Search

In the early 1980's independent research streams were launched by two of the 20th century's leading attention researchers. Anne Treisman's research program is best-known for distinguishing empirically between serial and pop-out search and for proposing feature integration theory and the idea of an attentional operator, that sequentially inspects items or groups of items when search is difficult. Among his many contributions to psychological science, Michael Posner is well-known for pioneering simple model tasks that made the allocation of visual attention in space amenable to scientific inquiry. When one version of the Posner cuing paradigm was used to explore visuospatial orienting it was serendipitously discovered that an “inhibitory” effect occurred in the aftermath of events that captured visuospatial attention involuntarily. This “inhibitory” phenomenon became known as Inhibition of Return (IOR), and, as implied by its name, the underlying mechanisms were thought to bias attention away from previously explored places. These two research programs were linked in 1988 when Raymond Klein exploited the distinction between pop-out and serial search to test and verify Posner's proposal that this inhibition might be a novelty seeking mechanism that could improve search efficiency. Subsequent research has identified at least two different inhibitory mechanisms that bias attention toward novelty. We present evidence using several diagnostics (central vs. peripheral targets, joint consideration of speed and accuracy, and the locus of slack logic embedded in the psychological refractory period effect) to illustrate the dual natures of IOR. The input form operates on a salience map that influences what will capture our attention, while the output form operates on a priority map that influences what behaviors (including orienting) are likely to be executed. The input form is generated when the reflexive oculomotor system is suppressed while the output form is generated when this system is not suppressed. We believe that both forms of IOR can serve the novelty seeking (and search facilitating) function proposed by Posner and others. Yet, many questions remain unanswered. Some of the many remaining puzzles will be described and we hope that our review will stimulate research to solve them.

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.

Attention, the recruitment of processing resources, is viewed as pivotal for understanding normal behaviour and thought as well as the disorganizations associated with brain damage and disease. A brief history foreshadows aspects of a proposed taxonomy of attention that builds upon Posner's tripartite taxonomy. Posner's influential taxonomy views attention as a set of isolable neural systems (alerting, orienting and executive control), often working together to organize behaviour. For measuring the efficacy of these three networks, Posner and colleagues created the Attention Network Test (ANT). The impact of the taxonomy and this model task for exploring it is illustrated by the facts that they have spawned numerous variants designed for different purposes and that one or another variant has been used in almost a thousand publications. We have previously built upon this conceptual framework by considering: two modes of control over resource allocation which we labelled exogenous and endogenous and three domains over which these modes of control are presumed to operate (space, time and task or activity). The Combined Attention Systems Test (or CAST) was developed to measure the efficacy of the six kinds of attention implied by revised taxonomy. Lastly, this taxonomic effort is further developed by incorporating the distinction between overt, observable behaviour in the "real" world and covert "behaviour" in the realm of thought and imagination.