Co,loyrieht 1992 by the American Psychological Association, Inc. O278-7393/92/S3.0O

Journal of Experimental Psychology: Learning, Memory, and Cognition 1992, Vol. 18, No. 3, 555-564

Spatial and Temporal Contributions to the Structure of Spatial Memory Timothy P. McNamara, John A. Halpin, and James K. Hardy

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Vanderbilt University Three experiments investigated the effects of spatial and temporal contiguity in item recognition, location judgment, and distance estimation tasks. Ss learned the locations of object names in spatial arrays, which were divided into 2 regions. The names of locations were presented during map learning so that critical pairs appeared close in space and close in time, close in space but far in time, far in space but close in time, and far in space and far in time. Names primed each other in recognition only when they were neighbors in both space and time. In contrast, the effects of spatial and temporal contiguity in priming in location judgments were additive. Finally, temporal contiguity affected estimates of Euclidean distance when locations were close together, but not when they were far apart.

When people retrieve information about an object from their memories of a spatial layout, performance can be affected by previous retrieval operations. For example, if people are required to decide whether a campus building is in one region of the campus versus another, the decision is facilitated if it is immediately preceded, or primed, by the name of an adjacent building. Spatial priming occurs in location judgments (e.g., Clayton & Chattin, 1989; McNamara, Altarriba, Bendele, Johnson, & Clayton, 1989) and in recognition (e.g., McNamara, Ratcliff, & McKoon, 1984) and has proved to be useful for investigating the structure and the content of spatial memories. Recently, the use of priming in recognition to investigate spatial memory has been questioned. The first sign of trouble appeared in studies investigating naturally acquired spatial memories. McNamara, Altarriba, et al. (1989) showed that spatial priming did not occur in a standard item recognition task when subjects were tested on their memory for a campus (see also, Clayton & Chattin, 1989; Merrill & Baird, 1987). Spatial priming does not seem to occur in naturally acquired spatial memories unless the task requires subjects to retrieve information about spatial location (Clayton & Chattin, 1989; McNamara, Altarriba, et al., 1989). Recent experiments by Clayton and Habibi (1991) and by Sherman and Lim (1991) may help to explain this finding. Clayton and Habibi set out to investigate the relative contributions of temporal contiguity and spatial contiguity to priming in recognition. In most previous investigations (but see McNamara et al., 1984, Experiment 2), temporal contiguity and spatial contiguity were confounded: When two items This research was supported in part by National Science Foundation Grant BNS 8820224. We are grateful to Keith Clayton and Ali Habibi for many thoughtful discussions of the issues examined in this article and for their comments on the article. We also thank Richard Sherman, Rose Zacks, and two anonymous reviewers for their helpful comments. Correspondence concerning this article should be addressed to Timothy P. McNamara, Department of Psychology, 301 Wilson Hall, Vanderbilt University, Nashville, Tennessee 37240.

were close in space, they were also experienced together in time. Clayton and Habibi unconfounded these variables by having a computer present the names of map locations one item at a time. Although subjects saw the entire configuration of locations on the computer screen, they saw only one name at a time during the learning phase. For one group of subjects, names were presented in an order that confounded temporal contiguity and spatial contiguity; that is, spatially close names followed each other in the learning sequence, and spatially distant names were separated by several other names in the learning sequence. For a second group of subjects, critical items were always temporally distant, even though their spatial distance might be close or far. Clayton and Habibi's results are reproduced in Table 1. The basic finding was this: Although spatial priming was found in the confounded group (superscript a), it was not found in the unconfounded group (superscript b). Clayton and Habibi (1991) extended this result in two additional experiments. In Experiment 2, temporal contiguity was held at close for one group (unconfounded-close), but at far for a second group (unconfounded-distant). The spatial priming effects were small (4 and 5 ms) and not significant. In Experiment 3, temporal contiguity was varied, but spatial contiguity was held constant at far. Primes and targets in the recognition test had been spatially far apart on the maps, but had appeared successively (temporally close) or separated by several other names (temporally far) in the study order. In this experiment, there was a 20-ms priming effect, which was significant. This series of experiments indicates that when temporal contiguity is controlled, spatial distance has no effects on priming in recognition. In another investigation of similar issues, Sherman and Lim (1991) had subjects learn the locations of objects in a real environment. Two types of learning protocols were used: In one, spatial contiguity and temporal contiguity were confounded; in the other, spatial contiguity and temporal contiguity varied independently, with the result that spatially close and spatially far pairs of locations were the same temporal distance apart on the average (about three intervening items). The second learning protocol corresponds to Clayton and 555

