Spatial representation of shelter locations in meerkats, Suricata suricatta

We used observations and manipulation experiments to investigate how meerkats, social mongooses living under high predation pressure, find shelter from predators quickly within their territory. We played back alarm calls to foraging meerkats and dug new boltholes and covered existing ones to see whether location or other cues were used. Meerkats almost always ran to the bolthole closest to them. This was not done by a simple rule of running back to a bolthole they had just passed, nor by escaping in any direction and finding a bolthole by chance. Meerkats nearly always ignored the boltholes that we dug but ran to those we had covered up. Our results support the hypothesis that meerkats know in which direction to run when an alarm call is given, without scanning the area for visual or olfactory cues of shelters. As meerkats have more than 1000 boltholes in their territory, our results suggest that they have detailed knowledge of the direction and the distance of specific locations. However, this does not necessarily mean that they have a spatial map of their territory; our results may be explained by place recognition or reorientation of specific landmark features.     

Distortions of Perceived Orientation

SEVERAL visual discriminations are best for vertical and horizontal test objects and worst for objects oriented at 45° to the main axes^1–3. For resolution acuity it is quite clear that the differences are not due to any optical defects¹ and it seems probable that the same is true for tasks involving the discrimination of differences in orientation^2,3. A likely source of these variations is the orientationally sensitive neurones of the type found in the cat and monkey visual cortex^4,5. Psychophysical evidence^1,3,6 suggests that similar neurones exist in the human visual system and so we might expect some aspect of the sensitivity of these units to vary as a function of the orientation to which they are maximally sensitive.     

Northern bats, Eptesicus nilssonii, use vision but not flutter-detection when searching for prey in clutter

We investigated the detection cues used by the aerial-hawking bat Eptesicus nilssonii foraging in a cluttered environment. The bats can detect and attack rapidly moving targets within the clutter, i.e. below grass panicles, by using prey motion as a cue. Stationary objects are attacked only above the grass, but still within the clutter overlap zone. To test if the bats were guided by flutter from moth wings or by vision when searching for stationary targets, they were presented with male ghost swifts mounted on top of steel wires. There was no difference in attack frequency on live, fluttering moths compared to dead and spread ones. However, when comparing white and dark moths, we found a significantly higher attack frequency on white ones. As the attacks always were guided by echolocation calls, we hypothesize that northern bats, at least in the initial search phase, use visual cues as a complement to detect stationary ghost swifts.     

Pathway-specific genetic attenuation of glutamate release alters select features of competition-based visual circuit refinement

A hallmark of mammalian neural circuit development is the refinement of initially imprecise connections by competitive activity-dependent processes. In the developing visual system retinal ganglion cell (RGC) axons from the two eyes undergo activity-dependent competition for territory in the dorsal lateral geniculate nucleus (dLGN). The direct contributions of synaptic transmission to this process, however, remain unclear. We used a genetic approach to reduce glutamate release selectively from ipsilateral-projecting RGCs and found that their release-deficient axons failed to exclude competing axons from the ipsilateral eye territory in the dLGN. Nevertheless, the release-deficient axons consolidated and maintained their normal amount of dLGN territory, even in the face of fully active competing axons. These results show that during visual circuit refinement glutamatergic transmission plays a direct role in excluding competing axons from inappropriate target regions, but they argue that consolidation and maintenance of axonal territory are largely insensitive to alterations in synaptic activity levels.     

Differences in cue use and spatial memory in men and women

Men and women differ in their ability to solve spatial problems. There are two possible proximate explanations for this: (i) men and women differ in the kind (and value) of information they use and/or (ii) their cognitive abilities differ with respect to spatial problems. Using a simple computerized task which could be solved either by choosing an object based on what it looked like, or by its location, we found that the women relied on the object's visual features to solve the task, while the men used both visual and location information. There were no differences between the sexes in memory for the visual features of the objects, but women were poorer than men at remembering the locations of objects.     

The "sense of being stared at" does not depend on known sensory clues.

