Spatial and semantic inhibitory processing in schizophrenia

Non-spatial inhibition of return attenuates audiovisual integration owing to modality disparities

Although previous studies have investigated the relationship between inhibition of return (IOR) and multisensory integration, the influence of non-spatial has not been explored. The present study aimed to investigate the influence of non-spatial IOR on audiovisual integration by using a "prime-neutral cue-target" paradigm. In Experiment 1, which manipulated prime validity and target modality, the targets were positioned centrally, revealing significant non-spatial IOR effects in the visual, auditory, and audiovisual modalities. Analysis of relative multisensory response enhancement (rMRE) indicated substantial audiovisual integration enhancement in both valid and invalid target conditions. Furthermore, the enhancement was weaker for valid targets than for invalid targets. In Experiment 2, the targets were positioned above and below to rule out repetition blindness (RB); this experiment successfully replicated the results observed in Experiment 1. Notably, Experiments 1 and 2 consistently found that the correlation between modality differences and rMRE for valid targets indicated that differences in signal strength between visual and auditory modalities contributed to a reduction in audiovisual integration. However, the absence of correlation with the invalid target suggests that attention, as a key factor, may play a significant role in this process. The present study highlights how non-spatial IOR reduces audiovisual integration and sheds light on the complex interaction between attention and multisensory integration.

Neural correlates of the preserved inhibition of return in schizophrenia

Inhibition of return (IOR) is an attentional mechanism that previously has been reported to be either intact or blunted in subjects with schizophrenia (SCZ). In the present study, we explored the neural mechanism of IOR in SCZ by comparing the target-locked N1 and P1 activity evoked by valid-cued trials with that evoked by invalid-cued trials. Twenty-seven schizophrenia patients and nineteen healthy controls participated in a task involving covert orienting of attention with two stimulus onset asynchronies (SOAs: 700 ms and 1200 ms) during which 64-channel EEG data were recorded. Behavioral reaction times (RTs) were longer in response to valid-cued trials than to invalid-cued ones, suggesting an intact IOR in SCZ. However, reduced N1 amplitude elicited by valid-cued trials suggested a stronger inhibition of attention from being oriented to a previously cued location, and therefore a relative inhibition of perceptual processing at that location in SCZ. These results indicate that altered N1 activity is associated with the preservation of IOR in SCZ and could be a sensitive marker to track the IOR effect.

Processing of Threat-related Information Outside the Focus of Visual Attention

This study investigates whether threat-related words are especially likely to be perceived in unattended locations of the visual field. Threat-related, positive, and neutral words were presented at fixation as probes in a lexical decision task. The probe word was preceded by 2 simultaneous prime words (1 foveal, i.e., at fixation; 1 parafoveal, i.e., 2.2 deg. of visual angle from fixation), which were presented for 150 ms, one of which was either identical or unrelated to the probe. Results showed significant facilitation in lexical response times only for the probe threat words when primed parafoveally by an identical word presented in the right visual field. We conclude that threat-related words have privileged access to processing outside the focus of attention. This reveals a cognitive bias in the preferential, parallel processing of information that is important for adaptation.

Inhibition of return: Twenty years after

When responding to a suddenly appearing stimulus, we are slower and/or less accurate when the stimulus occurs at the same location of a previous event than when it appears in a new location. This phenomenon, often referred to as inhibition of return (IOR), has fostered a huge amount of research in the last 20 years. In this selective review, which introduces a Special Issue of Cognitive Neuropsychology dedicated to IOR, we discuss some of the methods used for eliciting IOR and its boundary conditions. We also address its debated relationships with orienting of attention, succinctly review findings of altered IOR in normal elderly and neuropsychiatric patients, and present results concerning its possible neural bases. We conclude with an outline of the papers collected in this issue, which offer a more in-depth treatment of behavioural, neural, and theoretical issues related to IOR.

