Perception Psychophysics 1999 61 8 1624 1645 Range effects of an irrelevant dimension on classification SCOTT A HUETTEL and GREGORY R LOCKHEAD Duke University Durham North Carolina In univariate classification tasks subjects sort stimuli on the basis of the only attribute that varies In orthogonal classification tasks often called filtering tasks there additionally are trial to trial variations in irrelevant attributes that the subjects are instructed to ignore Performance is generally slower in filtering tasks than in univariate control tasks We investigated this slowing in experiments of how the range of irrelevant trial to trial variation affects responses in pitch loudness classification tasks Using two levels of pitch and of loudness as stimuli Experiment 1 replicated prior work showing that responses are slowed more when the range of the irrelevant dimension is made larger Also in Experiment 1 sequential analyses showed that response time depends both on sequence and on the stimulus set independent of sequence Experiments 2 and 3 used several levels on the irrelevant dimension and showed that responses to categorize loudness are slowed more by larger trial to trial pitch differences but only on trials when the response repeats When the response changes performance is essentially unaffected by trial to trial irrelevant variation This interaction supports the conclusion that slowed average performance in orthogonal classification tasks which is known as Garner interference is not due to difficulties that subjects have in filtering stimulus attributes It is due to how subjects process successive stimulus differences We call for more frequent reports of sequential analyses because these can reveal information that is not available from data averages Often people cannot ignore irrelevant information when they classify a stimulus attribute For example when people are asked to classify auditory tones according to pitch their performance is worse slower and with more errors when the timbre of the tone varies randomly between trials than if the timbre remains fixed between trials Crowder 1989 Irrelevant variation in loudness similarly interferes with performance when tones are classified according to pitch Lockhead 1992b Melara Mounts 1994 This result the fact that irrelevant variation on one dimension interferes with classification on another dimension is called Garner interference Garner 1974 Whenever there is such interference the stimulus dimensions interact which is contrary to what should occur if people could abstract a feature from a stimulus and process it independently of other features as Stevens 1975 proposed There have been many attempts to understand this apparent interference Garner 1970 Lockhead 1966 1992b Melara Marks 1990 Melara O Brien 1987 Pomerantz Garner 1973 Shepard 1964 none of which was fully successful Each of these attempts addressed characteristics of individual stimuli and all of these experimental approaches compared average perforThis research was partially supported by a National Science Foundation fellowship to S A H Correspondence should be addressed to S A Huettel Department of Psychology Duke University Durham NC 27708 e mail huettel psych duke edu Accepted by previous editor Myron L Braunstein Copyright 1999 Psychonomic Society Inc mance in one condition to average performance in another condition A factor that cannot be addressed by such studies of averaged data is any effect of the sequential structure of the stimuli because sequential information is lost when data are averaged across trials Sequence should be considered for at least two reasons stimulus sequences are different in tasks that have irrelevant stimulus variation than in tasks where there is no such variation and as Felfoldy 1974 showed performance depends on sequence Even so Garner interference essentially has not been examined for sequence effects beyond Felfoldy s study Some such examinations are reported here Another factor that is not examined in Garner tasks but should be studied is how the range of variation on the irrelevant dimension affects performance Range affects performance in absolute judgment tasks when stimuli differ on only one dimension Durlach Braida 1969 Gravetter Lockhead 1973 Parducci 1965 Pollack 1953 and in a bivariate Garner task when the range of the irrelevant dimension is increased Lockhead 1992b Melara Mounts 1994 In each case performance is poorer when range is larger One might expect sequence effects and the range of the irrelevant dimension to be related This is because performance is poor when the irrelevant range is large and because successive differences between stimuli within a task are large on average when the range is large This fact allows the suggestion that both range effects and Garner interference are associated with trialto trial sequence effects To consider this effects of both stimulus range and stimulus sequence are examined 1624 RANGE EFFECTS Theoretically one reason for examining sequence and range effects in Garner tasks is to pursue a proposal by Lockhead and King 1983 that describes processes that seem to be involved when people classify stimuli in magnitude estimation and absolute judgment tasks The proposal for these univariate tasks is that people judge a stimulus by comparing it with their memory of the prior stimulus and this comparison both requires less time and is more precise when successive stimuli are more similar the comparison task is then easier This thesis describes much of the univariate judgment data The experiments reported in this paper examined whether the thesis also describes performance in Garner tasks Range and sequence effects are appropriate empirical measures to use to examine this trial to trial comparative judgment thesis This is because it states that performance is less precise when successive stimuli are more different Successive stimuli are more different on average when the level of the irrelevant dimension changes between trials than when it remains fixed and the magnitude of this change will be greater when the range of irrelevant variation is greater Hence the predictions are that performance between tasks is poorer in conditions with a large stimulus range than in conditions with a small stimulus range and that performance within tasks is poorer on trials when successive stimuli are physically more different However Lockhead and King 1983 cannot predict without additional assumptions how
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