Perceptual and Motor Skills, 1976, 43, 51-57. @ Perceptual and Motor Skills 1976
AN AUDIOVISUAL TEST OF DIVIDED ATTENTION' M. J. BACH A N D D. L. BRUCE'
hTorthtoestern Universiry Medical School, Chicdgo, Illinois Summa7y.-A description is given of an audiovisual reaction time task, performance of which was maximal after 15 min. practice and which lasted at this level for 1 wk. Sensitiviq of the test was shown in an adverse effect of inhalation of traces of anesthetic gases. Comparing responses to auditory and visual stimuli, the control auditory reaction times were faster but were lengthened more in the presence of anesthetics than were the visual ones. This test may be useful in other studies of subtle depressant drug effects.
In the administration of anesthesia, gases and vapors are given to the patient by means of machines equipped with overflow valves through which these agents escape into the operating room air. Despite room air changes 8 to 12 times per hour, measurable amounts of anesthetics are present in the breathing zone of the anesthesiologist (Linde 81 Bruce, 1969). These concentrations approximate 1/1,000 of those given to the patient. Knowledge of this fact has caused equipment manufacturers to design gas "scavenging" systems to vent these gases from the room, while many groups have made studies of the possible health hazards of inhalation of trace gas. In a series of studies of behavioral effects of trace anesthetics on performance of healthy male volunteers, the most sensitive test was an audiovisual (A-V) task, specitically designed for chese invescigations (Bruce, et al., 1974; Bach, et al., 1974; Bruce & Bach, 1975). During an operation, the anesthesiologist monitors several sources of visual variables, such as: electrocardiographic display (ECG) on an oscilloscope; position of flowmeters on the anesthesia machine; flucmacion of pressure gauges in the breathing circuit; drip rate of fluids administered intravenously; and, oscillations of the gauge on the blood pressure recording apparatus. Concurrently, he must listen for: heart beat sounds in an esophageal stethoscope; the clicking of a pulse monitor if one is being used; the soft sound of normal breaching transmitted through the breathing tubes; the abnormal hissing sound of gas escaping from some point in the breathing circuit comprised of patient and machine, and the normal, rhythmic sound of the mechanical ventilator commonly used to breathe for the patient whose muscles of respiration are paralyzed by the use of muscle relaxant drugs. A task wherein the subject must monitor simultaneously a visual and an auditory pattern, each changing back and forth between two conditions, some'The project on which this publication was based was performed pursuant to Contract HSM-99-72-48 from the National Institute for Occupational Safety and Health, Center for Disease Control. 'Reprints available from D. L. Bruce, M. D., Department of Anesthesia, Nonhwestern University Medical School, 303 East Chicago Avenue, Chicago, Illinois 60611. U. S. A.
52
M. J. BACH
&
D. L. BRUCE
what simulates these tasks of the anesthesiologist. The test has not previously been described in detail sufficient to allow others to duplicate it. In the belief that chis sort of divided attention task mimics work performed by people other than anesthesiologists, a more complete description of it follows. Its extreme sensitivity to anesthetic agents suggests it may be useful in studying effects of low doses of other depressant drugs. In support of this idea are the studies reviewed by Wallgren and Barry ( 1970) in which alcohol differentially caused a greater increase in reaction rime to auditory than ro visual signals.
