Development of Form Similarity as a Gestalt Grouping Principle in ...

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Research Article DEVELOPMENT OF FORM SIMILARITY AS A GESTALT GROUPING PRINCIPLE IN INFANCY Paul C. Quinn,1 Ramesh S. Bhatt,2 Diana Brush,1 Autumn Grimes,1 and Heather Sharpnack1 1

Washington & Jefferson College and 2University of Kentucky

Abstract—Given evidence demonstrating that infants 3 months of age and younger can utilize the Gestalt principle of lightness similarity to group visually presented elements into organized percepts, four experiments using the familiarization/novelty-preference procedure were conducted to determine whether infants can also organize visual pattern information in accord with the Gestalt principle of form similarity. In Experiments 1 and 2, 6- to 7-month-olds, but not 3- to 4-montholds, presented with generalization and discrimination tasks involving arrays of X and O elements responded as if they organized the elements into columns or rows based on form similarity. Experiments 3 and 4 demonstrated that the failure of the young infants to use form similarity was not due to insufficient processing time or the inability to discriminate between the individual X and O elements. The results suggest that different Gestalt principles may become functional over different time courses of development, and that not all principles are automatically deployed in the manner originally proposed by Gestalt theorists. How during development do people come to know which edges and contours go together to form which objects? Gestalt psychologists have argued that the nervous system is constrained to follow certain classic grouping principles (e.g., closure, common movement, good continuation, proximity, and similarity) that specify how small pieces of a visual scene should be organized to form larger perceptual units (Wertheimer, 1923/1958). More modern experimental work has (a) confirmed that the classic principles are predictive of which elements in a visual display will group together in a variety of tasks measuring basic visual operations such as detection, discrimination, and identification (Palmer, 1999) and (b) indicated that new, additional principles (i.e., uniform connectedness and common region) are needed to account for the full range of perceptual grouping phenomena (Palmer, 1992; Palmer & Rock, 1994). The most recent studies from the adult literature have begun to suggest that not all Gestalt principles are equally powerful or operational at the same time in the overall course of processing. For example, there is evidence that grouping by proximity occurs more rapidly than grouping by form similarity or good continuation (Ben-Av & Sagi, 1995; Han, Humphreys, & Chen, 1999; Kurylo, 1997). Proximity-based grouping may require calculation of element distances only, a process that is presumed to be less computationally demanding than the identification of element features and pattern regularities that may be required in similarity- or continuity-based grouping. Developmental studies examining the emergence of perceptual organization in infants have confirmed that infants are capable of global-

Address correspondence to Paul C. Quinn, Department of Psychology, Washington & Jefferson College, 60 South Lincoln St., Washington, PA 15301; e-mail: [email protected].

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level processing (e.g., Bhatt, Rovee-Collier, & Shyi, 1994; Frick, Colombo, & Allen, 2000; Quinn & Eimas, 1986), and are also consistent with the idea that some Gestalt principles may have an earlier functional onset than other Gestalt principles (Kellman, 1996; Spelke, 1982). For example, Spelke (1982) proposed that infants may first perceive objects in accord with the core principles of common movement and connected surface, and only later, through learning, come to use principles such as similarity and good continuation as predictors of object continuity. Kellman (1996) likewise argued that perceptual unit formation by infants initially relies on a “primitive” edge-insensitive process that responds to common-movement information. This edgeinsensitive process is subsequently supplemented by a “rich” edgesensitive process that responds to good-continuation information and becomes available at approximately 7 months of age, although some evidence suggests an earlier deployment (Johnson & Aslin, 1996; Quinn, Brown, & Streppa, 1997). In a study relevant to the issue of which Gestalt principles become functional at which points during early development, Quinn, Burke, and Rush (1993) provided empirical data demonstrating that 3-monthold infants can organize visual patterns in accord with lightness similarity. As is depicted in Figure 1, Quinn et al. familiarized 3-montholds with arrays of elements that adults perceived as columns or rows on the basis of alternation of the lightness versus darkness of the elements. The infants were then given a novelty-preference test that paired horizontal versus vertical stripes. Infants familiarized with columns preferred horizontal stripes, whereas infants familiarized with rows preferred vertical stripes. This pattern of preferences could not be attributed to spatial-frequency filtering (cf. Ginsburg, 1986), as the infants were also shown to be capable of discriminating the individual light and dark elements forming the rows and columns. In addition, the infants discriminated between arrays organized by adults as columns versus rows via lightness similarity (shown in the top panel of Fig. 2), but did not discriminate between a pattern consisting of randomly arranged elements and its 90 rotation (shown in the bottom panel of Fig. 2). These findings indicate that 3-month-olds can use lightness similarity to represent the column versus row organization of arrays of elements, and have since been extended to newborns (Farroni, Valenza, Simion, & Umilta, 2000), which suggests an initial ability to group on the basis of luminance information. It has been suggested that lightness-based organization may be the most robust type of similarity grouping achieved by infants (Bremner, 1994). Also, in the adult literature, there is evidence for distinct systems for grouping on the basis of luminance and edge information (Gilchrist, Humphreys, Riddoch, & Neumann, 1997). These points, in combination with Kellman’s (1996) suggestion that the edge-sensitive process has a late functional onset, motivated us to examine when form-based grouping becomes functional in infants. Therefore, in the current experiments, we used the procedures and apparatus of Quinn et al. (1993; see also Quinn et al., 1997) to investigate whether infants VOL. 13, NO. 4, JULY 2002

