Inhibition of Return From Stimulus to Response

Visualizing the temporal dynamics of spatial information processing responsible for the Simon effect and its amplification by inhibition of return

Research has shown that the Simon effect is larger for targets suffering from inhibition of return (IOR). We used speed-accuracy trade-off (SAT) methodology to explore the temporal dynamics underlying this interaction. In Experiment 1, a new method for sorting the data was used to reveal a monotonic decay in the impact of task-irrelevant location information that is responsible for the Simon effect. In Experiment 2, we show that IOR delays both task-relevant identity and task-irrelevant location codes; a relatively longer delay for location than identity codes accounts for the effect of IOR on the Simon effect. When location information was made task-relevant in Experiment 3, IOR delayed the accumulation of this information by about the same amount as when location was irrelevant. The results suggest that IOR, therefore, has a greater effect on location than identity information.

Congruency reversals in an accessory signal Simon task with auditory and visual stimuli

In visual two-choice reaction-time tasks, a Simon-like effect occurs when a peripheral accessory signal is presented shortly before or together with the response signal. However, the effect reverses when the peripheral signal appears shortly after the response signal. This pattern also occurs when the peripheral signal appears relative to a go (nogo) signal, with the relevant signal presented well in advance. The reversal has been explained as the inhibition of exogenous response-code activation as soon as an action plan has been developed. In three experiments we investigated whether the inhibition also occurred with auditory and crossmodal stimuli. A Simon effect appeared in all experiments, but the reversal only occurred when peripheral and relevant response signals were auditory, and not when the relevant and irrelevant signals were in a different modality. We suggest that planned actions are protected against exogenous interference by a modality-specific inhibitory process, determined by the relevancy of the modality of the peripheral accessory signal.

Perceptual load interacts with involuntary attention at early processing stages: event-related potential studies

Perceptual load is known to influence the locus of attentional selection in the brain but through an unknown underlying mechanism. We used event-related potentials (ERPs) to investigate how perceptual load interacts with cue-driven involuntary attention. Perceptual load was manipulated in a line orientation discrimination task in which target location was cued involuntarily by means of peripheral cues. Attentional modulation was observed for P1m (the posterior midline P1 component with peak latency between 108 and 140 ms) with invalid trials eliciting larger P1m than valid trials. This attentional effect on P1m increased as a function of perceptual load, suggesting an early temporal locus for the interaction of perceptual load and involuntary attention. Attentional modulation for the C1 component (peak latency at approximately 80 ms) was also observed, but only for high-load stimuli that were presented intermixed with low-load stimuli. Results suggest that (a) perceptual load affects attentional selection at early processing stages; (b) perceptual load interacts with involuntary attention earlier and with different brain mechanisms relative to voluntary attention; and (c) attentional modulation in the C1 time range is possible under optimal experimental conditions.

Response-selection Conflict Contributes to Inhibition of Return

Here we examined the relationship between inhibition of return (IOR) and response-selection conflict. In two go/no-go and spatial-cueing experiments, we measured the amplitude of the fronto-central N2 event-related potential component to estimate the degree of response-selection conflict for validly cued and invalidly cued targets. When the probability of a go target was high (Experiment 1), both the amplitude of the N2 elicited on no-go trials and the number of false alarm errors were greater on invalid-cue than on valid-cue trials. When the probability of a go target was low (Experiment 2), neither of these effects was observed and the magnitude of the IOR effect was greatly reduced. These results show that a relative response bias toward responding on invalid-cue trials contributes to the IOR reaction time effect when the required response is prepotent.