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T. McNAMARA, J. HALPIN, AND J. HARDY

Table Summary of Results Obtained by Clayton and Habibi (1991) Spatial distance by experiment

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Experiment ! Close Far Experiment 2 Close Far Experiment 3 Close Far

Temporal distance Close

Far

623" —

6467604"

624" 628"

601" 606"

574a

594"

600"

Note. Within each experiment, conditions with a common superscript were varied within subjects; conditions with different superscripts were varied between subjects. Latencies are in milliseconds.

Habibi's (1991) unconfounded-distant condition. After learning the layout, subjects were given a recognition test or a location judgment test. In the latter task, subjects had to decide whether an object had been in one region of the space versus another. The major results were that (a) spatial priming occurred in recognition only when temporal contiguity and spatial contiguity were confounded and (b) spatial priming occurred in location judgments even when spatial contiguity and temporal contiguity were not confounded. Sherman and Lim (1991) used these results to explain why spatial priming does not occur in recognition, but does occur in location judgments if subjects' memories of a campus are tested. Sherman and Lim suggested that when people learn a large scale environment, like a campus, their paths through the environment may not force them to experience spatially contiguous objects, such as buildings, close together in time. In other words, incidental acquisition of a large-scale space leads naturally to a dissociation between spatial and temporal contiguity. The results of these studies indicate that priming in recognition is determined solely by temporal relations. This conclusion, however, may be premature. Although Clayton and Habibi (1991) factorially combined spatial and temporal contiguity, they did not include a location judgment task or have subjects estimate distances; and whereas Sherman and Lim (1991) included a location judgment task and a distance estimation task, they did not factorially combine spatial and temporal contiguity. These methodological issues turn out to have important theoretical consequences, because (anticipating our results) recognition, location judgments, and distance estimation are differentially sensitive to metric spatial relations, nonmetric spatial relations, and temporal relations. Experiments la and lb Experiments la and lb were conceptual replications of Clayton and Habibi's (1991) and Sherman and Lim's (1991) experiments. Subjects learned the locations of object names in simple maps. An example of one of the maps, with and without the names, is displayed in Figure 1. Panel A is presented for illustrative purposes only; at no time in the

experiment did subjects ever see all of the names displayed simultaneously. The entire configuration of dots (Panel B) was always present during map learning. However, only one name was displayed at a time during learning. Names were presented in an order such that spatial contiguity and temporal contiguity were factorially manipulated. For example, the order of learning for the map in Figure 1 was as follows: soap, comb, needle, candy, brick, stapler, zipper, fork, tape, boat, telephone, razor, wallet, block, and so on. Thus, candy-brick and tape-block were both spatially contiguous, but the former items were temporally contiguous and the latter were not; and zipperfork and stapler-telephone were both spatially far apart, but differed in temporal distance in the learning protocol. After learning a map, subjects received two or three tasks. Subjects in Experiment la received a recognition test and a location judgment test. In the latter task, subjects had to decide whether a name had been in the left-hand or the right-hand region of the map. Subjects in Experiment lb participated in these tasks plus Euclidean distance estimations.

Method Subjects The subjects were 32 undergraduate students from Vanderbilt University. All subjects participated voluntarily and were compensated for their participation with course credit or monetary payment.

