Journal of Experimental Psychology: Human Perception and Performance Copyright © 1977 by the American Psychological Association, Inc.
VOL. 3, No. 3
AUGUST 1977
Attention and Visual Dominance: A Chronometric Analysis Raymond M. Klein Dalhousie University, Halifax, Canada Three chronometric experiments, each comparing vision and kinesthesis, were conducted to study visual dominance. The time required to switch attention from vision and from kinesthesis was equal, while switching to kinesthesis was faster than switching to vision (Experiment 1). Responses to a combined visual-kinesthetic stimulus were slower than responses to a kinesthetic stimulus alone when the subject was expecting the bimodal stimulus. The visual dominance effect was shown to depend on the subject knowing the modality of the stimulus in advance (Experiment 2). When subjects were instructed to attend one modality they had equal difficulty with conflicting visual and kinesthetic information (Experiment 3). These findings suggest that visual dominance results from a bias to attend vision when that modality seems adequate for the task. The bias to attend vision may develop to overcome a deficiency in visual alerting.
A wide variety of information-processing activities involves the simultaneous stimulation of several sensory modalities. An interesting question arises when information from two (or more) modalities derives from
This article is based on a dissertation submitted by the author in partial fulfillment of the PhD requirement at the University of Oregon. Portions of the research were presented at the annual meeting of the Canadian Psychological Association, Quebec City, June 1975. The research was supported by the National Science Foundation Grant No. GB 40301X to Michael Posner. The author would like to express his appreciation to Steve Keele, John Fentress, Beth Kerr, Mary Jo Nissen, and especially to Michael Posner for. their advice and encouragement, and to John Barresi, Bruce Earhard, and Peter Jusczyck for their comments on a previous draft of the manuscript Requests for reprints should be addressed to Raymond M. Klein, Department of Psychology, Dalhousie University, Halifax, Nova Scotia, Canada.
the same object or event. Will the sources of feedback be coordinated so that perception is unitary, and performance is influenced by all relevant modalities? Or is our limited attention committed to one channel at a time? This question has a long history in experimental psychology. Realizing that the performance of many movements could be guided by two sensory modalities, vision and kinesthesis, Woodworth (1899) asked, "Will the movement obey two masters, or will it cleave to one and despise the other ?" (p. 13) Findings from a variety of experimental paradigms reveal that the subjective reports and performance of human subjects tend to be controlled by visual information. Although this phenomenon, usually referred to as visual dominance, has been most extensively studied by creating an artificial discrepancy between vision and kinesthesis (Gibson, 1943; Hay, Pick, & Ikeda, 1965; Kinney & Luria, 1970; Pick, Warren, &
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Hay, 1969; Rock, Mack, Adams, & Hill, 1965; Rock & Victor, 1964), its occurrence is not restricted to perceptual judgments made in the presence of visual-kinesthetic conflict. Visual dominance has also been obtained (a) with nonconflicting information (Jordan, 1972; Klein & Posner, 1974; Walker, 1972); (b) with modalities other than kinesthesis (Colavita, 1974; Pick et al., 1969) ; and (c) with memory (Klein & Posner, 1974), motor performance (Kinney & Luria, 1972), and reaction time (Colavita, 1974; Jordan, 1972; Klein & Posner, 1974) as the dependent variable. (For a more detailed review of the visual dominance literature, see Klein, 1976, or Posner, Nissen, & Klein, 1976.) Instead of focusing on the occurrence of visual dominance, this set of experiments will explore the relationship between the attentional mechanism and the two modalities, vision and kinesthesis, which so often show asymmetric effects. Because mental ohronometry has been shown to be an effective tool for exploring the flow of information (Posner, 1975b; Sternberg, 1969), three different chronometric paradigms will be used to explore this relationship. In the first experiment, the time to switch attention (see LaBerge, 1973) to and from each modality is measured. The second experiment examines divided attention to determine whether the suppression of kinesthetic information by visual information is automatic or the result of a strategy to selectively attend vision. The remaining experiment investigates focused attention. The findings from the three paradigns will be integrated in the general discussion. General Method The basic experimental setup was the same for all experiments. The subject sat in a student's chair facing a cathode-ray tube (CRT) display in a dimly illuminated room. The student's chair was outfitted with a motor that could move a lever pivoted under the subject's right elbow in the horizontal plane. His right forefinger was placed in one of two devices that could be attached to the lever. One device was a circular metal loop mounted on a metal rod. This device was used in Experiments 1 and 2. The subject's finger was
