Biomedical subjects

C G Ellard

Publications and source records attributed to C G Ellard.

14 recordsLinked to original sources

PubMed2000

The contribution of nonvisual information to simple place navigation and distance estimation: an examination of path integration.

In Experiment 1, participants walked without vision to a target location they had either previously viewed, were led to and from blindfolded, or both viewed and were led to and from blindfolded. A course to the target could be set and held without vision only if prior vision of its location was available. The locomotor group reproduced the heading and distance to the target less accurately than the other groups, which did not differ significantly. However, when nonvisual information accompanied vision of the target location, it served to subtly influence performance. Participants in Experiment 2 estimated the distance of a target they either viewed or were led to blindfolded. When vision was available, men overestimated target distance and women underestimated it. When target distance was learned nonvisually, no sex differences in distance estimations emerged. Our findings suggest that deriving navigation information from nonvisual locomotion is difficult and may be dependent on prior visual information.

Adult↗

PubMed1998

Comparative perspectives on multiple cortical visual systems.

This paper argues that any effort to extend theories of cortical visual systems based on primates to other orders, such as Rodentia, must take into account fundamental differences in visual system properties, such as retinal organization. Some examples are given of the effects of these differences, describing several studies using gerbils in which problems in object recognition appear to be solved using unique methods based on navigational information. I conclude by suggesting that closer consideration of comparative issues in visual cortical processing might lead to new insights regarding the evolutionary origins of object recognition as it is understood in humans and other primates, and I suggest that these evolutionary antecedents might help to explain the apparent linkage in humans between object recognition and movement.

Animals↗

PubMed1996

The effects of cortical lesions on recognition of object context in a visuomotor task in the Mongolian gerbil.

Two experiments were carried out in order to determine the effects of either parietal or temporal lesions on performance in a depth vision task in which gerbils normally use retinal image size (RIS) as a cue to distance. In the first experiment, gerbils were trained to jump to two training targets that differed in size and which were always presented with distinctive local features and in a particular spatial location. After lesions, gerbils were presented with further training trials and sets of probe trials in which they were presented with targets that differed in width from the training targets, and sets of local features and distal cues that either matched or mismatched those presented during training. Shams and temporal animals made predictable over- or underjumps when local feature and distal information matched, and stopped using retinal image size when they did not match. Parietal animals did not use retinal image size either during the match or the mismatch conditions. In a second experiment, gerbils with parietal lesions were shown capable of using retinal image size in a simpler task that did not contain distinguishing local features or distal cues. Taken together, these results suggest that parietal lesions in gerbils disrupt object recognition, when the purpose of the recognition process is to complete a distance estimate for a visuomotor act.

Animals↗

PubMed1996

Laboratory studies of antipredator behavior in the Mongolian gerbil (Meriones unguiculatus): factors affecting response attenuation with repeated presentations.

A series of experiments was conducted to study the properties of the attenuation of responding to repeated presentation of overhead visual transients in the gerbil (Meriones unguiculatus). Results suggest that this attenuation consists of habituation to the repeated association of a potentially threatening sensory stimulus with an increasingly familiar spatial context. The results of these experiments further suggest that the likelihood of eliciting fleeing is a conjoint function of the degree of risk posed by an overhead sensory transient and the degree of safety that is to be gained by fleeing. Results are discussed in the context of the ecology of predator recognition and the structural organization of the rodent visual system.

Animals↗

PubMed1995

The effects of lesions of anteromedial cortex on a ballistic visuomotor task in the Mongolian gerbil (Meriones unguiculatus).

Mongolian gerbils were trained to jump across a gap of randomly varying distance and then received one of three surgical treatments: Ten gerbils received aspiration lesions of anteromedial cortex (AMC), four gerbils received control lesions of a part of frontal cortex and nine gerbils received a sham procedure. Following a short recovery period, gerbils were tested in the jumping task. Gerbils with AMC lesions carried out fewer head movements than both sham and frontal gerbils. In addition, gerbils with AMC lesions were significantly less accurate in the distance estimation component of the jumping task, particularly at longer distances. These results suggest that anteromedial cortex participates in the generation of vertical head movements that are used to produce retinal motion information and confirms that these head movements are used to heighten the precision of distance estimation at longer testing distances.