EQUIPMENT Auditory and visual signals were recorded on, and played back from, a four-channel FM instrumentation tape recorder (Hewlett-Packard, Model 3960). The auditory signals were generated by a metronome beating at 100 or 200 times per minute into a microphone connected to the voice channel of the tape recorder, from which they were played back to the subject through earphones (Vanco, Model HF-1) modified from stereophonic to monaural. In more recent work, the faster frequency has been reduced to IGO/min., reducing the range to make discrimination more difficult. The visual pattern was generated by an ECG simulator (Hewlett-Packard, Model 4653B) containing a cassette tape of various ECG rhythms. Ventricular fibrillarion was chosen for its high frequency and amplitude wave-form pattern, making it easily discriminable from a straight line for the medically naive subject. Originally, this was recorded alternately on one of two tape channels, each of which was connected for playback to one channel of a two-channel oscilloscope (Hewlett-Packard, Model 7803B). Thus, the wave was either on the top or bottom channel and a move from one to the other was the cue for the subjecc to respond. Recently, the test has been simplified to a single tape channel recording either the spike pattern described or a flat line (ECG cape curned off). Now, only one oscilloscope channel is used, and the subject responds when the flat line changes to a spike pattern, or vice-versa. The oscilloscope screen is 3 X 4.5 in. and the sweep speed is 25 mm/sec. The appearance of this display differs markedly from that of a slower sweep across a larger screen and may be important in duplicating our task conditions. The subject's response to a change in signal requires the depression of one of four buttons on a unit custom-made by Hewlett-Packard. This device is simply a box containing two mercury batteries (Mallory Duracel TR 146X) connected through resistors to the buttons. When a button is depressed, a square wave of amplitude one-half or one volt, positive or negative, is transmitted to a blank channel of the FM tape recorder. The buttons are labeled as follows: visual spiked, audio fast; visual spiked, audio slow; visual flat, audio fast; and, visual flat, audio slow. The final item in this equipment array is a Grass polygraph (Model 7 ) to
AUDIOVISUAL TEST OF DIVlDED ATTENTION
53
which the tape recorder is attached after the subject completes the task, and the three channels (auditory, visual and the subject's responses) are recorded on chart paper moving at 10 rnm/sec. with a 1-sec. time base recorded simulcaneously.
PROGRAMMING The changes in auditory and visual stimuli were plotted on a time scale. The task was balanced so there would be equal numbers of changes to each of the four conditions, and each change would involve only one modality, i.e., either an audirory or a visual change. In this way, a differential effect on one of these perceptive processes could be detected. This limits the choice, at any given rime, to rwo of the four buttons. There are only three to which a change could occur and one of these would require alterations of both auditory and visual signal. The choice between the remaining two was made arbitrarily as the program was developed, keeping in mind the needs to finish with a balanced set of 25 changes to each of the four choices and to have an apparent, if not real, random presentation to the subject. These 100 changes were completed in 7 min. The program for the first 2 min. is shown in Table 1 and the remainder is available upon request from the second author (DLB).
RECORDING The cape speed for both recording and playback is 3% in./sec. The sound channel was recorded first, in order to obtain a well defined starting point on the tape. An electric metronome, beating at the fast speed programmed firsc, was placed by the microphone and a stopwatch was started as recording began. At times where auditory changes were programmed, the metronome dial was turned to 100 or 160 beats per minute. At the end of the run, the tape was rewound to the starting point for visual recording on another channel. The ventricular fibrillation (spikes) pattern of the ECG simulator cassette tape was played through the oscilloscope to this second tape channel. An off-on switch was interposed berween the ECG and the oscilloscope so that when the switch button was depressed, the patcern changed from spikes to a flat line. Once again using the stopwatch, and beginning from the first sound of the auditory recording just made, the pattern required for the visual program was thus recorded. At the end of this, the two channels were played through the polygraph and the record produced was compared with the program to verify its correctness.
TESTING For testing purposes, a connection is made from the output jack of the visual tape channel to the oscilloscope and from the auditory channel to the earphones. A third channel is used to record the subject's responses, by connecting the response box to the input jack of that channel. Thus, as the cape advances,
TABLE I PROGRAM FOR FIRSTm O MINUTESOF AUDIOVISUAL TASK
Time Elapsed
Min. Sec.