Inhibition of Return in the Covert Deployment of Attention: Evidence from Human Electrophysiology

People are slow to react to objects that appear at recently attended locations. This delay—known as inhibition of return (IOR)—is believed to aid search of the visual environment by discouraging inspection of recently inspected objects. However, after two decades of research, there is no evidence that IOR reflects an inhibition in the covert deployment of attention. Here, observers participated in a modified visual-search task that enabled us to measure IOR and an ERP component called the posterior contralateral N2 (N2pc) that reflects the covert deployment of attention. The N2pc was smaller when a target appeared at a recently attended location than when it appeared at a recently unattended location. This reduction was due to modulation of neural processing in the visual cortex and the right parietal lobe. Importantly, there was no evidence for a delay in the N2pc. We conclude that in our task, the inhibitory processes underlying IOR reduce the probability of shifting attention to recently attended locations but do not delay the covert deployment of attention itself.

Inhibition of Return Arises from Inhibition of Response Processes: An Analysis of Oscillatory Beta Activity

In the orienting of attention paradigm, inhibition of return (IOR) refers to slowed responses to targets presented at the same location as a preceding stimulus. No consensus has yet been reached regarding the stages of information processing underlying the inhibition. We report the results of an electro-encephalogram experiment designed to examine the involvement of response inhibition in IOR. Using a cue-target design and a target-target design, we addressed the role of response inhibition in a location discrimination task. Event-related changes in beta power were measured because oscillatory beta activity has been shown to be related to motor activity. Bilaterally located sources in the primary motor cortex showed event-related beta desynchronization (ERD) both at cue and target presentation and a rebound to event-related beta synchronization (ERS) after movement execution. In both designs, IOR arose from an enhancement of beta synchrony. IOR was related to an increase of beta ERS in the target-target design and to a decrease of beta ERD in the cue-target design. These results suggest an important role of response inhibition in IOR.

Temporal dynamics of the attentional spotlight: neuronal correlates of attentional capture and inhibition of return in early visual cortex

A stimulus that suddenly appears in the corner of the eye inevitably captures our attention, and this in turn leads to faster detection of a second stimulus presented at the same position shortly thereafter. After about 250 msec, however, this effect reverses and the second stimulus is detected faster when it appears far away from the first. Here, we report a potential physiological correlate of this time-dependent attentional facilitation and inhibition. We measured the activity in visual cortex representations of the second (target) stimulus' location depending on the stimulus onset asynchrony (SOA) and spatial distance that separated the target from the preceding cue stimulus. At an SOA of 100 msec, the target yielded larger responses when it was presented near to than far away from the cue. At an SOA of 850 msec, however, the response to the target was more pronounced when it appeared far away from the cue. Our data show how the neural substrate of visual orienting is guided by immediately preceding sensory experience and how a fast-reacting brain system modulates sensory processing by briefly increasing and subsequently decreasing responsiveness in parts of the visual cortex. We propose these activity modulations as the neural correlate of the sequence of perceptual facilitation and inhibition after attentional capture.

Reorienting attention and inhibition of return

In experiments examining inhibition of return (IOR), it is common practice to present a second cue at fixation during the cue-target interval. The purpose of this fixation cue is to reorient attention away from the cued location to ensure that the facilitative effects of spatial attention do not obscure IOR. However, despite their frequent use, relatively little is known about the relationship between fixation cues and IOR. In the present experiments, we examined the role of fixation cues by manipulating their presence in tasks that either did or did not require target identification. When the participants were required to either detect (Experiment 1A) or localize (Experiment 2A) a target, the magnitude of IOR was unaffected by the presence of a fixation cue. In contrast, when the participants were required to identify a target (Experiments 1B, 2B, and 3), IOR was observed only when a fixation cue was presented. This result was obtained regardless of the type of response that was required (two-alternative forced choice or go/no go). The effectiveness of the fixation cue in revealing IOR in these tasks is consistent with its putative role in reorienting attention away from the cued location.

The time required for perceptual (nonmotoric) processing in IOR

In an inhibition of return (IOR) paradigm, we used a threshold-tracking procedure combined with backward masking to measure the speed of perceptual processing in IOR independent of motoric factors. Instead of the conventional reaction time measure, this procedure yielded the critical exposure duration (DURc) that is required in order for a target to be identified reliably before the onset of a trailing mask. In Experiment 1, the facilitation effects conventionally found at short cue-target onset asynchrony (CTOA) were evidenced by shorter values of DURc at cued relative to uncued locations. Conversely, the retardation effects conventionally found at long CTOA were evidenced by correspondingly longer values of DURc. In Experiment 2, the DURc results strongly suggest that the directional reading bias previously observed in IOR studies is due, at least in part, to perceptual rather than motoric factors.

