Biomedical subjects

G Vallortigara

Publications and source records attributed to G Vallortigara.

At least 19 recordsLinked to original sources

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↗

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↗

PubMed1996

Lateral asymmetries due to preferences in eye use during visual discrimination learning in chicks.

Chicks were trained to discriminate between two boxes of the same colour (white) on the basis of their positions using the pecking response. Some chicks were trained to peck at the box on their right side, some at the box on their left side. They were then retrained with two boxes of different colours (one red the other green): in one group of chicks the position of the two boxes was randomly alternated in the various trials (thus making colour a conspicuous but irrelevant cue), in the other it was maintained unchanged. A control group was retrained with two white boxes identical to those used during training. In all of the three groups chicks had to discriminate between the two boxes on the basis of their positions. During training, chicks took less trial and errors to learn when the positive box was placed on their right side and the same occurred during retraining with boxes that maintained a fixed position and during retraining in the control condition. During retraining with position alternation, on the contrary, chicks took less trials and errors to learn when the positive box was placed on their left side. Video recording of the chicks' behaviour while approaching the boxes showed that these lateral asymmetries reflect head and body turning associated to preferences in eye use, likely due to the different specializations of contralateral brain structures. It is argued that position cues engage the right hemisphere, with consequent head turning to the right to allow lateral viewing by the left eye; object-specific cues engage the left hemisphere, with consequent head turning to the left to allow lateral viewing by the right eye.

Animals↗

PubMed1995

Lateralization of predator-evasion response in a teleost fish (Girardinus falcatus).

Evidence of lateral asymmetries in the direction of turning during escape behaviour in a species of poeciliid fish, Girardinus falcatus, is reported. When repeatedly faced with a simulated predator (in five successive sessions, spaced 7 days apart), immature Girardinus falcatus exhibited a significant population bias to turn right on the first session and a progressive bias to turn left in subsequent sessions. Mature Girardinus were then tested to check whether the shift in the direction of turn with repeated sessions depended on maturation or habituation. It was found that adult Girardinus showed a slight population bias to turn right in the first session and a strong subsequent bias to turn left after repeated sessions. The implications of these findings to our current understanding of the evolution of brain lateralization are discussed.

Animals↗

PubMed1995

Solving occlusion indeterminacy in chromatically homogeneous patterns.

Overlapping figures can produce consistent depth stratification even when chromatically homogeneous. Since neither T-junctions nor X-junctions are present in these patterns, the problem arises of what rules determine the direction of depth stratification, ie which surfaces appear in front and which behind. In a series of demonstrations and formal experiments involving perception of stereopsis, motion, transparency, motion in depth, and reversible figures, the validity of the principle that the visual system tends to minimise the formation of interpolated modal contours was tested. The reason why larger surfaces tend to be seen modally in front, rather than behind, would reflect the geometrical property that when, in overlapping objects, larger surfaces are closer there will be shorter occluding boundaries than when smaller surfaces are closer. It is shown that this constraint is independent of the empirical depth cue of relative size. An example is also given of a simple computational strategy that extracts, from chromatically homogeneous patterns, occluding subjective contours corresponding to those perceived by human observers.

Attention↗

PubMed1995

Perception of partly occluded objects by young chicks.

Completion of partly occluded objects is a ubiquitous phenomenon in human visual perception. It is unclear, however, whether it occurs at all in other species: Studies on visual discrimination learning have revealed that animals usually attend to parts and features of the discriminative stimuli rather than to global object properties. We provide here the first demonstration of recognition of partly occluded objects in a bird species, the domestic chick Gallus gallus, using the naturalistic setting made available by filial imprinting, a process whereby young birds form attachments to their mothers or some artificial substitute. In Experiment 1, newborn chicks were reared singly with a red cardboard triangle, to which they rapidly imprinted and therefore treated as a social partner. On Day 3 of life, the chicks were presented with pairs of objects composed of either isolated fragments or occluded parts of the imprinting stimulus. Chicks consistently chose to associate with complete or with partly occluded versions of the imprinting object rather than with separate fragments of it. Similarly, in Experiment 2, chicks reared with a partly occluded triangle chose to associate with a complete triangle rather than with fragmented one, whereas chicks reared with a fragmented triangle chose to associate with a fragmented triangle and not with a complete one. Newborn chicks thus appear to behave as if they could experience amodal completion.

Animals↗

PubMed1994

Olfactory lateralization in the chick.

Chicks using their right nostril (and so with direct olfactory input to the right hemisphere), and presented simultaneously with two objects identical in visual appearance with the rearing object, and differing only in odour, chose that which smelled like the rearing object. Chicks using the left nostril chose equally readily but at random. Earlier work, using similar tests, has shown special interest of the right hemisphere in change in visual properties of familiar stimuli, suggesting that analysis of a wide range of properties of a familiar stimulus may be an important function of the right hemisphere in the chick, with consequent detection of novelty.

