Modern theories of visual perception have treated PO as: A unitary phenomenon Operates at a single, early, preattentive stage In a bottom-up fashion Provides the substrate on which higher-level perceptual processes operate (e.g., Julesz, 1981; Marr, 1982; Neisser, 1967; Treisman, 1982, 1988).
PO: Not a monolithic entity but a multiplicity of processes (Behrmann & Kimchi, 2003; Kimchi, 2003) Time course (e.g., Han et al., 2002; Hadad & Kimchi, 2008; Kurylo, 1997; Kimchi, 1998, 2000; 2012; Razpurker-Apfeld & Kimchi, 2007) Developmental trajectory (e.g., Hadad & Kimchi, 2006; Hadad et al., 2010; Hayden et al., 2009; Kimchi, 2012; Kimchi et al., 2005; Kovacs, 2000; Scherf et al., 2009; Quinn & Bhatt, 2006) Multifaceted relationship with attention (e.g., Ben Av & Sagi, 1995; Freeman et al., 2001; Kimchi & Razpurker-Apfeld, 2004; Kimchi & Peterson, 2008; Kimchi et al., 2007; Moore et al., 2003; Russell & Driver, 2005; Shomstein et al., 2010 ) Influenced by experience and familiarity (e.g., Kimchi & Hadad, 2002; Peterson & Gibson, 1994; Vickery & Jiang, 2009; Zemel et al., 2002)
Ontogenesis of Perceptual Organization: Theoretical Approaches Gestalt (Koffka, 1935; Kohler, 1929; Wertheimer, 1923/1958): –most, if not all, of the basic organizational processes operate from birth. Hebb (1949): –perceptual organization is a learned process in which eye movements that are used to scan images generate the internal representation of objects. Contemporary (e.g., Baillargeon et al. 2009; Bhatt & Quinn, 2011; Johnson, 2009; Spelke, 1982): –A combination of innate and learning contributions.
Ontogenesis of Perceptual Organization Functional onset Rate of development The age at which ultimate functioning is attained
Infants Research: 3-month-olds are capable of grouping visual elements into unitary structures in accord with both classical and modern organizational principles: Common motion (Kellman et al., 1987; Kellman & Spelke, 1983; Kellman et al., 1986) Good continuation (Quinn & Bhatt, 2005a) Proximity (Quinn et al., 2008) Connectedness (Hayden et al., 2006) Common region (Bhatt et al., 2007) Lightness similarity (Quinn, et al., 1993) even newborns (Farroni et al., 2000), and 2-month-olds (Farran et al., 2008).
Sensitivity to global and local structures 3- to 4-month-olds sensitive to both structures, with a greater sensitivity to global (Freeseman, et al., 1993; Frick, et al., 2000; Ghim & Eimas, 1988; Quinn, et al., 1993; Quinn & Eimas, 1986) The ability to perceive the unity of partly occluded objects emerges at 2 months. Sensitivity to subjective contours 3- to 4 months. These completion abilities continue to develop during the first year of life (e.g., Craton, 1996; Csibra, 2001; Eizenman & Bertenthal, 1998; Ghim, 1990; Johnson & Aslin, 1995, 1996; Kavsek, 2002)
Some organizational principles have a later functional onset than other 3-month-olds are insensitive to closure (Gerhardstein et al, 2004) Grouping by form similarity only in 6- to 7- month-olds (Quinn & Bhatt, 2006)
6- to 7-month-olds, but not 3- to 4- month olds (Quinn et al. 2002) 3- to 4-month-olds can use form similarity to organize elements if they are provided with varied examples with which to abstract the invariant arrangement of the pattern (Quinn and Bhatt, 2005). Grouping by shape similarity
Studies beyond the 1-2 years: Protracted developmental trajectory for some perceptual organization abilities, even those that appear to emerge during infancy: Visual spatial integration (e.g., Hadad & Kimchi, 2006; Hadad et al., 2010; Kaldy & Kovacs, 2003; Kovacs, 2000; Kovacs et al., 1999) Subjective contours (e.g., Abravanel,1982; Hadad et al., 2010) Grouping multiple elements into a global shape (Burack et al., 2000; Enns et al., 2000; Kimchi et al., 2005; Mondloch et al., 2003; Scherf et al., 2009)
Although many perceptual organization abilities emerge early in life, organizational abilities vary in their rate of development and some reach the ultimate level of functioning only in late childhood or even in adolescence.
