Evidence for motor planning in monkeys: rhesus macaques select efficient grips when transporting spoons

McCarty and colleagues (1999) developed the elevated spoon task to measure motor planning in human infants. In this task, a spoon containing food was placed on an elevated apparatus that supported both ends of the spoon. The handle was oriented to the left or right on different trials. We presented naïve adult rhesus monkeys (Macaca mulatta) with the elevated spoon problem, and observed how monkeys learned the affordances of spoons over sessions. Strikingly, monkeys developed two different strategies for efficient spoon transport in just 12 to 36 trials. In subsequent testing with a novel double bowl spoon approximately 1 year later, monkeys demonstrated that they were attending to the baited spoon bowl and continued to select efficient grips for transporting the spoon. Monkey data were contrasted with previous studies in human infants using a perception‐action perspective in an effort to understand the fundamentals of tool use and motor planning that may be common in the development of these abilities across species and their origins in human behavior.     

Learning about tools in infancy

These experiments explored the role of prior experience in 12- to 18-month-old infants' tool-directed actions. In Experiment 1, infants' use of a familiar tool (spoon) to accomplish a novel task (turning on lights inside a box) was examined. Infants tended to grasp the spoon by its handle even when doing so made solving the task impossible (the bowl did not fit through the hole in the box, but the handle did) and even though the experimenter demonstrated a bowl-grasp. In contrast, infants used a novel tool flexibly and grasped both sides equally often. In Experiment 2, infants received training using the novel tool for a particular function; 3 groups of infants were trained to use the tool differently. Later, infants' performance was facilitated on tasks that required infants to grasp the part of the tool they were trained to grasp. The results suggest that (a) infants' prior experiences with tools are important to understanding subsequent tool use, and (b) rather than learning about tool function (e.g., hammering), infants learn about which part of the tool is meant to be held, at least early in their exposure to a novel tool.     

Limits of end-state planning

The end-state comfort effect is the tendency to use an uncomfortable initial grasp posture for object manipulation if this leads to a comfortable final posture. Many studies have replicated the end-state comfort effect across a range of tasks and conditions. However, these tasks had in common that they involved relatively simple movements, such as picking up a dowel or sliding a pan from one place to another. Here we asked whether the end-state comfort effect extends to more complex tasks. We asked participants to grasp a transparent bowl and move the bowl to an instructed location, positioning it in an instructed orientation. We either found an initial-state comfort effect or equal degrees of comfort for end-grasps and start-grasps depending on task instructions. The end-state comfort effect was not consistently observed. The results suggest that the end-state comfort effect may be restricted to relatively simple grasping movements.     

Facilitating Problem-Solving Performance Among 9- and 12-Month-Old Infants

The efficiency of infants' actions was observed as they picked up and used food-laden spoons that varied in orientation. Two interventions were designed to facilitate efficient action beyond when infants were presented with one spoon in alternating orientations: one spoon was presented in the same orientation for several consecutive trials to help the child use feedback from the previous trial, and two spoons were presented in different orientations to emphasize the effect of the spoon's orientation on performance. These interventions were given separately, and combined, to groups of 9- and 12-month-old infants. Performance was facilitated among 12-month-olds when one spoon was presented several times in the same orientation. The short-term facilitation of performance was limited both by developmental factors and by the type of intervention introduced.     

Sucking patterns are not predictive of further feeding development in healthy preterm infants

Preterm infants are at risk of experiencing difficulties in their feeding development. For a possible early identification of these, we examined the association between sucking patterns, assisted spoon feeding, and chewing skills in 40 healthy preterm infants, and the role of experience in the acquisition of these skills in a prospective longitudinal study. Sucking patterns were evaluated at 34, 37, and 44 weeks postmenstrual age (PMA), assisted spoon feeding was evaluated at 6, 9, and 12 months PMA, and chewing was evaluated at 9, 12, and 24 months PMA. Sucking patterns were rated using the Neonatal Oral Motor Assessment Scale, assisted spoon feeding was rated using the Observation List Spoon Feeding, and chewing was evaluated using the Mastication Observation and Evaluation Instrument.All infants showed progression in their oral motor skills during the study period, but not all demonstrated a stable progression of skills. Quality of sucking patterns was not associated with skill level achievement of assisted spoon feeding or with chewing. Length of experience in sucking was significantly associated with duration of supplemental tube feeding but not with the quality of the sucking pattern. Length of chewing experience was significantly associated with chewing abilities at 9 and 12 months PMA. No clinical characteristics were sufficiently predictive of oral motor skill development. Results show that sucking patterns are not predictive of subsequent feeding development in healthy preterm infants. The food consistency offered and the length of feeding experience influenced the acquisition and quality of oral motor skills differently.     

