Biomedical subjects

G Vallortigara

Publications and source records attributed to G Vallortigara.

At least 37 records · Page 2Linked to original sources

PubMed1999

Figure ground segregation modulates perceived direction of ambiguous moving gratings and plaids.

A translating oriented grating viewed through a circular aperture with an occluding area in the middle appeared to move alternately in an oblique or in a vertical direction depending on the foreground/background assignment on the central occluding area. The effect occurred even when the central area was simply removed from the display, thus giving rise to a 'subjective' occluder. Parametric studies revealed that the probability of seeing oblique or vertical motion was affected by the size of the central area but not by its contrast relationships with the grating. Similar phenomena of ambiguous motion direction were observed using changes in colour along a translating grating that produced neon colour spreading effects, or using oriented edge discontinuities that collapsed into subjective plaids composed of two one-dimensional gratings. These results are discussed with respect to the hypothesis that surface segmentation mechanisms play a crucial part in the interpretation of motion signals.

Color Perception↗

PubMed1999

Possible evolutionary origins of cognitive brain lateralization.

Despite the substantial literature on the functional architecture of the asymmetries of the human brain, which has been accumulating for more than 130 years since Dax and Broca's early reports, the biological foundations of cerebral asymmetries are still poorly understood. Recent advances in comparative cognitive neurosciences have made available new animal models that have started to provide unexpected insights into the evolutionary origins and neuronal mechanisms of cerebral asymmetries. Animal model-systems, particularly those provided by the avian brain, highlight the interrelations of genetic, hormonal and environmental events to produce neural and behavioural asymmetries. Novel evidences showing that functional and structural lateralization of the brain is widespread among vertebrates (including fish, reptiles and amphibians) have accumulated rapidly. Perceptual asymmetries, in particular, seem to be ubiquitous in everyday behaviour of most species of animals with laterally placed eyes; in organisms with wider binocular overlap (e.g., amphibians), they appear to be retained for initial detection of stimuli in the extreme lateral fields. We speculate that adjustment of head position and eye movements may play a similar role in mammals with frontal vision as does the choice for right or left lateral visual fields in animals with laterally placed eyes. A first attempt to trace back the origins of brain asymmetry to early vertebrates is presented, based on the hypothesis that functional incompatibility between the logical demands associated with very basic cognitive functions is central to the phenomenon of cerebral lateralization.

Animals↗

PubMed1999

What causes lateralization of detour behavior in fish? Evidence for asymmetries in eye use.

A consistent population bias to detour a vertical-bar barrier preferentially leftwise during approach to inspect a dummy predator was demonstrated in the poeciliid fish Girardinus falcatus. The asymmetry seems to be due to a preferential use of the lateral visual field of the right eye during fixation of biologically relevant stimuli such as a predator. Viewing tests revealed in fact that fish which tended to detour the barrier on the left side used the right eye to scrutiny a dummy predator and the left eye to scrutiny a neutral stimulus, whereas fish which tended to detour the barrier on the right side showed the reverse pattern of eye use; fish that did not show any consistent bias in the detour test did not reveal any significant preference in the viewing test.

Animals↗

PubMed1999

Roots of brain specializations: preferential left-eye use during mirror-image inspection in six species of teleost fish.

It has recently been reported that predator inspection is more likely to occur when a companion (i.e. the mirror image of the test animal) is visible on the left rather than on the right side of mosquitofish Gambusia holbrooki. This very unexpected outcome could be consistent with the hypothesis of a preferential use of the right eye during sustained fixation of a predator as well as of a preferential use of the left eye during fixation of conspecifics. We measured the time spent in monocular viewing during inspection of their own mirror images in females of six species of fish, belonging to different families-G. holbrooki, Xenotoca eiseni, Phoxinus phoxinus, Pterophyllum scalare, Xenopoecilus sarasinorun, and Trichogaster trichopterus. Results revealed a consistent left-eye preference during sustained fixation in all of the five species. Males of G. holbrooki, which do not normally show any social behaviour, did not exhibit any eye preferences during mirror-image inspection. We found, however, that they could be induced to manifest a left-eye preference, likewise females, if tested soon after capture, when some affiliative tendencies can be observed. These findings add to current evidence in a variety of vertebrate species for preferential involvement of structures located in the right side of the brain in response to the viewing of conspecifics.

Animals↗

PubMed1999

Detour behaviour, imprinting and visual lateralization in the domestic chick.

