A measure of vigilance in infancy

INFANT

BEHAVIOR

AND

DEVELOPMENT

A Measure

13,

I-20

I1 990)

of Vigilance

in Infancy

HOLLY A. Rum, MARY CAPOZZOLI, KAREN DUBINER, AND ROSEANNEPARRINELLO Albert Einstein College of Medicine These studies were designed to investigote visual vigilance, that is, attention to the location of an anticipated event, in infonts. The general paradigm was to present with intervals between events ranging the infants with interesting puppet events, from 5 to 25 seconds. The dependent measure was the amount of time the infant spent looking between events at the place of the events’ occurrence. In the first study with infants of 5, 7, 9, and I 1 months, there were no age differences in the duration of looking either at the events themselves or at the place of the puppet’s appearance and disappearance during the intervals between events. Compared to the inter-event looking of younger infants, however, the looking of the 9- and 1 I-month-olds was composed less of looks that were continuations of looks at the puppet before it disappeared and more of looks at that place later in the inter-event intervols. In two other studies of IO-month-olds, the amount of looking at the place of occurrence during inter-event intervals was influenced by the salience of those events, suggesting the effects of motivation. In all studies, the variation among individuals wos high; in addition, the correlations between the first half of the session and the second half were strong ond positive. The results suggest that elements of vigilance are present at an early age, and that there are consistent individual differences in the extent to which such attention is maintained.

attention

anticipation

viailance

expectation

The mechanisms that control sustained attention are considered to be basic processesimportant to learning about and adapting to the environment (Kahneman, 1973;Parasuraman& Davies, 1984). To some extent, the duration of sustained attention varies among individuals and may reflect individual differencesin responseto environmental events (Ruff, in press). There are now a number of studies that explore sustained attention in infants; investigators have employed duration measures of looking (e.g., Cohen, 1972),exploratory behavior (e.g., Ruff, 1986), and persistenceat “tasks” (e.g.,Yarrow et al., 1983)in an attempt to capture this sustained aspect of attention. Measures of sustained heart rate deceleration have also been illuminating (Richards, 1987). All of these measuresreflect the maintenanceof attention for the purpose of gathering The work BNS8519487,

reported and by

here was supported a Research Scientist

by a grant Development

Institute of Mental Heolth to the first author. The authors thoughtful comments on an earlier version of this article for

Study 1. Correspondence

Center,

Albert

and Einstein

requests College

far

reprints

of Medicine,

from the National Award, MH00652,

Science from

wish to thank Gerald and lgnaj Trokki for

should

be sent

1300

Morris

to Holly Park

Turkewitz for his building the stage

A. Ruff, Room

Avenue,

Bronx,

Foundation, the National

NY

222,

Kennedy

10461. 1

2

RUFF, CAPOZZOLI,

DUBINER,

AND

PARRINELLO

information about an event or of reaching a goal; they are all measured in contexts wherethe infants get continuous information from the ongoing events and/or from their ongoing activity. The most common measures of sustained attention in school-aged children are quite different. Investigatorsfrequently employ vigilance tasks, either extended simple reaction time or continuous performance procedures; dependent measuresinclude reaction time and number of missed signals and extraneous responses(e.g., Krupski & Boyle, 1978; Levy, 1980).These measuresare assumedto reflect, in part, the degreeto which the subject is attending to the task. The attentional processesrequired in thesetasks may well be different from those involved in watching ongoing events, interacting with objects, or working on complex tasks (Pribram & McGuinness, 1975).In the vigilance paradigms, subjectsmust maintain attention in the absenceof the event and cannot be influenced by continuously changing stimulation. With this possible differentiation in mind, we asked whether vigilance could be observed in infants. Becauseit cannot be observed under the conditions used with older children and adults, we tried to isolate the basic elements and find an appropriate context for assessingthem. If vigilance is the maintenance of attention for the purpose of responding to an expectedevent, the basic requirements for visual vigilance are (a) an expectation that an event will occur in a particular location; (b) the motivation to attend to that location when the event is not there; and (c) responsepreparation, though this last element could be very general. The question asked here is whether, and under what circumstances, infants can be motivated to attend to or wait for events to occur in a given location. We assumedthat the expectation would develop readily becauseit is such a low-level one. The infants need to learn only about location; they do not need to learn anything about the timing of an event, as in a study of 7-month-olds by Donohue and Berg (1988), or anything about the temporal-spatialpatterning of events occurring in two locations, as in the study of 3-month-olds by Haith, Hazan, and Goodman (1988). If developing such a simple expectation is easier than that required in the two cited studies, then it could occur very early in infancy and could easily develop with only one or two instances, particularly if the event is salient for the subject (see Piaget, 1954, Obs. 2, p. 9). Becausewe could not instruct infants to look at a particular place in the absenceof the event, we had to rely on the event being interesting enoughto elicit such a response,as the recently enteredmousehole is for a cat. The procedure we used involved the presentation of an exciting event in a particular placeand the measurementof the time spentattending to that location after the event was no longer there. Pilot work with 34 lo-month-old infants demonstrated the feasibility of the method. A distinctive doll appearedover the edge of a table at which the infant sat, moving and calling the child by name. All infants looked at the doll when

