TECHNICAL REPORT STANDARD TITLE PAGE 

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 

FAA-AM-71-7 

4. Title and Subtitle 5. Reoort Date 

EFFECTS OF CONFLICTING AUDITORY STIMULI March 1971 

ON COLOR-WORD INTERFERENCE AND AROUSAL 6. Performing Organization Code 

7. Author's) 8. Performing Organization Report No. 

Richard I. Thackray, Ph.D. 

Karen N. Jones, B.S. 

9. Performing Organization Name and Address 10. Work Unit No. 

FAA Civil Aeromedical Institute 11. Contract or Grant No. P. o. Box 25082 

Oklahoma City, Oklahoma 73125 13. Type of Report and Period Covered 

12. Sponsoring Agency Nome and Address 

Office of Aviation Medicine OAM Report Federal Aviation Administration 

800 Independence Avenue, s.w. 14. Sponsoring Agency Code 

Washington, D. c. 20590 

15. Supplementary Notes 

This study was conducted under Task AM-A-71-PSY-22. 

16. Abstract 

Although air traffic controllers are often required to 

perform in the presence of distracting stimuli, no adequate 

measures of distraction susceptibility exist. In the present 

study, 50 male subjects were tested to determine whether the 

interference effect produced by the Stroop color-word test 

(a potential measure of distraction susceptibility) might 

be enhanced through the use of simultaneously-presented, 

conflicting auditory stimuli. When instructed to respond 

only to the hue of visually-presented color-words printed 

in incongruent inks, neither task-related (conflicting 

color names) nor task-unrelated (random numbers) auditory 

stimuli resulted in any increase in the Stroop interference 

effect, and there were no indications of an increase in 

autonomic indices of arousal. A subsidiary aspect of the 

study revealed the Stroop interference effect did not occur 

when the irrelevant stimuli were shifted from the visual 

to the auditory modality. It was concluded that the use of 

simultaneous auditory stimuli, which are similar but irrelevant to the visual stimuli employed, contribute nothing 

additional to the basic Stroop test in terms of either task 

interference or level of arousal. 

17. Key Words 18. Distribution Statement 

Arousal, Distraction, Heart Availability is unlimited. Document may 

be released to the National Technical rate, Respiration, Stroop Information Service, Springfield, test Virginia 22151, for sale to the public. 

19. Security Classif. (of this report) 20. Security Clossif, (of this page) 21. No. of Pages 22. Price 

Unclassified Unclassified 7 $3.00 

Form DOT F 1700.7 IB·69l 
ACKNOWLEDGMENTS 

The authors wish to express their appreciation to Robert M. Touchstone 

for his technical assistance with the instrumentation employed. 
EFFECTS OF CONFLICTING AUDITORY STIMULI ON COLOR-WORD 

INTERFERENCE AND AROUSAL 

I. Introduction. 

Air traffic controllers are often required to 

maintain sustained attention to visual tasks in 

the midst of a variety of extraneous visual or 

auditory stimuli. Such stimuli, by momentarily 

distracting the controller from his primary tasks, 

could have potentially serious consequences. 

While it is commonly believed that some individuals are more easily distracted than others, 

relatively little research has been concerned with 

individual differences in susceptibility to distraction. Although there are signs of increasing interest in this area (Baker and Madell, 1965; Bee, 

1966, 1968; Mandell, 1966), no study thus far has 

provided much information relative to the consistency of individual differences in susceptibility 

across different types of distraction conditions. 

If it could be established that these differences 

represent consistent behavior patterns, this would 

have definite implications for selection of air 

traffic control personnel. 

One of the most promising tests for the systematic study of distraction and distraction 

susceptibility would appear to be the color-word 

interference test (Stroop, 1935). This test requires a high degree of concentration and has 

been suggested as a measure of an individual's 

ability to deal selectively with competing stimuli 

(Mandell, 1966) or of his interference proneness 

(Jensen and Rohwer, 1966). It may also reflect 

ability to make rapid decisions in the face of 

conflicting information (Grand and Segal, 1966). 

As such, the test would appear to tap qualities 

relevant to air traffic control performance. 

