Concurrent anticipation of two object dimensions during grasping in 10-month-old infants: A quantitative analysis

The anticipation of more than one object dimension while grasping for objects has been rarely investigated in infancy. The few existing studies by Newell et al. and Schum et al. have revealed mixed results probably mainly due to methodological limitations. Therefore, the present experiments tested concurrent anticipatory grasping for two object dimensions, namely, object size and object orientation using a quantitative motion capture system (Vicon), in 10-month-old infants and adults. We presented objects varying in size (small vs. large) and orientation (horizontally vs. vertically) and analyzed participants’ anticipatory hand configurations. As with adults, we observed that infants rotated their wrists, thumbs, and index fingers as a function of object orientation and adjusted their maximum grip apertures and their grip apertures shortly before they touched the objects as a function of object size. Analyses on an individual level showed that infants like adults anticipated both dimensions when the maximal values of aperture and angle were used but not when the measures shortly before touch were considered. Thus, the ability to anticipate more than one object dimension can already be observed at 10 months of age but seems to improve considerably over the first year of life.     

Object Size as a Determinant of Grasping in Infancy

The early development and patterns of development of prehensile ability were examined. Infants 5, 7, and 9 months old were presented five objects, 0.5, 1.0, 3.5, 7.0, and 14.0 cm in diameter. The findings revealed that infants as young as 5 months old were able to differentiate grip configurations as a function of object size. The number of grasps involving the two or three most radial digits (thumb, index finger, and long finger) increased greatly over this age span. At 9 months of age these kinds of grasps were 10 times more frequent than at 5 months of age. However, at each age level, when only the two or three most radial digits were used, the reaches were typically directed at the two smallest objects. These findings suggest that it was not a perceptual problem that the younger infants were facing, nor was the problem knowing when to use different kinds of grasps; rather, the problem was one of cortico-motoneural connections, which are better established in older infants. The findings also suggest that traditionally described sequential development of infants' prehension is rigid and conservative. The discrepancy with earlier results may also be attributed to the difference in the objects' sizes and the way they were presented.     

Recognizing the role of perception in action at 6 months

The present research examined whether infants as young as 6 months of age would consider what objects a human agent could perceive when interpreting her actions on the objects. In two experiments, the infants took the agent's actions of repeatedly reaching for and grasping one of two possible objects as suggesting her preference for that object only when the agent could detect both objects, not when the agent's perceptual access to the second object was absent, either because a large screen hid the object from the agent ( Experiment 1 ), or because the agent sat with her back toward the object ( Experiment 2 ). These results suggest that young infants recognize the role of perception in constraining an agent's goal‐actions.     

The stability of precision grip force in older adults

The exceedingly large grip forces that many older adults employ when lifting objects with a precision pinch grip (Cole, 1991) may compensate for a reduced capability to produce a stable isometric force. That is, their grip force may fluctuate enough from moment to moment to yield grip forces that approach the force at which the object would slip from grasp. We examined the within-trial variability of isometric force in old (68-85 years, n = 13) and young (n = 11) human subjects (a) when they were asked to produce a constant pinch force at three target levels (0.49, 2.25, and 10.5 N) with external support of the arm, hand, and force transducer and (b) when they were asked to grasp, lift, and hold a small test object with a precision grip. Pinch force produced in the first task was equally stable across the two subject groups during analysis intervals that lasted 4 s. The elderly subjects produced grip forces when lifting objects that averaged twice as much as those produced by the young subjects. The force variability during the static (hold) phase of the lift for the old subjects was comparable with that used by the young subjects, after adjusting for the difference in grip force. The failure to observe less stable grip force in older adults contradicts a similar recent study. Differences in task (isometric grip force versus isometric abduction torque of a single digit) may account for this conflict, however. Thumb and finger forces for grip are produced through coactivation of many muscles and thus promote smooth force output through temporal summation of twitches. We conclude that peripheral reorganization of muscle in older adults does not yield increased instability of precision grip force and therefore does not contribute directly to increased grip forces in this population. However, force instability may affect other grip configurations (e.g., lateral pinch) or manipulation involving digit abduction or adduction forces.     

