scholarly journals Cryptic cuckoo eggs hide from competing cuckoos

2014 ◽  
Vol 281 (1792) ◽  
pp. 20141014 ◽  
Author(s):  
Ros Gloag ◽  
Laurie-Anne Keller ◽  
Naomi E. Langmore
Keyword(s):  
Selective Agent ◽  
High Luminance ◽  
Arms Races ◽  
Low Luminance ◽  
Egg Mimicry ◽  
Egg Removal ◽  
Egg Crypsis

Interspecific arms races between cuckoos and their hosts have produced remarkable examples of mimicry, with parasite eggs evolving to match host egg appearance and so evade removal by hosts. Certain bronze-cuckoo species, however, lay eggs that are cryptic rather than mimetic. These eggs are coated in a low luminance pigment that camouflages them within the dark interiors of hosts' nests. We investigated whether cuckoo egg crypsis is likely to have arisen from the same coevolutionary processes known to favour egg mimicry. We added high and low luminance-painted eggs to the nests of large-billed gerygones ( Gerygone magnirostris ), a host of the little bronze-cuckoo ( Chalcites minutillus ). Gerygones rarely rejected either egg type, and did not reject natural cuckoo eggs. Cuckoos, by contrast, regularly removed an egg from clutches before laying their own and were five times more likely to remove a high luminance model than its low luminance counterpart. Given that we found one-third of all parasitized nests were exploited by multiple cuckoos, our results suggest that competition between cuckoos has been the key selective agent for egg crypsis. In such intraspecific arms races, crypsis may be favoured over mimicry because it can reduce the risk of egg removal to levels below chance.

Subjective and pupil responses to discomfort glare from small, high-luminance light sources

2018 ◽  
Vol 51 (4) ◽  
pp. 592-611 ◽  
Author(s):  
Y Tyukhova ◽  
CE Waters
Keyword(s):  
Pupil Size ◽  
Rating Scale ◽  
Light Sources ◽  
Background Luminance ◽  
High Luminance ◽  
Low Luminance ◽  
Point Rating Scale ◽  
Main Effect ◽  
Discomfort Glare ◽  
Relative Change

This study examined human subjective and pupil responses to small, high-luminance light sources seen against low-luminance backgrounds. Subjective judgements of glare using a seven-point rating scale and the change in pupil diameters following exposure to glare of 47 subjects were measured during evaluation of 36 conditions comprising three glare source luminances (20,000; 205,000; 750,000 cd/m2), two source positions (0°, 10°), two source sizes (10−5, 10−4 sr) and three background luminances (0.03; 0.3; 1 cd/m2). Data analysis suggests that the relative pupil size is correlated with subjective responses to discomfort glare to some extent (r = 0.659). Analysis of variance of relative pupil size measurements demonstrates a significant main effect of the background luminance suggesting that when the background luminance decreases, the relative pupil size increases. Relative pupil size shows the same trend as the relative change in illuminance at the eyes and the discomfort glare perception.

scholarly journals Brood parasitism selects for no defence in a cuckoo host

2011 ◽  
Vol 278 (1719) ◽  
pp. 2777-2783 ◽  
Author(s):  
Oliver Krüger
Keyword(s):  
Brood Parasitism ◽  
Adaptive Behaviour ◽  
Arms Races ◽  
Defence Behaviour ◽  
Egg Mimicry ◽  
Evolutionary Lag ◽  
Thick Shells ◽  
Defence Strategies ◽  
Coevolutionary Arms Race ◽  
Parasite Avoidance

