Test of a dynamic neural field model: spatial working memory is biased away from distractors.

Attention facilitates the encoding (e.g., Awh, Anllo-Vento, & Hillyard, J Cognit Neurosci 12(5), 840-847, 2000) and maintenance of locations in spatial working memory (Awh, Vogel, & Oh, Atten, Percept Psychophys 78(4), 1043-1063, 2006). When individuals shift their attention during the maintenance period of a spatial working memory task, their memory of a target location tends to be biased in the direction of the attentional shift (Johnson & Spencer, 2016). Dynamic field theory predicts that in certain conditions, inhibitory mechanisms will result in biases away from distractors presented during the maintenance period of the task. Specifically, dynamic field theory predicts that memory responses will be biased toward distractors that are near the target location and biased away from distractors that are farther from the target location. In two experiments, the current study tested adults in a spatial memory task that required memorization of a single target location. On a subset of trials, a distractor appeared during the memory delay at different distances and directions from the target location. In contrast to the prediction, memory responses were biased away from distractors that were near the target location and not biased by distractors that were far from the target location, providing challenges for, dynamic field theory and other theories of spatial working memory.

Individual differences in executive attention and inhibitory control are related to spatial memory biases in adults.

Executive attention is involved in working memory; however, the role of executive attention in the maintenance of information in spatial working memory is debated. This study examined whether inhibitory control was related to spatial working memory biases in adults in a simple spatial memory task where participants had to remember one location on an otherwise blank computer screen. On some trials, a distractor was presented during the maintenance period. Eighty-four participants completed the spatial working memory task and a battery of cognitive control measures. When a distractor was presented during the maintenance period of the spatial memory task, performance on two of the cognitive control measures, a measure of overall attention and a measure of inhibitory control was related to memory errors. When a distractor was not presented during the spatial memory task, memory errors were not related to performance on the cognitive control tasks. Overall, these effects demonstrated that attention is related to maintaining locations in spatial working memory in adults, and inhibitory control may also be related such that those with more efficient inhibitory control were less influenced by distractors presented during the maintenance period.

Contributions of Dynamic Systems Theory to Cognitive Development.

This paper examines the contributions of dynamic systems theory to the field of cognitive development, focusing on modeling using dynamic neural fields. A brief overview highlights the contributions of dynamic systems theory and the central concepts of dynamic field theory (DFT). We then probe empirical predictions and findings generated by DFT around two examples-the DFT of infant perseverative reaching that explains the Piagetian A-not-B error, and the DFT of spatial memory that explain changes in spatial cognition in early development. A systematic review of the literature around these examples reveals that computational modeling is having an impact on empirical research in cognitive development; however, this impact does not extend to neural and clinical research. Moreover, there is a tendency for researchers to interpret models narrowly, anchoring them to specific tasks. We conclude on an optimistic note, encouraging both theoreticians and experimentalists to work toward a more theory-driven future.

The relationship between the perception of axes of symmetry and spatial memory during early childhood.

Early in development, there is a transition in spatial working memory (SWM). When remembering a location in a homogeneous space (e.g., in a sandbox), young children are biased toward the midline symmetry axis of the space. Over development, a transition occurs that leads to older children being biased away from midline. The dynamic field theory (DFT) explains this transition in biases as being caused by a change in the precision of neural interaction in SWM and improvements in the perception of midline. According to the DFT, young children perceive midline, but there is a quantitative improvement in the perception of midline over development. In the experiment reported here, children and adults needed to determine on which half of a large monitor a target was located. In support of the DFT, even the youngest children performed above chance at most locations, but performance also improved gradually with age.

Test of a Relationship between Spatial Working Memory and Perception of Symmetry Axes in Children 3 to 6 Years of Age.

Children's memory responses to a target location in a homogenous space change from being biased towards the midline of the space to being biased away. According to Dynamic Field Theory (DFT) (e.g., Schutte & Spencer, 2009), improvement in the perception of the midline symmetry axis contributes to this transition. Simulations of DFT using a 3-year-old parameter setting showed that memory biases at intermediate target locations were related to the perception of midline. Empirical results indicated that better perception of midline was associated with greater memory biases away at the 20° and 40° targets in 3-year-olds, and greater biases away at 60° in 4- to 6-year-olds. Findings support the DFT in that perception of midline is associated with memory biases.

Generalizing the dynamic field theory of spatial cognition across real and developmental time scales.

