Development and initial validation of the Preschool Imitation and Praxis Scale (PIPS)

Abstract

The goal of this study was to develop and subsequently evaluate the internal construct and criterion-related validity of the Preschool Imitation and Praxis Scale (PIPS). Different task characteristics were selected considered to be important as unravelled in research in apraxic adults to tap a broad range of possible imitation mechanisms. Participants included 498 children without disabilities (1–4.9 years) and 47 children with autism spectrum disorders (ASD) (1.9–4.5 years). Exploratory factor analysis disclosed 4 dimensions in the scale, labelled: goal directed versus non-goal directed procedural imitation and single versus sequential bodily imitation. Internal consistency for the PIPS scale (α = .97) and subscales was high (α ranged from .79 to .96). In both samples, the PIPS scale score was strongly related to age (r = .78, respectively r = .56). Significant relationships between the PIPS score and mental, language, motor ages in the ASD sample supported criterion-related validity (r ranged from .59 to .74). The PIPS appears to have fundamentally sound psychometric characteristics, although more research is needed.

Introduction

Imitation is the capacity of an individual to replicate an observed behaviour. It involves the ability to transform perceptual information into a motor copy of it (Prinz, 2002). A more restrictive description of ‘true’ imitation requires that a novel action is learned by observing someone else performing it, and in addition to novelty, it requires a means/ends structure (Tomasello, Carpenter, Call, Behne, & Moll, 2005).

In young children, imitation is central to learn social behaviour and skilled acts or praxis (Masur, 2006). Imitation avoids time-consuming trial-and-error learning. In reproducing the exact and detailed features of the demonstrator's actions, children are likely to successfully complete the intended actions, even with a limited understanding of their purpose. Moreover, faithful copying can be used to disentangle the goal of an action to be imitated when it is not completely clear to the observer or to learn about initially opaque aspects of causality (Lyons, Young, & Keil, 2007).

Accumulating evidence from behavioural studies in typically developing children suggests that imitation is not a one-dimensional, but a polymorphous phenomenon. Imitation can have many forms depending on distinct action types. Neonates imitate facial movements, in particular tongue protrusion, and simple gestures (Meltzoff & Moore, 1977). Infants become capable of imitating meaningful communicative gestures by the age of 10 months (Masur, 2006). Procedural imitation, the copying of novel acts on objects, is seen from the age of 6 months (Barr, Dowden, & Hayne, 1996). Infants from the age of 9 months imitate parts of action sequences on objects (Elsner, Hauf, & Aschersleben, 2007). From the age of 1 year they imitate familiar and novel two- and three-act sequences on objects (Bauer & Mandler, 1992). Ten-month-olds imitate acts with an appropriate object, e.g., drinking from a cup (Užgiris, 1981). From the age of 14 months, children imitate novel and seemingly irrational acts with objects, substituted acts such as touching a box with the head instead of the hands to switch on a light (Meltzoff, 1988). From the age of 22 months, children imitate acts with a socially inappropriate or substituted object, e.g., drinking from a car (Užgiris, 1981).

In developmental, cognitive and social psychology research, imitation is seen as a window into the sensorimotor, cognitive and social abilities of young children, including those with atypical development, in particular children with autism spectrum disorders (ASD) (Rogers & Williams, 2006). In a comprehensive review Williams, Whiten, and Singh (2004) pooled the findings from well-controlled case–control studies, involving 196 individuals with ASD. They calculated the combined p-value of group differences with respect to imitation problems to an appropriate control group, resulting in a p-value of .00002. The size of the imitative problem was most apparent in younger age groups (Williams, Whiten, & Singh, 2004). However, a clear picture of imitative abilities in children with ASD is confounded by the heterogeneity of the clinical phenotype (Levy, Mandell, & Schultz, 2009), the lack of a consistent and operational definition of imitation, the wide variability across the types of imitation tasks and the absence of a comprehensive standardized imitation battery for children (Sevlever & Gillis, 2010). Such a measure should include familiar and unfamiliar tasks, tasks with and without objects, goal-directed and non-goal-directed tasks, tasks requiring tool use, and facial and gestural imitation tasks (Sevlever & Gillis, 2010).

There are currently four published measures (Ayres, 1989, Bergès and Lézine, 1963, Korkman et al., 1997, Užgiris and Hunt, 1987) that are frequently used in clinical settings to assess imitation abilities in young disabled children. Although these measures rely on a theoretical framework and prove consistency of the scores, they consider imitation as a one-dimensional construct and are limited to bodily imitation (Ayres, 1989, Bergès and Lézine, 1963, Korkman et al., 1997) or their construct validity regarding distinct domains of imitation was never investigated (Užgiris & Hunt, 1987). Therefore, the purpose of this study was to develop the Preschool Imitation and Praxis Scale (PIPS) designated to be a reliable and valid multidimensional instrument to measure the accuracy of imitation performance of preschool children.

The multifaceted components of imitation are supported by clinical and empirical accounts of brain lesion studies in adults that have been reported over the last century. Neuropsychologists went on investigating different action types (e.g., meaningful and non-meaningful, transitive and intransitive, opaque and transparent, uni- and bimanual) to unravel the existence of putative mechanisms involved in imitation problems and apraxia (Petreska, Adriani, Blanke, & Billard, 2007).

