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Background: Numerous studies have suggested, via the interpretation of negative priming effects, that subjects with schizophrenia are less able than controls to inhibit irrelevant distracting information. Further issues concerning impairment in inhibitory processes are investigated here. First, recent research has revealed that negative priming (NP) effects can be caused by different processes, distractor inhibition or perceptual review. Therefore, conclusions concerning reduced inhibition in patients with schizophrenia are not possible from previous NP research. Secondly, previous NP studies have required subjects to identify some feature of the target. This is the first study to examine NP that uses a spatial task in patients with schizophrenia., Method: Twenty-eight subjects with schizophrenia and 28 age and sex matched non-psychiatric control subjects completed a computerized NP task that eliminated the possible contribution of perceptual review., Results: Subjects with schizophrenia had reduced levels of NP compared to control subjects on this spatial NP task (t = 2.46, P < 0.02). Current age, positive, negative or total PANNS scores did not correlate with negative priming scores, but post hoc analyses revealed that clozapine-treated patients had significantly greater levels of negative priming than patients receiving typical antipsychotic medications., Conclusions: The present experiment eliminated the contribution of perceptual review to negative priming and demonstrated that when a pure measure of inhibition is taken on a localization task, patients with schizophrenia were less able to inhibit irrelevant distracting stimuli. The fact that NP was reduced in a spatial task suggested a more diffuse reduction in inhibition than previous studies that examined only identification-based responses.

A series of spatial localization experiments is reported that addresses the relation between negative priming and inhibition of return. The results of Experiment 1 demonstrate that slowed responses to repeated location stimuli can be obscured by repetition priming effects involving stimulus dimensions other than spatial location. The results of Experiments 2, 3A, and 3B demonstrate that these repetition priming effects may occur only when participants are required to respond to the prime display. Together, these results suggest that differences between attended and ignored repetition effects in selective attention studies of spatial localization do not provide a basis for distinguishing between spatial negative priming and inhibition of return.

Background: Impaired distractor inhibition may contribute to the selective attention deficits observed in depressed patients, but studies to date have not tested the distractor inhibition theory against the possibility that processes such as transient memory review processes may account for the observed deficits. A negative priming paradigm can dissociate inhibition from such a potentially confounding process called object review. The negative priming task also isolates features of the distractor such as colour and location for independent examination., Method: A computerized negative priming task was used in which colour, identification and location features of a stimulus and distractor were systematically manipulated across successive prime and probe trials. Thirty-two unmedicated subjects with DSM-IV diagnoses of non-psychotic unipolar depression were compared with 32 age, sex and IQ matched controls., Results: Depressed subjects had reduced levels of negative priming for conditions where the colour feature of the stimulus was repeated across prime and probe trials but not when identity or location was the repeated feature. When both the colour and location feature were the repeated feature across trials, facilitation in response was apparent., Conclusions: The pattern of results supports studies that found reduced distractor inhibition in depressed subjects, and suggests that object review is intact in these subjects. Greater impairment in negative priming for colour versus location suggests that subjects may have greater impairment in the visual stream associated with processing colour features.

A location-based ('select-what, respond-where') priming task was used to examine three measures of selective attention (interference (INT), negative priming (NP), and inhibition of return (IOR)) as a function of focal brain pathology and the complexity of target selection. Control subjects showed different patterns of performance for the three attentional measures as a function of complexity, suggesting some independence among INT, NP, and IOR. Brain-damaged subjects showed significant response slowing, as well as a number of lesion-specific attentional abnormalities. Right frontal (including bifrontal) damage resulted in proportionally increased interference related to task complexity. Left posterior damage increased IOR in the most complex task, while left frontal damage reversed the control pattern of IOR as a function of complexity. Right hemisphere (right posterior and right frontal damage) pathology resulted in a virtual loss of negative priming at all levels of task complexity; left and bifrontal damage resulted in diminished NP only related to increases in the complexity of selection. INT, NP, and IOR are mediated by different brain regions and their expression can be modulated by the complexity of the selection task.

Research with normal participants has demonstrated that mechanisms of selective attention can simultaneously gain access to internal representations of spatial information defined with respect to both location- and object-based frames of reference. The present study demonstrates that patients with unilateral spatial neglect following a right-hemisphere lesion are poorer at detecting information on the contralateral left side in both location- and object-based spatial coordinates simultaneously. Moreover, the extent of the neglect is modulated by the probability of a target's appearing in either reference frame; as the probability of sampling a target in a particular frame of reference increases, so does the severity of neglect in the frame. These findings suggest that attention can be flexibly and strategically assigned to a reference frame depending on the contingencies of the task.

We investigated whether inhibition of return (IOR) could be observed in location-based, scene-based, and object-centered frames of reference. IOR was found to move both with a separate cued object (scene-based) and with a location within a single rotating object (object-centered). Importantly, however, IOR was also associated with the environmental location cued when cuing was of a separate object (scene-based), whereas facilitation of the cued location was found when cuing was of a component within an object. These results suggest that location is of central importance to scene-based representations of separate objects, which appear to be encoded in viewer-centered coordinates, whereas environmental locus is of little relevance when attention orients within a single object. The results also provide further evidence for the coexistence of both excitation and inhibition associated with uninformative exogenous cues.