Within cognitive neuroscience, computational models are designed to provide insights into the organization of behavior while adhering to neural principles. These models should provide sufficient specificity to generate novel predictions while maintaining the generality needed to capture behavior across tasks and/or time scales. This paper presents one such model, the dynamic field theory (DFT) of spatial cognition, showing new simulations that provide a demonstration proof that the theory generalizes across developmental changes in performance in four tasks-the Piagetian A-not-B task, a sandbox version of the A-not-B task, a canonical spatial recall task, and a position discrimination task. Model simulations demonstrate that the DFT can accomplish both specificity-generating novel, testable predictions-and generality-spanning multiple tasks across development with a relatively simple developmental hypothesis. Critically, the DFT achieves generality across tasks and time scales with no modification to its basic structure and with a strong commitment to neural principles. The only change necessary to capture development in the model was an increase in the precision of the tuning of receptive fields as well as an increase in the precision of local excitatory interactions among neurons in the model. These small quantitative changes were sufficient to move the model through a set of quantitative and qualitative behavioral changes that span the age range from 8 months to 6 years and into adulthood. We conclude by considering how the DFT is positioned in the literature, the challenges on the horizon for our framework, and how a dynamic field approach can yield new insights into development from a computational cognitive neuroscience perspective.

Developmental Differences in the Influence of Distractors on Maintenance in Spatial Working Memory.

This study examined whether attention to a location plays a role in the maintenance of locations in spatial working memory in young children as it does in adults. This study was the first to investigate whether distractors presented during the delay of a spatial working memory task influenced young children's memory responses. Across two experiments, 3- and 6-year-olds completed a spatial working memory task featuring a static target location and distractor location. Results indicated a change between 3 and 6 years of age in how distractors influenced memory. Six-year-olds' memory responses were biased away from a distractor that was close to the target location and on the outside of the target location relative to the center of the monitor. Distractors that were far from the target or that were toward the center of the monitor relative to the target location had no effect. Three-year-olds' responses were biased toward a distractor when the distractor was on the outside of the target location and farther from the target. Distractors that were near the target location or toward the center of the monitor had no effect. These biases provide evidence that young children's maintenance of a location in memory is influenced by attention.

Toward a formal theory of flexible spatial behavior: geometric category biases generalize across pointing and verbal response types.

Three experiments tested whether geometric biases--biases away from perceived reference axes--reported in spatial recall tasks with pointing responses generalized to a recognition task that required a verbal response. Seven-year-olds and adults remembered the location of a dot within a rectangle and then either reproduced its location or verbally selected a matching choice dot from a set of colored options. Results demonstrated that geometric biases generalized to verbal responses; however, the spatial span of the choice set influenced performance as well. These data suggest that the same spatial memory process gives rise to both response types in this task. Simulations of a dynamic field model buttress this claim. More generally, these results challenge accounts that posit separate spatial systems for motor and verbal responses.

Tests of the dynamic field theory and the spatial precision hypothesis: capturing a qualitative developmental transition in spatial working memory.

This study tested a dynamic field theory (DFT) of spatial working memory and an associated spatial precision hypothesis (SPH). Between 3 and 6 years of age, there is a qualitative shift in how children use reference axes to remember locations: 3-year-olds' spatial recall responses are biased toward reference axes after short memory delays, whereas 6-year-olds' responses are biased away from reference axes. According to the DFT and the SPH, quantitative improvements over development in the precision of excitatory and inhibitory working memory processes lead to this qualitative shift. Simulations of the DFT in Experiment 1 predict that improvements in precision should cause the spatial range of targets attracted toward a reference axis to narrow gradually over development, with repulsion emerging and gradually increasing until responses to most targets show biases away from the axis. Results from Experiment 2 with 3- to 5-year-olds support these predictions. Simulations of the DFT in Experiment 3 quantitatively fit the empirical results and offer insights into the neural processes underlying this developmental change.

The dynamic nature of knowledge: insights from a dynamic field model of children's novel noun generalization.

This paper examines the tie between knowledge and behavior in a noun generalization context. An experiment directly comparing noun generalizations of children at the same point in development in forced-choice and yes/no tasks reveals task-specific differences in the way children's knowledge of nominal categories is brought to bear in a moment. To understand the cognitive system that produced these differences, the real-time decision processes in these tasks were instantiated in a dynamic field model. The model captures both qualitative and quantitative differences in performance across tasks and reveals constraints on the nature of children's accumulated knowledge. Additional simulations of developmental change in the yes/no task between 2 and 4 years of age illustrate how changes in children's representations translate into developmental changes in behavior. Together, the empirical data and model demonstrate the dynamic nature of knowledge and are consistent with the perspective that knowledge cannot be separated from the task-specific processes that create behavior in the moment.