VIGILANCE

IN INFANTS

3

it was present, 12 with soberexpressions,22 with smiles; 23 of the infants also reachedfor the doll, including 5 of the infants who did not smile. The responseto the doll demonstratesthe salienceof the event for them. The doll then disappearedfor 20 s, and the dependent variable was the duration of time the infant spent looking at the place of disappearance. There werethree such inter-event intervals. The mean duration of looking at the place of disappearanceduring the inter-event intervals ranged from 0 to 15 s per 20-s interval. These results demonstrate extended attention during the doll’s absencein some infants. The correlations between intervals in the overall duration of anticipatory looking were high (.61-.77) suggestingindividual consistency. There were three generalexpectationsthat influenced the design of the studies that followed this pilot work. First, it was hypothesized that attention to a location in the absenceof an event would be controlled, in part, by the salienceof the event. This hypothesis was based on the assumption that infants would wait longer or be more attentive in anticipation of a more exciting or interesting event than one that was less exciting. Second,basedon the pilot work, it was expectedthat individual infants would vary consistently in the duration of such anticipatory attention. Third, it was considered that there should, in principle, be a differencein the processesunderlying sustainedattention during a waiting or vigilant period and sustained attention during the active intake of information about an object or event. Therefore, it was expectedthat the two kinds of attention measured in the same infants would not be correlated. STUDY

1

In typical vigilance tasks, the subject is uncertain about when the signal is going to occur. With this uncertainty, efficient performance requires a more or less constant level of alertness and preparednessto respond throughout the interval betweenthe signals.In this Crst study, we therefore presentedeventswith randomly varied intervals betweenevents. We also changed events from trial to trial to diminish the possible effects of habituation. To manipulate the motivation to attend to and wait for the absentevent, we varied the salienceof the event by manipulating sound level, movement, and the variety and type of puppets.Finally, we studied infants between 5 and 11 months of age to determine whether or not there were age-relateddifferences in the extent to which attention is maintained in this context. Method

Subjects. There were 14 infants (9 girls, 5 boys) with a mean age of 23.1 weeks (SD = 0.9 weeks), 15 infants (7 girls, 8 boys) with a mean age

4

RUFF, CAPOZZOLI,

DUBINER,

AND

PARRINELLO

of 32.6 weeks (SD = 1.1 weeks), 13 infants (7 girls, 6 boys) with a mean age of 40.5 weeks (SD = 1.2 weeks), and 14 infants (7 girls, 7 boys) with a mean age of 49.3 weeks (SD = 1.2 weeks). The infants were selected on the basis of birth weights between 2500 and 3800 gms, estimated gestational ages between 38 and 42 weeks, and the absence of perinatal complications. Originally, 16 infants were seen in each age group, but after viewing the videotapes, some infants at each age were judged to be not involved at all in the puppet shows or too fussy, and their data were discarded. Because these infants were not replaced, the number of infants shown the low-salience condition first was not exactly the same as the number of infants shown the high-salience condition first; the numbers were 6 and 8, 8 and 7, 6 and 7, and 7 and 7 for the four age groups, respectively. Apparurus. For the presentation of the events, a stage was constructed with a base and two upright sides; all three pieces measured 91 cm X 61 cm. A curtain hung from the two upright sides and formed the third side of the stage. The stage was set up on a narrow hospital table that could be rolled into place in front of the infant at the appropriate time. Two sets of puppets were used in each session. The high-salience puppets included the following brightly colored characters with distinctive facial features: a large frog, Sesame Street’s Ernie with a striped shirt, a darkgreen frog with a bow tie, a red dragon, and a large doll with prominent eyes. The low-salience puppets included the following less colorful and smaller puppets with less distinctive features: a pink pig, a rooster, a yellow nondescript animal, a brown monkey, a green nondescript animal, and a brown bear. A green furry “Sprite” (a commercial doll with colorfully striped legs and a distinctive face) was used at the beginning of the session to catch the infant’s attention; it was not part of either the low- or highsalience series. A Sony portable videorecorder and camera were used to record the session, and a Commodore computer programmed to serve as an event recorder was used to code behavior from the videotapes. The puppet presentations and intervals between were timed by an audiotape played back through a GE recorder with an ear phone. Procedure. Prior to the puppet events, the infant was seated on the mother’s lap at a desk and presented with four pairs of small objects to manipulate freely. This part of the session lasted up to 20 min; although the details have no direct bearing on the results reported here, the procedure did provide us with a measure of attention during manipulative play. When this procedure was completed, the puppet stage was placed so that it sat over the desk, and the experimenter moved behind the stage and out of view. The infant remained on the mother’s lap, seated opposite the midpoint of the stage. The video camera was positioned so that the

VIGILANCE

IN INFANTS

5

lens came through the extreme right side of the curtain. Each puppet was presentedthrough the curtain at the far left side of the stage.The first event, not part of either series, was the Sprite doll moving through the curtain and saying, “Hi [infant’s name]. I’m a Sprite.” while moving up and down for about 6.5 s. As it was removed, the experimenter said, “Bye”; every puppet event ended in that same way. The appearanceof the next puppet started either the high- or low-salience condition. Each condition involved six 6- to 7-s events with different puppets. For each condition, there were six inter-event intervals, two each of 5, 15, and 25 s, irregularly scheduled.The reappearanceof the Sprite marked the end of the last interval of the secondcondition. The experimenter controlled the timing of events and intervals by listening to the audiotape which notedthe beginningand end of eachevent and counted secondsin between. The low- and high-salienceconditions differed not only in the type of puppet but also in the nature of the event. First, in the low-salience condition, the puppet was kept at the same location at the far left of the stage,and in the high-saliencecondition, the puppet moved from left to right acrossthe stageand back again.Second,in the low-saliencecondition, the experimenter said, “Hi [name]. Here I am. How are you? Bye.” in a subduedvoice, whereasin the high-saliencecondition, the experimenter said, “Hi there [name]! I’m a [friendly frog, e.g.]! I see you! Bye.” in a louder and more animated voice. DependentMeusures.The main dependentmeasurewas looking at the point of entry and departure during the inter-event intervals; it was recorded from the videotapes with good reliability. The looking of four infants (one at each age) was measured by two independent observers; the averagePearsonproduct-moment correlation between the observers’ total durations of looking in 12 inter-event intervals was .91. Becausethe looking time distributions in the intervals tended to be positively skewed, durations were transformed into logarithms to help normalize the distributions and reducevariability. For the trials involving manipulative play, we measuredduration of focusedattention or examining (Ruff, 1986) and the duration of looking at each object. Results The infants in this study spent an averageof 93% of available time looking at the events and 21% looking at the entry point on the stage between events. Two 4 X 2 (Age X Sex) analysesof variance were conducted, one with total duration of time spent looking during the events as the dependentvariable, and one with the logarithms of total time spent looking at the entry point during the intervals between events. There were no effectsof Age or Sex and no interactions between them, Fs < 1.10. The data from boys and girls were thereforecombined for subsequentanalyses,

