Ad W. Smitsman

Affordances, perceptual complexity, and the development of tool use.

Perceiving the affordance of a tool requires the integration of several complementary relationships among actor, tool, and target. Highers order affordance structures are introduced to deal with these forms of complex action from an ecological-realist point of view. The complexity of the higher order affordance structure was used to predict the difficulty of perceiving the tool function. Predictions were tested in 3 experiments involving children between 9 months and 4 years old. In a classical tool use task dating back to W. Köhler, a desirable target was obtained by using a hook as a tool. The relative positions of the hook and the target were systematically varied to obtain structures differing in complexity. The observed difficulty of the task was found essentially in accordance with the theoretical complexity of the higher order affordance structures involved in perceiving the tool function.

Variations of tool and task characteristics reveal that tool-use postures are anticipated.

The authors examined anticipation in tool use, focusing on tool length and tool-use posture. Adults (9 women and 9 men in each experiment) held a rod (length 0.4-0.8 m), with the tip upward; walked toward a cube; chose a place to stop; and displaced the cube with the rods tip. In 2 experiments, rod length, mass, and mass distribution, and the size of the cube were manipulated. Chosen distance depended on rod length and cube size. Because effects of cube size on distance resulted only from postural changes related to required control, distance anticipated displacement posture. A postural synergy comprising legs and trunk provided a stable platform for the displacement. An arm synergy was less extended for small cubes, longer rods, and handleweighted rods. Selected distance anticipated those postures.

Geometrics and dynamics of a rod determine how it is used for reaching

Abstract Displacing an object with a hand-held rod provided a simple paradigm for studying tool use. The authors asked how reaching was affected by manipulations of rod properties. Adults held a rod (length = .10 to 1.5 m), with its tip in the air; walked toward an object on a table; chose a place to stop; and displaced the object with the rods tip. In 3 experiments (Ns = 9, 22, and 17 participants), the authors manipulated rod length, mass, and mass distribution to determine whether and how geometric and dynamic properties affected the chosen distance and the posture. Both the chosen stopping distance and the postures were well accommodated to rod characteristics. Postural adaptations took place only in the arm, which was organized as a synergy. Predictably, rod length explained most of the variance, but small and reliable differences in both distance and posture depended on mass and mass distribution. The chosen distance anticipated not only rod length but also the upcoming posture needed to control the rod.

Young children’s use of a visual aid: an experimental study of the effectiveness of training

We report an experiment concerning the use of a stand magnifier by young children with visual impairments (21 males, 12 females; mean age 4y 8mo [SD 11mo]). Children had a normative developmental level and a visual acuity of 0.4 or less (≤20/50 in Snellen’s notation). To measure magnifier use objectively, we developed a task that closely resembled the dynamics of its real‐life (pre‐reading) use. Children had to follow trails visually, from a start location to an unseen end location. This could only be done successfully and reliably by proper use of the magnifier. In addition to this, we analyzed the effect of specific training with the magnifier by using a repeated‐measures (before and after training) matched‐groups (with respect to age and near‐visual acuity) design. Results established both the task’s efficacy as an instrument for measuring magnifier use in young children and the effectiveness of the training. Improvement in task performance after training was found in both groups, except for the youngest children (<3y 6mo). On average, 1.8 times as many paths were followed in both groups after training (p=0.001). The without‐magnifier training group became 2.5 times as good at finding the correct end location, whereas the with‐magnifier training group became 4.3 times as good (p=0.05).

Perseveration in Tool Use: A Window for Understanding the Dynamics of the Action-Selection Process

Two experiments investigated how 3-year-old children select a tool to perform a manual task, with a focus on their perseverative parameter choices for the various relationships involved in handling a tool: the actor-to-tool relation and the tool-to-target relation (topology). The first study concerned the parameter value for the tool-to-target relation by asking how children use a cane for either pushing an object further away (exclosure; outside the hook) or pulling an object nearby (enclosure; inside the hook). The second study concerned the parameter value for the hand-to-tool relation by assessing the hand used for grasping a spoon to feed a puppet. Results from both studies showed that on the first trial, choices were driven by task information. However, when the task switched from pulling to pushing or from left hand to right hand, or vice versa, children persevered with the choice they made during the 4 previous trials. Results are discussed in terms of the dynamical field modeling work of Esther Thelen and her colleagues. Our findings underscore Thelens hypotheses that: (a) the action-selection process is a dynamic affair, affected by multiple influences at different time scales and its own intrinsic dynamics; and (b) that perseverative behavior is a general phenomenon that is neither indicative for a specific period in the development, nor for a particular task. Similarly, we argue that the presence (or absence) of causal understanding emerges from the action-selection process, rather than determining this process.

