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Results for “Visual Perception”

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PubMed1990

The auditory P 300 correlates with specific cognitive deficits in Parkinson's disease.

An abnormally prolonged latency of the P 300 event-related potential has been reported in several types of dementing illnesses, including Parkinson's disease (PD). While some PD patients have dementia, a significant number of PD patients have less severe cognitive impairments. We examined the relationship between the auditory P 300 and a neuropsychological battery of 11 tasks in 43 PD patients. The quantitative relationship between the individual neuropsychological measures and the P 300 was examined using partial correlation and analysis of covariance techniques which controlled for age, education, and illness duration. The strongest correlations were between P 300 and both short-term memory and visual perception. Global cognitive deficits do not appear to relate to the abnormal P 300 responses in PD: instead, specific aspects of cognitive decline accounted for the electrophysiological abnormalities. An abnormally long or absent P 300 correlated with deficits on select cognitive tasks: those involving memory, visual perception, and abstract reasoning. The interactions between anatomical and neurochemical abnormalities in PD are discussed in light of the pattern of deficits seen in this study.

Adult↗

PubMed2000

Observation in laparoscopic surgery: overview of impeding effects and supporting aids.

Within a Dutch research program on minimally invasive surgery, a large literature survey has been carried out. This article describes the state of the art in research on observation in laparoscopy. It gives an overview of factors impeding the surgeon and technical developments designed to overcome these problems. A large number of journals, proceedings, patents, and books starting from the year 1991 have been consulted. The survey was completed with a thorough MEDLINE search. The survey showed that many authors have an incomplete background in the fundamentals of visual perception. This leads to a lack of understanding and to the design of supporting aids that often are not very useful. The new aspect of this study is that it gives a complete and structured overview of laparoscopic observation problems and current solutions. The observation problems are structured according to visual perception theory. The solutions are critically considered, and their benefits and drawbacks are identified. The study shows that the benefits of stereo-endoscopes and motorized endoscope positioners are questionable. The addition of shadows and movement parallax is still a very important research topic.

Humans↗

PubMed1996

Perception of visual motion with modulated velocity: effects of viewing distance and aperture size.

Subjects observed a random dot pattern that moved horizontally with modulated velocity within an invisible aperture. The velocity contrast, (V2-V1)/V1, was 2/3. Two different percepts occurred while observing this stimulus. At lower modulation frequencies, between 2 and 12 Hz, velocity changes were clearly seen; this percept is called "motion irregularity". At frequencies higher than 20 Hz velocity changes were no longer visible; the moving pattern appeared to be divided into stationary columns of different luminance. We call this percept "pattern irregularity". The critical frequency for detection of motion irregularity was independent of viewing distance; it was an inverted U-shaped function of the linear rather than the angular mean velocity of the pattern. At higher mean velocities the critical frequency increased with increasing aperture size; at lower mean velocities it was not affected by the size of the aperture. It is shown that detection performance is a function of the relative velocity of the pattern, i.e. of the ratio between the mean velocity in deg/sec and the aperture size in deg. Pattern irregularity could be detected at modulation frequencies even above 100 Hz. The critical frequency increased with increasing velocity and with decreasing viewing distance. It is suggested that detection of motion irregularity is determined by two distinct processes that are based on spatial analysis of motion at low relative velocities and temporal analysis at high relative velocities; both processes provide constancy of detection performance regardless of viewing distance. On the other hand, pattern irregularity seems to be detected on the basis of an analysis of the retinal luminance distribution at high modulation frequencies.

Adult↗

PubMed1989

Context-dependent migrations in visual word perception.