Kinematic descriptions of upper limb function using simulated tasks in activities of daily living after stroke

Assessment of upper limb function poststroke is critical for clinical management and determining the efficacy of interventions. We designed a unilateral upper limb task to simulate activities of daily living to examine how chronic stroke survivors manage reaching, grasping and handling skills simultaneously to perform the functional task using kinematic analysis. The aim of the study was to compare the motor strategies for performing a functional task between paretic and nonparetic arms. Sixteen chronic stroke survivors were instructed to control an ergonomic spoon to transfer liquid from a large bowl to a small bowl using paretic or nonparetic arm. Kinematic data were recorded using a Vicon motion capture system. Outcome measures included movement duration, relative timing, path length, joint excursions, and trial-to-trial variability. Results showed that movement duration, spoon path length, and trunk path length increased significantly when participants used paretic arm to perform the task. Participants tended to reduce shoulder and elbow excursions, and increase trunk excursions to perform the task with paretic arm and altered the relative timing of the task. Although participants used different motor strategies to perform the task with their paretic arms, we did not find the significant differences in trial-to trial variability of joint excursions between paretic and nonparetic arms. The results revealed differences in temporal and spatial aspects of motor strategies between paretic and nonparetic arms. Clinicians should explore the underlying causes of pathological movement patterns and facilitate preferred movement patterns of paretic arm.     

Infants' reasoning about others' false perceptions

Prior research suggests that children younger than age 3 or 4 do not understand that an agent may be deceived by an object's misleading appearance. The authors asked whether 14.5-month-olds would give evidence in a violation-of-expectation task that they understand that agents may form false perceptions. Infants first watched events in which an agent faced a stuffed skunk and a doll with blue pigtails; the agent consistently reached for the doll, suggesting that she preferred it over the skunk. Next, while the agent was absent, the doll was hidden in a plain box, and the skunk was hidden in a box with a tuft of blue hair protruding from under its lid. Infants expected the agent to be misled by the tuft's resemblance to the doll's hair and to falsely perceive it as belonging to the doll. These and other results indicate that 14.5-month-old infants can already reason about agents' false perceptions.     

Increasing task precision demands reveals that the reach and grasp remain subject to different perception-action constraints in 12-month-old human infants

The reach and grasp follow different developmental trajectories, but are often considered to have achieved nearly adult-like precision and integration by 12 months of age. This study used frame-by-frame video analysis to investigate whether increasing precision demands, by placing small reaching targets on a narrow pedestal rather than on a flat table, would influence the reach and grasp movements of 12-month-old infants in a complementary or differential fashion. The results reveal that placing the target atop a pedestal impaired the infants’s ability to direct an appropriate digit towards the small target, but did not produce a corresponding decrease in the frequency with which they used an index-thumb pincer grip to grasp the target. This was due to the fact that, although infants were more likely to contact the target with a suboptimal part of the hand in the pedestal condition, a greater proportion of these suboptimal contacts ultimately transitioned to a successful index-thumb pincer grip. Thus, increasing task precision demands impaired reach accuracy, but facilitated index-thumb grip formation, in 12-month-old infants. The differential response of the reach and grasp to the increased precision demands of the pedestal condition suggests that the two movements are not fully integrated and, when precision demands are great, remain sensitive to different perception-action constraints in 12-month-old infants.     

Spoon-to-cup fading as treatment for cup drinking in a child with intestinal failure

We treated a child with intestinal failure who consumed solids on a spoon but not liquids from a cup. We used spoon-to-cup fading, which consisted of taping a spoon to a cup and then gradually moving the bowl of the spoon closer to the edge of the cup. Spoon-to-cup fading was effective for increasing consumption of liquids from a cup.     