Inhibition of return for expected and unexpected targets

Inhibition of return (IOR) refers to slower reaction times (RTs) to targets that occur in the same, rather than in a different, location as a preceding onset cue. The present study examined IOR for expected (likely) and unexpected (unlikely) targets under conditions in which stimulus-response (S-R) expectancies were generated on a trial-by-trial basis or maintained across a block of trials. Three boxes were aligned along the vertical midline. In Experiments 1 and 2, the appearance of a cue in the upper or lower box was a signal to generate an expectancy about the most likely color of an impending discrimination target. In Experiment 3, one target color was more likely than another across a block of trials. In all cases, cue location did not predict target location. When S-R expectancies were generated on a trial-by-trial basis, IOR occurred for Unlikely targets but not for Likely targets; this was true across a range of cue-target stimulus onset asynchronies. In contrast, when S-R expectancies were maintained over a block of trials, IOR was larger for Likely than for Unlikely targets. These findings reveal a critical interaction of S-R expectancies with IOR. This interaction not only demonstrates the modulation of IOR by cognitive expectancies, but in doing so also provides evidence that is consistent with the view that IOR reflects a conservative response bias.

Semantic processing is affected in inhibition of return: evidence from an event-related potentials study

Inhibition of return refers to a slower responding to a target stimulus appearing at previously cued locations. We used the event-related potentials technique to investigate the effects of inhibition of return in semantic processing with the combination of a spatial cueing task and semantic N400 paradigm. The results showed that the N400 component, as an index of semantic processing, was suppressed when the target words were presented in the cued location relative to the uncued location. The results indicated that the semantic processing of the target word presented on the cued location is affected by inhibition of return. Moreover, our findings provided event-related potential evidence for the inhibition of attention theory of inhibition of return.

Interactions between endogenous and exogenous attention on cortical visual processing

Sensory processing is affected by both endogenous and exogenous mechanisms of attention, although how these mechanisms interact in the brain has remained unclear. In the present study, we recorded event-related potentials (ERPs) to investigate how multiple stages of information processing in the brain are affected when endogenous and exogenous mechanisms are concurrently engaged. We found that the earliest stage of cortical visual processing, the striate-cortex-generated C1, was immune to attentional modulation, even when endogenous and exogenous attention converged on a common location. The earliest stage of processing to be affected in this experiment was the late phase of the extrastriate-cortex-generated P1 component, which was dominated by exogenous attention. Processing at this stage was enhanced by exogenous attention, regardless of where endogenous attention had been oriented. Endogenous attention, however, dominated a later, higher-order stage of processing indexed by an enhancement of the P300 that was unaffected by exogenous attention. Critically, between these early and late stages, an interaction was found wherein endogenous and exogenous attention produced distinct, and overlapping, effects on information processing. At the same time that exogenous attention was producing an extended enhancement of the late-P1, endogenous attention was enhancing the occipital-parietal N1 component. These results provide neurophysiological support for theories suggesting that endogenous and exogenous mechanisms represent two attention systems that can affect information processing in the brain in distinct ways. Furthermore, these data provide new evidence regarding the precise stages of neural processing that are, and are not, affected when endogenous and exogenous attentions interact.

Different effects of exogenous cues in a visual detection and discrimination task: delayed attention withdrawal and/or speeded motor inhibition?

