Numerical modelling of floating debris in the world's oceans.

A global ocean circulation model is coupled to a Lagrangian particle tracking model to simulate 30 years of input, transport and accumulation of floating debris in the world ocean. Using both terrestrial and maritime inputs, the modelling results clearly show the formation of five accumulation zones in the subtropical latitudes of the major ocean basins. The relative size and concentration of each clearly illustrate the dominance of the accumulation zones in the northern hemisphere, while smaller seas surrounded by densely populated areas are also shown to have a high concentration of floating debris. We also determine the relative contribution of different source regions to the total amount of material in a particular accumulation zone. This study provides a framework for describing the transport, distribution and accumulation of floating marine debris and can be continuously updated and adapted to assess scenarios reflecting changes in the production and disposal of plastic worldwide.

Identifying possible contingencies during descriptive analyses of severe behavior disorders.

Contingencies of reinforcement involve, in part, relations between behavior and subsequent environmental events. In this study we observed 11 individuals with developmental disabilities and severe behavior problems while they interacted with their primary care providers in simulated environments (hospital therapy rooms). We compared the probability of obtaining attention, escape from instructional demands, or access to materials following instances of problem behavior with the background probability of those events. However, the focus of our analysis was the evaluation of comparative probabilities ("contingency values") in the context of relevant establishing operations such as diverted attention, instructional demands, and restricted access to materials. Results showed that the method was useful in identifying relations between behavior and subsequent environmental events. Implications for linking descriptive and functional analyses are discussed, and difficulties in identifying naturally occurring contingencies are considered.

Fixed-time schedule effects as a function of baseline reinforcement rate.

Using an arbitrary response, we evaluated fixed-time (FT) schedules that were either similar or dissimilar to a baseline (response-dependent) reinforcement schedule and extinction. Results suggested that both FT schedules and extinction resulted in decreased responding. However, FT schedules were more effective in reducing response rates if the FT reinforcer rate was dissimilar to baseline reinforcer rates. Possible reasons for this difference were evaluated with data analysis methods designed to identify adventitious response-reinforcer relations.

Evaluating self-control and impulsivity in children with severe behavior disorders.

Impulsivity and self-control involve a choice between a smaller, more immediate reinforcer and a larger, more delayed reinforcer. Impulsive behavior occurs when responding produces the more immediate, relatively smaller reinforcers at the expense of delayed larger reinforcers. Self-control occurs when responding produces delayed larger reinforcers at the expense of immediate smaller reinforcers. Recently, researchers in applied behavior analysis have suggested that evaluations of self-control and impulsivity are relevant to socially important behaviors. Further, common behavioral treatments such as differential reinforcement may be influenced by variables such as reinforcer delay. In this study, we showed that aggression, reinforced by access to food, could be maintained as impulsive behavior. The participants were 2 young boys with severe developmental disabilities. For both participants, descriptive observations, care provider report, and functional analyses suggested that aggression was reinforced by food access (and television access for 1 participant). Next, we introduced a differential reinforcement procedure in which appropriate mands were reinforced. After various manipulations, we showed that aggression occurred when it produced immediate but small reinforcers even though mands produced larger, more delayed reinforcers. However, both participants displayed self-control when the delay to reinforcement was signaled (with a hand gesture or a timer).