Preattentive information processing as measured by backward masking and texton detection tasks in adolescents at high genetic risk for schizophrenia

Mapping the Consequences of Impaired Synaptic Plasticity in Schizophrenia through Development: An Integrative Model for Diverse Clinical Features

Schizophrenia is associated with alterations in sensory, motor, and cognitive functions that emerge before psychosis onset; identifying pathogenic processes that can account for this multi-faceted phenotype remains a challenge. Accumulating evidence suggests that synaptic plasticity is impaired in schizophrenia. Given the role of synaptic plasticity in learning, memory, and neural circuit maturation, impaired plasticity may underlie many features of the schizophrenia syndrome. Here, we summarize the neurobiology of synaptic plasticity, review evidence that plasticity is impaired in schizophrenia, and explore a framework in which impaired synaptic plasticity interacts with brain maturation to yield the emergence of sensory, motor, cognitive, and psychotic features at different times during development in schizophrenia. Key gaps in the literature and future directions for testing this framework are discussed.

Visual masking & schizophrenia

Visual masking is a frequently used tool in schizophrenia research. Visual masking has a very high sensitivity and specificity and masking paradigms have been proven to be endophenotypes. Whereas masking is a powerful technique to study schizophrenia, the underlying mechanisms are discussed controversially. For example, for more than 25 years, masking deficits of schizophrenia patients were mainly attributed to a deficient magno-cellular system (M-system). Here, we show that there is very little evidence that masking deficits are magno-cellular deficits. We will discuss the magno-cellular and other approaches in detail and highlight their pros and cons.

Association of the Nicotinic Receptor α7 Subunit Gene (CHRNA7) with Schizophrenia and Visual Backward Masking

The nicotinic system is involved in the pathophysiology of schizophrenia. However, very little is known about its genetic basis and how it relates to clinical symptoms and potentially pharmacological intervention. Here, we investigated five single nucleotide polymorphisms (SNPs) [rs3826029] [rs2337506] [rs982574] [rs904952] [rs2337980] of the cholinergic nicotinic receptor gene, alpha 7 subunit (CHRNA7) and their association to schizophrenia. We found an association with rs904952 (p = 0.009) in a German sample of 224 schizophrenic patients and 224 healthy control subjects. The same trend was shown in an independent Georgian sample of 50 schizophrenic patients, 57 first order unaffected relatives, and 51 healthy controls. In addition, visual backward masking (VBM), a sensitive test for early visual information processing, was assessed in the Georgian sample. In line with prior studies, VBM performance deficits were much more pronounced in schizophrenic patients and their unaffected relatives compared to healthy controls (schizophrenic patients: 156 ms; unaffected relatives: 60 ms; healthy controls: 33 ms). VBM was strongly correlated with SNP rs904952 (H[2] = 7.3, p = 0.026). Our results further support the notion that changes in the nicotinic system are involved in schizophrenia and open the avenue for pharmacological intervention.

Fragile early visual percepts mark genetic liability specific to schizophrenia

Disruption of visual percepts by a subsequent stimulus (ie, backward masking) has been consistently noted in schizophrenia, with some evidence that this fragility in early perception is present in people with genetic liability for the disorder. Given the potential of backward masking paradigms to mark neural processes that confer risk for schizophrenia, it is important to test the diagnostic specificity of abnormalities in visual perception. To more fully assess whether masking visual stimuli reveals a marker of genetic liability (ie, endophenotype) specific to schizophrenia, we tested 44 people with the disorder, 29 people with bipolar disorder, 56 first-degree biological relatives of people with schizophrenia, 26 first-degree biological relatives of people with bipolar disorder, and 43 nonpsychiatric control participants using a magnocellular-biased visual backward masking procedure that included target-to-mask onset asynchronies ranging from 0 to 80 ms. Relatives of people with schizophrenia who were without schizophrenia spectrum disorders exhibited impaired performance compared with nonpsychiatric control participants and relatives of people with bipolar disorder when a visual mask interrupted early perception (eg, 27 ms). A similar vulnerability of early processes was noted in people with schizophrenia, yet they also had impaired performance when masks occurred at later time points (ie, 80 ms). Performance deficits were not attributable to intellectual function, measures of attention and memory, symptomatology, or medication dosage. Bipolar patients and their relatives failed to exhibit deficits on the backward masking task. Fragility of early visual percepts appears to mark genetic liability specific to schizophrenia and may serve as an endophenotype for the disorder.

