standardized communications and message reception

THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA VOLUME 30, NUMBER 1 JANUARY, 1958

Standardized Communications and Message Reception* IRWIN POLLACK AND JOSEPH TECCEi

Operational Applications Laboratory, Air Force Cambridge Research Center, Bolling Air Force Base, Washington 25, D.C. (Received September 26, 1957)

The reproduction of messages, selected from defined information sources, was studied in a multichannel listening task. Standardization of message procedures was controlled independently of standardization of message nomenclature. It is shown that the standardization of procedures or nomenclature is an effective determinant of message reproduction. And, the joint standardization of both nomenclature and procedure is more effective than either alone.

ILITARY operational analysts have long recog- nized that standardized communication procedures and nomenclatures are superior to unstandardized communications. Language engineeringl--the application of information theory and measurement to human operator communications--has provided a con- venient rationale for the superiority of standardized communications. In effect, in any given situation, the number of possible standardized messages may be considerably smaller than the number of possible unstandardized messages. And, thus, the selection of a specific message from the set of standardized messages might be expected to be accomplished more readily than the selection of the same messages from among the set of unstandardized messages.

Standardization of communications, intuitively, makes sense. The rationale for standardization of com-

munications provided by language engineering also makes sense. However, a clear-cut empirical demonstration of the advantage of standardized communications has been sorely lacking. 2 The present paper considers such a demonstration.

We suspected that unsuccessful demonstrations of the advantages of message standardization were the result, in part, of the fact that the operator's task was con- fined to message reception alone and, thus, the task was too easy. We, therefore, chose to force the operator to share his time and attention among three tasks simultaneously:

1. He piloted a "simulated airplane." Actually, the task was to match patterns of lights produced by his control movements with patterns of programed lights. (School of Aviation Medicine Complex Coordinator CM 701F).

2. He guarded 24 "Magic-eye" tubes for an "abnormal" operating condition. A warning signal--either a master buzzer warning signal or a speech annunciator

* This is Technical Note 57-5 ASTIA Document Number AD 110084 of the Air Force Cambridge Research Center. This research was carried out under Air Research and Development Command Project 7682, Information Processing by the Human Operator.

$ Now at The Catholic University of America, Washington, D.C. 1 G. A. Miller, J. Acoust. Soc. Am. 22, 720 (1950). "Several experiments have clearly demonstrated that a small

restricted vocabulary (usually of single isolated words) can be received correctly at lower signal-to-noise ratios than larger vocabularies.

62

--indicated the presence of the "abnormal" condition. The elapsed time before identification of the "abnormal" condition was recorded. The average rate of occurrence of warning signals was 5 signals per 5-minute period. The warning signal program was constructed independently of the message program and, thus, overlap of warning signals and messages was possible.•:

3. He reproduced messages presented to him in a multichannel listening situation. Two talkers read messages selected from defined message sources and interchanged identification call signs in a random order. The operator was instructed to respond to only one of two identification call signs. Furthermore, he was instructed to delay his response until the message was terminated, as in the time sharing of a radio channel. The operator's response and the presented messages were monitored as a check that the required delay was observed. The characteristics of the messages will now be discussed.

DESIGN OF MESSAGES

Four message-conditions were considered:

1. Standardized procedure and standardized nomenclature (SP-SN).

2. Standardized procedure and unstandardized nomenclature (SP-UN).

3. Unstandardized procedure and standardized nomenclature (UP-SN).

4. Unstandardized procedure and unstandardized nomenclature (UP-UN).

Each message consisted of four message elements. The elements are listed in the first column of Table I.

Examples of standardized nomenclature are given in the second column. Examples of unstandardized nomenclature are given in the third column. The range of numerical alternatives was identical for all conditions, i.e., nomenclature was manipulated independently of numerical assignment.

Messages of standardized procedure contained the 4 message elements in the order presented in Table I. The order was randomly scrambled for unstandardized procedure.

:• The speech annunciator was always preceded by the master buzzer indicator. A more detailed discussion of the warning signal task may be found in Experiment II reported by I. Pollack and J. Tecce [J. Acoust. Soc. Am. 30, 58 (1958), this issue].

