Acquisition of locational information about reference points during locomotion: The role of central information processing

Scandinavian Journal of Psychology, 1982,23, 207-218

Acquisition of locational information about reference points during locomotion: The role of central information processing

ERIK LINDBERG TOMMY GARLING

University of Umed, Sweden

Lindberg, E. & Garling, T.: Acquisition of locational information about reference points during locomotion: The role of central information processing. Scandinavian Journal of

The role of central information processing for the acquisition of information about locations in a large-scale environment was investigated in two experiments. Subjects with and without a concurrent backwards counting task traversed a locomotion path repeatedly attempting to learn the locations of six reference points designated along the path, then estimated direction and distance numerically to these reference points when traversing the same path further times in a subsequent test phase. The main dependent measures were the latencies and the constant and variable errors of the estimates. The results indicated that acquisition of information about the locations was disrupted when central information processing was interfered with. However, central processing seemed to be less critical for long-term storage of information about the locomotion path. The latter type of information could thus be used by the subjects with the concurrent task when estimating the locations. Finally, the results suggested that information about the path was used also by the subjects without any concurrent task when the test phase required them to remain oriented relative to several reference points at the same time. Tommy Garling, Department of Psychology, University of Urned, S-90187 t imed, Sweden.

Psychoiogy, 1 9 8 2 , ~ . 207-218.

Much research in environmental psychology has in recent years been devoted to people’s cognitive representations of their everyday physical environment (Stokols, 1978), and especially to the internal representations of the spatial layout of the environment that people have (e.g., Canter, 1977; Downs & Stea, 1973; Moore & Golledge, 1976; see Evans, 1980, for a review of recent empirical studies). These cognitive maps, as they have been called, have typically been investigated by asking people to estimate spatial relations in environments with which they are well acquainted (e.g., Appleyard 1969, 1970; Canter & Tagg, 1975; Gol- ledge et al., 1969; Herman et al., 1979; Sadalla et al., 1980; Sherman et al., 1979), but there are also a number of recent studies of the acquisition of cognitive maps (Allen et a]. , 1978; Crane, 1978; Kozlow- ski & Bryant, 1977; Lindberg & Garling, 19810, 1981b). The latter studies are of value since not only a description of the knowledge acquired but also an understanding of the way it is acquired

should guide our conceptualizations of the internal representation of the spatial layout.

Cognitive maps have frequently been classified with regard to the predominant type of information represented. So called survey or vector maps refer to information about directions and Euclidean distances to various reference points whereas representations of information about paths of travel have been termed route or network maps. However, as noted by e.g. Siege1 & White (1973, relying too heavily on the map metaphor may be misleading since human spatial representations often are frag- mented and may consist of several “mini-representations”. Especially, this should be the case in the present study where the acquisition of information about an unfamiliar environment is investigated. The two types of representations will therefore simply be referred to as stored information about locations and locomotion paths respectively.

An increasing amount of information about the locations of reference points may be stored in long-

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208 E . Lindberg and T . Garling

term memory as one repeatedly traverses the environment (see, e.g. Downs & Stea, 1973; Sadalla et al., 1980), but, as suggested by Book & Garling (1980a, 19806, 1981) and Lindberg & Garling (1981 a, 1981 b), a number of conditions should have to be fulfilled for this to occur. Firstly, the relevant features of the path traversed (i.e., distances and direction changes) must be attended to in order to be encoded in short-term memory. Secondly, the information temporarily stored must be further pro- cessed to yield the locations of reference points which cannot be directly perceived. Thereby, one’s own location relative to those of the reference points is updated. Finally, the updated information about the own location relative to those of the reference points is updated. Finally, the updated information about the locations must be permanent- ly stored. Each of these assumptions suggests that the acquisition of locational information should re- quire central information processing (Kahneman, 1973; Neisser, 1967), and that it thus should be impaired if central information processing is interfered with.