Although recent fMRI and single unit recording studies have shown that attention modulates neural activity in motion sensitive areas of extrastriate cortex, these approaches cannot reveal qualitative or quantitative effects of attention on perception of motion. To investigate this, we asked observers to select one of two orthogonal directions in a brief, transparent dot display (prime) and then measured their sensitivity to global directional motion in a second uni-directional dot display (probe) presented a short time later. When probe direction matched the attended prime direction, sensitivity was degraded. But, when probe direction matched the ignored prime direction, sensitivity was enhanced, even though both components were of equal physical strength. Sensitivity was unchanged for directions opposite to either previously seen direction. Neither sensory adaptation nor opponent direction mechanisms can account for these data. Rather, processes initiated by visual selection must underlie these dramatic changes in motion sensitivity.

Actions, which have effects in the external world, must be spatiotopically represented in the brain. The brain is capable of representing space in many different forms (e.g. retinotopic-, environment-, head- or shoulder-centred), but we maintain that actions are represented in action-centred space, meaning that, at the cellular level, the direction of movement is defined by the activity of cells. In reaching, for example, object location is defined as the direction and distance between the origin of the hand and the target. Most importantly, we argue that more than one task-relevant action can be evoked at any moment in time. Therefore, highly efficient selection processes that accurately link vision and action have had to evolve. Research is reviewed which supports the notion of action-based inhibitory mechanisms that select the target from competing distractors.

Subjects reached for visual target lights in the presence of distractor lights. Previous studies (e.g., Tipper, Lortie, & Baylis, 1992) have shown that distractors at locations between the starting position of the hand and the target location caused greater interference (as indexed by response time) than distractors beyond the target. This finding has been attributed to the former distractors being in the path of the response to the target, but we provide evidence that they interfere more because of their proximity to the starting position of the hand (a "proximity-to-hand effect"). Also, distractors located in the hemispace ipsilateral to the responding hand caused more interference than contralateral distractors (an "ipsilateral effect"). The proximity-to-hand and ipsilateral effects were found in both reaction and movement time, suggesting that the resolution of the selection problem caused by a distractor could occur before or after movement initiation. Further evidence for this suggestion was provided by individual differences in movement initiation strategies which were predictive of the temporal locus of distractor influence. Errors of touching the distractor location also showed proximity-to-hand and ipsilateral effects. We discuss applications of these findings to real-world situations in which people reach for the wrong object in multiple-object visual displays.

In most studies of selective attention, the experimenter informs the participant what the target is and what action is required. For example, participants may be told to name the red drawing. The present study shows that under such conditions of external selection, distractor inhibition is used to ensure that selection is efficient. In external selection, analysis of distractors is limited, causing later recognition of distractor items to be poor. In contrast, during real-world selection a person may be confronted with a number of potential targets and may have to decide what will be the target for action. Under these conditions of internal selection, inhibition of distracting information does not occur. Moreover, distractors are more fully analyzed and thus better recognized at a later test.

Object-based attention was examined in 2 split-brain patients. A precued object could move within a visual field or cross the midline to the opposite field. Normal individuals show an inhibition in detecting signals in the cued object whether it moves within or between fields. Both patients showed this effect when the cued object moved within a visual field. When it crossed the midline into the opposite visual field, however, detection was faster in the cued box. These results reveal both facilitatory and inhibitory effects on attention that are object based and may last for several hundred milliseconds. However, the inhibition requires an intact corpus callosum for interhemispheric transfer, whereas the facilitation is transferred subcortically.

Previous research has demonstrated that when a stimulus is to be ignored, the path of motion towards a target (saccade or manual reach) deviates away from the to-be-ignored stimulus. Path deviations in saccade and reaching tasks have, however, been observed in very different situations. In the saccade tasks subjects initially attended to a cue, then disengaged attention while saccading to a target. By contrast, in the selective reaching tasks attention was continuously withdrawn from the to-be-ignored stimulus, as this was irrelevant throughout the experiment. In the two experiments reported here, cues similar to those studied in saccade tasks are examined with selective reaching procedures. Experiment 1 shows that when a coloured light-emitting diode cue, upon which subjects engage and then subsequently disengage attention, is close to the responding hand, the hand deviates away from the cue. Experiment 2 confirms this cue avoidance by showing that, compared with central fixation alone, the hand veers away from a central cue. These results confirm that the path deviations observed in saccades can also be obtained in manual reaching movements. Such findings support the notion that eye and hand movements are both affected by inhibitory mechanisms of attention.

Whether visuospatial attention accesses object-centered representations, in addition to location-based coordinates, was investigated in patients with hemispatial neglect who detected a target on the left or right of a single object (2 connected circles or barbell) or of 2 objects (2 unconnected circles). The object or objects either remained static (left circle in left space) or rotated by 180 degrees (left circle now in right space). Relative to the static condition, in the rotating condition, detection times are facilitated on the left (contralateral) and inhibited on the right (ipsilateral) of space even when eye movements are controlled. This modulation of neglect was only observed for the single object, but not for the 2-object displays. The findings suggest that attention operates on object-centered as well as on location-based representations, and thus accesses multiple reference frames.

