Inhibition of return and the human frontal eye fields

Microsaccadic response during inhibition of return in a target–target paradigm

This study examined the relationship between inhibition of return (IOR) in covert orienting and microsaccade statistics. Unlike a previous study [Galfano, G., Betta, E., & Turatto, M. (2004)], IOR was assessed by means of a target-target paradigm, and microsaccade dynamics were monitored as a function of both the first and the second visual event. In line with what has been reported with a cue-target paradigm, a significant directional modulation was observed opposite to the first visual event. Because participants were to respond to any stimulus, this rules out the possibility that the modulation resulted from a generic motor inhibition, showing instead that it is peculiarly coupled to the oculomotor system. Importantly, after the second visual event, a different response was observed in microsaccade orientation, whose direction critically depended of whether the second visual event appeared at the same location as the first visual event. The results are consistent with the notion that IOR is composed of both attentional and oculomotor components, and challenge the view that covert orienting paradigms engage the attentional component in isolation.

Modulation of saccadic intrusions by exogenous and endogenous attention

Primary gaze fixation in healthy individuals is frequently interrupted by microsaccades and saccadic intrusions (SI). The neural systems responsible for the control of attention and eye movements are believed to overlap and in line with this, the behaviour of microsaccades appears to be affected by exogenous and endogenous attention shifts. In the current work we wished to establish whether SI would also be influenced by attention in order to provide evidence that SI and microsaccades exhibit similar behaviour and further investigate the extent of overlap between attention and eye movement systems. Twelve participants performed a cue-target task where they were cued exogenously or endogenously and had to respond to the appearance of a peripheral target with either a button press or saccade. Our results replicate earlier microsaccade research, indicating that SI are also influenced by exogenous and endogenous attention. In all conditions, SI frequency initially decreased following the cue, then rose to a maximum before falling to below baseline levels. Following the exogenous cue, SI were more frequently directed away from the cue as predicted by inhibition of return. Additionally, SI direction following the endogenous cue was biased towards the cue for the saccadic response mode only, suggesting that the degree to which the eye movement and attention systems overlap depends on whether an eye movement is required. In summary, our findings indicate that SI characteristics are modulated by exogenous and endogenous attention and in a similar way to microsaccades, suggesting that SI and microsaccades may lie on a continuum of fixational instabilities. Furthermore, as with microsaccades, SI are likely to provide additional insights into the relationship between attention and the oculomotor systems.

The effect of age on inhibition of return is independent of non-ocular response inhibition

Inhibition of return (IOR) refers to the slowing of a response to a target stimulus presented in the same location as a previous stimulus. Increased IOR has been observed in older adults, despite a reduction in other 'inhibitory' processes. However, cue-target tasks have been used in all previous studies and because of this, IOR may have been overestimated due to non-ocular response inhibition associated with withholding a response from the cue. Could increased levels of response inhibition account for the observations of increased IOR in older adults? This confound can be circumvented by using a target-target paradigm, in which a response is made to all stimuli. We tested three groups of 24 subjects: young (mean 22.5 years), young-old (mean 61.9 years) and old-old (mean 74.8 years). Subjects completed both visual cue-target and target-target tasks with identical inter-stimulus intervals of 1400 and 1800ms. IOR magnitude increased with age in both the cue-target task and the target-target task. Furthermore, the magnitude of visual IOR was found to increase with age even when individual differences in baseline response speed were taken into account. Thus, there appears to be a genuine increase in IOR magnitude with age.

The role of the basal ganglia in the control of automatic visuospatial attention

Cognitive impairments in patients with basal ganglia dysfunction are primarily revealed where performance relies on internal, voluntary control processes. Evidence suggests that this also extends to impaired control of more automatic processes, including visuospatial attention. The present study used a non-predictive peripheral cueing paradigm to compare and contrast visuospatial deficits in patients with Parkinson's disease (PD) with those previously revealed in patients with Huntington's disease (HD) (Fielding et al., 2006a). Compared to age-matched controls, both PD and HD patients exhibited increased distractibility or poor fixation, however only PD patients responded erroneously to cue stimuli more frequently than control subjects. All subjects demonstrated initial facilitation for valid versus invalid cues following the shorter stimulus-onset asynchronies (SOAs) and a performance decrement at the longer SOAs (inhibition of return), although there was a clear differentiation between these groups for immediate SOAs. Unlike both control and PD subjects, where IOR manifested between 350 and 1000 msec, IOR was evident as early as 150 msec for HD patients. Further, for PD patients, spatially valid cues resulted in hyper-reflexivity following 150 msec SOAs, with saccadic latencies shorter than those generated in response to un-cued targets. Thus contrasting deficits were revealed in PD and HD, emphasizing the important contribution of the basal ganglia in the control of more automatic behaviors

Disruption of reflexive attention and eye movements in an individual with a collicular lesion