Reasoning about a hidden object after a delay: evidence for robust representations in 5-month-old infants

The present research examined two alternative interpretations of violation-of-expectation findings that young infants can represent hidden objects. One interpretation is that, when watching an event in which an object becomes hidden behind another object, infants form a prediction about the event's outcome while both objects are still visible, and then check whether this prediction was accurate. The other interpretation is that infants' initial representations of hidden objects are weak and short-lived and as such sufficient for success in most violation-of-expectation tasks (as objects are typically hidden for only a few seconds at a time), but not more challenging tasks. Five-month-old infants succeeded in reasoning about the interaction of a visible and a hidden object even though (1) the two objects were never simultaneously visible, and (2) a 3- or 4-min delay preceded the test trials. These results provide evidence for robust representations of hidden objects in young infants.     

Body-scaled transitions in human grip configurations

This article reports two experiments that were set up to examine the preferred human grip configuration used to displace cubes that varied in length (Lc), mass (Mc), and density (ML3). In particular, the authors sought to provide a more precise test of a dimensional relation between the object and the hand that had previously been shown to predict the grip configuration used to transport an object from one location to another. The experiments examined 2 grip transitions (from 3 digits to 4 digits and from 1 hand to 2 hands) within 2 sets of object conditions. In Experiment 1, cubes with a low density and a small increment in size (1 mm) were used, whereas in Experiment 2, cubes with 2 fixed sizes and small increments in mass were used. The results showed that the body-scaled equation K = logLc + (logMc/a + bMh + cLh), where Mh and Lh are the anthropometric measures of the hand mass and length and a, b, and c are empirical constants, is the body-scaled information that predicts the grip configurations used to displace objects.     

Three-month-old infants attribute goals to a non-human agent

The present research examined whether 3-month-old infants, the youngest found so far to engage in goal-related reasoning about human agents, would also act as if they attribute goals to a novel non-human agent, a self-propelled box. In two experiments, the infants seemed to have interpreted the box’s actions as goal-directed after seeing the box approach object A as opposed to object B during familiarization. They thus acted as though they expected the box to maintain this goal and responded with increased attention when the box approached object B during test. In contrast, when object B was absent during familiarization and introduced afterwards, the infants’ responses were consistent with their having recognized that they had no information to predict which of the two objects the box should choose during test and therefore responded similarly when the box approached either object. However, if object B was absent during familiarization and object A was in different positions but the box persistently approached it, thus demonstrating equifinal variations in its actions, the infants again acted as though they attributed to the box a goal directed towards object A and expected the box to maintain this goal even when object B was introduced and hence responded with prolonged looking when the box failed to do so during test. These results are consistent with the notion that (a) infants as young as 3 months appear to attribute goals to both human and non-human agents, and (b) even young infants can use certain behavioral cues, e.g. equifinal variations in agents’ actions, to make inferences about agents’ goals.     

Functional coupling between the limbs during bimanual reach-to-grasp movements

While it is frequently advantageous to be able to use our hands independently, many actions demand that we use our hands co-operatively. In this paper we present two experiments that examine functional binding between the limbs during the execution of bimanual reach-to-grasp movements. The first experiment examines the effect of gaze direction on unimanual and bimanual reaches. Even when subjects' eye movements are restricted during bimanual reaches so that they may only foveate one target object, the limbs remain tightly synchronized to a common movement duration. In contrast, grip aperture is independently scaled to the size of the target for each hand. The second experiment demonstrates however, that the independent scaling of grip aperture is task dependent. If the two target objects are unified so that they appear to be part of a single object, grip apertures become more similar across the hands (i.e., grip aperture to the large target object is reduced in size while peak aperture to the small target item is increased in size). These results suggest that the coupling of the limbs can operate at a functional level.     