wrapped in cotton and placed through the loop. The other device, used in Experiment 3, was a felt-lined wooden block with an elastic strap to hold the subject's finger in a semicircular groove. A small coil and plunger were mounted in the wooden block directly under the subject's fingertip. The subject's right arm and hand were shielded from view by a cardboard box, and his left arm rested on a platform with several microswitches. The subject wore headphones which were connected to a noise generator. A PDP-9 computer controlled the oscilloscope and motor and noise generator, monitored level movements, and measured response latencies. The kinesthetic stimulus consisted of a 1.5-2.0cm movement of the subject's forefinger in either direction (left or right). These movements lasted about 250 msec. A dot was displayed at the center of the CRT display on all trials. The vifual stimulus was the movement of this dot in either direction (left or right) for a fixed distance (2 cm or 1.7°), and these movements also lasted about 250 msec.1 The oscilloscope was also used to display messages to the subject and, in some conditions, to provide feedback concerning errors and reaction time. In order to mask the sound of the motor (which might provide cues concerning the direction of the kinesthetic movement), white noise was presented to the subject over the headphones on every trial. The noise also served as a warning signal, since its onset preceded that of the imperative stimulus by 1 sec. Following a trial that involved a finger movement, the subject's finger was passively returned to the central starting location. The word "relax" was displayed during this adjustment so that the subject would not mistakenly respond to it. The intertrial interval was 3 sec. The micros witches were used by the subject to indicate when he was ready to begin a trial or block of trials and to make speeded responses to imperative stimuli. The latency between the imperative stimulus and the subject's response (reaction time) was timed to the nearest millisecond and recorded on magnetic tape for later analysis. Unless otherwise noted, reaction time will refer
1 Although the movement of the subject's finger will be referred to throughout this article as the kinesthetic stimulus, it should be noted that it included tactile stimulation as well. The visual stimulus was intended to appear to reflect the movement of the subject's finger. Although the visual movement was programmed to be approximately equal to the kinesthetic movement in duration and extent, the two movements were, of course, not identical. Furthermore, no attempt was made to equate the two stimuli psychophysically. Therefore, statements about the two modalities based on findings with these stimuli may be overgeneralizations.
ATTENTION AND VISUAL DOMINANCE to the mean of the subjects' median reaction times. In general, responses greater than 1 sec (less than .1% of the responses) were counted as errors. Right-handed subjects with normal hearing and normal or corrected-to-normal vision were secured by the University of Oregon employment service and were paid $1.50 or $2 per hour for their participation. Prior to the first experimental session each subject was given a typed instruction sheet to read, and the experimenter answered all questions. Subjects were always instructed to respond as quickly as possible without making too many errors.
Experiment 1 One aspect of attention is reflected in how deeply one is engaged in a task. A related property concerns the ease with which attention can be "summoned" by unexpected stimuli which require a response. The purpose of Experiment 1 was to determine whether these two aspects of attention differ for vision and kinesthesis. A paradigm developed by LaBerge (1973) was modified to allow separate measurements of the time required to switch attention to an unexpected modality and from an expected one. Although this switching paradigm does not involve the simultaneous stimulation of the two modalities which typifies the visual dominance literature, the view that vision has priority over other modalities for access to attention suggests that both switching parameters may favor the visual modality. In other words, visual dominance suggests that switching to vision might be faster than to kinesthesis, and switching from vision might be slower. A neutral modality, audition, was used to compare the switching parameters of vision and kinesthesis. Reaction time to an unexpected auditory stimulus was obtained when either vision or kinesthesis was attended. Since the unexpected task is identical whether the subject is attending vision or kinesthesis, differences in auditory reaction time must be due to differences in switching from the two modalities. Switching to vision and kinesthesis was measured by the increase in visual and kinesthetic reaction time that occurred when audition was the attended modality (compared to visual and kinesthetic reaction time in nonswitch
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trials). Any differences between the two modalities must be due to switching to either modality because the subject is switching from audition in both cases. Method Stimuli to three modalities (vision, kinesthesis, and audition) were used in this experiment. The visual and kinesthetic movements were those described in the General Method section. The auditory stimulus was simply the termination of the noise in one ear. This produces a subjective impression of movement of the noise from a central location to the side of the ear still being stimulated. The subject indicated the direction of the movement by making a compatible key-press with his left hand. The noise was terminated immediately after the subject's response. Three conditions were varied between blocks. Prior to each block the subject was shown a message ("attend eye," "attend ear," or "attend finger") instructing him to attend one of the three modalities for that block of trials. The subject was informed that on a given trial any stimulus could occur, but that most of the time the stimuli would be presented to the attended modality. There were 48 trials in a block; 40 trials contained attended modality stimuli, and the remaining 8 were divided equally between the two nonattended modalities. Thus, when the subject was attending one modality, there was a 16.67% chance that he would have to switch his attention to process a movement to either of the other two modalities. Eleven subjects were run for 3 days each.2 Day 1 was considered practice. On Days 2 and 3, the subjects were given some short practice blocks and then were run through the three types of blocks twice. The subjects were run through the different conditions in different fixed orders (i.e., permutations of kinesthesis, vision, and audition).