Animals↗

PubMed1994

Occlusion, transparency, and stereopsis: a new explanation for stereo capture.

Stereo capture occurs when a regular pattern of repeating elements with zero disparity is superimposed on a disparate subjective figure. The elements enclosed within the subjective contours, but not those outside them, are perceptually captured and pulled on the same depth plane of the disparate figure. The phenomenon has been interpreted as the result either of a spreading of disparity signals from the subjective figure or of the attribution of the depth of certain salient image features to the finer texture elements enclosed in them. We suggest here that, instead, the fact that stereo capture is limited to the texture elements lying within the boundaries of the subjective figure is simply due to ambiguous occlusion information at the monocular level. When the texture elements occlude the inducers of the subjective figure as well, the elements lying outside the boundaries of the subjective figure are also captured. We propose that stereo capture arises as the solution to a conflict between information provided by retinal disparity and occlusion, and show how this effect is related to other previously observed phenomena of conflicting cues to depth.

Cues↗

PubMed1993

What induces capture in motion capture?

The phenomenon of "motion capture" has been demonstrated by presenting, one after the other, two identical Kanizsa squares spatially separated and superimposed on a regular matrix of dots. For appropriate temporal intervals, one illusory square is seen to jump from one location to the other and the dots in it appear to move with it even though they are physically stationary. The standard explanation of the effect is that motion signals from the subjective figure are spontaneously attributed to the static elements laying on it. We have found, however, that if alternative removal of right-angle sectors (required to obtain apparent motion of the illusory square) is not accompanied by alternative appearance and disappearance of a few dots, motion capture does not occur. This suggests that the basic mechanism underlying capture is not the motion of the subjective figure per se, but the spreading of motion signals arising from those texture elements that alternately go on and off between frames. On the other hand, subjective contours do play a role by confining the spreading of motion signals to the texture elements located on the figure.

Eye Movements↗

PubMed1993

The role of depth stratification in the solution of the aperture problem.

When a plaid pattern composed of a stationary vertical grating and a horizontally drifting diagonal grating is shown behind a circular aperture, the pattern appears to move coherently in a vertical direction. When the bars of the stationary grating are narrower than those of the moving grating, only the latter is seen to move, in a direction orthogonal to its orientation (ie diagonal); but when the bars of the stationary grating are wider than those of the moving grating, vertical motion of the whole plaid predominates. It is argued that, in the absence of occlusion information, the motion of a plaid within an aperture depends on the unambiguous displacement of inner line terminators at the crossings of the two gratings. Relative motion and differences in bar width between the two gratings provide information about which set of bars is in front of the other. When these sources of information are consistent with each other, separation of the two gratings in depth occurs: inner line terminators no longer perceptually exist and the direction of motion becomes determined only by terminators at the edges, which causes a shift from vertical to orthogonal motion. Differences in luminance also provide (asymmetrical) information about depth relationships: when darker bars occlude lighter bars, the probability of orthogonal motion increases as a function of the difference in luminance, whereas when lighter bars are over darker bars, vertical motion prevails.

Depth Perception↗

PubMed1992

Motion aftereffects with rotating ellipses.

The perceptual outcome and the motion-aftereffect duration generated by the rotation on the frontal plane of an ellipse with a bar depend on whether the bar is placed along the major or the minor axis. When the bar is placed along the minor axis, a stereokinetic transformation occurs, and the pattern looks like a tilting ring with a perpendicular bar moving rigidly with it. Placing the bar along the major axis prevents the stereokinetic transformation: subjects report deformations and relative motion of the bar with respect to the ellipse. We found that motion aftereffects last longer when the bar is placed along the minor rather than along the major axis. A series of experiments was carried out to investigate whether differences in aftereffect duration are related to the stereokinetic transformation. Results seem to suggest that they are not.

Adult↗

PubMed1992

Right hemisphere advantage for social recognition in the chick.

Recognition of familiar and unfamiliar conspecifics was studied in pair-reared chicks tested binocularly or with only one eye in use. Chicks were tested on day 3 in pairs composed of either cagemates or strangers. Social discrimination, as measured by the ratio "number of pecks at the strangers/total number of pecks" was impaired in right-eyed chicks with respect to left-eyed and binocular chicks. Male chicks showed higher levels of social pecking than females, and chicks that used both eyes showed higher pecking than monocular chicks. There were no significant differences in the total number of pecks (i.e. pecks at companions plus pecks at strangers) between right- and left-eyed chicks: the impairment in social discrimination of right-eyed chicks seemed to be due partly to a reduction in pecking at strangers and partly to an increase in pecking at companions. It is suggested that neural structures fed by the left eye (mainly located at the right hemisphere) are better at processing and/or storing of visual information which allows recognition of individual conspecifics. This may be part of a wider tendency to respond to small changes in any of a variety of intrinsic stimulus properties.

Animals↗