Auditory Fast Slow Visual Spikes
Flat
0 00 04 09 12 17 21-25 29 35 38 44 48 52 54 x
x
X
x x
x x X
x
x
x X
x
x
x
X
x
X
X
x
x x
x x x
x
X
x
x
1 01 05 08 12 15 19 22 28 32 39 41 46 49 54 58
x
x X x
x
x
x
x
x x
x
x
x
x
x x x x x X
x x x
x
X
x
X x
x
AUDIOVISUAL TEST OF DIVIDED ATTENTION
55
the subject is presented with the auditory and visual patterns and his response is.recorded as he depresses the button corresponding to each change. At the end of the run, a complete recording of rest and responses exists. After playback through the polygraph, the test is re-used, the next subject's responses erasing those of the previous subject as the recording is made. The subject is told to place his preferred hand on the center of the response box, which is 8 in, wide, with the four buttons spaced 1% in. apart on a line parallel to the subject's shoulders. Thus, a response requires a lateral move from button to button. In practice, the subject's eyes are approximately 25 in. from the oscilloscope screen. The windows of the test room are covered by shades and overhead fluorescent lights provide uniform room lighting with no glare or reflections on the screen. The subject is allowed to vary the volume of the sound signal to a level he feels is comfortable. After the subject has left the laboratory, che outputs of the three tape channels are connecced to the polygraph on which is then recorded a chart of tesc and responses to be used for scoring subsequently. This is done by measuring the distance from change to response and converting rhis to time by reference to the 1-sec. time markers. A key is used to judge correct responses. Only correct responses are used to compute mean reaction time ( R T ) . Results from this tesc are arranged in a 2 X 2 table, listing order of exposure (first or second) vs exposure condition (air or air plus anesthetic). Statistical treatment of these data was by analysis of variance whereby the effect of anesthetic and practice could be evaluated separacely, as well as their interaction ( Winer, 1962 ) .
PILOTSTUDIES These studies were made using a previous program, which was of the same form but took 7.5 min. Ten members of the office and technical staff of this department were tested three times sequentially on one day, then once again, at the same time, a week later. In order to record the responses and rewind the tape, about 10 min. separated each test session of the first day. On each tesc, the first 50 responses were scored separately from the second 50. The subjects averaged 97% correct responses. Table 2 shows the effect of practice on RT. Improvement occurred rapidly, and comparison of adjacent means (Hays, 1963) showed only three significant decreases in RT, after 3.75, TABLE 2 MEAN REACTION TIMESIN LEARNING AND RETENTION STUDIES First Session
Elapsed Time (min.) Mean RT (sec.)
3.75 1.56
7.50 1.41
11.25 1.22
15.00 1.26
7 18.75 1.15
22.50 1.14
Days Later
3.75 7.50 1.11 1.11
M.J. BACH
56
8r D. L. BRUCE
7.5 and 15.0 min. There was no significance to the differences in scores obtained 1 wk. later. These data suggest thac 15 min. pracrice is sufficient to reach an asymptote on the learning curve and thac this is maintained at least for 1 wk., allowing retesting to occur without further pracrice sessions.
STUDIESUSINGT H E TEST Data from two studies are presented briefly to illustrate the sensitiviry of this test. Traces of the anesthetics, nitrous oxide ( N - 0 ) and halothane, given to subjects in concentrations similar to those found in operating room air, significantly increased RTs on this test (Bruce, et al., 1974). Data from those studies were analyzed further to determine any differentia1 effect on auditory versus visual RTs, and are summarized in Table 3. Since order of exposure to air or anesthetics was counterbalanced in the study and was not a significant source of variance, the data of Table 3 are collapsed across this variable. There was a significant ( p < .001) anesthetic effect on both RTs, but the originally faster auditory R T increased 29%, compared to an 18% increase in RT to visual signals in the anesthetic condition. TABLE 3 EFFECTS OF TRACE ANESTHETICSON AUDITORYAND VISUALREACTION TIME(SEC.)
Auditory Visual
Air
Condition N20 Halothane
1.42 1.84
1.83 2.17
+
% Increase in RT .41/1.42 .33/1.84
= 29
=
18
This auditory-visual cask not only reflects diminution in performance bur can also reflect enhancement. In another study (Winter, et al., 1975), the test was used to study the effect of replacement of the 80% of air that is nitrogen with the inert gas, helium. The idea for the study came from the notion that nitrogen narcosis at high pressures of N2 might also exist in a subtle form when breathing this "trace anesthetic" in ordinary air. The subjects of that study showed a statistically significant shortening of R T on chis task when breathing a helium-oxygen mixture as compared to air.