Results and Discussion Reaction time and error rates for each condition are shown in Table 1. Reaction time to an expected stimulus was faster than reaction time to the same stimulus when it was unexpected (p < .001, by sign test). As mentioned above, this increase reflects the time required to switch from the at-
2 Thirteen subjects were run, but two were excluded because of high error rates (over 30%) in some conditions. The inclusion of these subjects does not alter the pattern of results.
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Table 1 Reaction Time (in msec), Percent Errors, and Switching Times in Experiment 1 Visual response Modality attended Vision Kinesthesis Audition
Kinesthetic response
Auditory response
Reaction time
Percent error
Reaction time
Percent error
Reaction time
Percent error
402.0 S10.7 504.0
2.35 2.83 2.83
396.9 334.4 384.3
10.76 7.51 9.63
421.6 420.2 315.8
5.60 2.26 5.60
Note. Switching times computed from these data are as follows: to audition from vision, 105.8 msec; to audition from kinesthesis, 104.4 msec; to vision from audition, 102.0 msec; to vision from kinesthesis, 108.5 msec; to kinesthesis from audition, 49.9 msec; and to kinesthesis from vision, 62.5 msec.
tended modality and to the unattended mo- asymmetry may reflect a basic difference in dality. The increase in reaction time seems the alerting characteristics (see Posner, to be accompanied by an increase in errors, 1975a) of the two modalities. This idea will but this trend was inconsistent and not sig- be developed in the general discussion. nificant. Auditory reaction time was the same Experiment 2 whether the subject was switching from Although vision may not be dominant in vision or kinesthesis. The apparent difference in error rates for these two conditions the switching paradigm, the studies diswas not significant, F(2, 20) = 1.28. Thus, cussed in the introduction amply demonthere does not seem to be any asymmetry in strate that vision does have priority over the difficulty of switching from vision and kinesthesis for access to attention during 'bimodal stimulation. Two contrasting exkinesthesis. It can be seen in Table 1 that switching planations for this asymmetry might be proto kinesthesis was faster than switching to posed (see Figure 1). One explanation, vision, F(l, 10) = 13.62, p < .005. This is emphasizing "hardware," claims that the true when audition is the attended modality, nervous system is wired up so that visual F(l, 10) = 5.41, p < .05, and it is also true inputs suppress kinesthetic inputs at the when switching between vision and kines- level of conscious attention. This might be thesis is considered, F(l, 10) = 22.59, p < accomplished through inhibition of the kin.001.8 Although errors seem to increase esthetic pathways by visual inputs (see Figmore for unexpected kinesthetic stimuli than ure la). Alternatively, automatic suppresfor unexpected visual stimuli, this difference sion of kinesthesis could occur if vision has was not even marginally significant, F(l, more copious connections to attention than does kinesthesis (see Figure Ib). This 10) = .71. We can draw two conclusions about the would result in occlusion of kinesthesis durprocessing characteristics of the two mo- ing bimodal stimulation because attention is dalities. First, switching attention from limited in capacity. Either "hardware" view vision does not take longer than switching would imply that vision should capture atfrom kinesthesis. The notion that vision tention whenever visual and kinesthetic "captures" attention does not seem to apply stimuli are presented at the same time. An when one is expecting a modality to be stimulated. Second, vision does not access 3 this comparison confounds switching attention more quickly than does kinesthe- fromAlthough with switching to, it still provides a valid sis ; in this study, the opposite was true: measure of switching to vision and kinesthesis, The kinesthetic stimulus was superior to the since it has already been shown that switching visual stimulus in attracting attention. This time from the two modalities is the same.
