When a stimulus appears in a previously cued location several hundred milliseconds after the cue, the time required to detect that stimulus is greater than when it appears in an uncued location. This increase in detection time is known as inhibition of return (lOR). It has been suggested that lOR reflects the action of a general attentional mechanism that prevents attention from returning to previously explored loci. At the same time, the robustness of lOR has been recently disputed, given several failures to obtain the effect in tasks requiring discrimination rather than detection. In a series of eight experiments, we evaluated the differences between detection and discrimination tasks with regard to lOR. We found that lOR was consistently obtained with both tasks, although the temporal parameters required to observe lOR were different in detection and discrimination tasks. In our detection task, the effect appeared after a 400-msec delay between cue and target, and was still present after 1,300msec. In our discrimination task, the effect appeared later and disappeared sooner. The implications of these data for theoretical accounts of lOR are discussed.Attention is widely presumed to play an important role in the rapid and efficient scanning ofvisual environments. In particular, when search is difficult, the movement of attention from one location to another may improve discrimination at each location, and thus also improve overall search efficiency. However, the efficiency of search also depends on the ability to prevent attention from returning to previously examined locations. This issue has been the focus of considerable study by attention researchers over the past decade.Specifically, it has been shown that response to a target is speeded if the location at which the target appears is precued. In the cost-benefit paradigm (Posner, 1980), subjects are to respond to a target appearing in one of three boxes, one in the center ofthe screen and one to each side of the center. Before the target appears, the subject's attention is cued to one of the two peripheral locations. This attentional cuing is accomplished by making one of the two peripheral boxes flicker briefly. The target then appears in either the cued location (cued trials) or the uncued location (uncued trials). When the cue-target stimulus onset asynchrony (SOA) is less than about 300 msec, responses are faster on cued than on uncued trials.We thank Steven P. Tipper, Bruce Milliken, Arthur F. Kramer, an anonymous reviewer, and especially Raymond Klein for their useful comments. Bruce Milliken also helped improve our English. Pilar Gonzalvo helped us with data collecting. We are grateful to all of them.

Three experiments are presented that compare the cost found when switching from one task to another in two different conditions. In one of them, the tasks switch in predictable sequences. In the other condition, the tasks alternate at random. A smaller time cost is found in the random-switch condition when enough preparation time is allowed. Such an effect is due to the random-switch cost continuing to decrease with preparation time after the predictable-switch cost has reached an asymptote. Although the relationship between number of repetitions of one task and time cost is different in the random- and the predictable-switch conditions, only the latter shows the presence of an "exogenous" component of cost. The implications of this finding are discussed in relationship with the usual distinction between an endogenous component of switch cost that is affected by preparation time and another exogenous, residual component (e.g., Rogers & Monsell, 1995). It is proposed that a different kind of task-set preparation is at work when tasks alternate at random.

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Three experiments are presented that compare the cost found when switching from one task to another in two different conditions. In one of them, the tasks switch in predictable sequences. In the other condition, the tasks alternate at random. A smaller time cost is found in the random-switch condition when enough preparation time is allowed. Such an effect is due to the random-switch cost continuing to decrease with preparation time after the predictable-switch cost has reached an asymptote. Although the relationship between number of repetitions of one task and time cost is different in the random- and the predictable-switch conditions, only the latter shows the presence of an "exogenous" component of cost. The implications of this finding are discussed in relationship with the usual distinction between an endogenous component of switch cost that is affected by preparation time and another exogenous, residual component (e.g., Rogers & Monsell, 1995). It is proposed that a different kind of task-set preparation is at work when tasks alternate at random.

LexicalÁchromatic synaesthesia is a condition in which letters and/or words elicit percepts of synaesthetic colours, termed photisms. Anecdotal data suggest that synaesthetes are particularly sensitive to inconsistencies between their synaesthetic percepts and the real world, e.g., it can be annoying and unpleasant for them to see a letter printed in a colour different than the respective photism colour. For R, a synaesthete subject who participated in the present study, the photisms possess specific emotional values (a red photism is pleasing and attractive, green is repulsive and unpleasant, etc.). In contrast to the anecdotal data, R does not always find the colourÁphotism incongruence to be disturbing. More importantly, he states that it is the emotional coherence between the stimulus and the corresponding photism that matters. In a series of experiments, we studied this new concept of emotional coherence on three levels*subjective (self-report), behavioural, and physiological, corroborating R's introspective statements. Besides the implications of the concept of coherence itself, the results presented here suggest that even highly subjective cognitive constructs can be approached and measured experimentally, uncovering the workings of the underlying psychophysiological mechanisms.