Lindberg & Garling (1981 a , 1981 b) investigated the acquisition of locational information about reference points by having subjects repeatedly traverse the same locomotion path, designating as reference points places along it. Central information processing was assumed to be interfered with by means of a difficult backwards counting task performed by the subjects concurrently whilst walking. The results suggested that if no concurrent task was performed the subjects were able to update their own location recurrently relative to that of a reference point. However, if performing the additional counting task they were unable to do that but could still infer the location of the reference point after walking, assumedly by using encoded information about the locomotion path (distances and direction changes). Furthermore, the rate of improvement in performance across trials was essentially the same whether the concurrent task was performed or not. These findings were assumed to indicate that maintenance of orientation relative to reference points and storage of information about their locations re- quire central information processing to a considera- ble extent whereas encoding of information about the locomotion path may not (cf. Kellogg, 1980; Siege1 & White, 1975), thus enabling the further processing to be postponed until the entire locomotion path had been traversed.

An implication of this assumption is that if the conditions are changed so as to prevent central information processing after walking, the subjects who perform the concurrent task should not be able to learn the locations of the reference points and should thus be outperformed by those who do not perform any concurrent task. This hypothesis was subjected to test in Experiment 1 by introducing a separate learning phase during which the subjects with a concurrent task never were allowed to interrupt the counting for as long as should have been needed for inference of the locations of the reference points which were to be estimated in a subsequent test phase. In the second experiment, the role of central information processing was further investigated in the following respects. Firstly, even if encoding of information about the locomotion path in short-term memory can take place in spite of the fact that central information processing is interfered with, it may still be the case that the acquisition of a long-term memory representation of the locomotion path is prevented. Experiment 2 investigated this hypothesis by using a test phase with several types of estimates of location, some of which should not have been possible to perform by the subjects with a concurrent task in the learning phase unless they had acquired a long-term memory representation of the locomotion path. Secondly, if a long-term memory representation of the locomotion path is acquired although central information processing is interfered with, it seems likely that the same information is acquired when no interfering task is performed and that the memory representation in this case becomes more accurate. This question was also investigated in Experiment 2.

EXPERIMENT 1 The purpose with Experiment 1 was thus to investi- gate whether the acquisition of information about the locations of reference points along a locomotion path requires central information processing. The procedure adopted required the subjects to attempt to learn the locations of a number of designated reference points as they repeatedly traversed a locomotion path during a learning phase, then to estimate these locations when traversing the same path further times in a subsequent test phase. The subjects assigned to one of two conditions were given an additional task consisting of backwards counting to be carried out whilst walking, the sub-


Acquisition of information about locations 209

L U l s o F S , A

X

c A-Z reference points

s swing doors i .t- o outside view

S

i r O ,* - 0 10 50 meters

Fig. I. Graph of the path walked by the subjects in the culvert system. (See text for further explanation.)

jects in the other condition were given no such additional task. The concurrent task was assumed to interfere with central information processing and thereby prevent the subjects from updating their own location relative to those of the reference points during locomotion in the learning phase. Con- sequently, the subjects performing this task were not expected to acquire a memory representation of the locations of the reference points. In line with the effects of repeated exposure to the environment attributed to the acquisition of such a representation by Lindberg & Garling (1981a), it was predicted that these subjects would be slower and less accurate as compared to those not performing any concurrent task.

Since the subjects in the present experiment also traversed the environment in the test phase, this phase constitutes an additional opportunity for acquisition which may attenuate the effects of the concurrent task performed in the learning phase. However, by requiring half of the subjects with and without the concurrent task to perform the same task in the test phase stronger effects of interfering with central information processing in the learning phase can be predicted. In two experiments resem- bling the present test phase Lindberg & Garling (1981a, 1981b) found that the concurrent task affected performance negatively in that the latencies

became longer and accuracy decreased. The au- thors assumed that the subjects performing the concurrent task were unable to keep track of the locations of the reference points whilst walking and instead had to infer them from stored information about the locomotion path (i.e. distances and direction changes), which, in turn, led to the observed decrement in performance. This assumption was supported by the fact that the number of linear segments of the locomotion path affected performance negatively, most clearly in that the latencies increased almost linearly with the number of segments. in the present experiment the concurrent task performed in the test phase was predicted to have similar negative effects, but only for the subjects who performed the same task in the learning phase. In contrast, if the subjects without any concurrent task in the learning phase are able to acquire information about the locations of the reference points they should not have to employ information about the path, and, thus, their performance should not suffer when the concurrent task is performed in the test phase.