Visual context modulates potentiation of grasp types during semantic object categorization

Substantial evidence suggests that conceptual processing of manipulable objects is associated with potentiation of action. Such data have been viewed as evidence that objects are recognized via access to action features. Many objects, however, are associated with multiple actions. For example, a kitchen timer may be clenched with a power grip to move it but pinched with a precision grip to use it. The present study tested the hypothesis that action evocation during conceptual object processing is responsive to the visual scene in which objects are presented. Twenty-five healthy adults were asked to categorize object pictures presented in different naturalistic visual contexts that evoke either move- or use-related actions. Categorization judgments (natural vs. artifact) were performed by executing a move- or use-related action (clench vs. pinch) on a response device, and response times were assessed as a function of contextual congruence. Although the actions performed were irrelevant to the categorization judgment, responses were significantly faster when actions were compatible with the visual context. This compatibility effect was largely driven by faster pinch responses when objects were presented in use-compatible, as compared with move-compatible, contexts. The present study is the first to highlight the influence of visual scene on stimulus–response compatibility effects during semantic object processing. These data support the hypothesis that action evocation during conceptual object processing is biased toward context-relevant actions.     

Young infants' reasoning about hidden objects: evidence from violation-of-expectation tasks with test trials only

The present research examined alternative accounts of prior violation-of-expectation (VOE) reports that young infants can represent and reason about hidden objects. According to these accounts, young infants' apparent success in these VOE tasks reflects only novelty and familiarity preferences induced by the habituation or familiarization trials in the tasks. In two experiments, 4-month-old infants were tested in VOE tasks with test trials only. The infants still gave evidence that they could represent and reason about hidden objects: they were surprised, as indicated by greater attention, when a wide object became fully hidden behind a narrow occluder (Experiment 1) or inside a narrow container (Experiment 2). These and control results demonstrate that young infants can succeed at VOE tasks involving hidden objects even when given no habituation or familiarization trials. The present research thus provides additional support for the conclusion that young infants possess expectations about hidden objects. Methodological issues concerning the use of habituation or familiarization trials in VOE tasks are also discussed.     

Will any doll do? 12-month-olds' reasoning about goal objects

Infants as young as 5 months of age view familiar actions such as reaching as goal-directed (Woodward, 1998), but how do they construe the goal of an actor's reach? Six experiments investigated whether 12-month-old infants represent reaching actions as directed to a particular individual object, to a narrowly defined object category (e.g., an orange dump truck), or to a more broadly defined object category (e.g., any truck, vehicle, artifact, or inanimate object). The experiments provide evidence that infants are predisposed to represent reaching actions as directed to categories of objects at least as broad as the basic level, both when the objects represent artifacts (trucks) and when they represent people (dolls). Infants do not use either narrower category information or spatiotemporal information to specify goal objects. Because spatiotemporal information is central to infants' representations of inanimate object motions and interactions, the findings are discussed in relation to the development of object knowledge and action representations.     

General processes, rather than "goals," explain imitation errors

The goal-directed theory of imitation (GOADI) states that copying of action outcomes (e.g., turning a light switch) takes priority over imitation of the means by which those outcomes are achieved (e.g., choice of effector or grip). The object < effector < grip error pattern in the pen-and-cups task provides strong support for GOADI. Experiment 1 replicated this effect using video stimuli. Experiment 2 showed that shifting the color cue from objects to effectors makes imitation of effector selection more accurate than imitation of object and grip selection. Experiment 3 replicated this result when participants were required to describe actions. Experiment 4 indicated that, when participants are imitating and describing actions, enhancing grip discriminability makes grip selection the most accurately executed component of the task. Consistent with theories that hypothesize that imitation relies on task-general mechanisms (e.g., the associative sequence learning model, ideomotor theory), these findings suggest that imitation is no more or less goal directed than other tasks involving action observation.     