Materials and Design Layouts. Each of the two layouts comprised the locations of 30 object names, displayed within an 18.9 x 13.7-cm rectangle. The rectangle was divided in half by a vertical line, thereby creating two regions of equal size. The locations of the object names were designated by filled circles approximately 0.3 cm in diameter. Locations were homogeneously distributed across the layout, with 15 in each region. Six pairs of the locations were separated by a distance of approximately 0.84 cm (the spatially close pairs), and six pairs were separated by a distance of approximately 6.65 cm (the spatially far pairs). Each region contained an equal number of spatially close and spatially far pairs of locations. Half of the pairs at each level of distance were designated to be temporally close and half were designated to be temporally far during acquisition. The result was the appearance of three critical pairs in each of the four conditions: spatially close-temporally close, spatially close-temporally far, spatially far-temporally close, and spatially far-temporally far. In all cases, both members of a critical pair were located within the same region. The object names were selected from a list of 100 names, most of which were used previously by McNamara, Hardy, and Hirtle (1989). The names represented common objects and varied in length from 3 to 10 letters. Assignment of 30 names to each layout was random without replacement, with the restriction that the names were sufficiently varied in both length and meaning. Furthermore, each name was assigned randomly to a given location, such that there were no obvious phonological, semantic, or functional relations between names associated with critical pairs of locations. The remaining 40 names were used as foils in the subsequent recognition test for each layout (20 foils per layout). The two layouts differed from one another in both object names and locations. In addition, four versions of each layout were con-

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SPATIAL AND TEMPORAL MEMORY

A.

candy w

^ brick

shoe

zipper

match

soap

tape (

block

« comb • boat

•stapler gun

wrench

saucer

wallet * glove

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razor

^^

fork • needle record

tire fan

bottle

chalk* newspaper

*

watch

stool

telephone • pencil

B.

Figure 1. One of the spatial arrays that subjects learned in Experiment 1. (Panel A is presented for illustrative purposes only. Subjects saw the display in Panel B.)

structed such that across the four versions, each object name participated in each of the four critical conditions once, with the same six object names serving as fillers. No two names occurred together in a critical pair in more than one version. The resulting pairs contained object names that were not related to one another in any obvious way. The four versions therefore differed only in the assignment of names to locations (and hence to conditions); the assignment of locations to conditions remained constant. Versions were assigned to subjects in a fixed rotation determined by the order in which subjects participated in the experiment. Recognition. Four recognition lists were generated for each layout, one for each version. Each list contained 50 names, 30 positive items (names from the layout) and 20 negative items (foil names). The same foils appeared in all lists for a given layout. Twelve pairs of the positive items were involved in priming relations, three pairs per spatial-temporal condition. For each pair, one item was desig-

nated the prime and one item was designated the target. The prime had always preceded the target during map learning. The remaining positive items consisted of the filler names. Assignment of names to serial positions in the recognition list was random with the following constraints: (a) No critical name appeared in the first 5 serial positions, (b) the prime and the target members of each critical pair appeared in consecutive serial positions, (c) critical pairs from the same spatial-temporal condition never appeared sequentially in the list, and (d) no more than four successive names in the list had been located in the same layout region. Location judgments. A test list was constructed for each version of the two layouts. Each list contained 60 names, half of which corresponded to locations in the right-hand region and half of which corresponded to locations in the left-hand region. A test list was obtained by using all 30 names from a layout two times. Primes and targets in the four spatial-temporal conditions were therefore re-

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peated, yielding six prime-target pairs per subject per condition per map. (The same items served as primes and targets in both the recognition and the location-judgment test lists.) Assignment of names to the 60 serial positions was random, subject to the following constraints: (a) No item was repeated until all items had been presented once, (b) items serving as primes (or targets) in the first half of the list likewise served as primes (or targets) in the second half, (c) no critical name appeared in thefirst3 serial positions, (d) the prime and target members of each critical pair appeared in consecutive serial positions, (e) critical pairs from the same spatialtemporal condition never appeared sequentially in the list, and (f) no more than four successive names in the list had been located in the same layout region. Distance estimation. Four distance-estimation lists were generated for each version of the two layouts. Each list contained 24 base pairs of object names repeated once, for a total of 48 pairs. Twelve of the base pairs were the critical pairs in the four experimental conditions. The filler pairs were constructed by randomly pairing names in the critical pairs and filler names and were always taken from the same region of a layout. The ordering of members within a pair was reversed when they were repeated (e.g., soap-stool and stoolsoap). The distance-estimation lists contained an equal number of pairs from the two regions, the members of each pair always being from the same region. Assignment of pairs to the 48 serial positions in a list was random, with the following restrictions: (a) No pair was repeated until all pairs had been presented once, (b) no critical pair appeared in the first 3 serial positions, (c) critical pairs from the same spatial-temporal condition never appeared sequentially in the list, and (d) no more than four successive pairs in the list were from the same region of the layout.