6

RUFF, CAPOZZOLI,

The

Totol

Duration

of looking

ot the

looking

DUBINER,

TABLE 1 Events ond During

PARRINELLO

the

Inter-Event

ot Events

looking

low

Age

AND

High

Intervals-Study Between

I Events

low

High

5 months M

SD

33.1 5.1

fBS%l

37.1 2.6

(95%)

15.3 7.4

(17%)

13.7 9.5

ll5%1

35.7 3.4

192%)

37.2 3.1

l95%1

21.1 12.8

123%)

18.7 12.1

f21%1

35.9

192%)

37.1

195%)

22.9

125%)

20.9

(23%)

7 months M

SD 9 months

M SD

3.1

2.8

17.3

17.4

11 months M

34.9 3.3

SD Note.

Values

(90%)

in parentheses

37.6 (92%) I .5 ore

percent

of available

23.1 17.7

(26%)

16.0 13.2

(18%)

time.

but Age was retained as a factor because of interest in possible interactions of Age with other variables. We conducted two 4 X 2 X 2 (Age X Order: low-salience first vs. low-salience second X Level of Salience) analyses of variance; the dependent variable in the first analysis was total looking time during the events and in the second analysis was logarithms of total looking time between events at the entry point. For looking at the events, there were no effects of Age or Order, F(3,48) = 1.60 and F( 1,48) = 1.40, respectively, but there was a highly significant effect of Salience, F( 1,48) = 18.20, p < .OOl. This effect was not qualified by any significant interactions with Age or Order and was due to the consistently longer looking in the highsalience condition than in the low-salience condition (see Table 1). For looking at the entry point between events, there was a significant effect of Salience unqualified by any interactions, F(1,48) = 8.30, p = .005, but no effects of Age or Order, Fs < 1.00. In this case, the infants looked consistently less after the high-salience events than after the low-salience events. Less looking after the high-salience events was unexpected because it had been hypothesized that the high-salience events would lead to higher motivation to attend in the intervals that followed them than would the low-salience events. After the fact, however, it occurred to us that the movement of the puppets across the stage in the high-salience events and the static location in the low-salience events could be the critical difference. One possibility was that the infants’ expectations about where the event was going to reoccur were not as tightly tied to the entry point in the

VIGILANCE

IN INFANTS

7

high-salience condition, where the puppets moved across the stage, as in the low-salience condition, where the puppets always stayed in one Place. TO test this possibility, we scored the videotapes for the duration of looking across the stage, excluding looks at the entry point, during interevent intervals. We were careful to exclude any looks at the camera, which was on the far right of the stage. These durations, along with the durations of time spent looking at the entry point, were entered into a 4 X 2 X 2 (Age X Location: entry point vs. rest of stage X Salience) analysis of variance. Only the Location X Salience interaction was significant, F(1,52) = 4.50, p = .036. This interaction stemmed from the fact that the infants looked more at the entry point and less across the stage in the low-salience condition (MS = 20.3 s vs. 18.6 s), whereas they looked fess at the entry point and more across the stage in the highsalience condition (MS = 17.2 s vs. 19.7 s). This suggests that the infants monitored the whole stage more in the inter-event intervals when the puppet had moved across the stage during the event. Another possibility was that, when the infants had been looking at the entry point during the entire event (low salience), they continued to look at that point longer than when they had been following the puppet as it moved to a different place and then back again (high salience). In order to test this possibility, looks that were continuations of looking at the puppet before it disappeared were separated from all looks that occurred after any continuing look had ended. We then conducted a 4 X 2 X 2 (Age X Type of Look: continued vs. other looks X Salience) analysis of variance using the total duration of each type of look as the dependent variable. The effect of Salience, F(1,52) = 8.60, p = .005, however, was unqualified by any interaction with Type of Look or Age, suggesting that the difference between conditions was not due only to continued looks. In the preceding analysis, the only other significant result was an interaction between Age and Type of Look, F(3,54) = 3.40, p = .024. The duration of continued looks decreased from 7 to 11 months, whereas the duration of other looks increased. When each child was given a single score representing the proportion of total looking during the interval spent in continued looks, the proportions were .54, -61, .36, and .43 for the four age groups, respectively. A one-way ANOVA yielded a significant result, F(3,52) = 5.40, p = .003, and Neuman-Keuls post-hoc tests show that the proportion for 7-month-olds was significantly higher than that for the 9- and 1 1-month-olds, and the proportion for the 5-month-olds was significantly higher than that for the 9-month-olds. These data suggest that the older infants turn away sooner after the event has stopped but monitor the location longer into the interval. To show this pattern in more de*M, we divided the inter-event intervals into 5-s segments. The first segment represents a mean over all intervals because all intervals were at least 5 s long; the second and third segments represent a mean

RUFF, CAPOZZOLI,

Mean

Durations

fond

DUBINER,

TABLE Deviations)

Standard by 5-S

AND

2 of

looking

Segments-Study

(Months)

in the

Inter-Event

Interval

1

Seconds Age

PARRINELLO

in Interval

o-5

6-10

1 I-15

16-20

21-25

5

1.75 IO.901

0.29 IO.281

0.28 (0.24)

0.29 (0.391

0.63 (0.451

7

2.13 (0.65)

0.62 10.881

0.54

0.47

0.73

(0.57)

(0.55)

(0.78)

9

II

Note.

