Dissociating inhibition of return from endogenous orienting of spatial attention: Evidence from detection and discrimination tasks

Attention to space and time: Independent or interactive systems? A narrative review

While there is ample evidence for the ability to selectively attend to where in space and when in time a relevant event might occur, it remains poorly understood whether spatial and temporal attention operate independently or interactively to optimize behavior. To elucidate this important issue, we provide a narrative review of the literature investigating the relationship between the two. The studies were organized based on the attentional manipulation employed (endogenous vs. exogenous) and the type of task (detection vs. discrimination). Although the reviewed findings depict a complex scenario, three aspects appear particularly important in promoting independent or interactive effects of spatial and temporal attention: task demands, attentional manipulation, and their combination. Overall, the present review provides key insights into the relationship between spatial and temporal attention and identifies some critical gaps that need to be addressed by future research.

Electrophysiological evidence of crossmodal correspondence between auditory pitch and visual elevation affecting inhibition of return

Inhibition of return (IOR) has proved to be weakened by audiovisual integration because of the increased perceptual salience of targets. Although other audiovisual interactions, such as crossmodal correspondence, have also been shown to facilitate attentional processes, to the best of our knowledge, no study has investigated the interaction between crossmodal correspondence and IOR. The present study employed Posner's spatial cueing paradigm and manipulated the cue validity, crossmodal correspondence congruency and time interval of auditory and visual stimuli (AV interval) to explore the effect of crossmodal correspondence on the IOR effect. The behavioral results showed a reduced IOR effect under the correspondence congruency condition in contrast to the correspondence incongruency condition at the AV interval of 200 ms, whereas at an AV interval of 80 ms, the decreased IOR effect under crossmodal correspondence congruency was eliminated. The electrophysiological results showed a reduced amplitude difference in P2 between valid and invalid cue conditions when the crossmodal correspondence effect decreased the IOR effect. The present study provided the first evidence of the weakened effect of the crossmodal correspondence effect on the IOR effect, which could be eliminated by audiovisual integration.

Detection cost: A nonnegligible factor contributing to inhibition of return in the discrimination task under the cue-target paradigm

The three-factor model argues that the spatial orienting benefit triggered by the cue, the spatial selection benefit of cue-target matching, and the detection cost of distinguishing the cue from the target contribute to the measured inhibition of return (IOR) effect. According to the three-factor model, the spatial selection benefit dominates the occurrence of the IOR effect in the discrimination task, while the detection cost is negligible. The present study verified the three-factor model in the discrimination task under the cue-target paradigm by manipulating the spatial location and nonspatial feature consistency of the cue and the target as well as the promotion or hindrance of attentional disengagement from the cued location with a central reorienting cue. The results indicated that the three factors of the three-factor model contributed to the measured IOR effect in the discrimination task. Interestingly, the IOR effect was stable when the cue and target were perfectly repeated and attention was maintained at the cued location, implying that detection cost was not a negligible factor. The current study supported the contribution of all three factors in the three-factor model to the measured IOR effect; however, we argue that the role of detection cost in the discrimination task under different paradigms should be further refined.

The modulation of expectation violation on attention: Evidence from the spatial cueing effects

The study sought to investigate whether and how expectation violation can modulate attention using the exogenous spatial cueing paradigm, under the theoretical framework of the Memory Encoding Cost (MEC) model. The MEC proposes that exogenous spatial cueing effects are mainly driven by a combination of two distinct mechanisms: attentional facilitation triggered by the presence of an abrupt cue, and attentional suppression induced by memory encoding of the cue. In current experiments, participants needed to identify a target letter that was sometimes preceded by a peripheral onset cue. Various types of expectation violation were introduced by regulating the probability of cue presentation (Experiments 1 & 5), the probability of cue location (Experiments 2 & 4), and the probability of irrelevant sound presentation (Experiment 3). The results showed that expectation violation could enhance the cueing effect (valid vs. invalid cue) in some cases. More crucially, all experiments consistently observed asymmetrical modulation of expectation violation on the cost (invalid vs. neutral cue) and benefit (valid vs. neutral cue) effects: Expectation violation increased the cost effects while did not modulate or decreased (or even reversed) the benefit effects. Furthermore, Experiment 5 provided direct evidence that violation of expectations could enhance the memory encoding of a cue (e.g., color) and this memory advantage could manifest quickly in the early stages of the experiment. The MEC better explains these findings than some traditional models like the spotlight: Expectation violation can both enhance the attentional facilitation of the cue and memory encoding of irrelevant cue information. These findings suggest that expectation violation has a general adaptive function in modulating the attention selectivity.