Redistribution subject to ASA license or copyright; see http://acousticalsociety.org/content/terms. Download to IP: 84.88.136.149 On: Tue, 25 Nov 2014

08:11:09

STANDARDIZED COMMUNICATIONS 63

TABLE I. Examples of message-elements with standardized and unstandardized nomenclature.

Unstandardized Message element Standardized nomenclature nomenclature

1. Identification Air Force 82 or Same

call sign Air Force 56

2. Bearing Bearing +5 ø north

3. Altitude Altitude 10 angels

4. Range Range 15 miles

Bearing q- 5 ø north (or south)

or direction q- 5 ø north (or south)

Altitude 10 angels (or thousand feet)

or height 10 angels (or thousand feet)

Range 15 miles (or kilometers)

or distance 15 miles

(or kilometers)

An example of a message under SP-SN condition is: Air Force 56

Bearing q- 16 north Altitude 35 angels Range 12 miles

An example of a message under SP-UN condition is: Air Force 82

Bearing -- 18 south Height 15 thousand feet Distance 19 miles

An example of a message under UP-SN condition is: Altitude 12 angels Range 29 miles Air Force 82

Bearing -- 13 north An example of a message under UP-UN condition is:

Range 13 kilometers Air Force 56

Direction q- 29 north Height 38 angels

Two talkers recorded the four basic message-conditions, i.e., SP-SN, UP-UN, etc. In a given session, the operator was exposed to a single message condition.

Each 40-minute session was divided into eight 5-minute periods. In turn, the eight periods were assigned to the combination of two message densities, two conditions of message overlap, and two methods of presentation. For the two message densities, each talker announced either 4 messages per 5-minute period or 10 messages per 5-minute period. For the two conditions of message overlap, the two talkers either spoke succes- sively with no message overlap or spoke with at least two-thirds message overlap. For the two methods of information presentation, either the warning signals and messages were presented to separate ears or both signals were presented to both ears.

Both talkers spoke at about the same average rate of 9 seconds per message and both spoke at about the same sound level. The period available for reproduction

of the message in the non-overlap condition was at least 10 seconds and the period available in the overlap condition was at least 15 seconds. The messages and warning signals were spoken by different male voices.

PROCEDURE

Each operator served for 10 sessions. On the first and last sessions, his only task was to pilot the Coordinator. In the other eight sessions, he performed all three tasks. Each operator had extensive experience with the Coordinator and warning signals.

Motivation was maintained at a high level by sub- stantial rewards for superior performance on all three tasks. In addition, the operators were paid for their services.

In one half of the sessions, the operator responded to messages with the identification call sign Air Force 56. In the other half of the sessions, the operator responded to call sign Air Force 82. Each operator was exposed to each of the four message conditions twice--once with each call sign. The eight combinations of message conditions and call signs were counterbalanced among eight operators.

RESULTS AND DISCUSSION

The test results for the message-reproduction task are presented in Tables II and III. Table II presents a summary statement of the significant message variables and of the average scores associated with the significant variables.

Notable is the lack of effect upon message reproduction of the variable of warning signal condition. Mes- sages were reproduced as well with a speech annunciator as with a buzzer warning indicator. This negative finding is important because it suggests that a speech

TABLE II. Significant message-variables, and the average scores associated with the significant variables, upon the message- reproduction task. Each entry represents the average percentage of messages correctly reproduced. The average score for each variable is based on 3584 messages--8 operators, each exposed to 8 experimental sessions, with an average of 56 messages per session. The level of statistical significance between adjacent scores within each variable was the 0.0! significance level based upon a t test for significance of mean-scores with the second-order residual as the estimated error variance.

Mean percentage Variable correct messages

Message conditions SP-SN 70.3% UP-SN 63.5% SP-UN 56.0% UP-UN 51.5%

Message density 4 messages/period 62.4%

10 messages/period 58.3 %

Message overlap Nonoverlap 65.5% Overlap 55.2%


08:11:09

64 I. POLLACK AND J. TECCE

TABLE III. Analysis of variance for message-reproduction task. Significant variables indicated by asterisk (*) at 0.01 level of significance by F test. The significance of the first-order effects was evaluated against the first-order residual. Only the significant nteractioin terms are reported. The successive columns represent the sources of variation; the associated degrees of freedom; the associated sum of squares, and the associated F ratio and its statistical significance. Two o•her variables--changes between successive experimental sessions and changes within each exper!- mental session--were also significant. However, since the experimental design confounded these variables with other variables, their contribution to variance was not extracted.