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Fig. 1. Illustration of the generalization task used by Quinn, Burke, and Rush (1993) to test for perceptual organization by lightness similarity.

can organize visual patterns in accord with form similarity. All infants in each experiment underwent a general procedure in which looking times to familiarization and test stimuli were recorded by trained observers who were naive to the hypotheses under investigation.

Note that evidence for developmental change in the use of form similarity might require modification of the Gestalt claim that all organizational principles are automatically and equivalently applied (Kohler, 1929).

Fig. 2. Illustration of the discrimination task used by Quinn, Burke, and Rush (1993) to test for perceptual organization by lightness similarity. VOL. 13, NO. 4, JULY 2002

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Development of Form Similarity EXPERIMENT 1 In Experiment 1, we asked whether infants can organize visual patterns in accord with form similarity. Two age groups of infants, 3- to 4-month-olds and 6- to 7-month-olds, were familiarized with arrays of elements consisting of alternating columns or rows of Xs and Os and then given a novelty-preference test pairing horizontal versus vertical stripes (see Fig. 3). The stimuli were constructed so as to match those used by Quinn et al. (1993), except that Xs and Os were used as individual elements (instead of filled and unfilled square elements). During familiarization, half of the infants were presented with stimuli in which the individual elements were equated for visual angle (shown in Fig. 3), and the other half were presented with stimuli in which the individual elements were equated for amount of contour (i.e., dark area). Matching the elements in terms of amount of contour ensured that shape rather than contour amount would be the basis for similarity grouping.

Method Participants The participants were 64 infants, thirty-two 3- to 4-month-olds (16 females, 16 males) with a mean age of 108.50 days, SD  12.35 days, and thirty-two 6- to 7-month-olds (18 females, 14 males) with a mean age of 189.62 days, SD  11.37 days. Three additional 3- to 4-montholds were tested, but 1 failed to complete the procedure because of fussiness, and 2 were excluded from the data analysis because of position preference (n  1) and experimenter error (n  1). Two additional 6- to 7-month-olds were tested, but not included in the data analysis because of experimenter error. The participants in all experiments were predominantly Caucasian and from middle-class backgrounds.

Stimuli The stimuli presented during familiarization were composed of 16 black elements, 8 Xs and 8 Os, printed onto white cards and perceived as columns or rows when organized by form similarity. For one set of stimuli, the X and O elements were matched in terms of visual angle. In these stimuli, the line elements composing the X were 1.27 cm long (2.42) and 0.35 cm wide (0.67), and the O was 1.27 cm in diameter (2.42), with the width of the dark contour measuring 0.35 cm (0.67). The patterns created with the elements matched for visual angle are shown in Figure 3. For a second set of stimuli, the X and O elements were matched in terms of amount of contour. For these stimuli, the only change in the dimensions of the elements was that the O measured 1.00 cm in diameter (1.91). The test stimuli consisted of four black stripes, each measuring 8.89 cm in length (16.50) and 1.27 cm in width (2.42), oriented either horizontally or vertically on white cards. The center-to-center distance between the stripes was 2.54 cm (4.84). The test stimuli could be described as square-wave grating targets with a spatial frequency of 0.21 cycles/deg. They are shown in Figure 3.

Procedure Sixteen infants in each age group were randomly assigned to each of two experimental groups. Group C was familiarized with columns, and Group R was familiarized with rows. Half the infants in each group were familiarized with elements equated for amount of contour, and the other half with elements equated in terms of visual angle. For half of the infants in Group C, the left-most column was composed of Xs, and for the other half it was composed of Os. For half of the infants in Group R, the top row was composed of Xs, and for the other

Fig. 3. Examples of the familiarization and test stimuli used to test for perceptual organization by form similarity in Experiment 1.

