experiments examine how varying degrees of consistency determine the ... a monotonic function of the degree of consistency, decreasing to zero as the ...
Perception & Psychophysics 1982,31 (2), 160-168
Degree of consistent training: Improvements in search performance and automatic process development WALTER SCHNEIDER and ARTHUR D. FISK University ofIllinois, Champaign, Illinois 61820
Previous research has shown substantial improvements in detection performance when subjects consistently detect a subset of stimuli. In contrast, in conditions in which stimuli appear as both targets and distractors, there is little performance improvement with practice. The present experiments examine how varying degrees of consistency determine the improvement of detection accuracy with extended practice. The degree of consistency was varied by manipulating the frequency with which a letter was a distractor while holding the number of occurrences as a target constant. The experiments utilized a multiple-frame target-detection search paradigm in which subjects were to detect single-letter targets in a series of rapidly presented letters on four channels. Experiments showed that detection performance improvement with practice was a monotonic function of the degree of consistency, decreasing to zero as the target-to-distractor ratio increased from 10:0 to 10:20. As consistency decreased, detection performance asymptoted earlier and at a lower level. A dual-task experiment examined subjects' ability to perform the previously trained search task as a secondary task. Results showed that the previous targetto-distractor consistency had a marked effect on resource sensitivity of the detection task. The general issues of consistency in the development of skilled performance and in the development of automatic processing are discussed.
Human performance in almost any cognitive skill improves with practice. But the amount of improvement is dramatically increased when subjects are able to deal consistently with their task. In detection paradigms, research has shown that extended practice at consistently attending to a subset of stimuli results in quantitative and qualitative changes in performance (e.g., Moray, 1959, 1975; Schneider & Shiffrin, 1977). Reaction times are faster (e.g., Kristofferson, 1972a; Neisser, 1963; Schneider & Shiffrin, 1977), detection performance is less affected by memory load (e.g., Logan, 1979; Neisser, 1963; Schneider & Shiffrin, 1977) or number of channels (e.g., Duncan, 1980; Moray, 1975; Shiffrin, 1975), and performance becomes much less sensitive to attentional resource demands (LaBerge, 1973; Logan, 1979; Schneider & Fisk, Note 1). However, in COnditions in which subjects cannot consistently attend to a subset of stimuli, extended practice results in little, if any, improvement in performance. Performance may improve somewhat due to familiarization with the task, understanding of instructions, etc., but, performance does not improve as profoundly as when stimuli are dealt with conThis research was supported in part by funds from Office of Naval Research Personnel and Training Contract N()()()()14-78-C0012 (NR 1504(9) and NIMH Grant 5 ROI MH 3125. Reprint requests should be sent to Walter Schneider, Department of Psychology, University of Illinois, 603 E. Daniel, Champaign, Illinois 61820.
Copyright 1982 Psychonornic Society, Inc.
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sistently. In both visual search (e.g., Kristofferson, 1972b; Rabbitt, 1978; Schneider & Shiffrin, 1977) and detection paradigms (Schneider & Shiffrin, 1977), subjects show little performance change after the first session. Schneider and Shiffrin (1977) have emphasized that there are many quantitative and qualitative performance differences between tasks, depending on whether or not individual stimuli are consistently mapped. In a consistently mapped (CM) condition, given· stimuli appeared only as targets and never as distractors for a given subject. Therefore, in the CM condition, subjects could consistently deal with the stimuli, because a CM stimulus was always a valid target which required a positive response. Subjects' performance in the CM condition showed dramatic improvement. In conditions not consistently mapped, a given character could be a target On one trial and a distractor On the next. These were referred to as varied mapping (VM) conditions by Schneider and Shiffrin (1977). In the VM conditions, subjects could not deal consistently with the stimuli because a VM stimulus sometimes required a positive response (Le., a target) and sometimes had to be ignored (Le., a distractor). The subjects' performance in the VM condition did not improve even after thousands of trials. Visual search comparison slopes illustrate the large quantitative difference that can occur between CM and VM conditions. Schneider and Shiffrin (1977) 0031-5117/82/020160-09$01.15/0