Spatial attention is not affected by alpha or beta transcranial alternating current stimulation: A registered report

Using Electroencephalography (EEG) an event-related change in alpha activity has been observed over primary sensory cortices during the allocation of spatial attention. This is most prominent during top-down, or endogenous, attention, and nearly absent in bottom-up, or exogenous orienting. These changes are highly lateralised, such that an increase in alpha power is seen ipsilateral to the attended region of space and a decrease is seen contralaterally. Whether these changes in alpha oscillatory activity are causally related to attentional resources, or to perceptual processes, or are simply epiphenomenal, is unknown. If alpha oscillations are indicative of a causal mechanism whereby attention is allocated to a region of space, it remains an open question as to whether this is driven by ipsilateral increases or contralateral decreases in alpha power. This preregistered report set out to test these questions. To do so, we used transcranial Alternating Current Stimulation (tACS) to modulate alpha activity in the somatosensory cortex whilst measuring performance on established tactile attention paradigms. All participants completed an endogenous and exogenous tactile attention task in three stimulation conditions; alpha, sham and beta. Sham and beta stimulation operated as controls so that any observed effects could be attributed to alpha stimulation specifically. We replicated previous behavioural findings in all stimulation conditions showing a facilitation of cued trials in the endogenous task, and inhibition of return in the exogenous task. However, these were not affected by stimulation manipulations. Using Bayes-factor analysis we show strong support for the null hypotheses - that the manipulation of Alpha by tACS does not cause changes in tactile spatial attention. This well-powered study, conducted over three separate days, is an important contribution to the current debate regarding the efficiency of brain stimulation.

Effects of involuntary and voluntary attention on critical spacing of visual crowding

Visual spatial attention can be allocated in two distinct ways: one that is voluntarily directed to behaviorally relevant locations in the world, and one that is involuntarily captured by salient external stimuli. Precueing spatial attention has been shown to improve perceptual performance on a number of visual tasks. However, the effects of spatial attention on visual crowding, defined as the reduction in the ability to identify target objects in clutter, are far less clear. In this study, we used an anticueing paradigm to separately measure the effects of involuntary and voluntary spatial attention on a crowding task. Each trial began with a brief peripheral cue that predicted that the crowded target would appear on the opposite side of the screen 80% of the time and on the same side of the screen 20% of the time. Subjects performed an orientation discrimination task on a target Gabor patch that was flanked by other similar Gabor patches with independent random orientations. For trials with a short stimulus onset asynchrony between cue and target, involuntary capture of attention led to faster response times and smaller critical spacing when the target appeared on the cue side. For trials with a long stimulus onset asynchrony, voluntary allocation of attention led to faster reaction times but no significant effect on critical spacing when the target appeared on the opposite side to the cue. We additionally found that the magnitudes of these cueing effects of involuntary and voluntary attention were not strongly correlated across subjects for either reaction time or critical spacing.

Deficits in visuospatial attentional cueing following mild traumatic brain injury

Visual attentional deficits are frequently reported in patients with mild traumatic brain injury (TBI). In the present study, the ability to orient visual attention (i.e., the use of endogenous and exogenous visual cues) was investigated using a modified Posner visual search task, in which the participant was required to search for a target shape (radial frequency patterns) amongst distractor shapes. Participants were required to determine whether a target radial frequency pattern was present or absent from an array of distractors. Attention to the target location was cued using central or peripheral cueing procedures to investigate endogenous or exogenous attention allocation. Predictability was not manipulated between central and peripheral cues. Search difficulty was varied by systematically changing the radial frequency difference between target and distractors (and thereby shape difference), and cues could be valid or invalid in that they correctly or incorrectly indicated the position of the target shape. Both target discriminability (i.e., identifying the presence or absence of the target) and reaction times were measured. Thirteen patients with chronic mild TBI and 21 age-, sex-, and IQ -matched healthy controls participated in the study. For control participants, both discrimination accuracy and reaction times improved with visual search efficiency, and they were sensitive to the type of cue, with performance worst for cue invalid conditions than valid conditions. However, the results for TBI patients were strikingly different; we find that discrimination accuracy slightly improved with visual search difficulty (compared to controls), but not reaction times, and TBI patients were largely insensitive to the type of visual cue, and did not show a selective deficit for central or peripheral cues, suggesting an impairment in both endogenous and exogenous visual attention. In conclusion, patients with mild TBI exhibit a poor ability to orient visual attention.

