plans and written directions for complex tasks

JOURNAL OF VERBAL LEARNING AND VERBAL BEHAVIOR 21, 70--84 (1982)

Plans and Written Directions for Complex Tasks

P E T E R D I X O N

Bell Laboratories, Murray Hill

Sentence reading t ime was measured while subjects followed a set o f mult is tep directions for operat ing an unfamiliar "e lec t ronic device ." Sentences were read faster when action information (e.g., " T u r n the left knob" ) came first and condit ion information (e.g., " T h e alpha meter should read 20") came second. This effect was observed when the condition information was an an tecedent or a consequen t of the action, when the action was in the main or subordinate clause, and when the action was performed immediate ly or from memory. This robus t result suggests that procedural directions are organized internally around the actions to be performed, and that condit ion information is r emembered only with respect to part icular actions. In this view, action-first sen tences are easier to unders tand because they provide the information in the order in which it is needed.

An important use of written language is the communication of procedural directions. Tasks such as operating complex equipment, performing periodic mainte- nance, and even following a recipe all de- pend on the efficient and accurate use of language to specify the necessary procedures. It is assumed here that using written multistep directions entails first translating the directions into some sort of mental representation or plan. This plan would specify in a symbolic form what has to be done to perform the task, and could be used to guide subsequent performance. This paper is concerned with the nature of such plans, and the process of constructing them from the information in written directions.

Prev ious studies of d i rec t ions have shown that the form the directions take can have important effects on reading time and comprehension. For instance, indirect requests such as, "Can you color the circle blue?" take longer to respond to than the direct form, "Please color the circle blue" (Clark & Lucy, 1975). Similarly, directions

Por t ions o f this r e s e a r c h were r epo r t ed at the P s y c h o n o m i c s S o c i e t y M e e t i n g s in St. L o u i s , November , 1980. The author wishes to thank Dennis Egan and Erns t Rothkopf for commen t s on previous drafts. Reques t s for reprints should be sent to Peter Dixon, Depar tment o f Psychology, Univers i ty of Al- berta, Edmonton , Alberta, T6G 2E9, Canada.

0022-5371/82/010070-15502.00/0 Copyright @ 1982 by Academic Press, Inc. All rights of reproduction in any form reserved.

with negations in them are more difficult than logically equivalent affirmative sentences (Wright & Wilcox, 1979). These effects may arise because some forms of a direction are incongruent with a mental plan for performing the task. In the studies above, for example, plans may be represented in an essentially direct and affirmative form, and indirect or negative sentences may have to be recoded to be consistent with that representation. This argument suggests that in general the difficulty of different forms of a direction may tell us something about the nature of mental plans; some forms may be difficult in part because they are incongruent with a plan's representation. A similar rationale will be used here to investigate how different types of information are used in constructing mental plans.

The use-order principle. Evidence on the role of different types of information may be provided by applying a "use -o rde r" principle of sentence difficulty. The principle is that all other things being equal, a sentence should be easier to understand if it presents information in the order in which it is used in comprehension. This principle may underlie a number of previous findings in which the physical order of information within a sentence contributes to its difficulty. For instance, sentences seem to be

70

1~ O L L O W I N G D I R E C T I O N S 71

easier to understand when they begin with the topic of the sentence (Broadbent, 1977), when they mention successive events in the correct order (Clark & Clark, 1968), and when they begin with given information rather than new (cf. Haviland & Clark, 1974). In all of these examples, sentences presenting one kind of information first may be easier because the comprehension process requires that information first. This idea is also related to the "principle of con- gruence" (Clark, 1969) that seems to account for some results in simple reasoning tasks (e.g., Sternberg, 1980), and is analo- gous to the argument used above to infer that plans are represented in a direct and affirmative form. When applied to procedural directions, the use-order principle indicates that comprehension should be easier if the order of information within a direction is congruent with the order in which it is used to construct mental plans.

Action and condition in[orrnation. In this paper , the use -order principle will be applied to two kinds of information found in directions. One kind might be termed action information. For example, the sentence '"The left knob should be turned in order to set the alpha meter to 20" indicates that the action to be performed is to turn the left knob. Another kind of information might be termed condition information, and indicates the conditions that might be encountered in the course of performing the action. For example, the sentence above specifies what the consequence of turning the left knob should be. Research from domains such as problem solving (Simon, 1975), planning (Schank & Abelson, 1977), and story comprehension (Black, 1980) indicate that action and condition information may serve very different functions. A similar conclusion is suggested for directions by a study of pictograms for complex procedures (Marcel & Barnard, 1979). When subjects tried to descr ibe what the pic tograms meant, they sometimes omitted condition information, but never omitted action informat ion. This suggests that subjects treated actions and conditions differently,

and viewed the actions as the more important part of the directions.

The question addressed in the following experiments is whether action or condition information was generally used first in constructing a plan from written directions. Di- rections for operating an unfamiliar "electronic device" were phrased with either the action information first or the condition information first. Subjects encountered the device many times, but the procedure for operating it was different each time. Thus, subjects were forced to read the directions on every trial in order to perform the task correctly. The patterns of sentence reading times were used to infer whether plans were constructed beginning with actions or conditions. For instance, if action-first sentences are read faster than condition-first sentences, the use-order principle would suggest that the action information is used first.