Visual backward-masking performance in a longitudinal study of early onset schizophrenia

The aim of the present study was to examine the effect of visual backward-masking (VBM) in patients with early onset schizophrenia (EOS, n=28) compared to healthy controls (n=80) at baseline and at one- and two-year follow-ups. Seventeen patients and 40 controls performed a VBM task at all three sessions, which included five different interstimuli intervals (ISI) at 16.5, 33.5, 49.5, 116 and 166ms, and an additional no-masking control task. Patients with EOS revealed no impairment of VBM performance at baseline and at the two follow-ups compared to healthy controls at one- and two-year follow-ups. However, the patients demonstrated a deficit of simple early visual processing. Both groups showed effects of development over a period of 24 months for the shortest ISIs.

Visual masking by object substitution in schizophrenia

BACKGROUND

Schizophrenia patients demonstrate impairment on visual backward masking, a measure of early visual processing. Most visual masking paradigms involve two distinct processes, an early fast-acting component associated with object formation and a later component that acts through object substitution. So far, masking paradigms used in schizophrenia research have been unable to separate these two processes.

METHOD

We administered three visual processing paradigms (location masking with forward and backward masking, four-dot backward masking and a cuing task) to 136 patients with schizophrenia or schizoaffective disorder and 79 healthy controls. A psychophysical procedure was used to match subjects on identification of an unmasked target prior to location masking. Location masking interrupts object formation, four-dot masking task works through masking by object substitution and the cuing task measures iconic decay.

RESULTS

Patients showed impairment on location masking after being matched for input threshold, similar to previous reports. After correcting for age, patients showed lower performance on four-dot masking than controls, but the groups did not differ on the cuing task.

CONCLUSIONS

Patients with schizophrenia showed lower performance when masking was specific to object substitution. The difference in object substitution masking was not due to a difference in rate of iconic decay, which was comparable in the two groups. These results suggest that, despite normal iconic decay rates, individuals with schizophrenia show impairment in a paradigm of masking by object substitution that did not also involve disruption of object formation.

The shine-through masking paradigm is a potential endophenotype of schizophrenia

BACKGROUND

To understand the genetics of schizophrenia, a hunt for so-called intermediate phenotypes or endophenotypes is ongoing. Visual masking has been proposed to be such an endophenotype. However, no systematic study has been conducted yet to prove this claim. Here, we present the first study showing that masking meets the most important criteria for an endophenotype.

METHODOLOGY/PRINCIPAL FINDINGS

We tested 62 schizophrenic patients, 39 non-affected first-degree relatives, and 38 healthy controls in the shine-through masking paradigm and, in addition, in the Continuous Performance Test (CPT) and the Wisconsin Card Sorting Test (WCST). Most importantly, masking performance of relatives was significantly in between the one of patients and controls in the shine-through paradigm. Moreover, deficits were stable throughout one year. Using receiver operating characteristics (ROC) methods, we show that the shine-through paradigm distinguishes with high sensitivity and specificity between schizophrenic patients, first-order relatives and healthy controls.

CONCLUSIONS/SIGNIFICANCE

The shine-through paradigm is a potential endophenotype.

Regional brain activity during early visual perception in unaffected siblings of schizophrenia patients

BACKGROUND

Visual masking paradigms assess the early part of visual information processing, which may reflect vulnerability measures for schizophrenia. We examined the neural substrates of visual backward performance in unaffected sibling of schizophrenia patients using functional magnetic resonance imaging (fMRI).

