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At least 775 records · Page 43Linked to original sources
PubMed1981

Afferent properties of periarcuate neurons in macaque monkeys. II. Visual responses.

The visual response of single neurons of the periarcuate cortex have been studied in the macaque monkey. Two sets of neurons responding to visual stimuli have been found. The first set, located rostral to the arcuate sulcus, was formed by units that could be activated by stimuli presented far from the animal. These neurons had large receptive fields and were neither orientation nor direction selective. The second set, found predominantly caudal to the arcuate sulcus, was formed by units that were maximally or even exclusively activated by stimuli presented in the space immediately around the animal. These neurons were bimodal, responding also to somatosensory stimuli. According to the location of their visual responding regions the bimodal neurons were subdivided into pericutaneous (54%) and distant peripersonal neurons (46%). The former responded best to stimuli presented a few centimeters from the skin, the latter to stimuli within the animal's reaching distance. The visual responding regions were spatially related to the tactile fields. It is argued that neurons with a receptive field consisting of several responding areas, some in one sensory modality, some in another, have a praxic function and that they are involved in organizing sequences of movements.

Animals↗
PubMed1982

Comparing frontal and lateral viewing in the pigeon. I. Tachistoscopic visual acuity as a function of distance.

Pigeon's visual acuity has mainly been tested in free viewing conditions so that the direction of gaze could not be controlled. In order to be able to compare the resolving power of the two retinal areas of higher cellular density--the area dorsalis in the red field with frontal binocular projection and the fovea centralis with lateral monocular projection--a method of behavioural fixation was used. This method consists in a forced pecking schedule and a tachistocopic presentation of the stimulus. The pigeon has to discriminate the orientation (vertical, positive; horizontal, negative) of square gratings of increasing spatial frequency. Tests were done with the stimuli appearing 25 degrees below the beak for frontal and 80 degrees back from the beak for lateral viewing, at distances of 10, 20, 40 and 80 cm for each direction. Results show that while frontal acuity decreases with distance, lateral acuity increases with distance. These psychophysical data confirm previous dioptric measurements done on frozen eyes, showing that the pigeon is myopic in the frontal field and hyperopic in the lateral field. Pigeons seem to be well adapted for visually guided frontal tasks at near distances (feeding, landing) and for visually guided lateral tasks at far distances (warning).

Animals↗
PubMed1982

Contribution of striate inputs to the visuospatial functions of parieto-preoccipital cortex in monkeys.

In Experiments 1 and 2, monkeys received 3-stage operations intended to serially disconnect parieto-preoccipital from striate cortex. At each stage (unilateral parieto-preoccipital removal, contralateral striate removal and posterior callosal transection) the monkeys were tested for retention of the landmark task, a visuospatial discrimination sensitive to the effects of bilateral parieto-preoccipital damage. To check the effectiveness of the disconnection, the monkeys were also tested after removal of the remaining parieto-preoccipital cortex. The results demonstrated that corticocortical inputs from striate cortex are crucial for the visuospatial functions of parieto-preoccipital cortex, just as they had been shown earlier to be crucial for the pattern discrimination functions of inferior temporal cortex. Relative to inferior temporal cortex, however, parieto-preoccipital cortex was found to be especially dependent on ipsilateral (as compared with contralateral) striate inputs. In Experiment 3, monkeys received bilateral lesions of either lateral on medial striate cortex and were tested on both a pattern discrimination task, to assess residual inferior temporal function, and the landmark task, to assess residual parieto-preoccipital function. The results indicated that the pattern discrimination functions of inferior temporal cortex are especially dependent on inputs from lateral striate cortex, whereas the visuospatial functions of parieto-preoccipital cortex are equally dependent on inputs from lateral and medial striate cortex. The relatively greater contribution to parieto-preoccipital than to inferior temporal cortex made by ipsilateral and medial striate inputs (representing contralateral and peripheral visual fields, respectively) can also be seen in the receptive field properties of parieto-preoccipital and inferior temporal neurons. The differences in the organization of striate inputs to these two cortical association areas presumably reflect differences in the processing required for spatial vs object vision.

Animals↗
PubMed1983

Stimulus sampling and the use of distal visual cues in rats with lesions of the superior colliculus.

Rats with bilateral ablation of the superior colliculus (SC) were compared with sham-operated rats in two experiments. In the first, it was found that discrimination performance deteriorated as a function of S-R separation, to a similar extent in both groups. In this experiment, unlike earlier ones which found a deficit, the separation was introduced in a horizontal direction. In the second experiment, spatial orientation in the Morris Swimming Pool was found to be impaired in the SC rats both when the target platform was visible and when invisible. During their presence on the platform, these rats also engaged less often in upward orienting movements, although horizontal movements were of normal frequency. It is proposed (i) that there is an anisotropy in the SC's control of orienting head and eye movements in rats, and (ii) that the swimming pool deficit may be due to an impairment of ambient vision.