The experiments also manipulated the way in which the directions were used. On Immediate Performance trials, subjects performed each step while the sentence describing it was present. This task is similar to how people might use a cookbook; they could read one step from the book, perform that step, and then go on to read the next step. On Memory Performance trials, subjects had to read several sentences describing a sequence of steps, and then perform all of them from memory. This task is similar to how an automobile repair manual might be used. In both cases, it is not possible to refer to the directions between every step, and entire procedures may have to be remembered.

General Method

Each subject was shown a video display (such as that shown in Fig. la) and control panel (shown in Fig. lb), and told that they represented an imaginary electronic device that he or she would have to operate. Operating the device entailed making a series of knob adjustments and button presses, some of which were contingent on the meter readings° The required sequence

72 PETER DIXON

27 ~o I0~ ~40

0 ~ 5 0

GAMMA

20 3O 10 ~ t ,40

0 50

ALPHA

2p ~o t0~ ~40

O~ ,50

BETA

2O 3O t 0 ~ ~ 4 0

0 50

DELTA

I~ T.6 cm "1 (a)

© © ©

I,, 25~-crn "I (b)

FIG. 1. (a) Video display and (b) control panel used in Experiment 1.

of steps, the required meter settings, as well as the locations and names of the meters, all varied randomly from trial to trial. In order to perform the task, subjects had to follow the directions presented on each trial. Each time the subject pressed a foot pedal, a single sentence describing one of the steps appeared at the bot tom of the video display. For instance, the display might read " T h e left knob should be turned in order to set the alpha mete r to 20 . " This s en tence would then remain in view until the subject pressed the foot pedal to see the next sentence. The principle dependent measure in these experiments was the length of time subjects spent looking at each sentence between foot presses. Analyses were also per fo rmed on the t ime to pe r fo rm each step, and the pauses between steps, but such measures were generally statistically unreliable and did not suggest any modifi- cations to the present conclusions.

In Experiments 1 and 2, the display con- t a ined fou r m e t e r s l abe l ed " A l p h a , "

" B e t a , " " G a m m a , " and Del ta" (see Fig. la for an example). The meters were controlled by the three knobs on the control panel (shown in Fig. lb). Each of these knobs could be turned a total of 315°and was associated with two of the meters. As a knob was turned, one o f its meters increased (e.g., " A l p h a " in Fig. la), while the other decreased (e.g., "De l t a" ) . Two small black buttons were located below the outer knobs. Below the middle knob was a large red button labeled " R u n . " Pressing the " R u n " button was always the last step on a trial.

Two kinds of trials were used in the first two experiments: Immediate Performance trials and Memory Performance trials. On Immediate trials subjects could perform the action indicated by a sentence immediately after reading it. Consequent ly , subjects would read a sentence, perform that particular step, and then press the foot pedal to go on to the next sentence. Reading time for these trials was defined as the time from the onset of the sentence display to the first movement of the indicated knob or button. On Memory trials, all of the directions had to be read before touching any of the controls. On these trials, subjects would press the foot pedal after each sentence had been read, and remember what to do for that step. After going through all of the sentences, subjects performed the actions from memory. Reading time on Memory trials was measured from the sentence display onset to the next foot press.

The sequence of events on each trial was as follows. First the message " T u r n all knobs to the le f t" was displayed at the bot tom of a blank screen. When the knobs had been turned to their leftmost positions, the message was replaced by "Press the

p e d a l to see the first s tep." Pressing the pedal at this time displayed the meters and started the trial. The sentence displayed initially was " T h e knobs may be moved at any t ime" on Immediate trials, and "Read all the directions first" on Memory trials. The succeeding four sentences indicated adjustments of the knobs or buttons, and

FOLLOWING DIRECTIONS 73

will be described separately for each experiment. The last of the four sentences was always a direction to press the " R u n " button. Including a fourth sentence ensured that reading time measuremen t for the third sentence would be comparab le to that for the first and second. Reading time for the four th sen tence i tself was not ana lyzed since it contained no new information for the subject.

I f the subject per formed all the steps in the correct order, and if the meters were adjusted to within five units of their correct settings, the meters moved to 50, a high- pitched ringing was sounded, and the message " R U N N I N G " was shown at the top of the screen. I f the knobs were adjusted out of sequence, or the meters set to the wrong value, an error occurred. Errors were sig- naled by a low-pi tched buzzing, and the meters moving to 0. The screen was blank for about 5 seconds be tween this feedback and the start of the next trial.

Subjects were told that they were being t imed while they read the directions and opera ted the controls, but that they should be concerned primarily with accuracy. In Exper iments 1 and 2, trials were adminis- tered in blocks of 24. In order to minimize the possibility that subjects would develop task-spec i f ic s t ra teg ies , each subjec t in those exper iments had one block of practice trials fol lowed by only a single block of test trials. A session general ly took less than an hour.

Trials were control led by an Apple I I m i c r o c o m p u t e r sys tem. The la tency and dura t ion of each knob ad jus tment , foot press, and button press were recorded for l a t e r a n a l y s i s . The m e t e r d i sp l ay was shown light on dark on a 20-cm black and white video monitor. Directions appeared in u p p e r - and l o w e r c a s e on two 40- charac ter lines at the bo t tom of this screen. (Due to a technical difficulty about half of the subjects in Exper iment 1 saw the directions in uppercase only.) At a typical view- ing distance of 50 cm, letter spaces sub- tended about 0.6 ° of horizontal visual angle.