CONCLUSIONS A description is given of a simple test of reaction times to auditory and visual variation in signals presented concurrently. This test is easily assembled, programmed, performed and scored. It is quickly learned and well retained. It has been used to show both adverse and salutory effects of varying gas mixrures in the air breathed by the subjects. BACH, M. J., ARBIT, J.,
&
REFERENCES BRUCE.D. L. Trace anesthetic effect on vigilance. In C.
Xintaras, B. L. Johnson, & I. DeGroot (Eds.), Behavioral toxicology: early
AUDIOVISUAL TEST OF DIVIDED ATTENTION
57
detection o f occupational hrrzards. Washington, D. C . : U. S. Dept. of Hlth., Educ., Welf., 1974. Pp. 41-50. (PHs, Pub. NIOSH 74-126) BRUCE.D. L., & BACH,M. J. Psychologic studies of human performance as affected by traces of enflurane and nitrous oxide. Ane~therwlogy, 1975, 42, 194-196. BRUCE.D. L.. BACH,M. J.. & ARBIT,J. Trace anesthetic effect on perceprual. cognitive and motor skills. Anestheswlogy, 1974. 40. 453-458. HAYS,W. L. Statistics. New York: Holt, Rinehart & Winston, 1963. LINDE,H. W., & BRUCE,D. L. Occupational exposure of anesthetists to halothane, nitrous oxide and radiation. Anesthesiology, 1969, 30, 363-368. WALLGREN. H., & BARRY,H. Actions o f ulcohol. Amsterdam, Neth.: Elsevier, 1970. WINER.B. J. Statistical principles i n experimental design. New York: McGraw-Hill, 1962. WINTER. P. M.. BRUCE,D. L., BACH,M. J.. & JAY, G.W. The anesthetic effects of air at atmospheric pressure. Anesthesiology, 1975. 42. 658-661. Accepted May 3, 1976.
AN AUDIOVISUAL TEST OF DIVIDED ATTENTION' M. J. BACH A N D D. L. BRUCE'
hTorthtoestern Universiry Medical School, Chicdgo, Illinois Summa7y.-A description is given of an audiovisual reaction time task, performance of which was maximal after 15 min. practice and which lasted at this level for 1 wk. Sensitiviq of the test was shown in an adverse effect of inhalation of traces of anesthetic gases. Comparing responses to auditory and visual stimuli, the control auditory reaction times were faster but were lengthened more in the presence of anesthetics than were the visual ones. This test may be useful in other studies of subtle depressant drug effects.
In the administration of anesthesia, gases and vapors are given to the patient by means of machines equipped with overflow valves through which these agents escape into the operating room air. Despite room air changes 8 to 12 times per hour, measurable amounts of anesthetics are present in the breathing zone of the anesthesiologist (Linde 81 Bruce, 1969). These concentrations approximate 1/1,000 of those given to the patient. Knowledge of this fact has caused equipment manufacturers to design gas "scavenging" systems to vent these gases from the room, while many groups have made studies of the possible health hazards of inhalation of trace gas. In a series of studies of behavioral effects of trace anesthetics on performance of healthy male volunteers, the most sensitive test was an audiovisual (A-V) task, specitically designed for chese invescigations (Bruce, et al., 1974; Bach, et al., 1974; Bruce & Bach, 1975). During an operation, the anesthesiologist monitors several sources of visual variables, such as: electrocardiographic display (ECG) on an oscilloscope; position of flowmeters on the anesthesia machine; flucmacion of pressure gauges in the breathing circuit; drip rate of fluids administered intravenously; and, oscillations of the gauge on the blood pressure recording apparatus. Concurrently, he must listen for: heart beat sounds in an esophageal stethoscope; the clicking of a pulse monitor if one is being used; the soft sound of normal breaching transmitted through the breathing tubes; the abnormal hissing sound of gas escaping from some point in the breathing circuit comprised of patient and machine, and the normal, rhythmic sound of the mechanical ventilator commonly used to breathe for the patient whose muscles of respiration are paralyzed by the use of muscle relaxant drugs. A task wherein the subject must monitor simultaneously a visual and an auditory pattern, each changing back and forth between two conditions, some'The project on which this publication was based was performed pursuant to Contract HSM-99-72-48 from the National Institute for Occupational Safety and Health, Center for Disease Control. 'Reprints available from D. L. Bruce, M. D., Department of Anesthesia, Nonhwestern University Medical School, 303 East Chicago Avenue, Chicago, Illinois 60611. U. S. A.
