Janice J. Snyder

Inhibition of return to successively stimulated locations in a sequential visual search paradigm.

The inhibition of return (IOR) effect refers to a slowing in response time for a target that appears at a previously attended location. Many investigators have speculated that IORs inherent ecological validity may be to ensure an efficient search of a complex environment by creating a bias against returning to locations that have already been investigated. Unfortunately, this intriguing idea has lacked compelling empirical support. The current study addressed this issue. It was shown that in a novel visual search task, the IOR could dwell at a minimum of 3 spatially noncontiguous locations. These data suggest that IOR may serve as an important mechanism for facilitating visual search in complex environments, by inhibiting attention from returning to previously inspected locations.

Inhibition of return and visual search: How many separate loci are inhibited?

Using a novel sequential visual search paradigm Danziger, Kingstone, and Snyder (1998) demon-strated that inhibition of return (IOR) can reside at three spatial locations. In the present study, we extended the work of Danziger et al. by investigating whether there is a limit to the number of locations that can be inhibited in a sequential visual search task. Our study revealed that IOR can be measured at a minimum of five locations. The magnitude of the IOR effect was largest at the most recently searched location and declined from there in an approximately linear fashion. Two models that can account for our data are presented.

Attentional momentum does not underlie the inhibition of return effect.

J. Pratt, T. M. Spalek, and F. Bradshaw (1999) recently proposed that attentional momentum is the mechanism underlying the inhibition of return (IOR) effect. They suggested that momentum associated with an attentional movement away from a peripherally cued location and toward an uncued opposite location is essential and fundamental to the finding of an IOR effect. Although it is clear from the present study and from a reanalysis of data from Pratt et al. that response time can be facilitated at an uncued opposite location, this putative effect of attentional momentum is neither robust nor reliable. First, it occurs for only a minority of participants. Second, it occurs in only a subset of the cued display positions. And finally, it is uncorrelated with the occurrence of IOR. Together the data indicate that the attentional momentum hypothesis is an overgeneralization and that it does not underlie the robust and reliable IOR effect.

Spatial-temporal anisometries following right parietal damage

Patients with right parietal damage often have a lateralized deficit of spatial attention. In addition to a spatial deficit, such patients have also been reported to have a non-spatial deficit in temporal processing. Here, we tested the hypothesis that these spatial and temporal deficits might be linked if the right temporal-parietal cortex is important in integrating spatial and temporal attention. In AF, a patient with an acute right temporal-parietal stroke, we replicated previous observations showing that he was biased to judge ipsilesional stimuli as occurring before contralesional stimuli. More importantly, for vertically aligned stimuli, AF more accurately judged the temporal order of successive ipsilesional than contralesional stimuli. Furthermore, his contralesional performance improved with stimuli with larger vertical separations. Taken together, these findings provide additional evidence that right temporal-parietal damage produces a processing refractory period for stimuli in contralesional space that extends in both space and time. These findings are in agreement with other studies that suggest that the right temporal-parietal cortex is important in integrating the where and when of stimuli.

The Frontal Cortex and Exogenous Attentional Orienting

Normal functioning of the attentional orienting system is critical for effective behavior and is predicated on a balanced interaction between goal-directed (endogenous) processes and stimulus-driven (exogenous) processes. Although both systems have been subject to much investigation, little is known about the neural underpinnings of exogenous orienting. In the present study, we examined the early facilitatory effects and later inhibition of return effects of exogenous cues in patients with frontal and parietal lesions. Three novel findings emerged from this study. First, unilateral frontoparietal damage appears not to affect the early facilitation effects of exogenous cues. Second, dorsolateral prefrontal damage, especially lesions involving the inferior frontal gyrus, produces an exogenous disengage deficit (i.e., the sluggish withdrawal of attention from the ipsilesional to the contralesional field). Third, a subset of patients with dorsolateral prefrontal damage, with lesions involving the middle frontal gyrus, have a reorienting deficit that extends in duration well beyond established boundaries of the normal reflexive orienting system. These results suggest that the dorsolateral prefrontal cortex plays an important role in exogenous orienting and that component processes of this system may be differentially impaired by damage to different parts of the dorsolateral prefrontal cortex.

Inhibition of return at multiple locations in visual search: when you see it and when you don't.