The superior colliculus (SC) plays a central role in the control of saccadic eye movements and has also been implicated in control of covert spatial attention. While there is a growing body of evidence from studies of awake behaving primates that supports these proposals, direct evidence from humans has been sparse. In the present study we tested a patient with thiamine deficiency and a lesion of the SC, who performed both eye movement tasks (prosaccades and antisaccades, with or without a gap) and a covert spatial attention task assessing inhibition of return (IOR). For eye movements, the gap effect was disrupted, and abnormal saccade metrics occurred, with reflexive eye movements being disrupted moreso than voluntary eye movements. Each of these effects resolved coincident with thiamine treatment. The covert attention task revealed a complete absence of IOR. The unequal disruption of voluntary and reflexive eye movements supports the idea that oculomotor responses can be generated in an independent fashion by frontal cortical and lower level neural systems. The role of the SC and other structures in these orienting processes is discussed.

An event-related functional magnetic resonance imaging study of voluntary and stimulus-driven orienting of attention

Attention can be voluntarily directed to a location or automatically summoned to a location by a salient stimulus. We compared the effects of voluntary and stimulus-driven shifts of spatial attention on the blood oxygenation level-dependent signal in humans, using a method that separated preparatory activity related to the initial shift of attention from the subsequent activity caused by target presentation. Voluntary shifts produced greater preparatory activity than stimulus-driven shifts in the frontal eye field (FEF) and intraparietal sulcus, core regions of the dorsal frontoparietal attention network, demonstrating their special role in the voluntary control of attention. Stimulus-driven attentional shifts to salient color singletons recruited occipitotemporal regions, sensitive to color information and part of the dorsal network, including the FEF, suggesting a partly overlapping circuit for endogenous and exogenous orienting. The right temporoparietal junction (TPJ), a core region of the ventral frontoparietal attention network, was strongly modulated by stimulus-driven attentional shifts to behaviorally relevant stimuli, such as targets at unattended locations. However, the TPJ did not respond to salient, task-irrelevant color singletons, indicating that behavioral relevance is critical for TPJ modulation during stimulus-driven orienting. Finally, both ventral and dorsal regions were modulated during reorienting but significantly only by reorienting after voluntary shifts, suggesting the importance of a mismatch between expectation and sensory input.

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.

Selective visual attention and perceptual coherence

Conscious perception of the visual world depends on neural activity at all levels of the visual system from the retina to regions of parietal and frontal cortex. Neurons in early visual areas have small spatial receptive fields (RFs) and code basic image features; neurons in later areas have large RFs and code abstract features such as behavioral relevance. This hierarchical organization presents challenges to perception: objects compete when they are presented in a single RF, and component object features are coded by anatomically distributed neuronal activity. Recent research has shown that selective attention coordinates the activity of neurons to resolve competition and link distributed object representations. We refer to this ensemble activity as a "coherence field", and propose that voluntary shifts of attention are initiated by a transient control signal that "nudges" the visual system from one coherent state to another.

d-Amphetamine-induced enhancement of inhibitory mechanisms involved in visual search

The authors examined the effects of d-amphetamine on the ability to perform a cued target-detection task that measured inhibition of return (IOR). IOR is a reflexive inhibitory mechanism that delays attention from returning to a previously attended location and has been shown to increase the efficiency of a visual search. Adults (N=14) with a history of cocaine use performed the task under 4 doses of d-amphetamine (0, 10, 20, and 30 mg). The results showed active d-amphetamine doses increased the duration of IOR. By increasing the delay in returning attention to a previously attended location, d-amphetamine might reduce time spent searching previously attended locations, increasing the efficiency of visual searches.

Modulation of antisaccades by transcranial magnetic stimulation of the human frontal eye field

It has been suggested that the frontal eye field (FEF), which is involved with the inhibition and generation of saccades, is engaged to a different degree in pro- and antisaccades. Pro- and antisaccades are often assessed in separate experimental blocks. In such cases, saccade inhibition is required for antisaccades but not for prosaccades. To more directly assess the role of the FEF in saccade inhibition and generation, a new paradigm was used in which inhibition was necessary on pro- and antisaccade trials. Participants looked in the direction indicated by a target ('<' or '>') that appeared in the left or right visual field. When the pointing direction and the location were congruent, prosaccades were executed; otherwise antisaccades were required. Saccadic latencies were measured in blocks without and with single pulse transcranial magnetic stimulation (TMS) to the right FEF or a right posterior control site. Results showed that antisaccades generated into the hemifield ipsilateral to the TMS were significantly delayed after TMS over the FEF, but not the posterior control site. This result is interpreted in terms of a modulation of saccade inhibition to the contralateral visual field due to disruption of processing in the FEF.