52
M. J. BACH
&
D. L. BRUCE
what simulates these tasks of the anesthesiologist. The test has not previously been described in detail sufficient to allow others to duplicate it. In the belief that chis sort of divided attention task mimics work performed by people other than anesthesiologists, a more complete description of it follows. Its extreme sensitivity to anesthetic agents suggests it may be useful in studying effects of low doses of other depressant drugs. In support of this idea are the studies reviewed by Wallgren and Barry ( 1970) in which alcohol differentially caused a greater increase in reaction rime to auditory than ro visual signals.
EQUIPMENT Auditory and visual signals were recorded on, and played back from, a four-channel FM instrumentation tape recorder (Hewlett-Packard, Model 3960). The auditory signals were generated by a metronome beating at 100 or 200 times per minute into a microphone connected to the voice channel of the tape recorder, from which they were played back to the subject through earphones (Vanco, Model HF-1) modified from stereophonic to monaural. In more recent work, the faster frequency has been reduced to IGO/min., reducing the range to make discrimination more difficult. The visual pattern was generated by an ECG simulator (Hewlett-Packard, Model 4653B) containing a cassette tape of various ECG rhythms. Ventricular fibrillarion was chosen for its high frequency and amplitude wave-form pattern, making it easily discriminable from a straight line for the medically naive subject. Originally, this was recorded alternately on one of two tape channels, each of which was connected for playback to one channel of a two-channel oscilloscope (Hewlett-Packard, Model 7803B). Thus, the wave was either on the top or bottom channel and a move from one to the other was the cue for the subjecc to respond. Recently, the test has been simplified to a single tape channel recording either the spike pattern described or a flat line (ECG cape curned off). Now, only one oscilloscope channel is used, and the subject responds when the flat line changes to a spike pattern, or vice-versa. The oscilloscope screen is 3 X 4.5 in. and the sweep speed is 25 mm/sec. The appearance of this display differs markedly from that of a slower sweep across a larger screen and may be important in duplicating our task conditions. The subject's response to a change in signal requires the depression of one of four buttons on a unit custom-made by Hewlett-Packard. This device is simply a box containing two mercury batteries (Mallory Duracel TR 146X) connected through resistors to the buttons. When a button is depressed, a square wave of amplitude one-half or one volt, positive or negative, is transmitted to a blank channel of the FM tape recorder. The buttons are labeled as follows: visual spiked, audio fast; visual spiked, audio slow; visual flat, audio fast; and, visual flat, audio slow. The final item in this equipment array is a Grass polygraph (Model 7 ) to
AUDIOVISUAL TEST OF DIVlDED ATTENTION
53
which the tape recorder is attached after the subject completes the task, and the three channels (auditory, visual and the subject's responses) are recorded on chart paper moving at 10 rnm/sec. with a 1-sec. time base recorded simulcaneously.
PROGRAMMING The changes in auditory and visual stimuli were plotted on a time scale. The task was balanced so there would be equal numbers of changes to each of the four conditions, and each change would involve only one modality, i.e., either an audirory or a visual change. In this way, a differential effect on one of these perceptive processes could be detected. This limits the choice, at any given rime, to rwo of the four buttons. There are only three to which a change could occur and one of these would require alterations of both auditory and visual signal. The choice between the remaining two was made arbitrarily as the program was developed, keeping in mind the needs to finish with a balanced set of 25 changes to each of the four choices and to have an apparent, if not real, random presentation to the subject. These 100 changes were completed in 7 min. The program for the first 2 min. is shown in Table 1 and the remainder is available upon request from the second author (DLB).