Exploratory behavior in blind infants : How to improve touch?

A key issue for our understanding of exploration and how it evolves concerns the information that is gathered or the structure that emerges in flows of energy for sensory systems. It allows a state of awareness to be maintained or transformed into another state. The very essence of exploration must be the emergent property that information forms, and changes in this property when exploration is organized differently. We took the stance that information involves cooperative activity of different senses, which is promoted by the way flows of energy become structured in relation to how the exploratory system is organized. Moreover, we assumed that detrimental effects of sensory handicaps are not as much the result of the sense that is missing as they are of the cooperation between the senses that cannot take place. Guided by this assumption, we constructed surfaces that contained texture gradients to evoke haptic exploration and way finding in near space in congenitally blind young children on manual encounters with the surface. The surfaces extended in front of the child. We hypothesized that cooperation of the two submodalities of touch, i.e., kinesthesis and the cutaneous sense, afforded by the texture gradients would allow the child to gather an environmental frame coupled to the body frame. Results indeed showed enhanced exploration in 8- to 20-month-old congenitally blind infants and an evolving dynamic landscape of exploratory behavior that became adapted to the texture gradients. Way finding was studied in 4-year-old congenitally blind children. Results showed that way finding improved for the texture gradients compared to a surface that contained homogeneously distributed texture elements.

Geometric, but not kinetic, properties of tools affect the affordances perceived by toddlers

We asked what rod properties affected childrens reaching range. Children, 2 to 4 years old, held a rod (length 10-60 cm) with the tip in the air, walked toward a toy on a table, chose a place to stop, and displaced the toy with the rods tip. In 2 experiments rod length, mass, and mass distribution were manipulated to determine whether and how geometric and kinetic properties affected chosen distance and posture. Chosen distance depended only on the length of the rod. Postures were affected by length and mass properties of the rod. Not all adaptations in posture were prospectively reflected in the distance. Although we found variations over age, we did not find clear developmental trends. The results are discussed in broader perspectives of development of affordances and tool use.

Special Section: Towards an Embodiment of Goals

This paper discusses both a dissociation view and a dynamic view with respect to the study of voluntary, goal-directed behavior. The dissociation view builds on the recently reintroduced ideomotor principle, and conceives of clearly dissociated and hierarchical roles for the planning and control of action. The dynamic view has a more integral and dynamic conception of how planning, control, and timing merge in the guidance of behavior. This view, however, lacks a clear way of encompassing the goaldirectedness of behavior. For behavior to be effective and efficient, sensory information has to play an equally important role in guiding action as goal-related information does. As a third view, a dynamic action-selection approach is introduced by combining aspects of the former two. This model is able to merge ideomotor and sensorimotor processes continuously and in real time. In discussing the action-selection approach, a special emphasis is given to the role of long-term influences like preferences and goals.

Early math learning with tablet PCs: The role of action

Context: The present study is about computer assisted learning (CAI) and how it facilitates early math learning in 4-6-year-old children. Aim: Trying to demonstrate how changes in estimation accuracy are a result of different behavioral or action organizations during playing with a numerical board game on a tablet PC. Settings and Design: A pre-posttest design and a training intervention was used. Statistical Analysis Used: In order to measure childrens′ estimation accuracy (N = 179), the percent absolute error scores were calculated and compared in a pretest and a posttest. Further, each child′s best fitting linear function (R΂lin) was computed in order to find out whether children handled numbers in a linear way. Materials and Methods: A number line estimation task with a 0-10 interval was used in both the pretest and the posttest. For the intervention training, each child received a tablet computer and could play on a digital number line for four 15-min sessions. Children′s hand and finger movements were manipulated during instruction in different conditions: Freely jumping or pointing. Results : Children′s estimation accuracy increased after playing with the digital number line. However, the way in which behavior was organized during the training period resulted in different accuracy performances. Conclusions: These results show that minor changes in the behavioral system can lead to significantly different learning gains and that numerical knowledge is embodied in the system the child mobilizes.

Action-selection perseveration in young children: Advances of a dynamic model

Abstract This study presents an empirical test and dynamic model of perseverative limb selection in children of 14‐, 24‐, and 36‐months old (N = 66 in total). In the experiment, children repeatedly grasped a spoon with a single hand. In two separate conditions, the spoon was presented either four times on their right side or four times on their left side. In both conditions, following this training, the spoon was presented on midline for two more trials. This setup enabled us to determine whether childrens limb selection was influenced by their prior choices in the task (i.e., perseveration). Individual childrens handedness was determined in a third condition consisting of nine object presentations (laterally or on midline). A dynamic model for limb selection is presented combining external input, motor memory, and preferences. The model was used to simulate the experiment and reproduced the results, including the age‐related changes.