Stondord

1.87

0.83

(I.291

(0.84)

0.81 10.631

0.74 (0.76)

0.97 10.77)

I .67 fO.90)

0.75 I I .06)

0.88 10.941

0.66 (0.61)

1.1 I 10.90)

deviations

are

in parentheses.

over those two intervals in the 15-s and 25-s intervals; and the fourth and fifth segmentsare means from the 25-s intervals. As can be seenin Table 2, more looking occurred in the first 5 s than later in the interval; after the first 5 s, however, the amount of looking .wasevenly distributed within agegroups.A 4 X 5 (Age X Segment)analysisof variance revealed only a significant effect of Segment, F(4,208) = 76.40, p -c .OOl. A Newman-Keuls post-hoc analysis shows that the 6rst segment is significantly higher than all other segments,ps < .Ol. The only other significant differenceis betweenthe fourth and fifth segments,p < .05; this difference, however, should be viewed with caution becausethe procedureof putting the puppet through the curtain may have caused a little movement of the curtain before the appearanceof the puppet and consequently may have causeda slight rise in looking time. It has already been noted that variability was high. In order to obtain some estimate of the consistency of response within individuals, the looking time during intervals in the low-saliencecondition was correlated to the looking time in the high-saliencecondition. The Pearsonproductmoment correlations calculated separatelyfor the four age groups were high and significant, .84, .84, .70, and .75, respectively,ps < .Ol, thereby demonstrating considerableindividual consistency.There was little evidence for a relationship between anticipatory attention and attention during manipulative play. The correlations betweenlooking in the interevent intervals during the vigilance and looking at the free-playtoys were .lO, .25, -.05, and .48, all nonsignificant, for the 5-, 7-, 9-, and 1l-montholds, respectively; the equivalent correlations betweenanticipatory attention and focused examining (Ruff, 1986) were .25, .12, -.50, and .14, respectively, all nonsignificant. Becauseall of these measureshad high

VIGILANCE

IN INFANTS

9

variability, the generally low correlations are not due to a restriction of rangein any variable. Discussion

The study reveals relatively little changeover age in either the response to the puppet events themselves or the amount of time attending to the stagein the absenceof events. The ability to develop an expectation for an event and attend to the place of occurrence in its absenceseems to be thereby 5 months, though the older infants distribute their anticipatory looking more throughout the interval than the younger infants. Because the infants are very consistent from one half of the session to the next, individual differencesin this age range are more evident than developmental changes. Unfortunately, the attempt to show that vigilance, or attention to a location in the absenceof an event, varies with level of motivation was not successful.That we did vary the salienceof the event is demonstrated by the effectof saliencecondition on the looking during the actual events themselves.However, the fact that the puppets moved across the stage in one condition and not in the other confuses the issue of motivation with possible differencesin where the infants may have expected the events to reoccur. We therefore conducted another study where this confusion would not exist. STUDY

2

In this second study, we chose to observe infants at a single age, 10 months, and to manipulate the salienceof events which always occurred in the samelocation. We changedthe method and presentedeventsbehind a one-wayscreenwhich allowed us to more accuratelytime the beginning and end of events by turning lights behind the screen on and off. We manipulated salienceby the variety of puppets,the volume and animation of sound, the brightness of the lights, and the degreeof movement. Method

The method was generally the same as in Study 1, except that we tried to make the two levels of salience more extreme. As before, the infants were presentedwith a seriesof short puppet events separatedby intervals of 5, 15, or 25 s. There were 12 events; 6 were designedto be of lower saliencethan the other 6. The high- and low-salienceeventswere presented in blocks and counterbalancedacross infants. Within each block, two trials were followed by a 5-s interval, two with a 15-s interval and two with a 25-s interval; the intervals were randomly scheduled.All sessions were videotaped.

10

RUFF, CAPOZZOLI,

DUBINER,

AND

PARRINELLO

Subjects. There were 20 subjects (9 boys, 11 girls) with a mean age of 10 months, 9 days (SD = 4.3 days). The infants were selected on the basis of the same criteria as in the last study. Apparatus. The main part of the apparatus was a wooden box, 38 cm X 30 cm X 32 cm, which was open at the back. The box was painted matte black, and the front consisted of a piece of gray Plexiglas. The box was placed on the hospital table and a very large piece of black cloth was used to cover the entire table and all but the front of the box. Just inside the Plexiglas there were four strip lights connected to a single power supply outside the box so that they could be turned on and off together. When the lights were on, events inside the box could be seen; when the lights were off, nothing was visible. There were only two puppets in the low-salience condition-a brown monkey and a green dragon. There were six distinctive puppets used in the high-salience condition-a multicolor Sprite doll, a clown, a stuffed roadrunner, a rooster, a large brown bear, and a purple popple doll. A Sony portable camera and recorder were used to record the infant’s face during the procedures. A small night light was attached to the side of the apparatus out of the infant’s sight. It was connected to the switch operating the lights and was therefore turned on and off with the lights inside the box; this put a visible signal onto the videotape to mark the events. The timing of events was accomplished by the experimenter listening to an audiotape with instructions for setting up the low- or high-salience condition and with signals indicating the beginning and end of each event. Procedure. The infant was seated on the mother’s lap at about a 45” angle to the screen. The room lights were turned off, but considerable light came into the room from a window. This light made it possible to see the infant’s face on the videotape but kept the inside of the box invisible without the internal lights. The position of the infants allowed them to view the events within the box when the lights in the box were on, but kept them from seeing their reflections in the Plexiglas when the lights were out. Half of the infants were assigned to the low-salience condition first. For this condition, two lights were disconnected. To attract the infant’s attention, the experimenter quickly flashed the remaining two lights on and off three times; then the first puppet was put into place, the lights were turned on, and the puppet was displayed for 6 s while the experimenter said in a subdued voice, “Hi [infant’s name]. Look at me.” The experimenter, who sat under the black cloth, wore a long black glove and held the puppet still near the front of the box. This event was followed by a 5-, 15-, or 25-s interval of darkness before the second event. For the low-salience condition, the two puppets alternated trials for six trials; during the last interval, the other two lights were connected to the

