P e t c e p t ~ ~and a l Motor Skills, 1979, 48. 851-861. @ Perceptual and Motor Skills 1979
INFORMATION PROCESSING I N A BINARY CLASSIFICATION TASK1 CEPHAS J. ADKINS, JR., BEN B. MORGAN, JR., A N D EARL A. ALLUIS12 Performance Assessment Lboratory Old Dominion University Summary.-Three choice-reaction time studies were conducted to investigate whether information processing is exhaustive or self-terminating, serial or parallel, and N-dependent or N-independent. A total of 54 subjects were required to make key-pressing responses to one, two, or three digits presented in a circular display; one key was pressed if the display contained one or more target digits and another key was pressed if the display contained only nontarget digits. T h e first two studies utilized within-subjects designs in which the displays were constructed from only one target and one nontarget item (Study 1) o r from three target and seven nontarget items (Study 2 ) . T h e third srudy used a between-subjects design in which different groups of subjects responded to one-, two-, o r three-element displays. In general, the results indicate that CRTs increased as the total number of display elements increased and decreased as the number of target elements ( o r the ratio of target to nontarget items) increased for a given display size. W h e n only target elements were presented, C R T was independent of the number of elements displayed, and when only one target was presented. CRT increased as total number of elements increased. These cornbined results are interpreted as support for the inference that information processing in visual search tasks tends to be self-te~minating.serial, and N-dependent (of limited capaciry). .
Following the suggestion of Sternberg ( 1969a, 1975 ) , the measurement of choice reaction time (CRT) in binary classification tasks has become a widely recognized technique for analyzing visual search processes (Nickerson, 1972; Briggs, 1974; Theios, 1973). Typical results of recent studies in this area indicate that when subjects are required to make one response to a designated target and another response to the absence of a target, CRT is linearly related to the number of stimuli in both the target and nontarget sets ( Sternberg, 1966, 1969b; Atkinson, Holrngren, & Juola, 1969; Theios, Smith, Haviland, Traupmann, & Moy, 1973); however, some smdies have reported significant nonlinearity (Briggs & Blaha, 1969; Briggs & Swanson, 1970; Egeth, Atkinson, Gilmore, & Marcus, 1973). The obtained linear relationships have been characterized by similar slopes, but different intercepts, for the targec and nontarget functions. Responses to nontarget items are typically slower by approximately 40 msec. (Sternberg, 1966, 1969b; Theios, et al., 1973). The experimental paradigm of these studies--that of Sternberg's ( 1969b) 'Based in p a n a n a presentation made by the authors entitled "Human information processing in a binary classification task" at the meeting of the Southern Society for Philosophy and Psychology, Orlando, Florida, March, 1978. 'Currently o n assignment as Chief Scientist, Air Force Human Resources Laboratory, Brooks Air Force Base, T X 73235.
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C. J. ADKINS, JR.. ET AL.
"fixed-set" procedure--requires subjects to memorize a target set of items consisting of one or more digits, letters, or forms. They are then shown a display containing one or more of these target items, and required to indicate by appropriate CRT response the presence or absence of a target stimulus. The questions of particular interest in the analysis of such CRT data are those concerned with whether items in the display are searched one after the other (serial search) . or simultaneously (parallel search) ; whether all items in the display are exarnined (the search is exhnustiue) or the search is terminated upon the identification of any target item (search is self-terminnting); and whether the time required to process an item increases with number of stimulus elements (processing is N-dependent), or is independent of such increases (processing is N-independent) . The results of most studies seem to support the contention that processing is serial (Briggs & Blaha, 1969; Atkinson, et al., 1969), although some evidence suggests that it may be parallel (Grill, 1971; Van der Heijden & Menckenberg, 1974; Van der Heijden, 1975). Evidence with respect to N-independent versus N-dependent processing comes primarily from Van der Heijden ( 1975) whose findings provide support for N-dependent processing. The question of whether processing is exhaustive or self-terminating appears to be unsetrled and, therefore, constitutes the problem of greatest research interest. Shiffrin (1976) has observed that exhaustive search is more likely to occur in simple tasks and that self-terminating search is more likely to be used in more difficult tasks. This observation has not been supported by other findings, however, and the question is certainly open to (and in need of) additional research. Sternberg (1969a, 1975) has argued that his findings consistently support the notion of both serial and exhaustive processing. According to his interpretation, subjects search items one after the other, continuing until all