Search PubMed⌕ Search

Biomedical subjects

D R Schmitt

Publications and source records attributed to D R Schmitt.

11 recordsLinked to original sources
PubMed2001

Near point-source longitudinal and transverse mode ultrasonic arrays for material characterization.

Specially constructed near point-source ultrasonic transducers (0.75 MHz) were designed to preferentially stimulate and receive the one longitudinal (P) and two transverse (S) propagation modes. Arrays of these transducers were placed on a rectangular prism of common sodalime glass, which served as an ideal homogeneous, isotropic medium, to evaluate the uncertainty of a newly developed phase velocity measurement method. Through the use of the Radon transform, the data were transformed from the offset-time (x-t) domain to the intercept time--horizontal slowness (tau-p) domain. From the shape of the curves in the tau-p domain, the phase velocity of the propagating waves may be determined for a range of directions. The phase velocities determined using this method were accurate for incidence angles up to 76 degrees, 64 degrees, and 77 degrees for the P, SV, and SH wave modes, respectively. Phase velocities of 5724 +/- 64, 3411 +/- 30, and 3467 +/- 15 m/s were determined for the P-wave, SV-wave, and SH-wave modes, respectively. This agrees with the direct transmission P-wave and S-wave velocities of 5690 +/- 60 and 3440 +/- 26 m/s, respectively, to better than 1%.

Journal Article↗
PubMed2000

Effects of competitive reward distribution on auditing and competitive responding.

This study allowed subjects to audit each other's responding during a series of competitive contests. Six pairs of female college students competed in 3-min contests in which the competitive response was a knob pull. A sum of money was divided using a proportional distribution or a 100%/0% reward distribution. In the proportional distribution, a subject's proportion of the sum was her proportion of the total number of responses. Also, in every contest either subject could make a response that would end the contest prematurely and give both subjects the same amount: a sum equal to 33% of the competitive total. Each subject could press either or both of two audit buttons that displayed her own and the other's response total for 10 s. Results replicated earlier findings in showing the superiority of the proportional distribution in total number of competitive responses made. No subject audited continuously, and only 1 audited most of the time. Most audits were interpersonal, including both own and other's scores. Auditing typically was more frequent in 100%/0% contests in which subjects were more likely to stop the contest when they were far behind. Winners were more likely to audit than were losers. Competitive response rates increased when the differences revealed by audits were small and decreased when they were large. Overall audit patterns were consistent with the view that feedback as "news" is more often sought when it can lead to improved outcomes.

Adult↗
PubMed1987

Interpersonal contingencies: Performance differences and cost-effectiveness.

Three reinforcement contingencies were compared with regard to performance differences and cost-effectiveness (i.e., responses per unit reinforcer). Pairs of college students were studied under individual, cooperative, or competitive contingencies using a concurrent setting that included one of these three contingencies as one alternative and a lower paying individual contingency as the other alternative. With the individual and the cooperative contingencies, overall response rates were typically high; under competitive contingencies the overall response rates were substantially lower. Subjects responded at very high rates when competing, but chose not to compete most of the time. Competition and cooperation produced the most cost-effective responding, assessed as the number of responses made per $.01 of reinforcer. High overall rates of competitive responding were obtained when the contests were longer and the lower paying alternative contingency was not available.

Journal Article↗
PubMed1984

Interpersonal relations: Cooperation and competition.

Social relations between two persons require that consequences each receives depend at least in part on the responses of the other. Historically, research in several areas has focused on two contingencies, cooperation and competition, in which reinforcement is determined by the responses of both participants. A major research question in social psychology and applied behavior analysis has been: Which contingency is more effective with regard to the quantity or quality of some response? Although this question has not been addressed in the experimental analysis of behavior, this area provides a perspective and method to more fully investigate the relevant controlling variables. Among these are the frequency of opportunities to audit the performances of others, information (or lack of it) provided by social or nonsocial stimuli with regard to reinforcement and performance, degree of face-to-face interaction, types of reinforcement contingencies, and number of participants. A neglected dependent variable is cost effectiveness-amount of behavior maintained by a given reinforcer amount. The larger agenda for the experimental analysis of interpersonal relations includes a variety of forms of reinforcement interdependence that raise issues of basic and applied interest.

