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PubMed1995

Ocular torsion position and the perception of visual orientation.

Previous studies have shown that in patients with unilateral vestibular deafferentation (UVD) there is a close relationship between the change in ocular torsional position consequent on the UVD, and the visually perceived orientation of short dim lines in an otherwise darkened room (1). However that result may have been confounded because the UVD may have affected both ocular torsion and sensory information about head position re gravity which must be used in making the visual perceptual judgement. Therefore we have sought a means of testing the relationship between ocular torsional position and the visual perception of orientation which was not confounded by the possible effect of changes in perceived head position.

Afferent Pathways↗
PubMed2006

Evidence from two genetic syndromes for the independence of spatial and visual working memory.

This study aimed at investigating the possible dissociation between visual-object and visual-spatial working memory (WM) in individuals with Williams syndrome (WS) and Down syndrome (DS). Four study groups were included: WS group (10 males, 5 females) with a mean chronological age (CA) of 19 years 8 months (SD 6y 1mo) and a mean mental age (MA)of 6 years 11 months (SD 1y 5mo); WS comparison group (7 males, 8 females) comprised of typically developing children with a mean CA of 6 years 10 months (SD 10mo) and a mean MA of 6 years 11 months (SD 8mo)matched as a group with the participants with WS on the basis of mental age; DS group (11 males, 7 females) with a mean CA of 15 years 10 months (SD 5y 8mo) and a mean MA of 5 years 2 months (SD 8mo); and DS comparison group (10 males, 8 females) with a mean CA of 5 years and 1 month (SD 7mo)and a mean MA of 5 years 2 months (SD 8mo) selected to match the DS group on the basis of mental age. They were all administered tests that explored visual perception (Visual Perception Test - Subtest 4 and Line Orientation tests), visual imagery (imaging the colour of objects and the tail length of well-known animals), spatial imagery (mental rotation of visually presented or verbally evoked objects), and WM for visual-object and visual-spatial information. Individuals with WS exhibited specific difficulties in the visual-spatial, but not the visual-object, WM task. Instead, people with DS showed reduced performance in both tests. However, whereas the observed deficit in individuals with DS persisted when perceptual abilities were taken into account, the deficit in individuals with DS was compensated when their scores were adjusted for performance on perceptual tasks. These results support the hypothesis of a dissociation within the sketch-pad slave system in the WM model and reinforce the view of intellectual disability as a non-unitary condition.

Adolescent↗
PubMed2004

Human non-phase-locked gamma oscillations in experience-based perception of visual scenes.

Perception results from ongoing interactions between stimulus-driven visual processes and cognitive context. These reciprocal relations are emphasized when a visual stimulus is degraded, forcing the perceiver to fill the missing information in, based on internal representations. The neural mechanisms by which internal representations facilitate visual perception are still unclear. Here we investigated the role of EEG oscillations in the gamma band, thought to reflect the elaboration of internal visual representations, in the experience-based perception of visual scenes. Twelve subjects were trained with degraded images of natural scenes. EEG was recorded while they performed a detection task on trained and untrained degraded stimuli. Non-phase-locked gamma band responses in a large frequency spectrum (55-85 Hz) were observed around 200 ms post-stimulus onset at posterior sites, and were larger when subjects reported an accurate perception based on previous experience. These results suggest that mid-latency gamma oscillations in the visual cortex underlie the experience-based perception of visual scenes.

Adult↗
PubMed1997

Visually induced motion perception and visual control of postural sway in congenital nystagmus.

In congenital nystagmus (CN) the threshold for detecting motion of visual objects is increased. To determine whether this increase is due to a deterioration of visual motion signals or whether visual-vestibular interactions (which are necessary to judge object-motion in space) are also involved we examined how CN patients use visual motion signals to evaluate self-motion in perceptual and behavioral tasks. Using an optokinetic drum we measured the minimum optokinetic acceleration necessary to induced motion perception of the visual environment in CN patients. This threshold was significantly elevated in the CN patients compared with normals (20.1 deg/s2 to 3.25 deg/s2). We further addressed the question whether the elevation of this threshold is due to a deficiency in evaluating visual motion in general or to a specific modification affecting the percept of visual object-motion with respect to the inertial reference only. We thus measured the latency of visually induced self-motion perception, which was found to be very similar or even slightly smaller (1.7 +/- 0.7 s) compared with normals (2.2 +/- 1.7 s). Moreover, subjects with CN were found to use vision quite efficiently for the visual stabilization of posture (Romberg quotient 2.0 +/- 1.16), even if they did not reach the level of normals (Romberg quotient 3.7 +/- 1.1). The results indicate that CN affects the estimate of object-motion in a specific and much more severe way than the estimate of self-motion. The minimal effect of CN on self-motion perception can be explained by the low pass characteristics of the optokinetic input to self-motion perception. The specific deficiency in detecting object-motion indicates that adaptation to CN occurs on the level of visual--vestibular interactions for the perception of visual object-motion and not on the level of visual motion signals.