Animals↗

PubMed1993

Organization of escape movements from overhead threats in the Mongolian gerbil (Meriones unguiculatus).

Mongolian gerbils (Meriones unguiculatus) were presented with overhead visual stimuli in different environmental situations. The organization of escape movements was investigated with video-based image analysis methods. In Experiment 1, gerbils in an open field established a home base and organized their escape trajectories with reference to both the home base and the location of the stimulus. In Experiment 2, gerbils were provided pairs of refuges. They used these refuges as home bases and organized their responses with reference to the home base. In Experiment 3, pairs of gerbils were tested in a field with refuges. Gerbils organized their escape movements with reference to their distance to the home base in relation to the distance of the other member of the pair to the home base. The results of these experiments suggest that escape movements in gerbils can be characterized as orienting to safety rather than to fleeing from risk.

Animals↗

PubMed1991

The effects of posterior cortical lesions on responses to visual threats in the Mongolian gerbil (Meriones unguiculatus).

Mongolian gerbils received aspiration lesions of either primary visual cortex (PVC), medial extrastriate visual cortex, retrosplenial cortex (RSC), or sham operations. The responses of gerbils to the presentation of an overhead visual stimulus were recorded in an open field. In all groups, presentation of the stimulus produced an increase in rearing. This suggests that the stimulus was detected by all animals. Gerbils with RSC or PVC lesions showed reduced levels of response to the stimulus. We suggest that some of the observed deficits can be explained as failures to produce responses to threat that are appropriate to the context in which the the threat was presented.

Animals↗

PubMed1991

Calibration of retinal image size with distance in the Mongolian gerbil: rapid adjustment of calibrations in different contexts.

Mongolian gerbils were trained to jump from one platform to another across a gap whose size varied randomly from trial to trial. In test sessions, probe landing platforms differing in width from those used in training were used, and the distance that the animals jumped was measured. The first experiment demonstrated that the gerbils learned to calibrate the retinal image size of the landing platform with its distance and that they could learn more than one calibration at a time. The second experiment provided evidence that such calibrations are rapidly adjusted to environmental contingencies. These findings suggest that retinal image size might be a useful distance cue for gerbils in a variety of ecological contexts.

Animals↗

PubMed1990

Behavioural effects of neocortical and cingulate lesions in the Mongolian gerbil.

The experiments examine the effects of cortical lesions on a variety of behaviours in the Mongolian gerbil (Meriones unguiculatus). Gerbils with either large anterior or posterior lesions were compared with normal gerbils by administering a battery of tests of rodent behaviours such as grooming, eating, social interaction, ventral marking and foot-stomping. In a second experiment, a more detailed investigation was carried out of the effects of focal cortical lesions on ventral marking. The results of these experiments suggest that anterior cortical lesions in gerbils give rise to a number of different deficits in behaviour. The results further suggest that cingulate cortex is part of the neural substrate for ventral marking behaviour. The implications of these results for contemporary theories of frontal lobe function are discussed.

Animals↗

PubMed1990

The role of image size and retinal motion in the computation of absolute distance by the Mongolian gerbil (Meriones unguiculatus).

In a series of experiments in which Mongolian gerbils were trained to jump over a variable gap, it was demonstrated that computation of the distance to be jumped was dependent on both image size and retinal motion, the latter cue being generated by the production of vertical translation movements of the head (head bobs). When image size was not a reliable cue, the animals produced more head bobs, thereby increasing the availability of retinal motion cues. The performance of the gerbils on various probe trials strongly suggested that they computed absolute distance by combining information about the velocity (or amplitude) of their head bobs with information about the velocity (or displacement) of the moving image of the landing platform.

