Gestalt grouping effects in locating past events on timelines

Acta Psychologica 64 (1987) 139-149 North-Holland

139

GESTALT GROUPING EFFECTS IN LOCATING PAST EVENTS ONTIMELINES *

Simon KEMP University of Canterbury, Christchurch, New Zealand

Accepted February 1986

Two experiments required human subjects to date events from the recent or historic past by placing them on timelines. Experiment 1 used parallel sets of timelines containing events similar or related to the test event marked either early or late on the timeline. For three of the seven test events used, subjects located the test event significantly earlier on the ‘early’ than the ‘late’ timeline. In experiment 2, where subjects were required to place a pair of related and a pair of unrelated events on a timeline, related events were significantly more bunched together than unrelated events. The results were interpreted as the consequence of Gestalt principles of perceptual organization.

Introduction

According to Gestalt theory, perception is mediated by principles or laws of perceptual organisation (Koffka 1936). While the exact nature of the underlying mechanisms is in question, both the original Gestalt demonstrations and more recent experimentation (e.g., Coren and Girgus 1980; Olson and Attneave 1970; Restle 1979) have shown Gestalt principles to apply to the perception of static and mobile stimulus configurations.

It has also been proposed that Gestalt principles should apply to

* The author gratefully acknowledges the cooperation of Mary Harte and Richard George in performing the experiments and coding the results, and the helpful suggestions of Jim Pollard and Ken Strongman. I am also grateful for the comments and experimental suggestions of Dr. Crowder, Dr. Baaijmakers and an anonymous reviewer on an earlier version of the manuscript. ‘The research was supported by the New Zealand Department of Labour under the PEP scheme.

Author’s address: Simon Kemp, Psychology Dept., University of Canterbury, Christchurch, New Zealand.

OOOl-6918/87/$3.50 Q 1987, Elsevier 8cience Publishers B.V. (North-Holland)

140 S. Kemp / Gestalt grouping effects in dating past events

remembered as well as perceived stimuli (Wulf 1922; Koffka 1936). Koffka (1936: 496) suggested that irregular patterns might be remembered as more regular following ‘internal forces of organisation’. The experimental evidence for this proposition is mixed. Holmes (1968) reviewed a number of studies which investigated the remembered size of a gap in a circle. While the Gestalt principle of closure suggested that the width of the remembered gap should be less than that of the perceived gap, the majority of studies revealed the opposite effect. On the other hand, recent work suggests that distortions in remembered maps be derived from Gestalt principles. Stevens and Coupe (1978) found a tendency to distort the geographical relation between two locations to conform in the direction of the relation between super- ordinate units. (For example, people imagine the Atlantic entrance of the Panama Canal to lie due east of the Pacific entrance.) Tversky (1981) found the principles of proximity and common fate to operate in the alignment and rotation of geographical entities.

The present study was concerned to find Gestalt principles at work in memory for the time of occurrence of past events. It is well known that people may remember events which they are unable to date accurately; this applies both to events which have occurred within the lifetime of the observer (Brown et al. 1985; Loftus and Marburger 1983) and to historical events (Smith and Tomlinson 1977). According to the Gestalt principle of grouping, where the dating of events is uncertain, events that are related or similar ought to be erroneously perceived or remembered as occurring more closely in time than events that are unrelated or dissimilar. This prediction follows the finding in perception (Coren and Girgus 1980: 404) that ‘interior distances (within a perceptual unit or group) are underestimated relative to exterior distances’.

Experiment 1

Subjects in this experiment were asked to place well-known test events from the historical or recent past on timelines containing other past events. Two forms of each timeline were constructed, an ‘early timeline’, in which similar or related events to the test event occurred early in the period defined by the timeline, and a ‘late timeline’, in which similar or related events occurred late in the period defined by the timeline. The experimental hypothesis was that subjects confronted with the early timeline should place the test event earlier on average than those confronted with the late timeline.

S. Kemp / Gestalt grouping effects in dating past events 141

Method

Subjects Eighty undergraduate psychology students of the University of Canterbury, New

Zealand, served in the experiment.

Materials and design Each subject was given a questionnaire consisting of seven pages, each displaying

one timeline and one test event, preceded by an instruction page and an example. Each page of the questionnaire featured a vertical line approximately 18 cm in length to the right of which were 11 brief descriptions of past events with arrows leading from the descriptions to the line. Below this timeline was a brief description of the test events. Subjects were asked to indicate when they thought the test event had occurred by making a horizontal mark on the timeline.