ATTENTION AND VISUAL DOMINANCE
Vision
Kinesthesis
i
Other
n
Vision
Wnesthesis
other
Vision
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Kinesthesis
\ J
i
Other
i
Figure 1. Three possible mechanisms for visual dominance. (In each model, sensory information from vision, kinesthesis, and other modalities are shown converging upon a central attentional mechanism. In Section A, activation of the visual pathway inhibits the kinesthetic pathway and perhaps that of other modalities as well; in Section B, vision has more copious connections to the attentional mechanism; and in Section C, the dotted line represents a movable gate which is under the strategic control of the subject and which can be set to allow any modality easy access to attention while blocking other modalities from consciousness.)
alternative explanation, emphasizing "software," attributes visual dominance to a bias or strategy to selectively attend vision whenever visual information seems sufficient to perform the task (see Figure Ic). The bias could be habitual and need not be deliberate. Such voluntary control over attention is amply demonstrated by dichotic shadowing (e.g., Moray, 1966), attention switching (the present Experiment 1; LaBerge, 1973), and other paradigms (e.g., Posner & Snyder, 1975). This view implies that visual dominance will not be found when the bias is discouraged. Experiment 2 was designed to determine whether the software or hardware explanation accounts for visual dominance when reaction time is the dependent variable. Responses to kinesthetic stimuli are generally faster than responses to visual stimuli. Two studies have shown that reaction time to a redundant visual and kinesthetic stimulus is slower than reaction time to the kinesthetic stimulus alone (Jordan, 1972; Klein & Posner, 1974, Experiment 3). If subjects use information from both modalities in the bimodal situation, then a statistical redundancy gain should be found: Bimodal responses should be faster than responses to either modality alone.4 The findings that adding redundant visual information actually increases reaction time suggests that the kinesthetic information is suppressed or not used in the presence of the visual information. In these reaction time studies of visual dominance, the subject always knew in ad-
vance whether the stimulus would be visual, kinesthetic, or bimodal because these conditions were presented in separate blocks (Klein & Posner, 1974) or were a betweensubjects variable (Jordan, 1972). Keeping the conditions separate may have encouraged the subjects to bias their attention toward vision, since on every trial the subject can base his decision solely on the visual (or kinesthetic) information. A straightforward test of the two views of visual dominance can be made if the subjects are also run in a mixed condition in which the modality of the stimulus cannot be predicted in advance. Thus, in Experiment 2, the subjects were run in both pure (visual, kinesthetic, or bimodal stimuli in separate blocks) and mixed (visual, kinesthetic, and bimodal stimuli in each block) conditions. The hardware view predicts that visual dominance should be obtained in the mixed bimodal condition because kinesthesis will be automatically suppressed by the simultaneous visual information. If the software view is correct, two outcomes are possible: (a) Either the mixed condition will discourage the bias toward vision (see below), and thus visual dominance will not occur; or (b) the subjects will selectively attend vision in the mixed blocks, and dominance
4 This will be found whenever the subject uses both sources of information, and the response latency distributions for the two inputs overlap (see Nickerson, 1973, for a discussion).
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Table 2 Summary Statistics from Experiment 2 Pure block Condition Visual Kinesthetic Bimodal 1
Mixed block
Reaction time (in msec)
Percent error
SD*
Reaction time (in msec)
Percent error
SD'
317 248 261
2.9 4.0 4.6
56 73 60
337 260 243
1.8 10.7 7.9
61 84 61
Mean across subjects of the standard deviation of correct reaction times.
will be found. It is crucial to note that dominance due to a strategy can be distinguished from dominance due to hardware. In Experiment 1 it was shown that a bias to attend one modality results in reduced performance on the other. This may discourage a bias in the mixed condition because if the subject selectively attends vision, reaction time and errors will increase on 1/3 of the trials when the subject will have to switch attention to process the kinesthetic stimulus. Therefore, if the bias is not discouraged, dominance in the bimodal condition will be accompanied by a Modality X Condition interaction, that is, compared with pure condition performance, mixed kinesthetic reaction time will increase more than mixed visual reaction time. This interaction is not predicted by the hardware view. Method Three stimuli were used in this experiment: visual, kinesthetic, and bimodal. The visual and kinesthetic movements described in the General Method section were used. On bimodal trials the visual movement was timed to begin at the onset of the kinesthetic movement.6 The subject's task was to indicate the direction of movement of the stimulus by making a compatible key-press response with his left hand. The three types of stimuli were presented in two different conditions. In the pure condition, a block of 20 trials contained stimuli of the same type, with the direction of the movement varied randomly from trial to trial. Each subject was exposed to pure blocks for each of the three stimulus types (visual, kinesthetic, and bimodal). In the mixed condition, a block of 30 trials contained 10 of each stimulus type (with stimulus type and direction varied randomly). Two groups of six subjects each were run in this experiment.9 Each subject was run for 2
days. Twelve pure blocks (four of each type) were run on Day 1 and six more at the start of Day 2; six mixed blocks were run in the latter part of Day 2. The subjects in Group 1 were also tested on each of the pure conditions after half of the mixed blocks had been run.7 Each of the six subjects in a group encountered the pure blocks in a different fixed order.