EXPERIMENT 1

Method

The task in Exper iment l required the subject to perform four steps. The first step was to adjust a meter to 10, 20, 30, or 40 by turning one of the three knobs shown in Figure lb; the second step was to press one of the two small buttons; the third step was to adjust ano ther mete r with a different knob; and the last was to press the " R u n " button. The position of action and condition information was varied in the first and third sentence only. On half of the trials these sentences began with what the action should be (i.e., whether the left, right, or middle knob should be turned), and on the other half the sentences began with what the consequence of the action should be (i.e., what the relevant meter should read). Hal f of the sentences were E m b e d d e d Consequence sentences, in which the action information was in the main clause of the sentence and the consequence information was embedded in a subordinate clause (e.g., " T h e left knob should be turned in order to set the alpha meter to 20"). The other half were Embed- ded Action sentences in which the reverse was true (e.g., ~'The alpha meter should r ead 20 as a resu l t o f tu rn ing the lef t knob") . In addition to differing in embedding structure the two types of sentences also differed somewhat in vocabulary and verb structure. In both types of sentences the main clause could be put either first or last. Thus, the overall effect of information order was independent of whether the main clause or the subordinate was stated first. The same type of sentence was used on the first and third step on a given trial. The second sentence was " T h e left button should be p ressed , " or " T h e right button should be p re s sed . " The fourth sentence was " T h e Run button should be p re s sed . "

Twenty subjects part icipated in a block of practice trials and a block of test trials. Each block consisted of a random mixture of three Immedia te Performance and three Memory Performance trials for each of the

74 PETER DIXON

four types o f s en t ences . Reading t ime analyses were per formed on the median times f rom these three trials, excluding t r ia ls on wh ich e r r o r s o c c u r r e d . One analysis was per formed on the first and third sentence and had four within-subject factors : pe r fo rmance condi t ion, type of embedding, informat ion order , and sentence number. A similar analysis of Sen- tence 2 reading times was performed separately. Data from three subjects were not used b e c a u s e of med ian read ing t imes greater than 20 seconds in some conditions.

Results and Discussion

Overall, sentences with the action stated first were read faster than sentences with the consequence stated first, F(1,16) = 5.40, p < .05, Ems = 1,939,321.1 (see Fig. 2). When combined with the use-order principle, this result suggests that action information is used before consequence information in constructing a plan. This ordering may be determined by how plans are organized. For instance, plans could be organized as a hierarchy, with the actions to be performed at the top level, and the consequences linked to the actions at a lower, subord ina te level . At the highest level , then, a plan would be simply a list of the actions to be performed. The most natural way to construct such a plan would be to first find the action for each step, and then to find the consequence associated with that action. Consequences could not be in- corpora ted into a plan first, since there would be nothing to which to link them. Thus, Consequence -Ac t ion sentences may be diff icult to read because the consequence cannot be fully processed until after the action has been incorporated into the plan. Ac t i on -Consequence sentences may be easy to read because they provide the action information when it is needed.

This effect of information order was rep- l icated using E m b e d d e d Condi t ion sentences like, "Tu rn the left knob to set the

1 Error mean squares are expressed in mil l iseconds squared.

65°°i/ 6000

5 5 0 o E

5000

w 4500

A-C C-A

EMBEDDED CONSEQUENCE

51• MEMORY PERFORMANCE

/ MMED,ATE PERFORMANCE

I I A-C C-A

EMBEDDED ACTION

FIG. 2. Mean sen tence reading t ime for cor rec t trials in Exper iment t as a funct ion o f sentence number (1 or 3), information order ( A c t i o n - C o n s e q u e n c e or C o n s e q u e n c e - A c t i o n ) , type of sen tence (Embedded Consequence or Embedded Action), and type of performance ( Immediate or Memory) .

alpha meter to 20" and Embedded Action sentences like, " T h e alpha meter should read 20 after you turn the left knob . " The only major difference from the present results was that Embedded Action sentences took longer to read than Embedded Condi- tion sentences, perhaps because they contained more syllables. Thus, the present results are not restricted to a single vocabulary and syntactic structure.

Figure 2 also shows an interaction among sentence number (1 or 3), information order (whether the sentence began with the action or consequence) , and embedding (whether the action or consequence was in the main clause), F(1,16) = 4.82,p < .05,Es = 999,484. This interaction indicates that when compared to the first sentence, the third sentence was read relatively quickly when it began with the main clause. Since the second sentence always began with the main clause, this might be an effect of parallel structure; the third sentence might be easier to parse when it repeats the clause order


used in the second sentence. Some of the Sentence 2 results suggest a similar effect. Tab le 1 shows that Sen t ence 2 read ing times on Memory Per formance trials were shorter following sentences beginning with the main clause, F(1,16) -- 6.05, p < .05, Eros = 197,991. Further evidence on this kind of repetit ion effect will be considered in Ex- per iment 3. For no apparent reason, a repetition effect was not found on Immedia te P e r f o r m a n c e Sen tence 2. Ins tead , these sentences were read 72 milliseconds faster fo l lowing E m b e d d e d C o n s e q u e n c e sentences, F(1,16) = 9.82, p < .01, Eros = 9557.

