Perception & Psychophysics 1995,57 (5),715-723 Negative priming depends on ease ofselection ERIC RUTHRUFF University ofCalifornia, San Diego, La Jolla, California and JEFF MILLER University ofOtago, Dunedin, New Zealand Negative priming effects have been offered as evidence that distractor stimuli are identified. We conducted two experiments to determine ifsuch effects occur even when it is easy to discriminate target from distractor stimuli. In Experiment 1,we found the usual negative priming effect when tar­ get and distractor positions varied from trial to trial, but not when these positions remained fixed. Experiment 2 extended these results to a situation where the ease of selection varied only in the prime display. These findings argue that irrelevant inputs can be filtered out prior to stimulus iden­ tification under certain circumstances and therefore pose problems for strict late selection theories. A central and as yet unresolved issue in the field ofse­ 1974; Stroop, 1935). For instance, when subjects are asked lective attention concerns the point at which relevant to name the color in which a string of letters is printed, stimuli begin to be processed more extensively than ir­ naming latencies are very long ifthe letters happen to spell relevant ones. According to strict late selection theories a conflicting color name (Stroop, 1935).This phenomenon, (e.g., Deutsch & Deutsch, 1963), all stimuli are identi­ known as the Stroop effect, suggests that words are identi­ fied regardless oftheir relevance to the task at hand, but fied even when they are not relevant to the current task. only a subset ofthese are selected for input to later pro­ Although the identities ofirrelevant stimuli often in­ cesses (e.g., response selection). Early selection theo­ terfere with the concurrent processing of relevant stim­ ries, on the other hand, assert that unselected stimuli are uli, these interference effects have been shown to dimin­ "filtered out" at an early stage of processing, prior to ish in experimental conditions that facilitate selection of complete stimulus identification. The strongest early se­ relevant stimuli. The Stroop effect, for instance, is greatly lection theories (e.g., Broadbent, 1958) propose that un­ reduced when the object whose color is to be named is selected stimuli are discarded prior to identification; physically separated from the irrelevant color word (Kahn­ however, in weaker versions ofsuch theories, unselected eman & Henik, 1981). Similarly, Yantis and Johnston stimuli are attenuated rather than discarded (e.g., Treis­ (1990; but see Miller, 1991) were able to virtually elim­ man, 1960). In either case, early selection theories pre­ inate another type ofinterference effect by using condi­ dict that relevant stimuli are more likely to be identified tions designed to encourage optimal attentional focus­ than are irrelevant stimuli (which we will call selective ing. These findings support the view that irrelevant identification), whereas strict late selection theories pre­ objects can be filtered out at an early stage ofperception dict unselective identification. (i.e., selective identification is possible) but that the suc­ To determine whether selective identification is possible cess ofthe filter depends upon many factors, including in selective attention tasks, many researchers have ex­ the ease ofdiscriminating relevant from irrelevant stim­ amined the fate of irrelevant stimuli. The results indicate uli. It should be noted that this view is quite compatible that such stimuli are processed semantically (i.e., are iden­ with evidence that subjects can identify multiple objects tified) in many experimental settings (e.g., Corteen & simultaneously (e.g., Shiffrin & Gardner, 1972), because Dunn, 1974; Corteen & Wood, 1972; Eriksen & Eriksen, the claim that identification can be selective does not imply that it must be selective. Theorists favoring the view that selection occurs after During the course ofthis research, the first author received support identification, however, have pointed out that the iden­ from a National Science Foundation Graduate Fellowship and Public tification of distractors need not necessarily result in Health Service Training Grant 2T32-MHI4268. The research was also interference effects. Therefore, it is logically possible supported by National Institute of Mental Health Grant PHS-40733. We would like to thank Cassandra Fink and Ian Fisher for assistance that irrelevant stimuli are being identified even when in­ in testing subjects, and Gordon Logan, Cathleen Moore, Toby Mord­ terference effects are absent (e.g., Allport, Tipper, & koff, Janice Murray, Hal Pashler, Doug Rohrer, and two anonymous re­ Chmiel, 1985; Driver & Tipper, 1989). Allport et al. and viewers for useful comments on earlier versions of the manuscript. others have strengthened this position considerably by Correspondence concerning this article should be addressed to showing that a different measure can sometimes demon­ E. Ruthruff, Department of Psychology, UCSD, La Jolla, CA 92093­ 0109, or to 1. Miller, Department ofPsychology, University of Otago, strate semantic processing even when irrelevant stimuli P.O. Box 56, Dunedin, New Zealand. produce no interference. 