.5 mm) compared to the average normal value (38.5 mm). This elongation is combined with a marked elevation of the basilar artery above the apex (6.6 mm) and with lateral deviations up to 12 mm. Children up to 10 years had larger basal cisterns with a distance between basilar artery and clivus of 7.96 mm at the apex dorsi sellae, of 6.0 mm at the lower edge of the dorsum sellae and of 3.8 mm at a point 2 cm below the apex. The median length of the basilar artery was 41.5 mm. Children have the highest elevation of the basilar artery above the apex (7.8 mm) which is due to the relative retardation of osseous maturation of the skull base in comparison to the brain stem and vessels. It is of diagnostical value for infratentorial tumors when the basilar artery is pressed toward (less than 2 mm) or away from the clivus (more than 12 mm).
    Type of Medium: Electronic Resource
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