Features of perception of length of segments under conditions of ponzo and Müller-Lyer illusions in schizophrenia

In order to better appreciate the neurophysiologic mechanisms of perception of length under conditions of geometrical visual illusions, we studied sensitivity of mentally healthy subjects and schizophrenic patients to Ponzo and Müller-Lyer illusion. Patients with schizophrenia estimated length of segments of Müller-Lyer figure less precisely. Accuracy of perception of length of segments in Ponzo figure was ambiguously connected with the duration of the disease. Persons suffering from schizophrenia for a short time were less inclined to Ponzo illusion than mentally healthy subjects. On the contrary, patients who suffered from schizophrenia for a long time were more sensitive to this illusion. Ponzo illusion can be used as a marker of schizophrenia which is found out during the specific period of development of the disease. High sensitivity of patients with schizophrenia to Müller-Lyer and Ponzo illusions supports a hypothesis about the role of the global analysis of an image during processing of its low-frequency component in formation of the illusions under study.     

Frequency-contrast sensitivity of visual stimulus perception in patients with schizophrenia treated with atypical and typical antipsychotics

The effects of typical and atypical antipsychotics on the perception of visual stimuli that preferentially activate magnocellular or parvocellular visual channels have been studied. The threshold contrast sensitivity in healthy individuals and patients with schizophrenia has been recorded. The Gabor-like sinusoidal brightness gratings and spatial frequencies of 0.4, 3.6, and 17.9 cycles/degree were presented to the tested objects. The patients were divided into two groups, one receiving the therapy with atypical antipsychotics, and the other, with typical ones. The contrast sensitivity for low and medium spatial frequencies (i.e., for the stimuli corresponding to magnocellular channels) decreased compared to the norm. Note that the decrease in the contrast sensitivity for the low spatial frequencies in the patients treated with atypical antipsychotics is significantly more pronounced compared to the cohort that received typical antipsychotics.     

Characteristics of detection of the general direction of movement of visual objects by preschool-age children with typical and atypical cognitive development

The specifics of functioning of two channels for processing visual information, the magnocellular and parvocellular ones, in preschool children with normal and impaired cognitive development have been studied. Children with delayed psychological development have been found to have a diminished activity in the magnocellular channel due to weakening of the mechanism responsible for assessing the temporal parameters of the visual input. At the same time, children displaying a spectrum of infantile autism syndromes complicated by a delayed psychological development and mental retardation have a pronounced deficit in information processing in both channels of the visual system, manifested in an impaired ability to assess the direction of movement in terms of both temporal and spatial characteristics of the objects. The degree of this impairment is correlated with both the severity of the particular neurological disorder and the level of speech development of the child.     

Contrast dependency of VEPs as a function of spatial frequency: the parvocellular and magnocellular contributions to human VEPs

The present study investigated the contrast dependency of visual evoked potentials (VEPs) elicited by phase reversing sine wave gratings of varying spatial frequency. Sixty-five trials were recorded for each of 54 conditions: 6 spatial frequencies (0.8, 1.7, 2.8, 4.0, 8.0 and 16.0 c deg(-1)) each presented at 9 contrast levels (2, 4, 8, 11, 16, 23, 32, 64 and 90%). At the lowest spatial frequency, the waveform contained mainly one peak (P1). For spatial frequencies up to 8 c deg(-1), P1 had a characteristic magnocellular contrast response: it appeared at low contrasts, increased rapidly in amplitude with increasing contrast, and saturated at medium contrasts. With increasing spatial frequency, an additional peak (N1) gradually became the more dominant component of the waveform. N1 had a characteristic parvocellular contrast response: it appeared at medium to high contrasts, increased linearly in amplitude with increasing contrast, and did not appear to saturate. The data suggest the contribution of both magnocellular and parvocellular responses at intermediate spatial frequencies. Only at the lowest and highest spatial frequencies tested did magnocellular and parvocellular responses, respectively, appear to dominate.     

