Human and machine perception of biological motion

More than 30 years ago, Johansson was the first to show that humans are capable of recovering information about the identity and activity of animate creatures rapidly and reliably from very sparse visual inputs – the phenomenon of biological motion. He filmed human actors in a dark setting with just a few strategic points on the body marked by lights – so-called moving light displays (MLDs). Subjects viewing the MLDs reported a vivid impression of moving human forms, and were even able to tell the activity in which the perceived humans were engaged. Subsequently, the phenomenon has been widely studied and many attempts have been made to model and to understand it. Typical questions that arise are: How precisely is the sparse low-level information integrated over space and time to produce the global percept, and how important is world knowledge (e.g., about animal form, locomotion, gravity, etc.)? In an attempt to answer such questions, we have implemented a machine-perception model of biological motion. If the computational model can replicate human data then it might offer clues as to how humans achieve the task. In particular, if it can do so with no or minimal world knowledge then this knowledge cannot be essential to the perception of biological motion. To provide human data for training and against which to assess the model, an extensive psychophysical experiment was undertaken in which 93 subjects were shown 12 categories of MLDs (e.g., normal, walking backwards, inverted, random dots, etc.) and were asked to indicate the presence or absence of natural human motion. Machine perception models were then trained on normal sequences as positive data and random sequences as negative data. Two models were used: a k-nearest neighbour (k-NN) classifier as an exemplar of ‘lazy’ learning and a back-propagation neural network as an exemplar of ‘eager’ learning. We find that the k-NN classifier is better able to model the human data but it still fails to represent aspects of knowledge about body shape (especially how relative joint positions change under rotation) that appear to be important to human judgements.     

A cognitive behavioral workshop for subclinical obsessions and compulsions

The present study investigates the effectiveness of a 3-h cognitive behavioral workshop for individuals, ages 18-22, with subclinical obsessions and compulsions. It was hypothesized that, compared to individuals in an assessment-only waitlist group (n = 42), individuals assigned to the workshop group (n = 43) would experience a significant decrease in obsessive-compulsive (OC) symptomatology, comorbidity, and thought action fusion endorsement at 1-month and 5-month follow-up assessments. An additional outcome of interest was the number of incident cases of obsessive-compulsive disorder (OCD) over the course of the study. The results indicated that the workshop group reported a significantly fewer number of OC symptoms at 5-month follow-up and endorsed significantly less thought action fusion at both follow-up points. However, there were no differences between groups in severity of OC symptoms and number of comorbid diagnoses endorsed. Only one incident case of OCD was observed during the study, from a participant in the waitlist group. These results are discussed in reference to treatment of subclinical anxiety symptoms.     

Cognitive behavior therapy in treatment-naive children and adolescents with obsessive-compulsive disorder: an open trial

This work aims is to evaluate the therapeutic efficacy of cognitive behavior therapy (CBT) in pediatric patients with obsessive-compulsive disorder (OCD) who had not previously been treated with either pharmacotherapy or psychotherapy and who remained medication-free during CBT. Sixteen OCD outpatients, 8-17 years of age, were treated in a 12-week open trial with manualized CBT. Target symptoms were rated at two-week intervals with the Children's Yale-Brown Obsessive Compulsive Scale (CY-BOCS), the National Institute of Mental Health Global Obsessive-Compulsive Scale (NIMH Global), the Clinical Global Impression Scale (CGI), and the Hamilton Anxiety Rating Scale (Ham-A). Statistical analyses showed a significant benefit for treatment. Ten patients experienced at least a 50% reduction in symptoms on the CY-BOCS; seven were asymptomatic on the NIMH Global. These results build on previous reports that CBT may be effective in the acute treatment of pediatric OCD. Further, the results of this study suggest that CBT can be efficacious in alleviating OCD symptoms in the absence of pharmacotherapy. These results must be considered preliminary, given the small sample size and open administration of treatment.     

Inhibitory control in number-conservation and class-inclusion tasks: A neo-Piagetian inter-task priming study

We investigated whether success in number-conservation and class-inclusion tasks relies on a general ability to inhibit misleading strategies. Two groups of 10-year-olds performed inter-task priming between computerized versions of class-inclusion and number-conservation tasks (Experiment 1). In one group, the class-inclusion task served as a prime and the number-conservation task as an assessment probe and vice versa in the other group. Response times were shorter in the number-conservation task when performed after the class-inclusion task (and vice versa in the other group) than in control prime-probe sequences in which the primes did not require the inhibition of a misleading strategy. Experiment 2 showed that these inter-task priming effects did not simply reflect that class inclusion and number conservation rely on the reversibility of concrete operations as Piaget would have hypothesized. Taken together the results are consistent with the neo-Piagetian assumption that cognitive development is rooted in both the acquisition of knowledge of incremental complexity and the ability to resist (inhibit) previous knowledge. Critically, the present finding suggests that the inhibitory ability is not domain- or strategy-specific.     

Using finite mixture of GLMs to explore variability in children's flexibility in a task-switching paradigm

The present study illustrates the usefulness of finite mixture of generalized linear models (GLMs) to examine variability in cognitive strategies during childhood. More precisely, it addresses this variability in set-shifting situations where task-goal updating is endogenously driven. In a task-switching paradigm 5–6-year-olds had to switch between color- and shape-matching rules as a function of a predetermined, predictable task sequence. A finite mixture of GLMs was fitted to explore individual differences in performance. The statistical model revealed five response profiles, defined by accuracy and response times. These response profiles likely correspond to different cognitive strategies with varying efficiency and differential relations to working memory capacity (assessed by backward digit span). These results illustrate the heuristic value of statistical modeling to reveal the behavioral and cognitive variability in the temporal dynamics of children's cognitive functioning.     

Representing Spatial Structure Through Maps and Language: Lord of the Rings Encodes the Spatial Structure of Middle Earth

Spatial mental representations can be derived from linguistic and non‐linguistic sources of information. This study tested whether these representations could be formed from statistical linguistic frequencies of city names, and to what extent participants differed in their performance when they estimated spatial locations from language or maps. In a computational linguistic study, we demonstrated that co‐occurrences of cities in Tolkien’s Lord of the Rings trilogy and The Hobbit predicted the authentic longitude and latitude of those cities in Middle Earth. In a human study, we showed that human spatial estimates of the location of cities were very similar regardless of whether participants read Tolkien’s texts or memorized a map of Middle Earth. However, text‐based location estimates obtained from statistical linguistic frequencies better predicted the human text‐based estimates than the human map‐based estimates. These findings suggest that language encodes spatial structure of cities, and that human cognitive map representations can come from implicit statistical linguistic patterns, from explicit non‐linguistic perceptual information, or from both.