In coevolutionary arms races, like between cuckoos and their hosts, it is easy to understand why the host is under selection favouring anti-parasitism behaviour, such as egg rejection, which can lead to parasites evolving remarkable adaptations to ‘trick’ their host, such as mimetic eggs. But what about cases where the cuckoo egg is not mimetic and where the host does not act against it? Classically, such apparently non-adaptive behaviour is put down to evolutionary lag: given enough time, egg mimicry and parasite avoidance strategies will evolve. An alternative is that absence of egg mimicry and of anti-parasite behaviour is stable. Such stability is at first sight highly paradoxical. I show, using both field and experimental data to parametrize a simulation model, that the absence of defence behaviour by Cape bulbuls ( Pycnonotus capensis ) against parasitic eggs of the Jacobin cuckoo ( Clamator jacobinus ) is optimal behaviour. The cuckoo has evolved massive eggs (double the size of bulbul eggs) with thick shells, making it very hard or impossible for the host to eject the cuckoo egg. The host could still avoid brood parasitism by nest desertion. However, higher predation and parasitism risks later in the season makes desertion more costly than accepting the cuckoo egg, a strategy aided by the fact that many cuckoo eggs are incorrectly timed, so do not hatch in time and hence do not reduce host fitness to zero. Selection will therefore prevent the continuation of any coevolutionary arms race. Non-mimetic eggs and absence of defence strategies against cuckoo eggs will be the stable, if at first sight paradoxical, result.

Transient—Sustained Input to Directionally Selective Motion Mechanisms

Perception ◽  
1996 ◽  
Vol 25 (11) ◽  
pp. 1263-1280 ◽  
Author(s):  
Walter F Bischof ◽  
Adriane E Seiffert ◽  
Vincent Di Lollo
Keyword(s):  
Apparent Motion ◽  
Motion Sensor ◽  
Motion Sensors ◽  
Single Image ◽  
High Luminance ◽  
New Model ◽  
Low Luminance ◽  
Directional Motion ◽  
Combined Images ◽  
Psychophysical Studies

The characteristics of the sustained input to directionally selective motion sensors were examined in three human psychophysical studies on directional-motion discrimination. Apparent motion was produced by displaying a group of dots in two frames (F1 and F2), where F2 was a translated version of F1. All stimuli included parts that contained both F1 and F2 (combined images) and parts containing only F1 or F2 (single images). All displays began with a single image (F1), continued with the combined image, and ended with F2. Six durations of single and of combined images (10, 20, 40, 80, 160, or 320 ms) were crossed factorially. As the duration of the single image was increased, perception of directional motion first improved, and then declined at longer durations. This outcome contrasted with the monotonic increment obtained in earlier studies under low-luminance conditions. To account for the entire pattern of results, earlier models of the Reichardt motion sensor were modified so as to include a mixed transient – sustained input to one of the filters of the sensor. Predictions from the new model were tested and confirmed in two experiments carried out under both low-luminance and high-luminance viewing conditions.

Color Matches and Discrimination Functions for Selected Hues

1983 ◽  
Vol 27 (3) ◽  
pp. 249-253 ◽  
Author(s):  
Frank E. Ward ◽  
Fran Greene ◽  
Wayne Martin
Keyword(s):  
Color Discrimination ◽  
Color Matching ◽  
Ambient Illumination ◽  
Dominant Wavelength ◽  
Empirical Relationships ◽  
High Luminance ◽  
Low Luminance ◽  
Small Test ◽  
Space Data ◽  
High Adaptation

The purpose of this research was to investigate color discrimination under conditions of ambient illumination that may reduce CRT display saturation and contrast. Our research measured both the variability of color matching and the offsets from a match necessary for a 100% discrimination difference. We did this for four dominant wavelengths each at five saturation levels. Our subjects were tested at low, medium, and high adaptation levels for both large and small test stimulus sizes. In general, our results for the low luminance color matching conditions are in agreement with the published literature. For the high luminance and small field conditions, our data suggest that color discrimination should not be predicted from the CIE Uniform Chromaticity Space data. Color discrimination varies dramatically with dominant wavelength; reds and greens are more difficult to discriminate than yellows and yellow-greens. Empirical relationships that describe the discrimination are presented.

scholarly journals Color from Motion: Dichoptic Activation and a Possible Role in Breaking Camouflage

