Detecting binocular 3-D motion in static 3-D noise: No effect of viewing distance.

Relative binocular disparity cannot tell us the absolute 3-D shape of an object, nor its 3-D trajectory if it is moving, unless the visual system has independent access to how far away the object is at any moment. Indeed, as the viewing distance is changed, the same disparate retinal motions will correspond to very different real 3-D trajectories. In this paper we were interested in whether binocular 3-D motion detection is affected by viewing distance. We used a visual search task in which the observer is asked to detect a target dot, moving in 3-D, amidst 3-D stationary distractor dots. We found that distance does not affect detection performance. Motion-in-depth is consistently harder to detect than the equivalent lateral motion, for all viewing distances. For a constant retinal motion with both lateral and motion-in-depth components, detection performance is constant despite variations in viewing distance that produce large changes in the direction of the 3-D trajectory. We conclude that binocular 3-D motion detection relies on retinal, not absolute visual signals

Establishing the behavioural limits for countershaded camouflage

Countershading is a ubiquitous patterning of animals whereby the side that typically faces the highest illumination is darker. When tuned to specific lighting conditions and body orientation with respect to the light field, countershading minimizes the gradient of light the body reflects by counterbalancing shadowing due to illumination, and has therefore classically been thought of as an adaptation for visual camouflage. However, whether and how crypsis degrades when body orientation with respect to the light field is non-optimal has never been studied. We tested the behavioural limits on body orientation for countershading to deliver effective visual camouflage. We asked human participants to detect a countershaded target in a simulated three-dimensional environment. The target was optimally coloured for crypsis in a reference orientation and was displayed at different orientations. Search performance dramatically improved for deviations beyond 15 degrees. Detection time was significantly shorter and accuracy significantly higher than when the target orientation matched the countershading pattern. This work demonstrates the importance of maintaining body orientation appropriate for the displayed camouflage pattern, suggesting a possible selective pressure for animals to orient themselves appropriately to enhance crypsis

Is countershading camouflage robust to lighting change due to weather?

Countershading is a pattern of coloration thought to have evolved in order to implement camouflage. By adopting a pattern of coloration that makes the surface facing towards the sun darker and the surface facing away from the sun lighter, the overall amount of light reflected off an animal can be made more uniformly bright. Countershading could hence contribute to visual camouflage by increasing background matching or reducing cues to shape. However, the usefulness of countershading is constrained by a particular pattern delivering ‘optimal’ camouflage only for very specific lighting conditions. In this study, we test the robustness of countershading camouflage to lighting change due to weather, using human participants as a ‘generic’ predator. In a simulated three-dimensional environment, we constructed an array of simple leaf-shaped items and a single ellipsoidal target ‘prey’. We set these items in two light environments: strongly directional ‘sunny’ and more diffuse ‘cloudy’. The target object was given the optimal pattern of countershading for one of these two environment types or displayed a uniform pattern. By measuring detection time and accuracy, we explored whether and how target detection depended on the match between the pattern of coloration on the target object and scene lighting. Detection times were longest when the countershading was appropriate to the illumination; incorrectly camouflaged targets were detected with a similar pattern of speed and accuracy to uniformly coloured targets. We conclude that structural changes in light environment, such as caused by differences in weather, do change the effectiveness of countershading camouflage

Optic flow and scene structure do not always contribute to the control of human walking

AbstractUsing displacing prisms to dissociate the influence of optic flow and egocentric direction, previous research (Current Biology 8 (1998) 1191) showed that people primarily use egocentric direction to control their locomotion on foot, rather than optic flow. When wearing displacing prisms, participants followed the curved path predicted by the use of simple egocentric direction, rather than a straight path, as predicted by the use of optic flow. It has previously been suggested that, in rich visual environments, other visual information including optic flow and static scene structure may influence locomotion in addition to direction. Here we report a study where neither scene structure nor optic flow have any influence on the control of walking. Participants wearing displacing prisms walked along a well-lit corridor (containing rich scene structure and flow) and along the same corridor in darkness (no scene structure or flow). Heading errors were not significantly different between the dark and light conditions. Thus, even under conditions of rich scene structure and high flow when walking in a well-lit corridor, participants follow the same curved paths as when these cues are not available. These results demonstrate that there are conditions under which visual direction is the only useful source of visual information for the control of locomotion