of the items have been searched. They do not respond when the first target stimulus is identified; rather, they continue through the entire set before making their response. H e bases his argument on the finding that the target and nontarget functions are both linear (indicating a serial search) and parallel (indicating an exhaustive search). He further argues that if search were self-terminating, the slope of the function for the target set would be one-half that for the nontarget set. Sternberg uses a computer analogy to show that, in the long run, exhaustive search is a more efficient method despite its intuitive difficulties. Theios, et al. ( 1973) replicated Sternberg's ( 1969b) fixed-set study and obtained a similar outcome. However, they related their findings to Theios' ( 1973) self-terminating model and found it to be successfully supported by their data. They criticized Sternberg for failing to take into account the effects of stimulus probability. Other srudies have also provided some support for a self-terminating interpretation. For example, Van der Heijden (1975) gave subjects one, two, or
INFORMATION PROCESSING IN BINARY CLASSIFICATION
853
three stimuli in a circular array, with the letter "F" designated as the target and "En as the nontarget. Using tachistoscopic presentations wich a target probability of .5, he trained three subjects for nine days to respond with a verbal "Yes" or "No." Van der Heijden's interpretation of his results was based on a number of assumptions concerning the expected ordering of the magnitudes of the obtained reaction times. His major assumptions were that: ( 1 ) Search is exhrrastive if the response latencies for 2- and 3-element stimuli are independent of the number of target stimuli, i.e., if CRT(1/2) = CRT(2/2) and CRT(1/3) = CRT(2/3) = C R T ( 3 / 3 ) . The first digit of each pair indicates the number of targets; the second digit indicates the number of elements. ( 2 ) Search is self-terminaii?zg if the response latencies for 2- and 3-element stimuli decrease as the number of target stimuli increases, i.e., if CRT( 1/2) > CRT(2/2) and CRT(1/3) > CRT(2/3) > CRT(3/3). ( 3 ) When search is self-terminating, it is serial if the response latencies are equal for the I-, 2-, and 3-element stimuli that contain, only target items, i.e., if CRT(1/1) = CRT(2/2) = CRT(3/3). On the other hand, it is parallel if the response latencies change inversely with the number of elements, when all elements are targets, i.e., if CRT( 1/1) > CRT(2/2) > CRT(3/3). (4) Search is N-independent if the response latencies are equal for the I-, 2-, and 3-element stimuli that contain only one target element, i.e., if CRT( 1/1) = CRT( 1/2) = CRT(1/3). ( 5 ) Search is N-dependent if the response latencies increase for the I-, 2-, and 3-element stimuli that contain only one targec element, i.e., if CRT(1/1) CRT(1/2) < CRT(1/3). Van der Heijden found that CRTs decreased significantly across sessions; on the average, "Yes" responses were faster than "No" responses; CRTs for 2and $element stimuli decreased with increasing numbers of target elements; CRTs decreased wich increasing numbers of elements, when all elements were targets; and CRTs increased with number of elements, when each stimulus contained only one target element. From these findings, Van der Heijden inferred that the search was self-ternzinating rather than exhaustive (see assumption 2, above), parallel rather than serial ( based on assumption I ) , and N-dependent, or of limited capacity, rather than N-i.?zdepe?zdent (based on assumptions 4 and 5 and on an analysis of errors). The purposes of the present experiment were to see if the findings of Van der Heijden (1975) could be replicated and to extend his findings to the use of a circular array of digits (rather than letters) and manual (instead of verbal) responses. Specifically, the study was designed to determine whether, if interpreted on the basis of Van der Heijden's assumptions, the search and processing of digital displays is self-terminating, parallel, and N-dependent.
p > .05). AS shown in Fig. 3, these results appear quite similar to those of the two previous studies; the consistent ordering of stimuli within Groups 2 and 3 again supports the interpretation that processing was self-terminating and N-dependent. On the other hand, where all elements were targets, a significant increase in latency was produced by the increasing number .01). This finding was not covered by the asof targets (F2,?, = 8.60, p sumptions discussed above. However, Van der Heijden (1975) has suggested CRT(3/3), is that where this relationship, i.e., CRT( 1/1) < CRT(2/2) found with self-terminating search and limited capacity processing, either the serial or parallel search models are tenable. Separate analyses of variance were computed with the data of Study 3 to test for differences in CRT due to location of the three stimulus positions in the .05 for Group 1; display. All the F-tests were significant (F5,,, = 2.98, p F I I , I O= ~ 8.07, p .O1 for Group 2; and Fi,i2 = 5.64, 9 .O1 for Group 3 ) and, in general, the two upper positions (10 and 2 o'clock) were superior (faster CRTs) to the lower ( 6 o'clock) position. N o consistent superiority was found for the right or left upper position.
