Perceptual and motor inhibition of return: components or flavors?

Inhibition of return in a 3D scene depends on the direction of depth switch between cue and target

Inhibition of return (IOR) is a phenomenon that reflects slower target detection when the target appears at a previously cued rather than uncued location. In the present study, we investigated the extent to which IOR occurs in three-dimensional (3D) scenes comprising pictorial depth information. Peripheral cues and targets appeared on top of 3D rectangular boxes placed on the surface of a textured ground plane in virtual space. When the target appeared at a farther location than the cue, the magnitude of the IOR effect in the 3D condition remained similar to the values found in the two-dimensional (2D) control condition (IOR was depth-blind). When the target appeared at a nearer location than the cue, the magnitude of the IOR effect was significantly attenuated (IOR was depth-specific). The present findings address inconsistencies in the literature on the effect of depth on IOR and support the notion that visuospatial attention exhibits a near-space advantage even in 3D scenes consisting entirely of pictorial depth information.

Fixation offset decreases manual inhibition of return (IOR) in detection and discrimination tasks

Attention can be covertly shifted to peripheral stimuli to improve their processing. However, attention is also then inhibited against returning to the previously attended location; thus, both detection and discrimination of a stimulus presented at that location decrease (the inhibition of return [IOR] effect). The after-effect of the covert orienting hypothesis postulates a close link between attention shifting, IOR, and oculomotor control. The fixation offset, which improves the generation of saccades, decreases IOR in detection tasks, suggesting a close link between IOR and oculomotor control. However, according to some alternative views (e.g., the input-based IOR hypothesis and the object files segregation/integration hypothesis), IOR may be related to some sensory rather than motor processes. Some studies support that view and show that IOR may occur differently in detection and discrimination tasks and that oculomotor processes do not affect IOR in tasks where manual responses are required and eye movements are suppressed. Two experiments presented in this article show that removing the fixation point decreases manual IOR in detection and discrimination tasks. The results are discussed in terms of various theoretical approaches.

Foot cues can elicit covert orienting of attention

Humans tend to orient their attentional resources towards the same location indicated by spatial signals coming from the others, such as pointing fingers, head turns, or eye-gaze. Here, two experiments investigated whether an attentional orienting response can be elicited even by foot cues. Participants were asked to localize a peripheral target while a task-irrelevant picture of a naked human foot, oriented leftward or rightward, was presented on the centre of the screen. The foot appeared in a neutral posture (i.e., standing upright) or an action-oriented posture (i.e., walking/running). In Experiment 1, neutral and action-oriented feet were presented in two distinct blocks, while in Experiment 2 they were presented intermixed. The results showed that the action-oriented foot, but not the neutral one, elicited an orienting response, though this only emerged in Experiment 2. This work suggests that attentional shifts can be induced by action-oriented foot cues, as long as these stimuli are made contextually salient.

Using Speed and Accuracy and the Simon Effect to Explore the Output Form of Inhibition of Return

Inhibition of return (IOR) refers to slower responses to targets presented at previously cued locations. Contrasting target discrimination performance over various eye movement conditions has shown the level of activation of the reflexive oculomotor system determines the nature of the effect. Notably, an inhibitory effect of a cue nearer to the input end of the processing continuum is observed when the reflexive oculomotor system is actively suppressed, and an inhibitory effect nearer the output end of the processing continuum is observed when the reflexive oculomotor system is actively engaged. Furthermore, these two forms of IOR interact differently with the Simon effect. Drift diffusion modeling has suggested that two parameters can theoretically account for the speed-accuracy tradeoff rendered by the output-based form of IOR: increased threshold and decreased trial noise. In Experiment 1, we demonstrate that the threshold parameter best accounts for the output-based form of IOR by measuring it with intermixed discrimination and localization targets. Experiment 2 employed the response-signal methodology and showed that the output-based form has no effect on the accrual of information about the target's identity. These results converge with the response bias account for the output form of IOR.

Multisensory integration attenuates visually induced oculomotor inhibition of return

Inhibition of return (IOR) is a mechanism of the attention system involving bias toward novel stimuli and delayed generation of responses to targets at previously attended locations. According to the two-component theory, IOR consists of a perceptual component and an oculomotor component (oculomotor IOR [O-IOR]) depending on whether the eye movement system is activated. Previous studies have shown that multisensory integration weakens IOR when paying attention to both visual and auditory modalities. However, it remains unclear whether the O-IOR effect attenuated by multisensory integration also occurs when the oculomotor system is activated. Here, using two eye movement experiments, we investigated the effect of multisensory integration on O-IOR using the exogenous spatial cueing paradigm. In Experiment 1, we found a greater visual O-IOR effect compared with audiovisual and auditory O-IOR in divided modality attention. The relative multisensory response enhancement (rMRE) and violations of Miller's bound showed a greater magnitude of multisensory integration in the cued location compared with the uncued location. In Experiment 2, the magnitude of the audiovisual O-IOR effect was significantly less than that of the visual O-IOR in single visual modality selective attention. Implications for the effect of multisensory integration on O-IOR were discussed under conditions of oculomotor system activation, shedding new light on the two-component theory of IOR.