Rigid thinking about deformables: do children sometimes overgeneralize the shape bias?

Young children learning English are biased to attend to the shape of solid rigid objects when learning novel names. This study seeks further understanding of the processes that support this behavior by examining a previous finding that three-year-old children are also biased to generalize novel names for objects made from deformable materials by shape, even after the materials are made salient. In two experiments, we examined the noun generalizations of 72 two-, three- and four-year-old children with rigid and deformable stimuli. Data reveal that three-year-old, but not two- or four-year-old, children generalize names for deformable things by shape, and that this behavior is not due to the syntactic context of the task. We suggest this behavior is an overgeneralization of three-year-old children's knowledge of how rigid things are named and discuss the implications of this finding for a developmental account of the origins of the shape bias.

Planning "discrete" movements using a continuous system: insights from a dynamic field theory of movement preparation.

The timed-initiation paradigm developed by Ghez and colleagues (1997) has revealed two modes of motor planning: continuous and discrete. Continuous responding occurs when targets are separated by less than 60 degrees of spatial angle, and discrete responding occurs when targets are separated by greater than 60 degrees . Although these two modes are thought to reflect the operation of separable strategic planning systems, a new theory of movement preparation, the Dynamic Field Theory, suggests that two modes emerge flexibly from the same system. Experiment 1 replicated continuous and discrete performance using a task modified to allow for a critical test of the single system view. In Experiment 2, participants were allowed to correct their movements following movement initiation (the standard task does not allow corrections). Results showed continuous planning performance at large and small target separations. These results are consistent with the proposal that the two modes reflect the time-dependent "preshaping" of a single planning system.

Unifying representations and responses: perseverative biases arise from a single behavioral system.

A dominant account of perseverative errors in early development contends that such errors reflect a failure to inhibit a prepotent response. This study investigated whether perseveration might also arise from a failure to inhibit a prepotent representation. Children watched as a toy was hidden at an A location, waited during a delay, and then watched the experimenter find the toy. After six observation-only A trials, the toy was hidden at a B location, and children were allowed to search for the toy. Two- and 4-year-olds' responses on the B trials were significantly biased toward A even though they had never overtly responded to this location. Thus, perseverative biases in early development can arise as a result of prepotent representations, demonstrating that the prepotent-response account is incomplete. We discuss three alternative interpretations of these results, including the possibility that representational and response-based biases reflect the operation of a single, integrated behavioral system.

Generalizing the dynamic field theory of the A-not-B error beyond infancy: three-year-olds' delay- and experience-dependent location memory biases.

Thelen and colleagues recently proposed a dynamic field theory (DFT) to capture the general processes that give rise to infants' performance in the Piagetian A-not-B task. According to this theory, the same general processes should operate in noncanonical A-not-B-type tasks with children older than 12 months. Three predictions of the DFT were tested by examining 3-year-olds' location memory errors in a task with a homogeneous task space. Children pointed to remembered locations after delays of 0 s to 10 s. The spatial layout of the possible targets and the frequency with which children moved to each target was varied. As predicted by the DFT, children's responses showed a continuous spatial drift during delays toward a longer term memory of previously moved-to locations. Furthermore, these delay-dependent effects were reduced when children moved to an "A" location on successive trials, and were magnified on the first trial to a nearby "B" location. Thus, the DFT generalized to capture the performance of 3-year-old children in a new task. In contrast to predictions of the DFT, however, 3-year-olds' responses were also biased toward the midline of the task space-an effect predicted by the category adjustment (CA) model. These data suggest that young children's spatial memory responses are affected by delay- and experience-dependent processes as well as the geometric structure of the task space. Consequently, two current models of spatial memory-the DFT and the CA model-provide incomplete accounts of children's location memory abilities.

Testing the dynamic field theory: working memory for locations becomes more spatially precise over development.

The dynamic field theory predicts that biases toward remembered locations depend on the separation between targets, and the spatial precision of interactions in working memory that become enhanced over development. This was tested by varying the separation between A and B locations in a sandbox. Children searched for an object 6 times at an A location, followed by 3 trials at a B location. Two- and 4-year-olds', but not 6-year-olds', responses were biased toward A when A and B were 9-in. and 6-in. apart. When A and B were separated by 2 in., however, 4- and 6-year-olds' responses were biased toward A. Thus, the separation at which responses were biased toward A decreased across age groups, supporting the predictions of the theory.