VIGILANCE

IN INFANTS

11

power strip, and the first high-salience event was presented. In the highsalience condition, the experimenter moved the puppets up and down and said in a louder and more animated voice, “Hi [name]. Look at me. I like to play.” There were six of these events, each with a different puppet, and each followed by 5, 15-, or 25-s intervals. The last interval ended with three flashes of light. After the 12 trials and 12 intervals were complete, the child and mother moved to a desk and the infant was presented with four objects, one at a time, to play with in any way. Dependent Measures. The measure of vigilance or anticipatory looking was defined again as the amount of time spent looking at the place where the event had been. These durations were also transformed into logarithms. In addition, we measured the amount of time spent looking at the events themselves. For manipulative play with objects, we recorded both focused attention or examining and total duration of looking at each object. Results and Discussion The infants spent an average of 62.2 s (SD = 5.6 s) looking at the puppet events, or approximately 86% of the time that the puppets were visible. They spent an average of 74.4 s (SD = 25.9 s) looking at the Plexiglas side of the box in between events, or approximately 41% of the total interval time. We conducted two 2 X 2 (Order: low-salience first; high-salience first X Level of Salience) analyses of variance. As can be seen in Table 3 (p. 12), the first analysis showed that the infants looked more at the highthan the low-salience events, F( 1,18) = 11.20, p = .003. The second analysis of looking during the intervals also revealed an effect of Salience, F( 1,18) = 4.30, p = .05, with the infants looking more after high- than low-salience events. This effect, however, was qualified by a significant interaction between Order and Salience, F( 1,18) = 9.10, p = .007. The interaction stemmed from a highly significant effect of Salience for the infants who saw the high-salience events first, F(1,9) = 20.70, p < .OOl, and no effect for the children who saw the low-salience events first, F( 1,9) < 1.00. If the infants were responding to the novelty of the situation as well as to the level of salience, then having the high-salience events come second might have helped to offset a decline in looking due to the decreasing novelty of the situation. In addition, the infants in the high-low condition may have been somewhat disappointed by the low-salience events after having already experienced the high-salience events. Because the interaction between Order and Salience did not appear when looking at the events themselves was analyzed, the results may suggest that looking during the inter-event interval is more sensitive to changes in motivation. In order to explore the inter-event looking more thoroughly, we separated it as before into looks that were continuations into the inter-event

12

RUFF, CAPOZZOLI,

Totol

Duration

of

looking

at the

DUBINER,

TABLE 3 and During

Events

looking

at

salience

29.5

SD

Intervals-Study looking

2

Between

Events

low

High

182%)

32.6

(91%)

42.1

3.6

(47%)

14.7

40.3

i45%l

14.8

second

M

29.8 2.3

SD Note.

Inter-Event

High

5.4 salience

the

first

M

low

PARRINELLO

Events

low low

AND

Values

in parentheses

183%)

are

33.2 2.0

percent

(92%)

28.0

131%)

10.0

of available

37.8

142%)

10.5

time.

interval of looks at the puppet and looks that occurred after the infant had turned away, even briefly, from the Plexiglas screen. The 2 X 2 X 2 (Order X Type of Look X Salience) analysis revealed, as before, the salience effect and the interaction between Order and Salience. The total duration of other looks was significantly more than the duration of continued looks, F( 1,18) = 17.70, p <.OOl, but there were no interactions involving Type of Look. The Order by Salience interaction, therefore, appears to stem from total looking and not from a particular category of look. Table 4 shows that, as in the last study, more looking occurs in the first 5 s after the event than in any other 5-s interval. This pattern is confirmed by a significant effect of 5-s segment in an analysis of variance, F(4,76) = 27.50, p < .OOl, with a Newman-Keuls post-hoc test showing that looking time in the first segment was significantly higher, ps < .Ol, than in all other segments, which do not differ from each other. The fact that, as before, looking after that first 5 s was fairly steady is suggestive of a fairly constant level of monitoring of the target location. We again asked how consistent anticipatory looking or vigilance was by correlating the looking time on the first six trials with the looking time on the last six trials. The Pearson product-moment correlation was TABLE Mean

Durations

fond

4

Standard Deviotions) of bv 5-s Seaments-Studv

looking

Seconds o-5 low

High

salience

salience

Note.

Standard

2.89 (1.13)

in the

Inter-Event

Interval

2 in Interval

6-10

11-15

16-20

21-25

1.58 10.951

1.42 10.81)

1.13 (0.881

1.32 (0.82)

2.96

1.78

1.84

I .52

1.58

(0.94)

fO.801

(0.73)

(1.35)

(1.18)

deviotions

are

in parentheses.