"Slight" of hand: the processing of visually degraded gestures with speech

Co-speech hand gestures influence language comprehension. The present experiment explored what part of the visual processing system is optimized for processing these gestures. Participants viewed short video clips of speech and gestures (e.g., a person saying "chop" or "twist" while making a chopping gesture) and had to determine whether the two modalities were congruent or incongruent. Gesture videos were designed to stimulate the parvocellular or magnocellular visual pathways by filtering out low or high spatial frequencies (HSF versus LSF) at two levels of degradation severity (moderate and severe). Participants were less accurate and slower at processing gesture and speech at severe versus moderate levels of degradation. In addition, they were slower for LSF versus HSF stimuli, and this difference was most pronounced in the severely degraded condition. However, exploratory item analyses showed that the HSF advantage was modulated by the range of motion and amount of motion energy in each video. The results suggest that hand gestures exploit a wide range of spatial frequencies, and depending on what frequencies carry the most motion energy, parvocellular or magnocellular visual pathways are maximized to quickly and optimally extract meaning.     

Abnormal brain activation in neurofibromatosis type 1: a link between visual processing and the default mode network

Neurofibromatosis type 1 (NF1) is one of the most common single gene disorders affecting the human nervous system with a high incidence of cognitive deficits, particularly visuospatial. Nevertheless, neurophysiological alterations in low-level visual processing that could be relevant to explain the cognitive phenotype are poorly understood. Here we used functional magnetic resonance imaging (fMRI) to study early cortical visual pathways in children and adults with NF1. We employed two distinct stimulus types differing in contrast and spatial and temporal frequencies to evoke relatively different activation of the magnocellular (M) and parvocellular (P) pathways. Hemodynamic responses were investigated in retinotopically-defined regions V1, V2 and V3 and then over the acquired cortical volume. Relative to matched control subjects, patients with NF1 showed deficient activation of the low-level visual cortex to both stimulus types. Importantly, this finding was observed for children and adults with NF1, indicating that low-level visual processing deficits do not ameliorate with age. Moreover, only during M-biased stimulation patients with NF1 failed to deactivate or even activated anterior and posterior midline regions of the default mode network. The observation that the magnocellular visual pathway is impaired in NF1 in early visual processing and is specifically associated with a deficient deactivation of the default mode network may provide a neural explanation for high-order cognitive deficits present in NF1, particularly visuospatial and attentional. A link between magnocellular and default mode network processing may generalize to neuropsychiatric disorders where such deficits have been separately identified.     

Profound contrast adaptation early in the visual pathway

Prior exposure to a moving grating of high contrast led to a substantial and persistent reduction in the contrast sensitivity of neurons in the lateral geniculate nucleus (LGN) of macaque. This slow contrast adaptation was potent in all magnocellular (M) cells but essentially absent in parvocellular (P) cells and neurons that received input from S cones. Simultaneous recordings of M cells and the potentials of ganglion cells driving them showed that adaptation originated in ganglion cells. As expected from the spatiotemporal tuning of M cells, adaptation was broadly tuned for spatial frequency and lacked orientation selectivity. Adaptation could be induced by high temporal frequencies to which cortical neurons do not respond, but not by low temporal frequencies that can strongly adapt cortical neurons. Our observations confirm that contrast adaptation occurs at multiple levels in the visual system, and they provide a new way to reveal the function and perceptual significance of the M pathway.     

Perception of visual image size by school students of different ages

In psychophysical experiments, 209 high school students with normal vision, 8 to 16 years old, were examined to study the perception of visual image sizes. Observers assessed the length of linear arrow-like figures (the Müller-Lyer illusion) or the length of single lines without arrow-like ends. Distortion of line size perception by 17–21% was obtained in the Müller-Lyer illusion independent of the age of observers. Distortion of size perception was absent in the case of estimation of the length of single line segments. The size differentiation thresholds gradually decreased in both cases with increasing age of observers and were correlated with the acuity of vision. For single lines, they were, on average, 1.3 times lower than the thresholds in the Müller-Lyer illusion. The probable mechanisms of the Müller-Lyer illusion are discussed. The experimental results demonstrate stability of illusion for observers aged 8–16 years, which may be connected with preferential contribution of the lower levels of the visual system to the appearance of the illusion.     

Human magno- and parvo-systems and selective disruptions in their function

In psychophysical and electrophysiological investigations, we tested the hypothesis that in patients with multiple sclerosis at its early stage either phasic cells of the magnocellular pathway or tonic cells of the parvocellular pathway are disturbed. Healthy humans and patients with early stage of diseases have a contrast spatial-frequency sensitivity measure. The decrease in sensitivity at low, medium and high spatial frequency indicates changes in parvo- and magno-system activity. The data are separated into two clusters. Psychophysical data is in good accordance with electrophysiological data of visual evoked potentials (VEPs). First group of patients showed changes of the amplitude of positive wave P100 whereas in second group of patients changes of negative wave N80 dominated comparative to healthy subjects. According to some literature data these changes were specific for M-pathway and for P-pathway.     