INFORMATION PROCESSING I N A BINARY CLASSIFICATION TASK1 CEPHAS J. ADKINS, JR., BEN B. MORGAN, JR., A N D EARL A. ALLUIS12 Performance Assessment Lboratory Old Dominion University Summary.-Three choice-reaction time studies were conducted to investigate whether information processing is exhaustive or self-terminating, serial or parallel, and N-dependent or N-independent. A total of 54 subjects were required to make key-pressing responses to one, two, or three digits presented in a circular display; one key was pressed if the display contained one or more target digits and another key was pressed if the display contained only nontarget digits. T h e first two studies utilized within-subjects designs in which the displays were constructed from only one target and one nontarget item (Study 1) o r from three target and seven nontarget items (Study 2 ) . T h e third srudy used a between-subjects design in which different groups of subjects responded to one-, two-, o r three-element displays. In general, the results indicate that CRTs increased as the total number of display elements increased and decreased as the number of target elements ( o r the ratio of target to nontarget items) increased for a given display size. W h e n only target elements were presented, C R T was independent of the number of elements displayed, and when only one target was presented. CRT increased as total number of elements increased. These cornbined results are interpreted as support for the inference that information processing in visual search tasks tends to be self-te~minating.serial, and N-dependent (of limited capaciry). .
Following the suggestion of Sternberg ( 1969a, 1975 ) , the measurement of choice reaction time (CRT) in binary classification tasks has become a widely recognized technique for analyzing visual search processes (Nickerson, 1972; Briggs, 1974; Theios, 1973). Typical results of recent studies in this area indicate that when subjects are required to make one response to a designated target and another response to the absence of a target, CRT is linearly related to the number of stimuli in both the target and nontarget sets ( Sternberg, 1966, 1969b; Atkinson, Holrngren, & Juola, 1969; Theios, Smith, Haviland, Traupmann, & Moy, 1973); however, some smdies have reported significant nonlinearity (Briggs & Blaha, 1969; Briggs & Swanson, 1970; Egeth, Atkinson, Gilmore, & Marcus, 1973). The obtained linear relationships have been characterized by similar slopes, but different intercepts, for the targec and nontarget functions. Responses to nontarget items are typically slower by approximately 40 msec. (Sternberg, 1966, 1969b; Theios, et al., 1973). The experimental paradigm of these studies--that of Sternberg's ( 1969b) 'Based in p a n a n a presentation made by the authors entitled "Human information processing in a binary classification task" at the meeting of the Southern Society for Philosophy and Psychology, Orlando, Florida, March, 1978. 'Currently o n assignment as Chief Scientist, Air Force Human Resources Laboratory, Brooks Air Force Base, T X 73235.
852
C. J. ADKINS, JR.. ET AL.
"fixed-set" procedure--requires subjects to memorize a target set of items consisting of one or more digits, letters, or forms. They are then shown a display containing one or more of these target items, and required to indicate by appropriate CRT response the presence or absence of a target stimulus. The questions of particular interest in the analysis of such CRT data are those concerned with whether items in the display are searched one after the other (serial search) . or simultaneously (parallel search) ; whether all items in the display are exarnined (the search is exhnustiue) or the search is terminated upon the identification of any target item (search is self-terminnting); and whether the time required to process an item increases with number of stimulus elements (processing is N-dependent), or is independent of such increases (processing is N-independent) . The results of most studies seem to support the contention that processing is serial (Briggs & Blaha, 1969; Atkinson, et al., 1969), although some evidence suggests that it may be parallel (Grill, 1971; Van der Heijden & Menckenberg, 1974; Van der Heijden, 1975). Evidence with respect to N-independent versus N-dependent processing comes primarily from Van der Heijden ( 1975) whose findings provide support for N-dependent processing. The question of whether processing is exhaustive or self-terminating appears to be unsetrled and, therefore, constitutes the problem of greatest research interest. Shiffrin (1976) has observed that exhaustive search is more likely to occur in simple tasks and that self-terminating search is more likely to be used in more difficult tasks. This observation has not been supported by other findings, however, and the question is certainly open to (and in need of) additional research. Sternberg (1969a, 1975) has argued that his findings consistently support the notion of both serial and exhaustive processing. According to his interpretation, subjects search items one after the other, continuing until all of the items have been searched. They do not respond when the first