The "sense of being stared at" can be investigated by means of simple experiments in which subjects and lookers work in pairs, with the looker sitting behind the subject. In a random sequence of trials, the looker either looks at the back of the subject, or looks away and thinks of something else. More than 15,000 trials have already been conducted, involving more than 700 subjects, with an extremely significant excess of correct over incorrect guesses (Sheldrake [1999]). This effect was still apparent in experiments in which subjects were blindfolded and given no feedback, showing it did not depend on visual clues, nor on the subjects knowing if their guesses were right or wrong (Sheldrake [2000]). In this paper I describe experiments I conducted in schools in England in which the subjects were not only blindfolded and given no feedback, but looked at through closed windows. There was again a very significant excess of correct over incorrect guesses (p < 0.004). At my request, schoolteachers in Canada, Germany and the United States carried out similar experiments and found an even more significant positive effect than in my own experiments (p < 0.0002). The fact that positive results were still obtained when visual clues had been effectively eliminated by blindfolds, and auditory and olfactory clues by closed windows, implies that the sense of being stared at does not depend on the known senses. I conclude that peoples' ability to know when they are being looked at depends on an influence at present unknown to science.     

Extraocular vision in the sea urchin Diadema setosum

In most organisms, specific structures are responsible for detecting light patterns and vision. Several species of sea urchins appear to have a diffuse photoreceptor system that enables them to detect light and in some cases objects. The presence of extraocular vision was investigated on a sea urchin common in northern Oman, Diadema setosum. Urchins from 8- to 10-m deep coral communities were used in controlled experiments that quantified the orientation response of the urchins to various visual cues: size, contrast and colour of circular targets simulating urchins’ outlines. Urchins responded to black discs down to 11° initial visual angle but not to smaller discs. The minimum grey-scale value triggering a response was between 50 and 37% black. Urchins responded to red targets but not to green or blue ones. An average angular distance between spines of 5.3° suggested a visual acuity of about 10.6°. D. setosum thus showed extraocular vision allowing them to detect objects of different sizes, contrasts and to some extent colour, supporting the hypothesis that the whole sea urchin’s body acts as a single large compound eye.     

Associatieve visuele agnosie. De minder zichtbare gevolgen van een herseninfarct

After a cerebral infarction, some patients acutely demonstrate contralateral hemiplegia, or aphasia. Those are the obvious symptoms of a cerebral infarction. However, less visible but burdensome consequences may go unnoticed without closer investigation. The importance of a thorough clinical examination is exemplified by a single case study of a 72-year-old, right-handed male. Two years before he had suffered from an ischemic stroke in the territory of the left posterior cerebral artery, with right homonymous hemianopia and global alexia (i.e., impairment in letter recognition and profound impairment of reading) without agraphia. Naming was impaired on visual presentation (20%-39% correct), but improved significantly after tactile presentation (87% correct) or verbal definition (89%). Pre-semantic visual processing was normal (correct matching of different views of the same object), as was his access to structural knowledge from vision (he reliably distinguished real objects from non-objects). On a colour decision task he reliably indicated which of two items was coloured correctly. Though he was unable to mime how visually presented objects were used, he more reliably matched pictures of objects with pictures of a mime artist gesturing the use of the object. He obtained normal scores on word definition (WAIS-III), synonym judgment and word-picture matching tasks with perceptual and semantic distractors. He however failed when he had to match physically dissimilar specimens of the same object or when he had to decide which two of five objects were related associatively (Pyramids and Palm Trees Test). The patient thus showed a striking contrast in his intact ability to access knowledge of object shape or colour from vision and impaired functional and associative knowledge. As a result, he could not access a complete semantic representation, required for activating phonological representations to name visually presented objects. The pattern of impairments and preserved abilities is considered to be a specific difficulty to access a full semantic representation from an intact structural representation of visually presented objects, i.e., a form of visual object agnosia.     

Habitat modification when scent marking: shrub clearance by roe deer bucks

Marking activities in many ungulate species involve some aggression directed towards the vegetation which usually affects the understorey layer. Roe deer bucks (Capreolus capreolus) usually defend mating territories within the forest, where they mark the vegetation and the ground by using chemical signals which are typically associated with the visual ones used. Here we describe the presence of roe-made clearings of about 2700 m² average size which contained a clump of marks. Roe bucks affected the vegetation mainly by means of fraying and scratching with antlers around the stem of bushes, and defoliation by leaf-biting. The analysis of these activities suggests that their evolution may have been moulded by the effect of shrub clearing. Defoliation affecting more than 50% of leaves was only found within clearings. Also, fraying affected the whole perimeter of the stem and hence desiccated the bushes at higher rates within the clearings than outside. We found only one cleared area per male range, selectively located in a concave land formation. Producing a clump of scent marks within the mating territory may reduce the costs of scent marking, improve the effectiveness of scent guarding and fits well with the hypothesis of reliable scent matching by recipients. The concave shape of the clump, coupled with the cleared vegetation, may improve the perception of visual signals allowing for the location of scents. It is proposed that selection may favour the modification of the habitat as a component of roe deer marking behaviour, via its benefits in improving the broadcasting of visual signals associated with chemical ones.     

