Laminar cortical dynamics of visual form perception.
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Neural Networks, Computer↗
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Results for “Visual Perception”
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Orientation of selective effects of body tilt on visually induced perception of self-motion.
We examined the effect of body posture upon visually induced perception of self-motion (vection) with various angles of observer's tilt. The experiment indicated that the tilted body of observer could enhance perceived strength of vertical vection, while there was no effect of body tilt on horizontal vection. This result suggests that there is an interaction between the effects of visual and vestibular information on perception of self-motion.
Humans↗
[Superillusions (a new category of visual illusions)].
The author describes special type of visual illusion, specific to man, which he calls "super-illusion". It results from an erroneous decoding of a true visual perception, which in the observer's eye is in itself expected to be an illusory distortion of reality. The attached drawings (Fig. 1, 2, 3) illustrate the discussed forms of visual perception, and its possible distortion. Fig. 1: Undistorted, normal visual perception. Appropriate interpretation of a visual signal. A leaf is seen as a leaf. Fig. 2: "Appropriate" visual perception and interpretation of the defense mechanism called crypsis. Crypsis here serves its original purpose--visual illusion. Anaea butterfly, a leaf mimic, is perceived as a leaf. Fig. 3: "Inappropriate" interpretation of undistorted visual signal. Anticipation of crypsis, which is not present. A leaf is perceived as a leaf mimicking butterfly. This phenomenon, called "super-illusion" (anticipatory visual illusion) is common in entomologists--lepitopterists.
Diagnostic Errors↗
From visual function deficiency to handicap: measuring visual handicap in Mali.
BACKGROUND/AIMS: Blindness is a major public health problem in developing countries, even though most could be prevented by relatively simple hygienic and medical interventions. Relatively few patients use the quality health care services available, despite their low cost, due to problems of access or socio-cultural barriers. This health services research project stressed the need for measurement of subjective self-perceived health. The objectives of this study were twofold: a) To translate, adapt and integrate the cultural context found in Mali and validate two instruments for measuring, respectively, perceived vision and quality of life. b) To study the relationship between these variables and visual deficiencies by gender. METHODS: The perceived vision and quality of life questionnaires were based on a translation of the Aravind questionnaire, adapted to Mali. The resulting perceived vision questionnaire comprises 13 questions, grouped according to five subscales (global vision, visual perception, sensory adaptation, visual field and depth perception). Furthermore, the 13 questions on quality of life were grouped into four subscales (personal care, mobility, social life and psychological). For both questionnaires, a global score could be computed. These two questionnaires were administered to a representative sample of 203 subjects with impaired vision, aged over 40, in a rural area in Mali. RESULTS: The acceptability of the questionnaires was good (1% missing data). The convergent validity was adequate for all but one subscale (psychological). The discriminate validity is acceptable for three of the six subscales where measurement can be made (visual perception, personal care, mobility). The Cronbach alpha coefficients indicate good reliability for the global scores. CONCLUSIONS: Analysis of mean results confirms the validity of the International Classification of Disease (ICD) definition of blindness (seeing less than 0.05 results in a steep decrease in quality of life). Moreover, blindness affects the quality of life of women more severely than that of men; this may be related to the availability of social support.
Adult↗
Depth separation between foreground and background on visually induced perception of self-motion.
A uniformly moving visual pattern can induce observer's self-motion perception in the opposite direction (vection), and an additional static stimulus can modulate (facilitate or inhibit) the strength of it. The present study was designed to investigate the effects of stimulus depth order and the depth distances of the visual stimulus on the inhibition and facilitation of vection caused by the additional static stimulus, measuring duration and estimated magnitude of vection as indices of vection strength. Analysis of this psychophysical experiment with four participants indicated that the static foreground presented in front of the moving pattern can facilitate vection, whereas the static background inhibits it (Duration: F1,3= 12.06, p<.05; Estimation: F1,3= 13.87, p<.05). Furthermore, the depth distances from the observer or the depth separation between the foreground and the background did not affect the self-motion perception (F2,6 < 1.0 for duration and estimation).
Adult↗
Improvements in performance following optometric vision therapy in a child with dyspraxia.