Method Setting and design The experiment was carried out in the culverts beneath the University Hospital of Urne% shown in Fig. 1. The artificially lighted culverts were about 3 rn wide x 2.5 rn

I4-x21942 Scandinavian Journal of Psycho[ogy, 23

210 E. Lindberg and T . Garling

high, and, with the exception of the flow of people, gene- rally featureless. The paths had with one exception 90" angles of turns and were approximately level throughout. The subjects were with two exceptions prevented from outside views, and swing doors at the near end of the alleys prevented them from seeing from one alley to another.

The design was a 2 ~ 2 ~ 3 x 2 (concurrent taskho concurrent task in the learning phase x concurrent task/no concurrent task in the test phase X number of path segments x sets of reference points) factorial with repeated measures on the last two factors.

Procedure The subjects served individually in the experiment which consisted of a learning phase followed by a test phase. In all, the experimental sessions lasted for a little more than 1 hour.

Learning phase. The subjects were met by the experimenter at the reception hall of the hospital and received instructions for the learning phase. Briefly, these instructions required them to accompany the experimenter for a walk in the culverts and attempt to learn the relative locations of six reference points (labeled A, B, C, X, Y, and 2, see rig. 1) to be designated along the locomotion path. They were also told that the reference points formed two sets (ABC and XYZ) and that they were only required to learn the relative locations within each set. Finally, they were informed about the fact that a test phase would follow after a few learning trials.

After the subjects had read the instructions the experimenter took them to the culverts. Half of the subjects entered the culverts at a point immediately preceding A, the other half at a point immediately preceding X. The experimenter accompanied the subjects along the path three times, each time allowing them to stay at the reference points for 5 sec before the walk continued. The first time the subjects were stopped at the reference points which where then labeled by the experimenter, the second and third time the subjects were stopped and labeled the reference points themselves. The few labeling errors made were immediately corrected by the experimenter.

Half of the subjects were in the learning phase required to count backwards rapidly whilst walking. The counting was to be executed aloud in steps of three, four, six, or seven, beginning with a randomly chosen three-digit number read by the experimenter. The starting number and the size of the steps to be counted in were changed twice during each linear segment of the path in order to prevent the subjects from performing the counting task automatically. To avoid interference with the learning of the labels of the reference points, the subjects were allowed to interrupt the counting whilst standing at the reference points. Hcwever, since the counting was resumed immediately after a reference point had been labeled, the subjects should not have been able to infer the locations of the reference points not in view (cf. Lindberg & Garling, 1981~7, 1981b).

Test phase. Before the test phase the subjects received another set of instructions which thoroughly explained the task of estimating the directions and distances to the reference points required of them in this phase.

During the test phase the experimenter accompanied the subjects another three times along the path, each time labeling one of the reference points in each set (ABC or XYZ) when it was passed and then stopping the subjects at another reference point in the same set which was also labeled. Whilst standing at the second reference point, the subjects were required to estimate the direction and distance to the one first labeled. The reference points were selected so that the spatial relations to be estimated cor- responded to two (A from B and X from Y), four (B from C and Y from Z), and six (A from C and X from 2) linear segments of the locomotion path. All subjects estimated each of these relations once, the order between them being counterbalanced across subjects.

The direction estimates were to be given as the angle in degrees between the direction in which the subjects were facing when stopped and the direction to the previously labeled reference point. The subjects were each time provided with a protractor showing all directions in 5" steps and had to choose the angle value (0" to k 180") corresponding most closely to the direction to the reference point. They were also required to indicate the boundaries of a 90% confidence interval by giving two additional angle values. The distance estimates which were on each trial preceded by the other estimates were to be given as the crowflight distance in meters to the previously labeled reference point. Latencies of the direction estimates were measured manually to the nearest 10 msec by means of a digital stopwatch. The instructions emphasized accuracy and imposed no speed requirements.

Half of those subjects who performed the backwards counting task in the learning phase continued to do that in the test phase and half of the remaining subjects performed the same counting task for the first time in the test phase. The counting was interrupted when the subjects were stopped at a reference point, then resumed immediately after the estimates had been given.

Subjects Forty-eight high-school students and undergraduates from Ume% with a minimal familiarity with the setting in which the experiment was conducted participated as subjects, partly in order to fulfill a course requirement, partly in return for payment. Twelve subjects (6 men and 6 women) were randomly assigned to each of four between-subjects conditions (concurrent task/no concurrent task in the learning phase x concurrent task/no concurrent task in the test phase), educational status being equally distrib uted across conditions.