Abnormal inhibition of return: A review and new data on patients with parietal lobe damage

The study of the performance of patients with neurological disorders has been fruitful in revealing the nature and neural basis of inhibition of return (IOR). Thus, in recent years, studies have reported abnormal IOR in patients with Alzheimer's disease, patients diagnosed with schizophrenia, and brain-damaged patients. In the present study, we investigated the hypothesis that a spatial "disengagement deficit" (DD; Posner, Walker, Friedrich, & Rafal, 1984) contributed to the pattern of impaired IOR in the ipsilesional field of parietal patients, found in a previous work (Vivas, Humphreys, & Fuentes, 2003). In a first experiment, we replicated the attenuation of IOR for ipsilesional targets on those trials with a lateralized IOR procedure. With stimuli vertically aligned about fixation, we found intact IOR for both up and down targets. Most important, when we ameliorated the potential impact of a spatial DD by presenting both cues and target in the same hemifield, still we found impaired IOR in the ipsilesional field. We interpret these findings in terms of unilateral parietal damage leading to an imbalance of the relative salience of signals represented in a spatial map for directing attention.

Dynamics of the semantic priming shift: behavioral experiments and cortical network model

Multiple semantic priming processes between several related and/or unrelated words are at work during the processing of sequences of words. Multiple priming generates rich dynamics of effects depending on the relationship between the target word and the first and/or second prime previously presented. The experimental literature suggests that during the on-line processing of the primes, the activation can shift from associates to the first prime to associates to the second prime. Though the semantic priming shift is central to the on-line and rapid updating of word meanings in the working memory, its precise dynamics are still poorly understood and it is still a challenge to model how it functions in the cerebral cortex. Four multiple priming experiments are proposed that cross-manipulate delays and association strength between the primes and the target. Results show for the first time that association strength determines complex dynamics of the semantic priming shift, ranging from an absence of a shift to a complete shift. A cortical network model of spike frequency adaptive neuron populations is proposed to account for the non-continuous evolution of the priming shift over time. It allows linking the dynamics of the priming shift assessed at the behavioral level to the non-linear dynamics of the firing rates of neurons populations.

Inhibition of return and schizophrenia: a meta-analysis

Inhibition of return (IOR) is a phenomenon that involves inhibited or delayed orienting to previously cued locations in favor of attending to novel locations. To date, research on IOR in patients with schizophrenia has generated mixed, and seemingly conflicting, results. Some researchers report patients with schizophrenia exhibit blunted or delayed IOR, while other researchers report normal IOR, in terms of time course and magnitude. This meta-analysis summarizes the literature that has employed an IOR task in patients with schizophrenia and with controls while focusing upon a procedural feature, the use of a cue back to fixation, between the cue and target that is known to be important when executive control has been hampered in non-clinical populations. Fifteen experiments were located yielding a total sample of 362 patients with schizophrenia or schizoaffective disorder and 285 controls. Using a meta-analytic approach, results of the present analyses show that patients with schizophrenia demonstrate delayed IOR in the single cue procedure. In the cue back to fixation procedure, the time course of IOR among patients is more consistent with that of controls. Differences in measured IOR between patients with schizophrenia and controls are largely related to a deficit in endogenous disengagement of attention.

Deficient inhibition of return in chronic but not first-episode patients with schizophrenia

BACKGROUND

Inhibition of return (IOR) has been tested in patients with schizophrenia with contradictory results. Some studies indicated that patients with schizophrenia have normal levels of IOR; however, other studies reported delayed or blunted IOR. Inconsistency in findings might be due to differences across studies in relevant aspects associated with disease, such as heterogeneity of the disorder, different medications, onset and severity of the illness. The present study was to explore different patterns of IOR in antipsychotic medication free first-episode schizophrenia and chronic schizophrenia.

METHODS

Forty two patients with first-episode schizophrenia, 44 patients with chronic schizophrenia, and 38 healthy controls were included in the study. All subjects went through a covert orienting of attention task with seven stimulus onset asynchrony (SOA) intervals (400 ms, 500 ms, 600 ms, 700 ms, 800 ms, 1200 ms and 1500 ms).