Does the construction retrieval account apply to cross‐modal inhibition of return in semantic context?

The traditional attentional reorienting hypothesis is insufficient to explain spatial and nonspatial inhibition of return (IOR). Therefore, a construction retrieval account that includes the influence of top-down attentional sets has been proposed and can explain both spatial and nonspatial IOR. However, it remains unknown whether the construction retrieval account can be applied to non-surface features of stimuli, as well as whether its construction and retrieval mechanisms are supra-modal. The present study manipulated semantic feature congruency and spatial location congruency between the prime and the target in cross-modal audio-visual and visual-audio experimental conditions, respectively, by orthogonally combining spatial and nonspatial IOR paradigms. Our results showed that there was an interaction between semantic feature congruency and spatial location congruency controlled by the attentional sets, and that this interaction was consistent in cross-modal audio-visual and visual-audio conditions. These results suggest that the construction retrieval account can be applied to abstract semantic features and that its construction and retrieval mechanisms are supra-modal. The present study extends the application scope of the construction retrieval account and promotes the interpretation of IOR under a unified theoretical framework.

The dynamics of microsaccade amplitude reflect shifting of covert attention

Attention flexibly shifts between spatial locations to accommodate task demands. The present study examined if the dynamics of attentional shifting are seen in microsaccades whose direction has been shown to accompany the shifts of covert attention. In a spatial cueing task, the cue predicted the target location on 100%, 75%, or 50% of the trials. The results revealed that microsaccade rate and amplitude were both reduced following cue onset and then rebounded. Both microsaccade rate and amplitude were biased towards the opposite direction of the cue and then returned to the cued direction. Importantly, the cue validity modulated the temporal profile of microsaccade amplitude but had little impact on the temporal profile of microsaccade rate. In line with this, the cueing effect measured with target response accuracy was correlated with the microsaccade amplitude only. These results indicate that the temporal dynamics of microsaccade amplitude reflect shifting of covert attention.

Intention matters more than attention: Item-method directed forgetting of items at attended and unattended locations

This study embedded attentional cues in the study phase of an item-method directed forgetting task. We used an unpredictive onset cue (Experiment 1), a predictive onset cue (Experiment 2), or a predictive central cue (Experiments 3-6) to direct attention to the left or right. In Experiments 1-5, this was followed by a pink or blue study word that required a speeded colour discrimination; in Experiment 6, it was followed by a pink or blue word or nonword that required a lexical decision. Each study word was followed by an instruction to Remember or Forget. A yes-no recognition test confirmed better recognition of to-be-remembered words than to-be-forgotten words; a cueing effect confirmed the effectiveness of predictive cues in allocating attentional resources. There was, however, no evidence that the directed forgetting effect differed for attended and unattended words: Encoding depends more on the memory intention formed after a study word has disappeared than on the availability of processing resources when that word first appears.

Predictivity and Manifestation Factors in Aging Effects on the Orienting of Spatial Attention

OBJECTIVE

Prior attention research has asserted that endogenous orienting of spatial attention by willful focusing may be differently influenced by aging than exogenous orienting, the capture of attention by external cues. However, most such studies confound factors of manifestation (locational vs symbolic cues) and the predictivity of cues. We therefore investigated whether age effects on orienting are mediated by those factors.

METHOD

We measured accuracy and response times of groups of younger and older adults in a discrimination task with flanker distracters, under three spatial cueing conditions: nonpredictive locational cues, predictive symbolic cues, and a hybrid predictive locational condition.

RESULTS

Age differences were found to be related to the factor of cue predictivity, but not to the factor of spatial manifestation. These differences were not modulated by flanker congruency.

DISCUSSION

The results indicate that the orienting of spatial attention in healthy aging may be adversely affected by less effective perception or utilization of the predictive value of cues, but not by the requirement to voluntarily execute a shift of attention.