SS, an 8-year-old boy with dyspraxia, presented for behavioural optometry assessment. He had been diagnosed with a subtle form of dyspraxia by his paediatric occupational therapist, based on poor proprioception, delayed bilateral integration and poor visual perception. A full visual assessment was carried out. SS was given a programme of reflex inhibition exercises for 3 months. Then, a programme of optometric vision therapy (OVT) exercises was prescribed at home and in practice for a period of 8 months. SS was assessed using a battery of occupational therapy Sensory Integration and Praxis Tests (SIPT) before optometric intervention, and after OVT. There were significant improvements in fusional reserves, accommodative facility and oculomotor control of pursuit and saccadic eye movements. His reading level had changed by 4 years in 11 months. The SIPT results showed improvements in the visual and motor/visual perception subtests, confirming the significant changes in visual perceptual performance. Consideration is given to treatment modalities for dyspraxia, and the studies confirming their effectivity of approach. This case study provides evidence supporting the use of OVT eye exercises in dyspraxia, ocular motility, accommodative dysfunction, learning difficulties and sports performance. The need for further research and inter-professional working is discussed.
Apraxias↗
Stimulus size and eccentricity in visually induced perception of horizontally translational self-motion.
The effects of the size and eccentricity of the visual stimulus upon visually induced perception of self-motion (vection) were examined with various sizes of central and peripheral visual stimulation. Analysis indicated the strength of vection increased linearly with the size of the area in which the moving pattern was presented, but there was no difference in vection strength between central and peripheral stimuli when stimulus sizes were the same. Thus, the effect of stimulus size is homogeneous across eccentricities in the visual field.
Adult↗
Temporal window of integration in auditory-visual speech perception.
Forty-three normal hearing participants were tested in two experiments, which focused on temporal coincidence in auditory visual (AV) speech perception. In these experiments, audio recordings of/pa/and/ba/were dubbed onto video recordings of /ba/or/ga/, respectively (ApVk, AbVg), to produce the illusory "fusion" percepts /ta/, or /da/ [McGurk, H., & McDonald, J. (1976). Hearing lips and seeing voices. Nature, 264, 746-747]. In Experiment 1, an identification task using McGurk pairs with asynchronies ranging from -467 ms (auditory lead) to +467 ms was conducted. Fusion responses were prevalent over temporal asynchronies from -30 ms to +170 ms and more robust for audio lags. In Experiment 2, simultaneity judgments for incongruent and congruent audiovisual tokens (AdVd, AtVt) were collected. McGurk pairs were more readily judged as asynchronous than congruent pairs. Characteristics of the temporal window over which simultaneity and fusion responses were maximal were quite similar, suggesting the existence of a 200 ms duration asymmetric bimodal temporal integration window.
Acoustic Stimulation↗
Comparative assessment of visual perceptual abilities in the trainable mentally retarded.
Visual perceptual abilities of 47 institutionalized trainable retarded subjects were compared on selected measures of visual perception. Significant relationships were found between the Developmental Test of Visual Perception and the Matching and Copying subtests of the Metropolitan Readiness Test. Only moderate correlations were found between these two subtests and Motor-free Visual Perception Test.
Adolescent↗
Changes in horizontal oculomotor behaviour coincide with a shift in visual motion perception.
During full-field rotation of the visual field, subjects commonly experience an initial perception of object-motion which 'switches' to a perception of self-motion. We studied the characteristics of the horizontal optokinetic nystagmus responses evoked by a moving visual stimulus in these two perceptual states over a range of stimulus velocities. During self-motion perception mean eye position was found to shift more in the direction of the newly appearing stimulus elements with a slight reduction in slow phase gain in comparison to the nystagmus evoked during object-motion perception. The results may reflect a modified strategy of spatial attention with increased emphasis on anticipatory eye movements during visually induced self-motion perception.
Adult↗
Visual motion perception at the time of saccadic eye movements and its relation to spatial mislocalization.
The same retinal image motion can be produced by a variety of combinations of eye and target motion. In natural conditions, extraretinal information disambiguates retinal information for motion perception. By controlling the timing of visual motion with respect to saccades, it was possible to appraise the roles for motion perception of the signal related to saccades occurring in the vicinity of visual motion. When a visual motion was seen before or after a saccade, its perceived direction was biased in the direction opposite to the saccade. The magnitude of the bias depended on the timing of the visual motion with respect to the saccade and the meridian of the visual motion. The bias appears to be independent of the deformation of visual space reported to occur before and after saccades.
