S-cone discrimination for stimuli with spatial and temporal chromatic contrast

2008 ◽  
Vol 25 (3) ◽  
pp. 349-354 ◽  
Author(s):  
DINGCAI CAO ◽  
ANDREW J. ZELE ◽  
VIVIANNE C. SMITH ◽  
JOEL POKORNY
Keyword(s):  
Visual System ◽  
Natural Environment ◽  
Stimulus Condition ◽  
Spatial And Temporal Variation ◽  
Natural Scenes ◽  
Test Field ◽  
Temporal Contrast ◽  
Chromatic Contrast ◽  
Laboratory Methods ◽  
Spatio Temporal

In the natural environment, color discriminations are made within a rich context of spatial and temporal variation. In classical laboratory methods for studying chromatic discrimination, there is typically a border between the test and adapting fields that introduces a spatial chromatic contrast signal. Typically, the roles of spatial and temporal contrast on chromatic discrimination are not assessed in the laboratory approach. In this study, S-cone discrimination was measured using stimulus paradigms that controlled the level of spatio-temporal S-cone contrast between the tests and adapting fields. The results indicate that S-cone discrimination of chromaticity differences between a pedestal and adapting surround is equivalent for stimuli containing spatial, temporal or spatial-and-temporal chromatic contrast between the test field and the surround. For a stimulus condition that did not contain spatial or temporal contrast, the visual system adapted to the pedestal instead of the surround. The data are interpreted in terms of a model consistent with primate koniocellular pathway physiology. The paradigms provide an approach for studying the effects of spatial and temporal contrast on discrimination in natural scenes.

SIMULATION OF THE RETINA: A TOOL FOR VISUAL PROSTHESES

2010 ◽  
Vol 10 (04) ◽  
pp. 513-529
Author(s):  
BARTHÉLÉMY DURETTE ◽  
JEANNY HÉRAULT ◽  
DAVID ALLEYSSON
Keyword(s):  
Visual System ◽  
Visual Information ◽  
Vision System ◽  
Local Level ◽  
Photoreceptor Cells ◽  
Simulation Software ◽  
Natural Scenes ◽  
Temporal Properties ◽  
Spatio Temporal ◽  
High Level

To extract high-level information from natural scenes, the visual system has to cope with a wide variety of ambient lights, reflection properties of objects, spatio-temporal contexts, and geometrical complexity. By pre-processing the visual information, the retina plays a key role in the functioning of the whole visual system. It is crucial to reproduce such a pre-processing in artificial devices aiming at replacing or substituting the damaged vision system by artificial means. In this paper, we present a biologically plausible model of the retina at the cell level and its implementation as a real-time retinal simulation software. It features the non-uniform sampling of the visual information by the photoreceptor cells, the non-separable spatio-temporal properties of the retina, the subsequent generation of the Parvocellular and Magnocellular pathways, and the non-linear equalization of luminance and contrast at the local level. For each of these aspects, a description of the model is provided and illustrated. Their respective interest for the replacement or substitution of vision is discussed.

scholarly journals Spatial and temporal chromatic contrast: Effects on chromatic discrimination for stimuli varying in L- and M-cone excitation

2006 ◽  
Vol 23 (3-4) ◽  
pp. 495-501 ◽  
Author(s):  
ANDREW J. ZELE ◽  
VIVIANNE C. SMITH ◽  
JOEL POKORNY
Keyword(s):  
Test Field ◽  
Contrast Effects ◽  
Surrounding Area ◽  
Temporal Contrast ◽  
Chromatic Contrast ◽  
Parvocellular Pathway ◽  
Choice Procedure ◽  
Forced Choice Procedure ◽  
Temporal And Spatial ◽  
Contrast Discrimination

Discrimination for equiluminant chromatic stimuli that vary in L- and M-cone excitation depends on the chromaticity difference between the test field and the surrounding area. The current study investigated the effect of the proximity in space and time of a surround to the test field on chromatic contrast discrimination. The experimental paradigm isolated spatial, temporal, and spatial-and-temporal chromatic contrast effects on discrimination. Chromatic contrast discrimination thresholds were assessed by a four-alternative spatial forced-choice procedure. Stimuli were either metameric to the equal energy spectrum, or varied in L-cone activation along a line of constant S-cone activation. A model based on primate parvocellular pathway physiology described the data. Spatial and temporal contrast produced equivalent reductions in chromatic discriminability as the chromatic difference between the test and surround increased. For all test chromaticities, discrimination was best in the absence of chromatic contrast. Chromatic contrast discrimination is determined by either the spatial or temporal contrast component of the signal.