Results The results were subjected to ANOVAs (concurrent task/no concurrent task in the learning phase x concurrent task/no concurrent task in the test phase x number of path segments corresponding to the spatial relations) with repeated measures on the last factor, separately for latencies and confidence intervals of the direction estimates and constant and variable direction and distance errors.

The constant errors were calculated as the signed


Acquisition of information about locations 21 1

Concurrent task in the learning phase

401 35

b c 4

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10-

5 -

O' I I

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No concurrent task in the learning phase

2 NUMBER OF PATH SEGMENTS

differences between the estimates and the correct values. The direction errors were given a positive sign if the estimates were to the right of the correct directions, a negative sign if they were to the left; the distance errors were counted as positive if distance was overestimated, otherwise as negative.

While the constant errors reveal systematic distortions (as e.g. a general tendency to underestimate distance or to place the reference points too far to the right), they say little about intraindividual varia- tions in these distortions and may thus give an un- warranted impression of high accuracy if positive and negative errors tend to cancel out. Therefore, variable errors calculated as standard deviations of the constant errors across the two sets of reference points (ABC and XYZ) were included in the analyses after that preliminary ANOVAs had indicated that the constant errors did not differ sys- tematically for the two sets. As a further check on the validity of treating the two sets of reference points as replicates in the computation of the variable errors, the estimates of confidence intervals which were also assumed to reflect intraindividual variability were included.

Latencies AS Fig. 2 shows, the concurrent task raised the latencies whether performed in the learning or in the test phase, but only in the latter case was the effect significantly, F (1, 44)=3.95, p<O.IO, and

4 6

Fig. 2. Mean latencies of the direction estimates in the different concurrent task conditions in Experiment 1 as functions of the number of linear segments in the locomotion path. 0, Concur- rent task in the test phase; 0, no concurrent task in the test phase.

7.22, p<0.05, respectively. However, tests of simple effects revealed that the latencies were raised reliably by the concurrent task in the test phase only if the same task was performed in the learning phase as well (p<O.OS). The latencies further increased reliably with the number of path segments, F (2, 88)=5.00 pCO.01, and again the effect was significant only when the concurrent task was performed in both parts of the experiment (p<0.05).

Accuracy

The constant errors are displayed in Table 1. The ANOVAs yielded significant main effects of the number of path segments, F (2, 88)=11.32, p < 0.001, and 6.71, p<O.OI, for direction and distance respectively. For distance, the effect was reliably modified by the concurrent task in the learning phase, F (2, 88)=6.74, p<O.OI , but the concurrent task tended to affect the sign of the errors (under- estimates instead of overestimates) rather than their magnitude.

The variable errors which were transformed ac- cording to log (x'+ 1) before the ANOVAs in order to achieve a better approximation to the normal distribution increased significantly with the number of path segments, F (2, 88)=5.59, p<O.OI, and 11.55, p<O.OOl, for direction and distance respectively (see Table 2). The concurrent task in the test phase modified this effect reliably for distance, F (2, 88)=5.40, pcO.01, but the overall size of the

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Table 1. Mean constant errors of the direction and distance estimates in Experiment 1

E . Lindberg and T . Garling

Concurrent task condition in the test phase and number of path segments

Concurrent task No concurrent task Concurrent task condition in the learning phase 2 4 6 M 2 4 6 M

Direction errors (deg) Concurrent task 28.0 11.7 13.2 17.6 23.2 1.7 3.6 9.5 No concurrent task 18.8 0.5 9.2 9.5 25.3 -0.5 1.9 8.9

Distance errors (m) Concurrent task 1.6 -22.0 -13.2 -11.2 -31.7 -45.0 -36.7 -37.8 No concurrent task 6.6 12.5 56.2 25.1 2.5 -7.4 48.9 14.7

errors was not affected significantly by the concurrent task whether performed in the learning phase, the test phase, or both.

The confidence intervals are shown in Table 3. The results mirrored those for the variable errors in that the number of path segments had a significant main effect, F (2, 88)=3.95, p<O.OS, due to larger confidence intervals for six than for two and four segments, and in that the concurrent task did not have any reliable effects although it tended to slightly impair performance when carried out in the test phase.