Several studies examining spatial attention have found a discrepancy regarding the effects of exogenous cues on reaction times in visual detection and discrimination tasks. Namely, across a wide range of cue-target intervals, responses are slower for targets at cued than at uncued locations (inhibition of return) in detection tasks, whereas responses are faster for targets at cued than at uncued locations (facilitation) in discrimination tasks. Two hypotheses were proposed to account for this discrepancy. First, attention may dwell much longer on the exogenously cued location in discrimination tasks because stimuli have to be identified (i.e., the delayed attention withdrawal hypothesis). Secondly, due to increased motor preparation in detection tasks, cue-induced motor inhibition may rise much faster in these tasks than in discrimination tasks (i.e., the speeded motor inhibition hypothesis). We examined to what extent these hypotheses can account for effects of exogenous cues in a detection and discrimination task on the extrastriate P1 component, and the onset of motor activation, as indexed by the lateralized readiness potential. Some support was found for the delayed attention withdrawal hypothesis, as task-dependent cueing effects were found on the P1 component. Other aspects of our data, however, indicate that motor inhibition is also involved. Based on these findings, we propose that effects of exogenous cues in detection and discrimination tasks are determined by the interplay between two mechanisms, of which the time courses of activation may be modulated by the specific setting.

Task-dependent exogenous cuing effects depend on cue modality

Task-dependent exogenous cuing effects on reaction time in detection and discrimination tasks have been ascribed to delayed withdrawal of attention in discrimination tasks. Alternatively, these differences may be due to cue-induced response inhibition in detection tasks. Unimodal and crossmodal versions of the Posner paradigm were examined with short cue-target intervals. Targets above or below fixation required either detection or discrimination responses. Cuing effects were determined for the target-elicited P1 component and for the lateralized readiness potential (LRP). Task-dependent cuing effects on reaction time were found in the unimodal but not in the crossmodal version, but not for the P1 component. The LRP data indicated that inhibition of return in the unimodal detection task had a premotoric locus. These findings suggest that inhibition in the unimodal detection task resulted from speeded motor inhibition triggered by the visual cue.

Cortical expressions of inhibition of return

Inhibition of return (IOR) is a phenomenon that has been thought to be closely associated with attention mechanisms. In particular, it might arise from the operation of an attentional mechanism that facilitates visual search by inhibiting both covert attention and eye movements from returning to recently inspected locations. Although IOR has received a great deal of research interest, and mechanisms involving sensory, perceptual, and motor consequences have been proposed, no consensus has yet been reached regarding the stages of information processing at which IOR operates. In the present study, we utilized event-related potential (ERP) measures of visual and motor processes to investigate the processing changes underlying IOR. In three experiments, involving localization, detection, or Go-NoGo discrimination, participants were required to make manual responses to target stimuli. In each of these experiments, IOR was associated with a slowing of premotor processes as indicated by a modulation of the onset of the target-locked lateralized readiness potential (LRP). However, the duration of motor processes was not affected (response-locked LRP latency). Consistent with a perceptual locus of IOR, the amplitudes of the occipital ERP peaks were reduced for targets at cued locations relative to those at uncued locations. These and earlier results together provide considerable support for a model in which salience mechanisms that guide attention orienting are also affected by IOR, in that processing a stimulus at a location results in a lowering of its salience for future processing, making orienting to that location, and responding to targets presented there, more time consuming.

Brain-Electrical Correlates of Negative Location Priming Under Sustained and Transient Attentional Context Conditions

In the present study event-related potentials (ERPs) and event-related lateralizations (ERLs) were analyzed to investigate mechanisms of attentional inhibition engaged when a target stimulus has to be located within a simultaneous target-distractor display. The putative after-effects of inhibition were examined with a prime-probe technique by comparing a “DT” condition (the prime Distractor location becomes the probe Target location) with a control condition (the probe target appears at a previously empty position). The specific aim was to dissociate more “automatic” aspects from more “controlled” aspects associated with the inhibition of distractor locations. To do so, we compared physically identical prime-probe pairs in a sustained-attention context (same target throughout a block) and a transient-attention context (trial-by-trial target specification). Three early ERP/ERL components showed differential effects for DT compared to control: (1) the posterior N1 with a diminished amplitude contralateral to the visual half-field side of target presentation, (2) the N2pc with an enhanced amplitude contralateral to the visual half-field side of target presentation, and (3) the posteriorly distributed N2 with a nonlateralized enhancement for DT compared to control. These effects were differently affected by the context manipulation. While the N2pc effect was observed exclusively under sustained attention, the N1 lateralization effect and the N2 effect were not differentially modulated. The N1 lateralization effect seems consistent with an inhibition-of-return explanation. The N2pc and N2 effects are supposed to be reflecting different aspects of a biased-competition model of distractor inhibition.