Results wd Discussion Reaction time, percent errors, and standard deviations of correct reaction times are shown in Table 2. There were no significant differences between the two groups, and in general, the discussion will treat them as one. Bimodal reaction time in the pure blocks was 13 msec longer than kinesthetic reaction time. While smaller than the dominance ef0
This was done by starting the visual movement 80 msec after the instruction to move the lever. Since there was variability in the actual initiation of the lever movement, the visual and kinesthetic onsets might be separated by as much as 20 msec. 6 Fifteen subjects were run, but three were replaced. One subject was rejected because his error rate was five times greater than that for other subjects in this experiment Two subjects were eliminated after Day 1 because their kinesthetic reaction time was slower than their visual reaction time. Data from these subjects could not be used to assess visual dominance. Faulty equipment was probably responsible, because an adjustment was made after running these subjects, and since then all subjects have had faster kinesthetic reaction times. 7 The two groups differed in two other minor procedural details. The visual display for Group 1 contained two lines on either side of the fixation. Group 1 received reaction time feedback at the end of each block, while Group 2 did not.
ATTENTION AND VISUAL DOMINANCE feet obtained in previous reaction time studies, this difference is nevertheless significant, F(l, 11) =9.27, p < .025. The fact that the visual movement was not a direct reflection of the kinesthetic movement (see Footnote 5), as it was in the previous studies, may account for the reduced effect. Data from the mixed block conditions are crucial for distinguishing between the hardware and software explanations. Is there a bias to attend vision in the mixed blocks? Reaction times to visual and to kinesthetic stimuli increased slightly in the mixed blocks, but there was no interaction between modality (vision and kinesthesis) and condition (mixed vs. pure). Thus, the latency data suggest no bias to attend vision in the mixed blocks. There was, however, a significant interaction between modality and condition for accuracy, F(l, 11) = 18.0, p < .005. Kinesthetic errors increase significantly in the mixed blocks, while visual errors decrease nonsignificantly. Although this error pattern might suggest a bias toward vision in the mixed blocks, data discussed below show that if there is one, it is not potent enough to result in visual dominance in the bimodal trials. In the mixed blocks, bimodal reaction time was significantly faster than kinesthetic reaction time, F(l, 11) =7.48, p < .025. The interaction between conditions (pure and mixed) and stimulus (kinesthetic vs. bimodal) was significant, F(l, 11) = 10.49, p < .01. This reversal demonstrates that dominance is not a necessary consequence of the simultaneous presentation of visual and kinesthetic information and is strong evidence against the hardware view. There was a nonsignificant trend for visual dominance in the pure blocks to decrease with practice, and since the mixed condition was always run on Day 2, it might be argued that practice rather than modality uncertainty accounts for the reversal. It is easy to demonstrate, however, that the lack of a visual dominance effect in the mixed blocks is not due to practice. First, if the absence of visual dominance were due to practice, then dominance should not be
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found in the pure blocks that were embedded in the mixed blocks for the subjects in Group 1. This group did show dominance in these embedded pure blocks (kinesthetic reaction time = 221; bimodal reaction time = 263). Second, those subjects who show large dominance effects in the pure blocks on both days should be less likely to show a reversal in the mixed blocks, if the reversal is due to practice. These subjects, however, did show a reversal in the mixed blocks (kinesthetic reaction time = 273; bimodal reaction time = 256). Practice, then, cannot account for the failure to find visual dominance in the mixed blocks. The finding that bimodal reaction time is less than either visual or kinesthetic reaction time is exactly what one would expect to find if the subjects were attending both modalities and responding whenever the information to either modality was sufficient for a response. This divided-attention strategy was simulated by the following procedure: (a) A pair of responses was selected randomly, one from the subject's mixed visual response distribution and one from his mixed kinesthetic response distribution; (b) the faster of the two response times was selected as the bimodal reaction time for that trial; and (c) if that response was an error, it was assumed that the subject made an error on the simulated bimodal trial.8 It should be noted that any bias to attend vision is built into this simulation because the bias reflects itself in the actual visual and kinesthetic responses which are used to simulate the bimodal response. The mean reaction time, standard deviation of correct responses, error rates, and error reaction times were computed from these simulated responses. These simulated statistics and the actual data from the same subjects are shown in Table 3. The simulated data are
8 This procedure was repeated 1,000 times for each of eight subjects. Four subjects were not included in the simulation. Three were omitted because they did not show the redundancy gain in mean reaction time, and the data of one subject had been accidentally erased.