Detour behaviour was studied in chicks faced with a vertical-bar barrier behind where an imprinting object (a red ball) was located. Right-eyed chicks took less time to detour the barrier than left-eyed chicks, and binocular chicks showed a bias to detour the barrier on the left side, thus maintaining visual contact with the imprinting object using the lateral field of the right eye, while circling around the barrier. In males, the asymmetries were consistent all along the first two weeks of life, whereas in females they disappeared on days 8 and 11. When tested with a slightly novel version of the original imprinting object (i.e., a ball of a different color), binocular chicks showed a bias to detour the barrier on the right side, thus showing preferential use of the left eye. The same bias occurred when unfamiliar conspecifics were used as goal-objects. Results suggest that cerebral lateralization in birds can directly affect visually-guided motor responses through selective use of the lateral field of vision of the eye contralateral to the hemisphere which has to be put in charge of control of overt behaviour.

Age Factors↗

PubMed1999

Visual lateralization and monocular sleep in the domestic chick.

Behavioural sleep during the first 2 weeks of life was investigated in female chicks reared with an imprinting object or in social (visual) isolation. Binocular sleep tended to decrease and monocular sleep to increase with age in both rearing conditions. In chicks reared with an imprinted object. during the first week, monocular sleep with either right or left eye closure occurred with approximately the same frequency, except that on day 5 in which right eye closure dominated; during the second week, however, there was a clear bias towards more monocular sleep with left eye closure. During the second week, the pattern of monocular sleep was similar in both rearing conditions, but during the first week chicks reared with the imprinting object showed relatively more right eye closure compared to chicks reared without the imprinting object, an effect that might tentatively be associated with consolidation of imprinting memories in the left hemisphere. Binocular sleep occurred in all four body postures adopted by chicks during sleep: standing sleep, sleep with bill forward, sleep with bill on the ground, and sleep with head on the ground. Monocular sleep, in contrast, only occurred when chicks adopted the bill forward posture. When the colour of the imprinting object was suddenly changed on day 8, a striking shift towards predominant right eye closure during monocular sleep was observed. The same occurred when the imprinting object was suddenly removed from the home-cage on day 8, but not with other types of changes (i.e., when a novel different object was inserted into the home-cage or when a novel-coloured imprinting object was inserted into the home-cage together with the original one). It is argued that this phenomenon could be associated with right hemisphere involvement in response to novelty.

Aging↗

PubMed1999

Footedness in binocular and monocular chicks.

The first foot used during bouts of ground scratching in 16-day-old chicks searching for food in the floor of an arena covered with sawdust was recorded in animals with normal binocular vision and in animals with an eye temporarily occluded by an eye-patch. Binocular chicks showed a significant right foot bias, whereas monocular chicks tended to use the foot contralateral to the eye in use. Data for monocular chicks thus suggest that the activated hemisphere (contralateral to the eye in use) is the one that takes control of posture, leaving to the other hemisphere reflex-like responses associated with ground scratching or body wiping. It is argued that footedness in chicks might have arisen from the limb that is used to maintain postural and positional control, rather than from the limb that is used during motor activities.

Journal Article↗

PubMed1998

Complementary right and left hemifield use for predatory and agonistic behaviour in toads.

Cerebral lateralization, the differing specializations of the right and left sides of the brain once thought to be unique of humans, is now well known to occur in both birds and mammals. Here we report that in toads the right hemisfield of vision guides predatory tongue-striking responses towards moving prey and the left hemisfield guides agnostic tongue-striking responses towards conspecifics. This indicates, for the first time, complementary cerebral specializations for visual processing in anurans, and strongly supports the hypothesis that lateralized brain functions in birds and mammals may have arisen from a common lateralized ancestor. Complementary specializations in visual processing may have originally evolved to avoid problem of response competition during control of medial organs such as the tongue in organisms with laterally placed eyes and, in organisms with wider binocular overlap, it appears to be retained for initial detection of stimuli in the extreme lateral fields.

Agonistic Behavior↗

PubMed1998

Lateralized agonistic responses and hindlimb use in toads.