Determinants of territory size in the pomacentrid reef fish,Parma victoriae

Summary Factors governing the size of territories defended by the pomacentrid reef fish, Parma victoriae, were investigated, prompted by contradictory predictions in the literature concerning the effects of food supply and competitors. Observations were carried out over the non-breeding period (March–October) on a medium density population in which territories were partially contiguous. The territory size of adult fish varied between 3 and 26 m², and was inversely correlated with local densities of conspecifics. The same range in territory size was found for both males and females, which did not differ in the time they spent on territory defence and foraging activities. No correlation existed between territory size and the abundance of algal food, body size, age or time spent on territory defence. Also, there was little variation in territory size over time, despite seasonal changes in the abundance of food algae.Experimental reduction of food supplies on isolated territories of males and females had no effect on territory size. In a higher density habitat an experiment was carried out in which population density and food abundance were simultaneously manipulated. This showed that territory size was primarily determined by intraspecific interactions, as territories exhibited considerable increases in size upon removal of neighbours. No changes in the size of defended areas resulted from either artificial increases or decreases of food levels. There were also no changes in the time spent on defence of territories, foraging time or feeding rates associated with food manipulations or territory expansion, which suggested that food was not a limited resource. This conflicted with current theories proposed to explain territory defence and expansion. It is hypothesized that intraspecific interactions constrain territory size well below the optimum in terms of the abundance of preferred food algal species.     

Breeding territory fidelity in a partial migrant, the American dipper Cinclus mexicanus

American dipper Cinclus mexicanus populations are frequently composed of resident individuals that occupy permanent territories year round and migratory individuals that overwinter with residents but migrate to breeding territories on higher elevation creeks each spring. Between 1999 and 2004 we examined how migratory strategy (resident/migratory) and sex differences influence breeding territory fidelity of American dippers occupying the Chilliwack River watershed, British Columbia, Canada. Counter to expectation we found that the migratory strategy of American dippers did not influence whether birds breeding in one year were found on their former breeding territory in the next. Migratory strategy also did not affect the probability that known surviving dippers occupied the same breeding territory in the following year. Males and females were equally likely to be found on their former territory in the following year (females 43%, males 41%) and known survivors had similar levels of breeding territory fidelity (females 74%, males 68%). However, breeding territory fidelity of males and females varied in response to different factors. Surviving female dippers were more likely to be found on their former breeding territory in the subsequent year following a successful breeding attempt than an unsuccessful breeding attempt. Prior reproductive performance did not influence whether surviving male dippers were found on their former breeding territory. Male dippers were more likely to be found on their former territory and, if they survived, have higher breeding territory fidelity when their mate also returned to that same territory. Mate retention also influenced whether females were found on their former territory in the following year but had no effect on the breeding territory fidelity of known survivors. We argue that sex‐specific dispersal decision rules in American dippers are driven by sex differences in the predictability of breeding performance between years and sex differences in how mate retention influences subsequent reproductive success.     

Viewer-centered object representation in the human visual system revealed by viewpoint aftereffects

Are there neurons representing specific views of objects in the human visual system? A visual selective adaptation method was used to address this question. After visual adaptation to an object viewed either 15 or 30 degrees from one side, when the same object was subsequently presented near the frontal view, the perceived viewing directions were biased in a direction opposite to that of the adapted viewpoint. This aftereffect can be obtained with spatially nonoverlapping adapting and test stimuli, and it depends on the global representation of the adapting stimuli. Viewpoint aftereffects were found within, but not across, categories of objects tested (faces, cars, wire-like objects). The magnitude of this aftereffect depends on the angular difference between the adapting and test viewing angles and grows with increasing duration of adaptation. These results support the existence of object-selective neurons tuned to specific viewing angles in the human visual system.     

Distance and shape: perception of the 3-dimensional world by weakly electric fish.

