Extent to which array genotyping and imputation with large reference panels approximate deep whole-genome sequencing

Understanding the genetic basis of human diseases and traits is dependent on the identification and accurate genotyping of genetic variants. Deep whole-genome sequencing (WGS), the gold standard technology for SNP and indel identification and genotyping, remains very expensive for most large studies. Here, we quantify the extent to which array genotyping followed by genotype imputation can approximate WGS in studies of individuals of African, Hispanic/Latino, and European ancestry in the US and of Finnish ancestry in Finland (a population isolate). For each study, we performed genotype imputation by using the genetic variants present on the Illumina Core, OmniExpress, MEGA, and Omni 2.5M arrays with the 1000G, HRC, and TOPMed imputation reference panels. Using the Omni 2.5M array and the TOPMed panel, ≥90% of bi-allelic single-nucleotide variants (SNVs) are well imputed (r² > 0.8) down to minor-allele frequencies (MAFs) of 0.14% in African, 0.11% in Hispanic/Latino, 0.35% in European, and 0.85% in Finnish ancestries. There was little difference in TOPMed-based imputation quality among the arrays with >700k variants. Individual-level imputation quality varied widely between and within the three US studies. Imputation quality also varied across genomic regions, producing regions where even common (MAF > 5%) variants were consistently not well imputed across ancestries. The extent to which array genotyping and imputation can approximate WGS therefore depends on reference panel, genotype array, sample ancestry, and genomic location. Imputation quality by variant or genomic region can be queried with our new tool, RsqBrowser, now deployed on the Michigan Imputation Server.

Mapping genomic loci implicates genes and synaptic biology in schizophrenia

Schizophrenia has a heritability of 60-80%1, much of which is attributable to common risk alleles. Here, in a two-stage genome-wide association study of up to 76,755 individuals with schizophrenia and 243,649 control individuals, we report common variant associations at 287 distinct genomic loci. Associations were concentrated in genes that are expressed in excitatory and inhibitory neurons of the central nervous system, but not in other tissues or cell types. Using fine-mapping and functional genomic data, we identify 120 genes (106 protein-coding) that are likely to underpin associations at some of these loci, including 16 genes with credible causal non-synonymous or untranslated region variation. We also implicate fundamental processes related to neuronal function, including synaptic organization, differentiation and transmission. Fine-mapped candidates were enriched for genes associated with rare disruptive coding variants in people with schizophrenia, including the glutamate receptor subunit GRIN2A and transcription factor SP4, and were also enriched for genes implicated by such variants in neurodevelopmental disorders. We identify biological processes relevant to schizophrenia pathophysiology; show convergence of common and rare variant associations in schizophrenia and neurodevelopmental disorders; and provide a resource of prioritized genes and variants to advance mechanistic studies.

Effect of Practice on Visual Backward Masking

Five experiments studied practice effects for 4, 7, 11 subjects on visual backward masking using a signal-detection procedure under various conditions. Exp. I determined the minimum perceptible critical stimulus duration (CSD) for criterion identification of a target stimulus, the letter T or A. In Exp. II, the stimulus was presented at the critical stimulus duration (CSD) followed by a pattern mask at intervals of 20 to 120 msec. for 15 separate sessions. In Exp. III ( N = 4) the mask followed the CSD in intervals of 2-msec. increments until subjects reached criterion accuracy. Exps. IV and V ( Ns = 4, 7) provided partial replications of Exps. II and III. Naive subjects were used, and the stimulus duration was constant for all subjects. When masking functions were obtained at a threshold, considerable variability was found and subjects improve slowly or not at all over sessions. With a fixed suprathreshold stimulus, all subjects improve with practice. The importance of these findings is discussed as they relate to common (and largely untested) assumptions made in the backward masking and perception literature.

Association of DNA Methylation Differences With Schizophrenia in an Epigenome-Wide Association Study

IMPORTANCE

DNA methylation may play an important role in schizophrenia (SZ), either directly as a mechanism of pathogenesis or as a biomarker of risk.