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P.C. Quinn et al. half it was composed of Os. For both groups, the stimuli were presented to the infants for six 15-s periods. Immediately after familiarization, Groups C and R were administered the same preference test. Each infant was presented with horizontal stripes paired with vertical stripes for two 10-s periods. The left-right positioning of the horizontal and vertical stripes was counterbalanced across infants in the first test period and reversed in the second test period.

Results and Discussion Familiarization trials Individual looking times were summed over both stimuli on each trial, and then summed over the first three trials and over the last three trials. The mean looking times are shown in Table 1. An analysis of variance (ANOVA) performed on the individual scores, with factors of organization (columns vs. rows), stimulus type (elements equated for contour vs. visual angle), age (3–4 months vs. 6–7 months), and trial block (1–3 vs. 4–6), revealed main effects of trial block, F(1, 56)  26.24, p  .001, and age, F(1, 56)  22.95, p  .001. These effects indicate that (a) both age groups habituated to the stimuli presented during familiarization and (b) the younger infants looked more to these stimuli than the older infants did.

The findings suggest that the 6- to 7-month-olds, but not the 3- to 4-month-olds, used form similarity to organize the visual pattern information. The 3- to 4-month-olds exhibited no preference of any kind, for either novelty or familiarity (Hunter & Ames, 1988), and hence failed to provide evidence of organization.

EXPERIMENT 2 The purpose of Experiment 2 was to provide evidence convergent with the outcome of Experiment 1. As is depicted in Figure 4, infants in the two age groups, 3- to 4-month-olds and 6- to 7-month-olds, were randomly assigned to one of two discrimination conditions. In the organized discrimination condition (top panel), infants were familiarized with one organized pattern (e.g., columns) and then given a preference test that paired this pattern and its 90 rotation (e.g., rows). In the unorganized discrimination condition (bottom panel), infants were familiarized with a random arrangement of elements and then tested with this pattern and its 90 rotation. The rotation manipulation resulted in a new global identity for the pattern only in the organized discrimination condition, so successful discrimination performance would be expected in this condition if grouping by form similarity was in operation.

Method

Preference-test trials Each infant’s looking time to the stimulus with the novel organization was divided by the looking time to both test stimuli and converted to a percentage score. The mean preference scores are shown in Table 1. An ANOVA on individual preference scores, with factors of organization, stimulus type, and age, yielded only an effect of age, F(1, 56)  6.18, p  .02, indicating that older infants displayed higher preference scores than younger infants. Comparisons of the mean preferences to the chance value of 50% revealed that only the 6- to 7-month-olds looked reliably longer to the novel than to the familiar organization.

Participants The participants were 64 infants, thirty-two 3- to 4-month-olds (16 females, 16 males) with a mean age of 102.12 days, SD  10.77 days, and thirty-two 6- to 7-month-olds (15 females, 17 males) with a mean age of 185.53 days, SD  6.10 days. Three additional 3- to 4-montholds were tested, but 1 failed to complete the procedure because of fussiness, and 2 were excluded from the data analysis because of experimenter error. Six additional 6- to 7-month-olds were tested, but 4 failed to complete the procedure because of fussiness, and 2 were not

Table 1. Mean fixation times (in seconds) during familiarization and mean preference scores (percentages) for novel organization during the preference test in Experiment 1 Fixation time

Familiar stimulus

First half of familiarization M

(SD)

Last half of familiarization M

(SD)

Columns Rows Combined

29.64 34.26 31.95

(10.08) (6.45) (8.64)

3- to 4-month-olds 25.95 (10.47) 30.33 (10.56) 28.14 (10.59)

Columns Rows Combined

21.96 23.13 22.53

(8.31) (7.95) (8.04)

6- to 7-month-olds 19.29 (7.65) 17.37 (7.38) 18.33 (7.44)

Novelty preference M

(SD)

46.28 50.29 48.28

(16.91) (14.25) (15.52)

58.80 56.36 57.58

(12.81) (14.43) (13.48)

ta 0.88 0.08 0.04 2.75*** 1.76* 3.18****

a t tests compared mean preference scores with chance performance. *p  .05, one-tailed. ***p  .01, one-tailed. ****p  .005, one-tailed.