Analysis of Visual Cognitive Impairments in Schizophrenia at the Early Stages of the Disease and Their Correction by Interactive Virtual Environment

The paper describes the results of studies aimed at evaluating the effect of interactive virtual environments on the visual system, including the magno-and parvo-systems. Analysis was conducted in patients diagnosed with paranoid schizophrenia diagnosed from one to five years ago. Comparative analysis of visual evoked potentials during the perception of images that differed in their semantic (animate/inanimate) and physical characteristics (filtration images at high/low spatial frequencies) was used for the assessment of the impact of virtual environments. The images of objects were filtered via digital filtration for selective effect on the magno-and parvo-channels of the visual system. To evaluate the function of visual perception, the measurement of contrast sensitivity using Gabor elements was used. At the early stages of schizophrenia, the patients exhibited a decrease in the amplitudes of the components of cognitive visual evoked potentials to stimuli filtered at high spatial frequencies and reduced contrast sensitivity at high spatial frequencies. The effect of virtual environments on the visual system resulted in a significant increase in the amplitude of the cognitive components of visual evoked potentials in the paradigm of presentation of images filtered at the high spatial frequencies, which allows the conclusion about a stimulating effect of the virtual environment on the parvo-system functioning. The activation of the magno-system occurred to a lesser extent. The present study represents the findings obtained by the studies of cognitive impairments in schizophrenia and the methods of their correction conducted at the Laboratory of Physiology of Vision of the Pavlov Institute of Physiology of the Russian Academy of Sciences and at the Laboratory of Neurobiology of Action Programming of the Bechtereva Institute of the Human Brain of the Russian Academy of Sciences.     

Predicting Cortical Dark/Bright Asymmetries from Natural Image Statistics and Early Visual Transforms

The nervous system has evolved in an environment with structure and predictability. One of the ubiquitous principles of sensory systems is the creation of circuits that capitalize on this predictability. Previous work has identified predictable non-uniformities in the distributions of basic visual features in natural images that are relevant to the encoding tasks of the visual system. Here, we report that the well-established statistical distributions of visual features -- such as visual contrast, spatial scale, and depth -- differ between bright and dark image components. Following this analysis, we go on to trace how these differences in natural images translate into different patterns of cortical input that arise from the separate bright (ON) and dark (OFF) pathways originating in the retina. We use models of these early visual pathways to transform natural images into statistical patterns of cortical input. The models include the receptive fields and non-linear response properties of the magnocellular (M) and parvocellular (P) pathways, with their ON and OFF pathway divisions. The results indicate that there are regularities in visual cortical input beyond those that have previously been appreciated from the direct analysis of natural images. In particular, several dark/bright asymmetries provide a potential account for recently discovered asymmetries in how the brain processes visual features, such as violations of classic energy-type models. On the basis of our analysis, we expect that the dark/bright dichotomy in natural images plays a key role in the generation of both cortical and perceptual asymmetries.     

Visual search for apparent-length targets is modulated by the Müller-Lyer illusion

Is apparent object size represented in pre-attentive vision and can it influence visual search for size-defined targets in a spatially parallel manner? This question was investigated, using the Müller-Lyer illusion. Observers searched for a target line that was longer than the distractor lines. Test lines could be presented without context arrows (control); be adjoined by obtuse-angle context arrows (arrow heads pointing inward), making the lines appear longer; or by acute-angle arrows (heads pointing outward), making the lines appear shorter. These apparent-length modulations were larger for the target than for the distractor lines, thereby increasing and, respectively, decreasing the target-distractor length contrast. In line with these changes in contrast, target detection was found to be expedited by obtuse-angle arrows and impeded by acute-angle arrows, independently of the number of elements in the display. This finding provides further evidence for the pre-attentive processing of apparent object size.     

The Müller-Lyer Illusion in Ant Foraging

The Müller-Lyer illusion is a classical geometric illusion in which the apparent (perceived) length of a line depends on whether the line terminates in an arrow tail or arrowhead. This effect may be caused by economic compensation for the gap between the physical stimulus and visual fields. Here, we show that the Müller-Lyer illusion can also be produced by the foraging patterns of garden ants (Lasius niger) and that the pattern obtained can be explained by a simple, asynchronously updated foraging ant model. Our results suggest that the geometric illusion may be a byproduct of the foraging process, in which local interactions underlying efficient exploitation can also give rise to global exploration, and that visual information processing in human could implement similar modulation between local efficient processing and widespread computation.     