OBJECTIVE

To scan genome-wide DNA methylation data to identify differentially methylated CpGs between SZ cases and controls.

DESIGN, SETTING, AND PARTICIPANTS

Epigenome-wide association study begun in 2008 using DNA methylation levels of 456 513 CpG loci measured on the Infinium HumanMethylation450 array (Illumina) in a consortium of case-control studies for initial discovery and in an independent replication set. Primary analyses used general linear regression, adjusting for age, sex, race/ethnicity, smoking, batch, and cell type heterogeneity. The discovery set contained 689 SZ cases and 645 controls (n = 1334), from 3 multisite consortia: the Consortium on the Genetics of Endophenotypes in Schizophrenia, the Project among African-Americans To Explore Risks for Schizophrenia, and the Multiplex Multigenerational Family Study of Schizophrenia. The replication set contained 247 SZ cases and 250 controls (n = 497) from the Genomic Psychiatry Cohort.

MAIN OUTCOMES AND MEASURES

Identification of differentially methylated positions across the genome in SZ cases compared with controls.

RESULTS

Of the 689 case participants in the discovery set, 477 (69%) were men and 258 (37%) were non-African American; of the 645 controls, 273 (42%) were men and 419 (65%) were non-African American. In our replication set, cases/controls were 76% male and 100% non-African American. We identified SZ-associated methylation differences at 923 CpGs in the discovery set (false discovery rate, <0.2). Of these, 625 showed changes in the same direction including 172 with P < .05 in the replication set. Some replicated differentially methylated positions are located in a top-ranked SZ region from genome-wide association study analyses.

CONCLUSIONS AND RELEVANCE

This analysis identified 172 replicated new associations with SZ after careful correction for cell type heterogeneity and other potential confounders. The overlap with previous genome-wide association study data can provide potential insights into the functional relevance of genetic signals for SZ.

Robust differences in antisaccade performance exist between COGS schizophrenia cases and controls regardless of recruitment strategies

The impaired ability to make correct antisaccades (i.e., antisaccade performance) is well documented among schizophrenia subjects, and researchers have successfully demonstrated that antisaccade performance is a valid schizophrenia endophenotype that is useful for genetic studies. However, it is unclear how the ascertainment biases that unavoidably result from recruitment differences in schizophrenia subjects identified in family versus case-control studies may influence patient-control differences in antisaccade performance. To assess the impact of ascertainment bias, researchers from the Consortium on the Genetics of Schizophrenia (COGS) compared antisaccade performance and antisaccade metrics (latency and gain) in schizophrenia and control subjects from COGS-1, a family-based schizophrenia study, to schizophrenia and control subjects from COGS-2, a corresponding case-control study. COGS-2 schizophrenia subjects were substantially older; had lower education status, worse psychosocial function, and more severe symptoms; and were three times more likely to be a member of a multiplex family than COGS-1 schizophrenia subjects. Despite these variations, which were likely the result of ascertainment differences (as described in the introduction to this special issue), the effect sizes of the control-schizophrenia differences in antisaccade performance were similar in both studies (Cohen's d effect size of 1.06 and 1.01 in COGS-1 and COGS-2, respectively). This suggests that, in addition to the robust, state-independent schizophrenia-related deficits described in endophenotype studies, group differences in antisaccade performance do not vary based on subject ascertainment and recruitment factors.

Is there an association between advanced paternal age and endophenotype deficit levels in schizophrenia?