Figure 2 suggests a reversal in the information order effects for Embedded Action sentence on step 3 of Memory Performance t r ia ls . H o w e v e r , this r e v e r s a l was not statistically significant and can plausibly be a t t r ibu ted to the var iabi l i ty of M e m o r y r e a d i n g t i m e s . T h e r e was a lso a 302- mi l l i s econd ove ra l l d i f f e r ence b e t w e e n Sentence 1 reading times and Sentence 3 times, but this was not reliable either. The only other significant reading time effect was the difference be tween Immedia te and Memory reading times (for Sentence 1 and 3, F(1,16) = 57.32, p < .001, Ems = 7,141,946.; and for Sentence 2, F(1,16) = 67.81, p < .001, Eros = 977,263.).

The error rate on Immedia te trials was 2.0%; all of these errors were misadjustments of the meters on step 1 or 3. The er ror rate on M e m o r y trials was signifi- cantly larger at 16.7% (p < .01, two-tailed

TABLE 1 SENTENCE 2 READING TIMES (msec) IN EXPERIMENT 1

Sentence 1 type Reading time

Immediate Performance Action-embedded consequence 1345 Embedded consequence- action 1278 Embedded action-consequence 1383 Consequence- embedded action 1387

Memory Performance Action-embedded consequence 2644 Embedded consequence-action 3049 Embedded action-consequence 2705 Consequence-embedded action 2579

sign test). Of these errors, 50.0% involved turning the wrong knob on step 1 or 3, 35.3% were meter misadjustments on step 1 or 3, and the rest occurred on step 2. The number and type of errors did not vary sig- nificantly as a function of sentence type.

EXPERIMENT 2

The fact that action information seems to be used first in constructing a plan may re- flect the p lan ' s internal organization. As suggested above, one possibility is that a plan is organized as a hierarchy in which the topmost level consists of a list of the act ions to be pe r fo rmed . This might be t e rmed an ac t ion-sequence organizat ion. Condition information could be represented in the hierarchy as well, but at a subordinate level, where it would be linked with particular actions. Since conditions would be subordinate to actions, a given condition could not be incorporated into such a plan until after its associated action had been encoded. Thus, the use-order principle im- plies that action-first sentences should be easier to understand.

Another possibil i ty is that both action and condition information are put into the plan in the order in which they are used in performing the task. Thus, a strict temporal order would dominate any distinction between act ion and condit ion informat ion. Since an action must be started before the consequence of the action can be evaluated, actions would be needed before consequences. Thus, a temporal -order organizat ion predicts that Ac t ion-Consequence sen tences should be eas ie r than Conse- quence-Act ion sentences , jus t as the ac- t ion-sequence organization does.

However , these two organizations make different predictions about how antecedent condi t ions would be p roces sed . An an- t e c e d e n t cond i t ion mus t be met before the action is performed. I f plans are organized as lists of actions, the nature of a condition should not make any difference; an antecedent condition should still be remembered in relation to a particular action,

76 PETER DIXON

and that action would have to be incorporated into the plan before the condition. A different prediction would be made by the temporal-order organization. Since antecedent conditions have to be evaluated before the action, the antecedent information should be incorporated into the plan first. Thus, the temporal-order organization predicts that Antecedent-Action sentences should be easier than Action-Antecedent sentences, while the action-sequence organization predicts that action-first sentences should always be easier.

To test these predictions, a task variant was designed with a step that could be described equally well with antecedent and consequent sentences. The first two steps in the task involved setting the alpha and beta meters by turning the left and right knobs. As in Experiment 1, the gamma and delta meters also moved in the course of these adjustments. The critical third step was then to adjust either the gamma or delta meter to a new value by holding down one of the two small buttons below the left or right knobs. The gamma and delta meters moved as long as the button was depressed and stopped moving when it was released. Table 2 shows the antecedent and con-

sequent sentences used to describe this step.

Subjects were told that consequent sentences contained an implicit antecedent condition, and that antecedent sentences contained an implicit consequent condition. For example, with both the consequent sentence, "Hold the left button down to get the alpha meter above 20 ," and the antecedent sentence, "Hold the left button down if the alpha meter is below 20," subjects were told to behave as if the direction had been " I f the alpha meter is below 20 hold the left button down to get the alpha meter above 20." That is, with both sentences they were to hold the button down until the alpha meter was above 20, and were not to do anything if the alpha meter was already above 20. An error occurred if the button was held down longer than necessary (i.e., if the alpha meter was adjusted to 30 or more). Thus, subjects performed exactly the same task regardless of whether an antecedent or consequent condition was stated.

Method

The apparatus and general procedure were the same as in Experiment 1 except

TABLE 2

ERROR RATES AND SENTENCE 3 READING TIMES (msec) IN EXPERIMENT 2

Sentence 3 structure a

Immediate Immediate Memory Performance Performance Performance reading time errors (%) errors (%)

Action-Consequence 4561 Hold the (left/right) button down to get the (gamma/delta) meter (above/below) (10/20/30/40).

Consequence-Action 5183 To get the (gamma/delta) meter (above/below (10/20/30/40) hold the (left/right) button down.

Act ion- Antecedent 4803 Hold the (left/right) button down if the (gamma/delta) meter is (above/below) (10/20/30/40).

Antecedent - Action 5031 If the (gamma/delta) meter is (above/below) (10/20/30/40) hold the (left/right) button down.