Two of the seven timelines covered the period 1500-1950; two the period 1800-1950; and three the period Jan. 1976 to Jan. 1985. The seven test event descriptions used were: Abel Tasman visits New Zealand, French Revolution, Hone Heke chops down the flagpole, Alexander Graham Bell invents the telephone, Bob Hawke becomes Australian P.M., Air New Zealand DC10 crashed on Mt Erebus, and Outbreak of Iran-Iraq war. A brief survey of students not employed in experiment 1 revealed that the events had all been heard of but were frequently inaccurately dated. Note that two of the test events (and many of the event descriptions used elsewhere) refer to recent and historical events in New Zealand, which the subjects (but perhaps not the reader) were familiar with. Actual dates for the test events were, in order: 1642, 1788, 1844, 1876, Mar. 1983, Nov. 1979, and Sept. 1980. Subjects were given no information about the dates of either the test events or those appearing on the timelines; nor were any dates marked on the timelines. They were told, however, that the timelines were linear and that one inch of line represented the same period of time on each part of the timeline. Subjects were instructed to use the 11 events marked on each line to establish the time scale involved.

The 11 event descriptions placed on each time scale all referred to actual events and in all cases their arrowed position on the time scale was accurate. Each timeline and test event, however, contained one of two sets of 11 events. Each of these sets contained 3 events that were similar in some way to the test event: for example, the sets relating to Bell’s invention of the telephone each contained 3 events relating to scientific or industrial advances. In one of the two sets the 3 events occurred early in the time period covered in the timeline (early timeline), in the other the 3 events occurred late in the period (late timeline). Table 1, which contains a list of the two sets used with the Bell test event, illustrates the general principle.

Appropriate ‘filler’ events were used to balance the timelines, so that as far as possible the average date of all 11 events shown on each timeline was the same regardless of whether the 3 similar events occurred early or late on the timeline. Where this balancing was not exact, the average date of the 11 events was later for the early timeline than the late timeline; this was done to remove possible rival explanations in terms of general context.

For each of the seven test events, 40 early and 40 late timelines were prepared. The


Table 1 Event descriptions used with the Bell test event. Actual dates (not given to the subjects) are shown in parentheses. An asterisk denotes a similar event to the test event, relating to scientific or industrial advances.

Ear& timeline Napoleon becomes emperor of France George Stephenson builds first steam locomotive * First photograph produced * Samuel Morse’s telegraph first used * First four ships arrive in Lyttelton Eruption of Krakatoa ‘Jack the Ripper’ murders in London Death of Queen Victoria World War I begins Great Depression begins End of World War II

L.are limeline .Napole.on becomes emperor of France Battle of Waterloo Beethoven writes 9th (‘Choral’) Symphony Treaty of Waitangi First four ships arrive in Lyttelton Eruption of Krakatoa ‘Jack the Ripper’ murders in London Death of Queen Victoria Ford produces first model T * Alexander Fleming discovers penicillin * First atom bomb exploded *

(1804) (1814)

(1827) (1837) (1850) (1883) (1888)

(1901) (1914) (1929) (1945)

(1804) (1815) (1824) (1840) (1850) (1883) (1888)

(1901) (1908) (1928) (1945)

questiomaires were then composed by. randomly selecting an early or a late timeline for each test event; thus, in general, subjects received different questiomaires containing a combination of early and late timelines. Each subject placed each event once, either on an early or a late timeline. The order of the test events was the same for each subject.

Subjects responded during normal class times, typically taking about 10 minutes to complete the questionnaire.

Results and discussion

There were few failures to respond to any of the test events: 79. subjects responded to the Bell event; at the other extreme, 75 responded to the Tasman event.

The chief results of experiment 1, as mean test event dates chosen for the early and late timelines, are shown in table 2. Six of the seven test events were dated earlier in the early than the late timeline condition as predicted. For three of these six, the difference in dates was significant.


Table 2 Results of experiment 1. Abbreviated test event descriptors are shown in the left-hand column.

The next two cohunns show the mean dates corresponding to the average horizontal marks made by the subjects on the early and late timelines. The last column summarizes the result of a t-test on the difference between the mean dates.