Procedure Subjects learned the locations of object names in a layout and were then tested on their memory for the layout in two or three successive tasks: Subjects in Experiment la (n = 16) participated in a recognition task and a location-judgment task, and subjects in Experiment lb (n = 16) participated in these tasks plus distance estimations. This sequence was then repeated the following day for the second layout. Each session lasted between 90 and 120 min. The order in which layouts were learned was counterbalanced across subjects. Acquisition. Layouts were presented on an amber CRT monitor driven by a personal computer using Hercules-compatible graphics. For each layout, subjects were instructed to learn the locations of the 30 object names. Layout learning proceeded in a series of study-test trials. During a study trial, the layout and its 30 dot locations (minus the object names) were displayed on the computer screen. The acquisition list was then presented sequentially. Specifically, each object name was displayed on the screen beside its corresponding dot location for 3 s, during which time the dot blinked repeatedly. The name was then removed from the screen and replaced by the next item in the acquisition list, which in turn was displayed beside its blinking dot location for 3 s. This sequence continued until all 30 object names had been presented once at their corresponding locations in the layout. All dot locations were displayed throughout the entire study trial. At no time, however, was more than one object name displayed on the screen. Temporal condition was determined by the number of intervening items between two names in a critical pair: Names separated by zero items during learning were defined as temporally close, and names separated by four items during learning were defined as temporally far. Thus, the interstimulus intervals were 0 s for temporally close pairs and 12 s for temporally far pairs. Because temporal condition

was crossed with spatial condition (and because critical pairs were evenly distributed across the layout and its regions), the learning order did not reflect to subjects any manipulations of temporal and spatial contiguity. Subjects received the same learning order during every study-test trial. Identical orders of locations were used for each version of a given layout. After each study trial was a test trial in which subjects were evaluated for their memory of the layout. During each test trial, the layout and its dot locations were displayed on the computer screen. Subjects were asked to recall successively the object names corresponding to each dot location. Specifically, a dot location blinked for 3 s. Subjects were then prompted by the computer to type in the name of the object corresponding to the blinking location. If they were unsure of a response, subjects were encouraged to make their best guess. The computer recorded the response and displayed the correct name beside the previously blinking location for 3 s. Immediately thereafter, the dot location for the next item blinked for 3 s, followed by a prompt to recall its object name. This sequence continued until subjects were tested on the locations of all 30 object names. The order in which the locations were tested was identical to the order in which they were studied. The layout and its locations were displayed during the entire test trial. Object names, however, were tested and displayed one at a time. The identical sequence of study-test trials continued until subjects could correctly locate all object names on each of two consecutive trials. No dropout procedure was used. That is, subjects studied and were tested on all object locations on every trial until thefinalcriterion was reached. Recognition. Immediately before engaging in the recognition test, subjects were administered a practice test to familiarize them with the procedures. The practice test required state-nonstate judgments. Specifically, a series of 24 names (U.S. states and foreign countries) was displayed, one name at a time, on the computer screen. Subjects were instructed to press the m key if a name was a state and the z key if it was not a state. Instructions emphasized that subjects should respond as quickly and as accurately as possible. After the practice task, subjects engaged in the recognition test. A list of object names was presented on the screen, one name at a time, and subjects were required to decide whether each name was from the layout just learned. Subjects pressed the m key if a name was from the layout and the z key if it was not from the layout. Instructions emphasized both speed and accuracy and the necessity of constant vigilance during the task. An interval of 100 ms elapsed between the response to an item and the appearance of the next item. Location judgments. On completion of the recognition test, subjects were administered the location-judgment test. A series of object names was displayed, one name at a time, on the computer screen. Subjects were instructed to decide for each name whether it was from the right region (the m key) or the left region (the z key). Both accuracy and speed were emphasized. The response-stimulus interval was 100 ms. Distance estimation. The subjects in Experiment lb also participated in Euclidean distance estimations. Pairs of names were displayed one pair at a time in the lower left-hand corner of the computer screen. The names in each pair were displayed in adjacent positions, separated by a horizontal line approximately 0.3 cm in length. For each pair, subjects were required to adjust the length of the line until it equaled the interobject distance between the two names as they appeared in the original layout. Subjects pressed the m key to increase the length of the line and the z key to decrease its length. Both the left name and the left endpoint of the line remained fixed throughout each trial; subjects' adjustments served only to change the position of the right endpoint and right name. Subjects were instructed to take as much time as needed for each judgment, but no