The parvocellular LGN provides a robust disynaptic input to the visual motion area MT

Dorsal visual cortical areas are thought to be dominated by input from the magnocellular (M) visual pathway, with little or no parvocellular (P) contribution. These relationships are supported by a close correlation between the functional properties of these areas and the M pathway and by a lack of anatomical evidence for P input. Here we use rabies virus as a retrograde transynaptic tracer to show that the dorsal area MT receives strong input, via a single relay, from both M and P cells of the lateral geniculate nucleus. This surprising P input, likely relayed via layer 6 Meynert cells in primary visual cortex, can provide MT with sensitivity to a more complete range of spatial, temporal, and chromatic cues than the M pathway alone. These observations provide definitive evidence for P pathway input to MT and show that convergence of parallel visual pathways occurs in the dorsal stream.     

The Muller-Lyer illusion explained and its theoretical importance reconsidered

The Müller-Lyer illusion is the natural consequence of the construction of the vertebrate eye, retina and visual processing system. Due to imperfections in the vertebrate eye and retina and due to the subsequent processing in the system by ever increasing receptive fields, the visual information becomes less and less precise with respect to exact location and size. The consequence of this is that eventually the brain has to calculate a weighted mean value of the information, which is spread out over a population of neurons. In the case of the Müller-Lyer illusion this inevitably leads to extension of one and reduction of the other line. The arguments presented explain several published experimental results concerning the Müller-Lyer illusion and shed new light upon the philosophical neutrality of observation sentences.     

Excitatory and inhibitory receptive fields of tectal cells are differentially modified by magnocellular and parvocellular divisions of the pigeon nucleus isthmi

It has been known that magnocellular and parvocellular divisions of the pigeon nucleus isthmi exert excitatory and inhibitory actions on tectal cells, respectively. The present study shows that injection of N-methyl-D-aspartate into the parvocellular division results in an increase in responsive strength and extent of the inhibitory receptive fields, which expand into the excitatory receptive fields of tectal cells. This injection concurrently leads to a decrease in responsiveness and extent of the excitatory fields. On the other hand, injection of acetylcholine into the magnocellular division enhances visual responsiveness, although the excitatory field is not obviously changed in extent. Meanwhile, strength and extent of the inhibitory fields are decreased by acetylcholine. The excitatory and inhibitory fields are reduced in both strength and extent by magnocellular and parvocellular injection of lidocaine, respectively. It suggests that isthmic inputs from both parvocellular and magnocellular divisions converge onto the same tectal cells, and the magnocellular and parvocellular subnuclei can modulate excitatory and inhibitory receptive fields of tectal cells, respectively, with some interactions between both fields. Accepted: 1 March 2000     

Fragmented Perception: Slower Space-Based but Faster Object-Based Attention in Recent-Onset Psychosis with and without Schizophrenia

Background

Schizophrenia is associated with impairments of the perception of objects, but how this affects higher cognitive functions, whether this impairment is already present after recent onset of psychosis, and whether it is specific for schizophrenia related psychosis, is not clear. We therefore tested the hypothesis that because schizophrenia is associated with impaired object perception, schizophrenia patients should differ in shifting attention between objects compared to healthy controls. To test this hypothesis, a task was used that allowed us to separately observe space-based and object-based covert orienting of attention. To examine whether impairment of object-based visual attention is related to higher order cognitive functions, standard neuropsychological tests were also administered.

Method

Patients with recent onset psychosis and normal controls performed the attention task, in which space- and object-based attention shifts were induced by cue-target sequences that required reorienting of attention within an object, or reorienting attention between objects.

Results

Patients with and without schizophrenia showed slower than normal spatial attention shifts, but the object-based component of attention shifts in patients was smaller than normal. Schizophrenia was specifically associated with slowed right-to-left attention shifts. Reorienting speed was significantly correlated with verbal memory scores in controls, and with visual attention scores in patients, but not with speed-of-processing scores in either group.