METHODS

Twenty-one unaffected siblings of schizophrenia patients and 19 healthy controls performed a backward masking task and three functional localizer tasks to identify three visual processing regions of interest (ROI): lateral occipital complex (LO), the motion-sensitive area, and retinotopic areas. In the masking task, we systematically manipulated stimulus onset asynchronies (SOAs). We analyzed fMRI data in two complementary ways: 1) an ROI approach for three visual areas, and 2) a whole-brain analysis.

RESULTS

The groups did not differ in behavioral performance. For ROI analysis, both groups increased activation as SOAs increased in LO. Groups did not differ in activation levels of the three ROIs. For whole-brain analysis, controls increased activation as a function of SOAs, compared with siblings in several regions (i.e., anterior cingulate cortex, posterior cingulate cortex, inferior prefrontal cortex, inferior parietal lobule).

CONCLUSIONS

The study found: 1) area LO showed sensitivity to the masking effect in both groups; 2) siblings did not differ from controls in activation of LO; and 3) groups differed significantly in several brain regions outside visual processing areas that have been related to attentional or re-entrant processes. These findings suggest that LO dysfunction may be a disease indicator rather than a risk indicator for schizophrenia.

Functional neuroanatomy of visual masking deficits in schizophrenia

CONTEXT

Visual masking procedures assess the earliest stages of visual processing. Patients with schizophrenia reliably show deficits on visual masking, and these procedures have been used to explore vulnerability to schizophrenia, probe underlying neural circuits, and help explain functional outcome.

OBJECTIVE

To identify and compare regional brain activity associated with one form of visual masking (ie, backward masking) in schizophrenic patients and healthy controls.

DESIGN

Subjects received functional magnetic resonance imaging scans. While in the scanner, subjects performed a backward masking task and were given 3 functional localizer activation scans to identify early visual processing regions of interest (ROIs).

SETTING

University of California, Los Angeles, and the Department of Veterans Affairs Greater Los Angeles Healthcare System.

PARTICIPANTS

Nineteen patients with schizophrenia and 19 healthy control subjects. Main Outcome Measure The magnitude of the functional magnetic resonance imaging signal during backward masking.

RESULTS

Two ROIs (lateral occipital complex [LO] and the human motion selective cortex [hMT+]) showed sensitivity to the effects of masking, meaning that signal in these areas increased as the target became more visible. Patients had lower activation than controls in LO across all levels of visibility but did not differ in other visual processing ROIs. Using whole-brain analyses, we also identified areas outside the ROIs that were sensitive to masking effects (including bilateral inferior parietal lobe and thalamus), but groups did not differ in signal magnitude in these areas.

CONCLUSIONS

The study results support a key role in LO for visual masking, consistent with previous studies in healthy controls. The current results indicate that patients fail to activate LO to the same extent as controls during visual processing regardless of stimulus visibility, suggesting a neural basis for the visual masking deficit, and possibly other visual integration deficits, in schizophrenia.

A potential qualitative endophenotype for schizophrenia: backward masking response to red light

Past research with unaffected relatives of individuals with schizophrenia has suggested a new qualitative endophenotype for schizophrenia that involves a unique change in visual processing response to red light. The current study provides the first report of this "red light effect" in individuals with schizophrenia (N=15), compared with nonpsychiatric controls (N=16), using a location backward masking by pattern paradigm with red and green background conditions. Analyses revealed a statistically significant group difference in the overall change in accuracy to a red background. Controls tended to show an increase in accuracy with the red (compared with green) background, although the medium effect size was not statistically significant in the small sample. In contrast, participants with schizophrenia showed a statistically significant decrease in accuracy with the red background. Results support recent reports which have suggested that a unique change in visual processing in response to red light may represent a new endophenotype for schizophrenia. This effect is unique from most existing endophenotypes in that it represents a distinct qualitative performance pattern rather than simply poorer performance relative to a comparison group.