RESULTS

Compared with healthy controls, the magnitude and onset of IOR in first-episode patients with schizophrenia were intact. However, in patients with chronic schizophrenia, there was an attenuated cuing effect especially at SOA 700 ms; in addition, there was a robust IOR until at SOAs 800 ms or above. Moreover, the illness duration and the number of psychotic episodes were significantly correlated with the validity effect at SOAs 400 ms and 600 ms.

CONCLUSION

Our study suggests that deficient IOR presents in chronic but not in first-episode patients with schizophrenia. IOR deficit in schizophrenia may begin during the course of illness and deteriorate over the course of illness. Our findings are consistent with the neurodegenerative model of schizophrenia.

Determinants of multiple semantic priming: a meta-analysis and spike frequency adaptive model of a cortical network

Recall and language comprehension while processing sequences of words involves multiple semantic priming between several related and/or unrelated words. Accounting for multiple and interacting priming effects in terms of underlying neuronal structure and dynamics is a challenge for current models of semantic priming. Further elaboration of current models requires a quantifiable and reliable account of the simplest case of multiple priming resulting from two primes on a target. The meta-analytic approach offers a better understanding of the experimental data from studies on multiple priming regarding the additivity pattern of priming. The meta-analysis points to the effects of prime-target stimuli onset asynchronies on the pattern of underadditivity, overadditivity, or strict additivity of converging activation from multiple primes. The modeling approach is then constrained by results of the meta-analysis. We propose a model of a cortical network embedding spike frequency adaptation, which allows frequency and time-dependent modulation of neural activity. Model results give a comprehensive understanding of the meta-analysis results in terms of dynamics of neuron populations. They also give predictions regarding how stimuli intensities, association strength, and spike frequency adaptation influence multiple priming effects.

Confirmation for a delayed inhibition of return by systematic sampling in schizophrenia

Inhibition of return (IOR) is a phenomenon thought to reflect a mechanism to protect the organism from redirecting attention to previously scanned insignificant locations. A number of studies reported altered IOR in schizophrenia patients with a reduction of its amplitude. However, incomplete sampling of stimulus onset asynchronies (SOAs) makes data on IOR time course incomplete. We examined 14 stabilized young patients with recent onset schizophrenia and 16 healthy controls matched for gender, age, and years of education. Schizophrenia patients (13 males, 1 female) had a mean age of 26.3+/-5.8 years and a mean number of years of study of 9.6+/-3.6. Their illness had a mean duration of 147 weeks. Patients displayed moderate overall slow reaction times (387 ms) in comparison with controls (322 ms). Onset of IOR was found to be delayed in schizophrenia patients appearing between 700 and 800 ms following the cue onset while it appeared at 300 ms in controls. In patients, IOR was constant up to 1100 ms; however, its amplitude was weak with an average of 6 ms. Validity effects (overall and at each SOA value) were uncorrelated to age, years of study, duration of illness, or total or subscale scores on the Positive and Negative Syndrome Scale.

Gaze cueing of attention in schizophrenia: individual differences in neuropsychological functioning and symptoms

Inhibition of return (IOR) represents a well-known mechanism of human perception that biases attentional orienting to novel locations in the environment. Behaviorally, IOR reflects slower reaction time (RT) to stimuli presented in previously cued locations. In this study, we examined within patients with schizophrenia this inhibitory aftereffect using two different cue types--eye gaze and standard peripheral cues. Results indicated that patients showed evidence of IOR, as reflected in a 3.2% slowing in RT to previously peripherally cued locations. However, for eye gaze, patients failed to show evidence of IOR and instead had 1.7% faster RT to targets presented following delay in locations that had been previously cued. This inhibitory failure correlated strongly with reduced neuropsychological performance and global symptoms ratings of attention and bizarre behavior. Reduced inhibitory aftereffect in RT for eye-gaze cues may reflect disease-related abnormalities in social attention.