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Development of Form Similarity

Fig. 4. Examples of the familiarization and test stimuli used to test for perceptual organization by form similarity in Experiment 2.

included in the data analysis because of position preference (n  1) and sibling interference (n  1).

Stimuli The stimuli used in the organized discrimination condition were the equal-contour and equal-angle row and column X and O patterns used during the familiarization trials of Experiment 1. Examples are shown in the top panel of Figure 4. Four stimuli were used in the unorganized discrimination task. Two were equal-contour and equal-visualangle versions of a random arrangement of X and O elements. The other two were equal-contour and equal-visual-angle versions of a 90 clockwise rotation of the random arrangement. Examples of these stimuli are presented in the bottom panel of Figure 4.

Procedure Half of the infants in each age group were randomly assigned to each of the two discrimination tasks. Each discrimination task consisted of six 15-s familiarization trials in which the infant was repeatedly presented with two identical copies of the same stimulus. Half the infants assigned to the organized discrimination task were familiarized with rows, and the other half with columns. Half the infants in the unorganized discrimination task were familiarized with the random arrangement of elements, and the other half with its 90 rotation. Infants in both tasks were given two 10-s preference-test trials that paired the familiar stimulus with its novel 90 rotation. The left-right positioning of the familiar and novel stimuli was counterbalanced on the first test trial and reversed on the second test trial. Half the infants in each age group were familiarized and tested with elements equated

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for amount of contour, and the other half with elements equated in terms of visual angle.

Results and Discussion Familiarization trials The mean looking times are shown in Table 2. A Discrimination Condition (organized vs. unorganized)  Trial Block  Stimulus Type  Age ANOVA, performed on the individual scores, revealed main effects of trial block, F(1, 56)  33.41, p  .001, and age, F(1, 56)  18.34, p  .001. As was the case in Experiment 1, infants habituated to the stimuli presented during familiarization, and younger infants looked more to these stimuli than older infants did.

Preference-test trials The mean novelty-preference scores are shown in Table 2. A Discrimination Condition  Stimulus Type  Age ANOVA did not yield any significant effects. However, when the preferences were compared with chance, only the older infants in the organized discrimination condition displayed a novelty-preference score that was reliably higher than 50%. The overall pattern of results provides convergent evidence with Experiment 1 and indicates that 6- to 7-month-olds, but not 3- to 4month-olds, can organize visual patterns in accord with form similarity.

EXPERIMENT 3 The purpose of Experiment 3 was to examine whether 3- to 4month-olds would organize visual pattern information according to the Gestalt principle of form similarity when provided with additional VOL. 13, NO. 4, JULY 2002

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Table 2. Mean fixation times (in seconds) during familiarization and mean preference scores (percentages) for the novel stimulus during the preference test in Experiment 2 Fixation time

Familiar stimulus Organized Unorganized Organized Unorganized

First half of familiarization M 35.37 37.29 27.69 27.51

(SD)

Last half of familiarization M

(SD)

Novelty preference ta

M

(SD)

(7.56) (6.87)

3- to 4-month-olds 30.63 (8.91) 31.59 (10.98)

49.15 47.38

(17.66) (9.56)

0.19 1.10

(8.07) (8.55)

6- to 7-month-olds 22.98 (8.22) 24.60 (7.44)

59.76 48.11

(16.86) (13.72)

2.32** 0.55

a t tests compared mean preference scores with chance performance. **p  .025, one-tailed.

familiarization time. Experiment 1 was thus repeated with 3- and 4month-olds, but in this case, with double the familiarization time. Half of the infants were administered six 30-s familiarization trials, and the other half were administered twelve 15-s familiarization trials.

twelve 15-s familiarization trials and the other half with six 30-s familiarization trials.

Results and Discussion Method

Familiarization trials

Participants The participants were thirty-two 3- to 4-month-olds (18 females, 14 males) with a mean age of 103.38 days, SD  5.24 days. Six additional infants were tested, but 4 failed to complete the procedure because of fussiness, and 2 were excluded from the data analysis because of position preference (n  1) and experimenter error (n  1).

Mean looking times are shown in Table 3. An Organization  Stimulus Type  Familiarization Condition (six 30-s trials vs. twelve 15-s trials)  Trial Block (first half vs. second half) ANOVA, performed on the individual scores, yielded only an effect of trial block, F(1, 24)  10.69, p  .003, indicating that the infants habituated to the stimuli presented during familiarization.

Stimuli Preference-test trials

The stimuli were the same as those used in Experiment 1.