Correlates of Capture of Attention and Inhibition of Return across Stages of Visual Processing

How do visual signals evolve from early to late stages in sensory processing? We explored this question by examining two neural correlates of spatial attention. The capture of attention and inhibition of return refer to the initial advantage and subsequent disadvantage to respond to a visual target that follows an irrelevant visual cue at the same location. In the intermediate layers of the superior colliculus (a region that receives input from late stages in visual processing), both behavioral effects link to changes in the neural representation of the target: strong target-related activity correlates with the capture of attention and weak target-related activity correlates with inhibition of return. Contrasting these correlates with those obtained in the superficial layers (a functionally distinct region that receives input from early stages in visual processing), we show that the target-related activity of neurons in the intermediate layers was the best predictor of orienting behavior, although dramatic changes in the target-related response were observed in both subregions. We describe the important consequences of these findings for understanding the neural basis of the capture of attention and inhibition of return and interpreting changes in neural activity more generally.

Automatic versus contingent mechanisms of sensory-driven neural biasing and reflexive attention

Recent studies have generated debate regarding whether reflexive attention mechanisms are triggered in a purely automatic stimulus-driven manner. Behavioral studies have found that a nonpredictive "cue" stimulus will speed manual responses to subsequent targets at the same location, but only if that cue is congruent with actively maintained top-down settings for target detection. When a cue is incongruent with top-down settings, response times are unaffected, and this has been taken as evidence that reflexive attention mechanisms were never engaged in those conditions. However, manual response times may mask effects on earlier stages of processing. Here, we used event-related potentials to investigate the interaction of bottom-up sensory-driven mechanisms and top-down control settings at multiple stages of processing in the brain. Our results dissociate sensory-driven mechanisms that automatically bias early stages of visual processing from later mechanisms that are contingent on top-down control. An early enhancement of target processing in the extrastriate visual cortex (i.e., the P1 component) was triggered by the appearance of a unique bright cue, regardless of top-down settings. The enhancement of visual processing was prolonged, however, when the cue was congruent with top-down settings. Later processing in posterior temporal-parietal regions (i.e., the ipsilateral invalid negativity) was triggered automatically when the cue consisted of the abrupt appearance of a single new object. However, in cases where more than a single object appeared during the cue display, this stage of processing was contingent on top-down control. These findings provide evidence that visual information processing is biased at multiple levels in the brain, and the results distinguish automatically triggered sensory-driven mechanisms from those that are contingent on top-down control settings.

Inhibition of return and response repetition within and between modalities

Inhibition of return (IOR) refers to slower responding to stimuli at previously occupied spatial locations. IOR has been vigorously studied because of its possible deep involvement with attention mechanisms. Although IOR occurs both within and across modalities in several experimental paradigms for simple stimulus detection tasks, it has sometimes been difficult to demonstrate in perceptual discrimination tasks. In the preferred target-target paradigm, in which responses are made to a series of targets that vary in spatial location, failure to find IOR could possibly result from mixing of spatial IOR with the facilitating effects of stimulus and/or response repetition on discrimination response times. In this paper we report the first demonstration of auditory/auditory and cross-modality IOR in a target-target paradigm using a discrimination task. Our results show that IOR occurs in this task only on trials on which stimuli and responses are not repeated. These findings present a challenge to purely visual accounts of IOR and support the view that IOR arises within a more general, supra-modal mechanism of attention.