scholarly journals Ocular interaction in its relation to measurements of brightness threshold

1940 ◽  
Vol 128 (853) ◽  
pp. 552-559 ◽  
Keyword(s):  
Steady State ◽  
Visual Field ◽  
Light Stimulus ◽  
Visual Fields ◽  
Maximum Size ◽  
The Other ◽  
Great Care ◽  
High Brightness ◽  
Maxwellian View ◽  
Better Than

The question to which an answer is here sought is how far, if at all, the sensations from the two eyes of a subject add together in the measurement of brightness threshold. That is, do two eyes see better than one, or only equally well? Two aspects of the question have been investigated; first, the measurement of brightness threshold when the eyes are in equilibrium with a visual field of fixed brightness (steady state of adaptation); secondly, the measurement of the variation of brightness threshold with time after cutting off a conditioning field of more or less high brightness (changing state of adaptation). In an investigation of this kind the action of the eye pupils must be eliminated. This was done by the use of Maxwellian view for all visual fields, though the method of fixing the eye pupil at its maximum size by a mydriatic could also be used (Lythgoe and Phillips 1938). It was felt, however, that the Maxwellian view method was more generally satisfactory, though it necessitated more complicated apparatus and great care in equalizing the beams entering the two eyes. Consideration is also given to the effect of a light stimulus applied to one eye on threshold measurements made with the other eye.

Blindsight in Subjects with Homonymous Visual Field Defects

1999 ◽  
Vol 11 (1) ◽  
pp. 52-66 ◽  
Author(s):  
Heinz Schärli ◽  
Alison M. Harman ◽  
John H. Hogben
Keyword(s):  
Visual Field ◽  
Visual Fields ◽  
Neural Mechanism ◽  
Stray Light ◽  
Visual Field Defects ◽  
Optic Radiation ◽  
Visual Ability ◽  
Choice Tests ◽  
Visual Areas ◽  
Better Than

Brain damage in the visual system can lead to apparently blind visual areas. However, more elaborate testing indicates that some visual ability may still exist for specific stimuli in the otherwise blind regions. This phenomenon is called “blindsight” if subjects report no conscious awareness of visual stimuli but when forced to guess, nevertheless perform better than chance. It has mainly been suggested that secondary visual pathways are responsible for this phenomenon. However, no published study has clearly shown the neural mechanism responsible for blindsight. Furthermore, experimental artifacts may have been responsible for the appearance of the phenomenon in some subjects. In the present study, the visual fields of nine subjects were mapped and residual visual performance was examined in many areas using three different experimental procedures. Artifacts such as stray light or eye movements were well controlled. In addition, confidence ratings were required after each trial in the forced-choice tests. The results show that only one subject with a lesion in the optic radiation had blindsight in two discrete areas of the affected visual field. Spared optic radiation fibers of the main (primary) geniculo-striate visual pathway were most likely to account for this finding.

Mean alveolar gases and alveolar-arterial gradients in pulmonary patients

1979 ◽  
Vol 46 (3) ◽  
pp. 534-540 ◽  
Author(s):  
U. C. Luft ◽  
J. A. Loeppky ◽  
E. M. Mostyn
Keyword(s):  
Steady State ◽  
Mass Spectrometer ◽  
Dead Space ◽  
Best Approximation ◽  
The Other ◽  
Mean Values ◽  
The Best Approximation ◽  
The Mean ◽  
End Tidal ◽  
Better Than

In view of uncertainties about the best way to estimate mean alveolar gases in patients with ventilation-perfusion inequalities, three different methods were evaluated on 54 patients. 1) O2 and CO2 were recorded by mass spectrometer on an O2 (x)-CO2 (y) diagram. The coordinates at the intersect of the expiratory record with the mixed expired R line (RE) ives the mean alveolar values (PAo2 and PAco2. 2)pa'co2 was calculated with the Bohr equation using a predicted anatomic dead space and PA'o2 was derived with the alveolar equation. 3) End-tidal (ET) P02 were averaged over 1 min at rest in steady state. Mean RET calculated from 3 was identical with RE. Mean values for PAco2, PA'CO2. and PETco2 differed by less that 1 Torr, but the variance was least with the end-tidal method. There was a highly significant correlation between delta aAPco2 using PETco2 and VD/VT, better than with either of the other methods. The end-tidal measurement appears to give the best approximation of mean alveolar gas in pulmonary patients.