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Results

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Recognition The error rate on targets was very low (1%) and did not vary across conditions. Analyses of latencies were conducted on means computed for each subject and each condition. Only correct responses to targets preceded by correct responses to primes were included in the means. The mean response latencies, collapsing across Experiments la and lb, can be found in Table 2. The standard error of the difference (SED) for recognition latencies was 19.42 ms. This value was computed from the error term for the Space x Time interaction. The major result of this experiment was that spatial distance and temporal distance had interactive effects in recognition priming. In particular, priming occurred between pairs that were temporally and spatially close, but not for other pairs. The absence of spatial priming for temporally far pairs (722 vs. 725), Z(30) = 0.15, replicates the results of Clayton and Habibi (1991) and of Sherman and Lim (1991). However, the presence of spatial priming for temporally close pairs (648 vs. 710), r(30) = 3.19, and the absence of temporal priming for spatially distant pairs (710 vs. 725), /(30) = 0.77, are inconsistent with the results of Clayton and Habibi's experiments (see Table 1). These conclusions were supported by an overall analysis of variance (ANOVA) with variables corresponding to experiment (la vs. lb), spatial distance (close vs. far), and temporal distance (close vs. far). The latter two variables were within subjects. The ANOVA revealed that the interaction between spatial distance and temporal distance was reliable, F( 1, 30) = 4.53, p < .05, MSe = 6,036. The three-way interaction with experiment was not reliable, F(l, 30) = 0.66.

Location Judgments Analyses were conducted on median response latencies and on mean error rates computed for each subject and each condition. Median latencies were used because of the presence of some very long response latencies and because enough data Table 2 Results of Experiment 1

Close Far

Close

Recognition latency 648 710

Location judgment latency • Close 702 Far 824 Close Far

Distance Estimations Subjects in Experiment lb (n = 16) also participated in distance estimations. Analyses were again based on medians computed for each subject and each condition. There are two important results in the distance estimation data (see Table 2). First, subjects acquired spatial information in the experiment. The actual interpoint distances were 0.84 and 6.65 cm in the close and far conditions, respectively, which means that on the average, subjects underestimated both levels of distance. The second important result was that there were no detectable effects of temporal distance in distance estimations

Discussion Temporal distance

Spatial distance

were collected per subject per condition (12 observations) to ensure that the medians would be stable. Only correct responses preceded by correct responses were included in the median response latencies. The means of median latencies can be found in Table 2 (SED = 56.51 ms). Spatial and temporal contiguity had (statistically) additive effects in location judgment latencies. In an overall ANOVA, the spatial effect was reliable, F{\, 30) = 26.07, p < .001, MS, = 31,761; the temporal effect was reliable, F(l, 30) = 26.15, p < .001, MS, = 64,346; but the interaction was not reliable, F( 1, 30) = 0.93, MS, = 51,103. The pattern in error rates was similar, but only the effect of spatial distance was statistically reliable, F(l, 30) = 5.52, p < .05, MSe = 43.37. Mean error rates were 3.38% and 6.12% in the spatially close and far conditions, respectively. These findings replicate and extend the results reported by Sherman and Lim (1991), who demonstrated that spatial priming occurred in location judgments even when items were not temporally contiguous. The sizes of the location judgment latencies suggest that the priming effects might have been strategically mediated. Evidence against this possibility can be garnered from two sources. First, although average latencies were much faster in Experiment la than in Experiment lb (733 vs. 1,022 ms), the pattern of results was identical. Second, in other experiments (McNamara, Halpin, & Hardy, in press), we have shown that distance effects appear in location judgments even when the stimulus onset asynchrony (SOA) is 250 ms and processing time on the target is held to 550 ms.