Discussion

The present results confirmed the predictions concerning the latencies. When central information processing was interfered with in the learning phase by means of a concurrent task, the latencies measured in the test phase were longer and they were markedly affected by the concurrent task performed in that phase. In particular, the latencies increased with the number of path segments when

the concurrent task was performed in both phases of the experiment but not when it was performed only in the test phase, indicating that the subjects in the former case but not in the latter were unable to access a memory representation of the locations directly and instead had to use information about the locomotion path in order to perform the estimates. The conclusion that central information processing is required for the acquisition of a memory representation of the locations of reference points thus seems warranted.

The results regarding the accuracy measures were however not as encouraging as those for the latencies. Although Lindberg & Garling (1981 a , 1981 b ) found negative effects on accuracy of the concurrent task, the present results did not show any significant impairment whether this task was performed in the learning phase, the test phase, or both. It should however be noted that the direction errors tended to be as predicted. The negative findings concerning accuracy should moreover be con- sidered with caution since the present experiment

Table 2. Mean variable errorsa of the direction and distance estimates in Experiment 1


Concurrent task condition in the learning phase

Direction errors (deg) Concurrent task No concurrent task

Disrance errors (rn) Concurrent task No concurrent task

Concurrent task No concurrent task

2 4 6 M 2 4 6 M

10.1 22.1 27.5 18.3 9.6 17.7 21.8 15.4 11.3 17.5 16.6 14.8 10.9 20.9 12.1 13.9

13.5 18.6 17.5 16.3 6.0 18.2 22.6 13.4 20.4 28.0 26.4 24.7 7.0 14.5 35.8 15.3

Means are those obtained in the ANOVAs converted to variable errors.



Table 3. Mean confidence intervals ( in deg) of the direction estimates in Experiment I


Concurrent task No concurrent task Concurrent task condition in the learning phase 2 4 6 M 2 4 6 M

Concurrent task 22.5 22.9 24.0 23.1 19.4 18.5 20.8 19.6 No concurrent task 22.1 21.7 25.2 23.0 18.1 17.9 22.7 19.6

differed from the previous ones in some respects, the most important one being the introduction of the separate learning phase. A possible explanation may be that the subjects were able to acquire information about the locomotion path in the learning phase even though they performed the concurrent task. In addition, the subjects without any concurrent task may only have been able to remain oriented relative to one reference point at a time whilst walking (Lindberg & Garling, 19816), and hence, a larger number of learning trials than was used in the present experiment might be required in order to acquire a more accurate representation of the locations of all the reference points. The difference in accuracy between the subjects who performed the concurrent task in the learning phase and those who did not may for these reasons have been minimized.

While suggesting that central information processing is required for the acquisition of information about the locations of reference points, the present results thus also raise the question whether the same is true for information about the locomotion path. Lindberg & Garling (1981 a , 1981 b ) assumed that temporary storage of the latter type of information was not prevented when central information processing was interfered with by means of a concurrent task, but, if so, storage of the information in long-term memory may not be prevented either. However, it may still be the case that the information about the locomotion path is more accurately represented when central information processing is not interfered with. Experiment 2 was designed to clarify this issue.

EXPERIMENT 2 The second experiment was aimed at investigating whether the acquisition of a long-term memory representation of the locomotion path requires central information processing, and, if this is not the case, whether a more accurate representation is acquired

when central processing is not interfered with. The procedure adopted was the same as in the preceding experiment except that the test phase was changed so as to permit a test of the hypothesis that the subjects with the concurrent task in the learning phase are able to acquire a long-term memory representation of the locomotion path. This was done by including two types of estimates of location which should not be possible to perform by these subjects unless such a representation has been acquired. Firstly, the subjects were required to estimate the locations of reference points before they were passed in the test phase (i.e., reference points located “in front of’ the subjects instead of “behind” them). Secondly, they were required to estimate the direction and distance between two reference points when standing at a third. Since these estimates cannot be made merely by maintaining orientation relative to a reference point after it has been passed in the test phase, the accuracy of performance should be considerably less for these types of estimates unless the subjects are able to access a long-term memory representation of the locomotion path.