Four‐month‐old infants individuate and track simple tools following functional demonstrations

Two experiments examined whether 4‐month‐olds (n = 120) who were induced to assign two objects to different categories would then be able to take advantage of these contrastive categorical encodings to individuate and track the objects. In each experiment, infants first watched functional demonstrations of two tools, a masher and tongs (Experiment 1) or a marker and a knife (Experiment 2). Next, half the infants saw the two tools brought out alternately from behind a screen, which was then lowered to reveal only one of the tools (different‐objects condition); the other infants saw similar events except that the same tool was shown on either side of the screen (same‐object condition). In both experiments, infants in the different‐objects condition looked reliably longer than those in the same‐object condition, and this effect was eliminated if the demonstrations involved similar but non‐functional actions. Together, these results indicate that infants (a) were led by the functional demonstrations they observed to assign the two tools to distinct categories, (b) recruited these categorical encodings to individuate and track the tools, and hence (c) detected a violation in the different‐objects condition when the screen was lowered to reveal only one tool. Categorical information thus plays a privileged role in individuation and identity tracking from a very young age.     

Norms for grip agreement for 296 photographs of objects

An increasing number of studies are investigating the cognitive processes underlying human–object interactions. For instance, several researchers have manipulated the type of grip associated with objects in order to study the role of the objects’ motor affordances in cognition. The objective of the present study was to develop norms for the types of grip employed when grasping and using objects, with a set of 296 photographs of objects. On the basis of these ratings, we computed measures of agreement to evaluate the extent to which participants agreed about the grip used to interact with these objects. We also collected ratings on the dissimilarity between the grips employed for grasping and for using objects, as well as the number of actions that can typically be performed with the objects. Our results showed grip agreements of 67 % for grasping and of 65 % for using objects. Moreover, our pattern of correlations is highly consistent with the idea that the grips for grasping and using objects represent two different motor dimensions of the objects.     

The role of person and object in eliciting early imitation

The role of person and object in eliciting early imitation was examined in this study. Twenty-seven infants, between 5 and 8 weeks old were assigned randomly to two conditions. In the person condition (N = 12) they were presented with tongue protrusions and mouth openings modeled by an adult, whereas in the object condition (N = 15) they were presented with these gestures simulated by two objects. Two infant behaviors were coded; mouth openings and tongue protrusions. Infants in the person condition selectively reproduced the mouth open and tongue protrusion gestures at significant levels, infants in the object condition did not. Instead of reproducing the congruent gestures (mouth openings and tongue protrusions when they were modeled) infants in the object condition reproduced the incongruent gestures at significant levels. Together, the findings indicate that imitation is a social response, which has implications for the development of nonverbal communication and speech.     

Infant object segregation implies information integration

Researchers, including Needham (2001, this issue), have found that infants as young as 4.5 months of age have the ability to use featural information to segregate objects. However, considerable research on infants' perception of color, shape, size, orientation, and so on has shown that infants younger than 4.5 months are capable of using these featural cues to discriminate between objects or other test items. Infants as young as 2 months of age also can perceive a moving object as unified. In this article, we argue for an information processing explanation of these results, which centers on the development of infants' ability to integrate both featural and object information. The proposed explanation is based upon L. B. Cohen's (1991, 1998) information processing propositions and is consistent with the evidence on object segregation as well as evidence from our laboratory and others' on infant perception and cognition.     

The Sound of Grasp Affordances: Influence of Grasp‐Related Size of Categorized Objects on Vocalization

Previous research shows that simultaneously executed grasp and vocalization responses are faster when the precision grip is performed with the vowel [i] and the power grip is performed with the vowel [ɑ]. Research also shows that observing an object that is graspable with a precision or power grip can activate the grip congruent with the object. Given the connection between vowel articulation and grasping, this study explores whether grasp‐related size of observed objects can influence not only grasp responses but also vowel pronunciation. The participants had to categorize small and large objects into natural and manufactured categories by pronouncing the vowel [i] or [ɑ]. As predicted, [i] was produced faster when the object's grasp‐related size was congruent with the precision grip while [ɑ] was produced faster when the size was congruent with the power grip (Experiment 1). The effect was not, however, observed when the participants were presented with large objects that are not typically grasped by the power grip (Experiment 2). This study demonstrates that vowel production is systematically influenced by grasp‐related size of a viewed object, supporting the account that sensory‐motor processes related to grasp planning and representing grasp‐related properties of viewed objects interact with articulation processes. The paper discusses these findings in the context of size–sound symbolism, suggesting that mechanisms that transform size‐grasp affordances into corresponding grasp‐ and articulation‐related motor programs might provide a neural basis for size‐sound phenomena that links small objects with closed‐front vowels and large objects with open‐back vowels.     

