Modified Staff-ball Technique for Densely Vegetated Areas

Staff-ball technique is a method used to measure the horizontal cover of vegetation in an area. For the occupancy study of two threatened avian species, a modified version of this method has been developed, employed and standardized in the field, to collect data that has been used as proxy for visibility of these species through the undergrowth in plantations within Western Ghats, India. This modified cost-effective technique is very useful in areas which are highly vegetated with undulating terrain, as opposed to its original use in grasslands. Two staffs and a ball are the main equipment used, wherein a central staff with ball is placed within vegetation and viewed using a peripheral staff at a fixed height from different points in an imaginary circle. A weakness of this technique is the difficulty in alignment with the central staff-ball, which may be rectified by the use of a laser rangefinder.

Modified Staff-ball Technique for Densely Vegetated Areas

Staff-ball technique is a method used to measure the horizontal cover of vegetation in an area. For the occupancy study of two threatened avian species, a modified version of this method has been developed, employed and standardized in the field, to collect data that has been used as proxy for visibility of these species through the undergrowth in plantations within Western Ghats, India. This modified cost-effective technique is very useful in areas which are highly vegetated with undulating terrain, as opposed to its original use in grasslands. Two staffs and a ball are the main equipment used, wherein a central staff with ball is placed within vegetation and viewed using a peripheral staff at a fixed height from different points in an imaginary circle. A weakness of this technique is the difficulty in alignment with the central staff-ball, which may be rectified by the use of a laser rangefinder.

New Problems of Descriptive Geometry

Complex geometry consists of Euclidean E-geometry (circle geometry) and pseudo-Euclidean M-geometry (hyperbola geometry). Each of them individually determines an open system in which a correctly posed problem may give no solution. Analytical geometry is an example of a closed system, in which the previously mentioned problem always gives a solution as a complex number, whose one of the parts may turn out to be zero. Development of imaginary solutions and imaginary figures is a new task for descriptive geometry. Degenerated conics and quadrics set up a new class of figures and a new class of descriptive geometry’s problems. For example, a null circle, null sphere, null cylinder, and a cone as a hyperboloid degenerated to an asymptote. The last ones necessarily lead to imaginary solutions in geometric operations. In this paper it has been shown that theorems formulated in one geometry are also valid in conjugate geometry as well, while the same figures of conjugated geometries visually look different. So imaginary points exist only by pairs, the imaginary circle is not round one, the centers of dissimilar circles’ similarity do not belong to the centerline and other examples. For solution, a number of problems on geometric relations, and operations with degenerated conics and quadrics, as well as several problems from 4D-geometry are proposed. Solutions for above mentioned problems are given in section 9. In this paper some examples of new problems for descriptive geometry have been considered. It has been shown that the new problems require access to a complex space. New figures consist of two parts, a real figure and a figure of its imaginary complement.

A Direct Assessment of the Role of Expectation in Inhibition of Return

An object hidden among distractors can be found more efficiently if previously searched locations are not reinspected. The inhibition-of-return (IOR) phenomenon indexes the tendency to avoid reinspections. Two accounts of IOR, that it is due to inhibition and that it is due to expectation, are generally regarded as incompatible. The relevant evidence to date, however, has been indirect: Inhibition or expectation has been inferred from response times or similar indirect measures. This article reports the first direct measure of IOR, obtained by asking observers to predict the location of the next target in a display containing eight possible locations on an imaginary circle. On any given trial, the previously cued location was chosen less frequently (impairment)—and the opposite location was chosen more frequently (facilitation)—than chance (choice of all other locations was at chance). The impairment is consistent with both inhibition and expectation accounts; the facilitation is consistent only with expectation accounts. This work also shows that inhibition and expectation are not necessarily incompatible: Implementing expectations may entail inhibiting previously cued locations.

The gap effect is exaggerated in parafovea

In central vision, the discrimination of colors lying on a tritan line is improved if a small gap is introduced between the two stimulus fields. Boynton et al. (1977) called this a “positive gap effect.” They found that the effect was weak or absent for discriminations based on the ratio of the signals of long-wave and middle-wave cones; and even for tritan stimuli, the gap effect was weakened when forced choice or brief durations were used. We here describe measurements of the gap effect in the parafovea. The stimuli were 1 deg of visual angle in width and were centered on an imaginary circle of radius 5 deg. They were brief (100 ms), and thresholds were measured with a spatial two-alternative forced choice. Under these conditions we find a clear gap effect, which is of similar magnitude for both the cardinal chromatic axes. It may be a chromatic analog of the crowding effect observed for parafoveal perception of form.

Parallel Processing of Luminance Steps in the Presence of Luminance Gradients

Some features of complex visual displays are analysed effortlessly and in parallel by the human visual system, without requiring scrutiny. Examples for such features are changes of luminance, colour, orientation, and movement. We measured thresholds as well as reaction times for the detection of abrupt spatial changes in luminance in the presence of luminance gradients, in order to evaluate the ability of the system to ignore such gradients. Stimuli were presented on a 20 inch monitor under control of a Silicon Graphics workstation. Luminance was calibrated by means of a photometer (Minolta). We presented between 4 and 14 rectangles simultaneously on a homogeneous dark background. Rectangles were arranged on an incomplete, imaginary circle around the fixation point and luminance changed stepwise from one rectangle to the next. Five observers had to indicate whether all luminance steps between the rectangles were subjectively equal or whether one luminance step was larger. Detection thresholds were determined for the larger step as a function of the small steps (‘base step size’) by means of an adaptive staircase procedure. The smallest luminance steps were detected when the base step size was zero and when only few rectangles were presented. Thresholds increased slightly with the number of rectangles displayed simultaneously, and to a greater extent (by up to a factor of 2) with increasing base step size. The results of all observers improved significantly through practice, by about a factor of 2. We conclude that the visual system is unable to completely eliminate gradients of luminance and to isolate sharp transitions in luminance.