Left—Right Visual Field Asymmetry in Bistable Motion Perception

Perception ◽  
1988 ◽  
Vol 17 (6) ◽  
pp. 721-727 ◽  
Author(s):  
Clara Casco ◽  
Donatella Spinelli
Keyword(s):  
Visual Field ◽  
Visual Fields ◽  
Stimulus Presentation ◽  
The Other ◽  
Right Visual Field ◽  
The Third ◽  
Group Movement ◽  
Left Handed ◽  
Left And Right ◽  
Left Right Asymmetry

Twelve observers viewed two alternating frames, each consisting of three rectangular bars which were displaced laterally by one cycle in one frame with respect to the other. At long interframe intervals (IFIs) observers perceived a group of three elements moving as a whole (group movement), whereas with IFIs shorter than 40–60 ms the overlapping elements in each frame appeared stationary while the third element appeared to move from one end of the display to the other (end-to-end movement). The percentage of group movement responses in central viewing was compared to those obtained for stimulus presentation in the left and right visual fields (4 deg eccentricity), for opposite horizontal directions of motion. All ten right-handed subjects showed a left-field advantage in sensitivity to group movement. The two left-handed subjects showed a similar advantage in sensitivity with right-field presentation. The effects of monocular vision, hand used in the task, spatial frequency, and contrast on visual field asymmetry were all investigated in two right-handed subjects. None of these factors affected the left—right asymmetry.

Visual field inhomogeneous in brain-computer interfaces based on rapid serial visual presentation

2022 ◽  
Author(s):  
Shangen Zhang ◽  
Xiaogang Chen ◽  
Yijun Wang ◽  
Baolin Liu ◽  
Xiaorong Gao
Keyword(s):  
Visual Field ◽  
Visual Attention ◽  
Rapid Serial Visual Presentation ◽  
Visual Fields ◽  
Visual Presentation ◽  
Lower Visual Field ◽  
Horizontal Meridian ◽  
Vertical Meridian ◽  
Upper Visual Field ◽  
Better Than

Abstract Objective. Visual attention is not homogeneous across the visual field, while how to mine the effective EEG characteristics that are sensitive to the inhomogeneous of visual attention and further explore applications such as the performance of brain-computer interface (BCI) are still distressing explorative scientists. Approach. Images were encoded into a rapid serial visual presentation (RSVP) paradigm, and were presented in three visuospatial patterns (central, left/right, upper/lower) at the stimulation frequencies of 10Hz, 15Hz and 20Hz. The comparisons among different visual fields were conducted in the dimensions of subjective behavioral and EEG characteristics. Furthermore, the effective features (e.g. SSVEP, N2pc and P300) that sensitive to visual-field asymmetry were also explored. Results. The visual fields had significant influences on the performance of RSVP target detection, in which the performance of central was better than that of peripheral visual field, the performance of horizontal meridian was better than that of vertical meridian, the performance of left visual field was better than that of right visual field, and the performance of upper visual field was better than that of lower visual field. Furthermore, stimuli of different visual fields had significant effects on the spatial distributions of EEG, in which N2pc and P300 showed left-right asymmetry in occipital and frontal regions, respectively. In addition, the evidences of SSVEP characteristics indicated that there was obvious overlap of visual fields on the horizontal meridian, but not on the vertical meridian. Significance. The conclusions of this study provide insights into the relationship between visual field inhomogeneous and EEG characteristics. In addition, this study has the potential to achieve precise positioning of the target's spatial orientation in RSVP-BCIs.

scholarly journals Functional visual fields: a cross-sectional UK study to determine which visual field paradigms best reflect difficulty with mobility function

BMJ Open ◽  
2017 ◽  
Vol 7 (11) ◽  
pp. e018831
Author(s):  
Hikmat Subhi ◽  
Keziah Latham ◽  
Joy Myint ◽  
Michael Crossland
Keyword(s):  
Visual Field ◽  
Visual Fields ◽  
Roc Curves ◽  
Secondary Outcome ◽  
Patient Acceptability ◽  
Cross Sectional ◽  
Mobility Function ◽  
Kinetic Assessment ◽  
Better Than ◽  
Mobility Difficulty

