SEARCH · PubMed Health

Results for “Space Perception”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30Linked to original sources

PubMed1991

Polarity specific adaptation to motion in the human visual system.

Three experiments investigated polarity specific adaptation to movement. Experiment 1 tested for temporal polarity specific adaptation, using counterphase sawtooth gratings as adapting and test stimuli. Each counterphase grating contained oppositely moving sawtooth components, and was thus balanced for direction, but both components of the adapting grating created only one polarity of luminance change over time, whereas the components of the test grating presented different signs. After adaptation, only the test component containing the unadapted temporal change was visible. A second experiment, using an analogous procedure, found evidence for spatial polarity specific adaptation. Experimental results can be explained by motion detectors which preserve information about spatial and temporal polarity. A third experiment found that spatial and temporal polarity specific adaptation differ in their dependence on temporal frequency.

Adaptation, Ocular↗

PubMed1993

Pop-out of orientation but no pop-out of motion at isoluminance.

Line textures in which one line was orthogonally oriented to the rest were briefly presented at various colour and luminance contrasts to the background. Subjects were able to detect the single line element pre-attentively even when the texture pattern was defined only by colour, indicating that "pop-out" of orientation is achieved at isoluminance. To exclude the possibility that this result was caused by luminance artefacts, especially by chromatic aberration, we carried out two control experiments. First, we showed that subjects could not detect a single moving line in a stationary texture under comparable conditions. Secondly, we repeated the experiments with a deuteranope who was unable to detect the differently oriented target under conditions under which the normal subject still could see it.

Adult↗

PubMedDate not supplied

Dependence of speed and direction perception on cinematogram dot density.

In the present experiments, we find that with abrupt decreases in dot density of random-dot cinematograms, perceived speed decreases, while with abrupt increases in dot density, perceived speed increases. Further, in steady-state conditions, perceived speed is also affected in the same way, but to a lesser degree, by the dot density of cinematograms. Direction discrimination of random-dot cinematograms is enhanced when dot density increases abruptly from one stimulus to the next, but is degraded when dot density decreases abruptly. Finally, speed discrimination remains constant even when density changes abruptly. The perceived-speed and direction-discrimination data are consistent with the Motion Coherence theory which motivated this study, and with models that include a smoothing stage similar to this theory. Of the other models that we consider, most predict that increasing dot density reduces perceived speed. The speed-discrimination data could not distinguish between the different theories.

Discrimination, Psychological↗

PubMed1993

Can we attend to large and small at the same time?

Evidence from several sources suggests that visual attention is tuned to stimulus scale. This tuning impairs performance when the observer must attend to more than one scale at a time. In experiments originally designed to measure the bandwidth of attention to stimulus scale, we have found tasks in which observers show no attentional tuning for scale. In separate blocks, observers located or identified targets in arrays of elements, either numbers in arrays of letters or static squares in arrays of flashing squares. Each display contained two arrays, either of the same scale or of different scales. The accuracy of locating the target element was lower in mixed-scale than in single-scale displays, but the accuracy of identifying the target was unaffected by a mixing of scales within the same display. This holds for both high-level discriminations--numbers vs letters--and low-level discriminations--static vs flashing. Thus, at least for identifying, one can attend to large and small at the same time. The difference in bandwidth between "what" and "where" implies that stimulus identification is not dependent on prior localization.

Attention↗

PubMed1994

Spatial vision in the honeybee: the use of different cues in different tasks.

Much of the knowledge available on sensory performances in insects has been obtained from training experiments in honeybees. The present article reviews results of several behavioural studies on spatial vision in the bee. When considered jointly, they demonstrate the large amount of flexibility in the bee's visually guided behaviour. The visual cue that is used in a task depends on the experimental situation, e.g. the bee learns that particular cue that would most reliably guide it to its goal.

Animals↗

PubMed1994

Visual search in continuous, naturalistic stimuli.

In standard visual search experiments, subjects look for a target item among distractor items. Targets and distractors are generally presented as isolated entities on a blank background. Do theories based on results of such experiments have any application to the real world of spatially continuous stimuli where "items" are not so conveniently delineated? Experiment 1 examines search for conjunctions of color with form and with orientation in novel stimuli designed to resemble aerial views. As with artificially isolated items, conjunction search with these complex stimuli is highly efficient, holding out the promise that models of visual search based on laboratory data can be extended to real-world situations. Experiment 2 shows that some "serial" searches are made significantly less efficient when items are embedded in these specific naturalistic backgrounds. This suggests that even classic serial searches rely on some parallel processing--the processing required to locate the "items" to be serially searched.

