scholarly journals Spatial and temporal frequency in figure-ground organization

1989 ◽  
Vol 45 (5) ◽  
pp. 395-403 ◽  
Author(s):  
Victor Klymenko ◽  
Naomi Weisstein ◽  
Richard Topolski ◽  
Cheng-Hong Hsieh
Keyword(s):  
Temporal Frequency ◽  
Ground Organization

Figure and Ground in Space and Time: 2. Frequency, Velocity, and Perceptual Organization

Perception ◽  
1989 ◽  
Vol 18 (5) ◽  
pp. 639-648 ◽  
Author(s):  
Victor Klymenko ◽  
Naomi Weisstein
Keyword(s):  
Spatial Frequency ◽  
Temporal Frequency ◽  
Sine Wave ◽  
Stationary Condition ◽  
Velocity Difference ◽  
Lower Spatial Frequency ◽  
Spatial Frequencies ◽  
Spatiotemporal Tuning ◽  
Sine Wave Gratings ◽  
Ground Organization

The figure – ground organization of an ambiguous bipartite pattern in which the two regions of the pattern contained sine-wave gratings which differed in spatial frequency was examined for two pairs of spatial frequencies: 1 and 4 cycles deg−1, and 1 and 8 cycles deg−1. The region of higher spatial frequency underwent contrast reversal at one of four rates: 0, 3.75, 7.5, or 15 Hz. The region of lower spatial frequency was equated with either the temporal frequency or the velocity of the grating of higher spatial frequency in three sets of conditions: one stationary condition, three in which temporal frequency was equated, and three in which velocity was equated. For the 1 and 4 cycles deg−1 pair, the region of lower spatial frequency tended to be seen as the background a higher percentage of the time. There were significant linear trends for the appearance as background of the region of lower spatial frequency with respect to the magnitude of the velocity difference between the two regions of the pattern. The faster the 1 cycle deg−1 grating moved with respect to the 4 cycles deg−1 grating, the higher the percentage of the time it was seen as the ground. The results for the 1 and 8 cycles deg−1 pair were in some cases unexpected in that the 8 cycles deg−1 grating was seen as the ground behind the 1 cycle deg−1 grating even though it was of a higher spatial frequency and moved at a slower velocity. The spatiotemporal tuning of the visual system is discussed.

Figure and Ground in Space and Time: 1. Temporal Response Surfaces of Perceptual Organization

Perception ◽  
1989 ◽  
Vol 18 (5) ◽  
pp. 627-637 ◽  
Author(s):  
Victor Klymenko ◽  
Naomi Weisstein
Keyword(s):  
Spatial Frequency ◽  
Temporal Frequency ◽  
Sine Wave ◽  
Response Surfaces ◽  
Viewing Time ◽  
Temporal Response ◽  
Frequency Condition ◽  
Spatial Frequencies ◽  
Sine Wave Gratings ◽  
Ground Organization

The figure – ground organization of an ambiguous bipartite pattern can be manipulated by altering the temporal-frequency content of the two regions of the pattern. Ambiguous patterns in which the two regions of each pattern contained sine-wave gratings of either 8, 4, 1, or 0.5 cycles deg−1 undergoing contrast reversal at rates of 0, 3.75, 7.5, or 15 Hz were tested for figure–ground organization under conditions of equated space-averaged and time-averaged luminance and perceived contrast. All combinations of temporal-frequency differences between the two regions were tested at each spatial frequency. The data are reported for two levels of temporal resolution (15 and 30 s). The pattern region with the relatively higher temporal frequency tended to be seen as the background a higher percentage of the viewing time. There were significant linear trends for the appearance as background of the region of higher temporal frequency with respect to the magnitude of the temporal-frequency difference between the two regions of each pattern for all spatial frequencies and data intervals except the final 15 s interval of the lowest (0.5 cycle deg−1) spatial-frequency condition.

