Cooperative selection of movements: The optimal selection model

How one selects a movement when faced with alternative ways of doing a task is a central problem in human motor control. Moving the fingertip a short distance can be achieved with any of an infinite number of combinations of knuckle, wrist, elbow, shoulder, and hip movements. The question therefore arises: how is a unique combination chosen? In our model, choice is achieved by consideration of the similarity between the task requirements and the optimal biomechanical performance of each limb segment. Two variants of the model account for the movements that are selected when subjects freely oscillate the fingertip and when they tap against an obstacle. An important feature of both is that the impulse of collision with an obstacle (as in drumming with the hand or tapping with the finger) is assumed to be controlled in part by aiming for a point beyond the surface being struck. Thus, a force-related control variable may be represented and controlled spatially.     

NONCONTINGENT PRESENTATION OF ATTENTION AND ALTERNATIVE STIMULI IN THE TREATMENT OF ATTENTION-MAINTAINED DESTRUCTIVE BEHAVIOR

Previous research has demonstrated that destructive behavior may be reduced through noncontingent presentation of attention when attention is identified as the stimulus responsible for behavioral maintenance. Because it may not always be possible to deliver attention in all situations, we examined the extent to which alternative stimuli that have been identified through a choice assessment would substitute for attention (the functional analysis—based reinforcer) in a noncontingent reinforcement procedure. Prior to treatment, functional analyses demonstrated that the destructive behavior of 2 clients with mental retardation was maintained by adult attention. Next, a stimulus choice assessment identified highly preferred tangible items for the 2 clients. Finally, we compared the effectiveness of two noncontingent reinforcement procedures: continuous noncontingent access to attention and continuous noncontingent access to the tangible item identified in the choice assessment. For both clients, these noncontingent reinforcement procedures reduced destructive behavior. The results are discussed in terms of the clinical implications for the treatment of destructive behavior using functional and alternative stimuli.     

THE USE OF POSITIVE AND NEGATIVE REINFORCEMENT IN THE TREATMENT OF ESCAPE-MAINTAINED DESTRUCTIVE BEHAVIOR

We identified 3 clients whose destructive behavior was sensitive to negative reinforcement (break from tasks) and positive reinforcement (access to tangible items, attention, or both). In an instructional context, we then evaluated the effects of reinforcing compliance with one, two, or all of these consequences (a break, tangible items, attention) when destructive behavior produced a break and when it did not (escape extinction). For 2 clients, destructive behavior decreased and compliance increased when compliance produced access to tangible items, even though destructive behavior resulted in a break. For 1 client, extinction was necessary to reduce destructive behavior and to increase compliance. Subsequently, when the schedule of reinforcement for compliance was faded for all clients, destructive behavior was lower and fading proceeded more rapidly when compliance produced multiple functional reinforcers (i.e., a break plus tangible items or attention) and destructive behavior was on extinction. The results are discussed in terms of the effects of relative reinforcement value and extinction on concurrent operants.     

Diversity and deliberation: bioethics commissions and moral reasoning

This article considers the sort of diversity in perspective appropriate for a presidential commission on bioethics, and by implication, high-level governmental commissions on ethics more generally. It takes as its point of comparison the respective reports on human cloning produced by the National Bioethics Advisory Commission, appointed by President Bill Clinton, and George W. Bush's President's Council on Bioethics, under the leadership of its original chair, Leon Kass. I argue that the Clinton Commission Report exemplifies forensic diversity (the type of diversity between contesting parties in a legal case), while the Kass Council Report exemplifies academic diversity (the diversity found in a medieval disputatio). Drawing upon Thomas Aquinas, I argue that the type of diversity most appropriate for such advisory bodies is deliberative diversity, which facilitates the President's process of taking counsel. After considering their respective charges, I suggest that neither the Clinton Commission nor the Kass Council possessed an adequate degree of deliberative diversity for their respective tasks.     

What you see is what you get: functional equivalence of a perceptually filled-in surface and a physically presented stimulus

A perceptually filled-in surface, such as occurs during sustained attention to a peripheral stimulus (Troxler fading), can be functionally equivalent to a physically presented stimulus. Observers failed to detect probes that were presented in the location of a filled-in surface that had the same surface attributes as the probes; this was true even though, physically, the probes contrasted with the background. Probe stimuli with surface characteristics different from those of the filled-in surface were detected more often, though not quite as often as when there was no filled-in surface. Together, these findings support the idea that there are two components in perceptual filling: a neural filling-in component and a sustained-attention component, which actively suppresses perceptual processing at the filled-in location. More broadly, they illustrate the interplay of basic visual mechanisms in the creation and representation of visual surfaces and in the coding and detection of changes to these surfaces.     

Using food redistribution to reduce packing in children with severe food refusal

Positive- and negative-reinforcement-based procedures typically have targeted acceptance for children with severe food refusal; however, these procedures do not always result in successful swallowing. Once acceptance is achieved, some children expel the food repeatedly or pack (hold or pocket) it in their mouths for extended periods of time. This study evaluated the effects of using food redistribution with a bristled massaging toothbrush to reduce packing and increase consumption in 4 children with severe feeding disorders. Packing was reduced for all children. In addition, latency to clean mouth (the duration of time from acceptance to food no longer being present in the child's mouth in the absence of expulsion) for 2 children decreased when the food-redistribution procedure was used. Results are discussed in terms of the potential operant functions of the food-redistribution procedure.     

On the effectiveness of and preference for punishment and extinction components of function-based interventions

The current study describes an assessment sequence that may be used to identify individualized, effective, and preferred interventions for severe problem behavior in lieu of relying on a restricted set of treatment options that are assumed to be in the best interest of consumers. The relative effectiveness of functional communication training (FCT) with and without a punishment component was evaluated with 2 children for whom functional analyses demonstrated behavioral maintenance via social positive reinforcement. The results showed that FCT plus punishment was more effective than FCT in reducing problem behavior. Subsequently, participants' relative preference for each treatment was evaluated in a concurrent-chains arrangement, and both participants demonstrated a dear preference for FCT with punishment. These findings suggest that the treatment-selection process may be guided by person-centered and evidence-based values.     

Object updating and the flash-lag effect

Flash lag is a misperception of spatial relations between a moving object and a briefly flashed stationary one. This study began with the observation that the illusion occurs when the moving object continues following the flash, but is eliminated if the object's motion path ends with the flash. The data show that disrupting the continuity of the moving object, via a transient change in size or color, also eliminates the illusion. We propose that this is because a large feature change leads to the formation of a second object representation. Direct evidence for this proposal is provided by the results for a corollary perceptual feature of the disruption in object continuity: the perception of two objects, rather than only one, on the motion path.     

On the relative contributions of positive reinforcement and escape extinction in the treatment of food refusal

We compared the effects of positive reinforcement alone, escape extinction alone, and positive reinforcement with escape extinction in the treatment of the food and fluid refusal of 4 children who had been diagnosed with a pediatric feeding disorder. Consumption did not increase when positive reinforcement was implemented alone. By contrast, consumption increased for all participants when escape extinction was implemented, independent of the presence or absence of positive reinforcement. However, the addition of positive reinforcement to escape extinction was associated with beneficial effects (e.g., greater decreases in negative vocalizations and inappropriate behavior) for some participants.