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Table 3 Simulation of Divided Attention Strategy and Comparison with Actual Data Measure
Actual
Predicted
3«
|d| b
Mean correct reaction time (in msec) Mean percent errors Mean error reaction time (in msec) Mean standard deviation of correct reactions
259
266
-7
15
7.8
6.4
1.4
2.6
242
251
9
22
54
58
-4
8
• 3 refers to the mean difference between predicted and actual data. b 131 refers to the mean of the absolute differences.
remarkably close to the actual data. This is not merely the result of averaging out large differences between the subjects because the mean absolute differences are also rather small. It is apparent that the subjects are utilizing information from both modalities in the mixed bimodal trials, and therefore the hardware view is not supported. Is the software explanation adequate to account for the pure block data? The significant dominance effect in the pure blocks suggests that the kinesthetic information is not being fully used in the bimodal trials. But if the subjects are selectively attending vision on these trials, as the software view claims, then why isn't 'bimodal reaction time and error rate equal to visual reaction time and error rate? One explanation,9 consistent with the software view, is suggested by the difference in error rates between the visual and bimodal conditions. Suppose that the subject does selectively attend the visual information in the pure bimodal condition, but he responds more rapidly than to a visual stimulus alone because the "ignored" kinesthetic component of the bimodal stimulus speeds up the rate of his response. This explanation attributes the increased errors in the bimodal condition to a speed-accuracy trade-off: The more rapid response to the visual stimulus is based on less accurate information. Although this assumption may seem arbitrary, there is ample evidence that an irrelevant accessory stimulus presented to one modality may speed the rate of responding to stimuli presented to another
attended modality (see Nickerson, 1973, for a review). This view predicts a negative correlation between error rate differences and latency differences for the bimodal and visual conditions (i.e., the larger the decrease in reaction time due to the presence of the kinesthetic stimulus, the greater the increase in error rate). The correlation coefficient for these data is — .70 and is significant, f(10) = 3.04, p < .025. While certainly not conclusive, this post hoc analysis does support the view that the subjects may be responding to the visual information at a rate set by the kinesthetic stimulus. The next experiment will provide support for the two assumptions that this "software" explanation depends upon: (a) The subjects are attending vision selectively; and (b) a simultaneous, irrelevant kinesthetic stimulus tends to decrease both the latency and accuracy of visual response. Experiment 3 A fruitful and popular paradigm for studying attention requires that the subject selectively process information from a particular sensory modality or from a particular stimulus dimension while ignoring simultaneous irrelevant information presented via a second modality or stimulus dimension (for examples, see Moray, 1969; Garner, 1974; Dyer, 1973). Studies of focused attention reveal that while there is tremendous flexibility in the allocation of processing resources, we often cannot ignore ir-
9 An alternative explanation is that subjects attend vision on some trials and kinesthesis on others. This alternation-of-attention strategy would produce a mean reaction time somewhere between the visual and kinesthetic reaction times. Furthermore, since responses would be contributed from both the visual and kinesthetic response distributions, the variance of reaction time in the bimodal condition would be larger than either the visual or kinesthetic variances. This consequence of the alternation strategy was not obtained (see Table 2). Additional evidence against this strategy was obtained by simulating it. The standard deviation predicted by this strategy was significantly greater than the obtained standard deviation (/> < .OS).
