Inhibitory processes in covert orienting in patients with Alzheimer's disease

Previous studies of covert orienting in Alzheimer's disease (AD) have investigated exogenous and endogenous processes separately. We aimed to investigate how the 2 modes of orienting interact to control attention in healthy older participants and patients with AD. The covert orienting of visual attention task (COVAT) with abrupt onset cues was used in all experiments. In Experiments 1 and 2, predictive information was added to cues to initiate an endogenous orienting response. Results showed that healthy older participants were able to use endogenous processes to inhibit exogenous orienting. In contrast, patients with AD were unable to inhibit exogenous orienting to cues even when targets rarely appeared there. Experiment 3 investigated inhibition of return (IOR) in patients with AD. Both healthy older controls and patients with AD showed a normal IOR, suggesting that exogenous orienting processes are relatively unaffected by the normal aging process or in patients with AD. A model of covert orienting in which exogenous and endogenous orienting processes interact to control attentional behaviors is discussed.     

Attentional cues in chronic schizophrenia: Abnormal disengagement of attention.

M. I. Possner's 1980 reaction time (RT) paradigm was used to examine the engagement and disengagement operations of visual selective attention in patients with schizophrenia. In the 1st experiment 14 medicated, chronic schizophrenic Ss (diagnosed by criteria of the Diagnostic and Statistical Manual of Mental Disorders [DSM-I]), and 15 age-matched normal and control Ss made a speeded response to a target preceded by a valid, and invalid, or no cue. Control Ss showed the expected advantage and disadvantage in RT for valid and invalid cues, which suggests intact engagement and disengagement operations. For schizophrenic Ss, valid cues also enhanced RT, but invalid cues did not slow RT. Similar results were found in the 2nd experiment. The failure of unpredictable, invalid cues to inhibit RT in chronic schizophrenia may be related to an abnormality in the disengagement operation of selective attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Competition Between Endogenous and Exogenous Orienting of Visual Attention.

The relation between reflexive and voluntary orienting of visual attention was investigated with 4 experiments: a simple detection task, a localization task, a saccade toward the target task, and a target identification task in which discrimination difficulty was manipulated. Endogenous and exogenous orienting cues were presented in each trial and their validity was manipulated orthogonally to examine whether attention mechanisms are mediated by separate systems and whether they have additive and independent effects on visual detection and discrimination. The results showed that each orienting mechanism developed its typical and independent effect in every case except for the difficult identification task. A theoretical framework for understanding the relationship between endogenous and exogenous orienting of attention is proposed, tested, and confirmed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modal attention asymmetry in patients with schizophrenia and bipolar disorder.

This cross-sectional study examined modal attention asymmetries in patients with schizophrenia (n?=?47) and bipolar disorder (n?=?42), as contrasted to a matched-sample comparison group of normal participants (n?=?89). A test of continuous auditory and visual attention was the primary measure. The data were analyzed from 2 experimental conditions: simple modal responses (auditory and visual) and modal switching responses (ipsimodal and cross-modal switching). In the simple modal condition, patients with schizophrenia demonstrated a visual over auditory asymmetry; patients with bipolar disorder showed no differences. In modal switching conditions, however, patients with bipolar disorder displayed a significant auditory over visual asymmetry. No main effect was detected between medications and attention functioning. Results are discussed in light of differentiating these 2 populations on the basis of modal specificity of attention functioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attentional consequences of object appearance and disappearance.

This study compared the attentional effects of object appearances (onsets) and disappearances (offsets) in moderately complex displays. Four experiments showed that onsets produce the inhibition of return (IOR) effect that has been found with simpler displays. In contrast, although offsets did produce inhibitory effects, these effects did not follow the spatial or temporal pattern of IOR. Two further experiments used a very salient object disappearance to determine whether the typical pattern for IOR could be instantiated; it was not. The results indicate that object appearances are more potent perceptual events than object disappearances. In addition, object disappearances have different attentional consequences than object appearances: Disappearances provoke earlier and spatially narrower inhibition. The results are consistent with the view that inhibition serves a functional role in increasing the efficiency of visual search processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Space-Based Inhibition of Return in Children With Spina Bifida.