12.8 25.6

5.1 23.1

5.1 38.5

7.7 48.7

The notation "(left/right)" is used to indicate that only one of the words separated by slashes appears in the sentence.

F O L L O W I N G DIRECTIONS 77

that the middle knob was not used. The first step was to adjust the alpha meter with the left knob, and the second step was to adjust the be ta meter with the right knob. The gamma and delta meters also moved during these steps. The sentences describing the first two steps were of the form, '~Turn the (left /r ight) knob to set the (a lpha /be ta) meter to (10/20/30/40)." The third step was to adjust ei ther the gamma or delta meter to a new value by holding down either the left or right button. The four types of sentences for this step are shown in Table 2. How far and in what direction each meter was to be adjusted was chosen r andomly on each trial. On the average, about half of the sentences used the adjective ~ 'above ," and half ~ 'below." The fourth sentence was " T h e last step is to press the Run bu t ton . " In a block of trials each sentence type occurred three t imes in an Immedia te Performance trial and three t imes in a Memory Perfor- mance trial. One out of the three was a Catch trial on which no action was to be per formed on the third step. The other two were Execut ion trials on which the action was to be executed.

Thir teen college students each received two blocks of 24 randomly mixed trials; the first b lock was considered practice. The analysis of Immedia te Per formance reading times was per formed on the mean of the third sentence times for the two Execut ion t r i a l s , e x c l u d i n g e r r o r t r ia l s . The two wi th in - sub jec t f ac to r s were in fo rmat ion order and an teceden t versus consequen t condition. A similar analysis could not be performed on Memory Per formance trials because of an ex t remely high error rate; only three subjects had at least one correct trial for all sentence types. No significant effects could be found by including either error or Catch trials. The Memory Perfor- mance task appeared to be too difficult to collect reliable reading times under these c i rcumstances .


The results suggest that plans are organized around actions, ra ther than in a strict

tempora l sequence. In the Immedia te Per- formance condition, Sentence 3 was read faster when the action was stated first and the condition stated second, regardless of the nature of the condition F(1,12) = 5.17, p < .05, Eros = 455,596. (see Table 2). The average reading time for sentences with the t e m p o r a l l y a p p r o p r i a t e o rde r ( i .e . , Ac- t i o n - C o n s e q u e n c e and A n t e c e d e n t - A c - tion sentences) was somewhat faster than that for sentences with the reverse order, but this tendency did not approach signifi- cance, F(1,12) < 1, Eros = 971,436.

As can be seen in Table 2, errors were more numerous on Memory trials than on Immedia te trials (p < .001, two-tailed sign test). Of the Immedia t e Per fo rmance errors, 50.0% occurred on step 3 of Catch trials, 33.3% occurred on step 3 of Execu- tion trials, and 16.7% occurred on steps t and 2. Of the Memory Performance errors, 18.9% occurred on step 3 of Catch trials, 54.7% occu r r ed on step 3 of Execu t ion trials, and 26.4% occurred on steps 1 and ?. Among Memory Performance trials, errors were more numerous on Antecedent sentences than on Consequent sentences (p < .05, two-tailed sign test).

One strategy subjects could have adopted in this task would have been to recode antecedent sentences into consequent sentences. For example, the sentence " H o l d the left button down if the gamma meter is below 20," could be translated into " H o l d the left button down to get the gamma meter above 20." With this approach subjects would essentially be dealing with only con- s e q u e n t s e n t e n c e s . Bo th the ac t i on - sequence and temporal -order plan organizations would then predict that sentences with the action stated first would be read faster.

Several aspects of the results suggest that this did not occur. To begin with, none of the subjects reported doing this kind of recoding, although they were otherwise fairly candid about how they tried to do the task. Second, it might be expected that such recoding takes time, and would have led to i nc rea sed read ing t imes for a n t e c e d e n t

78 PETER DIXON

sen tences . On the average , a n t e c e d e n t sentences took only a nonsignificant 45 milliseconds longer to read. Finally, if the process of r e c o d i n g a n t e c e d e n t into consequent conditions was error free, there should not have been any differences in how well they were remembered. But more errors were made on antecedent Memory trials than on consequent Memory trials. (An error prone recoding process might account for this difference, but would also in- correct ly predict more errors on antecedent Immediate trials than on consequent Im- mediate trials.) Although none of these ar- guments prove conclusively that recoding did not occur, they do seem to detract from its plausibility.

EXPERIMENT 3

A possible problem with the previous experiments is that the action and condition information differed in many ways, only one of which was the qualitative distinction between actions and conditions. For instance, the number of alternative actions that could be specified in a sentence was always less than the number of alternative conditions. Similarly, the presence of nu- merical informat ion in the condi t ion also may have affected processing. Experiment 3 was designed as a replication of Experi- ment 2 that controlled for these kinds of differences. The conditional clauses in this experiment specified that one of three lights shou ld be on, and the ac t ion c l auses specified that one of three buttons should be p ressed . With this a r r a n g e m e n t the number of alternative actions and conditions was always three. Moreover , both actions and conditions were described with alphabetic labels (A, B, and C for the buttons and X, Y, and Z for the lights). The only difference between the two kinds of clauses would then seem to be whether an action or a condition was being specified.