Weakly electric fish orient at night in complete darkness by employing their active electrolocation system. They emit short electric signals and perceive the consequences of these emissions with epidermal electroreceptors. Objects are detected by analyzing the electric images which they project onto the animal's electroreceptive skin surface. This process corresponds to similar processes during vision, where visual images are cast onto the retinas of eyes. Behavioral experiments have shown that electric fish can measure the distance of objects during active electrolocation, thus possessing three-dimensional depth perception of their surroundings. The fundamental mechanism for distance determination differs from stereopsis used during vision by two-eyed animals, but resembles some supplementary mechanisms for distance deduction in humans. Weakly electric fish can also perceive the three-dimensional shape of objects. The fish can learn to identify certain objects and discriminate them from all other objects. In addition, they spontaneously categorize objects according to their shapes and not according to object size or material properties. There is good evidence that some fundamental types of perceptional invariances during visual object recognition in humans are also found in electric fish during active electrolocation. These include size invariance (maybe including size constancy), rotational invariance, and translational invariance. The mechanisms of shape detection during electrolocation are still unknown, and their discoveries require additional experiments.     

Patchy organization and asymmetric distribution of the neural correlates of face processing in monkey inferotemporal cortex

BACKGROUND: It is believed that a face-specific system exists within the primate ventral visual pathway that is separate from a domain-general nonface object coding system. In addition, it is believed that hemispheric asymmetry, which was long held to be a distinct feature of the human brain, can be found in the brains of other primates as well. We show here for the first time by way of a functional imaging technique that face- and object-selective neurons form spatially distinct clusters at the cellular level in monkey inferotemporal cortex. We have used a novel functional mapping technique that simultaneously generates two separate activity profiles by exploiting the differential time course of zif268 mRNA and protein expression. RESULTS: We show that neurons activated by face stimulation can be visualized at cellular resolution and distinguished from those activated by nonface complex objects. Our dual-activity maps of face and object selectivity show that face-selective patches of various sizes (mean, 22.30 mm2; std, 32.76 mm2) exist throughout the IT cortex in the context of a large expanse of cortical territory that is responsive to visual objects. CONCLUSIONS: These results add to recent findings that face-selective patches of various sizes exist throughout area IT and provide the first direct anatomical evidence at cellular resolution for a hemispheric asymmetry in favor of the right hemisphere. Together, our results support the notion that human and monkey brains share a similarity in both anatomical organization and distribution of function with respect to high-level visual processing.     

How (and why) the visual control of action differs from visual perception

Vision not only provides us with detailed knowledge of the world beyond our bodies, but it also guides our actions with respect to objects and events in that world. The computations required for vision-for-perception are quite different from those required for vision-for-action. The former uses relational metrics and scene-based frames of reference while the latter uses absolute metrics and effector-based frames of reference. These competing demands on vision have shaped the organization of the visual pathways in the primate brain, particularly within the visual areas of the cerebral cortex. The ventral ‘perceptual’ stream, projecting from early visual areas to inferior temporal cortex, helps to construct the rich and detailed visual representations of the world that allow us to identify objects and events, attach meaning and significance to them and establish their causal relations. By contrast, the dorsal ‘action’ stream, projecting from early visual areas to the posterior parietal cortex, plays a critical role in the real-time control of action, transforming information about the location and disposition of goal objects into the coordinate frames of the effectors being used to perform the action. The idea of two visual systems in a single brain might seem initially counterintuitive. Our visual experience of the world is so compelling that it is hard to believe that some other quite independent visual signal—one that we are unaware of—is guiding our movements. But evidence from a broad range of studies from neuropsychology to neuroimaging has shown that the visual signals that give us our experience of objects and events in the world are not the same ones that control our actions.     

A Mismatch between the Perceived Fighting Signal and Fighting Ability Reveals Survival and Physiological Costs for Bearers

Signals of fighting indicate an animal''s intention to attack and so they serve to prevent costly aggressive encounters. However, according to theory, a signal that is different in design (i.e. a novel signal) but that fails to inform fighting intentions will result in negative fitness consequences for the bearer. In the present study we used males of the territorial damselfly Hetaerina americana, which have a red wing spot during territory defense that has evolved as a signal of fighting ability. By producing a novel signal (covering the red spot with blue ink) in territory owners, we investigated: a) the behavioral responses by conspecific males; b) survival cost and c) three physiological mediators of impaired survival: muscular fat reserves, muscle mass and immune ability. We predicted that males with the novel signal would be attacked more often by conspecifics as the former would fail to convey fighting ability and intentions adequately. This will result in lower survival and physiological condition for the novel signal bearers. We found that, compared to control males (males whose red spot was not changed), experimental males had reduced survival, were less able to hold a territory, and had a reduced muscle mass. It seems that spot modified males were not able to effectively communicate their territory tenancy, which may explain why they lost their defended sites. Our results provide support for theoretical models that a novel signal that fails to informing fighting ability may lead to a fitness cost for bearers.     

