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  • 1995-1999  (3)
  • One-handed catching  (2)
  • Pyrrhosoma  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 129 (1999), S. 369-377 
    ISSN: 1432-1106
    Keywords: Key words Adaptation ; Selection ; Re-calibration ; Timing ; One-handed catching ; Binocular information
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract   A pre-exposure, exposure, post-exposure design was used to assess the adaptation of the timing of a one-handed catch during telestereoscopic viewing. More specifically, it was examined whether the adaptation involved: (1) ignoring binocular sources of information and selecting other information, or (2) a recalibration of the coupling between the effected binocular information and the catching movement, and (3), if it is recalibration, whether it is restricted to the manipulated binocular information. To test these hypotheses, subjects (n=16) were assigned to one of two groups, each group performing three blocks of 15 trials in the dark with only the ball visible. In the exposure condition, both groups were required to catch balls under binocular telestereoscopic viewing. In the pre-exposure and post-exposure conditions, subjects performed under binocular and monocular viewing, respectively. Kinematics of the grasping movement were recorded. It was predicted that, in the case of a selection process, no afterfeffects would occur in the post-exposure condition, whereas, in the case of recalibration, aftereffects would occur. Moreover, if the recalibration is restricted to the manipulated information, only the group that was provided with binocular vision during the pre- exposure and post-exposure conditions would show aftereffects. Significant condition (pre-exposure, exposure, post-exposure) by block (first three trials, last three trials) effects were found for the moments of grasp onset, peak opening velocity and hand closure, indicating that the hand was opened and closed earlier in the first three trials of telestereoscopic viewing. This coincided with an increase in catching failures. In addition, for the moments of hand closure and peak closing velocity, negative aftereffects were found in the post-exposure condition. The hand was closed later in the first three trials after removal of telestereoscope. With respect to the presence of the aftereffects, no differences were found between the groups. It was concluded that adaptation to telestereoscopic viewing in the timing of a one-handed catch is due to the recalibration of the coupling between information and movement, rather than a selection of another source of information. Moreover, it is likely that the recalibration was not restricted to the single, manipulated information. Rather, the recalibration involves multiple binocular and monocular optical and oculomotor sources of information.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 129 (1999), S. 362-368 
    ISSN: 1432-1106
    Keywords: Key words Binocular ; Monocular ; Disparity ; Vergence ; One-handed catching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The aim of this study was to examine the role of binocular and monocular information sources in specifying time-to-contact. More specifically, it was investigated whether the timing of the one-handed catch is consistent with a binocular tau-function strategy. Subjects (n=8) were required to time their grasp to catch a ball approaching with a constant spatial trajectory. The ball approached at three different constant velocities (1.5, 2.0 and 2.5 m/s). Vergence and disparity were manipulated through subjects wearing a telestereoscope to increase the effective interocular separation, under both binocular and monocular viewing. Subjects performed 24 trials in each of the four conditions. Subjects’ started the opening of the hand earlier in the binocular telestereoscope condition when a ball approached with velocity of 1.5 m/s. They then closed the hand earlier in the binocular telestereoscope condition at all ball approach velocities. There were no effects of telestereoscope on the timing of hand opening and closing under monocular viewing. This finding suggests the use of the binocular information in timing the grasp. However, there were effects of approach velocity under all conditions of monocular and binocular viewing. Subjects’ closed the hand earlier as a function of increasing approach velocity. Together, the effects of the telestereoscope and approach velocity indicate that timing of the one-handed catch is not consistent with the use of a binocular ”tau-function” variable. Rather, it is concluded that multiple sources of monocular and binocular information contribute to the regulation of timing.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-5117
    Keywords: Pyrrhosoma ; egg production ; egg mortality ; lifetime reproductive success
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Artificial oviposition sites were used to estimate egg deposition rates in the field. Females laid an average of 10.76 eggs/minute with a mean duration of 22.81 minutes, giving an average clutch size of 245 eggs. Since one mating corresponded to one clutch of eggs, lifetime mating success was used as a measure of the number of clutches produced. Mean lifetime clutch production was 5.91 clutches per female, equating to 1447 eggs per female per lifetime. Eggs were hatched in the laboratory at temperatures comparable with those in the field. Hatching was highly synchronised and the overall hatching success was 75.1%. Causes of egg mortality in the laboratory were limited to infertility and unhatchability. Since no other sources of egg mortality could be found at the study site, this value was a good reflection of hatching success in the field. Lifetime egg production and hatching success were used to estimate the number of viable offspring produced per female, giving a higher order estimate of reproductive success than has previously been published for a zygopteran.
    Type of Medium: Electronic Resource
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