Humans↗
Levodopa's awakening effect on patients with Parkinsonism.
The effects of levodopa on tests measuring auditory and visual perception, auditory, and visual short-term memory, verbal learning, and on attention and concentration were studied in 29 patients with Parkinsonism. Thirty-two control subjects matched with the Parkinsonism patients on age, educational level, and verbal IQ were administered the same tests to control for practice effects. Significant improvement occurred for the Parkinsonism patients in verbal learning (an intermediate memory test) and in auditory perception. These improvements were unrelated to changes in anticholinergic medications, increases in alertness or concentration, lessening of depression, or improved motor ability or control. There was no test evidence of levodopa improving visual perception, short-term auditory or visual memory, alertness or concentration. Thus, there is no objective test evidence for levodopa producing a generalized awakening or an alerting effect in Parkinsonism patients who are intellectually alert and well-orientated. Interpretation of the test findings suggests a specific awakening effect, that of improvement in intermediate memory but not in short-term memory. Overall, the Parkinsonism group scored below the control group on all tests, suggesting that cognitive impairment accompanies Parkinson's disease even in patients who are intellectually intact and well oriented.
Adult↗
Development behaviors: delayed appearance in monkeys asphyxiated at birth.
Developmental behaviors were studied in monkeys subjected to asphyxia at birth. Visual depth perception, visual pla ing, and locomotion appeared significantly later than in nonasphyxiated monkeys. After these behaviors had been established in asphyxiates, however, there was little difference from those observed in normal monkeys. These results were compared with reports of permanent learning deficits that occur in monkeys asphyxiated at birth for similar periods of time. Such comparison suggests that the neural structures responsible for the developmental behaviors studied are not damaged by asphyxia to the same extent as those for acquisition. Delay in development may be an early indication of brain damage with subsequent mental retardation.
Amnesia↗
Helping to solve problems associated with spina bifida: 1. Presentation of the TRS Project: organizing services for low frequency diagnostic groups and 2. Cognitive deficits often seen in young adults with spina bifida: effects in the school and work place.
1. A Presentation of the TRS Project: Counselling and (Re)habilitation Center. A Model Project in Organizing Services for Low Frequency Diagnostic Groups. Persons with low frequency disabilities often require services from a number of professions. The patient organizations claim that the patients themselves often have to coordinate their own treatment. The TRS project has been established as one of the initiatives under the Norwegian Government's Plan of Action for the Disabled. The project is one of three national projects designed to develop models for the coordination of services for persons with low frequency congenital disabilities. The TRS project deals with the following five diagnoses: Marfan syndrome, arthrogryphosis multiplex congenita, myelomeningocele/spina bifida, osteogenesis imperfecta and congenital limb deficiency. The project is based on patient (user) participation. The five patient organizations are represented on the board where they are in the majority. Patients along with professionals give lectures during group stays. The project offers its services to persons with the diagnosis from all parts of Norway (4.3 mill. inhabitants). Persons with spina bifida over 16 years are included in the project, as well as persons with the other diagnoses at all ages. We present the organization of the project and the repertoire of services that are on offer. 2. Cognitive Deficits Often Seen in Young Adults with Spina Bifida: Effects in the School and Work Place. As survival rates continue to increase with the use of shunting procedures for persons with spina bifida (SB), the need for improved educational and vocational planning also increases. Orbeck and Schanke reported that the cognitive deficits of young adults with SB have not received enough attention in educational and vocational planning. A thorough description of these deficits will aid in developing more effective individualized planning. With improved planning, insight into alternative methods for improving support may also then be investigated. The purpose of this study is to better define and describe the cognitive deficits often encountered while planning support in the school and work place for this group. Neuropsychological examinations are the basis for this description of observed cognitive deficits. The study included 46 young adults with SB aged 15 to 38 living in Norway. All persons were given a neuropsychological test battery which included tests for attention, memory, speed of information processing, visual perception and visual constructive function, arithmetic, fine motor coordination, and verbal functioning. The results indicated deficits in fine motor coordination, speed of information processing, and a slow learning curve. The consequences of these deficits in educational and vocational planning are discussed and guidelines for further studies are suggested.