Animals↗
PubMed1988

Size constancy in goldfish (Carassius auratus).

This study examines whether fish are able to judge the real size of objects taking distance into account, or if size judgements are based purely on the angle objects subtend on the retina. Goldfish were trained to discriminate between 2 targets which differed from one another only in their diameters (5 cm and 10 cm), presented initially equidistantly from the fish. A choice of the correct target was rewarded either by food or by access to other fish. Following successful training, the targets were shifted so that they both subtended the same visual angle. The fish continued to choose the target to which they had been trained, showing that they display size constancy. This ability was present in both monocular and binocular animals.

Animals↗
PubMed1990

Distance estimation in the hooded rat: experimental evidence for the role of motion cues.

The role of motion cues, generated by vertical head movements, in distance estimation by hooded rats was investigated in a jumping task in which animals were trained to jump randomly varying gaps between two elevated platforms. In the first experiment it was shown that the disposition of texture cues influenced the number of head movements made prior to jumping, showing that the movements are related to visual aspects of the task. In the second experiment it was shown that stroboscopic illumination disrupted accurate jumping but animals could jump accurately to a platform when only the leading edge was visible, showing that they depend on motion cues but not motion parallax.

Animals↗
PubMed1990

Homing behavior of hippocampus and parahippocampus lesioned pigeons following short-distance releases.

The avian hippocampal formation has been proposed to play a critical role in the neural regulation of a navigational system used by homing pigeons to locate their loft once in the familiar area near home. In support of this hypothesis, the homing performance of pigeons with target lesions of either the hippocampus or parahippocampus was found to be impaired compared to controls following releases of about 10 km. Further, radio tracking revealed that the in-flight behavior of the hippocampal lesioned homing pigeons was characterized by numerous direction changes and generally poor orientation with respect to the home loft. The results identify a local navigational impairment on the part of the hippocampal lesioned pigeons in the vicinity of the loft where landmark cues are thought to be important. Additionally, target lesions of the hippocampus or parahippocampus were found to be similarly effective in causing homing deficits.

Animals↗
PubMed1995

Acuities for textures and gratings in kittens assessed by preferential looking.

A forced-choice preferential looking paradigm, similar to that developed for human infants, was used to assess visual thresholds in kittens between 21 and 45 days of age. In agreement with the earlier work of Sireteanu [19,30], the technique was found to be successful for grating acuity measurement. Acuity for square wave gratings (vs. matched greys) increased from 0.12 cycles/degrees at 21 days to 1.6 cycles/degrees at 40 days of age. Comparable results were obtained at three viewing distances: 20, 40, and 60 cm, indicating that accommodation is not a limiting factor in spatial resolution over this range of distances. Kittens also showed preferences for texture arrays with strong oriented components and 'texture acuities' were found to be comparable to acuity for square wave gratings. A consistent orientation anisotropy favouring horizontal line elements was seen in very young kittens but disappeared by 5 weeks of age. Preferences for texture arrays composed of dots were much weaker and thresholds could not be determined in all cases. The results are discussed in the context of the Banks and Ginsberg [2] model of infant preferences.

Aging↗
PubMed1988

Brain potentials during mental distance judgments.

Visual event-related potentials were recorded from a group of 10 normal subjects while they judged the proximity of two letters of the alphabet. Subjects viewed singly the letters A, D, G, L, N, T, W and Z and indicated by button press whether the letter displayed occurred before or after the comparison letter M. Reaction times to close letters (L and N) were longer than ordinally more distant letters (A, D, G, T, W, Z). A late parietally positive potential of approximately 475 ms covaried in latency and amplitude with these judgments. Late potentials were delayed in latency and reduced in amplitude to close letter (L and N) judgments compared to the other letters. The results suggest that mental processes, such as alphabetic distance judgments, may be usefully studied by examining their associated event-related potentials.

Adult↗
PubMed1989

Selective spatial attention and length representation in normal subjects and in patients with unilateral spatial neglect.

