Biomedical subjects

G Vallortigara

Publications and source records attributed to G Vallortigara.

At least 55 records · Page 3Linked to original sources

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↗

PubMed1996

Rotational bias in mosquitofish (Gambusia holbrooki): the role of laterality and sun-compass navigation.

Spontaneous rotational preferences in swimming of mosquitofish (Gambusia holbrooki) were investigated. Females, but not males, swam in circular tanks preferentially anticlockwise in the afternoon but not in the morning. Females' rotational preferences appeared to be related to a sun-compass orientation mechanism, as they disappeared under diffuse lighting conditions and when using naive females (i.e. using individuals never exposed to sunlight). Under repeated testing, however, the bias produced by the sun-compass mechanism tended to disappear, but females still showed rotational preferences that became stable and consistent at the individual level. Males too showed consistent individual rotational preferences under repeated testing. It is concluded that rotational bias in mosquitofish is due to two independent phenomena: a sun-compass navigation mechanism, which is related to the intensity of predation, and a behavioural lateralisation at the individual level, which is likely to reflect neural asymmetries in motor or sensory systems.

Journal Article↗

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↗

PubMed1992

Affiliation and aggression as related to gender in domestic chicks (Gallus gallus).

Social discrimination in male and female domestic chicks (Gallus gallus) was investigated by using (a) latencies of approach response, (b) simultaneous free choice, and (c) intersubject aggressive-pecking tests. In approach-response tests, females showed shorter latencies when tested with cagemates than when tested with strangers, whereas males showed shorter latencies when tested with strangers than when tested with cagemates. In simultaneous-choice tests, females spent more time near a cagemate, whereas males spent more time near a strange chick. In aggressive-pecking tests, both sexes pecked more at strangers than at cagemates; aggressive pecking at strangers, however, was higher in males than in females. It is argued that gender effects in social discrimination can be accounted for in terms of stronger social attachment in females and aggressive responses in males.

Aggression↗

PubMed1991

Occlusion and the perception of coherent motion.

Recent work (Shimojo, Silverman & Nakayama, 1989; Vision Research, 29, 619-626) suggests that the visual system must discriminate between extrinsic boundaries (boundaries created by front occluding surfaces) and intrinsic boundaries (real object boundaries) in order to recognize objects and that this would importantly affect the way it solves the so-called "aperture problem" in motion. With the aid of a series of demonstrations (plus two formal experiments) we (1) propose a new explanation for the fact that edge line terminators in a "barber pole" display are perceived as intrinsic; (2) show that inner line terminators in a plaid pattern (i.e. those resulting from the intersection of the two sets of bars) specify coherent or incoherent motion depending on the availability of occlusion-related depth information; and (3) suggest a unitary scheme integrating the two current alternative solutions to the aperture problem, the one based on line terminators and the one based on a velocity space combination of orthogonal components.

Depth Perception↗

PubMed1991

Illusory depth from moving subjective figures and neon colour spreading.

If a pattern of concentric circles, interrupted so as to produce the perception of a subjective bar extending from the centre to the periphery of the pattern, was slowly rotated in a plane perpendicular to the line of sight, observers reported seeing the bar slanted in depth and moving over complete and stationary concentric circles. When the interrupted concentric circles were completed by red segments--thereby giving rise to a neon colour-spreading effect--observers reported seeing a reddish bar, which sometimes appeared to be slanted in depth, moving behind the plane of the concentric circles. A combination of the two patterns was found to originate a compelling percept of a unitary bar slanted in depth: part of the bar (the subjective half) appeared to be located in front of its inducing elements, whereas the other part (the neon-like half) appeared to continue behind them. When translatory instead of rotary motion was used, the bars did not look slanted in depth: however, the neon bar appeared either behind or in front of the inducing lines, depending on the luminance contrast between the segments and the inducing lines themselves.

Attention↗

PubMed1990

Geometric modules in animals' spatial representations: a test with chicks (Gallus gallus domesticus).

Recent work has shown that in place-finding tasks rats rely on the geometric relations between the goal object and the shape of the environment. We tested young chickens (Gallus gallus domesticus) on similar tasks in a reference memory paradigm to determine whether differences exist between species in the ability to use geometric and nongeometric spatial information. The main findings were that chicks: (a) encoded and used both geometric and nongeometric (featural) information; (b) did not use the overall spatial arrangement of the features; (c) relied primarily on nongeometric cues when faced with contradictory information. Two mechanisms are evident in chicks' spatial representations: a metric frame for encoding the spatial arrangement of surfaces as surfaces and a cue-guidance system for encoding conspicuous landmarks near the target. The possibility of hierarchical organization and species differences in these two mechanisms are discussed.

Animals↗

PubMed1990

Sex differences in social reinstatement motivation of the domestic chick (Gallus gallus) revealed by runway tests with social and nonsocial reinforcement.

Male and female chicks (Gallus gallus) were trained at 4 days old to run along a corridor to reach a goal box that contained either cagemates (social reinforcement) or food (nonsocial reinforcement). Females ran faster when social reinforcement was used, whereas males ran faster with nonsocial reinforcement. When social reinforcement was used with a V-shaped runway, in which chicks had to proceed toward the goal object in an indirect fashion, sex differences were reversed. The results may be due to stronger social reinstatement tendencies in females than in males: Higher levels of social motivation facilitate behavioral performance when the task is easy (straight runway) and inhibit it when the task is difficult (V-shaped runway).

Animals↗

PubMed1990

The magic wand: a new stereokinetic anomalous surface.

When a disc with two dots stuck on it a few centimetres apart is set in slow rotatory motion, the two dots appear displaced in depth and rigidly connected to form the two extremities of a rod. The rod appears as a diaphanous transparent object, slightly tinted to the same colour as the dots. Experimental analysis of the phenomenon shows that it is different from previously observed 'moving phantoms', 'motion-induced contours', and 'stereokinetic induced phantoms'. But it shows similarities with all three phenomena: the colour spreading along the apparent rod is facilitated by low illumination and is clearly visible under high illumination with bright colours only; it is seen only when the two dots appear to move with apparent displacement in depth and not when they appear to lie on the plane of the disc. When line-drawn circles instead of full colour dots are used, the anomalous surface of the rod appears to have colourless vitreous transparency. With half-line circles it is clearly visible as an opaque rod of the same colour as the background. When squares or diamonds are used instead of dots, a three-dimensional prism can be observed which has similar appearance to the rod.

Adult↗

PubMed1989

Behavioral asymmetries in visual learning of young chickens.

Two-week-old chicks were trained in a simultaneous color discrimination learning task using food reinforcement. They had to discriminate between two discs of a different color whose right-left position was alternated at random. Results showed that chicks made more errors when the nonreinforced color was placed on the left with respect to the animal's body rather than when it was placed on the right. When chicks were trained on a right-left discrimination with two discs of identical color the asymmetry disappeared. Results are discussed in relation to current evidence for functional lateralization in the avian brain.

Animals↗