Mexican Hat Modulation of Visual Acuity Following an Exogenous Cue

Classical models of exogenous attention suggest that attentional enhancement at the focus of attention degrades gradually with distance from the attended location. On the other hand, the Attentional Attraction Field (AAF) model (Baruch and Yeshurun, 2014) suggests that the shift of receptive fields toward the attended location, reported by several physiological studies, leads to a decreased density of RFs at the attentional surrounds and hence the model predicts that the modulation of performance by spatial attention may have the shape of a Mexican Hat. Motivated by these theories, this study presents behavioral evidence in support of a Mexican Hat shaped modulation in exogenous spatial tasks that appears only at short latencies. In two experiments participants had to decide the location of a small gap in a target circle that was preceded by a non-informative attention capturing cue. The distance between cue and target and the latency between their onsets were varied. At short SOAs the performance curves were cubic and only at longer SOAs- this trend turned linear. Our results suggest that a rapid Mexican Hat modulation is an inherent property of the mechanism underlying exogenous attention and that a monotonically degrading trend, such as advocated by classical models, develops only at later stages of processing. The involvements of bottom-up processes such as the attraction of RFs to the focus of attention are further discussed.

On the time course of spatial cueing: Dissociating between a set for fast reorienting and a set for cue-target segregation

The present study tests whether two different manipulations leading to an earlier appearance of Inhibition of Return might operate by setting the system in different ways. Whereas the use of a range of very long SOAs has been proposed to set the system for an early reorienting of attention (Cheal & Chastain, 2002), introducing a distractor at the location opposite the target seems to induce a set to represent the cue and the target as separated events instead of the same event (Lupiáñez et al., 1999, 2001). The effects of these two manipulations were directly compared by using a spatial stroop paradigm. Although both manipulations altered the time course of cueing effects, we report here a pattern of critical dissociations: (i) the distractor manipulation was unique in introducing a shift towards more negative cueing affecting generally all levels of SOA, including the shortest 100 ms SOA; and (ii) the distractor manipulation, but not the range of SOAs, was also able to prevent the expected interaction between spatial stroop effects and cueing effects at the shortest SOA, typically found in previous experiments in the absence of a distractor (Funes et al., 2003). This pattern of dissociations is well accommodated into the hypothesis that these two attentional sets are different in nature.

On the putative role of intervening events in exogenous attention

In exogenous attention, two main behavioural effects are usually observed across time: facilitation at short cue-target onset asynchronies (CTOAs), and Inhibition of Return (IOR) at longer CTOAs. The presentation of an intervening event (IE)-i.e., a cue presented at fixation between the peripheral cue and target period-favours the appearance of IOR. However, although there is a general consensus on this empirical modulation, there is no agreement about the putative role of IEs and/or the mechanism/s underlying their effect. While some authors consider IEs as a "cue-back", automatically reorienting attention to fixation, thus allowing IOR to occur, others have considered IEs as events modulating cue-target integration processes, consequently affecting exogenous cueing. Even in this later case, it is not clear whether IEs modulate cueing by inducing an attentional set (top-down) modulation or by inducing a trial-by-trial (bottom-up) online modulation. To disentangle this issue, in two experiments, we manipulated the proportion of trials in which the IE was presented, thus being able to measure the effect of the presence/absence and proportion of IEs. We observed a gradual influence of the % of IEs over cueing effects, which becomes less positive or more negative as the % of IEs increases. This pattern of findings fits well with the idea that facilitation and IOR depend on cue-target integration processes, and presents critical implications for the open debate about the mechanism/s underlying exogenous spatial cueing effects.

From alternation to repetition: Spatial attention biases contribute to sequential effects in a choice reaction-time task

Observers often take longer to respond to a visual target when it appears at a recently stimulated location than when it appears at a new location in the visual field. This behavioral impairment - known as inhibition of return (IOR) - is mirrored by a reduction of an event-related potential (ERP) component called the N2pc that has been associated with attentional selection. Together, these findings indicate that the mechanism underlying IOR operates to bias covert attention against re-visiting the most recently attended location. The goal of the present study was to determine how this inhibitory attention bias evolves across successive trials of a two-item search task. Initially, targets appearing at previously attended locations were associated with behavioral IOR and a concomitant reduction of the N2pc. After several successive trials, this initial inhibitory bias was superseded by expectancy-based biases associated with "predictable" inter-trial patterns of location repeats or location changes, in some cases leading to faster responses and a larger N2pc when the target location repeated (facilitation of return).  These results provide evidence that biases in the covert deployment of attention are updated dynamically according to the recent selection history and contribute to well-known sequential effects in serial choice reaction-time tasks.