The aim of this study was to assess whether perceptual representation along the horizontal axis is affected by hemispace position of the stimulus or by orienting attention to one side. Ten control subjects and 10 right brain damaged patients with left unilateral spatial neglect (USN) were asked to bisect lines of five lengths in three space positions (left, center, right) and under three cueing conditions (no cue, left cue, right cue). Normal controls showed significant displacement of bisection opposite to the side of hemispace presentation and toward the side of cueing. USN patients showed a bisection error toward the right end which increased with lines placed in the left hemispace and decreased with lines placed in the right hemispace and when attention was oriented toward the left side. We conclude that (1) In absence of cues normal subjects tend to overestimate the portions of space closer to their body midline; (2) both normal and USN patients tend to overestimate portions of space that they direct their attention to; (3) USN patients' performance without cueing is consistent with an attentional shift toward the right hemispace implying a gradient of overestimation of the right-most portions of space. A common neural substratum for directing attention and space representation can explain these findings.

Aged↗
PubMed2006

Car following decisions under three visibility conditions and two speeds tested with a driving simulator.

The National Highway Traffic Safety Administration web site reports that rear-end collisions in the United States exceed 1.5 million per year, or approximately 23% of all vehicle crashes. Car following behavior and the decision-making habits of drivers seem fundamental to understanding how to avoid these rear-end crashes. The present research aimed to reveal factors that govern car following under conditions of reduced visibility. It employed a KQ-Vection high-fidelity driving simulator to measure the behavior of automobile drivers following a lead vehicle at 13.4 m/s (30 MPH) or 22.4 m/s (50 MPH) under three visibility conditions--clear or one of two densities of simulated fog. At the higher speed, fog conditions separated participants into a group that stayed within visible range of the lead car, even though the headway time violated the NHTSA recommendations for the speed involved, and another group that lagged beyond the visible range. Data were compared to the model of Van Winsum for car following (The human element in car following models. Transportation Research Part F 2, 1999). Contrast and image size measurements allowed comparison to a standard contrast sensitivity function and allowed estimation of the JND term in the Van Winsum model.

Acceleration↗
PubMed2006

Modeling aggressive driver behavior at unsignalized intersections.

The processing of vehicles at unsignalized intersections is a complex and highly interactive process, whereby each driver makes individual decisions about when, where, and how to complete the required maneuver, subject to his perceptions of distances, velocities, and own car's performance. Typically, the performance of priority-unsignalized intersections has been modeled with probabilistic approaches that consider the distribution of gaps in the major-traffic stream and their acceptance by the drivers of minor street vehicles based on the driver's "critical gap". This paper investigates the aggressive behavior of minor street vehicles at intersections that are priority-unsignalized but operate with little respect of control measures. The objective is to formulate a behavioral model that predicts the probability that a driver performs an aggressive maneuver as a function of a set of driver and traffic attributes. Parameters that were tested and modeled include driver characteristics (gender and age), car characteristics (performance and model year), and traffic attributes (number of rejected gaps, total waiting time at head of queue, and major-traffic speed). Binary probit models are developed and tested, based on a collected data set from an unsignalized intersection in the city of Beirut, to determine which of the studied variables are statistically significant in determining the aggressiveness of a specific driver. Primary conclusions reveal that age, car performance, and average speed on the major road are the major determinants of aggressive behavior. Another striking conclusion is that the total waiting time of the driver while waiting for an acceptable gap is of little significance in incurring the "forcing" behavior. The obtained model is incorporated in a simple simulation framework that reflects driver behavior and traffic stream interactions in estimating delay and conflict measures at unsignalized intersections. The simulation results were then compared against real world observations, representing an important step in validating the model of aggressive driver behavior at unsignalized intersections.

Age Factors↗
PubMed2004

The effects of aging on location-based and distance-based processes in memory for time.

Retrieving when an event occurred may depend on an estimation of the age of the event (distance-based processes) or on strategic reconstruction processes based on contextual information associated with the event (location-based processes). Young and older participants performed a list discrimination task that has been designed to dissociate the contribution of both types of processes. An adapted Remember/Know/Guess procedure [Can. J. Exp. Psychol. 50 (1996) 114] was developed to evaluate the processes used by the participants to recognize the stimuli and retrieve their list of occurrence. The results showed that aging disrupts location-based processes more than distance-based processes. In addition, a limitation of speed of processing and working-memory capacities was the main predictor of age-related differences on location-based processes, whereas working-memory capacities mediated partly age differences on distance-based processes.

Adolescent↗
PubMed2006

Estimating the quantitative relation between incongruent information and response time.

In Eriksen's flanker paradigm, participants' responses are slower and more error-prone when task-relevant and simultaneously available task-irrelevant cues are incongruent. The influence of task-irrelevant information decreases as its distance from the task-relevant information increases. Here, we manipulated the quantity of task-irrelevant information while keeping the distance constant. We asked whether when the impact on response selection processes was stronger the more incongruent information was available, or whether the impact on response selection depended only on its presence or absence. We conducted an experiment, in which subjects had to discriminate the direction of motion of a central point-light-walker that was flanked by two, four, or eight point-light-walkers at an equal distance from the center. The experiment showed that reaction times increased with the number of incongruent walkers. This effect was modulated by the total number of walkers, showing that the effect of incongruent information saturates when the display is cluttered.