The children of older fathers have increased risks of developing schizophrenia spectrum disorders, and among those who develop these disorders, those with older fathers present with more severe clinical symptoms. However, the influence of advanced paternal age on other important domains related to schizophrenia, such as quantitative endophenotype deficit levels, remains unknown. This study investigated the associations between paternal age and level of endophenotypic impairment in a well-characterized family-based sample from the Consortium on the Genetics of Schizophrenia (COGS). All families included at least one affected subject and one unaffected sibling. Subjects met criteria for schizophrenia (probands; n = 293) or were unaffected first-degree siblings of those probands (n = 382). Paternal age at the time of subjects’ birth was documented. Subjects completed a comprehensive clinical assessment and a battery of tests that measured 16 endophenotypes. After controlling for covariates, potential paternal age–endophenotype associations were analyzed using one model that included probands alone and a second model that included both probands and unaffected siblings. Endophenotype deficits in the Identical Pairs version of the 4-digit Continuous Performance Test and in the Penn Computerized Neurocognitive Battery verbal memory test showed significant associations with paternal age. However, after correcting for multiple comparisons, no endophenotype was significantly associated with paternal age. These findings suggest that factors other than advanced paternal age at birth may account for endophenotypic deficit levels in schizophrenia.

The use of the Ego Impairment Index across the schizophrenia spectrum

The goal of this study was to assess perceptual and thought disturbance, as indexed by the Ego Impairment Index (EII; Perry & Viglione, 1991), a Rorschach-derived measure, across the schizophrenia spectrum. We hypothesized that there would be an increase in EII scores (indicating increased disturbance) across the spectrum from nonpatients to severely disturbed, hospitalized schizophrenia patients. Normal comparison participants (n = 66), students with elevated scores on either the Perceptual Aberration/Magical Ideation or the Physical Anhedonia Scales (n = 24), first-degree relatives of schizophrenia patients (n = 36), participants diagnosed with Diagnostic and Statistical Manual of Mental Disorders (4th ed. [DSM-IV]; American Psychiatric Association, 1994) schizotypal personality disorder (n = 36), outpatient schizophrenia participants (n = 33), and hospitalized schizophrenia patients (n = 56) were studied. As hypothesized, we found increased EII scores in all of the schizophrenia spectrum groups when compared against normal comparison participants. Furthermore, the EII was significantly different between the schizophrenia patients and the other schizophrenia spectrum groups. These findings support the use of the EII as a sensitive measure of perceptual and thought disturbance across the schizophrenia spectrum that yields specific information regarding the type of thinking problems that occur within schizophrenia spectrum subgroups.

Hemispheric and attentional contributions to perceptual organization deficits on the global-local task in schizophrenia

Right and left hemisphere hypotheses have been proposed to account for cognitive deficits in schizophrenia. To examine these hypotheses, perception of global-local patterns was studied in 22 patients with schizophrenia and 28 normal comparison participants. The patients with schizophrenia showed an abnormally exaggerated global processing advantage when attention was divided between global and local levels but not when participants were instructed to attend to either the local or global level. This finding suggested a local processing (left hemisphere) deficit, which was overcome through strategic attentional allocation (instructional set). When the stimulus visual angle was reduced from 9 degrees to 3 degrees, the normal participants showed a shift from a local to a global processing advantage, but the patients did not. This finding suggested a more subtle deficit in strategic attentional processes that develop through exposure to stimulus context.

Hemispheric and attentional contributions to perceptual organization deficits on the global-local task in schizophrenia

Right and left hemisphere hypotheses have been proposed to account for cognitive deficits in schizophrenia. To examine these hypotheses, perception of global-local patterns was studied in 22 patients with schizophrenia and 28 normal comparison participants. The patients with schizophrenia showed an abnormally exaggerated global processing advantage when attention was divided between global and local levels but not when participants were instructed to attend to either the local or global level. This finding suggested a local processing (left hemisphere) deficit, which was overcome through strategic attentional allocation (instructional set). When the stimulus visual angle was reduced from 9 degrees to 3 degrees, the normal participants showed a shift from a local to a global processing advantage, but the patients did not. This finding suggested a more subtle deficit in strategic attentional processes that develop through exposure to stimulus context.

The relationship between skin conductance hyporesponsivity and perseverations in schizophrenia patients

BACKGROUND

It has been reported that approximately 45% of schizophrenia patients versus 10% of normal comparison subjects are classified as skin conductance hyporesponders (SCOR-HR: the lack of a robust orienting response) when exposed to innocuous tones. We studied the skin conductance orienting response (SCOR) of schizophrenia patients during the exposure to complex and abstract stimuli. We investigated two questions: 1) would the same percentage of schizophrenia patients be classified as SCOR-HR when the orienting stimuli are complex and abstract as when they are innocuous tones; and 2) whether SCOR-HR schizophrenia patients have associated frontally mediated neurocognitive deficits.