Two series of studies: Grouping and individuation of multiple elements in the organization of hierarchical stimuli Grouping of shape by perceptual closure
Infants studies: Greater sensitivity to global than to local structures (e.g., Ghim & Eimas, 1988). Sensitivity to the global structure in hierarchical visual stimuli continues to develop into late childhood (Burack et al., 2000; Enns et al., 2000; Harrison & Stiles, 2009; Porporino et al., 2004; Scherf et al., 2009). Longer developmental progression for processing local structure (Mondloch et al., 2003). Development of the Perceptual Organization of Hierarchical Stimuli
Performance of 5- 10- and 14-year-olds and young adults on few- and many- element hierarchical displays, was compared in two tasks: * Visual search * Speeded classification Development of the Perceptual Organization of Hierarchical Stimuli
Visual Search Task: search for a diamond target among square distractors. Display size: 2, 6, or 10. Dependent variables: Baseline RT (display size=2; measures response speed independent of search rate). Search rate - The slop of the RT function over display size. Kimchi et al., 2005
Baseline RT (Display Size = 2, Target-present Trials) RT improved with age. Global advantage in the many-element stimuli. No age related changes in target-distractor discriminability. Kimchi et al., 2005
Few-element: Search rates for global target improved with age; the efficient search for local target did not vary with age. Many-element: Search rates for local target improved with age; the efficient search for global target did not vary with age. Significant improvement between 5 to 10. RT Slopes (Target-present Trials) Kimchi et al., 2005
Classify the central stimuli with the stimuli to the right or left side: global classification: based on similarity in global configuration local classification: based on similarity in local elements Speeded Classification
Few-element: Accuracy of global classification improved with age; no age related changes for local classification. Many-element: Accuracy of local classification improved with age; no age related changes for global classification. Significant improvement between age 5 – 10.
Summary of Results Search rates for global targets and accuracy of global classification improved with age for the few-element patterns did not change with age for the many-element patterns. Search rates for local targets and accuracy of local classification improved with age for the many-element patterns no age-related changes for the few-element patterns. Improvement mainly for the transition from ages 5 to 10.
Longer developmental progression for grouping a few large elements than many small elements Longer developmental progression for individuating many small elements than few large elements.
How processing might change developmentally to produce this pattern of results? Individuating elements within many-element patterns requires attentional change (e.g., narrowing the spatial focus or refocusing on a different detail level). The ability to flexibly deploy attention improves with age (e.g., Enns & Girgus, 1985; Plude, Enns, & Brodeur, 1994). The organization of the individuated few large elements into a global configuration requires apprehending the spatial relations among them. spatial abilities improves with age (e.g., Stiles, 2001).
Enns et al. (2000) used few-element hierarchical stimuli, and therefore concluded that grouping develops with age. Mondloch et al. (2003) used many- element stimuli, and therefore concluded that local processing develops with age. Local TargetGlobal Target Congruent Incongruent
In contrast to the early maturation of grouping many small elements Scherf et al. (2009), using primed matching, showed age-related improvement in the ability to encode the global shape of the many-element patterns at the short prime durations, which continued through adolescence. Clear early advantage for encoding the global shape was observed only in adults; children were biased to encode the local elements, and adolescents began to demonstrate the beginning of early global advantage.
Different tasks may require different representations for successful performance, crude versus more refined, which depend on relatively rudimentary ability to group elements into a shape versus more mature ability, respectively.