This experiment also looked more sys- temat ica l ly at the repe t i t ion ef fec t suggested by Exper iment 1. In the Memory trials of that experiment, the second sentence (which always began with the main

clause) was faster following first sentences that began with the main clause. Addition- ally, for both Memory and Immediate trials, third sentences were relatively fast when they began with the main clause, an effect that might be due to the repetition of the clause order used in the second sentence. To investigate this effect, the order of the different types of sentences was explicitly controlled in this experiment. The results should then show whether the repetit ion effect extends to sentences beginning with the subord ina te c lause , and whe the r it interacts with the type of condition used.

A different method of measuring reading time was used in Exper iment 3. On Imme- diate trials in the previous experiments , reading t ime included the t ime to start executing the action. One question left un- answered by this procedure is the extent to which o rde r of i n fo rma t ion af fec ts the execut ion of the indicated actions rather than the reading process. The assumption so far has been that the process of constructing a plan occurs during reading, and that the same plan is arrived at regardless of the order of information in the sentence. If this is true the effects of information order should be restricted to the reading process alone. The paradigm used in Exper iment 3 was designed so that the measured reading time could not include any part of the task execution. Thus, it provided a clear distinction between reading time and execution time.

Method

The apparatus in Experiment 3 consisted of a video display and a control panel as before. In this case the display consisted of three square " l ights" labeled X, Y, and Z. A filled square indicated that the light was on, and an empty square indicated that it was off. The controls consisted of three buttons labeled A, B, and C. Subjects used a four th bu t ton labeled " S e n t e n c e " to present sentences on the screen. Otherwise the apparatus was the same as in Experi- ments 1 and 2.

On each trial a subject read a sentence


describing an action to be per formed and a condition re levant to that action. Actions specified pressing one of the but tons, and conditions specified that a particular light should be on. A condition could be either an antecedent of the action (i.e., true before the act ion was pe r fo rmed) , or a consequence of the action (i.e., true after the action was performed). In addition, the sentence could state the action first, or the condit ion first. Ha l f of the subjects saw sentences in which the action was embedded in a subordinate clause, and half saw sentences in which the condition was embedded (see Table 3). As in Exper iment 1, the two types of embedding also differed in vocabulary and verb structure. The choice of A, B, or C and X, Y, or Z in a sentence was done randomly on each trial under the constraint that a corresponding button and light (e.g., A and X) never occurred to- gether in the same sentence.

Trials were ei ther Execut ion trials (on which the subject pressed the A, B, or C button) or Catch trials (on which no action was performed). In ei ther case, a trial began when the subject pressed and held down the Sentence button. When this happened the screen went blank for about 1 second and then a sentence appeared at the bo t tom of the screen. After reading the sentence, the subject re leased the Sentence button, and the sentence was replaced by the X, Y, and Z lights. Reading t ime was measured f rom the sentence display onset to the release of the Sentence button.

On Execut ion trials with antecedent conditions, the subjects had to turn off the light ment ioned in the sentence by pressing the indicated button. On Execut ion trials with consequent conditions, the light had to be turned on by pressing the button. The relevant light changed state after a button had been held down for a random interval f rom 0.5 to 2.0 seconds. The states of the other two, irrelevant, lights did not change and were chosen so that at least one of the three lights would be on and at least one would be off. On Catch trials, the sentence described

either a false antecedent condition or a true consequent condition, and subjects simply went on to the next trial by pressing the Sentence button. No feedback was given either on Execut ion or Catch trials. Sub- jects were told to use only one finger for pushing the Sentence and A, B, and C buttons. Execut ion time was measured f rom the onset of the lights display to the pressing of button A, B, or C. On Catch trials, condit ion evaluat ion t ime was measured from the onset of the lights display to the pressing of the Sentence but ton to start the next trial.

Each subject participated in six blocks of 26 trials. The first block and the first trial of each succeeding b lock were cons ide red practice. Of the 25 remaining trials in each block, five, or 20%, were Catch trials. The other 20 trials consisted of five Execut ion trials for each of the four types of sentences. For the purpose of assessing repetition effects, the 25 trials were divided into five equ ip robab le c lasses . Each type of Execut ion trial sentence was a class, and Catch trials made up the fifth class. The order of the trials was arranged so that each of the 25 possible combinat ions of trial class and preceding trial class occurred once.

Subjec ts were 20 N e w J e r s e y house- wives paid for their services. Ten saw the Embedded Action sentences and ten saw the Embedded Condition sentences f rom Table 3. Data f rom an additional subject in the first group were not used because of an error rate of 44% on Catch trials. Separate analyses were per formed for reading time, execution time, and evaluation time on the medians over blocks of trials, excluding trials on which subjects made an error . Reading times were expressed in terms of milliseconds per syllable to compensa te for the fact that Embedded Action sentences were longer than E m b e d d e d Cond i t ion sentences.


Reading time. Overall , sentences were read fas ter when they began with the action

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to be performed rather than the condition, F(1,18) = 8.80, p < .01, Eros = 2980. (see Table 3). However, this effect occurred only on Embedded Act ion sen tences , leading to a significant interaction between information order and embedding, F(1,18) = 8.30, p < .01, Eros = 2980. This pattern of results can be accounted for by two addi- tive effects: a 15-millisecond per syllable advantage for sentences beginning with action information, and a 17-millisecond per syllable advantage for sentences beginning with the subordinate clause. These two effects would tend to cancel each other out in Embedded Condition sentences, and to reinforce each other in Embedded Action sentences, resulting in the obtained in - teraction with embedding. The advantage for sentences beginning with the subordinate clause may have occurred because the preposition beginning the clause was the only indication of whether an antecedent or consequent condition was being stated. (This was not true of the sentences used in Experiments 1 and 2.) Since the type of condition may affect the nature of the plan being constructed, it might be important to have this information early in the sentence.