Using a novel sequential task, Danziger, Kingstone, and Snyder (1998) provided conclusive evidence that inhibition of return (IOR) can co-occur at multiple non-contiguous locations. They argued that their findings depended crucially on the allocation of attention to cued locations. Specifically, they hypothesized that because subjects could not predict whether an onset event was a target or a non-target, all onset events had to be attended. As a result, non-targets were tagged with inhibition. The present study tested this hypothesis by manipulating whether target onset was predictable or not. In support of Danziger et al., three experiments revealed that multiple IOR was only observed when attention had to be directed to the cued locations. Interestingly, when attention did not need to be allocated to the cued locations, and multiple IOR was abolished, an IOR effect was still observed at the most recently cued location. Two possible accounts for this single IOR effect were presented for future investigation. One account attributes the effect to motor-based inhibition as hypothesized by Klein and Taylor (1994). The alternative account attributes the effect to weak attentional capture by a peripheral cue. Together the data support the view that multiple IOR is an attentional phenomenon and, as hypothesized by Tipper, Weaver, and Watson (1996), its presence or absence is largely under the control of the observer.

The effects of treatment for posterior fossa brain tumors on selective attention

We sought to identify whether deficits in selective attention are present in pediatric brain tumor patients. Selective attention was assessed with covert-orienting, filtering, and visual-search tasks in 54 patients with either (1) posterior fossa (PF) tumors treated with cranial radiation and surgery (n = 22); (2) PF tumors treated with surgery alone (n = 17); or (3) non-CNS tumors (n = 15), who served as a patient control group. To account for normal development, patient performance was also compared with that of healthy age-matched controls (n = 10). We found that in PF tumor patients selective attention was impaired, regardless of whether they were treated with cranial radiation and surgery or surgery alone. However, patients treated with cranial radiation were most impaired. These patients may have greater damage to posterior brain regions know to mediate selective attention as the result of tumor location, effects of surgery, and higher doses of radiation to the posterior regions of the brain. These findings help to elucidate the potential impact of pediatric brain tumors and their treatment on discrete attentional skills.

Inhibition of return at multiple locations and its impact on visual search

Previous research has shown that when attention is directed sequentially to multiple locations, inhibition of return (IOR) can be observed at each location, with a larger magnitude of IOR at the more recently attended locations. In the present study we asked whether this “multiple IOR” effect influences search only for simple feature targets, as has been shown in the past, or whether it generalizes to more complex, attentionally demanding conjunction search situations. The results demonstrated that IOR effects (1) occur for more complex conjunction search environments, (2) are larger for the attentionally demanding conjunction search, and (3) occur at more locations for conjunction search than feature search. Together these data provide a clear demonstration of the robustness and responsiveness of the IOR effect across search situations—which is precisely what is expected of a phenomenon posited to facilitate efficient visual search of real-world environments. Nevertheless, these data do not firmly establish that IOR effects established by the cueing paradigm before search is implemented are the same as the IOR effects that are assumed to be established during search itself. We suggest that this disconnection between paradigms highlights a fundamental limitation of laboratory-based research.

Inhibition of return: Unraveling a paradox

Although inhibition of return (IOR) is widely believed to aid search by discouraging reexamination of previously inspected locations, its impact actually appears to decline as the number of target locations increases. We test three possible reasons for this paradoxical result: (1) IOR is capacity-limited, (2) IOR is sensitive to subtle changes in target location probability, and (3) IOR decays with distance from a previously attended location. The present investigation provides strong support for the third explanation, indicating that a gradient of inhibition is centered on previously attended locations. We note that this inhibitory gradient resolves a paradox in the literature. Moreover, we speculate that the inhibitory gradient may reflect a “similarity space” within which target locations near to the cue are tagged with inhibition due to their similarity to the cued location. The farther the target location is away, the less similar it is to the cued location, and thus the less inhibition it receives.

Role of the lateral prefrontal cortex in visual object-based selective attention

We demonstrate that attention to object representations is vitally dependent on the prefrontal cortex. Object-based selective attention was compared in neurologic patients with unilateral damage to either the dorsolateral prefrontal cortex (DLPFC) or the parietal cortex and in healthy controls. Our task required a top–down attentional modulation of object representations in which spatial location played no role. All groups could invoke top–down object-based selection, but the DLPFC patients showed a selective deficit when target stimuli were in the hemifield contralateral to the lesioned hemisphere. Our findings indicate that in the healthy brain, anterior cortical mechanisms are crucial for attending to object-centered representations, whereas posterior cortical mechanisms are necessary for attending to objects at locations in the visual scene.