Multi-scale habitat selection in highly territorial bird species: Exploring the contribution of nest,territory and landscape levels to site choice in breeding rallids (Aves: Rallidae)

Habitat selection often involves choices made at different spatial scales, but the underlying mechanisms are still poorly understood, and studies that investigate the relative importance of individual scales are rare. We investigated the effect of three spatial scales (landscape, territory, nest-site) on the occurrence pattern of little crake Zapornia parva and water rail Rallus aquaticus at 74 ponds in the Masurian Lakeland, Poland. Habitat structure, food abundance and water chemical parameters were measured at nests and random points within landscape plots (from 300-m to 50-m radius), territory (14-m) and nest-site plots (3-m). Regression analyses suggested that the most relevant scale was territory level, followed by landscape, and finally by nest-site for both species. Variation partitioning confirmed this pattern for water rail, but also highlighted the importance of nest-site (the level explaining the highest share of unique variation) for little crake. The most important variables determining the occurrence of both species were water body fragmentation (landscape), vegetation density (territory) and water depth (at territory level for little crake, and at nest-site level for water rail). Finally, for both species multi-scale models including factors from different levels were more parsimonious than single-scale ones, i.e. habitat selection was likely a multi-scale process. The importance of particular spatial scales seemed more related to life-history traits than to the extent of the scales considered. In the case of our study species, the territory level was highly important likely because both rallids have to obtain all the resources they need (nest site, food and mates) in relatively small areas, the multi-purpose territories they defend.     

An experimental analysis of cache recovery in Clark's nutcracker

Five hypotheses of cache recovery behaviour in Clark's nutcracker (Nucifraga columbiana) were examined experimentally. Most caches were made in soil within 5 cm of conspicuous large objects. Both seed-caching and non-seed-caching nutcrackers were able to locate caches. Seed-caching nutcrackers relocated caches using large objects as remembered visual cues. Soil microtopography and small (<2 cm diameter) objects may be used as cues to facilitate cache recovery but are not essential. Non-seed-caching nutcrackers located caches by using soil disturbances at cache sites as visual cues and by searching preferentially near objects where caches were concentrated. Success rates of seed-caching nutcrackers ranged from 52 to 78% and those of non-seed-caching nutcrackers ranged from 8 to 12%. Nutcrackers do not use random search or olfactory cues to locate caches.     

Visual Navigation during Colony Emigration by the Ant Temnothorax rugatulus

Many ants rely on both visual cues and self-generated chemical signals for navigation, but their relative importance varies across species and context. We evaluated the roles of both modalities during colony emigration by Temnothorax rugatulus. Colonies were induced to move from an old nest in the center of an arena to a new nest at the arena edge. In the midst of the emigration the arena floor was rotated 60°around the old nest entrance, thus displacing any substrate-bound odor cues while leaving visual cues unchanged. This manipulation had no effect on orientation, suggesting little influence of substrate cues on navigation. When this rotation was accompanied by the blocking of most visual cues, the ants became highly disoriented, suggesting that they did not fall back on substrate cues even when deprived of visual information. Finally, when the substrate was left in place but the visual surround was rotated, the ants'' subsequent headings were strongly rotated in the same direction, showing a clear role for visual navigation. Combined with earlier studies, these results suggest that chemical signals deposited by Temnothorax ants serve more for marking of familiar territory than for orientation. The ants instead navigate visually, showing the importance of this modality even for species with small eyes and coarse visual acuity.     

Determinants of territory size of the dusky gregory

To test the effect of food abundance and intruder pressure as determinants of territory size, the dusky gregory Stegastes nigricans were used as subjects on a coral reef in southern Taiwan during November to December 2000. Adults were used as intruders to provoke aggressiveness in a conspecific territory owner. The owner's maximum distance of attack (MDA) was used to delineate the territory size. While the owner of a territory appeared to defend a single boundary against different conspecifics, size variations among territories were evident. The effect of an intruder's identity on territory‐size regulation was not clear because for each territory examined, the MDA was found to be neither linked to the body size of the intruder nor to the amount of algae in the intruder's territory. Moreover, no significant differences were found between the MDAs that the owner maintained against neighbours and non‐neighbours even though, when conspecifics intruded in pairs, the probability was significantly higher for the first attack to be launched on a neighbour than on a non‐neighbour. Also when a neighbour and a non‐neighbour appeared simultaneously near the territory, the bite rate against the neighbour was also significantly higher. An inverse relationship between the amount of algae in the defended territory and the MDA of the owner indicates that food abundance might account for variations among territories. By contrast, territory size was not linked to the body size of the owner.