Wistar rats with high versus low rearing activity differ in radial maze performance

Substantial work has shown that rats although identical in stock, sex, age, and housing conditions can differ considerably in terms of behavior and physiology. Such individual differences, which can be detected by specific behavioral screening tests, are rather stable, that is, they probably reflect a behavioral disposition or trait. Here, we asked whether and how such differences might affect performance in a task of spatial learning and memory, the radial maze. As in our previous work, we used the degree of rearing activity in a novel open field to assign male adult outbred Wistar rats into those with high versus low rearing activity (HRA/LRA rats). They were then tested in a plus-maze for possible differences in anxiety-related behavior. Finally, and most importantly, they were food deprived and underwent maze training using an 8-arm radial maze with four non-baited and four baited arms. One of these arms consistently contained a larger bait size than the other three. In the open field, HRA rats not only showed more rearing behavior, but also more locomotor activity than LRA rats. In the plus-maze, HRA rats again showed more locomotion, but did not differ in open arm time or percentage of open arm entries, that is, conventional measures of anxiety-related behavior. In the radial maze, HRA rats consistently needed less time to consume all pellets than LRA rats, which was due to faster locomotion on the arms and less time spent at the food pits (especially in baited arms) of HRA rats. During the initial days of training, they were also more efficient in obtaining all food pellets available. Furthermore, HRA rats visited more arms and made relatively less reference memory errors than LRA rats. This allowed them to forage food quickly, but was paralleled by more working memory errors than in LRA rats. In general, working memory errors were more frequent in the arm with the large bait size, but there were no indications that HRA and LRA rats responded differently dependent on reward size. Finally, LRA rats lost slightly more weight than HRA rats during the period of food deprivation. These results are discussed with respect to the role of cognitive and motivational mechanisms, which as subject-inherent factors can contribute substantially to inter-individual variability in the radial maze.     

“We will work for you” – Social influence may suppress individual food preferences in a communicative situation in dogs

The level of motivation (i.e. incentive power) is thought to be one of the most important factors affecting performance and learning in various tasks. We investigated whether reward quality has an effect on the performance of family dogs in a two-way object choice test in which they can find the hidden food by relying on distal momentary human pointing cues. In three experiments we varied (1) the type of food reward according to the subjects’ own preference; (2) the quality of the reward offered at the same time in the indicated and not-indicated locations; and (3) the order of the high or low quality rewards in consecutive sessions. In Experiment 1, we first tested whether dogs prefer one kind of reward over another. Then one group was tested with the ‘preferred’ food as reward in the indicated bowl, while dogs in the other group received the ‘non-preferred’ food as reward. We did not find any difference between the performance and choice latencies of the two groups. In Experiment 2 for the first group, the indicated bowl contained a piece of carrot and the not-indicated bowl was empty. In the second group the indicated bowl contained carrot, but the not-indicated bowl contained sausage. According to a preliminary preference test, most dogs prefer sausage over carrot invariably. After 20 trials, the two groups performed surprisingly similarly. There was no difference found between groups in the number of correct choices, incorrect choices and non-choices. However, the comparison between the first and last five trials revealed that subjects who found sausage when they chose the not-indicated bowl (did not follow the pointing) chose the non-indicated bowl significantly more often toward the end of their test session. In Experiment 3, each dog received two sessions with 12 pointing trials in each. For the first session, one group was rewarded with sausage and the other with carrot upon choosing the indicated bowl. In the second session, the indicated bowl contained dry dog food for both groups. We found that correct choices and response latencies did not change over two sessions in the ‘sausage’ group. In the ‘carrot’ group, the dogs chose faster in the second session, but their performance did not improve; in fact, they chose the not-indicated bowl more often than the indicated bowl. As a conclusion, we can say that reward quality had some effect on dogs’ choice behavior in these experiments. The drop in their performance was not drastic, taking into account the general refusal to eat one of the ‘rewards’ (carrot) during the preference tests and also during the test trials. It seems that incentive contrast may play a relatively minor role in dog-human social interactions. Appropriate reward quality can be very important in asocial problem solving tasks, but, when interacting with humans, following human signals may override the effect of changed incentive power.     

Binocular vision and spatial perception in 4- and 5-month-old infants

Four experiments investigated the relation between the development of binocular vision and infant spatial perception. Experiments 1 and 2 compared monocular and binocular depth perception in 4- and 5-month-old infants. Infants in both age groups reached more consistently for the nearer of two objects under binocular viewing conditions than under monocular viewing conditions. Experiments 3 and 4 investigated whether the superiority of binocular depth perception in 4-month-olds is related to the development of sensitivity to binocular disparity. Under binocular viewing conditions in Experiment 3, infants identified as disparity-sensitive reached more consistently for the nearer object than did infants identified as disparity-insensitive. The two groups' performances did not differ under monocular viewing conditions. These results suggest that, binocularly, the disparity-sensitive infants perceived the objects' distances more accurately than did the disparity-insensitive infants. In Experiment 4, infants were habituated to an object, then presented with the same object and a novel object that differed only in size. Disparity-sensitive infants showed size constancy by recovering from habituation when viewing the novel object. Disparity-insensitive infants did not show clear evidence of size constancy. These findings suggest that the development of sensitivity to binocular disparity is accompanied by a substantial increase in the accuracy of infant spatial perception.     