The basic test consists of three parts : ( 1) reading the names of colors printed in black and 

white; (2) naming the colors in which circles or 

squares are printed; (3) naming the hue in which 

incongruent color-words are printed. The test is 

generally scored in terms of the difference in time 

required to complete parts 2 and 3. The diffi1 

culty involved can he appreciated by considering 

the problems associated with suppressing the 

tendency to name the printed words themselves 

when instructed to respond only to the colors in 

which the words are printed. 

In the most typical versions of the Stroop test, 

the subject's (S's) responses are vocal and the 

score is simply the number correct in a given 

amount of time. In order to provide a version 

which would have greater flexibility as a research instrument, a task was developed which 

(a) allowed individual presentation of each 

stimulus with precise control over stimulus duration and inter-stimulus intervals, (b) was capable 

of being either experimenter or subject paced, 

and (c) yielded a measure of response time to 

each stimulus. 

As noted, a primary purpose in developing 

this "performance" version of the Stroop test 

was to devise a versatile task which could be used 

in subsequent studies directly concerned with individual differences in distraction susceptibility. 

However, in order to possibly increase the test's 

effectiveness for this purpose, it seemed desirable 

to determine the extent to which the color-word 

intereference effect might be augmented by 

simultaneous auditory presentation of color 

names which conflicted with the visual stimuli. 

Thus, Frankenhaeuser, Froberg, Hakdahl, Rissler, 

Bjorkvall, and Wolff (1967), and others (Rissler, 

1965) have employed a version of the Stroop 

test similar to the one developed here except that 

conflicting color names are auditorily presented 

simultaneously with the visual stimuli. They 

have obtained significantly elevated catecholamine levels with their version which suggests 

that it is at least moderately stressful. In none 

o£ their studies, however, do they actually report 

data which would enable a determination of the 

relative increase in stress or performance interference resulting from the additional auditory 
stimuli. Presumably, if the additional stimuli 

act as distractors and compete with the visual 

task, this should increase performance impairment as well as stress level. 

The present study, then, was designed to determine whether irrelevant auditory stimuli of 

differing similarity to the visually presented 

color-words do have an influence on task performance when these are presented simultaneously with the visual stimuli. Two additional 

questions were also asked : ( 1) Is the Stroop interference effect dependent upon the irrelevant 

stimuli being presented within the same modality? 

Thus, would the interference effect be completely 

eliminated or would it be simply reduced if the 

irrelevant stimuli were shifted to the auditory 

sense? (2)Does the Stroop test itself act as a 

task induced stressor, i.e. does the interference 

resulting from the color-word stimuli produce 

corresponding changes in autonomic indices of 

arousal? 

II. Method. 

Subjects. Fifty paid male college students between the ages of 18 and 25 served as Ss. All 

were right-handed with no reported color-vision 

deficiencies. Each S was assigned to one of five 

groups on a simple rotational basis yielding a 

final N of 10 Ss per group. 

Apparatus. Located in one room was the S's 

console containing a rear projection screen and a 

Lafayette Model KT-800 Automatic Projection 

Tachistoscope. The S was seated in front of the 

console approximately 22 inches from the screen. 

His right hand rested on a shelf directly below 

FIGURE 1. Photograph of subject's console. The window at the right was used for one-way observation. 

2 
four buttons which actuated separate microswitches. The stimulus words were printeq directly above each button. A speaker for presenting either task instructions or auditory stimuli 

was placed to the left of the projection screen. 

Figure 1 shows a photograph of the S's console. 

The task programming equipment, as well as 

the equipment for recording the physiological and 

performance data, were located in an adjoining 

room. The method of programming the stimuli 

was as follows: Successive low frequency pulses 

from an audio oscillator were initially recorded 

on one channel of a stereo tape recorder. The interval between pulses was a constant three 

seconds. During playback each pulse actuated a 

sensitive relay which in turn triggered a bank of 

three DSI Model D-501 Time Interval Generators. These were used to activate the tachistoscope shutter and advance the slides. The duration of stimulus exposure was one--half second. 

The other channel of the tape recorder was used 

for instructions and for auditory stimuli. 

Response time to each stimulus was measured 

to the nearest liJ.oo second by means of a Welford 

Mark V SETAR (Welford Bioelectronics Enterprises) and punched on paper tape. The tape 

was later fed through a Friden Flexowriter 

which printed response time as well as recording 

which of the keys was pressed. 