METHODS

Thirty-one schizophrenia patients and 29 normal comparison subjects were presented with the Rorschach inkblot test while their SCORs were recorded. Schizophrenics were divided in two groups: SCOR-HR and SCOR responders. Demographic and clinical comparisons were made between the two groups. Rorschach responses were scored for the presence of perseverations.

RESULTS

Forty-five percent of the schizophrenia patients were classified as SCOR-HR versus 10% of the normal comparison subjects. Among the schizophrenia patients, SCOR-HR was associated with increased perseverations, which were in turn correlated with the Scale for the Assessment of Negative Symptoms scores.

CONCLUSIONS

It appears that SCOR-HR in schizophrenia is not a function of the "meaningfulness" of the stimuli. When SCOR status was combined with the measure of stuck-in-set perseverations, a pattern of results emerged lending indirect support to the hypothesis that relates SCOR-HR to frontal impairment and to the idea that SCOR-HR schizophrenia patients may represent a specific subgroup.

Relationship of neuropsychological and MRI measures to age of onset of schizophrenia

Age of onset of schizophrenia (AOS) may be largely determined by neurobiological factors. We examined in a diverse sample of schizophrenia out-patients the relationships of AOS with neuropsychological abilities and structural brain abnormalities as measured on cerebral magnetic resonance imaging (MRI). A total of 82 out-patients meeting DSM-III-R criteria for schizophrenia were evaluated with a comprehensive neuropsychological battery and semi-automated quantitatively analysed cerebral MRI. Earlier AOS correlated with poorer performance in learning and abstraction/cognitive flexibility, and with larger volumes of caudate and lenticular nuclei, and smaller volume of thalamus on MRI. A model for predicting AOS consisting of abstraction and thalamic and caudate volumes remained significant after controlling for duration of illness, current age and daily neuroleptic dose. In conclusion, AOS may be related to specific rather than general measures of cognitive performance and structural brain abnormalities.

Is it possible to be schizophrenic yet neuropsychologically normal?

This study identified and characterized a group of schizophrenic patients without neuropsychological (NP) impairment. A comprehensive NP battery was administered to 171 schizophrenic outpatients and 63 normal comparison participants. Each participant's NP status was classified through blind clinical ratings by 2 experienced neuropsychologists; 27% of the schizophrenics were classified as NP normal. The NP-normal and NP-impaired schizophrenics were similar in terms of most demographic, psychiatric, and functional characteristics, except that NP-normal patients had less negative and extrapyramidal symptoms, were on less anticholinergic medication, socialized more frequently, and were less likely to have had a recent psychiatric hospitalization. The existence of NP-normal schizophrenics suggests that the pathophysiology underlying the cognitive deficits often associated with schizophrenia may be distinct from that causing some of its core psychiatric features.

Is it possible to be schizophrenic yet neuropsychologically normal?

This study identified and characterized a group of schizophrenic patients without neuropsychological (NP) impairment. A comprehensive NP battery was administered to 171 schizophrenic outpatients and 63 normal comparison participants. Each participant's NP status was classified through blind clinical ratings by 2 experienced neuropsychologists; 27% of the schizophrenics were classified as NP normal. The NP-normal and NP-impaired schizophrenics were similar in terms of most demographic, psychiatric, and functional characteristics, except that NP-normal patients had less negative and extrapyramidal symptoms, were on less anticholinergic medication, socialized more frequently, and were less likely to have had a recent psychiatric hospitalization. The existence of NP-normal schizophrenics suggests that the pathophysiology underlying the cognitive deficits often associated with schizophrenia may be distinct from that causing some of its core psychiatric features.