A coarse representation of the global configuration may suffice to support performance in visual search and speeded classification tasks (Kimchi et al., 2005). Primed matching task (Scherf et al., 2009) requires a more precise, integrated representation of the global shape of the prime for facilitating responses to test figures similar to the prime in the global shape and/or interfering with responses to the test figures dissimilar in global shape to the prime.
Summary Children and adolescents are capable of grouping many small elements to a certain degree, which may support some global information and figural perception, but the full process of integrating local elements into coherent shapes to the extent of facilitating shape identification appears to develop late into adolescence. This long developmental trajectory coincides with what is known about the structural and functional development of the ventral visual pathway (Bachevalier, Hagger, & Mishkin, 1991; Gogtay et al., 2004).
The Role of Closure in Perceptual Organization The Gestalt psychologists noted that perceptual closure plays a crucial role in perceptual organization, in particular, in determining the shape of an object: “If a line forms a closed, or almost closed, figure, we see no longer merely a line on a homogeneous background, but a surface figure bounded by the line” (Koffka, 1935).
Several psychophysical studies with adults documented the role of closure in perceptual organization (e.g., Elder & Zucker, 1993, 1994, 1998, Hadad & Kimchi, 2008; Kimchi, 2000; Kovacs & Julesz, 1993; Saarinen & Levi, 1999). Greater contour detection sensitivity for closed fragmented contours than for open contours (Kovacs & Juleasz, 1993). Shape discrimination is more precise for closed contours than for non-closed contours (Saarinen & Levi, 1999). Search for a concave target among convex distractors is efficient for closed stimuli but inefficient for open stimuli (Elder & Zucker, 1993).
In natural scenes, closed connected contours often appear in the image as fragmented, due, for example, to occlusion. The perceptual system must group the image fragments and uncover the shape of the object
Research with adults: The efficiency of the grouping depends on The size of the gaps between the closure-inducing fragments (Elder & Zucker, 1993), and on The distribution of the gaps along the contour -- whether the gaps occur at points of change in contour direction or at straight contour segments (Kimchi, 2000; Spehar, 2002).
Adults utilize closure and its combination with collinearity and proximity to organize fragmented image contours into shapes. What is the developmental course of this ability?
Developmental Research 3-month-olds are able to rely on good continuation of contour elements, though their ability is far from adult-like, but they appear to be completely insensitive to closure (Gerhardstein, Kovacs, Ditre, & Feher, 2004). Kindergartners may be sensitive to closure (Enns & Girgus, 1985). We do not know of any study that directly examined the development of the ability to utilize closure for the perceptual grouping of shape in younger and older children.
Comparing the performance of 5- and 10-year-old children and young adults in a visual search task (similar to the one used by Elder and Zucker, 1993) Task: search for a concave target among convex distractors.
ConcaveConvex Basic Stimuli (similar to the ones used by Elder & Zucker, 1993 ): The line segments are the same for the concave and convex stimuli but their placement relative to each other differs, bending inward for the concave and outward for the convex. Therefore, the discrimination between the two stimuli requires grouping of the contour segments into coherent two-dimensional shapes.
Open vs. Closed Stimuli Task: search for a concave target among convex distractors. Display size: 2, 6, or 10. Dependent variables: Baseline RT (display size=2; measures response speed independent of search rate). Search rate - The slop of the RT function over display size.
Baseline RT (Display Size = 2, Target-present Trials ) RT improved with age. Faster RTs for closed than for open stimuli. Larger improvement with age for the open stimuli, indicating age- related change in target-distractor discriminability. Hadad & Kimchi, 2006
RT Slopes (Target-present trials) Closed stimuli: Equally efficient search for all age groups. Open Stimuli: Inefficient search. Significant improvement with age. Hadad & Kimchi, in press
Children, like adults, are able to derive the shape of a closed figure, while encountering difficulty when closure is absent. The age-related improvement for the open stimuli: improvement in spatial abilities Summary of Results
Noncollinear vs. Collinear Stimuli Noncollinear Collinear
Baseline RT (Display Size = 2, Target-present Trials) RT improved with age. Faster RTs for collinear stimuli than for noncollinear stimuli. No age related changes in target- distractor discriminability for the different stimuli. Hadad & Kimchi, 2006
RT Slopes (Target-present trials) Noncollinear: Efficient search for small gap and inefficient search for large gap for all age groups. Collinear: Efficient search for small gap for all age groups. Significant improvement from age 5 to 10 for large gap. Hadad & Kimchi, 2006
10-year-olds and adults: Spatial proximity between the closure- inducing line segments influenced grouping into a shape for the non-collinear stimuli, but not for the collinear stimuli 5-year-olds: Search depended critically on the spatial proximity between the closure-inducing line segments: efficient when the lines were close, inefficient when the lines were spatially distant, regardless of presence or absence of collinearity.