A Beckman Type R dynograph recorded the 

physiological variables. The electrocardiogram 

was obtained from Beckman biopotential electrodes attached to the lateral walls of the S's 

chest. Respiration was measured from two 

.~· 

FIGURE 2. Photograph of task programming and physiological recording equipment. 

3 
mercury-in-vinyl gauges; one was attached at the 

thoracic and the other at the abdominal level. 

The gauges were connected to two specially constructed bridge couplers. Beckman electrodes for 

electromyographic recording were also attached 

to the chin and forehead. Recordings obtained 

from these latter electrodes as well as those from 

the thoracic respiration gauge were used for exploratory purposes and will not be reported here. 

The physiological recorder and task programing 

equipment are shown in Figure 2. 

Visual stimuli were of three basic types: ( 1) 

the words BROWN, GREEN, ORANGE, or 

PURPLE printed in black letters; (2) colored 

rectangles corresponding to the colors of these 

words ; and ( 3) the above words printed in incongruent ink colors, e.g. the word BROWN 

would be printed in either green, orange, or 

purple ink. Stimuli were photographed and reproduced on 35 mm slides. All stimuli were of 

constant height (27 mm) and width (68 mm) as 

projected on the screen. A small white cross on 

the screen served as a fixation point. 

Procedure. After the initial orientation instructions, the various electrodes and respiration 

belts were attached and the procedure for Part I 

was explained. The Ss were told that, during 

this nart. each stimulus would consist of one of 

the following four words-brown, orange, green, 

or purple. Each time a stimulus was presented 

the S was instructed to push the button corresponding to that word as rapidly as possible 

and then look back at the fixation spot. After 

every response the S · rested his fingers on the 

shelf immediately below the buttons. Following 

four practice stimuli, the set of 72 stimuli, all 

printed in black letters, was presented. These 

were arangred in a quasi-random order with the 

restrictions that each stimulus appear an equal 

number of times and that no two adjacent stimuli 

be the same. A three-minute rest period followed 

the last slide which allowed time for the experimenter to change stimuli and make other necessary equipment adjustments. All Ss received the 

same stimulus order. 

Part II was essentially the same as Part I except that the stimuli consisted of the colored 

rectangles and a different random order was used. 

For Part Ilia, each group received different 

stimuli and/or instructions. These were as 

follows: 

4 

Group A received the same stimuli (colored 

rectangles) in the same order as they were 

presented in Part II. They were told that the 

purpose of this part was to check the reliability 

of Part II. 

Group B was administered the set of stimuli 

employed with Group A except that each time a 

visual stimulus was presented the name of one 

of the four colors was simultaneously spoken over 

the speaker. The S was instructed to ignore the 

spoken word and respond only to the color of 

the rectangle projected on the screen. The auditory stimuli were arranged in a quasi-random 

fashion similar to that employed with the visual 

stimuli. In every case the auditory stimulus was 

the name of an incongruent color. 

Group C was presented the conventional Stroop 

color-word stimuli, i.e. names of the four colors 

printed in incongruent inks. The Ss were instructed to ignore the word itself and respond 

only to the color of the word. In order to make 

conditions comparable to Groups A and B, the 

order in which the colors of the stimulus words 

were arranged was the same as that of the colored 

rectangles used for Groups A and B. Likewise, 

the order of the words themselves was the same 

as that of the spoken words presented to Group 

B. 

Groups D and E used the same sequence o£ 

stimuli as were used with Group C. The difference was in the addition of auditory stimuli 

presented simultanem,tsly with the visual. For 

Group D these stimuli consisted of the names of 

the four colors which were always incongruent 

with both the projected word and its hue. For 

Group E the auditory stimuli consisted of the 

following four randomly chosen numbers: 18, 83, 

56 and 25. Both groups were told to ignore the 

auditory stimuli and respond only to the color 

of the visually presented word.. Randomization 

of the auditory stimuli was similar to that described previously. 

As with Parts I and II, the Ss in each group 

in Part Ilia received four practice trials and 

72 visual stimuli (with or without auditory 

stimuli). 