Estimated distance 0.61 5.79

Far 722 725 893 1092 0.76 5.84

Note. For recognition and location judgments, n = 32; for estimated distances, n = 16. Recognition and location judgment latencies are in milliseconds. Estimated distances are in centimeters.

These experiments and those reported by Clayton and Habibi (1991) and by Sherman and Lim (1991) converge on some results, but diverge on others. The major point of convergence is this: When spatially contiguous names were not experienced close together in time, spatial priming did not occur in a recognition test for those names. This result held up despite large differences in materials and procedures. The divergent results are that (a) we obtained a spatial priming effect in recognition even when primes and targets had been temporally contiguous during acquisition, but Clayton and Habibi did not, and (b) we did not obtain a temporal priming effect in recognition when primes and targets had been spatially distant on the maps, but Clayton and Habibi did.

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There are several differences in methods that could account for these differences in results. For example, the manipulation of spatial distance was stronger in our experiments than in Clayton and Habibi's (1991); we manipulated temporal and spatial contiguity within subjects, whereas Clayton and Habibi manipulated one or the other of these variables between subjects; our maps contained more locations than theirs (30 vs. 18); and finally, our maps were divided into two regions. An examination of the maps used in the two studies yields one obvious difference, which is that the distance manipulation was much stronger in our experiments than in Clayton and Habibi's (1991; distance ratio of 8 : 1 vs. 5 : 1). The close pairs on our maps were perceptually quite close (see Figure 1, Panel B). This difference may account for the fact that we obtained a spatial effect for temporally contiguous items, but Clayton and Habibi did not. We do not know why temporal priming did not occur for spatially distant items, but we doubt that this null result can be attributed to a weak manipulation of temporal distance. The temporal effect was quite large in location judgments at both levels of distance. In addition, nearly all of the subjects reported that they had learned the temporal order of the object names to facilitate acquisition of the map. Finally, data reported by McNamara et al. (1984) show that temporal priming may not occur in recognition even when a temporal manipulation is quite strong. The recognition data in Table 2 replicate data reported by McNamara et al. (1984). In the second experiment of that study, subjects learned fictitious road maps in which critical pairs of cities were close in Euclidean distance and close in route distance (CE-CR), close in Euclidean distance but far in route distance (CE-FR), and far in both (FE-FR). Although subjects saw the entire map when they studied it, they were forced by the experimenter to rehearse the cities and to recall their locations in an order that guaranteed that names in the CE-CR condition and in the CE-FR condition were temporally contiguous. Names in the FE-FR condition were always temporally far apart in the learning order. Given that route distance was the primary determinant of priming in that experiment, one can reclassify the conditions as follows: CECR = close in space, close in time; CE-FR = far in space, close in time; and FE-FR = far in space, far in time. The data from this experiment are reproduced in Table 3. Note that for temporally contiguous items, there was still a spatial priming effect. This effect might have been caused by the strong manipulation of spatial distance in the experiment: Items close in route distance were directly connected by a line, but items far in route distance were not. Importantly, the temporal priming effect for spatially distant items was Table 3 Results of Experiment 2 of McNamara, Ratcliff and McKoon (1984)