The causal role of the left parietal lobe in facilitation and inhibition of return

Following non-informative peripheral cues, responses are facilitated at the cued compared to the uncued location at short cue-target intervals. This effect reverses at longer intervals, giving rise to Inhibition of Return (IOR). The integration-segregation hypothesis (Lupiáñez, 2010) suggests that peripheral cues always produce an onset-detection cost regardless the behavioral cueing effect that is measured - either facilitation or IOR. In the present study, we used transcranial magnetic stimulation (TMS) to investigate the causal contribution of this detection cost to performance. We used a cueing paradigm with a target discrimination task that was preceded by a non-informative peripheral cue. The presence-absence of a central intervening event was manipulated. Online TMS to the left superior parietal lobe (compared to an active vertex stimulation) lead to an overall more positive effect (faster responses for cued as compared to uncued trials), by putatively impairing the detection cost contribution to performance. The data revealed a strong association between overall RT and the TMS effect, and also between overall RT and the integrity of the first branch of the left superior longitudinal fascicule. These results have critical implications not only for the open debate about the mechanism/s underlying spatial orienting effects, but also for the growing literature demonstrating that white matter connectivity is crucial for explaining inter-individual behavioral variability.

Remember to blink: Reduced attentional blink following instructions to forget

This study used rapid serial visual presentation (RSVP) to determine whether, in an item-method directed forgetting task, study word processing ends earlier for forget words than for remember words. The critical manipulation required participants to monitor an RSVP stream of black nonsense strings in which a single blue word was embedded. The next item to follow the word was a string of red fs that instructed the participant to forget the word or green rs that instructed the participant to remember the word. After the memory instruction, a probe string of black xs or os appeared at postinstruction positions 1-8. Accuracy in reporting the identity of the probe string revealed an attenuated attentional blink following instructions to forget. A yes-no recognition task that followed the study trials confirmed a directed forgetting effect, with better recognition of remember words than forget words. Considered in the context of control conditions that required participants to commit either all or none of the study words to memory, the pattern of probe identification accuracy following the directed forgetting task argues that an intention to forget releases limited-capacity attentional resources sooner than an instruction to remember-despite participants needing to maintain an ongoing rehearsal set in both cases.

Inhibition of return modulates the flash-lag effect

Transient events are known to draw exogenous attention, and visual processing at the attended location is transiently facilitated, but after several hundred milliseconds, attentional processing at the cued location becomes poorer than processing elsewhere, resulting in a slower reaction to a target stimulus that subsequently appears at the cued location. Despite a number of previous studies on this effect, termed inhibition of return (IOR), it is still unclear whether a perceptual process related to the subjective onset time of the target stimulus is disrupted when IOR occurs. In the present study, we used a distinct visual phenomenon termed the flash-lag effect (FLE) as a tool to quantify IOR. The FLE is an illusion in which a flashed stimulus appears to lag behind a moving stimulus, despite being physically aligned. We used an identical stimulus configuration and asked observers to conduct two independent tasks in separate sessions. The first was a simple reaction task to measure the onset reaction time (RT) to an abruptly appearing target. The second was an orientation judgment task to measure the degree of the FLE. Both the RT and the FLE were found to be altered in accordance with IOR, and a significant correlation was demonstrated between the changes in the RT and those in the FLE. These results demonstrate that the perceptual process related to the stimulus onset can be compromised by IOR.

Sluggish dorsally-driven inhibition of return during orthographic processing in adults with dyslexia

Dyslexia (D) is a neurodevelopmental reading disorder characterized by phonological and orthographic deficits. Before phonological decoding, reading requires a specialized orthographic system for parallel letter processing that assigns letter identities to different spatial locations. The magnocellular-dorsal (MD) stream rapidly process the spatial location of visual stimuli controlling visuo-spatial attention. To investigate the visuo-spatial attention efficiency during orthographic processing, inhibition of return (IOR) was measured in adults with and without D in a lexical decision task. IOR is the delay in responding to stimuli displayed in a cued location after a long cue-target interval. Only adults with D did not showed IOR effect during letter-string recognition, despite the typical left-hemisphere specialization for word identification. A specific deficit in coherent-dot-motion perception confirmed an MD-stream disorder in adults with D. Our results suggest that adults with D might develop an efficient visual word form area, but a dorsal-attentional dysfunction impairs their reading fluency.