VIGILANCE

IN INFANTS

13

.71, p < .Ol. We then assessedthe relationship between anticipatory attention and exploratory attention by correlating the total duration of looking during all inter-event intervals with the amount of time spent examining the objects during manipulative play; the correlation was -.49, p < .05. The correlation between duration of anticipatory attention and duration of looking at the objects was -.22, nonsignificant. These results suggesteven more strongly than the previous study that the two types of attention may be quite different. STUDY

3

Another way to vary the salienceof an event is to repeat it. As the infant habituatesto the event, there should be a decline in motivation to look at it and to wait for it in the intervals. The purpose of this study was to examine the changesin vigilance that occur as the result of repetition. In the previous two studies, there was little indication of a change over trials in the amount of anticipatory attention; this lack of change was most likely due to the fact that there was a different event on each trial, but could also be due, in part, to the unpredictable interval between events.In this study, therefore,eventswere repeatedunder two conditions, one in which the interval betweeneventswas constant, the other in which the interval between events varied as in the earlier studies. Method

We useda within-subjectsdesign,and eachinfant receivedboth conditions; the order of the conditions was counterbalancedacrossinfants. One event was repeatedin eachof the first six trials, and another event was repeated in the next six trials, regardlessof the order of conditions; in this way, each event occurred equally often in each condition. In the constantinterval condition, there were six 15-s intervals; in the variable-interval condition, there were two 5-s,two 15-s,and two 25-s intervals irregularly scheduled. Subjects. The subjects for this study were 14 infants (7 boys, 7 girls) with a mean age of 10 months, 8 days (SD = 4.9 days). The data from three other infants were not used; two infants were excluded becausethey were extremely fussy during the session and another infant was then excluded to keep the design balanced. Procedure. All infants were seen in the same circumstances and with the sameapparatusas the infants in Study 2. Three flashesof light signaled the beginning of the session,and the experimenter then presented a toy roadrunner who moved around in a lively fashion and “talked” to the infant. The event lasted for 10 s before the lights were.turned out. If the

14

RUFF, CAPOZZOLI,

DUBINER,

AND

PARRINELLO

constant-interval condition was first, the dark interval was 15 s long; if the variable-interval condition was first, the interval was either 5, 15, or 25 s long. The lights were turned back on and the event was repeated. This sequence was continued until six repetitions of the event and six intervals had occurred; three flashes of light signaled the end of the first half. In the second half, the infant was presented with the other condition and saw six repetitions of an event involving the Sprite doll dancing around and talking to the child with a somewhat different script. The final interval was ended with three flashes of light. The same dependent variables were coded from videotapes as were coded in the previous studies. To prepare data for analysis, we summed looking time to the puppet over the first three trials and then over the second three trials to obtain a measure for each half of each condition. We then did the same thing for looking during the interval; these latter numbers were transformed into logarithms. Results and Discussion The infants spent an average of 108.8 s (SD = 1.8) looking at the events, or approximately 91% of the time the puppets were visible. They spent an average of 63.3 s (SD = 25.5) looking at the front of the box in between events, or approximately 35% of the total interval time. We first conducted two 2 X 2 X 2 (Order: variable interval first vs. constant interval first X Condition X Half) analyses of variance. In the first analysis, the dependent variable was duration of looking at the puppet. Despite the fact that looking was near a ceiling, there were significant main effects of Order, Condition, half, and a significant interaction between Order and Condition. All of these were considered to be qualified, however, by the Order X Condition X Half interaction, F( 1,12) = 9.70, p = .008. When the variable condition came first, there was no change from the first to the second half of the six trials, but there was a decline in the constant condition; when the constant condition came first, there was no change from the first to the second half of that condition, but there was a decline from the first to the second half in the variable condition. In other words, there was no decline within the first condition, but there was a decline within the second condition, regardless of the nature of the intervals (see Table 5). The data show that the infants looked less overall at the puppet in the second condition. Whether this difference was due to the order of the conditions or to the particular puppet used in the second condition cannot be determined because the two puppets always appeared in the same order. In the second analysis with the logarithms of duration of looking during the inter-event interval, there was only an Order X Condition interaction, F( 1,12) = 18.50, p < .OO1; when the variable-interval condition came tirst, there was less looking in the constant than in the variable condition;

VIGILANCE

IN

TABLE Totol

-

Duration

of Looking

at the

Events First

Variable

interval

28.5

SD

27.5

Conditions-Study Second

Second

First Half

Half

3

Condition Second

Half

(95%)

28.1 0.7

(94%)

29.1 0.6

(97%)

27.6 1.5

(92%)

192%)

27.2 3.5

191%)

26.4 2.1

(88%)

23.2 2.6

(77%)

2.1 Values

the Two

first

M SD Note.

of

Condition

1.4 interval

Half

first

M Constant

5

in Each

First Holf

Grow

15

INFANTS

in parentheses

are

percent

of

ovoiloble

time.

when the constant-intervalcondition came first, there was less looking in the variable condition than in the constant condition. Again, the important factor seems to be whether the condition came first or second and not the nature of the intervals in the condition. Therefore, we collapsed over the two groupswho were presentedwith the conditions in different orders and examined the duration of continued and other looks in a 2 X 2 X 2 (Type of Look X Order: first or second X Half) analysis of variance. Table 6 presents the means and standard deviations relevant to this analysis. The main effect of Order is qualified by a Type of Look X Order interaction, F( 1,13) = 7.40, p = .017; there is less looking in the secondcondition for other looks but not for continued looks. In this case, the decline in other looks from the first to the second condition mirrors what happensto the duration of looking at the event itself. Although we don’t know whether the decline was due to the order per se or to the particular puppet, the important point to note here is that the difference shown in inter-event looking is considerably greater (31%) than the differenceshown in looking at the puppet itself (7%); as with the results of Study 2, this differential effect may suggestthat inter-event looking is somewhat more sensitive to changesin motivation than looking at the events themselves. There was significantly less looking in the second’three trials than in the first three when the data are collapsedover the two conditions, F( 1,13) = 4.50, p = .05. Although the Type of Look X Half interaction did not reach significance,F(1,13) = 4.00, p = .07, the means in Table 6 (p. 15) suggestthat the effect is carried mainly by the continued looks. These results suggestthat looking during the inter-event interval is sensitive to changesthat occur over trials as the result of observing the same event repeatedly. TO explore, as before, the temporal course of looking within the interevent intervals, we calculated the duration of looking in 5-s portions of the interval. For the variable-interval conditions, these calculations were