Attention↗

PubMed1986

Role of input factors in visual-field asymmetries.

This paper examines the implications of lateral tachistoscopic presentation of information for the processing efficiency of the intact cerebral hemispheres. Considering that the understanding of the processes underlying the particular competences of each hemisphere may require, as a preliminary step, the specification of the characteristics of the input on which the brain operates, anatomical, physiological, and psychophysical consequences of briefly stimulating the retinal periphery for the representation of information in the brain are outlined, with special reference to the spatial-frequency spectral composition of the stimuli. Retinal eccentricity and brief exposure duration converge to making the representation of information qualitatively different from the information that the brain normally operates on, which constrains the interpretation of findings with respect to the normal functions of the cerebral hemispheres. A review and discussion of empirical findings relevant to these issues suggest that manipulation of procedural variables may differentially affect the processing efficiency of the cerebral hemispheres and indicate that a given pattern of visual-field asymmetry may be overdetermined by a multitude of variables interacting in complex ways.

Discrimination Learning↗

PubMed1993

Cerebral lateralization.

Recent findings suggest that cerebral laterality will not be understood in terms of simple dichotomies, such as the idea that the left hemisphere is analytic and the right holistic. Rather, hemisphere differences can be better explained in terms of relatively specific principles that extend over limited domains. For visual perception and mental imagery, the left hemisphere appears to be relatively better than the right at encoding component parts, representing visual categories, and encoding categorical spatial relations; in contrast, the right hemisphere appears to be relatively better at encoding overall patterns, representing specific instances, and encoding coordinate metric spatial relations. Recent neural network models support a hypothesis that ties together these disparate findings.

Dominance, Cerebral↗

PubMed2007

Is there a general task switching ability?

Participants were tested on two analogous task switching paradigms involving Shape/Size tasks and Vertical/Horizontal tasks, respectively, and three measures of psychometric intelligence, tapping fluid, crystallized and perceptual speed abilities. The paradigms produced similar patterns of group mean reaction times (RTs) and the vast majority of the participants showed switching cost (switch RT minus repeat RT), mixing cost (repeat RT minus single-task RT) and congruency effects. The shared intra-individual variance across paradigms and with psychometric intelligence served as criteria for general ability. Structural equations modeling indicated that switching cost with ample preparation ("residual cost") and mixing cost met these criteria. However, switching cost with little preparation and congruency effects were predominantly paradigm specific.

Female↗

PubMed2004

The effect of hemispatial neglect on the perception of centre.

Highly variable bisection performance in neglect patients has been attributed to an increased 'zone of indifference'. The indifference zone indicates the discrepancy between two line lengths which are judged as equal in length. Following this argumentation, the central area of a line should be expanded in neglect patients. The present two experiments investigated for the first time the expansion of the central area using a modified version of the Landmark Task. The location of a central or asymmetrical bisection mark on a horizontal line had to be judged (centre/left/right). In both experiments neglect patients, unlike healthy and patient controls, showed clear deficits in judging the location of the mark correctly and tended to judge asymmetrical marks of up to 4 cm as centrally positioned. The results are in agreement with and provide the first clear evidence of an enlarged perceptual zone of indifference in patients with hemispatial visual neglect.

Aged↗

PubMed2005

Local advantage in the visual processing of hierarchical stimuli following manipulations of stimulus size and element numerosity in monkeys (Cebus apella).

Previous studies suggest that monkeys process local elements of hierarchical visual patterns more quickly and more accurately than they process the global shape. These results could be indicative of differences between relatively high visual functions of humans and non-human primates. It is, however, important to rule out that relatively low-level factors can explain these differences. We addressed this issue with two experiments carried out on capuchin monkeys (Cebus apella) using matching-to-sample tasks featuring hierarchical stimuli. The first experiment assessed whether manipulations of stimulus size can affect the local advantage so far observed in this New World monkey species. An overall local versus global advantage still emerges in capuchins, irrespectively of the amplitude of the visual angle subtended by the hierarchical shapes. Moreover, a local-to-global interference, indicative of a strong local advantage, was observed for the first time. In the second experiment, we manipulated size and numerosity of the local elements of hierarchical patterns, mimicking procedures that in human perception relegate the local elements to texture and enhance a global advantage. Our results show that in capuchin monkeys, a local advantage emerges clearly even when these procedures are used. These results are of interest since extensive neurophysiological research is carried out on non-human primate vision, often taking for granted a similarity of visual skills in human and non-human primates. These behavioural results show that this assumption is not always warranted and that more research is needed to clarify the differences in the processes involved in basic visual skills among primates.