The effect of red light on backward masking in individuals with psychometrically defined schizotypy

INTRODUCTION

Previous research has suggested that individuals with schizophrenia and their relatives show a change in backward masking performance with a red background that is in the opposite qualitative direction as that found in nonpsychiatric controls. The present study examines this effect in individuals with psychometrically defined schizotypy to explore the potential of this effect to be a useful new qualitative endophenotype for schizophrenia-spectrum traits.

METHODS

The Abbreviated Youth Psychosis At-Risk Questionnaire was used to screen a large number of undergraduates for schizotypy symptoms. A sample of 23 participants scoring high on this measure were compared to a sample of 26 controls on a location backward masking task that was presented on both red and green backgrounds.

RESULTS

Consistent with findings in patients with schizophrenia, the participants reporting a high number of schizotypy features showed a decrease in performance to the red (compared to green) background and the controls showed a nonsignificant increase in performance--although this finding was limited to the stimulus-onset asynchrony (SOA) value that approximated the SOA with the largest effect size in the previous schizophrenia study (69 ms).

CONCLUSIONS

Although limited to one SOA, results extend earlier findings approximating this SOA to include a psychometrically defined schizotypy sample.

Forward and backward visual masking in unaffected siblings of schizophrenic patients

BACKGROUND

Visual masking tasks assess the earliest stages of visual processing. This study examined visual masking performance for forward and backward masking tasks in siblings of schizophrenic patients and healthy comparison subjects.

METHODS

A staircase method was used to ensure that unmasked target identification was equivalent across subjects to eliminate differences due to discrimination of simple perceptual inputs. Four computerized visual masking tasks were administered to 43 siblings of patients and 42 normal comparison subjects. The tasks included: 1) locating a target; 2) identifying a target with a high-energy mask; 3) identifying a target with a low-energy mask; and 4) a paracontrast/metacontrast procedure with nonoverlapping target and mask.

RESULTS

Across masking conditions, there was a significant group by forward/backward interaction, meaning that siblings showed a larger difference from control subjects in backward versus forward masking. This group difference was more pronounced in the location condition.

CONCLUSIONS

These results support the theory that visual masking procedures may be indicators of vulnerability to schizophrenia. The pattern of findings in this report (larger group differences on backward versus forward masking and on the location condition) suggests that the activity of transient visual channels may be particularly linked to vulnerability.

Perceptual Organization in Schizophrenia Spectrum Disorders: Empirical Research and Theoretical Implications

The research into perceptual organization in schizophrenia spectrum disorders has found evidence for and against a perceptual organization deficit and has interpreted the data from within several different theoretical frameworks. A synthesis of this evidence, however, reveals that this body of work has produced reliable evidence for deficits in schizophrenia, as well as for the clinical, stimulus, and task parameters associated with normal and abnormal performance. Recent models of cognition have also advanced understanding of the underlying pathophysiological processes of perceptual organization dysfunction in schizophrenia spectrum disorders. These suggest that deficits in perceptual organization may be one manifestation of a wider disturbance in the integration of contextually related information across space and time.

The magnocellular visual system and schizophrenia: what can the color red tell us?

Previous research has suggested that genetic loading for schizophrenia is related to a dysfunctional magnocellular (M) subcortical visual pathway-responsible for processing movement and location. However, data substantiating this mechanism remains inconclusive. The present study used a novel technique to selectively suppress the M system in order to investigate the impact of genetic loading for schizophrenia on its functioning. A visual backward masking task was administered to 28 healthy first-degree relatives of persons with schizophrenia and 31 healthy controls. The task was administered on both a red and neutral background, as diffuse red light has been shown to selectively suppress the M system in basic vision research. On a location condition of backward masking, controls demonstrated reduced accuracy on the red compared to the neutral background. In contrast, relatives did not display differential performance between the two backgrounds. The differential effect on the two groups appears to be attributable to a difference in activity of the M pathway. Performance in the relatives was consistent with the notion of a hyperactive M pathway.

