Apraxia in corticobasal degeneration.

Corticobasal degeneration (CBD) is a degenerative disease that often presents with an asymmetric progressive ideomotor limb apraxia. Some apraxic subjects may fail to perform skilled purposive movements on command because they have lost the memories or representations that specify how these movements should be performed (representational deficit). In contrast, other apraxic subjects may have the movement representations but are unable to utilize the information contained in them to execute skilled purposive movements (production-execution deficit). To learn if the apraxic deficit in CBD is induced by a representational or a production-execution deficit, we tested three nondemented subjects with CBD on tasks requiring production of meaningful or meaningless gestures to command, gesture imitation, gesture discrimination, and novel gesture learning. A fourth subject with incomplete data also is presented. The results suggest that the apraxia associated with CBD is initially induced by a production-execution defect with relative sparing of the movement representations.     

Encoding Shape and Spatial Relations: The Role of Receptive Field Size in Coordinating Complementary Representations

An effective functional architecture facilitates interactions among subsystems that are often used together. Computer simulations showed that differences in receptive field sizes can promote such organization. When input was filtered through relatively small nonoverlapping receptive fields, artificial neural net-works learned to categorize shapes relatively quickly; in contrast, when input was filtered through relatively large overlapping receptive fields, networks learned to encode specific shape exemplars or metric spatial relations relatively quickly. Moreover, when the receptive field sizes were allowed to adapt during learning, networks developed smaller receptive fields when they were trained to categorize shapes or spatial relations, and developed larger receptive fields when they were trained to encode specific exemplars or metric distances. In addition, when pairs of networks were constrained to use input from the same type of receptive fields, networks learned a task faster when they were paired with networks that were trained to perform a compatible type of task. Finally, using a novel modular architecture, networks were not preassigned a task, but rather competed to perform the different tasks. Networks with small nonover-lapping receptive fields tended to win the competition for categorical tasks whereas networks with large overlapping receptive fields tended to win the competition for exemplar/metric tasks.     

Affect and between-meal snacking in daily life: the moderating role of gender and age

Objective: Affect-related energy intake from snacks remains relatively unexplored in daily life. This study examines the associations between momentary positive affect (PA) and momentary negative affect (NA) and subsequent energy intake from snacks. In addition, the moderating role of BMI, gender, age and level of education is investigated.

Design: Adults (N = 269), aged 20–50, participated in this study. Demographics were assessed in an online composite questionnaire. An experience sampling smartphone application was used to map momentary NA/PA and energy intake (kilocalories) from snacks in the context of daily life.

Main outcome measures: Energy intake from moment-to-moment self-reported snacks in real-life settings.

Results: A significant negative main effect of momentary NA on moment-to-moment energy intake was found. The higher the momentary NA, the lower the subsequent amount of kilocalories consumed. There was no main effect with regard to PA. Interaction analyses showed that men decreased their energy intake after experiencing NA, and increased their intake after experiencing PA. No associations were found in women. Additionally, young adults (20–30) increased their energy intake after experiencing PA. No associations were found in the other age groups.

Conclusion: Interventions aiming at reducing energy intake might also address PA-related snacking in young adults and men.     

Learning to visually perceive the relative mass of colliding balls in globally and locally constrained task ecologies

Novice observers differ from each other in the kinematic variables they use for the perception of kinetic properties, but they converge on more useful variables after practice with feedback. The colliding-balls paradigm was used to investigate how the convergence depends on the relations between the candidate variables and the to-be-perceived property, relative mass. Experiment 1 showed that observers do not change in the variables they use if the variables with which they start allow accurate performance. Experiment 2 showed that, at least for some observers, convergence can be facilitated by reducing the correlations between commonly used nonspecifying variables and relative mass but not by keeping those variables constant. Experiments 3a and 3b further demonstrated that observers learn not to rely on a particular nonspecifying variable if the correlation between that variable and relative mass is reduced.