ATTENTION AND VISUAL DOMINANCE
relevant information. Failures of selective attention have been found when the stimulus dimension to be ignored is "integral" with the attended dimension, when simultaneous messages cannot be segregated on the basis of physical properties and in other situations. Of course, visual dominance also reflects a failure of selective attention: When asked to base a judgment on kinesthetic information, subjects frequently use visual information instead. The results of Experiment 2 suggest that visual dominance may be due to an inappropriate strategy rather than a built-in relationship between the two modalities and attention. The application of chronometric methods to the focused-attention paradigm may provide additional evidence for (or against) this view. One relevant parameter that can be derived from a focused-attention experiment is the relative difficulty of ignoring visual and kinesthetic information. The hardware view of visual dominance suggests that vision may be more difficult to ignore. On the other hand, if the strategic view is correct, there may be no asymmetry at all. Whether or not an asymmetry is found, the data from a focused-attention experiment can shed light on the assumptions used to explain the pattern of results in the pure blocks of Experiment 2. To account for the lack of a redundancy gain in the pure bimodal condition, it was proposed that the subject was ignoring kinesthesis and selectively attending vision in that condition. To account for the difference between the bimodal and visual latencies, we proposed that the "ignored" kinesthetic stimulus decreases the latency of the "visual" response. Since the focused-attention paradigm will sometimes require the subject to ignore kinesthesis and selectively process vision (exactly the "strategy" attributed to the subjects in the pure bimodal condition of Experiment 2), a similarity of reaction time and error patterns between comparable conditions of the two experiments would support both propositions. Experiment 3 examines reaction time to visual and kinesthetic stimuli in a focusedattention paradigm. Prior to each block of
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trials the subject was told which modality to attend or respond to, and that he should ignore any movements presented to the other modality. Half of the movement trials were unimodal, while the remaining trials were bimodal. Since the bimodal trials were either congruent (i.e., the two movements were in the same direction) or conflicting (the attended and nonattended movements were in opposite directions), the direction of the nonattended movement was completely uninformative. The presence of conflicting trials required the subject to focus his attention upon the attended modality. Visual and tactile detection tasks were randomly interspersed with the three movement conditions to prevent the subject from making peripheral adjustments to shut out the irrelevant information. Method The subject's right forefinger was placed in the wooden carriage described in the General Method section. The subject's left hand rested above three microswitches. The visual and kinesthetic movements were the same as in the previous experiments. Two other stimuli were used in this experiment: a visual detection stimulus and a tactile detection stimulus. The visual detection stimulus was the appearance of a .45° X .62° rectangle on the scope superimposed on the fixation dot. The tactile detection stimulus was a vibration administered by the coil and plunger mentioned in the General Method section. The subject responded to the relevant movements by pressing one of two keys with the middle finger or forefinger of his left hand. The subject •responded to either detection stimulus by pressing the key under his left thumb. Detection stimuli were terminated by the subject's response. If the subject did not respond within 2 sec, the trial was counted as an error. To discourage the subject from making anticipatory responses on some trials (catch), no stimulus was presented. There were three types of blocks in this experiment. The visual attention blocks contained 12 visual movements (unimodal), 12 bimodal movements (6 congruent and 6 conflicting), 24 detection trials (12 to each modality), and 8 catch trials. The kinesthetic attention blocks were the same as the visual blocks, except that the unimodal movements were kinesthetic. A message preceded each block informing the subject of the modality to be attended. Detection blocks consisting solely of detection and catch trials were also presented. However, since they do not provide data relevant to this report they will not be
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Table 4 Reaction Time (in msec) and Percent Errors in the Detection Task of Experiment 3 Tactile
Visual
Type of block
Reaction time
Percent error
Visual Kinesthetic
494 498
2.73 4.05
Reaction Percent error time 543 571
5.62 7.20
discussed further. The order of the different trial types within a block and the direction of the relevant movement were randomized. Six subjects were run for 5 days each. Day 1 was devoted to explaining the experimental tasks and giving the subject practice in all of the conditions. On Days 2-5 the subjects were run through each of the three types of blocks twice. An ABCCBA order was used for each day. The order of conditions was varied between subjects and within subjects on different days.