Visual masking as a probe for abnormal gamma range activity in schizophrenia

BACKGROUND

Visual masking procedures assess very early stages of visual perception. Patients with schizophrenia consistently show deficits on visual masking tasks, and these deficits likely reflect vulnerability to schizophrenia. We conducted two experiments to determine whether visual masking procedures can reveal underlying abnormalities in gamma range oscillations in schizophrenia.

METHODS

In the first experiment, we conducted nonlinear modeling of visual masking performance data from 89 male schizophrenic patients and 20 male comparison subjects. In the second experiment, electrophysiological recordings of event-related gamma activity were taken during a visual masking task in a subset of eight patients and seven control subjects.

RESULTS

In the first experiment, nonlinear modeling of the performance data revealed evidence of oscillations in the gamma range (30 and 35 Hz) for the comparison group but not patients. In the second experiment, the comparison group, but not the patients, showed a burst of gamma range activity 200-400 msec following target presentation. The difference between patients and comparison subjects in this time period was significant (p <.05).

CONCLUSIONS

Visual masking procedures can serve as a probe for underlying gamma range activity, which appears to be aberrant in schizophrenia. Perceptual problems in schizophrenia may, at least in part, be due to a failure to establish and/or maintain gamma range oscillations.

Transliminality correlates positively with aberrations in memory

During the course of a larger study on sensory thresholds and transliminality, 22 men and 28 women (M = 23.1 yr., SD = 2.9) mostly composed of students selected from a snowball sampling approach completed the Revised Transliminality Scale and a brief measure of everyday aberrations in memory. Scores on the measures correlated .59 (p < .001), and this result was not due to the confounding effects of age or sex. These preliminary results are consistent with the hypothesis that transliminality involves a state of increased activation that can induce a loss of conscious experience, thereby lending support to the definition of transliminality as the tendency for psychological material to cross thresholds into or out of consciousness.

The visual backward masking deficit in schizophrenia

1. Subjects with schizophrenia have an impairment very early in visual information processing, requiring a longer minimal stimulus duration than normal controls to identify a target stimulus. Subjects with schizophrenia have a deficit in visual backward masking, identifying fewer target stimuli than normal controls when the target is briefly obscured by a second visual stimulus When interstimulus interval is increased parametrically, subjects with schizophrenia have trouble identifying target stimuli at intervals that do not affect the performance of normal controls. 2. The visual backward masking deficit: is trait-related; is associated with negative symptoms but has also been associated with measures of thought disorder; may or may not be related to treatment with neuroleptic medication or other neurocognitive deficits of schizophrenia; is of unclear etiology, though researchers have speculated that it involves magnocellular channels and/or the cortical dorsal visual processing stream; has been shown to be heritable in one study. 3. If visual information processing deficits are observed in the unaffected siblings of schizophrenic patients, it may be a candidate intermediate phenotype.

Schizotypy and leadership: a contrasting model for deficit symptoms, and a possible therapeutic role for sex hormones