Abnormalities, Multiple↗
Dog phobia in a motion-blind patient.
INTRODUCTION: A prominent neurophysiological model of phobia generation holds that specific phobia might result from the uncoupling of unaware subcortical fear responses from aware cortical fear responses. Former responses are thought to be automatic and fast, providing approximate information about the external stimulus, whereas the latter responses are more controlled and allow comparison with previous experience. Since only the cortical pathway carries information available to awareness, this model also accounts for the striking irrationality of specific phobia in humans. METHODS: Here, we report neuropsychological and neuro-ophthalmological findings in a 41-year-old patient who developed severe dog phobia following bilateral parietal lobe damage. RESULTS: The examinations showed a severe deficit in visual motion perception (visual motion blindness or akinetopsia) as well as spatial vision. Importantly, the patient was largely unaware of his visual deficits. CONCLUSION: Based on the present observation it is argued that irrational fear, as found in specific phobia, might not only result from a general uncoupling of aware cortical from unaware subcortical fear responses, but also from a functionally similar dissociation at the cortical level.
Journal Article↗
Dissociation between the effects of damage to perirhinal cortex and area TE.
Perirhinal cortex and area TE are immediately adjacent to each other in the temporal lobe and reciprocally interconnected. These areas are thought to lie at the interface between visual perception and visual memory, but it has been unclear what their separate contributions might be. In three experiments, monkeys with bilateral lesions of the perirhinal cortex exhibited a different pattern of impairment than monkeys with bilateral lesions of area TE. In experiment 1, lesions of the perirhinal cortex produced a multimodal deficit in recognition memory (delayed nonmatching to sample), whereas lesions of area TE impaired performance only in the visual modality. In experiment 2, on a test of visual recognition memory (the visual paired comparison task) lesions of the perirhinal cortex impaired performance at long delays but spared performance at a very short delay. In contrast, lesions of area TE impaired performance even at the short delay. In experiment 3, lesions of the perirhinal cortex and lesions of area TE produced an opposite pattern of impairment on two visual discrimination tasks, simple object discrimination learning (impaired only by perirhinal lesions), and concurrent discrimination learning (impaired only by TE lesions). Taken together, the findings suggest that the perirhinal cortex, like other medial temporal lobe structures, is important for the formation of memory, whereas area TE is important for visual perceptual processing.
Animals↗
Hemianopic anosognosia.
In a prospective study of 32 consecutive patients with homonymous visual field defects due to ischemic infarcts we found hemianopic anosognosia (HAN), defined as the unawareness of visual loss in the homonymous hemifield (or hemiquadrant), in 20 patients (62%). HAN, although occurring predominantly in right-side lesions in 16 of 26 patients (62%) was also present in four of six patients (or 67%) with left-side lesions. This group of patients has been presented in a prior report on positive spontaneous visual phenomena. HAN was associated with somatic anosognosia in nine patients and hemineglect in 17 patients. Dissociation between somatic and hemianopic anosognosia, as well as between hemineglect and HAN, was present in several patients, indicating that these phenomena may be independent of each other. Eight patients had pure homonymous hemianopia; that is, hemianopia without cognitive, motor, or somatosensory deficits. Four of these patients (Group A) had awareness of the visual deficit, whereas three patients (Group B) had HAN. Patients in these two groups had similar anatomic lesions. Patients with phosphenes, photopsias, or visual hallucinations were usually aware of their visual field loss. We suggest that HAN is most often related to failure of discovery of the deficits, occasionally to severe visual hemineglect, sometimes to generalized cognitive impairment, or to a combination of these factors. We further conclude (1) there is no specific cortical area for conscious visual perception; (2) visual awareness is processed by a distributed network including multiple visual cortices, parietal and frontal lobes, the pulvinar, and lateral geniculate bodies (lesions localized at various nodes or centers in the network may produce similar phenomena); and (3) both hemispheres are involved in visual processing and conscious awareness.
Aged↗
The perception of a visual object during stimulation of the vestibular system.
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Humans↗