Animals↗

PubMed2005

Sound lateralization in subjects with callosotomy, callosal agenesis, or hemispherectomy.

The question of whether there is a right-hemisphere dominance in the processing of auditory spatial information in human cortex as well as the role of the corpus callosum in spatial hearing functions is still a matter of debate. Here, we approached this issue by investigating two late-callosotomized subjects and one subject with agenesis of the corpus callosum, using a task of sound lateralization with variable interaural time differences. For comparison, three subjects with left or right hemispherectomy were also tested by employing identical methods. Besides a significant reduction in their acuity, subjects with total or partial section of the corpus callosum exhibited a considerable leftward bias of sound lateralization compared to normal controls. No such bias was found in the subject with callosal agenesis, but merely a marginal reduction of general acuity. Also, one subject with complete resection of the left cerebral cortex showed virtually normal performance, whereas another subject with left hemispherectomy and one subject with right hemispherectomy exhibited severe deficits, with almost total loss of sound-lateralization ability. The results obtained in subjects with callosotomy indicate that the integrity of the corpus callosum is not indispensable for preservation of sound-lateralization ability. On the other hand, transcallosal interhemispheric transfer of auditory information obviously plays a significant role in spatial hearing functions that depend on binaural cues. Moreover, these data are compatible with the general view of a dominance of the right cortical hemisphere in auditory space perception.

Acoustic Stimulation↗

PubMed2005

Egocentrism, allocentrism, and Asperger syndrome.

In this paper, we attempt to make a distinction between egocentrism and allocentrism in social cognition, based on the distinction that is made in visuo-spatial perception. We propose that it makes a difference to mentalizing whether the other person can be understood using an egocentric ("you") or an allocentric ("he/she/they") stance. Within an egocentric stance, the other person is represented in relation to the self. By contrast, within an allocentric stance, the existence or mental state of the other person needs to be represented as independent from the self. We suggest here that people with Asperger syndrome suffer from a disconnection between a strong naïve egocentric stance and a highly abstract allocentric stance. We argue that the currently used distinction between first-person and third-person perspective-taking is orthogonal to the distinction between an egocentric and an allocentric stance and therefore cannot serve as a critical test of allocentrism.

Asperger Syndrome↗

PubMed2006

The impact of object size and rigidity on infant reaching.

Although the changes in kinematics of infant reaching have been studied, few researchers have investigated the improvement of reaching regarding objects of distinct physical properties. The aim of this longitudinal study was to verify the impact of object size and rigidity on the development of reaching in 4-6-month-old infants. Four infants were observed with a motion capture system during trials with four objects of distinct sizes and rigidity. A total of 188 reaches were analyzed by using the 3D movement reconstruction. Our results showed that reaching frequency, mean velocity, and straightness index increased with age. The number of movement units decreased with age and increased for small objects. Rigidity was not shown to affect reaching trajectories. These findings suggest that infants are capable of perceiving the more relevant object properties, thus using their available motor capabilities to modify the essential variables so that they can reach the target more accurately.

Distance Perception↗

PubMed2006

Neural representations of perceived bodily actions using a categorical frame of reference.

In object-centered, or categorical, visual representations of an agent's actions, the spatial positions of (parts of) the body action are defined with respect to the principal axis of the agent, rather than in relation to the observer. Some cells in the superior temporal sulcus (STS) of the macaque monkey have been reported to use such a categorical frame of reference to code for bodily postures and actions, but their small numbers prevented a detailed investigation. Here we report for the first time that anterior sites in the STS contain a relatively large number of cells that use an object-centered frame of reference to code for animate objects and their actions. We further show that these cells are selectively responsive to much more restricted sections of an action trajectory than previously thought, and that they generalize over highly unusual, hitherto untested, orientations (such as upside-down walking). Quite remarkably, some cells coded for the position of a body part not only with respect to the object's body structure, but also with respect to objects in the immediate surrounding, such as the supporting substrate the agent was standing on. We illustrate these properties using three cell populations: one responding to rotations of the upper body with respect to the lower body, one responding to forward or backward walking actions, and one responding to flexions of the knees. We discuss a possible role for the object-centered STS cell populations in representing the abstract object structure of flexible, animate objects, which could enable their recognition even when presented in highly unusual poses. We further discuss their possible role in representing goal-directed or intentional actions, and in imitation.