Event

Tasman visits N.Z.

French Revolution

Hone Heke fells flagpole Bell invents telephone Hawke Australian P.M.

Erebus crash Iran-Iraq war

Timeline

Early

1720 1717

1849

1868 May 1981 Dec. 1979 Nov. 1979

Late

1698

1732

1866 1893

Feb. 1982 March 1980 Feb. 1980

Significance

t(74) =1.21, n.s.

t(76) = - 0.85, n.s.

t(77) = - 4.29, p < 0.05 t(78) = -4.11, p < 0.05 t(77) = - 2.48, p < 0.05 t(77) = -0.66, n.s. t(75) = - 0.66, n.s.

The results indicate that a significant shift in dating the test event took place for three of the seven test events, and hence that events are sometimes erroneously perceived as closer in time to similar or related events. The fact that four of the seven test events did not show a significant effect in the hypothesised direction does not necessarily vitiate this conclusion, as the simplest explanation of these results is that the similar events used in these four pairs of timelines were either not similar or not salient enough to attract the test event.

For some of the test events there appears to have been a systematic bias away from the true event date regardless of whether the early or late timeline was used. Systematic errors in temporal estimation have been reported before (Brown et al. 1985; Ferguson and Martin 1983; Loftus and Marburger 1983). Table 2 does not indicate any strong relationship between the existence of a systematic error and a significant effect of the timeline manipulation.

Experiment 2

Experiment 2 aimed to investigate the effect of similarity or relatedness of events on the perceived proximity of the events in time using a more direct method than experiment 1. In experiment 2 subjects were confronted with timelines marked with dates and asked to place four past events on the timeline. Each set of events comprised two events that were similar or related to one another and two events that were comparatively dissimilar and unrelated to one another. The experimental hypothesis was that the similar or related events should be placed more closely together on the timeline than their actual dates of occurrence would suggest, while the dissimilar or unrelated events should tend to remain apart.


Method

Subjects

Seventy volunteers, recruited during the summer vacation at the University of Canterbury, served in the experiment. Thirty-five received questionnaire form A and thirty-five received form B. Each was tested individually in the presence of an experimenter.

Materials and design Each subject was given a questionnaire consisting of an instruction page and six

pages, each containing a vertical timeline in the upper three-quarters of the page and four brief event descriptions at the bottom. The timelines contained date indicators. Three (historical events) timelines displayed 1750, 1800,1850, 1900, and 1950 at 5 cm intervals. Three (recent event) timelines were marked off with nine 2 cm intervals; the intervals were labelled 1976,1977, to 1985, and the endpoints marked Jan. 1 1976 and Jan. 1 1986. The actual dates of the four events described at the bottom of the page ,always fell within the extreme date limits indicated on the timeline above.

Two forms (A and B) of the questiomaire were produced. The six sets of event descriptions used for each form are shown in table 3 with the actual dates of occurrence (which were not made available to the subjects). The basic principle of construction was that the similar historical or recent event pairs used in form A were broken up and used to make up the dissimilar historical or recent event pairs in form B and vice versa.

The four events shown on each page were labelled A, B, C, and D, in order of presentation on the page. For each set of events several different random orderings of the events were used so that the four events within a set were generally labelled with different letters for different subjects. The pagination of the questionnaires was also randomly varied.

Subjects were asked to place four horizontal lines on each timeline corresponding to the time at which they felt the four events occurred. They were further asked to place the appropriate letter beside the line to indicate the particular event marked. Subjects were forbidden to turn back to make changes or to check answers given on pages already completed. Typically, questionnaires required about 10 minutes to complete.

Results and discussion

The distance between the events in the similar pair and the distance between the events in the dissimilar pair in each set were measured regardless of direction and comprised the data for further analysis. Measurement error was f 0.5 mm, corresponding to six months on the historical and about one week on the recent event timelines. For each subject the actual time interval was subtracted from the estimated time interval for each pair of similar and dissimilar events, to form a period difference measure. A negative value on these period difference measures is readily interpretable as an underestimation by the subject of the real time between two events. For the experimental hypothesis to be upheld, the period difference measure should, on


Table 3 Events used in experiment 2. The six sets of event descriptions used in each form (A and B) of the questionnaire used in experiment 2. For each form, sets 1,2 and 3 are of historical events and sets 4, 5 and 6 are of recent events. The first two events shown in each set comprise the similar pair, the last two the dissimilar pair. Actual dates of occurrence are shown beside each description.