Biasing the organism for novelty: A pervasive property of the attention system

Although the functional and anatomical independences between the orienting and the executive attention networks have been well established, surprisingly little is known about the potential neural interaction between them. Recent studies point out that spatial inhibition of return (IOR), a mechanism associated with the orienting network, and nonspatial inhibition of return, a mechanism associated with the executive network, might bias the organism for novel locations and objects, respectively. By orthogonally combining the spatial and the nonspatial IOR paradigms in this fMRI study, we demonstrate that the orienting and the executive networks interact and compensate each other in biasing the attention system for novelty. Behaviorally, participants responded slower to the target at the old location only when the color of the target was novel, and participants responded slower to the old color representation only when the target appeared at a novel spatial location. Neurally, the orienting network was involved in slowing down responses to the old location only when the nonspatial IOR mechanism in the executive network was not operative (i.e., when the color of the target was novel); the prefrontal executive network was involved in slowing down responses to the old color representation only when the spatial IOR mechanism in the orienting network was not functioning (i.e., when the target appeared at a novel location).

Is semantic memory impaired in schizophrenia? A systematic review and meta-analysis of 91 studies

INTRODUCTION

Semantic memory impairments in schizophrenia have been reported across a wide range of neuropsychological tests. Set against a backdrop of fairly widespread cognitive impairments, it is difficult to know whether there is a primary, or secondary, impairment of semantic memory in schizophrenia. Also, whether there is a profile of differential impairment across the range of neuropsychological tests.

METHODS

Employing a systematic search strategy, 91 papers were identified which have assessed participants with schizophrenia on a measure of semantic memory. A series of meta-analyses were then conducted which provided combined weighted means for performance on tasks of naming, word-picture matching, verbal fluency, priming, and categorisation.

RESULTS

An uneven profile of impairment is reported with large effect sizes for tests of naming and verbal fluency, medium effect sizes for word-picture matching and association and small effect sizes for categorisation and priming tests.

CONCLUSIONS

This uneven profile supports the claim that a degradation of semantic knowledge may not be adequate in explaining the semantic memory impairment in schizophrenia. This conclusion is supported by the data which report a relationship between an executive dysfunction and poor priming and fluency performance particularly. The data support a link between Formal Thought Disorder and semantic memory impairments on tests of naming and verbal fluency but on other tests evidence is equivocal.

Pharmacological modulation of the neural basis underlying inhibition of return (IOR) in the human 5-HT2A agonist and NMDA antagonist model of psychosis

RATIONALE

Attentional deficits are common symptoms in schizophrenia. Recent evidence suggests that schizophrenic patients show abnormalities in spatial orienting of attention, particularly a deficit of inhibition of return (IOR). IOR is mostly thought to reflect an automatic, inhibitory mechanism protecting the organism from redirecting attention to previously scanned, insignificant locations. Pharmacologic challenges with hallucinogens have been used as models for psychosis.

OBJECTIVES

The aim of this study was to investigate the neural correlates underlying orienting of attention in the human N-methyl-D-aspartic acid antagonist and 5-HT2A agonist models of psychosis.

MATERIALS AND METHODS

Fourteen healthy volunteers participated in a randomized, double-blind, cross-over event-related functional magnetic resonance imaging (fMRI) study with dimethyltryptamine (DMT) and S-ketamine. We administered a covert orienting of attention task with nonpredictive peripheral cues, and we scanned the subjects on two separate days at least 14 days apart with a placebo and a verum condition on each day.

RESULTS

DMT, but not S-ketamine, slowed down reaction times significantly. IOR was blunted after DMT, but not after S-ketamine. Relative to placebo, S-ketamine increased activation in the IOR condition in the right superior frontal gyrus, left superior temporal gyrus, and right midfrontal frontal gyrus.

CONCLUSIONS

The discrepancy between the behavioral and functional imaging outcome indicates that pharmacological fMRI might be a sensitive tool to detect drug-modulated blood oxygenation level-dependent signal changes in the absence of behavioral abnormalities. Our findings might help to further clarify the contradictory findings of IOR in schizophrenic patients and might, thus, shed more light on possible differential pathomechanisms of schizophrenic symptoms.