The emergence of kind-based object individuation in infancy

Four experiments investigated whether 12-month-old infants use perceptual property information in a complex object individuation task, using the violation-of-expectancy looking time method (Xu, 2002; Xu & Carey, 1996). Infants were shown two objects with different properties emerge and return behind an occluder, one at a time. The occluder was then removed, revealing either two objects (expected outcome, if property differences support individuation) or one object (unexpected outcome). In Experiments 1-3, infants failed to use color, size, or a combination of color, size, and pattern differences to establish a representation of two distinct objects behind an occluder. In Experiment 4, infants succeeded in using cross-basic-level-kind shape differences to establish a representation of two objects but failed to do so using within-basic-level-kind shape differences. Control conditions found that the methods were sensitive. Infants succeeded when provided unambiguous spatiotemporal information for two objects, and they encoded the property differences during these experiments. These findings suggest that by 12 months, different properties play different roles in a complex object individuation task. Certain salient shape differences enter into the computation of numerical distinctness of objects before other property differences such as color or size. Since shape differences are often correlated with object kind differences, these results converge with others in the literature that suggest that by the end of the first year of life, infants' representational systems begin to distinguish kinds and properties.     

Object individuation and labelling in 6-month-old infants

The ability to determine how many objects are involved in physical events is fundamental for reasoning about the world that surrounds us. Previous studies suggest that infants can fail to individuate objects in ambiguous occlusion events until their first birthday and that learning words for the objects may play a crucial role in the development of this ability. The present eye-tracking study tested whether the classical object individuation experiments underestimate young infants’ ability to individuate objects and the role word learning plays in this process. Three groups of 6-month-old infants (N = 72) saw two opaque boxes side by side on the eye-tracker screen so that the content of the boxes was not visible. During a familiarization phase, two visually identical objects emerged sequentially from one box and two visually different objects from the other box. For one group of infants the familiarization was silent (Visual Only condition). For a second group of infants the objects were accompanied with nonsense words so that objects’ shape and linguistic labels indicated the same number of objects in the two boxes (Visual & Language condition). For the third group of infants, objects’ shape and linguistic labels were in conflict (Visual vs. Language condition). Following the familiarization, it was revealed that both boxes contained the same number of objects (e.g. one or two). In the Visual Only condition, infants looked longer to the box with incorrect number of objects at test, showing that they could individuate objects using visual cues alone. In the Visual & Language condition infants showed the same looking pattern. However, in the Visual vs Language condition infants looked longer to the box with incorrect number of objects according to linguistic labels. The results show that infants can individuate objects in a complex object individuation paradigm considerably earlier than previously thought and that linguistic cues enforce their own preference in object individuation. The results are consistent with the idea that when language and visual information are in conflict, language can exert an influence on how young infants reason about the visual world.     

Linguistic and cognitive abilities in infancy: when does language become a tool for categorization?

Infants' ability to form new object categories based on either visual or naming information alone was evaluated at two different ages (16 and 20 months) using an object manipulation task. Estimates of productive vocabulary size were also collected. Infants at both ages showed evidence of using visual information to categorize the objects, while only the older ones used naming information. Moreover, there was a correlation between vocabulary size and name-based categorization among the 20-month-olds. The present results establish that infants as young as 20 months can use the non-obvious cue of naming to categorize objects. The possibility of a link between this ability and lexical development is discussed.