Set event description

Form A 1. Karl Marx publishes the ‘Communist Manifesto’

Russian revolution American civil war begins First public television service in Britain

2. Women first get the vote in N.Z. First Labour govt. elected in N.Z. Te Rauparaha captures Kaiapoi Invention of the telephone by Alexander Gaham Bell

3. Stockton and Darlington railway (world’s first) opens N.Z. main trunk rail line completed American revolution begins Te Kooti campaigns in the North Island

4. Death of Mao TssTung, Chinese communist leader Death of Leonid Brezhnev, Russian communist leader Abbotsford slip Release of U.S. Embassy hostages by Iran

5. Gleneagle’s agreement on sporting contacts with South Africa Beginning of last Springbok tour of N.Z. Ranfurly Shield won by Canterbury from Wellington Invercargill flooded

6. Pope John Paul II elected; first non-Italian pope for hundreds of years

Pope John Paul II shot by Turkish gunman Revolution in Iran. Shah flees to exile Ranfurly Shield lost by Canterbury to Auckland

Form B 1. Invention of the telephone by Alexander Graham Bell

First public television service in Britain N.Z. main trunk rail line completed Russian revolution

2. American revolution begins American civil war begins Kar Marx publishes the ‘Communist Manifesto’ Women first get the vote in N.Z.

3. Te Rauparaha captures Kaiapoi Te Kooti campaigns in the North Island Stockton and Darlington railway (world’s first) opens First Labour govt. elected in N.Z.

4. Abbotsford slip Invercargill flooded Beginning of last Springbok tour of N.Z. Death of Leonid Brezhnev, Russian communist leader

(1848) (1917) (1861) (1929) (1893) (1935) (1830) (1876) (1825)

(1908) (1775) (1868) (Sept. 1976) (Nov. 1982) (Aug. 1979) (Jan. 1981) (June 1977) (Aug. 1981) (Sept. 1982) (Jan. 1984)

(Oct. 1978) (May. 1981) (Jan. 1979) (Sept. 1985)

(1876) (1929)

(1908) (1917) (1775) (1861) (1848) (1893) (1830) (1868) (1825) (1935) (Aug. 1979) (Jan. 1984) (Aug 1981) (Nov. 1982)


Table 3 (continued)

Set event description

5. Revolution in Iran. Shah flees to exile Release of U.S. Embassy hostages by Iran Death of Mao Tse-Tung, Chinese communist leader Pope John Paul II elected; first non-Italian for

hundreds of years 6. Ranfurly Shield won by Canterbury from Wellington

Ranfurly Shield lost by Canterbury to Auckland Gleneagle’s agreement on sporting contacts with South Africa Pope John Paul II shot by Turkish gunman

(Jan. 1979) (Jan. 1981) (Sept. 1976)

(Oct. 1978) (Sept. 1982) (Sept. 1985) (June 1977) (May 1981)

Table 4 Results of experiment 2. Mean period differences for similar and dissimilar event pairs, for each set of four events and each form. Negative differences indicate underestimation of the period between events; positive differences indicate overestimation. The result of a t-teat on the similar and dissimilar event differences is shown in the right-hand column. The top half of the table shows the results for historical events and the bottom half the results for recent events. The last row in each half gives the average result for historical and recent events; note that the average results are based on data from 70 subjects while the set results are based on data from 35 subjects.

Form Set Event Significance

A A A B B B

Average

Average period difference (years) for historical events

- 23.6 34.4 t(34) = -5.96, p < 0.05 -13.5 0.7 t(34) = - 3.00, p < 0.05 - 3.0 - 20.6 t(34) = 2.26, p < 0.05 15.0 34.6 t(34) = - 2.57, p < 0.05

-51.3 -8.8 t(34) = - 5.79, p < 0.05 - 6.1 - 19.8 t(34) = 1.87, n.s.

- 13.8 3.4 t(69) = - 5.14, p -= 0.05

Average period difference (years) for recent events

A A A B B B

Average

4 - 2.21 0.36 t(34) = - 6.47, p < 0.05 5 -1.33 0.32 r(34) = -4.09, p < 0.05 6 -1.15 -1.46 t(34) = 0.75, ns. 4 -0.51 0.87 t(34) = - 3.63, p < 0.05 5 0.33 0.44 t(34) = -0.23, ns. 6 -0.17 - 0.66 ” t(34) = 1.18, n.s.