Adolescent↗
PubMed1997

Visual search, perception, and visual-motor skill in "healthy" children born at 27-32 weeks' gestation.

Visual-perceptual, attentional, and visual-motor skills were examined in a group of 16 school-age children, born at 27-32 gestational weeks, who had performed normally on pediatric screening tests. Compared with 16 matched full-term controls, the preterms performed poorly on only two measures: they took longer to point to the missing arc of an annulus displayed on a computer screen and failed to find targets more often in a complex visual search task. They showed no deficits on tests of visual form extraction and closure. These data suggest that in the absence of any disability that is clinically detectable, prematurity results in a cluster of small but significant visual-motor impairments that persist into middle childhood. These relate to the maintenance of attention and visual-motor coordination, though visual form perception is not measurably affected. The results are discussed in the context of current neurobiological models of visual system organization.

Analysis of Variance↗
PubMed2002

Spatial and temporal characteristics of visual motion perception involving V5 visual cortex.

The anatomical substrates of the perception of motion have not yet been established in a detailed way on an individual level. The aim of this study was to develop a systematic procedure for mapping the visual cortex using Transcranial Magnetic Stimulation (TMS). The results showed that such an individual and detailed map of the spatial and temporal characteristics of motion perception can be constructed using TMS.

Adult↗
PubMed2006

Noise characteristics and prior expectations in human visual speed perception.

Human visual speed perception is qualitatively consistent with a Bayesian observer that optimally combines noisy measurements with a prior preference for lower speeds. Quantitative validation of this model, however, is difficult because the precise noise characteristics and prior expectations are unknown. Here, we present an augmented observer model that accounts for the variability of subjective responses in a speed discrimination task. This allowed us to infer the shape of the prior probability as well as the internal noise characteristics directly from psychophysical data. For all subjects, we found that the fitted model provides an accurate description of the data across a wide range of stimulus parameters. The inferred prior distribution shows significantly heavier tails than a Gaussian, and the amplitude of the internal noise is approximately proportional to stimulus speed and depends inversely on stimulus contrast. The framework is general and should prove applicable to other experiments and perceptual modalities.

Bayes Theorem↗
PubMed2002

Feeling with the mind's eye: contribution of visual cortex to tactile perception.

Visual imagery is implicated in the normal tactile perception of certain object properties. This is an example of cross-modal interactions that characterize normal perception. Here we review recent studies from our laboratory on cross-modal interactions between vision and touch in normally sighted humans. Positron emission tomography was used to demonstrate activation of a region of extrastriate visual cortex, near the parieto-occipital fissure, during tactile discrimination of grating orientation. Transcranial magnetic stimulation (TMS) over this region interfered with performance of this tactile task. In both studies, visual cortical involvement was found for tactile discrimination of orientation but not spatial frequency. Thus, this cortical region is not only active during but also necessary for optimal tactile sensing of orientation. Recent findings implicating visual cortex in Braille-reading in the blind should be evaluated from this perspective.

Animals↗
PubMed1978

Kindergarten predictors of three aspects of reading achievement.

Kindergarten measures of intelligence, auditory perception, visual perception, and associative learning were used to predict three aspects of reading achievement (word attack, word recognition, and comprehension) at the end of Grades 1,2, and 3 for 79 subjects. The predictability of each measure was a function not only of grade, but also of the aspect of reading achievement being predicted. Multiple correlations of the predictors tended to increase across grade levels and were highest for the comprehension aspect of reading. The Number Facility subtest of the PMA was the over-all best predictor or reading achievement. Possible reasons for this and other findings are discussed.

Achievement↗
PubMed1984

[Comparative study of features of the perceptive and intellectual activity of schizophrenic children].

A comparative study of the formation of the intellectual and perceptive activity in schizophrenic children aged 5 to 13 years (n = 102) as compared to healthy age-matched controls (n = 150) was carried out. Two complexes of techniques were employed, aimed at investigation of two interrelated aspects (operational and selective) of intellectual and perceptive (visual perception) activity. Dissociation of these components of cognitive activity observed in schizophrenic children already during the formation of perception gets more pronounced in the formation of thought. Dissociation of the development of the intellectual and perceptive activity of schizophrenic children may be considered as a component of abnormal mental development.

Adolescent↗
PubMed2005

Benign childhood epilepsy with occipital paroxysms: neuropsychological findings.

