Cue search and comparison processes in visual search for letters.

In two experiments, subjects searched fourand eight-letter arrays for the presence of a T or an F. The position of the target was indicated by a bar marker presented at one of seven stimulus onset asynchronies (SOA'S); — 100, — 25, 50, 125, 200, 275, or 350 msec. In Experiment 1, SOA conditions were blocked; in Experiment n, SOA conditions varied randomly from trial to trial. In both experiments array size and SOA interacted. With eight-letter arrays, reaction time increased linearly with SOA with a slope less than one. With four-letter arrays, reaction time increased with SOA but reached asymptote at the level of no-cue control reaction times at the 125 msec SOA. The results were interpreted as supporting the notion that cue search and comparison processes may function concurrently. When people search through arrays for a particular target letter, their search times are typically shorter when the position of the target is cued than when position cues are withheld. Effective cues have been bar markers presented adjacent to the target (Holmgren, 1974; Jonides, 1976; Logan, 1977) or properties of the letters themselves other than their identity, e.g., orientation or colour, which distinguish the target from the non-targets (Logan, 1976a). Two explanations of the effect have been offered, both of which distinguish two processes, a cue-search process to deal with the cue, and a comparison process to deal with the target (Gardner, 1973; Holmgren, 1974). Both suggest that cueing will reduce search time whenever cue search coupled with comparison is faster than comparison by itself. Since cue search and comparison both must extend in time, it is reasonable to ask whether information relevant to comparison may be gained before cue search finishes. Indeed, the two explanations differ on this issue. Holmgren (1974) would argue that it cannot. He suggests that cue search precedes comparison. It locates the cue and directs the comparison process to the appropriate position. Only then does the comparison process gain information from the array. Alternatively, Gardner (1973) has suggested that the cue search process simply increases the weight of information from the cued position as it converges on the comparison process. He would argue, then, that information relevant to comparison could be gained before cue search finished, but at a slower rate corresponding to the lower weight. From Gardner's suggestion, it follows that the more information gained during cue search, the less remains to be gained after cue search finishes. Thus, the more time spent in cue search, the less time need be spent subsequently in comparison. Holmgren's suggestion has no such implications, so distinguishing predictions can be developed as follows: from Gardner's *This research was funded by a grant to Gordon Logan from the Queen's University Advisory Research Council. William Cowan was supported by a Postdoctoral Fellowship from the National Research Council of Canada. We would like to thank D.J.K. Mewhort for the use of his computer laboratory, supported by Grant No. APA-318 to D.J.K. Mewhort from the National Research Council of Canada. Gordon Logan and Michael Withey reported the experiments at the annual meeting of the Eastern Psychological Association, New York, N.Y., April 1976. tGordon Logan and Michael Withey are members of the Psychology Departments at their respective universities; William Cowan is a member of the Department of Theoretical Physics at McMaster. Address reprint requests to Gordon D. Logan, Department of Psychology, Erindale College, University of Toronto, Mississauga, Ontario,