- 0.84 - 0.02 t(69) = - 4.89, p < 0.05


average, be less for the similar than the dissimilar pairs within a set. Further, the period difference measures should be negative for the similar pairs.

Table 4 shows the period differences for each set averaged over subjects. Seven of 12 sets showed significant differences in the expected direction: period differences were significantly less for the similar than the dissimilar event pairs.

Also shown in table 4 are the period differences obtained by averaging over all the similar and dissimilar historical event pairs and all the similar and dissimilar recent event pairs. These average historical and average recent period differences are the critical results of the experiment since the impact of particular events being placed too early or too late in the timeline is reduced both by averaging and as a consequence of the experimental design. Both average period differences were significantly less for the similar than dissimilar event pairs as hypothesised. It is also noteworthy that the average period differences reveal a moderate overall underestimation of the real time interval to have taken place in response to the similar but not the dissimilar event pairings.

General discussion

Both experiments produced results in accordance with the hypothe- ses and thus provide support for the operation of Gestalt principles in estimating the time of occurrence of past events. The support is strengthened by the fact that the two experiments differed considerably in their design.

In neither experiment did all the experimental manipulations produce significant effects. This result reflects the fact that each timeline and event set is subject to a wide range of influences besides a Gestalt grouping effect. Because each timeline and event set involves actual particular events, the influences in any one timeline and event set might well work in the opposite direction to a grouping effect. For example, the possibility that dissimilar or unrelated events might attract a test event through, e.g., misperception of the actual historical or recent event sequence, cannot be ruled out. Hence overall the experiments suggest that a Gestalt grouping effect is possible and does occur rather than demonstrate that it invariably takes place.

Two additional issues are raised by the experiments reported here. Firstly, it will have been noted that four of the seven timelines in experiment 1 and three of the six in experiment 2 covered periods of greater than 100 years, and the events to be placed on them were historical, i.e., did not occur within the living memory of the subjects. The other timeline and event combinations used were recent: all events


occurred within the previous 10 years and clearly were within living memory of the subjects. One might expect that dating of these two kinds of events would follow different kinds of processes since recent events could be linked to other events occurring in the subject’s own past. Recent research (Loftus and Marburger 1983) has in fact shown that landmarking does occur in memory for personally experienced events. The results of the present study, however, suggest that both kinds of event are subject to the Gestalt principles of organisation. Either historical and recent events are dated in essentially similar ways or the Gestalt principles apply in two different kinds of dating process.

Secondly, Gestalt principles have generally been applied to form perception, and extensions of the theory to cover remembered stimuli have generally involved remembering forms of some kind. It is prob- able that visual imagery plays an important role in remembering form; there is good evidence, for example, that memory for maps often involves mental imagery (e.g., Kerst and Howard 1978; Kosslyn 1980). Thus the research showing Gestalt principles at work in memory for maps (Stevens and Coupe 1978; Tversky 1981) could be explained in terms of perceptual principles operating in the domain of visual imagery. Such an explanation is strengthened by considerable evidence illustrating similarities between perceptual and imaginal processes (e.g., Finke 1980; Finke and Schmidt 1977; Kerst and Howard 1978; Thomdyke 1981). It is difficult, however, to see any major role for visual imagery in the present study. Hence there is also a difficulty in conceptualising how Gestalt principles of perception might operate in dating past events. There seem to the author to be two possibilities. The first is that Gestalt principles might apply over a very wide range of human perception and cognition; indeed wherever a pattern of any kind is abstracted. In the present context, such a pattern might consist of the perceived or remembered interrelationships between different historical or recent events. The second is that when the events in the present study were placed on timelines, the perception of the stimuli (i.e., what was physically present on the page) was expanded to include the meaning and interrelationships of the events referred to. For example, experiment 2 required subjects to place the letters A, B, C, D on timelines. It is possible that the perception of the letters by the subjects embraced the fact that, for example, A and D represented related events (e.g., the American revolution and the American civil war) while B and C did not. This possibility, however, requires the


perception of the letters to be unrelated to any of their physical properties, since in experiment 2 the assignation of letters to events was both varied and arbitrary.

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Gestalt grouping effects in locating past events on timelines

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