Young children can utilize closure as efficiently as adults for the perceptual grouping of shape for closed or nearly closed stimuli. When the closure-inducing fragments are spatially distant, older children and adults, but not 5-year-olds, can utilize collinearity to enhance closure for the perceptual grouping of shape. Summary of Results
The significant improvement in the ability to utilize collinearity for spatially distant fragments between age 5 and 10 suggests a longer developmental progression in the ability to employ long-range contour interpolation (see also, Kovacs, 2000, Kovacs et al., 1999). It has been suggested (Kovacs, 2000) that cortical connectivity in layers 2/3 of V1 that seem to be immature even at 5 years of age (Burkhalter, Bernardo, & Charles, 1993), on the one hand, and a delayed development of feedback connections between V1 and V2 (Burkhalter, 1993), on the other, may underlie the lower contour integration ability in young children.
Conclusions Organizational processes may vary in their developmental trajectory: Infant research: organizational principles vary in their functional onset some are functional as early as 3 to 4 months of age (e.g., common region, connectedness, good continuation, lightness similarity, and proximity others are not functional until 6 to 7 months of age (e.g., shape similarity).
Studies with older children: Some organizational processes mature relatively early: Individuation of a few large elements (Kimchi et al., 2005) Grouping spatially close fragments into a shape ( Hadad & Kimchi, 2006) Other organizational processes develop with age and reach adult-like levels only in late childhood Grouping multiple elements into a global shape (Kimchi et al., 2005, Scherf et al., 2009) Grouping spatially distant fragments by collinearity into a shape (Hadad & Kimchi, 2006)
Even processes that appear to emerge early in life may have a long developmental course: Infant are sensitive to the global configuration of hierarchical stimuli (e.g., Ghim & Eimas, 1988) The ability to group multiple elements into a global shape continues to develop, and adult-like performance is not observed before the age of 10. Infant are sensitive to good continuation (e.g., Quinn & Bhatt, 2005) The ability to group fragments by collinearity matures between ages 5 and 10.
Infants’ behavior reflects some rudimentary organization skills but these skills are not fully mature. Grouping involves two distinct processes: –unit formation or clustering determines which elements belong together and are segregated from other elements –shape formation or configuring determines how the grouped elements appear as a whole based on the interrelations of the elements (Kimchi & Razpurker-Apfeld, 2004; Koffka, 1935; Rock, 1986; Trick & Enns, 1997). Infants may show an early ability to determine what elements cluster together but are much less skilled at organizing such clusters into integrated, distinct shapes.
The developmental changes in perceptual organization abilities May depend on maturation of the visual system May be acquired through learning and experience May be a function of developmental improvements in other processes, such as flexibility of attention
Organizational abilities are present, at various levels of functioning, across the developmental course, and can support perceptual performance to a certain degree. Implies that different tasks may tap into different levels of the organizational abilities. Consequently, depending on the task, adult- like performance may be observed at different ages, sometimes leading to a wrong conclusion regarding the age at which the ability reaches ultimate, adult-like functioning.
Batsheva Hadad Suzy Scherf Marlene Behrmann Steve Palmer Allegra Dan Gilad Goldstein Israel Science Foundation (ISF) Israel-US Binational Foundation Max Wertheimer Minerva Center for Cognitive Processes and Human Performance