showed this trend), than responses to the kinesthetic movements. In general, latencies to respond to unimodal movements were longer than in the earlier studies. This probably reflects the increased complexity of the subject's overall task in this experiment: He must make one of three responses to any one of five different stimuli. Was an asymmetry in the fqrm of visual dominance obtained in the conflict conditions? Analyses of variance performed on the reaction time and error data from the unimodal and conflict conditions revealed significant effects of conditions [for RT, F(l, 5) = 8.65, p < .05; for percent error, F(l, 5) = 14.17, p < .025], but neither the main effect of modality nor the Modality X Condition interaction was significant. In general, errors and reaction time increase with conflict in both modalities. In this con-
Results and Discussion One purpose of the detection task was to prevent the subject from making peripheral adjustments to help shut out the irrelevant movements. As shown in Table 4, performance is good enough in (both conditions to suggest that the subjects were not closing their eyes or removing their fingers from the apparatus. It is worth noting that while tactile responses were equal in latency in the visual and kinesthetic blocks, visual detection responses were slower when the subject was attending kinesthesis, F(l, 5) = 38.76, p < .005. Since the occurrence of a detection stimulus to the nonattended modality requires a switch of attention, this pattern of results confirms the finding of Experiment 1 that switching time for vision is longer than for kinesthesis (touch). The fact that the tactile detection task was not affected at all by the modality the subject was attending confirms the subjects' frequent reports that they did not need to attend their finger's to respond to the tactile stimulus. Reaction time and error rates for the three visual and three kinesthetic movement conditions are shown in Figure 2. As found in the earlier studies, responses to unimodal visual movements were slower, F(l, 5) = 12.80, p < .05, and tended to be more accurate, F(l, 5) = 3.11 (five out of six
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Figure 2. Reaction time and error rates for the movement task in Experiment 3. (Solid lines represent responses to kinesthetic movements; broken lines represent responses to visual movements.)
ATTENTION AND VISUAL DOMINANCE flict situation the two modalities appear to have roughly equal detrimental effects.10 A comparison of the congruent and conflict conditions revealed a significant main effect of conditions for both reaction time, F(l, 5) = 15.33, p < .025, and errors, F(l, 5) = 16.14, p < .025. Neither the main effect of modality nor the interaction between modality and condition was significant for either dependent variable. Both error rates and response latencies were higher in the conflict conditions, demonstrating that even with focused-attention instructions, the direction of the unattended stimulus was not completely ignored. What might be the cause of these selective attention failures? One possibility is that the degree of divided attention forced upon subjects by the detection tasks prevented completely successful filtering of the irrelevant movement stimuli. Alternatively, since subjects attended to visual and kinesthetic movement stimuli in alternate blocks, they may have found it difficult to suppress responses to the irrelevant stimuli once these responses had become highly practiced (see, e.g., Greenwald, 1970; Lewis, 1970). A subsequent experiment (Klein, 1974, Experiment V) demonstrated that neither of these explanations can fully account for the effect. The movement conditions of Experiment 3 were replicated in a between-subjects design (different subjects responded to each modality) with no detection tasks. Thus, no subject was forced to attend or respond to the irrelevant modality. In Klein's (1974) experiment, conflict had little effect on median reaction times, but all other main findings of Experiment 3 were replicated. Together, the two experiments suggest that an irrelevant directional stimulus may automatically activate a compatible directional response tendency (see also Simon & Craft, 1970,1971). The unimodal and congruent conditions were compared to evaluate the suggestion that an unattended kinesthetic stimulus produces changes in alertness. The interaction between conditions and modality was significant for both errors, F(l, 5) = 10.48, p < .025, and reaction time, F(l, 5) = 9.32, p < .05. Individual analyses of variance revealed that the decrease in visual reaction time in
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the congruent condition was significant, F ( I , 5) = 19.19, p < .01, while the increase in errors was only marginally significant, F(l, 5) = 4.12, .05 < p < .10. The decrease in kinesthetic errors in the congruent condition was also significant, F(l, 5) = 12.66, p < .025. This pattern of results is consistent with the alerting role assigned to kinesthetic stimuli in the previous experiments. An irrelevant kinesthetic stimulus speeds up the rate of the subject's response, often at the expense of errors. Congruent visual information only affected the accuracy of the subjects' kinesthetic responses. It should be noted that incomplete filtering of the "nonattended" kinesthetic stimulus discussed above for the conflict conditions must also be occurring in the congruent visual attention condition. A proportion of kinesthetic responses in the congruent visual attention conditions would have the effect of increasing errors and decreasing reaction time compared to performance in the unimodal condition. However, the actual effects upon speed and accuracy are too great to be accounted for by a 1Q%-15'% rate of selective attention failures (10%-15% kinesthetic responding is assumed on the basis of the error rate difference between the visual unimodal and conflict conditions). In order to determine if there were any practice effects, the movement data from the first block in each movement condition on Day 2 and the last block on Day 5 were subjected to analyses of variance. Both modalities showed a decrease in reaction time with practice [for kinesthesis, F(l, 5) = 8.25, p