Probabilistic versus "Pure" Volitional Orienting: a Monocular Difference

Human volitional orienting is typically assessed using Posner's endogenous cuing task. As a volitional process, the literature has long emphasized the role of neocortical structures in this higher cognitive function. Based on recent data, we explored the possibility that subcortical channels may have a functional role in volitional orienting as measured by a Posner cuing task in which a nonspatial feature of a centrally presented cue is predictively related to the location of the target. In addition, we have compared this typical cuing task to a "purer" version, which does not involve the probability manipulation. A sensitive behavioral method was used to probe the contribution of monocular channels (mostly subcortical) in the two types of endogenous orienting tasks. In both tasks, a spatially informative cue and its ensuing target were presented to the same or different eyes at varying cue-target intervals. In the typically used endogenous task, the onset of facilitation was apparent earlier when the cue and target were presented to the same eye. In contrast, in the "pure" task no difference was found between the two eye-of-origin conditions. These data support the notion that endogenous facilitation, as measured in the typical Posner cuing task, involves lower monocular regions. Hence, in the typical endogenous task, which was developed to explore "volitional" orienting, a simple associative learning mechanism might elicit monocular, rapid orienting responses. Notably, the typical volitional orienting paradigm might be contaminated by simple contingency benefits and thus may not provide a pure measure of volitional processes.

Evidence for an attentional component of inhibition of return in visual search

Inhibition of return (IOR) is typically described as an inhibitory bias against returning attention to a recently attended location as a means of promoting efficient visual search. Most studies examining IOR, however, either do not use visual search paradigms or do not effectively isolate attentional processes, making it difficult to conclusively link IOR to a bias in attention. Here, we recorded ERPs during a simple visual search task designed to isolate the attentional component of IOR to examine whether an inhibitory bias of attention is observed and, if so, how it influences visual search behavior. Across successive visual search displays, we found evidence of both a broad, hemisphere-wide inhibitory bias of attention along with a focal, target location-specific facilitation. When the target appeared in the same visual hemifield in successive searches, responses were slower and the N2pc component was reduced, reflecting a bias of attention away from the previously attended side of space. When the target occurred at the same location in successive searches, responses were facilitated and the P1 component was enhanced, likely reflecting spatial priming of the target. These two effects are combined in the response times, leading to a reduction in the IOR effect for repeated target locations. Using ERPs, however, these two opposing effects can be isolated in time, demonstrating that the inhibitory biasing of attention still occurs even when response-time slowing is ameliorated by spatial priming.

Is Inhibition of Return Modulated by Involuntary Orienting of Spatial Attention: An ERP Study

Inhibition of return (IOR) is a mechanism that indicates individuals’ faster responses or higher accuracy to targets appearing in the novel location relative to the cued location. According to the “reorienting hypothesis,” disengagement from the cued location is necessary for the generation of IOR. However, more and more studies have questioned this theory because of dissociation between voluntary or involuntary spatial orienting and the IOR effect. To further explore the “reorienting hypothesis” of IOR, the present experiment employed an atypical cue-target paradigm which combined a spatially non-predictive peripheral cue that was presumed to trigger IOR with a spatially non-predictive central cue that was used to reflexively trigger a shift of attention. The results showed that a significant IOR effect did not interact with automatic spatial orienting as measured in mean RTs and accuracy as well as the Nd component. These findings suggested that the IOR effect triggered by peripheral cue was independent of automatic orienting generated by a central cue. Therefore, the present study provided evidence from location task and neural aspects, which again challenged the “reorienting hypothesis” of IOR.

Implicit learning: A way to improve visual search in spatial neglect?

Studies have shown that neglect patients are able to use stimulus regularities to orient faster toward the neglected side, without necessarily being aware of that information, or at the very least without being able to verbalize their knowledge. In order to better control for the involvement of explicit processes, the present study sought to test neglect patients' ability to detect more complex associations between stimuli using tasks similar to those used in implicit learning studies. Our results demonstrate that neglect patients had difficulties implicitly learning complex associations, contrary to what we found with controls. The possible influence of attentional and working memory impairments are discussed.

Endogenous temporal and spatial orienting: Evidence for two distinct attentional mechanisms

The requirement to orient attention in space and time usually occurs simultaneously. Previous reports were indecisive regarding possible interactions between temporal and spatial orienting. The present study examined whether temporal and spatial orienting can operate simultaneously and independently in the framework of a detection task. Participants completed three consecutive target detection tasks: in the first two tasks a central cue provided predictive information regarding either the temporal delay of the target or its spatial location. In a third task the temporal and spatial cues from the first two tasks were combined into a single cue. Temporal and spatial information provided by the combined cue could be valid or invalid for each type of information separately. Results from the combined temporal-spatial task revealed that at a short cue-to-target interval temporal validity effects were significant at the attended and unattended spatial locations and were not modulated by spatial validity conditions. Spatial validity effects were also significant and comparable between the valid and invalid temporal conditions. Moreover, temporal and spatial validity effects in the combined task were equivalent to those attained in the separate tasks. At a long cue-to-target delay, spatial validity effects were significant and were not modulated by temporal validity but there were no temporal validity effects. Overall, the results suggest that participants were able to extract temporal and spatial information provided by a single cue simultaneously and independently. We conclude that temporal and spatial endogenous orienting function orthogonally in a task that does not require demanding perceptual discrimination.