Orienting of attention in unmedicated patients with schizophrenia, prodromal subjects and healthy relatives

In typical orienting of attention tasks subjects have to respond as fast as possible to targets which appear in the periphery of the visual field and are preceded by spatial cues (e.g. brightening of a peripheral box where the target may subsequently appear). Reaction times (RT) are facilitated when cue and target appear at the same location (valid cueing) and the cue target interval is short (<250 ms). However, RTs slow down again when the target follows a valid cue after an interval of 250 ms and longer. This latter phenomenon is called Inhibition of Return (IOR) and is thought to reflect an automatic, inhibitory mechanism to protect the organism from redundant and distracting stimuli. Deficits of IOR were repeatedly reported in patients with schizophrenia. However, the role of medications and the nature of the deficit (trait or vulnerability indicator?) were unclear. In the present study we examined 15 unmedicated patients with schizophrenia (age: 31.2+/-11.1, m/f: 11/4, global scores SAPS: 48.33+/-33.09, SANS: 19.22+/-26.16), 29 subjects who were putatively in a prodromal state of psychosis, 30 first-degree relatives, another 8 first-degree relatives who had one child and at least one more relative with schizophrenia, and 50 healthy controls. We found an impairment of IOR only in the unmedicated patient group. In conclusion, blunted IOR in schizophrenia is not secondary to medications. According to this and previous studies blunted IOR may be most probably viewed as a trait cognitive feature of the schizophrenic disorder.

[Inhibition of return in schizophrenia: a review]

INTRODUCTION

Most visual environments contain more information than the human brain can process in real time. To overcome this limitation, the attention system acts as a filter by selectively orienting attention to specific regions of the visual field. This ability to orient attention can be reflected in covert shift processes of attention.

LITERATURE FINDINGS

In a typical covert orienting task, subjects have to maintain fixation on a central cross and respond as quickly as possible to a target, which appears in a peripheral box following a cue that summons attention to the direction where the target is going to appear (valid cueing) or to the contralateral direction (invalid cueing). When the cues are nonpredictive, the response characteristics critically depend on stimulus-onset asynchrony (SOA). With short SOAs (<300ms), valid cues result in a reaction time advantage over invalid trials, which is due to a reflexive shift of attention towards the source of stimulation. In contrast, with longer SOAs, valid cues result in longer reaction times to the subsequent target.

DISCUSSION

This phenomenon is known as the inhibition of return and is mostly thought to reflect an inhibitory mechanism protecting the organism from redirecting attention to previously scanned insignificant locations. Many studies have reported blunted or delayed inhibition of return in patients with schizophrenia. However, some authors reported normal amounts of inhibition of return. This can be partly explained by the use of manipulations of the covert orienting of the attention paradigm that is known to enhance the course of inhibition of return.

CONCLUSION

The deficit of inhibition of return seems to be time-stable and to be unrelated to psychopathology or length of illness. The contribution of neuroleptic medication to this deficit cannot be determined. Recent data suggest a deficit of inhibition of return in two human models of psychosis (dimethyltryptamine and ketamine). Further studies should clarify whether blunted inhibition of return might represent a trait marker of schizophrenia.

Inhibitory control of proactive interference in adults with ADHD

OBJECTIVE

Attention deficit hyperactivity disorder (ADHD) is associated with poor inhibition of prepotent responses and deficits in distractor inhibition, but relatively few studies have addressed inhibitory control of proactive interference (PI) in individuals with ADHD. Thus, the goal of the present study was to evaluate resistance to spatial and verbal PI in adults with ADHD.

METHOD

Adults with ADHD (n = 32) and adults without ADHD (n = 32) performed a spatial inhibition of return (IOR) task and a semantic IOR task.

RESULTS

Adults with and without ADHD showed effective spatial IOR. On the semantic IOR task, adults without ADHD showed semantic inhibition, whereas adults with ADHD showed semantic facilitation (positive priming) instead.

CONCLUSION

Adults with ADHD may have domain-specific deficits in resistance to proactive interference. Research has theoretical and clinical implications for adults with ADHD.