16

RUFF, CAPOZZOLI,

Comporison

of Continued

DUBINER,

looks

and

AND

PARRINELLO

TABLE 6 Other looks

Intervol-Study

in Seconds

First Condition looks

in the

Inter-Event

Second

Condition

3

First

Half

Second

Holf

7.0 3.6

(16%)

6.1 5.2

(14%)

11.3 6.4

(25%)

12.9 5.9

(29%)

First Half

Second

Holf

Continued M

SD

7.1 4.1

(16%)

5.0 5.2

II 1%)

6.6 5.6

(15%)

Other M

SD Note.

Values

in porentheses

ore

percent

7.3 (16%) 6.7

of ovailoble

time.

identical to those of Studies 1 and 2. For the constant condition, we simply divided each 15-s interval into three segments. For the data from the variable condition, we conducted a 2 X 5 (Order: first vs. second X Segment) analysis of variance. Only the main effect of Segment was significant, F(4,48) = 9.20, p < .OOl (see Table 7). A Newman-Keuls post-hoc analysis confirms that the first segment is significantly different from all others, which are not different from each other. The same situation held in the analysis of the constant-interval data, F(2,24) = 14.00, p < .OOl. A comparison of the two conditions (collapsed across order) for the first three 5-s segments reveals exactly the same effect and no interaction of Condition with Segments, further confirmation that there was no difference in response as a result of whether the interval was variable or fixed. This may be a little puzzling, given the effects found in fixedinterval procedures (e.g., Donahue & Berg, 1988), but six trials is not very many if the goal is to teach the infant to begin to anticipate the actual timing of an event. Finally, the correlation between inter-event looking in the first condition and such looking in the second condition was 54, somewhat lower than TABLE Meon

Durotions

fond

7

Stondord Deviations) of Looking by 5-s Segments-Study 3 Seconds

Interval

o-5

Voriable

Constant

6-10

2.66

1.16

11.11

(1 .Ol

2.65

I .41

(I.01 Note.

Standard

deviations

(1 .Ol are

in porentheses.

in the

Inter-Event

Interval

in Interval

1 I-15 1.31 il.01 I .37 (0.91

16-20 1.39 (1.4)

21-25 1.25 il.51

VIGILANCE

the correlations p < .05.

in the first two studies but still substantial

GENERAL

Attention

17

IN INFANTS

and significant,

DISCUSSION

to an event’s location in the absence of the event implies an that the event will reoccur at that place and an interest in having the event reoccur. In addition, the degree to which infants are tilling to monitor a location for the occurrence of an event is influenced, as hypothesized, by the salience of the events, suggesting that such attention is, in part, related to differences in motivation. As noted in the introduction, we assumed that an expectation for the event’s reoccurrence would be rapidly developed, and the goal of the studies was not to study the development of the expectation as such. However, it might be argued that the looking we observed between events was the consequence of what occurred before and not a consequence of what the infants expected to see. One problem with positing some perseverative or residual effect is that even more complex expectations and anticipations have been demonstrated in younger infants (Haith et al., 1988). Another problem is that it is not easy to spell out ways in which an event might influence looking in its absence without involving expectation or anticipation. If an individual has been looking at an event in a particular location, a continuation of the look despite the absence of the event might be due to perseveration or failure to inhibit a response that is no longer appropriate. The fact that, in Study 1, continued looks became shorter with age might support such an explanation. On the other hand, even though the low- and high-salience conditions differed in the amount of time the infants had been looking at the entry point before the puppet disappeared, there was no difference in the way continued and other looks were distributed across the two conditions; and it is hard to attribute the other looks to perseveration. In addition, perseveration could not easily account for the interaction between order and salience which occurred in the looking in the inter-event intervals of the second study or the effects of order (puppet) on the other looks in the third study. In summary, some perseverative process might account for the continued looks, but the fact that infants tend to look and look away from the relevant location several times during the intervals is more suggestive of their monitoring the location for the occurrence of something. Another explanation might be that some events are more arousing and that looking is more likely to occur when the infant is aroused. The fact that, reliably, more looking occurs in the first 5 s after the event than in other 5-s segments of the inter-event interval may indicate that arousal is dissipating over the interval. The same, however, is the case in vigilance tasks where adults become less likely to respond to signals as the interval expectation