Perception ◽  
1997 ◽  
Vol 26 (11) ◽  
pp. 1367-1380 ◽  
Author(s):  
Carol M Cicerone ◽  
Donald D Hoffman
Keyword(s):  
Visual System ◽  
Apparent Motion ◽  
Stimulus Display ◽  
Background Field ◽  
The Other ◽  
White Background ◽  
High Luminance ◽  
Low Luminance ◽  
Random Placement ◽  
Multiple Frames

‘Color from motion’ describes the perception of a spread of subjective color over achromatic regions seen as moving. The effect can be produced in a display of multiple frames shown in quick succession, each frame consisting of a fixed, random placement of colored dots on a high-luminance white background with color assignments of some dots, but not dot locations, changing from frame to frame. Evidence is presented that the perception of apparent motion and the spread of subjective color can be activated by binocular combination of disjoint signals to each eye. The dichoptic presentation of every odd-numbered frame of the full stimulus sequence presented to one eye and, out of phase, every even-numbered frame to the other eye produces a compelling perception of color from motion equal to that seen with the full sequence presented to each eye alone. This is consistent with the idea that color from motion is regulated in sites at or beyond the convergence of monocular pathways. When the background field in the stimulus display is of low luminance, an amodally complete object, fully colored and matching the dots defining the moving region in hue and saturation, is seen to move behind a partially occluding screen. Observers do not perceive such an object in still view. Hence, color from motion can be used by the visual system to produce amodal completion, which suggests that it may play a role in enhancing the visibility of camouflaged objects.

Text Font Affects Reading Speed at a Low Luminance but Not at a High Luminance

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 51-51
Author(s):  
D Yager ◽  
K Aquilante ◽  
R Plass
Keyword(s):  
Eye Movements ◽  
Visual Field ◽  
Low Vision ◽  
Reading Speed ◽  
Visual Presentation ◽  
High Luminance ◽  
Low Luminance ◽  
Significant Difference ◽  
Simulation Results ◽  
Parameter Values

We are beginning a series of studies in which we shall investigate which characteristics of text fonts may be successful in allowing text to be read with different kinds of degradations that may be experienced by low-vision patients. As a first attempt to simulate one of the problems that certain patients might have, we measured reading speeds with two proportionally spaced fonts at a high photopic luminance (146 cd m−2) and at a very low luminance (0.146 cd m−2). We used the RSVP (rapid serial visual presentation) reading method, which eliminates the need for scanning eye movements. The two fonts were ‘Swiss’, a simple sans-serif font, and ‘Dutch’, a serif font similar to Times Roman, both presented at the 20/80 size; letters were white on black, with a contrast of 0.94. Subjects were young, normally sighted high-school and optometry-college students. The reading speed results from 47 subjects were as follows, for four conditions: high luminance, Swiss 531 and Dutch 540 words min−1; low luminance, Swiss 479 and Dutch 429 words min−1. At the high luminance, there is no significant difference between reading rates. There is a significant advantage for the Swiss font at the low luminance: p=0.005. There may be a significant difference in reading speed with different fonts when the patient's perceptions are degraded by disease and/or aging processes. Other parameters to be investigated with this method include contrast, size, blur, and visual field position. The simulation results will suggest parameter values to test on low-vision patients.

scholarly journals How to evade a coevolving brood parasite: egg discrimination versus egg variability as host defences

2011 ◽  
Vol 278 (1724) ◽  
pp. 3566-3573 ◽  
Author(s):  
Claire N. Spottiswoode ◽  
Martin Stevens
Keyword(s):  
Visual Cues ◽  
Field Experiments ◽  
Brood Parasite ◽  
Arms Races ◽  
Egg Discrimination ◽  
Fitness Advantage ◽  
Evolutionary Trajectories ◽  
Negative Frequency Dependent Selection ◽  
Egg Mimicry ◽  
Host Rejection