Inhibition of return (IOR) refers to an increase in time to react to a target in a previously attended location. Children with spina bifida meningomyelocele (SBM) and hydrocephalus have congenital dysmorphology of the midbrain, a brain region associated with the control of covert orienting in general and with IOR in particular. The authors studied exogenously cued covert orienting in 8- to 19-year-old children and adolescents (84 with SBM and 37 age-matched, typically developing controls). The exogenous cue was a luminance change in a peripheral box that was 50% valid for the upcoming target location. Compared with controls, children with SBM showed attenuated IOR in the vertical plane, a deficit that was associated with midbrain dysmorphology in the form of tectal beaking but not with posterior brain volume loss. The data add to the emerging evidence for SBM deficits in attentional orienting to salient information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Automatic versus volitional orienting and the production of the inhibition-of-return effect.

A single, to-be-ignored peripheral flash (i.e., cue) reflexively attracts an orienting response (oculomotor/attention/head turn) that ultimately causes reaction time delays to target stimuli that later arise at this cued location, in relation to when the target appears at a new position (i.e., the inhibition-of-return [IOR] effect). The basic question posed here dealt with whether an IOR effect is also produced following volitional orienting. Results from paired cue-trial stimulations, one a distractor and one a target (nonsalient/salient) event, positioned more or less symmetrically on either side of fixation, supported the net vector model of IOR (R. Klein, J. Christie, & E. P. Morris, 2005). Automatic orienting did not yield an IOR effect at the stimulated positions. When the need to later report cue-trial target location was added, an IOR effect appeared at distractor-occupied, but not at target-occupied, locations. Seemingly, an IOR effect can follow volitional orienting. In this instance, the IOR process seems capable of undergoing modulation; however, such modulation was not evident following automatic orienting. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inhibitory mechanisms of attentional networks: Spatial and semantic inhibitory processing.

Four experiments assessed the relationships between the orienting and the executive networks of visual attention. Experiment 1 showed spatial inhibition of return (IOR) with target words. Experiment 2 showed a type of semantic inhibition that mimicked spatial IOR. Reaction times to targets preceded by 2 consecutively presented words, the prime and the intervening stimulus, were longer when the target and prime were related than when they were unrelated. Experiment 3 combined spatial and semantic inhibition in a lexical-decision task. Spatial IOR was observed with both related and unrelated targets, but semantic inhibition was observed only when target words were presented in uncued locations. A similar interaction between IOR and positive semantic priming was observed when the intervening stimulus was not presented (Experiment 4). Implications for the relationships between the 2 attentional networks are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatiotemporal distribution of facilitation and inhibition of return arising from the reflexive orienting of covert attention.

Currently, there is debate regarding both the spatial and temporal relationship between facilitation and inhibition of return (IOR) components of attention, as observed on the covert orienting of visual attention task (COVAT). These issues were addressed in a series of experiments where the spatial and temporal relationships between cue and target were manipulated. Facilitation occurred only when the stimulus onset asynchrony (SOA) was short and there was temporal overlap between cue and target. IOR occurred only when SOA was long and there was no temporal overlap between cue and target. Facilitation encompassed the cued location and all locations between the cue and fixation, whereas IOR arose for the entire cued hemifield. These findings suggest that the facilitation and IOR found on COVATs that use noninformative peripheral cues are separable and stimulus-driven processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attentional bias in drug dependence: Vigilance for cigarette-related cues in smokers.