Neuroleptics reverse attentional effects in schizophrenia patients

Patients with schizophrenia show attention deficit characterized by a larger validity effect (fast responses to cued than uncued stimuli) in the right visual field than in the left visual field. In addition, schizophrenia patients do not show inhibition of return (IOR--a mechanism that enables efficient visual search), unless attention is summoned back to the center after the peripheral cue. The present study examined the short-term effect of neuroleptic medications on these two components of visual spatial attention in schizophrenia patients. In order to do this we tested schizophrenia patients that were treated with long-acting neuroleptic medication. These patients were treated once a month, which allowed us to test them with either low or high levels of medication. Here we show that neuroleptic medications reverse the attentional hemispheric asymmetry. In the group with a high level of medication fast RTs to cued trials were found in the right visual field, while in the group with a low level of medication the opposite pattern was found - fast RTs to cued trials were found in the left visual field. In addition, level of medication did not influence IOR - regardless of the level of medication, IOR was observed only when attention was summoned back to the center, unlike control group. These finding suggest an imbalance in dopaminergic activity, possibly in subcortical structures such as the basal ganglia. This study also shows a dissociation between the two components of visual orienting of attention and suggests that facilitation and inhibition are independent processes.

Attentional network task performance in patients with schizophrenia-spectrum disorders: evidence of a specific deficit

Although attentional deficits are frequently displayed by schizophrenia and spectrum patients, the precise nature of the impairment is unclear. The present study investigates attentional performance in 26 schizophrenia-spectrum outpatients and 24 healthy controls using the Attentional Network Task (ANT). We assessed the efficiency of the segregated alerting, orienting, and executive control networks by measuring how response latencies were influenced by alerting cues, spatial cues, and flanking stimuli. In overall ANOVAs we found main effects of cue condition and flanker congruency. The data also revealed a significant interaction of group and flanker type, with schizophrenia-spectrum patients taking longer on average to resolve conflict. These results suggest that compared to the healthy nonpatients, schizophrenia-spectrum patients show a deficit in their executive control network. Considered together, these findings support the notion that schizophrenia-spectrum patients have a specific attentional deficit, rather than a global one. The significance of these findings is considered from both experimental and clinical perspectives.

Impaired control of visual attention in schizophrenia

To investigate attentional impairment in schizophrenia, the authors examined the performance of 22 patients with schizophrenia and 16 healthy control subjects in 4 visual search tasks that varied in perceptual requirements and in the need for precise attentional control. The rate of search was slowed in the patients in all tasks. However, the degree of slowing was largest in tasks requiring precise attentional control and smallest in tasks that were perceptually difficult but required less attentional control. This pattern of results indicates that the primary impairment of attention in schizophrenia lies in the control of attention and not in the selection processes that operate once attention has been directed to an object.

The inter-trial effects of stimulus and saccadic direction on prosaccades and antisaccades, in controls and schizophrenia patients

We investigated the influence of the direction of preceding saccadic trials on the latency of current prosaccades and antisaccades, in healthy subjects and patients with schizophrenia. When prosaccades and antisaccades were performed in separate, single-task blocks, we found that only prosaccades were delayed if the saccade in the prior trial was in the same direction, consistent with the expected directional effect from an 'inhibition of return'-like alternation advantage. However, both types of saccades were executed more quickly when the saccade in the penultimate trial was in the same direction, consistent with previous demonstrations of directional plasticity in monkeys. In blocks of randomly mixed prosaccades and antisaccades, the directional effects in healthy subjects were greatest when a prosaccade was preceded by an antisaccade, consistent with a summation of effects of alternation advantage (from the prior stimulus) and directional plasticity (from the prior saccade). Schizophrenic patients showed an additional phenomenon, a directionally specific inhibition of upcoming saccades by preceding antisaccades. These results suggest that saccades in humans are modulated by inter-trial effects attributable to both an 'inhibition of return'-like alternation advantage and directional plasticity.