The Use of Visual Statistical Features in Empirical Aesthetics

2020 ◽  
Author(s):  
Daniel Graham
Keyword(s):  
Visual System ◽  
Natural Environment ◽  
Natural Images ◽  
Natural Scenes ◽  
Statistical Features ◽  
Statistical Structure ◽  
Future Directions ◽  
Visual Aesthetics ◽  
Processing Strategies ◽  
The Brain

Evolution generally demands that the brain take advantage of the probable statistical structure in the natural environment. Much research in recent decades has confirmed that regular statistical features in natural scenes—especially low-level spatial regularities—can help explain processing strategies in the human visual system. Basic statistical features in various classes of human-created images broadly match those found in natural scenes. Such regularities can be seen as evolved constraints on the visual structure of aesthetic images and therefore human visual aesthetics. Some researchers have also attempted to find statistical features whose variation from natural images is associated with variations in preference and other aesthetic variables. There is evidence that variations in statistical features of luminance and color could be exploited by the visual system in certain situations. However, there is much ambiguity and variability in most reported relationships between variations in image statistical features and variations in measures of human aesthetics. In contrast, basic statistical constraints that align with efficient visual system processing are almost never violated in aesthetic images. Put simply, statistical features may constrain but may not explain variability in visual aesthetics. The chapter concludes with an outlook on future directions for research.

scholarly journals Transformation from independent to integrative coding of multi-object arrangements in human visual cortex

2017 ◽  
Author(s):  
Daniel Kaiser ◽  
Marius V. Peelen
Keyword(s):  
Visual Cortex ◽  
Visual System ◽  
Activity Patterns ◽  
Spatial Arrangement ◽  
Living Room ◽  
Natural Scenes ◽  
Response Patterns ◽  
Object Representations ◽  
Individual Object ◽  
Object Coding

AbstractTo optimize processing, the human visual system utilizes regularities present in naturalistic visual input. One of these regularities is the relative position of objects in a scene (e.g., a sofa in front of a television), with behavioral research showing that regularly positioned objects are easier to perceive and to remember. Here we use fMRI to test how positional regularities are encoded in the visual system. Participants viewed pairs of objects that formed minimalistic two-object scenes (e.g., a “living room” consisting of a sofa and television) presented in their regularly experienced spatial arrangement or in an irregular arrangement (with interchanged positions). Additionally, single objects were presented centrally and in isolation. Multi-voxel activity patterns evoked by the object pairs were modeled as the average of the response patterns evoked by the two single objects forming the pair. In two experiments, this approximation in object-selective cortex was significantly less accurate for the regularly than the irregularly positioned pairs, indicating integration of individual object representations. More detailed analysis revealed a transition from independent to integrative coding along the posterior-anterior axis of the visual cortex, with the independent component (but not the integrative component) being almost perfectly predicted by object selectivity across the visual hierarchy. These results reveal a transitional stage between individual object and multi-object coding in visual cortex, providing a possible neural correlate of efficient processing of regularly positioned objects in natural scenes.

scholarly journals Spatio-temporal ecological and evolutionary dynamics in natural butterfly populations

2017 ◽  
Vol 40 ◽  
pp. 31-36
Author(s):  
Zachariah Gompert ◽  
Lauren Lucas
Keyword(s):  
Evolutionary Dynamics ◽  
Natural Populations ◽  
Distance Sampling ◽  
Spatial And Temporal Variation ◽  
Insect Community ◽  
Long Term Study ◽  
Greater Yellowstone Area ◽  
Genome Wide ◽  
Spatio Temporal