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.

Is the premotor theory of attention essentially about pre-reflective intentionality?

The Premotor Theory of Attention (PToA) is a prominent, albeit controversial, modern experimental account of attentional processes. According to the PToA, motor preparation is both necessary and sufficient for spatial attention. Explaining the cognitive process of attention in terms of sensori-motor machinery can be considered as embedded in the idea of embodied cognition. The vocabulary adopted by the PToA seems to bear a particular resemblance to Merleau-Ponty’s phenomenological notion of pre-reflective intentionality. He articulates it by means of directness towards the lived world, which is constituted in the spatial motility of the body-subject. In this epistemological state of affairs, we come up with two leading questions: (a) can the main tenets of PToA be essentially reconstructed in terms of the notion of pre-reflective intentionality and since the bodily motility is meant by the French phenomenologist to be at the root of all forms of intentionality, (b) can the PToA be expanded to account for all kinds of attention? In conclusion, we advocate a positive answer for the former question and point to serious doubts as to why it can rather not be retained regarding the latter.

Examining the Role of Attention and Sensory Stimulation in the Attentional Repulsion Effect

It has been suggested that visual attention warps space, such that stimuli appearing near its locus are perceived as farther away than they actually are. This is known as the attentional repulsion effect (ARE). Recent data challenge the role of attention as the sole factor responsible for the ARE, suggesting instead that the ARE is, at least in part, a product of low level sensory interactions between a peripheral orienting cue and the Vernier target stimulus used to measure the effect. Here, we directly test whether attentional orienting, without a cue in peripheral vision to guide attention, is sufficient for generating an ARE. In Experiment 1, attention was guided to the visual periphery by a central symbolic cue that reliably indicated the locations of to-be-identified targets in peripheral vision. On a subset of trials, we probed for an ARE with Vernier targets. Reaction time (RT) data revealed that the cue guided attention but there was no trace of an ARE. In Experiment 2, we ensured that the Vernier targets were sensitive to the ARE by using the standard spatially uninformative peripheral cue to guide attention instead of the central symbolic cue. RT data again revealed that the cue guided attention, while the Vernier targets revealed an ARE. Collectively, these data suggest that attentional orienting without peripheral sensory stimulation is not sufficient for generating an ARE.

Electrophysiological Correlates of the Effect of Task Difficulty on Inhibition of Return

Inhibition of return (IOR) refers to slower responses to targets that occur at a previously attended location than to those at control locations. Previous studies on the impact of task difficulty on IOR have shown conflicting results. However, these studies failed to match low-level characteristics of stimuli (e.g., size, color, and luminance) across difficulty levels, and so might have confounded the effect of task difficulty with that of stimulus characteristics. Hence, whether and how task difficulty modulates IOR remain largely unknown. This study utilized the event-related potentials (ERPs) technique in combination with a cue-target paradigm to tackle this question. Task difficulty was manipulated by changing the position of a gap in a rectangle stimulus, while stimulus size, color, and luminance were precisely matched. IOR was observed in reaction times across all difficulty levels but was found in accuracy at the medium level only. The modulation effect of task difficulty on IOR was also evident in the N1 and P2 ERP components, which showed significantly weaker IOR effects at the medium difficulty level than at the easy and hard levels. It is suggested that the modulation of IOR by task difficulty involves both perceptual and post-perceptual processes.

Using Rescorla's truly random control condition to measure truly exogenous covert orienting

Studies of exogenous covert orienting use peripheral cues (stimuli) that are spatially uninformative about the locations of subsequent targets. When the time course of the cue's influence on performance is explored (by varying the cue target onset asynchrony; CTOA), a biphasic pattern is usually seen with better performance at the cued location when the CTOA is short (typically attributed to attentional capture) and worse performance at the cued location when the CTOA is long (attributed to inhibition of return). However, while spatially uninformative, these cues (even when a nonaging foreperiod is used) entail a temporal contingency with the subsequent target. Consequently, this so-called capture may reflect an unintended consequence of endogenous allocation of temporal attention. Following Lawrence and Klein (Journal of Experimental Psychology: General, 142(2), 560-572, 2013) we used Rescorla's (Psychological Review, 74, 71-80, 1967) truly random control condition to ensure that the spatially uninformative peripheral stimuli were temporally completely uninformative. Even such completely uninformative peripheral stimuli generated the prototypical biphasic pattern.