Inhibition of return and attentional facilitation: Numbers can be counted in, letters tell a different story

Prior research has provided strong evidence for spatial-numerical associations. Single digits can for instance act as attentional cues, orienting visuo-spatial attention to the left or right hemifield depending on the digit's magnitude, thus facilitating target detection in the cued hemifield (left/right hemifield after small/large digits, respectively). Studies using other types of behaviourally or biologically relevant central cues known to elicit automated symbolic attention orienting effects such as arrows or gaze have shown that the initial facilitation of cued target detection can turn into inhibition at longer stimulus onset asynchronies (SOAs). However, no studies so far investigated whether inhibition of return (IOR) is also observed using digits as uninformative central cues. To address this issue we designed an attentional cueing paradigm using SOAs ranging from 500 ms to 1650 ms. As expected, the results showed a facilitation effect at the relatively short 650 ms SOA, replicating previous findings. At the long 1650 ms SOA, however, participants were faster to detect targets in the uncued hemifield compared to the cued hemifield, showing an IOR effect. A control experiment with letters showed no such congruency effects at any SOA. These findings provide the first evidence that digits not only produce facilitation effects at shorter intervals, but also induce inhibitory effects at longer intervals, confirming that Arabic digits engage automated symbolic orienting of attention.

Motor IOR revealed for reaching

Inhibition of return (IOR) is a spatial phenomenon that is thought to promote visual search functions by biasing attention and eye movements toward novel locations. Considerable research suggests distinct sensory and motor flavors of IOR, but it is not clear whether the motor type can affect responses other than eye movements. Most studies claiming to reveal motor IOR in the reaching control system have been confounded by their use of peripheral signals, which can invoke sensory rather than motor-based inhibitory effects. Other studies have used central signals to focus on motor, rather than sensory, effects in arm movements but have failed to observe IOR and have concluded that the motor form of IOR is restricted to the oculomotor system. Here, we show the first clear evidence that motor IOR can be observed for reaching movements when participants respond to consecutive central stimuli. This observation suggests that motor IOR serves a more general function than the facilitation of visual search, perhaps reducing the likelihood of engaging in repetitive behavior.

Beyond the inhibition of return of attention: reduced habituation to threatening faces in schizophrenia

Attention deficits are prominent among the core symptoms of schizophrenia. A recent meta-analysis has suggested that patients with schizophrenia have a deficit in endogenous disengagement of attention. In this research, we used a standard spatial cueing paradigm to examine whether the attention deficit of such patients is due to impaired attentional disengagement or defective novelty detection/habituation processes. In a spatial cueing procedure with peripheral non-predictive cues and a detection task, we manipulated the valence of either the cue or the target (i.e., a threatening vs. scrambled face) in two separate experiments. The control group exhibited a smaller inhibition of return (IOR) effect only when the target had an emotional load, not when the cue had an emotional load. In the patient group, a larger emotional effect appeared when the threatening face was the target; by contrast, no effect of valence was observed when the threatening face was the cue: IOR was delayed or completely absent independently of valence. The present findings are in conflict with the hypothesis that IOR is due to the disengagement of attention and the subsequent inhibition to return. Instead, they seem to suggest a cost in detecting new information at a previously cued location. From this perspective, it seems that patients with schizophrenia might have a deficit in detecting new information and considering it as new in the current context.

Is “Inhibition of Return” due to the inhibition of the return of attention?

Inhibition of Return (IOR) is usually explained in terms of orienting–reorienting of attention, emphasizing an underlying mechanism that inhibits the return of attention to previously selected locations. Recent data challenge this explanation to the extent that the IOR effect is observed at the location where attention is oriented to, where no reorienting of attention is needed. To date, these studies have involved endogenous attentional selection of attention and thus indicate a dissociation between the voluntary attention of spatial attention and the IOR effect. The present work demonstrates a dissociation between the involuntary orienting of spatial attention and the IOR effect. We combined nonpredictive peripheral cues with nonpredictive central orienting cues (either arrows or gaze). The IOR effect was observed to operate independent of involuntary spatial orienting. These data speak against the “ reorienting hypothesis” of IOR. We suggest an alternative explanation whereby the IOR effect reflects a cost in detecting a new event (the target) at the location where another event (a cue) was coded before.

