Biomedical subjects

Ben A Williams

Publications and source records attributed to Ben A Williams.

6 recordsLinked to original sources

PubMed2007

Active spatial perception in the vibrissa scanning sensorimotor system.

Haptic perception is an active process that provides an awareness of objects that are encountered as an organism scans its environment. In contrast to the sensation of touch produced by contact with an object, the perception of object location arises from the interpretation of tactile signals in the context of the changing configuration of the body. A discrete sensory representation and a low number of degrees of freedom in the motor plant make the ethologically prominent rat vibrissa system an ideal model for the study of the neuronal computations that underlie this perception. We found that rats with only a single vibrissa can combine touch and movement to distinguish the location of objects that vary in angle along the sweep of vibrissa motion. The patterns of this motion and of the corresponding behavioral responses show that rats can scan potential locations and decide which location contains a stimulus within 150 ms. This interval is consistent with just one to two whisk cycles and provides constraints on the underlying perceptual computation. Our data argue against strategies that do not require the integration of sensory and motor modalities. The ability to judge angular position with a single vibrissa thus connects previously described, motion-sensitive neurophysiological signals to perception in the behaving animal.

Animals↗

PubMed2005

Heuristics or general learning processes?

The concept of heuristics implies that the rules governing choice behavior may vary with ecological constraints. Behavior analysis, in contrast, seeks general principles that transcend specific situations. To the extent that search is successful, the concept of heuristics is unlikely to play a significant role in the analysis of animal behavior.

Algorithms↗

PubMed2003

Arousal, changeover responses, and preference in concurrent schedules.

Pigeons were trained on multiple schedules that provided concurrent reinforcement in each of two components. In Experiment 1, one component consisted of a variable-interval (VI) 40-s schedule presented with a VI 20-s schedule, and the other a VI 40-s schedule presented with a VI 80-s schedule. After extended training, probe tests measured preference between the stimuli associated with the two 40-s schedules. Probe tests replicated the results of Belke (1992) that showed preference for the 40-s schedule that had been paired with the 80-s schedule. In a second condition, the overall reinforcer rate provided by the two components was equated by adding a signaled VI schedule to the component with the lower reinforcer rate. Probe results were unchanged. In Experiment 2, pigeons were trained on alternating concurrent VI 30-s VI 60-s schedules. One schedule provided 2-s access to food and the other provided 6-s access. The larger reinforcer magnitude produced higher response rates and was preferred on probe trials. Rate of changeover responding, however, did not differ as a function of reinforcer magnitude. The present results demonstrate that preference on probe trials is not a simple reflection of the pattern of changeover behavior established during training.

Animals↗

PubMed2002

Inhibition and superconditioning.

Superconditioning is said to occur when learning an association between a conditioned stimulus (CS) and unconditioned stimulus (US) isfacilitated by pairing the CS with the US in the presence of a previously established conditioned inhibitor. Previous demonstrations of superconditioning have been criticized because their control conditions have allowed alternative interpretations. Using a within-subjects autoshaping procedure, the present study unambiguously demonstrated superconditioning. The results support the view that super-conditioning is the symmetric opposite of blocking.

Animals↗

PubMed2002

Behavioral contrast redux.

Behavioral contrast is defined as a change in response rate during a stimulus associated with a constant reinforcement schedule, in inverse relation to the rates of reinforcement in the surrounding stimulus conditions. Contrast has at least two functionally separable components: local contrast, which occurs after component transition, and molar contrast. Local contrast contributes to molar contrast under some conditions, but not generally. Molar contrast is due primarily to anticipatory contrast. However, anticipatory contrast with respect to response rate has been shown to be inversely related to stimulus preference, which challenges the widely held view that contrast effects reflect changes in stimulus value owing to the reinforcement context. More recent data demonstrate that the inverse relation between response rate and preference with respect to anticipatory contrast is due to Pavlovian contingencies embedded in anticipatory contrast procedures. When those contingencies are weakened, anticipatory contrast and stimulus preference are positively related, thus reaffirming the view that the reinforcing effectiveness of a constant schedule is inversely related to the value of the context of reinforcement in which it occurs. The underlying basis of how the context of reinforcement controls reinforcement value remains uncertain, although clear parallels exist between contrast and the effects of contingency in both Pavlovian and operant conditioning.

Animals↗

PubMed2002

Preference and resistance to change in concurrent variable-interval schedules.

Pigeons were trained on a multiple schedule in which separate concurrent schedules were presented in the two components of the schedule. During one component, concurrent variable-interval 40-sec variable-interval 80-sec schedules operated. In the second component, concurrent variable-interval 40-sec variable-interval 20-sec schedules operated. After stable baseline performance was obtained in both components, extinction probe choice tests were presented to assess preference between the variable-interval 40-sec schedules from the two components. The variable-interval 40-sec schedule paired with the variable-interval 80-sec schedule was preferred over the variable-interval 40-sec schedule paired with the variable-interval 20-sec schedule. The subjects were also exposed to several resistance-to-change manipulations: (1) prefeeding prior to the experimental session, (2) a free-food schedule added to timeout periods separating components, and (3) extinction. The results indicated that preference and resistance to change do not necessarily covary.

Animals↗