In the present study we investigate the effect of context--that is, a prime--on migration errors. Migration errors, or migrations, are caused by perceptual interactions between two words in a visual display, such as line-lace. After postcuing, subjects sometimes report lane or lice, instead of the requested word line. This phenomenon has been demonstrated by previous studies. In the experiments reported here, we replicate this phenomenon. We also find that more migrations of the lane type occur (compared with lice type), when the display line-lace is preceded by a prime related to lane (but not to lice). This shows that higher order word knowledge, in the form of semantic relations between words, influences the migration phenomenon. Further, we show that the number of migration errors are not a result of only a summation of activation from the letters in the display. The method we developed to isolate context-dependent migrations also gives valuable information about the effect of contextual information on word perception.

Attention↗

PubMed1981

The effects of early middle ear pathology on auditory perception and academic achievement.

Two groups of children were compared to determine the effects of early middle ear pathology on the development of auditory perceptual skills and academic achievement. The conductive loss (CL) group consisted of 15 children, aged seven to nine years, with histories of middle ear pathology. The normal control (NC) group was matched for age, sex, and socioeconomic status and had negative histories of middle ear pathology. Both groups were from a suburban community of primarily mild socioeconomic status. A test battery consisting of 12 auditory perceptual tests as well as measures of academic achievement, non-verbal intelligence and visual perception was administered. Results showed that the overall performance of the CL group on the test battery was significantly lower than that of the NC group. Performance of the CL group was also significantly lower in specific auditory perceptual areas. No significant differences were found on test of non-verbal intelligence or visual perception. Although scores were not significantly different on academic achievement tests, school records indicate that the CL loss group had received more special support services than the controls. This investigation suggests that early middle ear pathology may produce secondary effects that can persist well beyond the episodes of temporary conductive hearing loss.

Achievement↗

PubMed1994

Measuring right-hemisphere dysfunction in children: validity of two new computer tests.

The validity of two new computer-mediated tests for the detection of right-cerebral hemisphere lesions in children--the Right-hemisphere Dysfunction Test and the Visual Perception Test--was evaluated. Normative data were drawn from a group of 91 children (aged five to 14 years) and 14 young adults. The tests were also administered to 14 children with acquired lesions of either right- or left-cerebral hemisphere. The results demonstrate that the Right-hemisphere Dysfunction Test and the Visual Perception Test, with predictive values of 71 per cent and 88 per cent, respectively, are useful in clinical practice for detection of right-hemisphere dysfunction in children.

Adolescent↗

PubMed2005

Dissociation between perceptual processing and priming in long-term lorazepam users.

Acute effects of lorazepam on visual information processing, perceptual priming and explicit memory are well established. However, visual processing and perceptual priming have rarely been explored in long-term lorazepam users. By exploring these functions it was possible to test the hypothesis that difficulty in processing visual information may lead to deficiencies in perceptual priming. Using a simple blind procedure, we tested explicit memory, perceptual priming and visual perception in 15 long-term lorazepam users and 15 control subjects individually matched according to sex, age and education level. Explicit memory, perceptual priming, and the identification of fragmented pictures were found to be preserved in long-term lorazepam users, contrary to what is usually observed after an acute drug intake. The processing of visual contour, on the other hand, was still significantly impaired. These results suggest that the effects observed on low-level visual perception are independent of the acute deleterious effects of lorazepam on perceptual priming. A comparison of perceptual priming in subjects with low- vs. high-level identification of new fragmented pictures further suggests that the ability to identify fragmented pictures has no influence on priming. Despite the fact that they were treated with relatively low doses and far from peak plasma concentration, it is noteworthy that in long-term users memory was preserved.

Adult↗

PubMed1992

Relationships between orientation-preference pinwheels, cytochrome oxidase blobs, and ocular-dominance columns in primate striate cortex.