ObjectivesTo develop an appropriate method of assessing visual field (VF) loss which reflects its functional consequences, this study aims to determine which method(s) of assessing VF best reflect mobility difficulty.SettingThis cross-sectional observational study took place within a single primary care setting. Participants attended a single session at a University Eye Clinic, Cambridge, UK, with data collected by a single researcher (HS), a qualified optometrist.Participants50 adult participants with peripheral field impairment were recruited for this study. Individuals with conditions not primarily affecting peripheral visual function, such as macular degeneration, were excluded from the study.Primary and secondary outcome measuresParticipants undertook three custom and one standard binocular VF tests assessing VF to 60°, and also integrated monocular threshold 24–2 visual fields (IVF). Primary VF outcomes were average mean threshold, percentage of stimuli seen and VF area. VF outcomes were compared with self-reported mobility function assessed with the Independent Mobility Questionnaire, and time taken and patient acceptability were also considered. Receiver operating characteristic (ROC) curves determined which tests best predicted difficulty with mobility tasks.ResultsGreater VF loss was associated with greater self-reported mobility difficulty with all field paradigms (R20.38–0.48, all P<0.001). All four binocular tests were better than the IVF at predicting difficulty with at least three mobility tasks in ROC analysis. Mean duration of the tests ranged from 1 min 26 s (±9 s) for kinetic assessment to 9 min 23 s (±24 s) for IVF.ConclusionsThe binocular VF tests extending to 60° eccentricity all relate similarly to self-reported mobility function, and slightly better than integrated monocular VFs. A kinetic assessment of VF area is quicker than and as effective at predicting mobility function as static threshold assessment.

scholarly journals A.02 Assessing visual functions in children with an optic pathway glioma using steady-state visual evoked potentials

2017 ◽  
Vol 44 (S2) ◽  
pp. S8-S9
Author(s):  
S Zakaib Rassi ◽  
L Ospina ◽  
Y Samson ◽  
D Saint-Amour ◽  
S Perreault
Keyword(s):  
Steady State ◽  
Visual Field ◽  
Evoked Potentials ◽  
Visual Evoked Potentials ◽  
Visual Fields ◽  
Optic Pathway Glioma ◽  
Optic Pathway ◽  
Central Visual Field ◽  
Non Invasive ◽  
Visual Evoked

Background: Optic pathway gliomas (OPG) represent 5% of pediatric brain tumours. Visual acuity measures are used to evaluate treatment response. Current clinical tests to assess visual field integrity are subjective and require verbal cooperation. Thus, the objective of this study was to evaluate the clinical effectiveness of Steady State Visual Evoked Potentials (ssVEPs) to measure visual field integrity in a non-invasive and objective manner. Methods: SsVEPs were obtained in ten children with OPGs and 42 controls ages 3 to 21. The stimuli consisted of two circular dartboard patterns stimulating fovea and peripheral zones at two flickering frequencies, so that central and peripheral visual fields could be assessed simultaneously. The test consisted of eight stimuli presentations of 10 seconds. Results: Results indicate significantly lower ssVEP amplitudes in children with OPGs (M=2.52, 95% CI [1.13, 3.92]) compared to controls (M=13.26, 95% CI [8.85, 17.67]) in the central visual field (p=.021). However, no between group differences were detected in the peripheral field (p >.05). There were no significant differences between age groups (p>0.05). Conclusions: This objective, affordable, and non-invasive method appears to be effective in detecting central visual field deficits in children with OPGs rapidly and consistently.

Closing the GAP—A 5Å Scanning Microscope

1969 ◽  
Vol 27 ◽  
pp. 6-7
Author(s):  
A. V. Crewe
Keyword(s):  
Normal Form ◽  
The Other ◽  
Resolving Power ◽  
Scanning Microscope ◽  
Conventional Microscope ◽  
Other Hand ◽  
Closing The Gap ◽  
Thermal Sources ◽  
Better Than ◽  
Transmission Microscope

We have become accustomed to differentiating between the scanning microscope and the conventional transmission microscope according to the resolving power which the two instruments offer. The conventional microscope is capable of a point resolution of a few angstroms and line resolutions of periodic objects of about 1Å. On the other hand, the scanning microscope, in its normal form, is not ordinarily capable of a point resolution better than 100Å. Upon examining reasons for the 100Å limitation, it becomes clear that this is based more on tradition than reason, and in particular, it is a condition imposed upon the microscope by adherence to thermal sources of electrons.