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found display comparison slopes ranging from about 6,720 trials per subject was examined in Experi3 msec per item in the CM condition to 75 msec in ment 1. A dual-task paradigm was employed in Exthe VM condition (see Schneider & Shiffrin, 1977, periment 2 in order to examine the effect of degree Figure 6, memory set size 4, positive response). A of consistency in training on the ability of subjects transfer experiment showed a major qualitative dif- to perform the search task as a secondary task. ference in that CM training resulted in substantial EXPERIMENT 1 negative transfer when the target and distractor set stimuli were reversed (Shiffrin & Schneider, 1977, Experiment 1). However, there was no effect of Method Subjects. Five females and four males were paid for their parchanging stimuli in VM conditions (Shiffrin & ticipation in the present experiment. All subjects were students at Schneider, 19=77, Experiment 2). These two results the University of Illinois. One subject was left-handed. illustrate only two of many differences between CM Equipment. The experiment was controlled by a Digital Equipand VM conditions (for reviews, see Schneider, ment Corporation PDP-ll/34 computer. The computer was proDumais, & Shiffrin, 1982; Shiffrin & Schneider, 1977). grammed to present the appropriate stimuli, collect responses, and The profound changes in performance that occur control timing of the display presentation. The stimuli were presented on Tektronics Model 604 and Model 620 cathode ray scopes, when subjects consistently respond to stimuli have which contained P-31 phosphors. Each subject wore a headset caused many researchers to suggest that there are two through which white noise (SO dB) and an error tone were carried. Stimuli. The characters used in the present experiment were qualitatively different modes of human information processing (Hasher & Zacks, 1979; James, 1890; uppercase letters of the English alphabet. The characters were constructed from dots on a rectangular grid, 32 dots wide x 48 LaBerge, 1973, 1975, 1976; Logan, 1978, 1979; dots high, with an average of 43 dots used to specify a character. Norman, 1976; Posner & Snyder, 1975; Shiffrin & The characters were .52 deg in width x .58 deg in height. The Schneider, 1977). In this paper, we will refer to these refresh rate of the dots making up the stimuli was 10 msec. The two modes as control and automatic processing. display of the characters was divided into frames, with each frame Control processing is expected to occur in novel or consisting of four characters positioned to form a square around a center fixation dot. The distance from the focus dot to the center varied mapping situations. Control processing re- of each letter was 1 deg of visual angle. The subjects' eyes were quires little training to initiate and is easy to modify, approximately 45 cm from the display. The characters used were: but is slow, effortful, generally serial in nature and A, C, D, E, M, R, S, U, and Z. These letters were chosen (through highly dependent on load (see Schneider, Dumais, pilot testing) such that each letter was approximately equally confusable with the other letters. The room was dimly lit (.4 fc in& Shiffrin, 1982; Shiffrin & Schneider, 1977). Auto- cidentallight), with each dot easily visible on the display (.005 fL matic processing occurs after extended practice in per dot). consistent mapping situations. Automatic processing Trial sequence. Subjects searched for one letter (memory set is a relatively fast, effortless, parallel processing size 1) in frames containing four letters. When the subjects detected the target letter, they pushed one of four buttons in a square mode. indicating the position of the target. Consistently mapped training appears to be a necEach trial consisted of the following sequence: the presentation essary condition for improvements in the subjects' of a memory set letter and accuracy feedback, a fixation dot, 12· ability to timeshare tasks. Logan (1979) found that .., frames of letters, and either a "correct response" indicator or an extended timesharing practice with a varied mapping error tone (see Figure 1). The memory set letter was presented in the upper left-hand corner of the scope. In addition, accuracy search task and a short-term memory task did not feedback was presented in this display and will be described below. eliminate the dual-task interaction. However, if the The subjects were given up to 30 sec to study the target item. The search stimuli were consistently mapped, extended subjects initiated the frame sequence by pushing the initiate button practice eliminated the memory X search task inter- with the index finger of the nonpreferred hand. After the initiaaction. Schneider and Fisk (Note 1) gave subjects tion button was pushed, a fjxation dot was presented for 500 msec. This provided a fixation point corresponding to the central fixaextensive training at performing simultaneous CM tion dot, which remamed on for the entire frame sequence. The and VM search. They found that with extended practice·, performance in the consistently mapped condition became insensitive to the difficulty level of the MEMORY varied mapping condition. Although we know that varying degrees of consistency result in quite different performance characteristics, we do not know how performance declines ACCURACY as the degree of consistency is reduced. The purpose of the present experiments was to examine the effects ( I) (2) 3·-----