The relationships between cytochrome oxidase blobs, ocular-dominance columns, and iso-orientation domains, subsystems underlying visual perception, were explored in primary visual cortex of macaque monkey. High-resolution maps of these three subsystems were acquired. Optical imaging based on activity-dependent intrinsic signals revealed that the most prominent organizational feature of orientation preference was a radial arrangement, forming a pinwheel-like structure surrounding a singularity point. More than 80% of these pinwheels were centered along the midline of ocular-dominance columns. The iso-orientation contours of adjacent pinwheels crossed borders of ocular-dominance columns at approximately right angles. Pinwheels with the same or opposite directions of orientation-preference change were smoothly connected with each other. On the average, all orientations were equally represented. In exactly the same cortical area, the cytochrome oxidase blobs, thought to be involved in color processing, were also mapped, using cytochrome oxidase histology. Like the centers of pinwheels, the centers of blobs also lie along the midline of ocular-dominance columns. However, the centers of pinwheels did not coincide with the centers of blobs; these two subsystems are spatially independent. "Hypercolumn" modules, each including two complete pinwheels in two adjacent columns of complementary ocularity, as well as portions of a few blobs, were frequently found but did not seem to be the primary unit of cortical organization. An alternative to hypercolumns is proposed.

Animals↗

PubMed2003

Microstimulation of the frontal eye field and its effects on covert spatial attention.

Many studies have established that the strength of visual perception and the strength of visual representations within visual cortex vary according to the focus of covert spatial attention. While it is clear that attention can modulate visual signals, the source of this modulation remains unknown. We have examined the possibility that saccade related mechanisms provide a source of spatial attention by studying the effects of electrical microstimulation of the frontal eye fields (FEF) on spatial attention. Monkeys performed a task in which they had to detect luminance changes of a peripheral target while ignoring a flashing distracter. The target luminance change could be preceded by stimulation of the FEF at current levels below that which evoked saccadic eye movements. We found that when the target change was preceded by stimulation of FEF, the monkey could detect smaller changes in target luminance. The increased sensitivity to the target change only occurred when the target was placed in the part of the visual field represented by neurons at the stimulation site. The magnitude of improvement depended on the temporal asynchrony of the stimulation onset and the target event. No significant effect of stimulation was observed when long intervals (>300 ms) between stimulation and the target event were used, and the magnitude of the increased sensitivity decreased systematically with increasing asynchrony. At the shortest asynchrony, FEF stimulation temporally overlapped the target event and the magnitude of the improvement was comparable to that of removing the distracter from the task. These results demonstrate that transient, but potent improvements in the deployment of covert spatial attention can be obtained by microstimulation of FEF sites from which saccadic eye movements are also evoked.

Animals↗

PubMedDate not supplied

The effects of sensorimotor-based intervention versus therapeutic practice on improving handwriting performance in 6- to 11-year-old children.

OBJECTIVE: The aim of this study was to investigate the effects of two interventions (sensorimotor and therapeutic practice) on handwriting and selected sensorimotor components in elementary-age children. METHOD: Thirty-eight children 6 to 11 years of age with handwriting dysfunction but no identified educational need were randomly assigned to one of the two intervention groups or a control group. Intervention groups met four times per week over 5 weeks. Handwriting was measured pre- and postintervention using the Test of Handwriting Skills. Visual perception (motor-reduced), visual-motor integration, proprioception, and in-hand manipulation were also measured. RESULTS: Children receiving therapeutic practice moderately improved handwriting whereas children receiving sensorimotor intervention declined in handwriting performance. The control group did not change significantly. Sensorimotor impairment was noted at pretest in three or four components and selected sensorimotor component function improved with intervention. CONCLUSION: Therapeutic practice was more effective than sensorimotor-based intervention at improving handwriting performance. Children who received sensorimotor intervention improved in some sensorimotor components but also experienced a clinically meaningful decline in handwriting performance.

Child↗

PubMed1982

Functional optical invariants: a new methodology for aviation research.

The application to aviation psychology of Gibson's (4) "ecological approach to visual perception" demands information-rich visual displays to adequately and unambiguously enable a pilot to perform flight maneuvers. Optical information often takes the form of invariant properties of a changing optic array, and functional invariants are defined as psychologically effective optical invariants. Their effectiveness is determined by empirical test, but standard experimental paradigms are shown to be inappropriate for testing the effectiveness of information-rich displays. This is due to the presence of inherent and unavoidable confounding factors that are here termed "secondary independent variables" in contradistinction to the "primary independent variables" manipulated by the experimenter. Recommendations for a new methodology and statistical treatment are offered, and the implications for aviation psychology are discussed.