The test phase was also changed as compared to Experiment 1 in that the subjects were not told in advance which location they would be required to estimate at the next stop. Lindberg & Garling (19816) found that this led to an increase in the latencies for subjects without any concurrent task and suggested as an explanation that difficulties in maintaining orientation relative to several reference points simultaneously whilst walking may have led the subjects to use stored information about the locomotion path when estimating the locations. If this explanation is valid, information about the locomotion path should also be used by the subjects without any concurrent task in the learning phase in the present experiment. Further, if the subjects with the concurrent task are able to acquire a representation of this type of information, a compari-

Scandinavian Journal of Psychology. 23

214 E . Lindberg a n d 7. Garling

5 20 b- < 2

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Concurrent task i n the learning phase

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No concurrent task in the learning phase

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NUMBER OF PATH SEGMENTS

son of the performances in the two conditions should reveal if acquisition is facilitated by the availability of central information processing capacity.

The subjects were thus expected t o base their estimates of locations on information about the locomotion path whether the concurrent task was performed in the learning phase or not, and, con- sequently, the latencies were predicted to increase with the number of path segments for the estimates of the locations of reference points in front and behind in both conditions. However, the latencies for the estimates of the direction and distance between two reference points performed at a third should differ since in that case six path segments must be retrieved in order to localize the two reference points regardless of the number of segments corresponding to the spatial relation between them. The latencies should therefore be as long as when the number of path segments equals six for the remaining types of estimates, and they should not vary with the number of segments corresponding to the spatial relation estimated. In addition, a n extra amount of time may be needed t o determine the direction and distance between the two reference points after they have been localized.

Method Serring and design The setting as well as the locomotion path and the locations of the reference points were the same as in Experi- ment 1 (see Fig. 1).

Scandinavian Journal of Psychology. 23

4 6

Fig. 3. Mean latencies of the direction estimates in the different concurrent task conditions in Experiment 2 as functions of type of estimate and number of path segments. 0, Reference point behind; A, reference point in front; 0, two reference points.

The design was a 2 x 3 ~ 3 ~ 2 (concurrent task/no concurrent task in the learning phase x type of estimate X

number of path segments X sets of reference points) factorial with repeated measures on the last three factors.

Procedure The individually serving subjects went through a learning phase followed by a test phase. In all, the experimental sessions lasted for about If hours.

Learning phase. The learning phase was identical to that in Experiment 1, including that half of the subjects performed the concurrent task of backwards counting.

Test phase. The subjects received instructions about the different types of estimates to be performed and were given one practice trial for each type with temporary reference points in view. The experimenter thereafter accompanied the subjects three times along the path, each time stopping them at each reference point and requiring them to perform one of the following estimates: (a) Esti- mates of the direction and distance to another reference point behind them (from B to A, from C to A and B, from Y to X, and from Z to X and Y); (b ) Estimates of the direction and distance to another reference point in front of them (from A to B and C, from B to C, from X to Y and Z, and from Y to Z); and (c) Estimates of the direction and distance between two other reference points (between B and C at A, between A and C at B, between A and B at C, between Y and Z at X, between X and Z at Y, and between X and Y at Z) (see Fig. 1). All subjects performed each of these estimates once (two of each type during each traversal of the path), the order between them being counterbalanced across subjects. The subjects were not informed in advance about which type of estimate they were to perform when reaching the next reference point. Half of the subjects performed the direction estimates in one direction (e.g., from A to B at A), the other half in the reverse direction (i.e., from B to A at A). The estimation

Acquisition of itlformation about locations 215

Table 4. Mean constant errors of the direction and distance estimates in Experiment 2

Type of estimate and number of path segments ~~ ~

Concurrent task Reference point behind Reference point in front Two reference points condition in the learning phase 2 4 6 M 2 4 6 M 2 4 6 M

Direction errors (deg) Concurrent task 27.8 -1.8 10.0 12.0 10.3 7.2 68.2 28.6 -4.5 47.2 51.3 31.3 No concurrent task 18.0 3.8 6.7 9.5 4.2 9.9 38.0 17.4 -24.5 36.1 38.2 16.6

Distance errors (m) Concurrent task -10.9 -32.3 1.0 -14.1 -5.1 -54.2 -17.9 -25.7 -3.4 -49.2 -10.9 -21.2 No concurrent task -17.9 -53.4 -22.3 -31.2 -12.2 -41.3 -0.9 -18.1 -6.9 -40.5 -17.5 -21.6

procedure was the same as in Experiment 1 , using the direction faced by the subjects when stopped as the reference direction for the direction estimates.

Subjects Another 24 Ume% high-school students and undergraduates minimally familiar with the experimental setting participated as subjects, partly in order to fulfill a course requirement, partly in return for payment. Twelve subjects (6 men and 6 women) were randomly assigned to each of two between-subjects conditions (Concurrent tasklno concurrent task in the learning phase), educational status being equally distributed across conditions.