Mean square Source of variation df variation F ratio

Message condition 3 8 774 40.4* Message density ! 2 178 10.0' Message overlap ! 13 592 62.6* Method of presentation 1 24 0.1 Subject 7 3 772 17.4* Warning signal 1 0 0

(lst residual) 497 217

Condition X density 3 862 4.16' Overlap X subject 7 604 2.92*

(2nd residual) 487 207

• 70

• 60

• 50

4O SP UP SP UP

warning indicator may be satisfactorily employed even in tasks where speech communication is an integral portion of the total task complex. a

The message variables, with the exception of message- density, had no significant effect upon the Coordinator task and warning signal identification task. Therefore, we shall simply consider the effect of the message variables upon the message-reproduction task alone.

In Table II, the average percentage of messages Fro. 1. Accuracy of

80 message reproduction in

• 10/prd. a multichannel listening •- situation. Message con- (o •J•?':'"•.......'• 4/prd. dition is indicated along

abscissa. The average percentage of message elements correctly reproduced is scaled on the ordinate, the shad- ing represents two conditions of message density•4 messages per 5- minute period and 10 messages per 5-minute period. Each score is based upon 256 and 640 messages for the low and

$N $N ON ON high message densities, respectively.

a The negative finding of lack of influence upon message- reproduction, however, should not overshadow the positive advantages of the speech annunciator. The speech warning indicator was associated with significantly superior performance on the noncommunication variables--the Coordinator task and upon elapsed warning signal identification time. That the speech warning indicator, in addition, does not interfere with message reproduction removes an important objection to a speech annunciator warning system.

correctly reproduced varied from somewhat over 50% for the unstandardized procedure and nomenclature (UP-UN) to somewhat over 70O-/o for the standardized procedure and nomenclature (SP-SN). Furthermore, unstandardized nomenclature with standardized procedure produced significantly lower scores than unstandardized procedure with standardized nomenclature. The differences among the scores of successive message conditions are statistically significant. 4

Message density and message overlap were also significant variables, wi, th significantly higher performance associated with the lower message density and with the nonoverlap condition. The method of presentation, i.e., the routing of warning signals and messages to separate ears or to both earsmwas insignifi- cant in its effect upon either message reception or warning signal identification.

The significant interaction of message condition and message density is presented in Fig. 1. The percentage of messages correctly received for high and low message densities, for a .given message condition, is plotted for each of the message conditions. Significant differences between corresponding scores for each message condition are observed only for unstandardized procedures (UP-SN and UP-UN).

The Analysis of Variance 5 examination of the experimental results is presented in Table III. The un- accounted variance in the experiment--the mean variance associated with the second-order residual--is

about -• of 1% of the total variance. The estimated standard error of each estimate of the percentage of message-errors per 5-min period for each subject is (207)• or about 14.4%.

In summary, standardization of communications procedures and standardization of communications nomenclature have been shown to be effective deter-

minants of message reproduction. And, the joint standardization of both nomenclature and procedure is more effective than either alone.

4 The results clearly suggest that unstandardized nomenclature results in significantly poorer message-reproduction scores. How- ever, it may be reasonably argued that the specific words added in the unstandardized nomenclature tests (thousand feet vs angels; kilometers vs miles; direction vs range, etc.) simply constituted an inferior vocabulary. To test this objection, we reanalyzed all of the responses to the individual messages in the unstandardized nomenclature tests. Messages were first classified according to their nomenclature. Messages which employed the nomenclature restricted to the SN tests were separated from messages which employed only the additional nomenclature of the UN tests. (See Table I.) The reproduction scores showed no significant advantage for messages of either classification. (The additional nomenclature of the UN tests scored 4% higher than the nomenclature of the SN tests.) Stated otherwise, message diversity in the trials with unstandardized nomenclature was the important factor, and not the specific words employed.

s For further details, see J. C. R. Licklider and I. Pollack, J. Acoust. Soc. Am. 20, 42 (1948), especially Appendix and Table V, pp. 50-51.


08:11:09

standardized communications and message reception

Documents