target stimulus is identified; rather, they continue through the entire set before making their response. H e bases his argument on the finding that the target and nontarget functions are both linear (indicating a serial search) and parallel (indicating an exhaustive search). He further argues that if search were self-terminating, the slope of the function for the target set would be one-half that for the nontarget set. Sternberg uses a computer analogy to show that, in the long run, exhaustive search is a more efficient method despite its intuitive difficulties. Theios, et al. ( 1973) replicated Sternberg's ( 1969b) fixed-set study and obtained a similar outcome. However, they related their findings to Theios' ( 1973) self-terminating model and found it to be successfully supported by their data. They criticized Sternberg for failing to take into account the effects of stimulus probability. Other srudies have also provided some support for a self-terminating interpretation. For example, Van der Heijden (1975) gave subjects one, two, or
INFORMATION PROCESSING IN BINARY CLASSIFICATION
853
three stimuli in a circular array, with the letter "F" designated as the target and "En as the nontarget. Using tachistoscopic presentations wich a target probability of .5, he trained three subjects for nine days to respond with a verbal "Yes" or "No." Van der Heijden's interpretation of his results was based on a number of assumptions concerning the expected ordering of the magnitudes of the obtained reaction times. His major assumptions were that: ( 1 ) Search is exhrrastive if the response latencies for 2- and 3-element stimuli are independent of the number of target stimuli, i.e., if CRT(1/2) = CRT(2/2) and CRT(1/3) = CRT(2/3) = C R T ( 3 / 3 ) . The first digit of each pair indicates the number of targets; the second digit indicates the number of elements. ( 2 ) Search is self-terminaii?zg if the response latencies for 2- and 3-element stimuli decrease as the number of target stimuli increases, i.e., if CRT( 1/2) > CRT(2/2) and CRT(1/3) > CRT(2/3) > CRT(3/3). ( 3 ) When search is self-terminating, it is serial if the response latencies are equal for the I-, 2-, and 3-element stimuli that contain, only target items, i.e., if CRT(1/1) = CRT(2/2) = CRT(3/3). On the other hand, it is parallel if the response latencies change inversely with the number of elements, when all elements are targets, i.e., if CRT( 1/1) > CRT(2/2) > CRT(3/3). (4) Search is N-independent if the response latencies are equal for the I-, 2-, and 3-element stimuli that contain only one target element, i.e., if CRT( 1/1) = CRT( 1/2) = CRT(1/3). ( 5 ) Search is N-dependent if the response latencies increase for the I-, 2-, and 3-element stimuli that contain only one targec element, i.e., if CRT(1/1) CRT(1/2) < CRT(1/3). Van der Heijden found that CRTs decreased significantly across sessions; on the average, "Yes" responses were faster than "No" responses; CRTs for 2and $element stimuli decreased with increasing numbers of target elements; CRTs decreased wich increasing numbers of elements, when all elements were targets; and CRTs increased with number of elements, when each stimulus contained only one target element. From these findings, Van der Heijden inferred that the search was self-ternzinating rather than exhaustive (see assumption 2, above), parallel rather than serial ( based on assumption I ) , and N-dependent, or of limited capacity, rather than N-i.?zdepe?zdent (based on assumptions 4 and 5 and on an analysis of errors). The purposes of the present experiment were to see if the findings of Van der Heijden (1975) could be replicated and to extend his findings to the use of a circular array of digits (rather than letters) and manual (instead of verbal) responses. Specifically, the study was designed to determine whether, if interpreted on the basis of Van der Heijden's assumptions, the search and processing of digital displays is self-terminating, parallel, and N-dependent.
p > .05). AS shown in Fig. 3, these results appear quite similar to those of the two previous studies; the consistent ordering of stimuli within Groups 2 and 3 again supports the interpretation that processing was self-terminating and N-dependent. On the other hand, where all elements were targets, a significant increase in latency was produced by the increasing number .01). This finding was not covered by the asof targets (F2,?, = 8.60, p sumptions discussed above. However, Van der Heijden (1975) has suggested CRT(3/3), is that where this relationship, i.e., CRT( 1/1) < CRT(2/2) found with self-terminating search and limited capacity processing, either the serial or parallel search models are tenable. Separate analyses of variance were computed with the data of Study 3 to test for differences in CRT due to location of the three stimulus positions in the .05 for Group 1; display. All the F-tests were significant (F5,,, = 2.98, p F I I , I O= ~ 8.07, p .O1 for Group 2; and Fi,i2 = 5.64, 9 .O1 for Group 3 ) and, in general, the two upper positions (10 and 2 o'clock) were superior (faster CRTs) to the lower ( 6 o'clock) position. N o consistent superiority was found for the right or left upper position.