715 Copyright 1995 Psychonomic Society, Inc. 716 RUTHRUFF AND MILLER In one experiment, Allport et al. (1985) asked subjects asked subjects to count the number ofred items in a dis­ to name a line drawing of a target object, displayed in play while ignoring the black items. Because both red red, while ignoring a distractor drawing displayed in and black items could appear in any of the eight possi­ green. In a difficult-selection condition, the locations of ble stimulus locations, it seems unlikely that selection the target and distractor drawings varied randomly from was especially easy. Fox (1994, 1995) precued target lo­ trial to trial, whereas in an easy-selection condition, the cation 150 msec before stimulus onset, but the cue nei­ target always appeared at fixation. They found little or ther significantly reduced overall RT nor completely no interference in the easy-selection condition-that is, eliminated distractor-based interference effects, so it the semantic category ofthe distractor item had little ef­ probably did not allow efficient selection of the relevant fect on the time to name a simultaneously presented tar­ stimulus. Perhaps the most convincing evidence ofneg­ get. They did find, however, that subjects were slower to ative priming in conditions thought to favor efficient se­ name a target picture when it was semantically related to lection comes from the easy-selection condition studied the distractor picture displayed on the preceding trial. To by Allport et al. (1985), in which the target always ap­ explain this slowing, which was termed negative prim­ peared at fixation. In this condition, however, the dis­ ing, they suggested that the distractor on the preceding tractor location varied randomly from trial to trial, and trial was identified and then suppressed by inhibitory it is possible that the putative early filter can prevent the mechanisms. So when the subsequent target was seman­ identification of irrelevant objects much more effec­ tically related to this distractor, a certain amount ofextra tively when the locations of these objects are known in time was required to overcome the residual inhibtion. advance. Ifso, then selection might have been further fa­ The most important conclusion was that irrelevant pic­ cilitated by using predictable distractor locations. tures were identified, as evidenced by negative prim­ In sum, because previous experiments may not have ing, even though identification did not result in interfer­ done enough to facilitate selection, and because of the ence. From this conclusion, Allport et al. argued that theoretical importance of negative priming effects, the previous reports of negligible or reduced interference present experiments were designed as stronger tests of (e.g., Eriksen & Eriksen, 1974; Francolini & Egeth, the claim that negative priming persists even when se­ 1980; Kahneman & Henik, 1981; Kahneman & Treis­ lection is easy. Ifselective identification is possible, then man, 1984) do not unambiguously support early selec­ negative priming effects should diminish greatly and tion. Similar findings ofnegative priming in conditions perhaps even disappear under more ideal conditions for producing small or negligible interference effects have selection. But if the identification of irrelevant stimuli since been reported by Driver and Tipper (1989) and cannot be prevented, then priming effects (negative or Fox (1994, 1995). facilitory) should be preserved despite our attempts to Negative priming, which has now been observed with create optimal conditions for efficient selection. a variety of stimuli and tasks (e.g., Dalrymple-Alford & Budayr, 1966; Neill, Terry, & Valdes, 1994; Tipper, EXPERIMENT! 1985), is a particularly important source ofevidence for nonselective identification because it occurs even when The basic design of Experiment 1 replicated Allport interference is greatly reduced or eliminated. Assuming et al.'s (1985, Experiments 6-8) manipulation of the un­ that the absence of interference implies optimal condi­ certainty ofthe target location and extended this manip­ tions for selection, the accompanying negative priming ulation by including conditions in which selection was appears to indicate that irrelevant stimuli are identified made even easier by using