Spatial and Temporal Frequency Tuning of Motion-in-Depth Aftereffect

2008 ◽  
Vol 128 (7) ◽  
pp. 1015-1022
Author(s):  
Sheng Ge ◽  
Makoto Ichikawa ◽  
Atsushi Osa ◽  
Keiji Iramina ◽  
Hidetoshi Miike
Keyword(s):  
Frequency Tuning ◽  
Temporal Frequency ◽  
Motion In Depth

scholarly journals Growing Stock Volume Retrieval from Single and Multi-Frequency Radar Backscatter

Forests ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 944
Author(s):  
Mihai A. Tanase ◽  
Ignacio Borlaf-Mena ◽  
Maurizio Santoro ◽  
Cristina Aponte ◽  
Gheorghe Marin ◽  
...  
Keyword(s):  
Learning Algorithm ◽  
Temporal Frequency ◽  
National Forest Inventory ◽  
Easy Access ◽  
Estimation Errors ◽  
Growing Stock ◽  
L Band ◽  
Stock Volume ◽  
Global Datasets ◽  
Relative Root

While products generated at global levels provide easy access to information on forest growing stock volume (GSV), their use at regional to national levels is limited by temporal frequency, spatial resolution, or unknown local errors that may be overcome through locally calibrated products. This study assessed the need, and utility, of developing locally calibrated GSV products for the Romanian forests. To this end, we used national forest inventory (NFI) permanent sampling plots with largely concurrent SAR datasets acquired at C- and L-bands to train and validate a machine learning algorithm. Different configurations of independent variables were evaluated to assess potential synergies between C- and L-band. The results show that GSV estimation errors at C- and L-band were rather similar, relative root mean squared errors (RelRMSE) around 55% for forests averaging over 450 m3 ha−1, while synergies between the two wavelengths were limited. Locally calibrated models improved GSV estimation by 14% when compared to values obtained from global datasets. However, even the locally calibrated models showed particularly large errors over low GSV intervals. Aggregating the results over larger areas considerably reduced (down to 25%) the relative estimation errors.

scholarly journals Status of Phenological Research Using Sentinel-2 Data: A Review

2020 ◽  
Vol 12 (17) ◽  
pp. 2760
Author(s):  
Gourav Misra ◽  
Fiona Cawkwell ◽  
Astrid Wingler
Keyword(s):  
Vegetation Index ◽  
Temporal Frequency ◽  
Short Wave ◽  
Current State ◽  
Red Edge ◽  
Natural Grasslands ◽  
Wide Range ◽  
Normalised Difference Vegetation Index ◽  
Satellite Sensors ◽  
Sentinel 2

Remote sensing of plant phenology as an indicator of climate change and for mapping land cover has received significant scientific interest in the past two decades. The advancing of spring events, the lengthening of the growing season, the shifting of tree lines, the decreasing sensitivity to warming and the uniformity of spring across elevations are a few of the important indicators of trends in phenology. The Sentinel-2 satellite sensors launched in June 2015 (A) and March 2017 (B), with their high temporal frequency and spatial resolution for improved land mapping missions, have contributed significantly to knowledge on vegetation over the last three years. However, despite the additional red-edge and short wave infra-red (SWIR) bands available on the Sentinel-2 multispectral instruments, with improved vegetation species detection capabilities, there has been very little research on their efficacy to track vegetation cover and its phenology. For example, out of approximately every four papers that analyse normalised difference vegetation index (NDVI) or enhanced vegetation index (EVI) derived from Sentinel-2 imagery, only one mentions either SWIR or the red-edge bands. Despite the short duration that the Sentinel-2 platforms have been operational, they have proved their potential in a wide range of phenological studies of crops, forests, natural grasslands, and other vegetated areas, and in particular through fusion of the data with those from other sensors, e.g., Sentinel-1, Landsat and MODIS. This review paper discusses the current state of vegetation phenology studies based on the first five years of Sentinel-2, their advantages, limitations, and the scope for future developments.