Journal Article↗
PubMed1976

Some conditions affecting the choice to cooperate or compete.

Three experiments investigated conditions affecting the choice to cooperate or compete. Experiment I compared the effects first of an individual activity, then of a competitive task as an alternative to cooperation. For both comparisons, subjects could earn more by cooperating. Choice of competition, but not individual activity, was found to depend on the task choice contingencies. Competition predominated when both subjects could compete if either or both chose competition. Previously competitive pairs cooperated when both subjects could cooperate if either or both chose cooperation. Experiment II investigated the effects of differences in magnitude of the reinforcers for cooperating or competing. Choice between the two alternatives was manipulated in all pairs by varying reinforcer difference. Competition was chosen over cooperation only within the limits within which competition was potentially profitable. Experiment III replicated the findings of Experiment II using triads. Subjects in triads, however, were more likely to withdraw from the experiment. Thus, the data for pairs and triads suggest an orderly relation between reinforcer difference for cooperating or competing and task choice. Motivation of subjects to maximize relative gain by competing can be overridden by moderate reinforcer differences favoring cooperation.

Journal Article↗
PubMed1974

Effects of reinforcement rate and reinforcer magnitude on choice behavior of humans.

Two experiments with human subjects investigated the effects of rate of reinforcement and reinforcer magnitude upon choice. In Experiment 1, each of five subjects responded on four concurrent variable-interval schedules. In contrast to previous studies using non-human organisms, relative response rate did not closely match relative rate of reinforcement. Discrepancies ranged from 0.03 to 0.43 (mean equal to 0.19). Similar discrepancies were found between relative amount of time spent responding on each schedule and the corresponding relative rates of reinforcement. In Experiment 2, in which reinforcer magnitude was varied for each of five subjects, similar discrepancies ranging from 0.05 to 0.50 (mean equal to 0.21), were found between relative response rate and relative proportion of reinforcers received. In both experiments, changeover rates were lower on the long-interval concurrent schedules than on the short-interval ones. The results suggest that simple application of previous generalizations regarding the effects of reinforcement rate and reinforcer magnitude on choice for variable-interval schedules does not accurately describe human behavior in a simple laboratory situation.

Journal Article↗
PubMed1971

Taking and the disruption of cooperation.

Subjects could either cooperate or respond on a lower-paying individual task. In Exp. I and II, either subject could make a response that took $1.00 of the other's earnings whenever subjects chose to cooperate. The two experiments differed as to whether taking responses were effective continuously or intermittently. Both experiments showed that the opportunity to take disrupted cooperative behavior. Experiment III indicated that if taking was possible regardless of whether the subjects cooperated or responded on the individual task, subjects either cooperated or terminated the experiment.

Journal Article↗
PubMed1971

Avoidance of risk as a determinant of cooperation.

Pairs of subjects could either cooperate or respond on a lower paying individual task. Whenever both subjects chose to cooperate, either subject could make a response that took $1.00 of the other's earnings. In Exp. I, a stimulus signalled when a "take" response had been made. Either subject could avoid the loss by switching to the individual task within 5 sec after the stimulus appeared. Rates of cooperation were high when losses could be avoided but decreased again when the avoidance condition was removed. In Exp. II, a response prevented "takes" from occurring for a specified time interval after the response. This procedure also maintained cooperation. When each avoidance response subtracted from earnings, both avoidance responding and cooperation were eliminated.

Journal Article↗
PubMed1968

Stimulus control in the experimental study of cooperation.

The cooperative responses of pairs of human subjects were reinforced under several stimulus conditions in two settings designed to require a "social" response, i.e., where at least one of the two persons is responding to the behavior of the other. The first task, designed by Lindsley and Cohen, required individual responses within 0.5 sec of one another for reinforcement. The second (modified) task required a delay of 3 sec between individual responses. To determine dependence of cooperation on social stimuli, rates of cooperative behavior on these tasks were compared in the presence and absence of a stimulus indicating to each subject the other's response and a stimulus which indicated the duration of the timeout after reinforcement. The results indicated that only in the modified task was a high rate of cooperation always contingent upon the presence of the social stimuli.

Humans↗