quite small (10 ms), even though the temporal manipulation was very strong. Subjects in the experiment were required to recall all of the city names after learning a map. Seven of the 12 subjects recalled all 16 cities on each of three maps in exactly the same order as the cities had been learned, and an 8th subject got the order right for all three maps, but left out one city on one map. Across all 12 subjects and three maps learned, the mean distances between primes and targets in the recall protocols (where a value of 1 means the cities were next to each other) were 1.18 in the CE-CR condition (also known as close in space, close in time), 1.34 in the CE-FR condition (also known as far in space, close in time), and 6.46 in the FE-FR condition (also known as far in space, far in time). In summary, a consideration of the location judgments and subjects' informal reports in the present study and of the data collected by McNamara et al. (1984) indicates that temporal priming may not occur in recognition even when temporal distance is varied. Of course, the same may be said of spatial priming in recognition. The causes of these results are not obvious, but they must have something to do with the kinds of information that can be used to make a recognition judgment and the relative availability of these sources of information in various learning situations. Experiment 2 The spatial priming effect for temporally close items might have been caused by the strong manipulation of spatial distance. Experiment 2 was conducted to test this hypothesis. The method of Experiment 2 was identical to that of Experiment 1 with one change: The distance between pairs of locations in the spatially close condition was more than doubled, from an average of 0.84 cm to an average of 1.85 cm. This reduced the distance ratio from 8 : 1 to only 3.6 : 1, which is even lower than that in Clayton and Habibi's (1991) experiments.

Method Subjects The subjects were 32 undergraduates at Vanderbilt University. Subjects were compensated for their participation with course credit.

Materials, Design, and Procedure The design and procedure were the same as in Experiment lb; in particular, after learning a map, subjects participated in recognition, location-judgment, and distance-estimation tasks. The only difference between this and the previous experiment was in the materials: Spatially close locations were separated by 1.85 cm, rather than by 0.84 cm.

Results and Discussion

Temporal distance Route distance Close Far

Close 620 658

Far

Recognition

668

The error rate on targets was 2.34% and did not vary reliably across the four conditions. Analyses of response laten-

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SPATIAL AND TEMPORAL MEMORY

cies were based on means computed for each subject and each condition. Only correct responses preceded by correct responses were included in the mean response latencies. In addition, two response latencies over 3 s were excluded. The mean recognition latencies can be found in Table 4 (SED = 18.55 ms). The pattern of response latencies in Experiment 2 is nearly identical to that in Experiment 1. Although the omnibus interaction between spatial and temporal distance was not reliable, F(\, 31) = 1.74, MSt = 5,507, pairwise comparisons showed that the spatial priming effect was reliable for temporally close pairs, r(31) = 2.10; but not for temporally far pairs, /(31) = 0.27; and that the temporal priming effect was not significant for spatially distant pairs, /(31) = 0.86. Apparently, the spatial priming effect for temporally close pairs in Experiment 1 cannot be attributed to an unusually strong manipulation of spatial distance. Note that in both Tables 2 and 4, there is a small temporal priming effect in recognition for spatially distant locations (15 and 16 ms, respectively). To test the reliability of this priming effect, the data from Experiments 1 and 2 were combined in an ANOVA that included variables corresponding to experiment, spatial distance, and temporal distance. The Space x Time interaction was significant, F(l, 62) = 6.04, p = .017, MSC = 5,739; but the three-way interaction with experiment was not reliable (F < 1). The temporal priming effect for spatially distant pairs was still not reliable, /(62) = 1.16.

Location Judgments The error rate on targets was 6.18% and did not vary across conditions. Analyses of response latencies were based on medians computed for each subject and each condition. Only correct responses preceded by correct responses were included in the median latencies. Means of median latencies can be found in Table 4 (SED = 43.60 ms). As in Experiment 1, spatial distance and temporal distance had additive effects in location-judgment latencies. The overall analysis revealed that the effects of spatial distance were reliable, JF(1, 31) = 5.77, p = .0225, MSe = 29,332; the effects of temporal distance were reliable, F(l, 31) = 29.78, p

Spatial and temporal contributions to the structure of spatial memory.

Three experiments investigated the effects of spatial and temporal contiguity in item recognition, location judgment, and distance estimation tasks. S...
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