Development of oral motor behavior related to the skill assisted spoon feeding

Milestones in the typical development of eating skills are considered to be nippling (breast or bottle), eating from a spoon, drinking from a cup, biting and chewing.The purpose of this research was to study the development and consolidation of oral motor behavior related to the skill assisted spoon feeding in young infants. The present study longitudinally investigated the development of this skill in 39 healthy children from the start of spoon feeding until the skill was acquired. The Observation List Spoon Feeding with 7 observation items for oral motor behavior and 6 items for abnormal behavior was used. Results showed that infants between 4 and 8 months of age needed 5.7 weeks (SD 2.1), with a range of 8 weeks (from 2 to 10 weeks) to acquire this skill. No significant correlation (p = .109) between age at start spoon feeding and weeks needed to develop the skill was found. During this period oral motor behavior consolidated and abnormal behavior diminished.With this study it is shown that the period in weeks needed to acquire the oral motor behavior for the skill assisted spoon feeding is important in case of feeding problems.     

THE COSTS OF EATING: A BEHAVIORAL ECONOMIC ANALYSIS OF FOOD REFUSAL

Behavioral economic concepts were applied to the analysis and treatment of pediatric feeding disorders in a clinical setting. In Experiment 1, children who chronically refused food were presented with varying amounts of food on a spoon (empty, dipped, quarter, half, and level). Each child exhibited a different but orderly demand function of response (acceptance, expulsion, and mouth clean) by cost (increasing spoon volume) for a constant pay-off of toys and social interaction. In Experiment 2, physical guidance or nonremoval of the spoon for food refusal was initiated at the smallest spoon volume with low levels of acceptance, and was subsequently introduced at the largest spoon volume with moderate levels of acceptance. Treatment was effective in increasing acceptance, and these effects generalized hierarchically across untargeted spoon volumes. The results of both studies provide preliminary support that increasing spoon volume can be equated conceptually with increasing response effort, and that the change from differential reinforcement to physical guidance or nonremoval of the spoon appears to have altered the elasticity of each child's demand function.     

AQS security scores: What do they represent? A study in construct validation

In a sample of 129 Dutch 15‐month‐old infants, attachment security was assessed both with the Attachment Q‐Set (AQS; Waters, 1995) and with a short version of Ainsworth, Blehar, Waters, and Wall's (1978) Strange Situation (SSS). Infants classified as secure using the SSS had significantly higher AQS scores than insecure and disorganized infants in particular. At the AQS item level, disorganized infants were described as significantly more noncompliant, fussy, and angry relative to secure infants. When security as assessed using the SSS was controlled, the observed quality of parental interactive behavior, parental ego‐resilience, high levels of infant task orientation and pleasure, and low levels of infant anger proneness were found to explain significant and unique portions of the variance in the AQS security scores. The apparently unfavorable set of characteristics associated with low AQS security scores suggests such scores to predict later developmental problems. ©2004 Michigan Association for Infant Mental Health.     

Infants' visual anticipation of object structure in grasp planning

The coordination between visual and manual domains is a cornerstone of learning in early development. If infants anticipate an object's physical characteristics prior to contact (i.e., from visual inspection), they could learn more about the physical world through visual observation only than if manual exploration is required. In this experiment, infants grasped a series of four round balls quite similar in size and overall shape, but different in structure. Two were composed of solid hard plastic (one transparent, one opaque) in a rigid structure, and two were composed of more flexible plastic in a nonrigid structure. This nonrigid structure afforded grasping using a precision grasp with fingertips extending inside the ball's outer edge. In contrast, the rigid balls could be grasped only by a full-hand power grasp (due to the relative sizes of ball and infants' hands). The infants' manual anticipations were assessed in their first reach for each ball, prior to their first contact with the ball. In addition, grasping and other exploratory behaviors were assessed after contact with the ball. Results from this study suggest that infants from 5 to 15 months of age incorporate visible information about an object's structure into their action on the object. This provides evidence that visuomotor connections are present as soon as infants start reaching for objects, allowing them to select the appropriate grasp for an object's structure, even if they are not always capable of executing a pickup of the object using this grasp. Further research should investigate the discrepancies between infants' grasp planning and their grasp execution.     