Aerospace Medicine↗

PubMed1990

Visual memory and the perception of a stable visual environment.

The visual world appears stable and continuous despite eye movements. One hypothesis about how this perception is achieved is that the contents of successive fixations are fused in memory according to environmental coordinates. Two experiments failed to support this hypothesis; they showed that one's ability to detect a grating presented after a saccade is unaffected by the presentation of a grating with the same spatial frequency in the same spatial location before the saccade. A third experiment tested an alternative explanation of perceptual stability that claims that the contents of successive fixations are compared, rather than fused, across saccades, allowing one to determine whether the world has remained stable. This hypothesis was supported: Experienced subjects could accurately determine whether two patterns viewed in successive fixations were identical or different, even when the two patterns appeared in different spatial positions across the saccade. Taken together, these results suggest that perceptual stability and information integration across saccades rely on memory for the relative positions of objects in the environment, rather than on the spatiotopic fusion of visual information from successive fixations.

Attention↗

PubMed2006

Grouping does not require attention.

Many theories of visual perception stipulate that Gestalt grouping occurs preattentively. Subjects' failure to report perceiving even salient grouping patterns under conditions of inattention challenges this assumption (see, e.g., Mack, Tang, Tuma, Kahn, & Rock, 1992), but Moore and Egeth (1997) showed that although subjects are indeed unable to identify grouping patterns outside the focus of attention, effects of these patterns on visual perception can be observed when they are assessed using implicit, rather than explicit, measures. However, this finding, which is the only one to date demonstrating grouping effects without attention, is open to an alternative account. In the present study, we eliminated this confound and replicated Moore and Egeth's findings, using the Müller-Lyer illusion (Experiments 1 and 2). Moreover, we found converging evidence for these findings with a variant of the flanker task (Experiment 3), when the amount of available attentional resources was varied (Experiments 4 and 5). The results reinforce the idea that, although grouping outside the focus of attention cannot be the object of overt report, grouping processes can occur without attention.

Attention↗

PubMed2004

[Visual cortex in the Tolosa-Hunt syndrome. Functional imaging for the detection of a psychogenic disorder--a case report].

Besides painful ophthalmoplegia, patients suffering from Tolosa-Hunt syndrome often present increasing loss of visual perception. The impairment of the optic nerve leads to a delay of the VEP (visual evoked potentials) responses. Using the method of magnetic resonance imaging (MRI), some patients present unspecific alterations in the vicinity of the optic nerve. However, both methods (VEP and MRI) are unsuitable to assess the effect of an impaired optic nerve function on neuronal processing in the visual cortex. We report one patient suffering from Tolosa-Hunt syndrome affecting the optic nerve. We used fMRI (functional magnetic resonance imaging) to show how this impairment of the optic nerve alters cortical processing of visual information. The activity of the unaffected visual cortex was bilaterally reduced when compared to healthy volunteers but greater that obtained from patients suffering from bilateral occipital infarction. Our results offer new opportunities to assess the efficiency of therapy in patients with increasing loss of visual perception due to the Tolosa-Hunt syndrome. Further studies are necessary to investigate, whether fMRI also provides the possibility to assess the efficiency of drug therapy on optic nerve function.

Humans↗

PubMed1998

The effect of pictorial illusion on prehension and perception.

