inhibitory influence from prior information at the same spatial location. It appears that the basic sensory effect is to favor a novel or previously quiet channel of stimulation rather than to favor the channel that is more probable or biased for selection. If this account is correct, it leaves the problem of selection for higher level processes that depend upon active orienting to the selected channel. Such an active orienting would be best maintained if the subject is continually processing events and might even be enhanced when the discriminability of events makes it quite difficult to distinguish targets from noise on the attended channel as would happen with high rates of input.
We believe that our results with trial-by-trial cueing ( Posner & Cohen, in press) taken together with findings with clinical patients and alert animals have provided a start toward a fundamental understanding of the way in which phasic orienting based on central and peripheral cues is achieved by the nervous system. While the current experiments do not add too much to our understanding of the mechanisms, they do provide evidence that they are involved in a fundamental way in sustained concentration at least to visual signals. If this is the case, we may be able to provide a better basis for an understanding of sustained concentration through basic studies of the properties of visual orienting.
This work was supported in part by a grant from the National Science Foundation (BNS-7923527) and the Sloan Foundation to the University of Oregon. The work on divided attention was carried out while Dr. Hockey held a travel fellowship and was in residence at the University of Oregon, Eugene.
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