Inhibition of return in the human 5HT2A agonist and NMDA antagonist model of psychosis

Patients with schizophrenia exhibit disturbances of orienting of attention. However, findings have been inconsistent. Pharmacologic challenges with hallucinogens have been used as models for psychosis. The NMDA antagonist state (PCP, ketamine) resembles undifferentiated psychoses with positive and negative symptoms, while the 5-HT(2A) agonist state (LSD, dimethyltryptamine (DMT)) is thought to be an appropriate model for psychoses with prominent positive symptoms. The aim of this study was to investigate orienting of attention in the human NMDA antagonist and 5-HT(2A) agonist models of psychosis. A total of 15 healthy volunteers participated in a randomized, double-blind, crossover study with a low and a high dose of DMT and S-ketamine, which elicited subtle 'prepsychotic' or full-blown psychotic symptoms (low and high dose, respectively). Nine subjects completed both experimental days with the two doses of both drugs. Overall, both hallucinogens slowed down reaction times dose dependently (DMT >S-ketamine) and DMT diminished the general response facilitating (alerting) effect of spatially neutral cues. Inhibition of Return (IOR), that is, the normal reaction time disadvantage for validly cued trials with exogenous cues and long cue target intervals, was blunted after both doses of DMT and the low dose of S-ketamine. IOR reflects an automatic, inhibitory mechanism of attention, which is thought to protect the organism from redundant, distracting sensory information. In conclusion, our data suggest a deficit of IOR in both hallucinogen models of psychosis, with the effect being clearer in the serotonin model. Blunted IOR may underlie or predispose to different psychotic manifestations, but particularly to those with prominent positive symptoms.

Deficient inhibition of return in schizophrenia-further evidence from an independent sample

Previous studies on spatial orienting of attention in schizophrenia demonstrated a deficit of Inhibition of Return (IOR). However, other studies reported a delay in the manifestation, but an overall normal amount of IOR in patients with schizophrenia. However, the latter studies used a cue-back manipulation which is known to reinstate or speed up IOR. Hence, it is not clear whether even very long cue target intervals would allow IOR to develop in patients with schizophrenia in the absence of a cue-back manipulation. The aim of the present study was to study IOR in patients with schizophrenia using a single cue paradigm and a very long cue target interval of >1 s in order to differentiate between blunted and delayed IOR. We examined 32 inpatients with schizophrenia and 16 healthy controls with a covert orienting of attention task (COVAT) with non-predictive peripheral cues and three stimulus onset asynchronies (SOA: 100 ms, 800 ms and 1050 ms). We found a lack of Inhibition of Return (IOR) in patients with schizophrenia with both long SOAs of 800 and 1050 ms. As in a previous study of our group, the IOR deficit was unrelated to psychopathology, length of illness, number of previous psychotic episodes and type of neuroleptic medication. In summary, our study confirms and extends previous reports of deficient IOR in patients with schizophrenia. IOR seems to be not just delayed, but rather profoundly disturbed in schizophrenia. Deficient IOR in patients with schizophrenia might be viewed as a trait or alternatively as a vulnerability marker of the disorder.

Blunted inhibition of return in schizophrenia-evidence from a longitudinal study

Previous cross-sectional studies on covert orienting of visual attention in schizophrenia have been inconsistent. In the present longitudinal study, we examined 40 medicated acutely ill inpatients with a covert orienting of attention task (COVAT) shortly after admission, and again 12-16 weeks after the initial examination, while most patients were in (partial) remission. We administered a COVAT with nonpredictive peripheral cues and two stimulus-onset asynchronies (SOA; 100 and 800 ms). In addition, we examined 34 healthy control subjects twice (2 weeks apart). The most important finding was a lack of inhibition of return (IOR) in patients with schizophrenia, both at the first examination in an acute psychotic state and at the follow-up examination after considerable clinical improvement. The IOR deficit was unrelated to psychopathology, length of illness, number of previous psychotic episodes, and type of neuroleptic (NL) medication. Deficient IOR in patients with schizophrenia appears to be state-independent and might be viewed as a trait or vulnerability marker of the disorder. Subsequent studies with never-medicated populations and with schizotypal or high-risk subjects are needed in order to further analyze the possible role of NL medications and to clarify whether blunted IOR might represent a vulnerability marker of schizophrenia.