The present study examined the effect of a size-contrast illusion (Ebbinghaus or Titchener Circles Illusion) on visual perception and the visual control of grasping movements. Seventeen right-handed participants picked up and, on other trials, estimated the size of "poker-chip" disks, which functioned as the target circles in a three-dimensional version of the illusion. In the estimation condition, subjects indicated how big they thought the target was by separating their thumb and forefinger to match the target's size. After initial viewing, no visual feedback from the hand or the target was available. Scaling of grip aperture was found to be strongly correlated with the physical size of the disks, while manual estimations of disk size were biased in the direction of the illusion. Evidently, grip aperture is calibrated to the true size of an object, even when perception of object size is distorted by a pictorial illusion, a result that is consistent with recent suggestions that visually guided prehension and visual perception are mediated by separate visual pathways.

Adult↗

PubMed1998

Prefrontal hypooxygenation during language processing assessed with near-infrared spectroscopy.

Near-infrared spectroscopy (NIRS) is a noninvasive optical method which allows in vivo measurements of relative concentrations of oxygenated (O2Hb) and desoxygenated hemoglobin (HHb). It has been successfully applied to assess the blood oxygenation changes during cerebral ischemia in man. An interesting application of NIRS is the investigation of regional cerebral blood oxygenation during physiological brain functions. In the present study, left and right anterior prefrontal brain areas of 10 healthy subjects were investigated with 2-channel NIRS during language processing (reading aloud). Nonverbal visual perception (picture observation) was performed as a control condition. Compared to the respective baseline conditions, a significant HHb increase and an O2Hb decrease as a trend were found during language processing but not during the nonverbal perceptual task, and no hemispheric differences were found. The metabolic activation patterns differed significantly between the tasks indicating the changes due to the language-related efforts but not to visual perception. Based on previous findings of metabolic brain imaging studies the results are best explained as a complementary phenomenon consisting in relative anterior prefrontal hypoperfusion due to a blood volume redistribution which favors language-related temporal areas.

Adult↗

PubMed2001

Activation of striate cortex in the absence of visual stimulation: an fMRI study of synesthesia.

It has been suggested that internally generated visual perception involves the primary visual cortex V1. To test this hypothesis, a functional MRI study was conducted with a female subject with orthographic color-word synesthesia. This subject was selected as she reported clear involuntary visualization of auditorily presented verbal material. Hearing a word resulted in seeing the word in a particular color. fMRI scans were acquired while the subject performed two verbal tasks (passive listening to words and verbal fluency). Significant activity was detected in primary visual cortex, in the absence of external visual stimulation. This finding provides evidence for a role of modulatory feedback connections between associative and primary visual areas in visual experience without direct visual stimulation.

Acoustic Stimulation↗

PubMed1985

The common mirror dream, dreamer, and the dream mirror.

From the widely diverse category of so-called mirror dreams, we have differentiated the most frequent, which we have designated the common mirror dream (CMD). It is one in which the dreamer at some point looks into a mirror and reports seeing himself, a part of himself or a distorted though recognizable version of himself. Mirror dreams, including CMDs, are distinctly uncommon. Every dreamer of CMDs in our series had felt enjoined by the mother (in most cases with the father's collusion) not to see and regard her clearly and not to be an accurately reflecting mirror for her. The intensity with which the maternal injunction against accurate visual perception and evaluation was feared was an important distinguishing feature in our patients with CMDs. The essence of the CMD has been hypothesized to be a reciprocal, reverberating, visual-exhibitionistic dyad representative of the mother-child relationship. The dream mirror may represent the wish that the analyst-mother counter a feared parental injunction against accurate visual perception and evaluation so as to correct the distorted perceptions of self and objects and provide visual affirmation of the value and integrity of the self-representation. For some patients, defense against the dangers of castration and loss of maternal love was accomplished by the mirror mechanisms of magically transforming images in the mirror, the ease of creating illusion in the mirror, and a fetishistic mechanism of visually reintrojecting a phallic symbol from the mirror. Our data failed to confirm many of the hypotheses of previous contributors as to specific symbolic meanings of the dream mirror. More relevant than the symbolism of the dream mirror are the many functions of the dream mirror for the dreamer. These are analyzed and discussed.

Adult↗