Results The same dependent variables as in Experiment 1 were separately subjected to ANOVAs (concurrent tasWno concurrent task in the learning phase x type of estimate x number of path segments corresponding to the spatial relations) with repeated measures on the last two factors. The results concerning the confidence intervals were again very similar to those for the variable direction errors and have therefore been omitted here.

Latencies

As Fig. 3 shows, the latencies were not much affected by performance of the concurrent task in the learning phase. The overall increase due to the concurrent task did not approach significance. The latencies were longer for the estimates of the direction between two reference points, F (2, 44)=20.01, p<O.OOl , and they increased with the number of path segments, F (2, 44)=4.38, p<0.05. Tests of simple effects revealed that the increase with the number of segments.was reliable only for the estimates of the direction to a reference point in front and behind (p<0.05 or less).

Accuracy

The constant errors are given in Table 4. The direction errors were significantly larger if the concurrent task was performed, F (1, 22)=5.16, p c 0 . 0 5 . They also differed reliably depending on which type of estimate was made, F (2, 44)=6.04, p<O.Ol, ac- counted for by larger errors in the estimates of the directions to a reference point in front and between two reference points. Only for the distance errors did the concurrent task interact reliably with the type of estimate, F (2, 44)=7.01,p<0.01, but in this case the errors were not negatively affected by the concurrent task. Both the direction and distance errors were significantly affected by the dumber of path segments, F (2,44)=22.89 and 46.88,p<0.001, in the former case due to an increase with the number of segments and in the latter due to larger errors for four path segments. The effect was for the direction errors significantly modified by the type of estimate, F (4,88)= 14.47,p<0.001, because the errors did not increase with the number of path segments when direction was estimated to a reference point behind.

The variable errors were as Table 5 shows larger if the concurrent task was performed, but only for the direction errors did the effect reach significance, F(1, 22)=7.45,p<0.05. The direction errors were also larger for the estimates of the direction between two reference points, F(2, 44)= 13.72, p<O.OOl. Both the direction and distance errors increased reliably with the number of path segments F(2, 44)=7.15 and 5.33, ~ ( 0 . 0 1 , an effect which was modified by the type of estimate, F(4,88)=3.43 and 2.60, p<0.05, and for distance by the concurrent task, F(2, 44)=4.72, p<0.05, and by this factor and the type of estimate, F(4, 88)=3.31, p<0.05.

Scandinavian Journal of Psychol0g.V. 23

216 E. Lindberg and T . Garling

Table 5 . Mean variable errorsa of the direction and distance estimates in Experiment 2

Type of estimate and number of path segments

Concurrent task Reference point behind Reference point in front Two reference points condition in the learning phase 2 4 6 M 2 4 6 M 2 4 6 M

Direction errors (deg) Concurrent task 14.6 16.3 35.1 20.3 6.7 22.0 14.7 13.0 43.2 33.7 24.9 33.1 No concurrent task 5.4 16.5 10.5 9.8 4.6 12.3 13.8 9.2 21.7 21.3 18.4 20.4

Distance errors (m) Concurrent task 15.9 21.5 19.9 19.0 13.1 10.5 18.5 13.7 13.1 7.0 21.2 12.5 No concurrent task 12.1 11.8 9.9 11.2 4.0 17.8 20.1 11.3 11.9 18.3 15.1 14.9

@ Means are those obtained in the ANOVAs converted to variable errors.

Tests of simple and simple simple effects showed that the increase in direction errors with the number of path segments was confined mainly to the directions to a reference point in front and behind (p<O.OS). The distance errors increased reliably with the number of path segments only for the distances to reference points in front in the condition without any concurrent task (p<O.OOl) and for the distances between two reference points when the concurrent task was performed (p<O.O1).

Discussion The results of Experiment 2 supported the hypothesis that a long-term memory representation of information about a locomotion path can be acquired even if central information processing is interfered with during the locomotion. As predicted, the latencies of the estimates of the direction to a reference point in front increased with the number of path segments in the condition with the concurrent task in the learning phase. The Iatencies were also longer when the direction between two reference points was estimated. These effects should not have been obtained if the subjects were guessing when performing these estimates, but if they were using long-term stored information about the locomotion path the latencies should be expected to increase with the amount of information to be retrieved. As regards the accuracy measures, the estimates of the direction to a reference point in front and between two reference points were less accurate than to a reference point behind but the availability of central processing capacity in the learning phase did not affect this difference. Furthermore, the decrease in accuracy for a reference point in front was confined to the constant errors which should not have been

the case if the subjects were unable to use a memory representation.