The overall information order effect sup- ports the general conclusion that directions are read faster when they begin with an action rather than a condition, and eliminates several possible explanations for this effect. It cannot be attributed to different numbers of alternative actions and conditions because the action and condition information were entirely equivalent. Clause order repetition effects like those in Experiment 1 cannot affect the results because the order of sentences was completely balanced. Task execution factors were also minimized by the way in which reading time was measured. Finally, a temporal-order explanation cannot account for the fact that the information-order effect occurred for both antecedent and consequent sentences, rep- licating Experiment 2. The most likely explanation seems to be that subjects use the directions to form mental plans for per-

forming the task, and that these plans are organized around the actions to be performed. Sentences beginning with the action information are read quickly because they are congruent with the internal representation being constructed.

Reading time was also affected by the nature of the previous trial, F(4,72) = 7.09, p < .001, Eros = 2401. Sentences preceded by an Execution trial with exactly the same form (e.g., an Action-Consequence sentence preceded by another Act ion-Con- sequence sentence) took 27 milliseconds less per syllable than the other sentences. This effect could be due to the exact repetition of sentence wording, or to a more general clause order repetition effect like that suggested by Experiment 1. However, the type of condi t ion (an tecedent or consequent) must be repeated as well as the clause order. No advantage was found for sentences that repeated the clause order but used a different type of condition. This lim- itation would not have been apparent in Experiment 1 because only consequent conditions were used. In addition, trials preceded by a Catch trial took 20 milliseconds per syllable longer to read than those preceded by Execution trials. No other reading time effects or interactions were significant.

E x e c u t i o n and eva lua t ion t ime. Sen- tences beginning with a condition had faster execution times, F(1,18) = 7.20, p < .05, Eros = 86633., and slower evaluation times, F(1,18) = 4.63, than sentences beginning with an action. A tentative explanation of this result is that condition-first sentences increased a subject's expectation that the antecedent condition would be true, and that the action would have to be performed. Although this bias would improve the time to execute the action, it would have to be overcome on Catch trials, and would lead to longer evaluation times. The essential feature of this account is that mental plans varied somewhat with information order, and that this lead to the differences in execution and evaluation time.

82 PETER DIXON

A n o t h e r poss ib le e x p l a n a t i o n is tha t there was a t rade-off be tween execut ion time and reading time. Subjects may have released the Sentence button too soon with action-first sentences, and finished forming the mental plan during the execution interval. Al though this would pred ic t longer execut ion times with action-first sentences, it does not explain why evaluation times were shorter. It is also important to note that this sort of explanation does not suffice for the effect of information order on reading time. The execut ion t ime effect was small compared to the reading time effect, and an analysis of the total, reading plus execution, time revealed the same significant effects as reading time alone.

Both the execut ion and evaluation t imes were slower for antecedent sentences than for consequent sentences, F(1,18) = 4.41, p = . 05, Ems = 74,954.; F (1,18) = 8.21, p < . 05, Ems = 212,678. Perhaps subjects possessed a s tereotype that buttons should turn lights on. Since the effect of pressing a button on an teceden t sentence trials was to turn a light off, extra time may have been needed to o v e r c o m e this be l i e f while dec id ing whether or not to perform the action. No other execution or evaluation time effects were significant.

Errors. Error trials are shown in Table 3. Subjects reading E m b e d d e d Act ion sentences tended to make more errors than those reading E m b e d d e d Condi t ion sentences, part icularly on Catch trials. How- ever, these differences were not reliable.

GENERAL DISCUSSION

These exper iments show that in the present type of task, directions are read faster if the action information is placed first and the condition information second. This is true regardless of whe the r the act ion is per- fo rmed immedia te ly or is to be r emembered, whether the action is to turn a knob or to press a button, whether the condition is the value of a meter or the state of a light, w h e t h e r the ac t ion o c c u r s in the main clause or a subordinate clause, and whether

an tecedent or consequen t condit ions are used. In short, the finding appears to be fairly robust and general.

If the information-use principle can be applied in this situation, it suggests that action information is used first in constructing a plan. This in turn may be due to the way in which a plan is organized internally. One possibility consistent with the present results is that a plan is organized as a list of the actions to be performed. Condition information (such as when an action is to be performed, or what its consequence should be) would only be stored subordinate to particular actions. In this kind of organization, the condit ion information in a sentence could be processed only after the action information had been incorporated into the plan. I f the condition occurs first in a sentence, its processing would have to be deferred until the end of the sentence. In contrast , the action-first order would sup- ply the action and condition in the order in which they are required. Although this particular model is clearly speculative, the data strongly suggest that the early acquisition of action information in some way aids the construct ion of plans f rom written directions.