The recent discovery of forepaw preferences (handedness) in toad species has provided some insight into the evolution of brain lateralization. We tested the prediction that, as in higher vertebrates, visual lateralization and other motor preferences (footedness) also exists in toad species. During feeding periods, South American cane toads, Bufo marinus, showed a population bias to strike with the tongue at other toads occupying their left visual field. This is the first demonstration of lateralized visual behaviour in an amphibian species. Tongue striking at an individual's eyes or head may sometimes delay its approach to prey already seen by the attacker, or may dislodge prey from its mouth. In addition, we report hindlimb preferences (footedness) for contact righting in three species of toad (B. marinus, the European green toad, B. viridis, and the European common toad, B. bufo). After being fully overturned on to their back on a horizontal surface, toads initiated and completed righting using the hindlimbs and with only perfunctory use of the forepaws. Together, the findings of visual lateralization and footedness demonstrate that in toads, as in higher vertebrates, behavioural lateralization is not restricted to handedness. The hypothesis that lateralized brain functions in birds and mammals might have arisen from a common lateralized ancestor is therefore supported. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1998

The origins of cerebral asymmetry: a review of evidence of behavioural and brain lateralization in fishes, reptiles and amphibians.

Early evidence for lateralization at a population and/or individual level in 'lower' vertebrates is reviewed. The lateralities include structural asymmetries in the epithalamus of several species of fish and amphibians, asymmetries in the location of both eyes on the same side of the head and of the dorsal/ventral crossing at optic-chiasma in flatfish, asymmetries in copulatory organs of several species of fishes, asymmetries in lung size and direction of coiling in reptiles, and asymmetrical distribution of scarring in whitefish. More recent data on functional lateralization at population level in lower vertebrates are also reviewed. These include: lateral asymmetries in the direction of turning during escape behaviour and in eye use in poeciliid fish; lateralization of pectoral stridulation sounds in catfish; neural lateralization for control of vocalization in the frogs; pawedness in toads; lateralization of courtship behaviour in newts; and lateralization of aggressive responses in lizards. Several cases of behavioural asymmetries at the individual level are also described, and possible relationships between lateralization at the individual level and fluctuating asymmetries arising from reduced heterozygosity are discussed. It is argued that the overall evidence now available supports the hypothesis of an early origin of brain lateralization in vertebrates.

Amphibians↗

PubMed1998

Lateralization of detour behaviour in poeciliid fish: the effect of species, gender and sexual motivation.

We studied detour responses of two species of poeciliid fish (Gambusia hoolbroki and Girardinus falcatus) faced with a vertical-bar barrier, through which conspecifics of the same or different sex or a simulated-predator (which induced detour behaviour for predator-inspection responses) were visible. Both species showed a consistent bias to turn leftward when faced with the predator, and a consistent bias to turn rightward when faced with an opaque barrier. Sexual stimuli (conspecifics of different sex) elicited a leftward bias in females that had been deprived of the presence of males for 2 months, whilst no bias was apparent in non-deprived females. Social stimuli (conspecifics of the same sex) elicited a consistent rightward bias in females but not in males in both species. Results suggest that males and females of both species show basically the same pattern of laterality and that sex differences, when present, can be accounted for in terms of differences in sexual and/or social motivation.

Animals↗

PubMed1997

Laterality in detour behaviour: interspecific variation in poeciliid fish

We measured whether males of five species of poeciliid fish made detours to the right or left of a vertical-bar obstacle in order to approach a group of females. Three of these species, Gambusia holbrookiGambusia nicaraguensis and Poecilia reticulata showed a significant bias to the left, whereas Brachyrhaphis roseni and Girardinus falcatus showed a significant bias to the right. When tested for direction of turning in front of an opaque barrier, or when a dummy predator was used as a target in a detour test, G. holbrooki and G. falcatus showed similar biases to the right (opaque barrier) and left (predator), thus suggesting that the difference observed when females were used as a target could arise from species differences in the degree of sexual motivation in a novel environment. The two species that showed bias to the right with the females were less likely to exhibit sexual behaviour when placed in a novel environment. Moreover, manipulation of the factors affecting the relative strength of sexual motivation and of fear of a novel environment, such as how long fish were maintained in captivity or in the test apparatus before being tested, caused shifts in the direction of the lateral asymmetries. These results suggest that the presence of functional asymmetries in behaviour could be widespread among vertebrates and that the direction of such asymmetries tends to be strikingly similar in closely related species, thus supporting the hypothesis of an early evolution of laterality in brain and behaviour.Copyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour

Journal Article↗

PubMed1997

Young chickens learn to localize the centre of a spatial environment.