The predictions concerning the latencies were also confirmed in the condition without any concurrent task in the learning phase, indicating that these subjects also had acquired information about the locomotion path and were using that information when estimating the locations of the reference points. However, in this case the estimates were more accurate than in the condition with the concurrent task, suggesting that even if interfering with central information processing during locomotion does not prevent the acquisition of information about the locomotion path it still leads to a less accurate long-term memory representation of that information.

The findings of Lindberg & Garling (1981 6 ) indicating that the subjects without any concurrent task used information about the locomotion path when estimating the location of one of several possible reference points after locomotion were thus repli- cated in the present experiment. A tentative explanation offered in that study was that the subjects were only able to remain oriented relative to one reference point at a time and therefore focused on information about the locomotion path which could be used regardless of the particular spatial relation to be estimated on a given trial. While in line with the results of the present experiment, this account needs to be slightly modified in order to encompass the finding in Experiment 1 that the subjects with a concurrent task only in the test phase did not seem to use information about the path although maintenance of orientation should have been interfered with in that case too. Possibly, when the subjects have the option of choosing between information

Scundinaviun Journal of Psychology, 23


about the locations acquired in the learning phase and more recent information about the locomotion path, the relative quality of the representations of the two types of information determines which one will be used. If the concurrent task interferes with the acquisition of information about the path whereas the presence of several reference points does not, this may explain why that type of information was used in the present experiment but not in Experi- ment 1.

GENERAL DISCUSSION

As shown in the present experiments, the acquisition of a cognitive map of an environment through which one moves repeatedly is affected in more than one way by the availability of central information processing capacity. In agreement with the suggestion by Lindberg & Garling (1981 a , 1981 b), the present results indicated that central information processing is a nececessary prerequisite for the acquisition of information about the locations of reference points out of sight. On the other hand, long-term storage of information about the locomotion path was found to take place whether or not central processing was being interfered with, thus making it possible to infer the locations of the reference points at a later point in time. However, central information processing still seemed to be useful, presumably by leading to a more accurate long-term memory representation of information about the locomotion path.

A cognitive map may thus contain at least two types of spatial information of relevance for the localization of reference points out of sight, viz. information about relative locations and information about the locomotion path. Acquisition of the former type of information requires central processing but the information may then be directly accessed, whereas the latter type may be acquired even if central processing is interfered with but requires time-consuming retrieval and combin- ation of the stored information in order to yield the location of a reference point. That a cognitive representation should encompass both types of information also seems functionally justified, since each type may compensate for gaps in the other. That is, given knowledge about a locomotion path the locations of reference points along it may be correctly inferred, and, conversely, given information about the direction and distance

to a reference point the shortest locomotion path leading to that reference point may be chosen. Thus, a back-up system would be provided to prevent one from getting lost when moving about in novel as well as more familiar surroundings. Interestingly enough, Kuipers (1978), although without much empirical support, has expressed a similar view in his computer simulation of a cognitive map.

To conclude, the emerging picture of the cognitive maps that people have is that of complex and highly dynamic information structures, difficult to subject to empirical study. Nevertheless, the availability of central information processing capacity has been possible to disentangle as one of the factors controlling the acccretion of such internal representations of the spatial layout of the environment. However, a number of questions still remain to be answered by future research, as, e.g., the question how the internal organization of the cognitive map is affected by the number of salient locations in the environment. A related question con- cerns the order in which new information is incor- porated into the cognitive map as the environment becomes increasingly familiar. Finally, it may also be asked in what respects the use of a cognitive map resembles that of an ordinary map. Perhaps, “reading” the cognitive map is more similar to our ability to perceive three-dimensional space, with different information being tied to different locations in the environment, than to the more abstract task of map reading (see, e.g., Attneave & Farrar, 1977; Attneave & Pierce, 1978; Gibson, 1979).

The present research was supported financially by grants from the Swedish Council for Building Research.

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Acquisition of locational information about reference points during locomotion: The role of central information processing