Long term studies of wild populations indicate that natural selection can cause rapid and dramatic changes in traits, with spatial and temporal variation in the strength of selection a critical driver of genetic variation in natural populations. In 2012, we began a long term study of genome-wide molecular evolution in populations of the butterfly Lycaeides ideas in the Greater Yellowstone Area (GYA). We aimed to quantify the role of environment-dependent selection on evolution in these populations. Building on previous work, in 2017 we collected new samples, incorporated distance sampling, and surveyed the insect community at each site. We also defined the habitat boundary at anew, eleventh site. Our preliminary analyses suggest that both genetic drift and selection are important drivers in this system.   Featured photo from Figure 1 in report.

Assessing variation in assemblages of large marine fauna off ocean beaches using drones

2020 ◽  
Vol 71 (1) ◽  
pp. 68 ◽  
Author(s):  
Brendan P. Kelaher ◽  
Andrew P. Colefax ◽  
Alejandro Tagliafico ◽  
Melanie J. Bishop ◽  
Anna Giles ◽  
...  
Keyword(s):  
Temporal Dynamics ◽  
Bottlenose Dolphins ◽  
Spatial And Temporal Variation ◽  
Marine Animals ◽  
Marine Fauna ◽  
South Wales ◽  
Carcharhinus Leucas ◽  
Spatio Temporal ◽  
Marine Wildlife

The turbulent waters off ocean beaches provide habitat for large marine fauna, including dolphins, sharks, rays, turtles and game fish. Although, historically, these assemblages have proven difficult to quantify, we used a new drone-based approach to assess spatial and temporal variation in assemblages of large marine fauna off four exposed beaches in New South Wales, Australia. In total, 4388 individual large marine animals were identified from 216 drone flights. The most common taxa, bottlenose dolphins (Tursiops spp.) and Australian cownose rays (Rhinoptera neglecta), occurred in 25.5 and 19.9% of flights respectively. White (Carcharodon carcharias), bull (Carcharhinus leucas) and other whaler (Carcharhinus spp.) sharks were observed in <1% of flights. There was significant variation in the structure of assemblages of large fauna among beaches, with those adjacent to riverine estuaries having greater richness and abundance of wildlife. Overall, drone surveys were successful in documenting the spatio-temporal dynamics of an impressive suite of large marine fauna. We contend that emerging drone technology can make a valuable contribution to the ecological information required to ensure the long-term sustainability of sandy-beach ecosystems and associated marine wildlife.

Spatial and temporal variation in morphology in Australian whistlers and shrike-thrushes: is climate change causing larger appendages?

2020 ◽  
Vol 130 (1) ◽  
pp. 101-113
Author(s):  
Isabelle R Onley ◽  
Janet L Gardner ◽  
Matthew R E Symonds
Keyword(s):  
Climate Change ◽  
Body Size ◽  
Temporal Variation ◽  
Relative Size ◽  
Bird Species ◽  
Spatial And Temporal Variation ◽  
Climatic Warming ◽  
Morphological Response ◽  
Allen’S Rule ◽  
Spatio Temporal

Abstract Allen’s rule is an ecogeographical pattern whereby the size of appendages of animals increases relative to body size in warmer climates in order to facilitate heat exchange and thermoregulation. Allen’s rule predicts that one consequence of a warming climate would be an increase in the relative size of appendages, and evidence from other bird species suggests that this might be occurring. Using measurements from museum specimens, we determined whether spatio-temporal variation in bills and legs of Australian Pachycephalidae species exhibits within-species trends consistent with Allen’s rule and increases in temperature attributable to climatic warming. We conducted regression model analyses relating appendage size to spatio-temporal variables, while controlling for body size. The relative bill size in four of the eight species was negatively associated with latitude. Tarsus length showed no significant trends consistent with Allen’s rule. No significant increases in appendage size were found over time. Although bill size in some species was positively correlated with warmer temperatures, the evidence was not substantial enough to suggest a morphological response to climatic warming. This study suggests that climate change is not currently driving adaptive change towards larger appendages in these species. We suggest that other adaptive mechanisms might be taking place.

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