Spatio-temporal visual properties in the ascending tectofugal system

2010 ◽  
Vol 5 (1) ◽  
pp. 21-30 ◽  
Author(s):  
Alice Rokszin ◽  
Zita Márkus ◽  
Gábor Braunitzer ◽  
Antal Berényi ◽  
Marek Wypych ◽  
...  
Keyword(s):  
Visual Information ◽  
Frequency Tuning ◽  
Temporal Frequency ◽  
Neuronal Population ◽  
Neuronal Responses ◽  
Temporal Properties ◽  
Visual Receptive Field ◽  
Detailed Statistical Analysis ◽  
Spatio Temporal ◽  
Visual Properties

AbstractOur study compares the spatio-temporal visual receptive field properties of different subcortical stages of the ascending tectofugal visual system. Extracellular single-cell recordings were performed in the superficial (SCs) and intermediate (SCi) layers of the superior colliculus (SC), the suprageniculate nucleus (Sg) of the posterior thalamus and the caudate nucleus (CN) of halothane-anesthetized cats. Neuronal responses to drifting gratings of various spatial and temporal frequencies were recorded. The neurons of each structure responded optimally to low spatial and high temporal frequencies and displayed narrow spatial and temporal frequency tuning. The detailed statistical analysis revealed that according to its stimulus preferences the SCs has markedly different spatio-temporal properties from the homogeneous group formed by the SCi, Sg and CN. The SCs neurons preferred higher spatial and lower temporal frequencies and had broader spatial tuning than the other structures. In contrast to the SCs the visually active SCi, as well as the Sg and the CN neurons possessed consequently similar spatio-temporal preferences. These data support our hypothesis that the visually active SCi, Sg and CN neurons form a homogeneous neuronal population given a similar spatio-temporal frequency preference and a common function in processing of dynamic visual information.

Special Items: A Descriptive Analysis

2011 ◽  
Vol 25 (3) ◽  
pp. 511-536 ◽  
Author(s):  
Peter M. Johnson ◽  
Thomas J. Lopez ◽  
Juan Manuel Sanchez
Keyword(s):  
Firm Value ◽  
Temporal Frequency ◽  
Descriptive Analysis ◽  
Financial Statements ◽  
Comprehensive Analysis ◽  
The Other ◽  
Future Earnings ◽  
Special Items ◽  
Increasing Function ◽  
Frequency Magnitude

SYNOPSIS We provide a comprehensive analysis of special items and the characteristics of the firms that recognize them. Our analysis reveals that the temporal frequency, magnitude, and persistence of special items has increased significantly in the last 30 years, and that such increases are primarily driven by negative special items. More recently, however, our evidence is consistent with both a decline in frequency and magnitude of negative special items. On the other hand, we find that the frequency of reporting of positive special items, which remained relatively constant through 2002, has increased in more recent years. We also find strong evidence that subsequent special item reporting is an increasing function of the frequency of “prior” special item reporting. Using a random subsample of firms reporting special items, we document that 22 percent of the amounts reported in Compustat do not reconcile with the amounts reported on the firms' actual financial statements. Our comprehensive analysis should be of interest to regulators, academics, and managers interested in the implications of special items on firm-related consequences such as future earnings and firm value. Our examination can also serve as a catalyst for researchers interested in extending this important area of inquiry.

Apparent Velocity of Motion Aftereffects in Central and Peripheral Vision

Perception ◽  
1986 ◽  
Vol 15 (5) ◽  
pp. 603-612 ◽  
Author(s):  
Michael J Wright
Keyword(s):  
Visual Field ◽  
Time Course ◽  
Peripheral Vision ◽  
Temporal Frequency ◽  
Motion Aftereffect ◽  
Apparent Velocity ◽  
Real Motion ◽  
Temporal Decay ◽  
Spatial Grain ◽  
Motion Aftereffects

Adapting to a drifting grating (temporal frequency 4 Hz, contrast 0.4) in the periphery gave rise to a motion aftereffect (MAE) when the grating was stopped. A standard unadapted foveal grating was matched to the apparent velocity of the MAE, and the matching velocity was approximately constant regardless of the visual field position and spatial frequency of the adapting grating. On the other hand, when the MAE was measured by nulling with real motion of the test grating, nulling velocity was found to increase with eccentricity. The nulling velocity was constant when scaled to compensate for changes in the spatial ‘grain’ of the visual field. Thus apparent velocity of MAE is constant across the visual field, but requires a greater velocity of real motion to cancel it in the periphery. This confirms that the mechanism underlying MAE is spatially-scaled with eccentricity, but temporally homogeneous. A further indication of temporal homogeneity is that when MAE is tracked, by matching or by nulling, the time course of temporal decay of the aftereffect is similar for central and for peripheral stimuli.

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