J. Pratt and R.A. Abrams (1995) reported that the inhibition of return of attention is found only for the most recently attended of 2 cued locations. This study does not dispute their findings, but suggests that a more ecologically valid experiment would have more than 2 possible target locations. Twelve male students participated in an experiment in which the target may occur in 1 of 4 possible locations, after 3 of those locations have been cued exogenously in sequence. Inhibition of return was found for each of the cued locations. This result suggests that inhibition may be an important mechanism for aiding visual search in complex environments.

This paper discusses the role of inhibition in neural and cognitive control, in particular its role in selective processes in perception and action. We first review neuroanatomical and physiological evidence that cortical control is mediated by a variety of local-circuit inhibitory neurons, distributed throughout all layers and areas of the cortex. We then consider the use of inhibition in control processes in behavioral neural network models, focusing on two areas: selective attention and sequential action. Relations between the architecture and dynamics of these models and relevant neurological findings are discussed. We conclude that a full understanding of inhibitory control of mental functioning will require the integration of data from both the behavioral and neural levels, and that formal neural network models can play an important role in bridging this epistemological divide.

Efficient search for an object often requires that attention be prevented from returning to recently examined environmental loci. M. I. Posner and Y. A. Cohen (1984) proposed that inhibition of return (IOR) of visual attention is a search mechanism that prevents such attentional perservation. The internal representations upon which IOR functions were examined and the following conclusions were drawn: First, IOR mechanisms have access to both object- and environment-based representations. Second, environment-based inhibition can be associated with a featureless environmental location, whereas the object-based mechanism requires that attention be oriented to a visible object. These findings are discussed in terms of physiological pathways that may mediate location- and object-based effects.

Most studies of selective attention briefly present static 2-dimensional stimuli and require arbitrary responses such as verbal naming or a keypress. Many of our perceptual-motor interactions with the environment, however, require reaching directly toward an object while ignoring other objects in the scene. A series of experiments examines selective attention in the latter reaching situation. Effects previously observed in the traditional experimental procedures were obtained, suggesting that the models developed (which propose inhibitory mechanisms, e.g.) apply to ecologically valid situations. Attention accesses action-centered internal representations during such tasks.

This paper examines three properties of attentional inhibition mechanisms. First, previous research has suggested that the inhibitory mechanism of selective attention has a central locus between perception and action. We attempt to confirm the locus of this inhibition. Second, the processing of an unattended stimulus has been observed via the effects of the stimulus on a concurrent target (interference), and on a subsequent target (negative priming). The former effect demonstrates that distractors interfere with the processing of the target, and the latter negative priming effect implies that distractors are inhibited during selection. We demonstrate that these two measures of unattended processing can be dissociated. Third, we reveal that inhibition appears to be a stable mechanism of selection, in that effects do not decline after a large number of experimental trials.

It has been proposed that 1 component of the mechanism of visual selective attention is active inhibition of distracting information. A series of studies examines the time course of inhibition and the possible interfering effects of other task demands. Results demonstrate that inhibition can last at least 7 s after selection processes and that it is unaffected by predictable, unrelated intervening events. However, intervening events that are less predictable, or are the same as the inhibited stimulus, disrupt inhibition. Such results motivate a reconsideration of the previous view of distractor inhibition as a transient, fragile phenomenon.

Our response to visual events can be delayed at positions we have recently examined attentively. Such inhibition could organize visual search through static scenes by suppressing those loci already searched, but this mechanism would fail in moving scenes as objects' locations then change during search. We cued attention to a moving object and found subsequent inhibition at the locus the object later occupied. This implies that previously examined objects are suppressed. Such object-centred inhibition would be highly adaptive, but would require a sophisticated neural implementation for a mechanism held to be sub-cortical.

Research studying visual selective attention has largely examined filtering tasks in which stationary targets are selected from stationary distractors by a physical cue such as location and identity is the reported attribute. During many interactions with the visual environment however, target stimuli are selected by what they are, whereas action is controlled by where the stimulus is located. This study demonstrates that the interference and negative priming effects observed in standard filtering tasks, which suggest that distractors are analyzed and subsequently inhibited during selection, are also observed when targets are selected on the basis of identity and spatial location is the reported attribute. Furthermore, experimental results suggest that inhibition associated with distracting objects in this new task is object-centered, so that if the object is moving through space, inhibition moves with it.

A model of selective attention is proposed which contains a number of properties. First, stimuli which are irrelevant to the subjects' task can be analyzed to semantic levels automatically, and such stimuli can produce intrusion/interference effects. Second, two mechanisms by which selection is achieved are habituation to, and inhibition of, these irrelevant stimuli. A series of studies demonstrates that both the ability to process automatically irrelevant stimuli and the habituation mechanisms of attention are observable by Grade 2, whereas the inhibitory mechanism is not always evident at this stage. It is suggested that the greater distractability of children in certain situations may be due in part to the underutilization of this inhibitory mechanism. We further propose that children may be able to employ inhibitory mechanisms in more familiar perceptual-motor tasks.