Practical Correction of Three Fold Astigmatism in the Philips CM TEM

1996 ◽  
Vol 54 ◽  
pp. 418-419
Author(s):  
Arno J. Bleeker ◽  
Mark H.F. Overwijk ◽  
Max T. Otten
Keyword(s):  
Optical Properties ◽  
Phase Contrast ◽  
The Other ◽  
Objective Lens ◽  
Symmetric Part ◽  
A Posteriori ◽  
Contrast Transfer Function ◽  
High Brightness ◽  
Rotationally Symmetric ◽  
Brightness Field

With the improvement of the optical properties of the modern TEM objective lenses the point resolution is pushed beyond 0.2 nm. The objective lens of the CM300 UltraTwin combines a Cs of 0. 65 mm with a Cc of 1.4 mm. At 300 kV this results in a point resolution of 0.17 nm. Together with a high-brightness field-emission gun with an energy spread of 0.8 eV the information limit is pushed down to 0.1 nm. The rotationally symmetric part of the phase contrast transfer function (pctf), whose first zero at Scherzer focus determines the point resolution, is mainly determined by the Cs and defocus. Apart from the rotationally symmetric part there is also the non-rotationally symmetric part of the pctf. Here the main contributors are not only two-fold astigmatism and beam tilt but also three-fold astigmatism. The two-fold astigmatism together with the beam tilt can be corrected in a straight-forward way using the coma-free alignment and the objective stigmator. However, this only works well when the coefficient of three-fold astigmatism is negligible compared to the other aberration coefficients. Unfortunately this is not generally the case with the modern high-resolution objective lenses. Measurements done at a CM300 SuperTwin FEG showed a three fold-astigmatism of 1100 nm which is consistent with measurements done by others. A three-fold astigmatism of 1000 nm already sinificantly influences the image at a spatial frequency corresponding to 0.2 nm which is even above the point resolution of the objective lens. In principle it is possible to correct for the three-fold astigmatism a posteriori when through-focus series are taken or when off-axis holography is employed. This is, however not possible for single images. The only possibility is then to correct for the three-fold astigmatism in the microscope by the addition of a hexapole corrector near the objective lens.

Optical characteristics of the hitachi HF-2000 cold field-emission TEM

1993 ◽  
Vol 51 ◽  
pp. 1076-1077
Author(s):  
L. F. Allard ◽  
E. Völkl ◽  
T. A. Nolan
Keyword(s):  
Field Emission ◽  
Recent Literature ◽  
Electron Gun ◽  
High Brightness ◽  
Condenser Lens ◽  
Illumination System ◽  
High Resolution Images ◽  
Imaging Mode ◽  
Better Than ◽  
Illuminating System

The illumination system of the cold field emission (CFE) Hitachi HF-2000 TEM operates with a single condenser lens in normal imaging mode, and with a second condenser lens excited to give the ultra-fine 1 nm probe for microanalysis. The electron gun provides a guaranteed high brightness of better than 7×l08 A/cm2/sr, more than twice the guaranteed brightness of Schottky emission guns. There have been several articles in the recent literature (e.g. refs.) which claim that the geometry of this illumination system yields a total current which is so low that when the beam is spread at low magnifications (say 10 kX), the operator must “keep his eyes glued to the binoculars” in order to see the image. It is also claimed that this illuminating system produces an isoplanatic patch (the area over which image character does not vary significantly) at high magnification which is so small that the instrument is ineffective for recording high resolution images.

Fidelity of J1269 and J24523

2007 ◽  
Vol 35 (2) ◽  
pp. 94-117 ◽  
Author(s):  
James A. Popio ◽  
John R. Luchini
Keyword(s):  
Steady State ◽  
Rolling Resistance ◽  
Test Methods ◽  
The Other ◽  
Reference Condition ◽  
Test Standards

Abstract This study compares data from the two Society of Automotive Engineers test methods for rolling resistance: J-2452 (Stepwise Coast-Down) and J-1269 (Equilibrium) steady state. The ability of the two methods to evaluate tires was examined by collecting data for 12 tires. The data were analyzed and the data showed that the two methods ranked the tires the same after the data were regressed and the rolling resistance magnitude was calculated at the Standard Reference Condition. In addition, analysis of the two methods using this matched set of testing provided an opportunity to evaluate each of these test standards against the other. It was observed that each test has merits absent from the other.

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