A number of other studies are consistent with the results and conclusions presented here. Subjects verbally interpreting pictograms for complex procedures often omitted condi t ions but neve r act ions (Marcel & Barnard, 1979). In a story recall exper iment Black (1980) found that subjects r emembered action information bet ter than condition information. It has also been found that action themes aid in remember ing informa- t ion p r e s e n t e d in a p i c tu re ( G o o d m a n , 1980). Final ly , Wright & Wilcox (1978) found that subjects took an average of 100 milliseconds less t ime to read action-first sentences such as " D r a w a circle above a square" than condition-first sentences such as " A b o v e a square draw a circle ." This seems to be an in fo rmat ion-order effect similar to that found here. In sum, the results f rom a var iety of different paradigms


seem to converge on the idea that action information has a special status in mental representations.

It is possible that different plan organizations are used in different tasks. In the experiments reported here the actions followed each other in a fixed order. How- ever, in many tasks conditional branching is possible, and actions have to be selected on the basis of the current conditions. (Al- though subjects in Experiments 2 and 3 did choose whether or not to press a button, this choice was not between competing actions.) Condition information may be relatively more important when it specifies which of a var ie ty of possible actions should be performed. Thus, the present results may generalize only to situations in which the actions specified by the directions have a linear ordering.

However, if the present results do hold up across a range of situations, it would lead to fairly straightforward recommenda- tions for writing better directions: All other things being equal, action information should be stated prior to any associated conditions. The critical element in applying such a r e c o m m e n d a t i o n would be in evaluating whether in fact other things were equal. In any practical situation, changing the structure of a sentence involves trading off a variety of other factors that have been shown to be important in comprehension, such as active or passive voice, syntactic structure, and sentence length. Thus, care must be taken to ensure that an advantage in information order is not offset by other kinds of problems. An additional consid- eration is that the order of action and condition information affected primarily reading time in these experiments, not errors. Thus, the usefulness of this recommenda- tion may be limited to situations in which time is an important performance measure. (One example where time is important is the direction, "Break glass in case of fire," which may be preferable to " In case of fire break glass. ")

An alternative explanation of these re-

suits is that the information-order effect merely reflects linguistic convention, and has no bearing on the information require- ments of constructing a plan. People may expect directions to state the action first, and may be surprised or otherwise unpre- pared when this expectation is violated. This explanation seems unlikely since vary- ing other linguistic conventions had little effect on reading time. For instance, it is customary to place the main clause first in a sentence . Howeve r , placing the main clause last did not increase reading time. Similarly, it might be conventional to place action information in the main clause. But again, no effect of embedding was found when sentences were equated for syllable length. Thus, an appeal to linguistic convention cannot be a complete explanation of these results. An account must also be provided for why some conventions affect reading time and others do not.

The task in these experiments was designed to be devoid of semantic content. The names and settings of the meters were meaningless, the assignment of knobs to meters was arbitrary, and no information was provided about the internal operation of the device. This was done to minimize the effects of prior knowledge on task performance, and to avoid interactions among successive trials of the experiment. How- ever, people generally bring a wealth of information (and misinformation) to tasks in- volving written directions. Consequently, an important area for future research is the investigation of how the information-order effect isolated here interacts with the variety of other sources of information available in most uses of written directions.

REFFERENCES

BLACK, J. B. Memory for state and action information in narratives. Paper presented at the Psychonomic Society Meetings, St. Louis, 1980.

BROADBENT, D.E . Language and ergonomics. Ap- plied Ergonomics, 1977, 8, 15-18.

CLARK, H. H. Linguistic processes in deductive reasoning. PsychologicalReview, 1969, 76, 387-404.

CLARK, H. H., & CLARK, E. V. Semantic distinctions

84 PETER DIXON

and memory for complex sentences. Quarterly Journal of Experimental Psychology, 1968, 20, 129-138.

CLARK, H. H., & LucY, P. Understanding what is meant from what is said: A study in conversation- ally conveyed requests. Journal of Verbal Learn- ing and Verbal Behavior, 1975, 14, 56 -72 .

COKE, E. U. The effects of readability on oral and si- lent reading rates. Journal of Educational Psy- chology, 1974, 66, 406-409.

GOODMAN, G.S . Picture memory: How the action schema affects retention. Cognitive Psychology, 1980, 12, 473-495.

HAVlLAND, S. E., & CLARK, H. H. What 's new? Ac- quiring new information as a process in comprehension. Journal of Verbal Learning and Ver- bal Behavior, 1974, 13, 512-521.

MARCEL, T., & BARNARD, P. Paragraphs of pictograms: The use of non-verbal instructions for equipment. In P. A. Kolers, M. E. Wrolstad, & H. Bouma (Eds.), Processing of visible language. New York: Plenum, 1979.

SCHANK, R., & ABELSON, R. Scripts, plans, goals, and understanding. Hillsdale, N.J.: Erlbaum, 1977.

SIMON, H. A. The functional equivalence of problem solving skills. Cognitive Psychology, 1975, 7, 268-288.

STERN~ERG, R . J . Representat ion and process in transitive inference. Journal of Experimental Psy- chology: General, 1980, 109, 119-159.

WRIGHT, P., & WILCOX, P. Following instructions: An exploratory trisection of imperatives. In W. J. M. Levelt & G. B. Flores d' Arcais (Eds.), Studies in the perception of language, New York: Wiley, 1978.

WRIGHT, P., & WILCOX, P. When two no's nearly make a yes: A study of conditional imperatives. In P . A . Kolers, M . E . Wrolstad, & H. Bouma (Eds.) Processing of visible language. New York: Henum, 1979.

(Received December 19, 1980)

plans and written directions for complex tasks

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