Animals↗

PubMed2006

Inferring thought and action in motor neurone disease.

The traditional assumption that classical motor neurone disease (MND) invariably spares cognitive function is now recognised to be incorrect. Deficits have most commonly been demonstrated on executive tasks suggesting impaired function of frontal systems. Yet, crucial aspects of frontal lobe function have not hitherto been explored. The study used tests of theory of mind (ToM) (interpretation of cartoons and stories) to examine the ability of 16 patients with MND to interpret social situations and ascribe mental states to others. Only minor differences were elicited in the MND group as a whole compared to controls, and performance was not differentially affected for cartoons and stories requiring inference of another's mental state (mental) compared to control (physical) cartoons and stories. However, abnormalities were elicited on both mental and physical tasks in a subgroup of patients with bulbar signs. Moreover, examination of individual patient scores revealed a spectrum of performance ranging from normal to severely impaired. Errors were qualitatively similar to those seen in frontotemporal dementia (FTD). Performance on the ToM tasks was significantly correlated with conventional, untimed measures of executive function, suggesting that ToM deficits in MND are likely to be linked to a more general executive failure. The findings contribute to the understanding of ToM performance in neurodegenerative disease and provide further evidence of the association between MND and FTD.

Aged↗

PubMed2005

Effect of Morris water maze diameter on visual-spatial learning in different mouse strains.

The Morris water maze task is a widely used tool to assess hippocampus-dependent learning and memory in rodents. Performance depends upon several factors including not only the traits of the experimental animals, but also apparatus and protocol characteristics. The present study aimed at investigating the effect of maze diameter on acquisition and probe trial performance in three commonly used strains: C57Bl/6, BALB/c, and 129/SvEvBrd mice. Three maze diameters (150, 120, and 75 cm) were used under identical protocol and testing conditions. Downscaling maze dimensions, hence reducing difficulty and stress levels, did not allow BALB/c mice, commonly known as poor learners, to acquire this visual-spatial learning task. C57Bl/6 mice performed satisfactory in all three maze settings, with superior probe trial performance in the 120-cm-diameter setting. Further downscaling of maze dimensions might even render this task too simple for this strain. If the 129S5/SvEvBrd background strain is preferred, testing of visual-spatial learning abilities should be performed in a small sized MWM pool, as this strain performed only adequately in the smallest maze setting. Attention is drawn to the importance of supplying a detailed description 129 substrain nomenclature in future studies. Generalization of observations from one strain to another and from data obtained with a specific strain and maze diameter to other maze dimensions should be dealt with very carefully. The present study emphasizes the importance of a well-substantiated choice of background strain and water maze characteristics when researchers plan to investigate visual-spatial learning and memory in a chemically/lesion-induced or targeted mutagenesis model.

Animals↗

PubMed2005

Investigation of social and emotion information processing in temporal lobe epilepsy with ictal fear.

This study examined whether patients with temporal lobe epilepsy (TLE) and ictal fear (IF) show emotion recognition deficits similar to those associated with amygdala damage. Three groups of patients (13 with TLE and IF, 14 with TLE and nonfear auras (non-IF), and 10 with idiopathic generalized epilepsy (IGE)) completed tests of visual and face processing, face emotion recognition and social judgment, together with measures of psychological adjustment (Hospital Anxiety and Depression Scale; SCL-90-R) and Quality of Life (QOLIE-31). All three epilepsy groups had fear recognition deficits, with relatively greater impairments in the IF group. Fear recognition deficits were associated with impaired social judgment of trustworthiness, duration of epilepsy, and a measure of quality of life. Social cognition impairments previously associated with amygdala dysfunction are also a feature of the neuropsychology of TLE, and extend the hypothesis in that they may additionally play a role in IGE.

Adult↗