Following the completion of Part Ilia, Ss in 

each group were informed that they would now 

be required to perform again the task they had 

just completed, only at a much faster pace. 

After four practice trials each group received 
the same stimuli they were presented during the 

preceding part except that the inter-trial interval 

was reduced from three seconds to one and onehal£ seconds. 

III. Results. 

Mean reaction times for parts II, Ilia, and 

IIIb are shown in Table 1. An analysis of 

TABLE 1. Mean response time in seconds for each group. 

Group 

Part 

A B c D E 

II _________ 0.78 0.73 0.85 0.80 0.80 

Ilia _______ 0.72 0.72 1.02 0.94 0.98 

IIIb ___ ---- 0.76 0.74 0.95 0.86 0.90 

variance of part II revealed no differences between the groups (F=1.29; p>.05) in their 

response times to the colored rectangles. For 

part Ilia, however, the differences between the 

groups were significant (F=14.6; p<.Ol). A 

Newman-Keuls test (Winer, 1962) revealed that 

groups A and B were different from groups C, D, 

and E (p<.Ol), but there were no significant 

differences between A and B or between C, D, 

and E. Presenting the stimuli at twice the initial 

rate resulted in no apparent change in the basic 

relationships betwee~ the five groups. The 

analysis of variance for part IIIb was significant 

(F=12.56; p<.Ol) and Newman-Keuls tests 

again revealed groups A and B to differ from 

groups C, D, and E (p<.Ol) with no differences 

between A and B or between C, D, and E. 

Mean levels of heart rate for all groups during 

parts II, Ilia, and IIIb are shown in Table 2. 

TABLE 2.-Mean heart rate in beats per minute for each 

group. 

Group 

Part 

A B c D E 

II_ __ ------ 72.4 79.3 79.0 74.4 68.5 

Ilia _______ 72.0 79.2 77.8 75.7 71.1 

IIIb _______ 75.1 83.4 81.7 82.6 76.3 

A repeated measures two-way analysis of variance revealed no significant differences between 

5 

groups (F=l.Ol; p>.05) and no significant interaction (F=2.21; p>.05). There was, however, a highly significant difference between parts 

(F=44.97; p<.Ol). The analysis of variance on 

the respiration data shown in Table 3 yielded 

TABLE 3.-Mean respiration rate in cycles per minute 

for each group. 

Group 

Part 

A B c D E 

II _________ 20.5 18.8 18.2 18.9 20.2 

Ilia _______ 19.7 19.5 17.2 19.7 20.2 IIIb _______ 22.7 22.0 19.0 23.1 23.5 

similar results. Thus, the difference between 

parts was quite significant (F=34.96; p<.Ol), 

while neither the group (F=1.15; p>.05) nor 

interaction (F < 1.00) effects were significant. 

Examination of Tables 2 and 3 clearly indicates 

that these significant effects were the result of 

the increase in both heart rate and respiration 

rate during part IIIb. 

IV. Discussion. 

The results revealed that the method employed in this study for presenting the Stroop 

color-word stimuli was successful in eliciting the 

characteristic interference effect. However, when 

auditory stimuli were simultaneously presented 

with the visual color-word stimuli, neither the 

task-related (incongruent color names) nor the 

task-unrelated (random numbers) stimuli had 

any apparent effect on performance whatsoever. 

This lack of effect held regardless of whether the 

stimuli were presented at a moderate pace or at 

a quite rapid one. In addition, the data also revealed the Stroop effect to occur only when both 

relevant and irrelevant stimuli were presented 

within the same (visual) modality. Thus, shifting the irrelevant stimuli to the auditory 

modality completely eliminated the interference 

effect. 

With regard to the physiological measures 

taken, none o£ the groups differed in either heart 

rate or respiratory rate during either the first or 

second half of part III, although the faster pace 

of part IIIb resulted in uniformly higher levels 

for all groups. 
This finding is rather surpnsmg in view of 

the apparent frustration and tension which has 

been reported to attend Stroop performance 

(Klein, 1964) and in view of the elevated 

catecholamine levels found by the previously 

noted investigators (Frankenhaeuser, et al., 1967) 

using a similar version of the Stroop test. However, in observing the behavior of the Ss in those 

groups receiving the color-word stimuli and in 

questioning them later, it appeared that they 

were often less emotionally "upset" than they 

were surprised and even somewhat amused at 

their difficulty in responding to the hue of the 

color-word stimuli. This suggests that the 

perceptual conflict produced by the Stroop 

stimuli may reflect attentional processes which 

are only minimally associated, if at all, with 

shifts in general level of "arousal." There is increasing evidence that changes in attentional demands may produce significant changes in task 

performance which are not accompanied by any 

observable shift in physiological indicants of 

activation (Malmo, 1966). 