Delaying gratification for food and tokens in capuchin monkeys (Cebus apella) and chimpanzees (Pan troglodytes): when quantity is salient, symbolic stimuli do not improve performance

Capuchin monkeys have been tested for the capacity to delay gratification for accumulating rewards in recent studies and have exhibited variable results. Meanwhile, chimpanzees have consistently excelled at this task. However, neither species have ever been tested at accumulating symbolic tokens instead of food items, even though previous reports indicate that tokens sometimes facilitate performance in other self-control tasks. Thus, in the present study, we tested capuchin monkeys and chimpanzees for their capacity to delay gratification in a delay maintenance task, in which an experimenter presented items, one at a time, to within reach of an animal for as long as the animal refrained from taking them. In Experiment 1, we assessed how long capuchin monkeys could accumulate items in the delay maintenance task when items were food rewards or tokens exchangeable for food rewards. Monkeys accumulated more food rewards than they did tokens. In Experiment 2, we tested capuchin monkeys and chimpanzees in a similar accumulation test. Whereas capuchins again accumulated more food than tokens, all chimpanzees but one showed no difference in performance in the two conditions. These findings provide additional evidence that chimpanzees exhibit greater self-control capacity in this task than do capuchin monkeys and indicate that symbolic stimuli fail to facilitate delay maintenance when they do not abstract away from the quantitative dimension of the task. This is consistent with previous findings on the effects of symbols on self-control and illuminates what makes accumulation a particularly challenging task.     

The role of context and functionality in the interpretation of quantifiers

The aim of the three experiments that are reported was to investigate the role of context, especially size and functionality, in the interpretation of quantifiers. The studies all used a task in which participants rated the appropriateness of quantifiers describing the number of balls in a bowl. The size of the balls was found to have an effect: Identical numbers of balls were given different ratings depending on ball size. It was also found that quantifiers were rated as more appropriate when the balls were in their natural functional relationship with the bowl (i.e., contained within the bowl), than when the functional relationship was breached (i.e., the balls overflowed the bowl). Tilting the bowl had surprising effects in that it led to some quantifiers being rated as more appropriate. The results are interpreted as indicating that quantifiers carry little specific meaning in themselves but instead derive their meaning from the context in which they occur.     

Development of co-feeding behavior in young wild Japanese macaques (Macaca fuscata)

This study describes the developmental course of the social context of feeding behavior in infants and yearlings of Japanese macaques in a provisioned free-ranging troop. Results of this longitudinal study revealed that infants and yearlings exhibited synchronous feeding behavior in the majority of cases in which they had feeding neighbors within 1 m. They consistently showed feeding behavior more often when their closest neighbor fed than when they did not. In feeding situations, infants tended mainly to be in close proximity with their mothers in the early stages of life and, later, also with peers. The results imply that potential opportunities for the social transmission of food selection habits are available for young Japanese macaques in the wild.     

INDUCTION AND MAINTENANCE OF SWALLOWING RESPONSES IN INFANTS WITH DYSPHAGIA

A treatment package was used to induce and maintain swallowing with three infants who did not swallow food or liquid. Prior to treatment, they received all nutrition and hydration via gastrostomy tube feedings. The treatment package consisted of least-to-most intrusive physical prompts, an eliciting stimulus, contingent social reinforcement, and repeated trials to induce and maintain swallowing. The design combined elements of reversal and changing criterion designs for all three infants. The package was applied across feeding devices (nipple, cup, spoon), situations (liquid, pureed foods), and persons (trainer, primary nurses, mothers). The number of swallows or ounces per feeding (from 0 to 8 ounces) and the number of feeding sessions per day (from one to five) were progressively increased. In each case, the infant received baseline conditions alternated with the treatment package. Follow-up probes were done at 15 months, 21 months, or 24 months, respectively, after the last phase for the three patients. The package was successful in that the gastrostomy tube was no longer needed for Patients 1 and 3. Patient 2 maintained functional swallowing responses but received supplemental gastrostomy feedings because of unrelated medical problems. Results are discussed in terms of the need to isolate components of the package. The package can be used in cases in which the preexisting treatments (reinforcement with preferred foods, force-feeding) are not feasible because of age, physical fragility, or the lack of a swallowing response following the presentation of food.