Transcranial magnetic stimulation of the left human frontal eye fields eliminates the cost of invalid endogenous cues

Humans are able to selectively attend to specific regions of space without moving their eyes. However, there is mounting evidence that these covert shifts of attention may employ many of the same brain regions involved when executing the eye movements. For example, functional magnetic resonance imaging (fMRI) studies show that the oculomotor region known as the frontal eye fields (FEF) are activated by the covert shifts of attention. However, it remains possible that the activations seen in these studies result from actively inhibiting eye movements rather than as a direct result of modulating perceptual processing. Here we provide direct evidence for the role of this region in endogenously driven spatial attention. We show that briefly disrupting the left FEFs with transcranial magnetic stimulation (TMS) eliminated the slow response times associated with the invalid strategic cues when the target appeared in the right visual field. At first glance, our findings appear incompatible with the results reported by Grosbras and Paus (Grosbras, M. -H., & Paus, T. (2002). Transcranial magnetic stimulation of the human frontal eye field: effects on visual perception and attention. Journal of Cognitive Neuroscience, 14(7), 1109--1120) and we suggest this is likely due to the design differences. Specifically, we disrupted the FEF at the time of cue onset, rather than target onset. Taken together with the findings of Grosbras and Paus, our findings suggest that the FEF plays an early role in the inhibition of perceptual information. Furthermore, our findings complement work by Ro et al. (Ro, T., Farne, F., & Chang, E. (2003). Inhibition of return and the frontal eye fields. Experimental Brain Research, 150, 290--296) who report that stimulation of the frontal eye fields disrupts the inhibitory consequences of reflexive attention shifts.

Single-pulse transcranial magnetic stimulation over the frontal eye field can facilitate and inhibit saccade triggering

The aim of this study was to investigate the effect of single-pulse transcranial magnetic stimulation on the triggering of saccades. The right frontal eye field was stimulated during modified gap and overlap paradigms with flashed presentation of the lateral visual target of 80 ms. In order to examine possible facilitating or inhibitory effects on saccade triggering, three different time intervals of stimulation were chosen, i.e. simultaneously with onset of the target, during the presentation and after target end. Stimulation applied simultaneously with target onset significantly decreased the latency of contralateral saccades in the gap but not in the overlap paradigm. Stimulation after target end significantly increased saccade latency for both sides in the gap paradigm and for the contralateral side in the overlap paradigm. Stimulation during presentation had no effect in either paradigm. The results show that, depending on the time interval and the paradigm tested, a facilitation or inhibition of saccade triggering can be achieved. The results are discussed in a context of two probable transcranial magnetic stimulation effects, a direct interference with the frontal eye field on the one hand and a remote interference with the superior colliculus on the other hand.

The brain circuitry of attention

From an operational perspective, attention is a matter of organizing multiple brain centres to act in concert on the task at hand. Taking focal visual attention as an example, recent anatomical findings suggest that the pulvinar might act as a remote hub for coordinating spatial activity within multiple cortical visual maps. The pulvinar can, in turn, be influenced by signals originating in the frontal and parietal eye fields, using common visuomotor neural circuitry, with the superior colliculus acting as an important link. By identifying a complex, real neural architecture ('RNA') model for attention, it is possible to integrate several different modes of operation - such as parallel or serial, bottom-up or top-down, preattentive or attentive - that characterize conflicting cognitive models of attention in visual search paradigms.

An event-related fMRI study of exogenous orienting: supporting evidence for the cortical basis of inhibition of return?

This event-related fMRI experiment examined the neural substrates of exogenous visuospatial attention. Exogenous attention produces a biphasic response pattern denoted by facilitation at short cue-target intervals and inhibition of return (IOR) at longer intervals. Whereas the volitional orienting of attention has been well described in the literature, the neural systems that support exogenous facilitation and IOR in humans are relatively unknown. In direct comparisons to valid facilitation trials, valid IOR trials produced unique foci of activation in the right posterior parietal, superior temporal, middle temporal, middle occipital, anterior cingulate, and dorsal medial thalamic areas. Valid IOR trials also resulted in activation of motor exploratory and frontal areas previously associated with inhibition and oculomotor control. In contrast, invalid IOR compared to facilitation trials only activated anterior cortical structures. These results provide support for both attentional and oculomotor theories of IOR and suggest that IOR may be mediated by two networks. One network may mediate the inhibitory bias following an exogenous cue, whereas a separate network may be activated when a response must be made to stimuli that appear in inhibited locations of space.

Alcohol-induced impairment of inhibitory mechanisms involved in visual search

The present study examined the effects of alcohol on the ability to perform a cued target detection task that measured inhibition of return (IOR). IOR is a reflexive inhibitory mechanism that delays attention from returning to a previously attended location and has been shown to increase the efficiency of a visual search. Ten social drinkers performed the task under 3 alcohol doses: 0.0 g/kg (placebo), 0.45 g/kg, and 0.65 g/kg. The results showed both active alcohol doses reduced the IOR effect by shortening its duration of influence. The reduced duration of IOR under alcohol suggests that repeated searches in previously explored locations might be more likely under the drug, thereby reducing search efficiency.