Clinical and experimental characteristics of "hypothetically psychosis prone" college students

The study of individuals at the boundaries of schizophrenia has historically involved genetic relatives of schizophrenia patients or individuals who meet criteria for schizotypal personality disorder (SPD). Recently, many investigators have turned to the use of psychometric scales, developed to measure psychotic traits or vulnerability to developing schizophrenia, to screen large populations of college students in order to identify individuals who are "psychosis prone" or "schizotypal". To help answer the question of whether students identified with psychometric scales are indeed psychosis prone, we screened 1115 college students with the Perceptual Aberration/ Magical Ideation (PerMag) and Physical Anhedonia (PhysAn) Scales. Individuals who scored 2 standard deviations (SD) above the mean on the scales were selected as experimental subjects (N = 13 PerMag, N = 10 PhysAn) and a subpopulation of matched subjects who scored less than 0.5 SD above the mean were selected as control subjects (N = 24). All subjects then received a full battery of tests, including structured clinical interviews, the MMPI, and psychophysiological measures of information processing, including prepulse inhibition and habituation of the human startle response, visual backward masking and reaction time measures. The results suggest that the PerMag scale, but not the PhysAn scale, identifies individuals with some psychotic, affective and anxiety symptoms when compared to the controls. Neither scale predicts a diagnosis of schizotypal personality disorder or deficits on measures of information processing that characterize schizophrenia or schizotypal personality disordered patients.

Gender differences on thought disturbance measures among schizophrenic patients

OBJECTIVE

This study examined gender differences on three measures of thought disturbance among patients with schizophrenia and the relation between thought disturbance and social competency.

METHOD

Fifty-three male and 34 female patients diagnosed with schizophrenia according to the DSM-III-R criteria were assessed on measures of thought disturbance: subscales of the Scale for the Assessment of Positive Symptoms (SAPS), subscales of the Brief Psychiatric Rating Scale (BPRS), and the Ego Impairment Index. Gender differences on the three measures of thought disturbance and the relation of these measures to demographic variables and other variables, such as social competency, were examined.

RESULTS

Male and female schizophrenic patients demonstrated similar degrees of thought disturbance on the pertinent subscales of the SAPS and the BPRS, but the male schizophrenic patients had scores showing greater impairment on the Ego Impairment Index. Furthermore, a relationship between thought disturbance and social competency was confirmed.

CONCLUSIONS

These findings support other studies in which female patients were found to have a "milder" form of schizophrenia, generally characterized by better social functioning, than their male counterparts. The literature regarding gender-related differences in thought disturbance in schizophrenia has been unclear and complicated by design issues such as obtaining adequate samples of subjects and optimizing measurement selection. The findings of this study suggest that use of a converging-measures strategy allows a better assessment of thought disturbance in severely ill schizophrenic patients and an understanding of the importance of thought disorder with respect to gender-related patterns of clinical characteristics, such as social competency.

Amphetamine on Rorschach measures in normal subjects

Twenty-two normal undergraduate men were administered either d-amphetamine (0.2 mg/kg or 0.4 mg/kg) or placebo in a double-blind, counterbalanced design. The test sessions were exactly three weeks apart and included, among other measures, the Rorschach test. Rorschach anxiety and thought disorder variables were measured under drug and placebo conditions. The results suggest that amphetamine causes an increase in Rorschach anxiety indices but does not elevate Rorschach indices of thought disorder. The observed dissociation of anxiety and thought disorder on the Rorschach has implications for the role of the Rorschach in studying anxiety disorders and schizophrenic disorders.