RECORDING The cape speed for both recording and playback is 3% in./sec. The sound channel was recorded first, in order to obtain a well defined starting point on the tape. An electric metronome, beating at the fast speed programmed firsc, was placed by the microphone and a stopwatch was started as recording began. At times where auditory changes were programmed, the metronome dial was turned to 100 or 160 beats per minute. At the end of the run, the tape was rewound to the starting point for visual recording on another channel. The ventricular fibrillation (spikes) pattern of the ECG simulator cassette tape was played through the oscilloscope to this second tape channel. An off-on switch was interposed berween the ECG and the oscilloscope so that when the switch button was depressed, the patcern changed from spikes to a flat line. Once again using the stopwatch, and beginning from the first sound of the auditory recording just made, the pattern required for the visual program was thus recorded. At the end of this, the two channels were played through the polygraph and the record produced was compared with the program to verify its correctness.
TESTING For testing purposes, a connection is made from the output jack of the visual tape channel to the oscilloscope and from the auditory channel to the earphones. A third channel is used to record the subject's responses, by connecting the response box to the input jack of that channel. Thus, as the cape advances,
TABLE I PROGRAM FOR FIRSTm O MINUTESOF AUDIOVISUAL TASK
Time Elapsed
Min. Sec.
Auditory Fast Slow Visual Spikes
Flat
0 00 04 09 12 17 21-25 29 35 38 44 48 52 54 x
x
X
x x
x x X
x
x
x X
x
x
x
X
x
X
X
x
x x
x x x
x
X
x
x
1 01 05 08 12 15 19 22 28 32 39 41 46 49 54 58
x
x X x
x
x
x
x
x x
x
x
x
x
x x x x x X
x x x
x
X
x
X x
x
AUDIOVISUAL TEST OF DIVIDED ATTENTION
55
the subject is presented with the auditory and visual patterns and his response is.recorded as he depresses the button corresponding to each change. At the end of the run, a complete recording of rest and responses exists. After playback through the polygraph, the test is re-used, the next subject's responses erasing those of the previous subject as the recording is made. The subject is told to place his preferred hand on the center of the response box, which is 8 in, wide, with the four buttons spaced 1% in. apart on a line parallel to the subject's shoulders. Thus, a response requires a lateral move from button to button. In practice, the subject's eyes are approximately 25 in. from the oscilloscope screen. The windows of the test room are covered by shades and overhead fluorescent lights provide uniform room lighting with no glare or reflections on the screen. The subject is allowed to vary the volume of the sound signal to a level he feels is comfortable. After the subject has left the laboratory, che outputs of the three tape channels are connecced to the polygraph on which is then recorded a chart of tesc and responses to be used for scoring subsequently. This is done by measuring the distance from change to response and converting rhis to time by reference to the 1-sec. time markers. A key is used to judge correct responses. Only correct responses are used to compute mean reaction time ( R T ) . Results from this tesc are arranged in a 2 X 2 table, listing order of exposure (first or second) vs exposure condition (air or air plus anesthetic). Statistical treatment of these data was by analysis of variance whereby the effect of anesthetic and practice could be evaluated separacely, as well as their interaction ( Winer, 1962 ) .
PILOTSTUDIES These studies were made using a previous program, which was of the same form but took 7.5 min. Ten members of the office and technical staff of this department were tested three times sequentially on one day, then once again, at the same time, a week later. In order to record the responses and rewind the tape, about 10 min. separated each test session of the first day. On each tesc, the first 50 responses were scored separately from the second 50. The subjects averaged 97% correct responses. Table 2 shows the effect of practice on RT. Improvement occurred rapidly, and comparison of adjacent means (Hays, 1963) showed only three significant decreases in RT, after 3.75, TABLE 2 MEAN REACTION TIMESIN LEARNING AND RETENTION STUDIES First Session
Elapsed Time (min.) Mean RT (sec.)
