31. An Exploring Expedition-Trouble Commences-Lost in the Cave-Total Darkness-Found but not Saved

2019 ◽  
pp. 222-232
Keyword(s):  
Total Darkness

Germination Behavior of Florida Pusley Seeds. I. Effects of Storage, Light, Temperature and Planting Depths on Germination

Weed Science ◽  
1975 ◽  
Vol 23 (5) ◽  
pp. 400-403 ◽  
Author(s):  
P. K. Biswas ◽  
P. D. Bell ◽  
J. L. Crayton ◽  
K. B. Paul
Keyword(s):  
Constant Temperature ◽  
Total Darkness ◽  
Moist Storage ◽  
Ph Range

Freshly harvested Florida pusley (Richardia scabraL.) seeds do not germinate in continuous dark, but do germinate if exposed to more than 2 hr of light each day. Increasing periods of illumination up to 16 hr per day increases the germination percentages. Scarification increases the rate of germination in the presence of light. Scarification also causes germination of seeds stored for 8 months or longer in total darkness. The seeds fail to germinate at constant temperatures of 15 C or less and at 40 C. Almost complete germination occurs at a constant temperature of 30 C, or at alternating temperatures of 20 and 30 C. The seeds germinate equally well in the pH range of 3 to 8. Increasing depths of planting reduces percent emergence, and none of the seedlings emerge from a depth of 1.5 cm or more. Air-dried seeds can be stored either at 5 or at 25 C without losing viability, at least up to a period of 1 year after harvest. Moist storage of seeds at 5 C reduces germinability.

Eye-Head Movement Coordination: Vestibulo-Ocular Reflex Suppression with Head-Fixed Target Fixation1

1991 ◽  
Vol 1 (2) ◽  
pp. 161-170
Author(s):  
Jean-Louis Vercher ◽  
Gabriel M. Gauthier
Keyword(s):  
Eye Movements ◽  
Time Course ◽  
Mental Arithmetic ◽  
Visual Space ◽  
Head Movements ◽  
Total Darkness ◽  
Fixed Target ◽  
Ocular Reflex ◽  
Optokinetic Reflex ◽  
Vestibulo Ocular Reflex

To maintain clear vision, the images on the retina must remain reasonably stable. Head movements are generally dealt with successfully by counter-rotation of the eyes induced by the combined actions of the vestibulo-ocular reflex (VOR) and the optokinetic reflex. A problem of importance relates to the value of the so-called intrinsic gain of the VOR (VORG) in man, and how this gain is modulated to provide appropriate eye movements. We have studied these problems in two situations: 1. fixation of a stationary object of the visual space while the head moves; 2. fixation of an object moving with the head. These two situations were compared to a basic condition in which no visual target was allowed in order to induce “pure” VOR. Eye movements were recorded in seated subjects during stationary sinusoidal and transient rotations around the vertical axis. Subjects were in total darkness (DARK condition) and involved in mental arithmetic. Alternatively, they were provided with a small foveal target, either fixed with respect to earth (earth-fixed target: EFT condition), or moving with them (chair-fixed-target: CFT condition). The stationary rotation experiment was used as baseline for the ensuing experiment and yielded control data in agreement with the literature. In all 3 visual conditions, typical responses to transient rotations were rigorously identical during the first 200 ms. They showed, sequentially, a 16-ms delay of the eye behind the head and a rapid increase in eye velocity during 75 to 80 ms, after which the average VORG was 0.9 ± 0.15. During the following 50 to 100 ms, the gain remained around 0.9 in all three conditions. Beyond 200 ms, the VORG remained around 0.9 in DARK and increased slowly towards 1 or decreased towards zero in the EFT and CFT conditions, respectively. The time-course of the later events suggests that visual tracking mechanisms came into play to reduce retinal slip through smooth pursuit, and position error through saccades. Our data also show that in total darkness VORG is set to 0.9 in man. Lower values reported in the literature essentially reflect predictive properties of the vestibulo-ocular mechanism, particularly evident when the input signal is a sinewave.

scholarly journals Fast Recovery of the Amblyopic Eye Acuity of Kittens following Brief Exposure to Total Darkness Depends on the Fellow Eye

2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Donald E. Mitchell ◽  
Elise Aronitz ◽  
Philip Bobbie-Ansah ◽  
Nathan Crowder ◽  
Kevin R. Duffy
Keyword(s):  
Visual Acuity ◽  
Neural Activity ◽  
Early Life ◽  
Monocular Deprivation ◽  
Total Darkness ◽  
Visual Recovery ◽  
Fast Recovery ◽  
Fellow Eye ◽  
Neural Connections ◽  
Short Period

Recent studies conducted on kittens have revealed that the reduced visual acuity of the deprived eye following a short period of monocular deprivation imposed in early life is reversed quickly following a 10-day period spent in total darkness. This study explored the contribution of the fellow eye to the darkness-induced recovery of the acuity of the deprived eye. Upon emergence of kittens from darkness, the fellow eye was occluded for different lengths of time in order to investigate its effects on either the speed or the extent of the recovery of acuity of the deprived eye. Occlusion of the fellow eye for even a day immediately following the period spent in darkness blocked any recovery of the acuity of the deprived eye. Moreover, occlusion of the fellow eye two days after the period of darkness blocked any further visual recovery beyond that achieved in the short period when both eyes were open. The results imply that the darkness-induced recovery of the acuity of the deprived eye depends upon, and is guided by, neural activity in the mature neural connections previously established by the fellow eye.

Progressive changes in kitten striate cortex during monocular vision

1975 ◽  
Vol 38 (1) ◽  
pp. 26-32 ◽  
Author(s):  
C. R. Olson ◽  
R. D. Freeman
Keyword(s):  
Striate Cortex ◽  
Ocular Dominance ◽  
Monocular Vision ◽  
Single Units ◽  
Total Darkness ◽  
Severe Reduction ◽  
Different Ages ◽  
Eye Closure

Following initial rearing in either total darkness or normal illumination, kittens at different ages were subjected to right-eye closure and various periods of vision through the left eye. After the period of monocular vision, single units in striate cortex were tested for visual responsiveness through each eye. A severe reduction in the proportion of units responsive to the deprived eye occurred over the first few days of monocular vision. Functional abnormalities were variably present after 1 day, marked after 2.5 and 3.5 days, and complete after 10 days. Monocular vision produced very much the same effect on ocular dominance of striate units, provided age and duration of suture were identical, regardless of whether kittens had received prior dark- or light-rearing.

scholarly journals Orientation of Birds in Total Darkness

2008 ◽  
Vol 18 (8) ◽  
pp. 602-606 ◽  
Author(s):  
Katrin Stapput ◽  
Peter Thalau ◽  
Roswitha Wiltschko ◽  
Wolfgang Wiltschko
Keyword(s):  
Total Darkness

Kinetic Visual Imagery

1973 ◽  
Vol 37 (2) ◽  
pp. 423-425 ◽  
Author(s):  
Leonard Brosgole ◽  
Ann Neylon
Keyword(s):  
Visual Imagery ◽  
Total Darkness ◽  
Theoretical Considerations

Movement of the hand in total darkness by 7 sighted Ss gave rise to a sense of motion visually. This phenomenon was called kinetic visual imagery. The kinetic imagery was followed by the impression of being able to see the hand. The phenomenal visualization of the hand was clearly distinguished from the images of imagination, memory, and hallucination. The conditions necessary to produce the effect were described, along with theoretical considerations and implications.

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