Procedure Experiment 3 employed the same experimental design as Experiment 1, with the exception that half of the infants were presented with

Mean preference scores for the novel organization are shown in Table 3. An Organization  Stimulus Type  Familiarization Condition ANOVA revealed no significant effects. Comparisons of the mean preference scores with chance indicated that the infants did not reliably prefer the novel organization. Thus, even when 3- and 4-month-

Table 3. Mean fixation times (in seconds) during familiarization and mean preference scores (percentages) for novel organization during the preference test in Experiment 3 Fixation time

Familiar stimulus Columns Rows Combined a

First half of familiarization

Last half of familiarization

M

(SD)

M

(SD)

M

(SD)

ta

75.48 73.95 74.72

(15.80) (18.85) (17.13)

64.88 65.76 65.32

(22.78) (22.53) (22.29)

51.90 46.21 49.05

(19.43) (18.53) (18.90)

0.39 0.82 0.20

Novelty preference

t tests compared mean preference scores with chance performance.

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Development of Form Similarity olds were provided with additional familiarization time, there was still no evidence of perceptual organization achieved by form similarity.

EXPERIMENT 4 We conducted Experiment 4 to explore one potential explanation for why the 3- to 4-month-olds did not demonstrate the ability to organize visual pattern information in accord with form similarity in Experiments 1 through 3. It is possible that the performance of these young infants reflects an inability to discriminate between the X and O shapes. If the infants could not differentiate the shapes, then there would be no basis for grouping the elements into larger perceptual units (i.e., columns vs. rows). An additional objective for Experiment 4 was to determine if the 6- to 7-month-olds who had responded to the familiarization stimuli in Experiments 1 and 2 as if they had formed emergent perceptual units (i.e., columns vs. rows) also retained access to the individual shapes making up these units. Positive evidence for representation of individual-shape information would be consistent with the idea that infants remember both the global and the local levels of information contained in complex visual patterns. To examine the abilities of infants to differentiate the X and O shapes, we familiarized half of the infants with columns or rows of Xs and Os and then gave them a preference test in which the choice was between the familiar array and a novel array consisting entirely of Xs or Os. This novel array thus differed from the familiar array only in the shape of the X or O elements. The other half of the infants were familiarized with a pattern consisting entirely of X or O elements, and were then given a preference test pairing the familiar array with a pattern consisting of columns or rows of Xs and Os. For all the infants, a preference for the novel array would suggest that they had detected and processed the element information contained within the columns

or rows. Representative experimental sequences are presented in Figure 5.

Method Participants The participants were 64 infants, thirty-two 3- to 4-month-olds (16 females, 16 males) with a mean age of 111.12 days, SD  8.31 days, and thirty-two 6- to 7-month-olds (15 females, 17 males) with a mean age of 193.75 days, SD  7.56 days. Three additional 3- to 4-montholds were tested, but failed to complete the procedure because of fussiness. One additional 6- to 7-month-old was tested, but failed to complete the procedure because of fussiness.

Stimuli The stimuli included the column and row X and O patterns used in Experiments 1 through 3. In addition, an all-X pattern was used, as were two all-O patterns, one in which the diameter of individual Os was 1.27 cm (2.42), the equal-visual-angle case, and one in which the diameter of the individual Os was 1.00 cm (1.91), the equal-contour case.

Procedure Infants in each of the two age groups were given a discrimination task involving a heterogeneous pattern (either columns or rows) and a homogeneous pattern (either all Xs or all Os). Half of the infants were familiarized with a heterogeneous pattern and half with a homogeneous pattern. During the six 15-s familiarization trials, the infant was

Fig. 5. Examples of the familiarization and test stimuli used to test for discrimination of elements in Experiment 4.

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P.C. Quinn et al. repeatedly presented with two identical copies of the same stimulus. Immediately after familiarization, two 10-s test trials were administered; in the test trials, the familiar stimulus was presented with a novel stimulus. The left-right positioning of the familiar and novel stimuli was counterbalanced on the first test trial and reversed on the second test trial. Half of the infants were familiarized and tested with the equal-visual-angle stimuli, and the other half with the equal-contour stimuli.

Results and Discussion Familiarization trials The mean looking times are shown in Table 4. A Discrimination Condition (row vs. column)  Stimulus Type  Age  Trial Block ANOVA, performed on the individual scores, revealed main effects of trial block, F(1, 56)  36.08, p  .001, and age, F(1, 56)  26.17, p  .001. As was true in Experiments 1 and 2, infants habituated to the stimuli presented during familiarization, and younger infants looked more to these stimuli than older infants did.