18

RUFF, CAPOZZOLI,

DUBINER,

AND

PARRINELLO

between signals lengthens, also perhaps because of decreasing arousal (Parasuraman, 1984). The effects of arousal, therefore, may not be related directly to anticipation but would be an important aspect of the process underlying vigilance. Was the anticipatory looking observed in these studies sustained enough to warrant being called vigilance? We would argue that it was: Although the infants spent an average of only 2 1% to 41% of available time watching the place where the puppets disappeared, some infants spent as much as 70% of available time in such anticipatory looking. These individual differences may be related to differences that would be consistent across situations, but it is also possible that other kinds of events may be more effective for some infants. For example, the standard Strange Situation would provide an opportunity to observe the extent to which children attend to the door through which their mothers disappeared, but a separate quantitative measure of such attention has not been gathered, though it has been referred to (e.g., Ainsworth & Bell, 1970). For infants at some ages, the mother’s disappearance might lead to a longer period of anticipatory attention than the episodes observed here. Systematic investigation of the effect of different events would be useful in determining what motivates and maintains anticipatory attention in different infants. How does the behavior observed in the infants differ from that observed in adult studies? One difference between the looking during inter-event intervals in these studies and behavior of adults in vigilance tasks is the extent to which such attention can be controlled by factors other than the event itself, such as instructions or desire to succeed. A second possible difference is that the physiological concomitants of vigilance may not be present in mature form in infancy. Although we have little evidence in this regard, Donohue and Berg (1988) suggested that the adult heart rate pattern seen in fixed foreperiod reaction time tasks is observable in 7month-old infants. The contingent negative variation (CNV) that typically occurs in the EEG in the same kind of task does so whether or not a response is required (Ruchkin, Sutton, Mahaffey, & Glaser), making it possible that the CNV may be present quite early as well. However, much less is known about responses in variable foreperiod designs, even in the adult, and those designs are more comparable to the typical vigilance task. A third possible difference between infants and adults might be that the vigilance of infants is less linked to response preparation. The preparation for a specific motor response involves inhibition of irrelevant responses and general somatic activity (Obrist, Webb, & Sutterer, 1969), and it is known that such inhibition undergoes quite dramatic changes in the preschool years (Reed, Pien, & Rothbart, 1984). Although it is possible that the infants in this study were prepared to look at and otherwise respond to the puppets when they appeared, their preparation would definitely have been more general than is the case for adults.

VIGILANCE

IN INFANTS

19

In summary, the method used in our studies may be assessing the elements involved in vigilance, but these aspects of attention would not have been as tightly constrained as in vigilance tasks with adults. The results of these studies show that there was consistency across trials in duration of looking, raising the possibility that there are stable individual differences among infants in the context of vigilance. Thkre was little evidence of any relationship between anticipatory attention and exploratory attention, suggesting that they are independent of each other. Evidence of different physiological concomitants would strengthen the argument for the existence of two kinds of sustained attention in infancy. Finally, the method outlined in this report could be used with preschoolers as well as infants and, therefore, provides the means for investigating the origins and the development of at least some of the processes involved in vigilance. REFERENCES A&worth, M.D.S., & Bell, S.M.V. (1970). Attachment, exploration, and separation: Illustrated by the behavior of one-year-olds in a strange situation. Child Development, 41. 49-67. Cohen, L.B. (1972). Attention-getting and attention-holding processes of infant-visual preferences. Child Development, 43, 869-879. Donohue, R.L., & Berg, W.K. (1988, April). 7-month-old infants anticipate interesting events: Heart rate responses during a fixed joreperiod (Sl-S2) paradigm. Paper presented at the International Conference on Infant Studies, Washington, DC. Haith, M.M., Hazan, C., & Goodman, G.S. (1988). Expectation and anticipation of dynamic visual events by 3.5-month-old babies. Child Development, 59, 467-479. Kahneman, D. (1973). Attention and effort. Englewood Cliffs, NJ: Prentice-Hall. Krupski, A., & Boyle, P.R. (1978). An observational analysis of children’s behavior during a simple reaction-time task. Child Development, 49, 340-347. Levy, F. (1980). The development of sustained attention (vigilance) and inhibition in children: Some normative data. Journal of Child Psychology and Psychiatry, 21, 77-84. Obrist, P.A., Webb, R.A., & Sutterer, J.R. (1969). Heart rate and somatic changes during aversive conditioning and a simple reaction time task. Psychophysiology, 5, 696-723. Parasuraman, R. (1984). Sustained attention in detection and discrimination. In R. Parasuraman & D.R. Davies (Eds.), Varieties of attention. Orlando, FL: Academic. Parasuraman, R., & Davies, D.R. (1984). Varieties of attention. Orlando, n: Academic. Piaget, J. (1954). The construction of reality in the child. New York: Basic Books. Pribram, K.H., & McGuinness, D. (1975). Arousal, activation, and effort in the control of attention. Psychological Review, 82, 116-149. Reed, M.A., Pien, D.L., & Rothbart, M.K. (1984). Inhibitory self-control in preschool children. Merrill-Palmer Quarterly, 30. 13 l-l 46. Richards, J.E. (1987). Heart rate responses and heart rate rhythms, and infant visual sustained attention. In P.K. Ackles, J.R. Jennings, & M.G.H. Coles (Eds.), Advances in psychophysiology (Vol. 3). Greenwich, CT: JAI Press. Ruchkin, D.S., Sutton, S., Mahaffey, D., & Glaser, J. (1986). Terminal CNV in the absence of motor response. Electroencephalography and Clinical Neurophysiology, 63, 445-463. Ruff, H.A. (1986). Components of attention during infants’ manipulative exploration of objects. Child Development, 57, 105-l 14.

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RuK, H.A. (in press). Individual differences in infants’ maintenance of attention. In J. Colombo & J.W. Fagen (Eds.), Individual digeences in infancy: Reliability, stability, and prediction. Hillsdale, NJ: Erlbaum. Yarrow, L.J., McQuiston, S., MacTurk, R.H., McCarthy, M.E., Klein, R.P., & Vietze, P.M. (1983). Assessment of mastery motivation during the first year of life: Contemporaneous and cross-age relationships. Developmental Psychology, 19, 159- 17 1. IO August

1988;

Revised

8 August

1989

W