Two experiments investigated attentional biases for smoking-related cues in smokers and nonsmokers, using the visual probe task. In Experiment 1, when pictures were displayed for 500 ms, smokers who had made repeated quit attempts showed an attentional bias for smoking-related scenes. Experiment 2 replicated this finding and revealed that when pictures were presented for 2,000 ms, the smoker group as a whole showed vigilance for smoking-related cues, but nonsmokers did not. The findings from the 500-ms exposure condition suggest that initial orienting of attention to smoking cues was associated with repeated unsuccessful attempts at abstinence in smokers. Results are discussed with reference to incentive-sensitization theories of addiction and to component processes of selective attention, such as initial orienting versus maintenance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Enhanced facilitation of spatial attention in schizophrenia.

Objective: While attentional functions are usually found to be impaired in schizophrenia, a review of the literature on the orienting of spatial attention in schizophrenia suggested that voluntary attentional orienting in response to a valid cue might be paradoxically enhanced. We tested this hypothesis with orienting tasks involving the cued detection of a laterally presented target stimulus. Method: Subjects were chronic schizophrenia patients (SZ) and matched healthy control subjects (HC). In Experiment 1 (15 SZ, 16 HC), cues were endogenous (arrows) and could be valid (100% predictive) or neutral with respect to the subsequent target position. In Experiment 2 (16 SZ, 16 HC), subjects performed a standard orienting task with unpredictive exogenous cues (brightening of the target boxes). Results: In Experiment 1, SZ showed a larger attentional facilitation effect on reaction time than HC. In Experiment 2, no clear sign of enhanced attentional facilitation was found in SZ. Conclusions: The voluntary, facilitatory shifting of spatial attention may be relatively enhanced in individuals with schizophrenia in comparison to healthy individuals. This effect bears resemblance to other relative enhancements of information processing in schizophrenia such as saccade speed and semantic priming. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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° to 3°, 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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Examining Task Difficulty and the Time Course of Inhibition of Return: Detecting Perceptually Degraded Targets.

The ability to efficiently direct visual attention to salient features in the environment is a critical function of the visual system. The finding that people are slower to detect a target that appears at a previously cued location is thought to reflect a mechanism known as inhibition of return (IOR). Past research has shown that difficult target discriminations result in a greater amount of time needed to inhibit previously attended locations (i.e., a delayed onset of inhibition), suggesting that task difficulty plays a critical role in the allocation of attention. In this study, IOR was measured at a wide range of SOAs while participants detected either a perceptually degraded target or a standard, high luminance target. When responses were made to a perceptually degraded target, the time course of IOR was delayed by approximately 250 ms (relative to the control group), suggesting that the difficulty in detecting targets also influences the allocation of attention. The results are consistent with the notion that IOR is not simply a reflexive subcortical mechanism but rather involves top-down attentional control settings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Object- and location-based inhibition of return in younger and older adults.

When a cued object moves to new spatial coordinates, inhibition of return (IOR) with younger adults is found at the original cued location (location-based IOR) and at the current location of the object (object-based IOR). Older adults, however, show only location-based IOR. To determine whether this pattern of results represents a general age-related deficit in object-based IOR, the authors used static displays in which the placeholders (i.e., objects) were either present (location-based IOR + object-based IOR) or absent (location-based IOR only). Both age groups showed location-based IOR, but the older adults failed to show object-based IOR, consistent with age-related differences in visual pathways. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A new component of visual orienting: Implicit effects of peripheral information and subthreshold cues on covert attention.

Four experiments examined effects of peripheral cue stimuli on covert spatial attention. In Experiment 1 target stimuli were preceded by a pair of bilaterally presented cue letters. The relative location of the cues predicted target location (left or right), but participants were not informed of this. After a brief practice period, visual orienting was influenced by the letter cues. This implicit peripheral cuing effect was unrelated to participants' awareness of the cue-target relationship. Experiments 2 and 3 showed that visual orienting may occur independently of both perceptual awareness of the peripheral cue event itself and contingency awareness concerning the cue–target relation. Experiment 4 demonstrated that implicit peripheral cuing is qualitatively distinct from voluntary orienting. These findings are discussed in relation to work on spatial attention, implicit learning, and perception without awareness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial and semantic inhibitory processing in schizophrenia.