Dissociating Orienting Biases From Integration Effects With Eye Movements

Despite decades of research, the conditions under which shifts of attention to prior target locations are facilitated or inhibited remain unknown. This ambiguity is a product of the popular feature discrimination task, in which attentional bias is commonly inferred from the efficiency by which a stimulus feature is discriminated after its location has been repeated or changed. Problematically, these tasks lead to integration effects; effects of target-location repetition appear to depend entirely on whether the target feature or response also repeats, allowing for several possible inferences about orienting bias. To parcel out integration effects and orienting biases, we designed the present experiments to require localized eye movements and manual discrimination responses to serially presented targets with randomly repeating locations. Eye movements revealed consistent biases away from prior target locations. Manual discrimination responses revealed integration effects. These data collectively revealed inhibited reorienting and integration effects, which resolve the ambiguity and reconcile episodic integration and attentional orienting accounts.

Placeholders dissociate two forms of inhibition of return

Decades of research using Posner's classic spatial cueing paradigm has uncovered at least two forms of inhibition of return (IOR) in the aftermath of an exogenous, peripheral orienting cue. One prominent dissociation concerns the role of covert and overt orienting in generating IOR effects that relate to perception- and action-oriented processes, respectively. Another prominent dissociation concerns the role of covert and overt orienting in generating IOR effects that depend on object- and space-based representation, respectively. Our objective was to evaluate whether these dichotomies are functionally equivalent by manipulating placeholder object presence in the cueing paradigm. By discouraging eye movements throughout, Experiments 1A and 1B validated a perception-oriented form of IOR that depended critically on placeholders. Experiment 2A demonstrated that IOR was robust without placeholders when eye movements went to the cue and back to fixation before the manual response target. In Experiment 2B, we replicated Experiment 2A's procedures except we discouraged eye movements. IOR was observed, albeit only weakly and significantly diminished relative to when eye movements were involved. We conclude that action-oriented IOR is robust against placeholders but that the magnitude of perception-oriented IOR is critically sensitive to placeholder presence when unwanted oculomotor activity can be ruled out.

Peripheral stimuli generate different forms of inhibition of return when participants make prosaccades versus antisaccades to them

Inhibition of return (IOR) is usually viewed as an inhibitory aftermath of visual orienting typically seen in the form of slower responses to targets presented in a previously oriented to location. As shown by Taylor and Klein (2000. Journal of Experimental Psychology: Human Perception and Performance, 26, 1639-1656), the nature of the inhibitory effects resulting from an uninformative cue seem to be contingent on the activation state of the oculomotor system. Here we contrast target discrimination performance following either a prosaccade or antisaccade in the spatial cueing paradigm. Our findings suggest that the level of activation of the reflexive oculomotor system determines the dynamics of the inhibitory effect, wherein an effect nearer to the input end of processing is observed when the reflexive oculomotor system is actively suppressed, and an effect nearer to the output end of processing is observed when the reflexive oculomotor system is actively engaged. These effects interact differently with the Simon effect-providing converging evidence that they are dissociable inhibitory phenomena.

The Time Course of Inhibition of Return: Evidence from Steady-State Visual Evoked Potentials

Inhibition of return (IOR) refers to slower responses to targets at a previously cued location than that at an uncued location. The time course of IOR has long been a topic of interest in the field. Investigations into the time course of IOR are typically performed by examining the magnitude of IOR under various cue-target onset asynchrony (CTOA) conditions. Therefore, the results are vulnerable to influence of factors that could affect the target processes (e.g., the frequency of the target type). In the present study, steady-state visual evoked potentials (SSVEPs) were implemented to directly take a continuous measurement of the degree to which cued location is processed, eliminating the influence mentioned above. The results indicate that, relative to the baseline interval (−400 to 0 ms), the presence of peripheral cues generated a typical two-stage effect on the SSVEP amplitude evoked by a 20 Hz flicker. Specifically, after the onset of the peripheral cues, the SSVEP amplitude first showed a significant increase, which subsequently turned into a significant inhibition effect after 200 ms. These results provide a continuous time course diagram of the cueing effect and suggest an effective way for future investigations of controlling the masking effects of target stimuli processing on IOR.