The nature of learning and memory impairments in schizophrenia

The California Verbal Learning Test was used to characterize the learning and memory impairment in schizophrenia (SC) and to evaluate potential clinical and demographic factors associated with this impairment. SC patients (n = 175) performed worse than normal comparison (NC) subjects (n = 229) on all learning, recall, and recognition memory measures. The most important clinical correlates of these impairments were earlier age of onset, more negative symptoms, and greater anticholinergic medication dosage. SC patients showed a prominent retrieval deficit as indicated by disproportionate improvement when tested in a recognition, rather than a free recall, format. A residual impairment seen with recognition testing suggests a mild encoding deficit as well. In contrast, the relative absence of a storage deficit is suggested by the lack of rapid forgetting. Using a discriminant function analysis that differentiates cortical dementia [i.e., Alzheimer's disease (AD)], subcortical dementia [i.e., Huntington's disease (HD)], and normals, it was found that 50% of the SC patients were classified as having a subcortical memory profile and 35% were classified as having a normal profile, whereas only 15% were classified as having a cortical memory profile. Although these findings reflect the clinical heterogeneity often found in SC, results suggest that most SC patients demonstrate a pattern of learning and memory impairments that resembles the pattern seen in patients with primary subcortical (specifically striatal) pathology.

Neuropsychological deficits in schizophrenics. Relationship to age, chronicity, and dementia

BACKGROUND

We sought to determine whether neuropsychological impairment in schizophrenia is related to current age, age at onset, or duration of illness, and whether the pattern of such impairment can be distinguished from that caused by progressive dementias of Alzheimer's type. We administered a comprehensive neuropsychological test battery to a normal control group (n = 38), a group of ambulatory patients with Alzheimer's disease (n = 42), and three ambulatory schizophrenic groups: early onset-young (n = 85), early onset-old (n = 35), and late onset (n = 22). Tests were grouped and analyzed according to eight major ability areas, and published procedures were used to remove the expected effects of normal aging.

RESULTS

The three schizophrenic groups were found to be neuropsychologically similar to one another and different from normal controls and patients with Alzheimer's disease. There were no significant differences among the schizophrenic groups in level or pattern of neuropsychological functioning. Patients with Alzheimer's disease demonstrated less efficient learning and particularly more rapid forgetting than did the other groups.

CONCLUSIONS

These findings suggest that neuropsychological impairment in schizophrenia is unrelated to current age, age at onset, or duration of illness. The study further suggests that the encephalopathy associated with schizophrenia is essentially nonprogressive and produces a pattern of deficits that is different from that seen in progressive cortical dementias.

Startle gating deficits occur across prepulse intensities in schizophrenic patients

The effects of prepulse stimuli of different intensities in inhibiting the startle reflex was assessed in 14 age-matched and gender-matched schizophrenic patients and 14 normal controls. The subjects were presented with startling stimuli consisting of bursts of white noise (106 dBA) with or without prepulse stimuli. Four intensities of prepulse stimuli were utilized: 75, 80, 85, and 90 dBA. Throughout the testing, the background noise was maintained at 70 dBA. The prepulse stimuli more effectively inhibited the startle reflex in the control group compared to the schizophrenic patients who showed deficient prepulse inhibition (gating) of the startle reflex. These results suggest that schizophrenics have impaired central inhibitory mechanisms over a fairly broad range of background noise to prepulse ratios. Further studies are needed to clarify exactly which ratios are optimal in eliciting prepulse inhibition (PPI) and in differentiating between schizophrenic and control groups.

The Ego Impairment Index and schizophrenia: a validation study

This study is an extension of our work on a new scale, the Ego Impairment Index (EII; Perry & Viglione, 1991). The index is theoretically based on Beres's (1956) model of ego assessment and was empirically developed on a sample of melancholic, depressed outpatients, diagnosed according to the Diagnostic and Statistical Manual of Mental Disorders (3rd ed. [DSM-III]; American Psychiatric Association, 1980). The EII is derived from the Rorschach Inkblot Test and offers a single composite score of ego impairment. This study validates the use of the EII with a heterogeneous sample of schizophrenic patients. In support of the trait-like characteristics of the scale, the EII continues to be expressed as a single factor, with a correlation of .98 when comparing the original factor derived from a melancholic population with this sample of schizophrenic patients. Significant correlations were also found between the EII and other clinical indices, including the Magical Ideation Scale, the Schizophrenia Index, and the Minnesota Multiphasic Personality Inventory (MMPI). Finally, the EII was found to differentiate between a paranoid subgroup and a mixed undifferentiated/disorganized subgroup who theoretically have more ego impairment. These results offer support for the use of the EII as an empirical means of quantitatively and qualitatively assessing thought disorder within a theoretical framework. Further research is needed to understand the application of the EII across different diagnostic groups and its relationship to other indices of psychological disturbance.