Benign childhood epilepsy with occipital paroxysms is classified among childhood benign partial epilepsies. The absence of neurological and neuropsychological deficits has long been considered as a prerequisite for a diagnosis of benign childhood partial epilepsy. Much evidence has been reported in literature in the latest years suggesting a neuropsychological impairment in this type of epilepsy, particularly in the type with Rolandic paroxysms. The present work examines the neuropsychological profiles of a sample of subjects affected by the early-onset benign childhood occipital seizures (EBOS) described by Panayotopulos. The patient group included 22 children (14 males and 8 females; mean age 10.1+/-3.3 years) diagnosed as having EBOS. The patients were examined with a set of tests investigating neuropsychological functions: memory, attention, perceptive, motor, linguistic and academic (reading, writing, arithmetic) abilities. The same instruments have been given to a homogeneous control group as regards sex, age, level of education and socio-economic background. None of the subjects affected by EBOS showed intellectual deficit (mean IQ in Wechsler Full Scale 91.7; S.D. 8.9). Results show a widespread cognitive dysfunction in the context of a focal epileptogenic process in EBOS. In particular, children with EBOS show a significant occurrence of specific learning disabilities (SLD) and other subtle neuropsychological deficits. We found selective dysfunctions relating to perceptive-visual attentional ability (p<0.05), verbal and visual-spatial memory abilities (p<0.01), visual perception and visual-motor integration global abilities (p<0.01), manual dexterity tasks (p<0.05), some language tasks (p<0.05), reading and writing abilities (p<0.01) and arithmetic ability (p<0.01). The presence of cognitive dysfunctions in subjects with EBOS supports the hypothesis that epilepsy itself plays a role in the development of neuropsychological impairment. Supported by other studies that have documented subtle neuropsychological deficits in benign partial epilepsy, we stress the importance of reconsidering its supposed "cognitive benignity", particularly in occipital types.

Adolescent↗
PubMed1991

Perception, cognition, and visualization.

Visualization refers to the cognitive functions of visual perception. In visualization, pictures combine aspects of naturalistic representation with more formal shapes to enhance cognitive understanding. These "diagrammatic" shapes derive from geometrical elements and thereby bestow visual concreteness to concepts conveyed by the pictures. Leonardo da Vinci's anatomical drawings survive as masterful prototypes exemplifying these traits.

Anatomy, Artistic↗
PubMed2004

Visual function and subjective perception of visual ability after macular hole surgery.

PURPOSE: To evaluate the functional and anatomical results of macular hole surgery and to explore its effect on patients' Health-Related Quality Of Life (HR-QOL) and to investigate the associations between self-reported HR-QOL and conventional measures of visual function. DESIGN: Case series. METHODS: The National Eye Institute 25-Item Visual Function Questionnaire (VFQ-25) and the 36-Item Short-Form Health Survey (SF-36) were self-administered by 30 patients before and 4 months after macular hole surgery. Preoperative, intraoperative, and postoperative clinical data were collected including visual acuity, contrast sensitivity, and metamorphopsia. Multi-item scales rating different aspects of HR-QOL were compared before and after surgery, and their correlation with traditional methods of outcome evaluation was analyzed. RESULTS: Macular hole closure was achieved in 26 patients (87%). Mean LogMAR visual acuity improved by 6 +/- 10 letters for distance and 7 +/- 12 letters for near. Metamorphopsia was reduced by a mean of 35 +/- 70 squares on Amsler chart, and Pelli-Robson contrast sensitivity decreased by a mean of -0.09 +/- 0.3 log units postoperatively. The VFQ-25 composite score as well as scale scores associated with general vision, near vision, vision-related mental health, and role difficulties were significantly improved (P < .05) after successful closure of macular hole. Conversely out of the eight SF-36 health concepts, limitation in usual role activities because of emotional problems was the only one that significantly improved postoperatively. Both baseline and postoperative best-corrected visual acuity significantly correlated with most of the VFQ subscale scores before and after surgery, respectively. CONCLUSIONS: In this case-series, macular hole surgery appears to have a beneficial effect on patients' subjective perception of visual function. The use of vision-targeted health status questionnaires in conjunction with detailed clinical examination provides a more comprehensive overview of individuals' daily well-being after surgical intervention. Further controlled studies are required to confirm our findings.

Aged↗
PubMed1990

Delineation of single-word semantic comprehension deficits in aphasia, with anatomical correlation.

In 3 of 18 aphasic patients pure deficits in semantic comprehension at the single-word level were defined through a series of tasks that excluded possible confounding deficits in auditory perception, visual perception, or speech production. In these pure cases, deficits were found at the superordinate, equivalence, and subordinate levels of single-word semantic processing. Pure semantic deficits were found to be correlated with damage to the left posterior temporal and inferior parietal region; patients whose damage spared this area did not evince such deficits, and the converse was also true. This study confirms the existence of separable deficits in semantic comprehension and points conclusively to the left posterior temporal and inferior parietal region as being critical for semantic processing. This anatomical localization is in keeping with anatomical studies from nonhuman primates, suggesting that these regions may be concerned with multimodal processing and integration of language.

Aphasia↗