Conclusions

deficits of object-perception and spatial attention shifting are not only associated with schizophrenia, but are common to all psychosis patients. Schizophrenia patients only differed by having abnormally slow right-to-left visual field reorienting. Deficits of object-perception and spatial attention shifting are already present after recent onset of psychosis. Studies investigating visual spatial attention should take into account the separable effects of space-based and object-based shifting of attention. Impaired reorienting in patients was related to impaired visual attention, but not to deficits of processing speed and verbal memory.     

Alpha 1-antitrypsin types in schizophrenia

The gene and phenotype frequencies of alpha 1-antitrypsin were studied in patients with (49) and without (92) a family history of schizophrenia. A significant difference with respect to phenotype (p less than 0.05) and gene (p less than 0.025) frequencies was found between the two groups of patients. Among patients with a family history of schizophrenia there was a significant increase of the M1 gene and a decrease of the M2 gene. There were no significant differences between schizophrenic patients and controls.     

Effects of chronic alcoholic disease on magnocellular and parvocellular hypothalamic neurons in men.

Although numerous data showing severe morphological impairment of magnocellular and parvocellular hypothalamic neurons due to chronic alcoholic consumption have been gathered from animal experiments, only one study (Harding et al., 1996) was performed on POST MORTEM human brain. This study showed a reduction in the number of vasopressin (VP)-immunoreactive neurons in the supraoptic (SON) and paraventricular (PVN) nuclei, but did not provide any data regarding the effect of chronic alcohol intake on human parvocellular neurons. In order to assess whether the changes observed in the animal model also occur in humans and provide a structural basis for the results of clinical tests, we performed immunohistochemical and morphometric analysis of magnocellular (VP and oxytocin, OT) and parvocellular (corticotropin-releasing hormone, CRH) neurons in post-mortem brains of patients afflicted with chronic alcoholic disease. We analyzed 26-male alcoholics and 22 age-matched controls divided into two age groups--"young" (< 40 yr) and "old" (> 40 yr). Hypothalamic sections were stained for OT, VP, and CRH. The analysis revealed: 1) decrease in VP-immunoreactivity in the SON and PVN as well as OT-immunoreactivity in the SON in alcoholic patients; 2) increase in OT-immunoreactivity in the PVN; 3) increase in CRH-immunoreactivity in parvocellular neurons in the PVN. Furthermore, the proportion of cells containing CRH and VP was increased in alcoholics. These findings indicate that chronic alcohol consumption does indeed impair the morphology of magnocellular neurons. The enhancement of CRH-immunoreactivity and increased co-production of CRH and VP in parvocellular neurons may be due to a decline in glucocorticoid production, implied by the hypoplasic impairment of adrenal cortex we observed in alcoholics during the course of this study.     

Autonomic modulation and health-related quality of life among schizophrenic patients treated with non-intensive case management

Background

Schizophrenia is associated with autonomic dysfunction and this may increase cardiovascular mortality. Past studies on autonomic modulation of schizophrenic patients focused on inpatients rather than individuals in a community setting, especially those receiving non-intensive case management (non-ICM). Besides, autonomic modulation and its association with health-related quality of life (HRQoL) in this population remain unexplored.

Methods

A total of 25 schizophrenic patients treated by non-ICM and 40 healthy volunteers were matched by age, gender and body mass index; smokers were excluded. Between the two groups, we compared the individuals'' 5 min resting assessments of heart rate variability and their HRQoL, which was measured using EuroQoL-5D (EQ-5D). Patients with schizophrenia were assessed for psychopathology using the Positive and Negative Syndrome Scale for Schizophrenia (PANSS). We examined the relationship between heart rate variability measurements, HRQoL scores, PANSS scores, and other clinical variables among the schizophrenic patients treated by non-ICM.

Results

Compared to the controls, patients with schizophrenia showed a significant impairment of autonomic modulation and a worse HRQoL. Cardiovagal dysfunction among the schizophrenic patients could be predicted independently based on lower educational level and more negative symptoms. Sympathetic predominance was directly associated with anticholinergics use and EQ-5D using a visual analogue scale (EQ-VAS).

Conclusion

Patients with schizophrenia treated by non-ICM show a significant impairment of their autonomic function and HRQoL compared to the controls. Since the sympathovagal dysfunction is associated with more negative symptoms or higher VAS score, the treatment of the negative symptoms as well as the monitoring of HRQoL might help to manage cardiovascular risk among these individuals. In addition, EQ-VAS scores must be interpreted more cautiously in such a population.