Delayed onset of inhibition of return in schizophrenia

Peripheral visual cues occuring before a subsequent target result in an almost immediate facilitatory and then a later inhibitory effect on target detection. In a detailed parametric investigation, the authors compared schizophrenic subjects (SCZ) and control subjects (CONT) to examine whether they showed any differences in the time course of these nonpredictive peripheral cuing effects. Subjects fixated a central position and made saccadic responses to visual targets. Targets were presented 10 degrees to the left or right of fixation and were preceded at various time intervals by visual cues. Targets occurred with equal probability in either the same position as the cue or in the opposite, uncued location, and 10 delay periods were used corresponding to stimulus onset asynchronies (SOAs) of 66, 79, 106, 133, 159, 226, 305, 505, 705, and 1000 ms. All subjects showed facilitation for short cue-target delays and inhibition of return (IOR) for longer delays. SCZ, however, showed an apparent shift in the time course of cuing effects in the form of a delayed onset of IOR. Using a task of reflexive orienting, these results support findings of a delayed rather than an absent inhibitory process in medicated SCZ.

Attentional asymmetry in schizophrenia: disengagement and inhibition of return deficits

This research examined 2 components of visual orienting in medicated schizophrenia patients: the validity effect and the inhibition of return (IOR). In the 1st experiment, patients showed the expected asymmetry in orienting attention, that is, larger validity effect in the right visual field than in the left. However, this asymmetry was due to a deficit in facilitatory processes rather than a disengagement deficit. In addition, patients showed a deficit in IOR. In the 2nd experiment, a 2nd central cue for summoning attention, explicitly, back to the center was used. In this experiment, normal IOR in schizophrenia patients was found. Because it was shown that schizophrenia patients do not have a disengagement deficit, IOR possibly could not be observed because of the increased facilitation in that location. It was proposed that the abnormality in visual attention in schizophrenia is due to a deficit in inhibitory processes.

Stroop interference is affected in inhibition of return

In previous research, we have shown that the processing of targets that are presented to locations subject to inhibition of return (IOR) is affected by an inhibitory tagging mechanism. This mechanism acts by disconnecting activated representations of stimuli at inhibited locations from their associated responses. In two experiments, we assessed whether this inhibitory tagging mechanism of visual attention is also applied to task-irrelevant but prepotent dimensions of target stimuli, such as words in the Stroop task. To test this hypothesis, we examined the Stroop effect in an IOR procedure. The results showed that (1) IOR can be found in a color discrimination task, (2) the Stroop interference was reduced (Experiment 1) or eliminated (Experiment 2) when stimuli appeared at cued locations, as compared with cases in which they were presented at uncued locations, and (3) the effect of inhibitory tagging was limited to the shortest stimulus onset asynchrony value, replicating previous findings. These results agree with the idea that inhibitory tagging, occurring in IOR, affects the efficiency with which color words compete for responses in Stroop-like situations.

Inhibitory processing in visuospatial attention in healthy adults and schizophrenic patients

This study assessed visuospatial attention in healthy adults and medicated schizophrenic patients. Participants performed a visual orientation task in which a peripheral cue was followed. at different intervals, by a target presented either at valid or invalid locations. When the long stimulus onset asynchrony (SOA) was used, participants were presented with either a single peripheral cue (single-cue condition) or two cues, the peripheral cue followed by a central cue (the double-cue condition). Healthy adults showed marginal facilitation effects with the short SOA and similar inhibition of return effects with the long SOA in both single-cue and double-cue conditions. Schizophrenic individuals showed a big facilitation effect with the short SOA and normal inhibition of return with the long SOA in both cue conditions. Results with the short SOA replicated previous findings (Huey, E.D., Wexler, B.E., 1994. Schizophrenia Research 14, 57-63) but, in contrast, we did not observe blunted inhibition of return with the long SOA. An inspection of the differences in the procedures used in both studies may help both to account for the discrepancies and to reveal what processes involved in visuospatial attention are affected in schizophrenia.