Two experiments assessed inhibitory mechanisms associated with the posterior and anterior attention networks in schizophrenia. Experiment 1 assessed the inhibition of return effect of the posterior network. Both healthy adults and schizophrenic adults showed inhibition of return, suggesting that this inhibitory mechanism of visual orienting is preserved in schizophrenia. Experiment 2 assessed semantic inhibition, which supposedly taps the anterior network, in a lexical-decision task. Healthy adults showed semantic inhibition effects in both visual fields. Schizophrenic adults showed semantic inhibition effects when targets were presented to the left visual field, involving the right hemisphere. However, semantic facilitation rather than inhibition was observed when targets were presented to the right visual field, involving the left hemisphere. These results reflect left hemisphere dysfunction associated with deficits in attentional control in schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual masking during the attentional blink: Tests of the object substitution hypothesis.

When 2 masked targets are presented in a rapid sequence, correct identification of the 1st hinders identification of the 2nd. Visual masking of the 2nd target plays a critical role during this 2nd-target deficit, or "attentional blink" (AB). The object substitution hypothesis (B. Giesbrecht and V. Di Lollo, 1998) predicts that late-stage visual processes involved in object substitution mediate masking of the 2nd target during AB, whereby stronger masking should produce a more severe deficit. Six experiments are presented, together testing this hypothesis. Although masking by object substitution was observed, it did not interact with the AB. An alternative hypothesis is proposed stating that mostly early-stage visual processes mediate the masking effects that are critical to the AB. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mild stress increases attentional bias in social drinkers who drink to cope: A replication and extension.

The authors investigated the effects of a laboratory stressor task on rapid initial orienting and delayed disengagement aspects of attentional bias for alcohol-related cues in social drinkers (N = 58). Participants were randomly allocated to receive a stress induction or control manipulation before completing a visual probe task in which alcohol cues were presented for either 100 ms or 500 ms. Results indicated that participants who reported drinking alcohol to cope with negative affect had increased attentional bias for alcohol cues after stress induction. This effect of stress induction on attentional bias was evident when cues were presented for 100 ms and 500 ms, which suggests that stress increases both the initial orienting of attention toward and the delayed disengagement of attention from alcohol-related cues. Theoretical implications of this robust finding are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

What is inhibited in inhibition of return.

Research on temporal-order judgments, reference frames, discrimination tasks, and links to oculomotor control suggest important differences between inhibition of return (IOR) and attentional costs and benefits. Yet, it is generally assumed that IOR is an attentional effect even though there is little supporting evidence. The authors evaluated this assumption by examining how several factors that are known to influence attentional costs and benefits affect the magnitude of IOR: target modality, target intensity, and response mode. Results similar to those previously reported for attention were observed: IOR was greater for visual than for auditory targets, showed an inverse relationship with target intensity, and was equivalent for manual and saccadic responses. Important parallels between IOR and attentional costs and benefits are indicated, suggesting that, like attention, IOR may in part affect sensory-perceptual processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial Attention as a Necessary Preliminary to Early Processes in Reading.

One major theory of the relation between spatial attention and visual word recognition holds that the former is a necessary condition for the latter to begin. A different major theory asserts that although spatial attention can facilitate the latter, it is not a necessary condition. These two theories were pitted against each other experimentally. Spatial attention was operationalized in terms of the effect of a spatial precue on the time to name a target word that appeared above or below fixation. A masked prime word was presented before the target. The critical difference between experiments was cue validity (50% in Experiments 1a and 2a and 100% in Experiments 1b and 2b). Repetition priming was observed when the prime appeared in the uncued prime location in Experiments 1a and 2a but not in Experiments 1b or 2b. These results are inconsistent with the claim that visual word recognition does not depend on spatial attention. Discussion centres on the distribution of spatial attention across target locations as a function of cue validity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)