Arms races between avian brood parasites and their hosts often result in parasitic mimicry of host eggs, to evade rejection. Once egg mimicry has evolved, host defences could escalate in two ways: (i) hosts could improve their level of egg discrimination; and (ii) negative frequency-dependent selection could generate increased variation in egg appearance (polymorphism) among individuals. Proficiency in one defence might reduce selection on the other, while a combination of the two should enable successful rejection of parasitic eggs. We compared three highly variable host species of the Afrotropical cuckoo finch Anomalospiza imberbis , using egg rejection experiments and modelling of avian colour and pattern vision. We show that each differed in their level of polymorphism, in the visual cues they used to reject foreign eggs, and in their degree of discrimination. The most polymorphic host had the crudest discrimination, whereas the least polymorphic was most discriminating. The third species, not currently parasitized, was intermediate for both defences. A model simulating parasitic laying and host rejection behaviour based on the field experiments showed that the two host strategies result in approximately the same fitness advantage to hosts. Thus, neither strategy is superior, but rather they reflect alternative potential evolutionary trajectories.

Estimating the Position of Simulated Phosphenes Using a Tactile Guide

2011 ◽  
Vol 24 (2) ◽  
pp. 125-140 ◽  
Author(s):  
Jin Fan ◽  
Jing Wang ◽  
Qiushi Ren ◽  
Yanyu Lu ◽  
Ying Zhao ◽  
...  
Keyword(s):  
Visual Information ◽  
Visual Prosthesis ◽  
Average Error ◽  
Simulation Studies ◽  
High Luminance ◽  
Flickering Light ◽  
Low Luminance ◽  
Polar Coordinate ◽  
Repeated Training ◽  
Better Than

AbstractA visual prosthesis provides usable visual information to the patient in the form of phosphenes, that is, punctate photic sensations seen after electrical stimulation. Stimulation via different electrodes results in phosphenes in different positions within the visual field. Simulation studies can provide data on the possible limitations of prosthetic stimulation. We used a head mounted screen to monocularly present constant or flickering light spots of different sizes, or luminance to normally sighted subjects. Subjects were asked to judge the location of the spots using a polar coordinate tactile guide; positioning average error and dispersion were analyzed. With the increase of eccentricity, the positioning average error and dispersion were also increased. The performances under large, stable and high luminance conditions were better than that under small, flickering and low luminance conditions, respectively. Repeated training sessions were shown to significantly improve the positioning performance.

Resolution of binocular rivalry: Perceptual misbinding of color

2006 ◽  
Vol 23 (3-4) ◽  
pp. 561-566 ◽  
Author(s):  
SANG WOOK HONG ◽  
STEVEN K. SHEVELL
Keyword(s):  
Binocular Rivalry ◽  
Luminance Contrast ◽  
Binding Problem ◽  
High Luminance ◽  
Binding Process ◽  
Neural Representations ◽  
Low Luminance ◽  
Neural Binding ◽  
The Right

Is neural binding of color and form required for perception of a unified colored object? Individual cells selectively tuned to both color and orientation are proposed to moot the binding problem. This study reveals perceptual misbinding of color, thereby revealing separate neural representations of color and form followed by a subsequent binding process. Low luminance-contrast, rivalrous chromatic gratings were presented dichoptically. Each grating had alternating chromatic and gray stripes (e.g., red/gray in the left eye, green/gray in the right eye). Observers viewed the two rivalrous, 2 cpd gratings for 1 min. The duration of exclusive visibility was measured for four percepts: left-eye stimulus, right-eye stimulus, fusion of the two colors, or a two-color grating (e.g. a red/green grating). The percept of a two-color grating (misbinding) was observed with Michelson luminance contrast in the grating up to 20%. In general, for a given level of luminance contrast either misbinding (low luminance contrast) or color mixture (high luminance contrast) was observed, but not both of them. The perceived two-color gratings show that two rivalrous chromaticities are both represented neurally when color and form are combined to give a unified percept. “Resolution” of competing chromatic signals from the two eyes is not restricted to color dominance and color mixture. The transition from misbinding to color mixture by increasing luminance contrast shows that luminance edges have an important role in correct localization of color.

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