Orientation to the sun by animals and its interaction with crypsis

1. Orientation with respect to the sun has been observed in a wide range of species and hasgenerally been interpreted in terms of thermoregulation and/or ultraviolet (UV) protection. For countershaded animals, orientation with respect to the sun may also result from the pres-sure to exploit the gradient of coloration optimally to enhance crypsis.2. Here, we use computational modelling to predict the optimal countershading pattern for anoriented body. We assess how camouflage performance declines as orientation varies using acomputational model that incorporates realistic lighting environments.3. Once an optimal countershading pattern for crypsis has been chosen, we determineseparately how UV protection/irradiation and solar thermal inflow fluctuate with orientation.4. We show that body orientations that could optimally use countershading to enhance crypsisare very similar to those that allow optimal solar heat inflow and UV protection.5. Our findings suggest that crypsis has been overlooked as a selective pressure on orientationand that new experiments should be designed to tease apart the respective roles of these different selective pressures. We propose potential experiments that could achieve this

Perceiving Monocular Regions in Binocular Scenes

Our visual systems combine the two, slightly different, retinal images to arrive at a stable and continuous percept of a given scene around us. While a large proportion of any scene is binocular, there are a host of regions that can only be seen by one eye. Rather than being ignored, these monocular regions are integrated with the surrounding binocular regions and their content is consciously accessible to us. However, our perception of the information contained in monocular regions seems to be slightly different from that of information that is seen by both eyes (binocularly). Ono et al (2003)[1], for example, report that monocular regions appear slightly displaced and compressed, as if to 'fit' into the surrounding binocular space. Here we discuss two experiments that investigate our perception of monocular regions further. We used two relative numerosity tasks to study whether monocular regions lead to a percept that is comparable to that of binocular regions, and we explored how the two types of regions are integrated to form a seemingly stable and continuous percept. This record was migrated from the OpenDepot repository service in June, 2017 before shutting down

Reindeer and the quest for Scottish enlichenment

Funding Information: The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Data were collected with funding from the Goodman Fund, Dartmouth College and the Global Fellowship Scheme, University of St Andrews.In the hall of animal oddities, the reindeer (Rangifer tarandus) is the only mammal with a color-shifting tapetum lucidum and the only ruminant with a lichen-dominated diet. These puzzling traits coexist with yet another enigma––ocular media that transmit up to 60% of ultraviolet (UV) light, enough to excite the cones responsible for color vision. It is unclear why any day-active circum-Arctic mammal would benefit from UV visual sensitivity, but it could improve detection of UV-absorbing lichens against a background of UV-reflecting snows, especially during the extended twilight hours of winter. To explore this idea and advance our understanding of reindeer visual ecology, we recorded the reflectance spectra of several ground-growing (terricolous), shrubby (fruticose) lichens in the diets of reindeer living in Cairngorms National Park, Scotland.Publisher PDFPeer reviewe

Oncologist's perspectives and factors influencing school re-entry recommendations for children with acute lymphoblastic leukemia

Currently, there are no established guidelines among pediatric oncologists regarding school attendance recommendations during cancer treatment. Practices vary widely, ranging from continued school attendance following the initial phase of cancer treatment to complete abstention from school for the majority of the treatment protocol. This survey project explored the current practices of attendance recommendations among oncologists as well as their knowledge and perceptions of how school absence affects their patients' academic and psychosocial functioning. In an attempt to better understand why oncologists make the school re-entry recommendations, a prediction model was created and found to significantly predict oncologist's re-entry recommendations.  M.A

The Multidimensional Media Literacy & Engagement Framework: A Tool for Fostering Informed Civic Participation

Teaching media literacy helps students interpret media messages accurately and supports their informed civic participation