Young chickens were trained to find food by ground-scratching in the centre of a closed uniform arena and were then tested in arenas of similar areas but of different shapes. Chickens showed localized searching behaviour in the square-shaped arena, and maintained this behaviour when placed in a circular or triangular (both equilateral and isosceles) arena. With a rectangular-shaped arena, obtained by doubling the original square-shaped one, chickens showed more dispersed searching along the major axis, but searching tended to be concentrated around the centres of the composing squares and around the centre of the rectangle itself. When trained in a square- or triangle-shaped arena and then tested in an arena of the same shape but a larger area, chickens displayed searching behaviour at two different distances from the wall of the arena, one corresponding to the correct distance (i.e. centre) in the smaller (training) arena, the other to the actual centre of the test arena. On the other hand, in a circular arena, chickens searched mainly at a distance midway between the radius of the small (training) and of the large (testing) circular arena. These results suggest that, during training, chickens encoded information on both the absolute and the relative distance of the food from the walls of the arena, the latter information being more accurate when the arena displayed identifiable features such as corners.

Animals↗

PubMed1997

Lateral asymmetries during escape behavior in a species of teleost fish (Jenynsia lineata).

Lateral asymmetries in the direction of turning during escape behavior in a species of teleost fish, Jenynsia lineata, are reported. When faced with the visual image of a simulated predator, approximately half of the individuals exhibited a significant bias to turn rightwards or leftwards, and the asymmetry tended to be retained when the same fish were retested 1 month later. Some morphological characters (pectoral fin rays, scales in natural row, supraorbital, preopercular, and postotic pores) were measured to check whether the degree of behavioral asymmetry was correlated with morphological fluctuating asymmetries associated with environmental stress or reduced heterozygosis. The results showed that it was not. The implications of these results for the interpretation of behavioral lateralization at the individual and population level are discussed.

Animals↗

PubMed1997

Rotational swimming preferences in mosquitofish: evidence for brain lateralization?

Rotational preferences of mosquitofish (Gambusia holbrooki) were investigated in circular tanks with a group of females or a group of predators located at the centre, or during spontaneous swimming in absence of any particular target. Mosquitofish swam preferentially clockwise in presence of the predators, whilst no significant preferences appeared with the females or during spontaneous swimming. Similar rotational biases have been reported previously only for rodents and marine mammals: the present findings suggest that even teleost fish may possess lateralized brains.

Animals↗

PubMed1997

Detour tests reveal task- and stimulus-specific behavioral lateralization in mosquitofish (Gambusia holbrooki).

We studied detour responses of male mosquitofish faced with a vertical-bar barrier through which a group of females was visible. Mosquitofish showed a consistent population bias to detour the barrier preferentially leftwise when a straight barrier was used, whilst the asymmetry disappeared if a U-shaped barrier was used. The leftward bias was apparent even when using a simulated-predator as a target (which induced detour behaviour for predatory-inspection responses), but not when using an empty environment or a group of males as a target. Moreover, when faced with an opaque barrier, mosquitofish tended to turn on their right side. These lateral biases could be accounted for in terms of a right eye preference during lateral (monocular) fixation of any stimulus of interest, suggesting functional lateralization in a teleost species for the analysis of visual information.

Animals↗

PubMed1997

Pawedness and motor asymmetries in toads.

Pawedness was investigated in three species of toads, Bufo bufo , Bufo viridis , and Bufo marinus. Samples from natural populations were collected in two successive years and tested during attempts to remove a strip of paper stuck onto the snout ( Bufo bufo and Bufo viridis ) or during attempts to remove an elastic balloon wrapped around the head ( Bufo bufo ). A preferential right forelimb use at the population level was observed in Bufo bufo in both tests, whereas no clear pawedness was observed in Bufo viridis. Bufo marinus also showed no laterality in the paper-strip test, but it appeared to be strongly lateralised in another test that investigated which side the toad rotated when turned on its back underwater. Preferentially turning to the toad's left side as part of a righting response, Bufo marinus released the left forelimb first, using the right forelimb to control the roll to the upright position, and push to the surface. These results suggest that preferential limb use has a long evolutionary history, which dates back to early tetrapods.

Journal Article↗

PubMed1996

Lateralization of displays during aggressive and courtship behaviour in the Siamese fighting fish (Betta splendens).

Evidence for right-left asymmetries in eye use at the individual level in the Siamese fighting fish, Betta splendens, is reported. When faced with their mirror image (in two daily trials of 10 min each), adult male Betta splendens showed consistency in their right or left eye use during threat lateral displays. Moreover, if one side was preferred by an individual to exhibit the lateral displays, then the duration of the displays on that side was longer than the duration of the displays on the other side. Similar findings were obtained when a sample of animals was tested for eye use during courtship displays in the presence of a female. Furthermore, consistency in eye use was observed in fish tested first with the mirror and then, 2 months later, with the female. Results are discussed with respect to the issue of the evolution of brain lateralization.

Aggression↗