Memory instruction interacts with both visual and motoric inhibition of return

In the item-method directed forgetting paradigm, the magnitude of inhibition of return (IOR) is larger after an instruction to forget (F) than after an instruction to remember (R). In the present experiments, we further investigated this increased magnitude of IOR after F than after R memory instructions, to determine whether this F > R IOR pattern occurs only for the motoric form of IOR, as predicted, or also for the visual form. In three experiments, words were presented in one of two peripheral locations, followed by either an F or an R memory instruction. Then, a target appeared either at the same location as the previous word or at the other location. In Experiment 1, participants maintained fixation throughout the trial until the target appeared, at which point they made a saccade to the target. In Experiment 2, they maintained fixation throughout the entire trial and made a manual localization response to the target. The F > R IOR difference in reaction times occurred for both the saccadic and manual responses, suggesting that memory instructions modify both motoric and visual forms of IOR. In Experiment 3, participants made a perceptual discrimination response to report the identity of a target while the eyes remained fixed. The F > R IOR difference also occurred for these manual discrimination responses, increasing our confidence that memory instructions modify the visual form of IOR. We relate our findings to postulated differences in attentional withdrawal following F and R instructions and consider the implications of the findings for successful forgetting.

Spatial interactions between consecutive manual responses

We have shown that the latency to initiate a reaching movement is increased if its direction is the same as a previous movement compared to movements that differ by 90° or 180° (Cowper-Smith and Westwood in Atten Percept Psychophys 75:1914-1922, 2013). An influential study (Taylor and Klein in J Exp Psychol Hum Percept Perform 26:1639-1656, 2000), however, reported the opposite spatial pattern for manual keypress responses: repeated responses on the same side had reduced reaction time compared to responses on opposite sides. In order to determine whether there are fundamental differences in the patterns of spatial interactions between button-pressing responses and reaching movements, we compared both types of manual responses using common methods. Reaching movements and manual keypress responses were performed in separate blocks of trials using consecutive central arrow stimuli that directed participants to respond to left or right targets. Reaction times were greater for manual responses made to the same target as a previous response (M = 390 ms) as compared to the opposite target (M = 365 ms; similarity main effect: p < 0.001) regardless of whether the response was a reaching movement or a keypress response. This finding is broadly consistent with an inhibitory mechanism operating at the level of motor output that discourages movements that achieve the same spatial goal as a recent action.

In search of a reliable electrophysiological marker of oculomotor inhibition of return

Inhibition of return (IOR) operationalizes a behavioral phenomenon characterized by slower responding to cued, relative to uncued, targets. Two independent forms of IOR have been theorized: input-based IOR occurs when the oculomotor system is quiescent, while output-based IOR occurs when the oculomotor system is engaged. EEG studies forbidding eye movements have demonstrated that reductions of target-elicited P1 components are correlated with IOR magnitude, but when eye movements occur, P1 effects bear no relationship to behavior. We expand on this work by adapting the cueing paradigm and recording event-related potentials: IOR is caused by oculomotor responses to central arrows or peripheral onsets and measured by key presses to peripheral targets. Behavioral IOR is observed in both conditions, but P1 reductions are absent in the central arrow condition. By contrast, arrow and peripheral cues enhance Nd, especially over contralateral electrode sites.

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.

On the nature of the delayed "inhibitory" cueing effects generated by uninformative arrows at fixation

When the interval between a spatially uninformative arrow and a visual target is short (<500 ms), response times (RTs) are fastest when the arrow points to the target. When this interval exceeds 500 ms, there is a near-universal absence of an effect of the arrow on RTs. Contrary to this expected pattern of results, Taylor and Klein (J Exp Psychol Hum Percept Perform 26:1639-1656, 2000) observed that RTs were slowest when a to-be-localized visual target occurred in the direction of a fixated arrow presented 1 s earlier (i.e., an "inhibitory" Cueing effect; ICE). Here we examined which factor(s) may have allowed the arrow to generate an ICE. Our experiments indicated that the ICE was a side effect of subthreshold response activation attributable to a task-induced association between the arrow and a keypress response. Because the cause of this ICE was more closely related to subthreshold keypress activation than to oculomotor activation, we considered that the effect might be more similar to the negative compatibility effect (NCE) than to inhibition of return (IOR). This similarity raises the possibility that classical IOR, when caused by a spatially uninformative peripheral onset event and measured by a keypress response to a subsequent onset, might represent, in part, another instance of an NCE. Serendipitously, we discovered that context (i.e., whether an uninformative peripheral onset could occur at the time of an uninformative central arrow) ultimately determined whether the "inhibitory" aftermath of automatic response activation would affect output or input pathways.