Preference-test trials The mean novelty-preference scores are shown in Table 4. A Discrimination Condition  Stimulus Type  Age ANOVA did not yield any significant effects. When the preferences were compared with chance, the infants in both age groups and in both discrimination conditions displayed a novelty-preference score that was reliably higher than 50%. These results indicate that the failure of the 3- to 4-montholds in Experiments 1 through 3 to perform in accord with the formsimilarity principle was not due to an inability to discriminate between the constituent X and O shapes. The findings also indicate that the 6to 7-month-olds in Experiments 1 and 2 represented both global (i.e., columns or rows) and local (i.e., Xs and Os) components of these visual patterns.

GENERAL DISCUSSION Older infants (6- to 7-month-olds), but not younger infants (3- to 4month-olds), responded to the generalization task of Experiment 1 and the organized discrimination task of Experiment 2 by preferring the novel stimulus organization. The preferences indicate that 6- to 7month-olds, but not 3- to 4-month-olds, can organize visual patterns in accord with form similarity. The data from Experiments 3 and 4 indicate that the failure of 3- to 4-month-olds to organize visual patterns by form similarity is not the result of insufficient familiarization time or an inability to discriminate the individual X and O elements of the visual patterns. The findings from Experiment 4 suggest that 6- to 7month-olds retain information about the X and O elements, in addition to forming larger perceptual units (i.e., columns vs. rows), thereby suggesting that infants represent multiple levels of information when presented with complex visual patterns. In combination with the outcomes of Farroni et al. (2000) and Quinn et al. (1993) indicating that newborns and 3-month-olds can use lightness similarity to organize visual pattern information, the present findings indicating that only 6- to 7-month-olds can use form similarity are consistent with models of object perception which suggest that different Gestalt principles may become functional over different time courses of development. The outcomes are consistent, in particular, with the hypothesized age of onset for the edge-sensitive process (Kellman, 1996), and more generally with suggestions that adults have independent luminance- and edge-based grouping mechanisms (Gilchrist et al., 1997). The findings are also consistent with Spelke’s (1982) proposal that some Gestalt principles may be learned in a constructivist framework, rather than automatically deployed as originally conceived by the Gestaltists (e.g., Kohler, 1929). The present experiments emphasize bottom-up, configurally based contributions toward the establishment of perceptual coherence for complex, but abstract visual patterns. It is also important to recognize that object recognition in real-world contexts is likely to be assisted by top-down contributions, including physical knowledge of support and

Table 4. Mean fixation times (in seconds) during familiarization and mean preference scores (percentages) for the novel stimulus during the preference test in Experiment 4 Fixation time

Familiar stimulus

First half of familiarization

Last half of familiarization

M

M

(SD)

(SD)

Columns Rows Combined

33.54 36.66 35.10

(7.68) (5.72) (6.84)

3- to 4-month-olds 29.03 (10.67) 32.52 (7.68) 30.77 (9.31)

Columns Rows Combined

24.91 27.50 26.21

(5.93) (10.88) (8.69)

6- to 7-month-olds 20.87 (5.27) 21.24 (8.63) 21.05 (7.04)

Novelty preference M

(SD)

ta

61.40 64.49 62.95

(18.01) (11.54) (14.96)

2.53** 5.02***** 4.90*****

69.50 63.50 66.50

(17.52) (12.11) (15.12)

4.45***** 4.46***** 6.18*****

a t tests compared mean preference scores with chance performance. **p  .025, one-tailed. *****p  .0005, one-tailed.

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Development of Form Similarity solidity relations, and experiential knowledge of objects and object kinds (Needham, Baillargeon, & Kaufman, 1997). Models explaining how bottom-up configural information can be integrated with topdown physical and experiential knowledge to achieve coherent object representations will be needed for a full accounting of the early development of object perception (Quinn & Bhatt, 2001). The present findings contribute to the development of such models by demonstrating that different types of similarity grouping have different developmental trajectories. Acknowledgments—This research was supported by National Science Foundation Grants BCS-0096300 to P.C.Q. and SBR-9600724 (a CAREER award) to R.S.B. A portion of the work was presented at the July 2000 International Conference on Infant Studies, Brighton, England. We thank Carrie Banaszak, Kara Giron, Jaimee Heffner, Heather Wood, and Laurie Yarzab for their assistance in testing participants; Jason Parkhill and Jason Pergola from the Instructional Technology Center at Washington & Jefferson College for their assistance with the figures; and Amy Needham and Carolyn Rovee-Collier for their comments on an earlier version of the manuscript.

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