Associational loosening, slow and faulty information processing, poor gating of irrelevant stimuli, poor ability to shift attention, poor working memory, passivity, ambivalence, anhedonia, and impaired motor coordination are cardinal features of schizophrenia but, unlike delusions and hallucinations, they are related more to negative/deficit symptoms. As summarized by Bass, numerous studies have correlated leadership with 'ambition, initiative and persistence' (opposite of passivity), 'speed and accuracy of thought', 'finality of decision,' or decisiveness (the opposite of ambivalence), 'mood control, optimism and sense of humor' (opposite of anhedonia), etc. Andreasen et al postulate that a disruption in the circuitry among nodes located in the prefrontal regions, the thalamic nuclei, and the cerebellum produces 'cognitive dysmetria', meaning difficulty in prioritizing, coordinating, and responding to information, and that it can account for the broad diversity of symptoms of schizophrenia. A relationship between cognitive processes and cerebellar and basal ganglia functions, and a role of neocerebellum in rapidly shifting attention, have been demonstrated. The cognitive styles, including a proficiency to quickly shift attention, of several famous leaders are used as examples of this contrasting model. Julius Caesar and Napoleon, for instance, could dictate to up to six secretaries simultaneously, using their exceptional working memories, and proficiency in quickly and effortlessly shifting attention while flawlessly gating irrelevant external and internal stimuli. It is suggested that specific brain imaging studies could illustrate this contrast. Gray et al noted positive correlations between 'dominance', an important leadership trait, and serum levels of dehydroepiandrosterone (DHEA) and testosterone (T), but not of more potent dihydrotestosterone (DHT), in over 1700 older men. Though not scientifically rigorous, the author noted positive correlations (P = 0.0162) between the self-rated ratings of voice depth (promoted by T) and of leadership, but none between those of body hair (DHT dependent) and of leadership in 47 male US National Academy of Sciences members. And 43 male US Senators had deeper voices than 36 male House members (P<0.01) who, in turn, had deeper voices than either of two groups (numbers 102 and 72) of male scientists (P<0.01). Therapeutically, before chlorpromazine, DHEA had been used in young schizophrenics with modest success in improving deficit symptoms. DHEA, or other sex hormones, or some of their natural and synthetic derivatives may prove to be valuable to treat deficit symptoms of schizophrenia in both sexes.

Illusory conjunctions and perceptual grouping in a visual search task in schizophrenia

This report describes part of a series of experiments, conducted within the framework of feature integration theory, to determine whether patients with schizophrenia show deficits in preattentive processing. Thirty subjects with a DSM-III-R diagnosis of schizophrenia and 30 age-, gender-, and education-matched normal control subjects completed two computerized experimental tasks, a visual search task assessing the frequency of illusory conjunctions (i.e. false perceptions) under conditions of divided attention (Experiment 3) and a task which examined the effects of perceptual grouping on illusory conjunctions (Experiment 4). We also assessed current symptomatology and its relationship to task performance. Contrary to our hypotheses, schizophrenia subjects did not show higher rates of illusory conjunctions, and the influence of perceptual grouping on the frequency of illusory conjunctions was similar for schizophrenia and control subjects. Nonetheless, specific predictions from feature integration theory about the impact of different target types (Experiment 3) and perceptual groups (Experiment 4) on the likelihood of forming an illusory conjunction were strongly supported, thereby confirming the integrity of the experimental procedures. Overall, these studies revealed no firm evidence that schizophrenia is associated with a preattentive abnormality in visual search using stimuli that differ on the basis of physical characteristics.

Preattentive visual search and perceptual grouping in schizophrenia

To help determine whether patients with schizophrenia show deficits in the stimulus-based aspects of preattentive processing, we undertook a series of experiments within the framework of feature integration theory. Thirty subjects with a DSM-III-R diagnosis of schizophrenia and 30 age-, gender-, and education-matched normal control subjects completed two computerized experimental tasks, a visual search task assessing parallel and serial information processing (Experiment 1) and a task which examined the effects of perceptual grouping on visual search strategies (Experiment 2). We also assessed current symptomatology and its relationship to task performance. While the schizophrenia subjects had longer reaction times in Experiment 1, their overall pattern of performance across both experimental tasks was similar to that of the control subjects, and generally unrelated to current symptomatology. Predictions from feature integration theory about the impact of varying display size (Experiment 1) and number of perceptual groups (Experiment 2) on the detection of feature and conjunction targets were strongly supported. This study revealed no firm evidence that schizophrenia is associated with a preattentive abnormality in visual search using stimuli that differ on the basis of physical characteristics. While subject and task characteristics may partially account for differences between this and previous studies, it is more likely that preattentive processing abnormalities in schizophrenia may occur only under conditions involving selected 'top-down' factors such as context and meaning.