Past substance abuse and clinical course of schizophrenia

To evaluate the effects of previous alcohol and drug use on the course and symptoms of schizophrenia, the authors compared 34 patients with schizophrenia who had histories of substance abuse with 17 patients with schizophrenia who were lifelong abstainers. Surprisingly, they did not find that individuals with past histories of abuse were more impaired or had more symptoms.

Effects of rare non-target stimuli on brain electrophysiological activity and performance

In order to assess the effects of non-target stimuli on task performance and electrophysiological activity, 16 subjects performed reaction time (RT) experiments under 3 conditions. In all conditions, subjects had to press a button upon detection of rare (15%) target stimuli (1600 Hz) presented among frequent (85%) non-target stimuli. The 3 conditions differed based on their non-target stimuli. In one condition, the non-targets consisted of 'standard' stimuli (900 Hz). In the two other conditions, rare and deviant non-target stimuli were randomly added to the standard stimuli. These deviant non-target stimuli consisted of either constant (700-Hz tones) or novel (buzzes, filtered noises and other unusual sounds) stimuli. Both the rare target and non-target stimuli elicited P300, responses. Behavioral (RT) and electrophysiological (event-related potential) data showed that stimuli that followed standard stimuli were processed differently compared to stimuli that followed deviant non-target stimuli. In the conditions containing deviant non-target stimuli, the P3b to the target stimuli was smaller and later, and the mean RT longer than in the condition with no deviant stimuli. These behavioral and electrophysiological changes induced by the deviant non-target stimuli were discussed with reference to two factors, distraction and increased level of task difficulty. It was suggested that each of these factors were differentially sensitive to the novelty of the rare deviant stimuli.

Effect of practice on visual backward masking

Five experiments studied practice effects for 4, 7, 11 subjects on visual backward masking using a signal-detection procedure under various conditions. Exp. I determined the minimum perceptible critical stimulus duration (CSD) for criterion identification of a target stimulus, the letter T or A. In Exp. II, the stimulus was presented at the critical stimulus duration (CSD) followed by a pattern mask at intervals of 20 to 120 msec. for 15 separate sessions. In Exp. III (N = 4) the mask followed the CSD in intervals of 2-msec. increments until subjects reached criterion accuracy. Exps. IV and V (Ns = 4, 7) provided partial replications of Exps. II and III. Naive subjects were used, and the stimulus duration was constant for all subjects. When masking functions were obtained at a threshold, considerable variability was found and subjects improve slowly or not at all over sessions. With a fixed supra-threshold stimulus, all subjects improve with practice. The inportance of these findings is discussed as they relate to common (and largely untested) assumptions made in the backward masking and perception literature.

Therapist A--B score and treatment outcome with psychiatric in patients: a table of random numbers

The study evaluated the relationship between therapist personality and treatment success for 141 schizophrenics and 94 non-schizophrenics randomly assigned to short or long hospitalization. The 47 therapists were self-rated on the Whitehorn--Betz A--B scale in both the original and the Campbell versions. Outcome was assessed on the Health--Sickness Rating Scale and the Psychiatric Evaluation Form at discharge and at 1 and 2 year follow-up. The hypothesis of greater success for A--type therapists with schizophrenics was not confirmed, nor were alternative relationships evident in the data.

Unresponsiveness of catatonic symptoms to naloxone

A case report of a catatonic patient is presented. Because of the similarity of catatonia to the animal behavior produced by intracerebral administration of beta-endorphin, an endogenous opioid, naloxone was administered. No effect was observed with naloxone, whereas both amobarbital and diazepam were able to reverse catatonic behavior. Testing of catatonic patients with naloxone may help further elucidate naloxone's reported anti-psychotic properties.