A prominent model of imitation and the assumed neural underpinnings addressing this issue rely on current cognitive neuroscience and brain imaging studies in healthy and apraxic adults. Based on a series of studies conducted in the laboratory, Rumiati and colleagues tested the “dual route hypothesis of imitation”, according to which imitation is not accomplished by a unique operation but by two different mechanisms (Carmo and Rumiati, 2009, Rumiati and Tessari, 2002, Rumiati et al., 2005, Tessari et al., 2007, Tessari and Rumiati, 2004;). The study with healthy adults revealed that speeded imitation was significantly more accurate for meaningful (e.g., hammering) than for non-meaningful gestures (e.g., by modifying the relationship between the hand-arm and the trunk of the hammering action) when they were presented in separate lists, suggesting that two different routes were used. When the two types of gestures were presented intermingled, the advantage of meaningful over non-meaningful imitation disappeared, suggesting that participants selected the same route for imitating both stimulus types (Tessari & Rumiati, 2004). Similar behavioural patterns were observed in unilateral brain-damaged patients (Tessari et al., 2007). Hence, the group of Rumiati assumed the existence of two distinctive routes of imitation regarding the representational content of the gestures and two differential neural mechanisms. The first is the imitation of non-meaningful and/or novel unfamiliar gestures of which the goal can only be identified retrospectively. This imitative performance can only take a direct route, bypassing long-term memory and transforming visuospatial characteristics directly into motor representations. Results of PET-studies in healthy (Rumiati et al., 2005) and apraxic adults (Tessari et al., 2007) revealed that this direct imitation mechanism involves visuospatial transformation processes by activation of areas belonging to the dorsal stream. The second is the imitation of meaningful and/or familiar, and/or well-trained gestures for which the observer can identify a meaning or a goal and possesses a template in the long-term memory. This indirect imitation mechanism involves semantic processing by activation of areas belonging to the ventral stream (Rumiati et al., 2005, Tessari et al., 2007). Recently, these researchers found that imitation performance among healthy adults engaged in a speeded imitation task was significantly poorer when meaningful gestures involved objects (e.g., hammering with an imaginary hammer), rather than no objects (e.g., waving good-bye), suggesting that the use of objects increases processing demands (Carmo & Rumiati, 2009).

Based on a deductive test construction approach, we selected action types for the Preschool Imitation and Praxis Scale (PIPS) considered to be important on the basis of the above mentioned theoretical ground of the dual-route theory of imitation (Carmo and Rumiati, 2009, Rumiati and Tessari, 2002, Rumiati et al., 2005, Tessari et al., 2007, Tessari and Rumiati, 2004) and the influence of action types as unravelled in research in apraxic adults (Petreska et al., 2007).

First, we have selected action types with different effects. The effect of bodily imitation (i.e., of actions without objects, either gestural or facial) is by definition internal. The child observes hand postures and facial expressions and must generate a matching posture or facial expression. In contrast, the effect of procedural imitation (i.e., of actions with objects) is by definition external. It causes salient effects and environmental changes.

Second, we have selected action types with different representational levels: meaningful and non-meaningful bodily imitation tasks, goal directed and non-goal directed procedural imitation tasks. Copying a meaningful or goal-directed action involves a proper discrimination of the features of the action, the comprehension of the meaning of the action and the linkage to previous knowledge about the result of the perceived action. If the child understands the meaning of an action, the action is probably familiar to the child. Previous experience with the action to be imitated can contribute to the imitation performance. Meaningful gestures, transitive as well as intransitive, are symbolic. Transitive gestures with an imaginary object (e.g., to pretend to comb your hair with an imaginary comb) demonstrate a certain level of symbolisation and knowledge of the object and tool use. Although an imaginary object is used, transitive gestures are goal directed. Intransitive gestures without an imaginary object are communicative gestures (e.g., to wave good-bye). In contrast to meaningful and goal-directed actions, children are not acquainted with non-meaningful and non-goal-directed actions, which rely on perceptual motor processes of accurate discrimination and duplication of the features of the action. By definition, non-meaningful and non-goal-directed actions are always novel and unknown.

Third, we have selected action types with different temporal complexities: single and sequential. Sequences demand a temporal organisation of familiar or unfamiliar acts.

Finally, we have selected action types with different visual monitoring possibilities. When the child imitates perceptually transparent gestures and hand postures, the child can see his/her own hands and can use visual monitoring to achieve the match, even though his/her visual perspective on the own and the demonstrator's hands is different. When the child copies facial expressions and opaque gestures and hand postures, the child observes the examiner's but not his/her own face and hands. It is plausible that facial and opaque gestural imitations are founded on cross-modal guidance.

Combinations of these action characteristics resulted in ten task categories of the PIPS: six gestural, three procedural and one facial (Table 1). The six task categories of gestural imitation are: meaningful intransitive gestures (i-MG; e.g., communicative gestures such as ‘perform the gesture to wave good-bye’); meaningful goal directed transitive gestures (t-MG; e.g., ‘pretend to comb your hair with an imaginary comb’); non-meaningful single hand postures (si-NMG; e.g., ‘raise your outstretched arm till 90° anteflexion and make a fist’); non-meaningful bimanual hand postures (bi-NMG; e.g., ‘place one fist on top of the other’); non-meaningful hand postures to the face and head (fa-NMG; e.g., ‘touch the top of your nose with the extended index finger’); non-meaningful sequences of hand postures (sq-NMG; e.g., ‘hit the table with the palm of your hands, cross the arms and hit the table again, return to the original position and hit the table once more’). The three task categories of procedural imitation are: goal directed substituted actions upon objects (sao-P; e.g., ‘raise a toy bear by pulling a cord’), goal directed actions upon substituted objects (aso-P; e.g., ‘turn a cup upside-down and play drums on it with two spoons’) and non-goal directed action sequences upon objects (sq-P; e.g., ‘open a box, put the lid on the table, turn the box upside-down, put a block on the bottom of the box’). There is one facial imitation category (f; e.g., ‘shake the head, eyes closed to say “no” with an expression of disapproval’). Facial expressions have a communicative meaning.

For each task category, we have selected 4 imitation tasks, which are possible to be performed by young children, but unlikely to be exhibited spontaneously (see appendix for details of the 40 PIPS items).