The present study suggests that the elevated 

catecholamine levels found by Frankenhaeuser 

and her co-workers may be more the result of 

task pacing and/or the instructions employed 

than any "stress" resulting from the Stroop 

stimuli themselves. During the second half of 

part III, Group D received essentially the same 

visual and aduitory stimuli at approximately the 

same pace as employed by the above investigators. 

Yet, although both heart rate and respiration 

were increased by the more rapid rate of stimulus 

6 

presentation, this increase did not differ from 

that of the control group administered the 

colored rectangles. Finally, it should be noted 

that Frankenhaeuser et al. administered instructions to their Ss which implied that students in 

general were able to perform the task perfectly 

after some practice. Because of the frustrating 

nature of the task itself, such instructions could 

be quite threatening and might well have accounted for, or at least contributed to, the increase in catecholamine levels. 

The results clearly suggest that the use of 

simultaneous auditory stimuli, which are similar 

but irrelevant to the visual stimuli employed, 

contribute nothing additional to the basic Stroop 

test in terms of either task interference or level 

of arousal. This, of course, should not be taken 

to imply that auditory stimlili per se are necessarily ineffective as distractors. Broadbent 

(1958), for example, has indicated certain 

stimulus conditions (e.g. intensity levels above 

90 db, long duration exposure, sudden onset or 

offset, frequencies above 2000 Hz, etc.) which 

have been shown to impair performance. The 

present study was concered only with the limited 

question of whether the Stroop interference effect might be enhanced through simultaneous 

presentation of irrelevant, but similar, stimuli. 

Research is currently being planned to determine 

whether this test, which was shown to be quite 

uninfluenced by the particular "distractors" employed here, is predictive of performance on 

other tasks under conditions of auditory distraction more likely to produce impairment. 
REFERENCES 

1. Baker, R. W. and T. 0. Madell: A continued investigation of susceptibility to distraction in academically 

under-achieving and achieving male college students. 

Journal of Educational Psychology, 56: 254-258, 1965. 

2. Bee, H. I. : Individual differences in susceptibility to 

distraction. Perceptua7 and Motor Skills, 23: 821-

822, 1966. 

3. Bee, H. I.: Cognitive style and performance under 

distraction: A partial replication. Perceptual and 

Motor Skills, 26: 863-867, 1968. 

4. Broadbent, D. E.: Perception and Communication. 

New York: Pergamon Press, Inc., 1958. 

5. Frankenhaeuser, M., J. Frobert, R. Hagdahl, A. 

Rissler, C. Bjorkvall and B. Wolff: Physiological, 

behavioral, and subjective indices of habituation to 

psychological stress. Physiology and Behavior, 2: 

229-237, 1967. 

6. Grand, S. and S. J. Segal: Recovery in the absence 

of recall: An investigation of color-word interference. 

Journal of Experimental Psychology, 72: 138-144, 

1966. 

7. Jensen, A. R. and W. D. Rohwer: The Stroop colorword test : A review. Acta Psychologica, 25 : 36-93, 

1966. 

8. Klein, G. S. : Semantic power measured through the 

interference of words with color-naming. American 

Journal of Psychology, 77: 576-588, 1964. 

9. Mandel, S. J. : Children's resistance to competing 

and distracting stimuli in the classroom. (Doctoral 

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Arbor, Mich., University Microfilms, 1966. No. 66-

11, 578. 

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Experimental Psychology, 71: 184-189, 1966. 

11. Rissler, A.: Performance in a task involving perceptual conflict. In Levi, L. (Ed.), Emotional Stress. 

New York: American Elsevier Publishing Co., Inc., 

1965. 

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13. Winer, B. J. : Statistical principles in experimental 

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