Adult↗
PubMed2005

Gender differences in object location memory in a real three-dimensional environment.

In this preliminary study we investigate gender differences in object location memory. Our purpose is to extend the results about object location memory obtained in laboratory settings to a real 3-D environment and to further distinguish the specific components involved in this kind of memory by considering the strategies adopted to perform the task. To do this, we join the three-level model of spatial representations (landmark, route, and survey) proposed by Siegel and White (1975) with the three subcomponents of spatial memory (what, where, and what + where) identified by Postma and De Haan (1996). We adopted the object relocation task devised by Postma and De Haan (1996), adapted to a real environment. Seven common objects were placed on the floor of a cylindrical room. Sixty-four males and 64 females were asked to memorize the spatial layout. Next, the experimenter moved the objects to a different position along with seven new objects and the participants had to relocate the original objects to their initial positions. In line with Postma, Izendoorn, and De Haan (1998), we found no gender difference in object recognition, and in recalling absolute distance and categorical spatial relations; however males were better than females in recalling the distance between objects and the size of the layout. Overall, the data show a male advantage in some components of spatial cognition closely linked to the encoding of the metric structure of the spatial relationships at both route and survey level.

Adult↗
PubMed2004

Participation of the thalamofugal visual pathway in a coarse pattern discrimination task in an open arena.

The purpose of this study was to examine the role of the thalamofugal pathway in far-field visual processing. Experiment 1 examined the role of the visual wulst and the ectostriatum in a far-field pattern discrimination task in a large open arena. Control pigeons, pigeons with ectostriatum lesions, and pigeons with wulst lesions were trained to discriminate between four patterns within the arena. Ectostriatum-lesioned pigeons were unimpaired and behaved similar to controls. By contrast, wulst-lesioned pigeons were severely impaired in the pattern discrimination task in the open arena and performed poorer than control pigeons and pigeons with ectostriatum lesions. Statistical analyses of regional contributions to the observed impairment identified the left visual wulst and bilateral hyperstriatum ventrale, which lies outside the wulst, as interesting areas. To ensure that the impairment was not due to a general learning deficit, experiment 2 involved training the pigeons in a pattern discrimination task carried out in an operant chamber, which presumably required use of near-field visual information. Wulst-lesioned pigeons were able to learn the task and performed at a level no different from control pigeons. The results of these experiments support the proposal that the wulst may be important for processing far-field information.

Animals↗
PubMed2006

What do European badgers (Meles meles) know about the spatial organisation of neighbouring groups?

European badgers (Meles meles) live in groups. Although they can distinguish between a member of their own group, a member of a neighbouring group and a stranger, their ability to understand that neighbouring individuals belong to different groups inhabiting different places, and possibly to build up some representation of the spatial organisation of neighbouring groups remains to be shown. In this study, we conducted a pilot homing experiment to test such ability. Radio-collared badgers were displaced to the home ranges of neighbouring groups and their homing performances were compared to those of badgers displaced either to the periphery of their own group's home range or beyond the neighbouring home ranges. When released in their own home range, badgers homed rapidly and efficiently, whereas when released beyond the neighbouring groups' home ranges (whatever the distance) they did not home. In contrast, badgers released in the home range of a neighbouring group performed some random search there, before returning to their setts quite efficiently. These results suggest that badgers may consider their neighbours as members of different groups inhabiting different places close to their own home range, but their ability to build up some spatial representation of neighbourhood relationships could not be demonstrated.

Animals↗
PubMed2006

Mnemonic functions of the hippocampus: a comparison between animals and humans.

This review summarizes a series of experiments aimed at answering the question whether the hippocampus in rats and humans performs parallel functions focusing on studies that assess spatial and temporal pattern separation, sequential learning, spatial and temporal pattern association, spatial and temporal pattern completion, and short-term and intermediate-term memory. It is recognized that a comparison of the functions of the rat hippocampus with human hippocampus is difficult, because of differences in methodology, differences in complexity of life experiences, and differences in the degree of hippocampal damage as well as damage to interconnected brain regions. Yet, in general the data support the idea that with respect to spatial and temporal pattern separation, sequential learning, spatial and temporal pattern associations, spatial and temporal pattern completion, and short-term and intermediate-term memory, similar functions are observed in rats and humans with hippocampal damage using analogous tasks. These data provide support for evolutionary continuity in cognitive function assigned to the hippocampus of rats and humans.

Animals↗