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.

Two cognitive and neural systems for endogenous and exogenous spatial attention

Orienting of spatial attention is a family of phylogenetically old mechanisms developed to select information for further processing. Information can be selected via top-down or endogenous mechanisms, depending on the goals of the observers or on the task at hand. Moreover, salient and potentially dangerous events also attract spatial attention via bottom-up or exogenous mechanisms, allowing a rapid and efficient reaction to unexpected but important events. Fronto-parietal brain networks have been demonstrated to play an important role in supporting spatial attentional orienting, although there is no consensus on whether there is a single attentional system supporting both endogenous and exogenous attention, or two anatomical and functionally different attentional systems. In the present paper we review behavioral evidence emphasizing the differential characteristics of both systems, as well as their possible interactions for the control of the final orienting response. Behavioral studies reporting qualitative differences between the effects of both systems as well as double dissociations of the effects of endogenous and exogenous attention on information processing, suggest that they constitute two independent attentional systems, rather than a single one. Recent models of attentional orienting in humans have put forward the hypothesis of a dorsal fronto-parietal network for orienting spatial attention, and a more ventral fronto-parietal network for detecting unexpected but behaviorally relevant events. Non-invasive neurostimulation techniques, as well as neuropsychological data, suggest that endogenous and exogenous attention are implemented in overlapping, although partially segregated, brain circuits. Although more research is needed in order to refine our anatomical and functional knowledge of the brain circuits underlying spatial attention, we conclude that endogenous and exogenous spatial orienting constitute two independent attentional systems, with different behavioral effects, and partially distinct neural substrates.

Changes in search rate but not in the dynamics of exogenous attention in action videogame players

Many previous studies have shown that the speed of processing in attentionally demanding tasks seems enhanced following habitual action videogame play. However, using one of the diagnostic tasks for efficiency of attentional processing, a visual search task, Castel and collaborators (Castel, Pratt, & Drummond, Acta Psychologica 119:217-230, 2005) reported no difference in visual search rates, instead proposing that action gaming may change response execution time rather than the efficiency of visual selective attention per se. Here we used two hard visual search tasks, one measuring reaction time and the other accuracy, to test whether visual search rate may be changed by action videogame play. We found greater search rates in the gamer group than in the nongamer controls, consistent with increased efficiency in visual selective attention. We then asked how general the change in attentional throughput noted so far in gamers might be by testing whether exogenous attentional cues would lead to a disproportional enhancement in throughput in gamers as compared to nongamers. Interestingly, exogenous cues were found to enhance throughput equivalently between gamers and nongamers, suggesting that not all mechanisms known to enhance throughput are similarly enhanced in action videogamers.

Covert attention regulates saccadic reaction time by routing between different visual-oculomotor pathways

Covert attention modulates saccadic performance, e.g., the abrupt onset of a task-irrelevant visual stimulus grabs attention as measured by a decrease in saccadic reaction time (SRT). The attentional advantage bestowed by the task-irrelevant stimulus is short-lived: SRT is actually longer ∼200 ms after the onset of a stimulus than it is when no stimulus appears, known as inhibition of return. The mechanism by which attention modulates saccadic reaction is not well-understood. Here, we propose two possible mechanisms: by selective routing of the visuomotor signal through different pathways (routing hypothesis) or by general modulation of the speed of visuomotor transformation (shifting hypothesis). To test them, we designed a cue gap paradigm in which a 100-ms gap was introduced between the fixation point disappearance and the target appearance to the conventional cued visual reaction time paradigm. The cue manipulated the location of covert attention, and the gap interval resulted in a bimodal distribution of SRT, with an early mode (express saccade) and a late mode (regular saccade). The routing hypothesis predicts changes in the proportion of express saccades vs. regular saccades, whereas the shifting hypothesis predicts a shift of SRT distribution. The addition of the cue had no effect on mean reaction time of express and regular saccades, but it changed the relative proportion of two modes. These results demonstrate that the covert attention modification of the mean SRT is largely attributed to selective routing between visuomotor pathways rather than general modulation of the speed of visuomotor transformation.