3.75 1.56
7.50 1.41
11.25 1.22
15.00 1.26
7 18.75 1.15
22.50 1.14
Days Later
3.75 7.50 1.11 1.11
M.J. BACH
56
8r D. L. BRUCE
7.5 and 15.0 min. There was no significance to the differences in scores obtained 1 wk. later. These data suggest thac 15 min. pracrice is sufficient to reach an asymptote on the learning curve and thac this is maintained at least for 1 wk., allowing retesting to occur without further pracrice sessions.
STUDIESUSINGT H E TEST Data from two studies are presented briefly to illustrate the sensitiviry of this test. Traces of the anesthetics, nitrous oxide ( N - 0 ) and halothane, given to subjects in concentrations similar to those found in operating room air, significantly increased RTs on this test (Bruce, et al., 1974). Data from those studies were analyzed further to determine any differentia1 effect on auditory versus visual RTs, and are summarized in Table 3. Since order of exposure to air or anesthetics was counterbalanced in the study and was not a significant source of variance, the data of Table 3 are collapsed across this variable. There was a significant ( p < .001) anesthetic effect on both RTs, but the originally faster auditory R T increased 29%, compared to an 18% increase in RT to visual signals in the anesthetic condition. TABLE 3 EFFECTS OF TRACE ANESTHETICSON AUDITORYAND VISUALREACTION TIME(SEC.)
Auditory Visual
Air
Condition N20 Halothane
1.42 1.84
1.83 2.17
+
% Increase in RT .41/1.42 .33/1.84
= 29
=
18
This auditory-visual cask not only reflects diminution in performance bur can also reflect enhancement. In another study (Winter, et al., 1975), the test was used to study the effect of replacement of the 80% of air that is nitrogen with the inert gas, helium. The idea for the study came from the notion that nitrogen narcosis at high pressures of N2 might also exist in a subtle form when breathing this "trace anesthetic" in ordinary air. The subjects of that study showed a statistically significant shortening of R T on chis task when breathing a helium-oxygen mixture as compared to air.
CONCLUSIONS A description is given of a simple test of reaction times to auditory and visual variation in signals presented concurrently. This test is easily assembled, programmed, performed and scored. It is quickly learned and well retained. It has been used to show both adverse and salutory effects of varying gas mixrures in the air breathed by the subjects. BACH, M. J., ARBIT, J.,
&
REFERENCES BRUCE.D. L. Trace anesthetic effect on vigilance. In C.
Xintaras, B. L. Johnson, & I. DeGroot (Eds.), Behavioral toxicology: early
AUDIOVISUAL TEST OF DIVIDED ATTENTION
57
detection o f occupational hrrzards. Washington, D. C . : U. S. Dept. of Hlth., Educ., Welf., 1974. Pp. 41-50. (PHs, Pub. NIOSH 74-126) BRUCE.D. L., & BACH,M. J. Psychologic studies of human performance as affected by traces of enflurane and nitrous oxide. Ane~therwlogy, 1975, 42, 194-196. BRUCE.D. L.. BACH,M. J.. & ARBIT,J. Trace anesthetic effect on perceprual. cognitive and motor skills. Anestheswlogy, 1974. 40. 453-458. HAYS,W. L. Statistics. New York: Holt, Rinehart & Winston, 1963. LINDE,H. W., & BRUCE,D. L. Occupational exposure of anesthetists to halothane, nitrous oxide and radiation. Anesthesiology, 1969, 30, 363-368. WALLGREN. H., & BARRY,H. Actions o f ulcohol. Amsterdam, Neth.: Elsevier, 1970. WINER.B. J. Statistical principles i n experimental design. New York: McGraw-Hill, 1962. WINTER. P. M.. BRUCE,D. L., BACH,M. J.. & JAY, G.W. The anesthetic effects of air at atmospheric pressure. Anesthesiology, 1975. 42. 658-661. Accepted May 3, 1976.