Animals↗

PubMed1988

A functional analysis of the collicular output pathways: a dissociation of deficits following lesions of the dorsal tegmental decussation and the ipsilateral collicular efferent bundle in the Mongolian gerbil.

Mongolian gerbils received either lesions of the superior colliculus, small lesions of the uncrossed efferents of the superior colliculus, knifecuts of the dorsal tegmental decussation, or sham operations. The animals were subsequently tested for avoidance of overhead visual threat, orientation and locomotion toward small targets, and negotiation of a large barrier in order to reach a small target. Animals with collicular lesions showed no responses to overhead threat and had severe deficits in orienting to small targets. Animals with lesions of the uncrossed tectal efferents showed diminished responses to overhead threat but had no deficits in orienting to targets. Animals with lesions of the dorsal tegmental decussation showed only slight reductions in responses to overhead threats but clear impairments in the orientation tasks. The impairments in orientation, however, were less severe than those seen in collicular animals. Animals in all groups were able to negotiate barriers efficiently. These results suggest that separate output pathways of the superior colliculus mediate different types of visuomotor behaviours. The results further suggest that visual orientation to small targets does not depend completely on output through the predorsal bundle, but must also involve other collicular outputs.

Animals↗

PubMed1986

The role of the predorsal bundle in head and body movements elicited by electrical stimulation of the superior colliculus in the Mongolian gerbil.

Thirty-two Mongolian gerbils received bilateral chronic implants of stainless steel electrodes in the superior colliculus. The movements elicited by electrical stimulation were recorded on videotape and measured by means of a computer-assisted image analyzing procedure. Ipsiversive body movements were elicited by stimulation of the anterior part of the superior colliculus. Contraversive head and body movements could be elicited by stimulation over the entire superior colliculus. Amplitudes of head and body movements were dependent upon both stimulation parameters (current and train duration) and the animal's posture at stimulus onset. In a second experiment, the predorsal bundle was cut at its decussation by means of a stereotaxic microknife. After such cuts, contraversive turns were either abolished or were replaced by ipsiversive movements. Ipsiversive movements were unaffected by the knife cuts. This experiment provides evidence that the distinct types of movements that can be elicited by collicular stimulation are subserved by anatomically separate output pathways.

Animals↗

PubMed1986

Visual cortical lesions abolish the use of motion parallax in the Mongolian gerbil.

Mongolian gerbils received lesions of either the visual cortex, pretectal nuclei, superior colliculus or a sham operation. Visual distance estimation was tested by means of a jumping task on which gerbils have previously been shown to employ motion parallax information generated by head movements. Videotaped jumps were analyzed to determine latency to jump, jump distance, and head movement frequency. While all of the lesion groups showed some changes in performance, the most severe deficits in jump accuracy were seen after the visual cortical lesions. In none of the lesion groups, however, were head movements abolished. The results suggest that the visual cortex subserves a critical aspect of dynamic distance estimation but that the motor program for generating head movements is located elsewhere.

Animals↗

PubMed1984

Distance estimation in the Mongolian gerbil: the role of dynamic depth cues.

The role of dynamic depth cues in distance estimation was investigated in the Mongolian gerbil. Animals were trained to jump randomly varied distances on a jumping stand under both binocular and monocular conditions. Videotape analysis revealed that prior to jumping, the gerbils executed a series of vertical head movements, the amplitude and velocity of which were related to the gap distance and to each animal's accuracy. This suggested that the gerbils were employing motion parallax cues to judge distance. An inverse relation between the magnitude of forward movement and the frequency of vertical head movements suggested that loom cues were also being used to judge distance. This hypothesis received support from a second experiment in which forward movements were constrained by a short take-off platform. In this condition, frequency of vertical head movements increased, suggesting that a compensation had occurred for the loss of information from loom.

Animals↗