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Biomedical subjects

D R Williams

Publications and source records attributed to D R Williams.

At least 325 records · Page 18Linked to original sources
PubMed1971

Classical conditioning of a complex skeletal response.

The pigeon's so-called "arbitrary" response of pecking an illuminated disk can be established and maintained by procedures resembling those of classical conditioning. This phenomenon was shown to be independent of the specific signaling relationships between illumination of the pecking disk and presentation of food; it will appear as long as the key is differentially associated with food. When a nondifferential condition is introduced, pecking "extinguishes" even if it has previously been established and even when the new condition involves as much reinforcement as the old one. Reinstating differential conditions reestablishes pecking. The initial conditions determine the speed and apparently the asymptote of pecking rates in the differential condition; initial exposure to a nondifferential procedure retards subsequent acquisition, possibly quite permanently. These findings are discussed in the context of mechanisms of adaptive learning, not involving reward and punishment, which lead to selection of effective behaviors on a nonarbitrary basis.

Animals↗
PubMed1971

Discrete-trials spaced responding in the pigeon: the dependence of efficient performance on the availability of a stimulus for collateral pecking.

Four pigeons were exposed to a discrete-trial schedule in which only responses spaced by at least 6 sec were reinforced. After 45, fifty-trial sessions, they failed to meet the spacing requirement in over 90% of the trials. When an alternative, non-contingent key (pecks on which had no consequence) was illuminated concurrently with the first key, the spacing performance of the three pigeons that pecked the non-contingent key improved so that they were obtaining 75% of the possible reinforcers. These data demonstrated the importance of collateral behavior in mediating spaced performance. It was suggested that pigeons may successfully refrain from responding on the spacing procedure only when another stimulus correlated with reinforcement is available for pecking, and that the form that collateral behavior takes may, in general, be non-arbitrary, and species dependent.

Journal Article↗
PubMed1969

Auto-maintenance in the pigeon: sustained pecking despite contingent non-reinforcement.

If a response key is regularly illuminated for several seconds before food is presented, pigeons will peck it after a moderate number of pairings; this "auto-shaping" procedure of Brown and Jenkins (1968) was explored further in the present series of four experiments. The first showed that pecking was maintained even when pecks turned off the key and prevented reinforcement (auto-maintenance); the second controlled for possible effects of generalization and stimulus change. Two other experiments explored procedures that manipulated the tendency to peck the negatively correlated key by introducing alternative response keys which had no scheduled consequences. The results indicate that pecking can be established and maintained by certain stimulus-reinforcer relationships, independent of explicit or adventitious contingencies between response and reinforcer.

Journal Article↗
PubMed1968

The structure of response rate.

Interresponse time distributions of the terminal rate under fixed-interval and fixed-ratio schedules were examined, using data from three rats in each case. By means of a sequential analysis, the overall interresponse time distributions were separated into orderly components. Consideration of the component distributions suggested that multiple determinants of rate act in succession, not simultaneously, and that probability of reinforcement has an important effect on the probability of occurrence of interresponse times.

Animals↗
PubMed1967

Time-dependent contrast effects in a multiple schedule of food reinforcement.

Four rats were rewarded for running in a wheel under two alternating conditions of food reinforcement. These periods of frequent and infrequent reinforcement, each accompanied by a particular stimulus, were presented a number of times in each daily session. Following shifts from high to low frequency of reinforcement, responding decreased suddenly and markedly, and then recovered within the next few minutes. The magnitude of this temporary depression was an increasing function of the duration of the immediately preceding component of high-frequency reinforcement. A transient elevation in performance, which did not vary with the duration of the prior component, was noted in two subjects following shifts from low to high frequency of reinforcement. The elevation and depression effects did not appear simultaneously during the 48 experimental sessions. A possible relation between the difficulty of the discrimination and the extent of contrast effects is discussed.

Animals↗
PubMedDate not supplied

Anal complications in Crohn's disease.

Anal fissures, fistulas, and abscesses occurred as complications in 22 per cent of our population of 1,098 patients with Crohn's disease. Crohn's colitis was much more frequently associated with an anal lesion than Crohn's disease of the small bowel (52 per cent vs. 14 per cent). When an anal lesion is the manifesting sign, Crohn's disease will soon develop elsewhere in the intestine. Since these lesions frequently herald the onset of intestinal Crohn's disease, the physician must always be aware of the possibility of inflammatory bowel disease when dealing with suspicious anal lesions.

Abscess↗
PubMedDate not supplied

Credentialing certified nurse-midwives.

As the U. S. health care system struggles to respond to demands for accessible, quality, sensitive, and cost-effective care, the contribution of nurse-midwives is receiving renewed attention. Many institutions are seeking assistance as they move to credential certified nurse-midwives for the first time or as they reassess their credentialing policies and procedures. This article provides an extensive review of multiple issues relating to credentialing nurse-midwives including nurse-midwifery education, licensure, scope of practice, professional liability, relationship with physicians, and delineation of privileges. The article also reviews Medicare Hospital Conditions of Participation and Joint Commission on Accreditation of Healthcare Organizations requirements as they relate to nurse-midwifery practice.

Credentialing↗
PubMedDate not supplied

The JCAHO medical staff standards. Impact on clinical privileges for nurse-midwives.

This article reviews the history and structure of the Joint Commission on Accreditation of Healthcare Organizations (JCAHO). With particular focus on the Licensed Independent Practitioner, it reviews the significant content of the 1996 JCAHO Medical Staff Standards. A plan of action is proposed that supports the development of professional staff bylaws that accurately reflect CNM education and licensure and that provide access to the same system of due process available to physicians and dentists.

Accreditation↗