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Biomedical subjects

A Silberberg

Publications and source records attributed to A Silberberg.

At least 73 records · Page 4Linked to original sources
PubMed1976

Aging and the interstitial content of loose connective tissue. A brief note.

The concentration of hyaluronic acid which is the fixed loose connective tissue component determining water and other potentials in the interstitium remains constant with age. Since the collagen fiber network in the native tissue state is unstressed, changes in collagen fiber morphology and in collagen content with age have no influence.

Aging↗
PubMed1976

Conditions of flow at interfaces with flexible walls.

It is shown that the presence of highly deformable surface layers of low elastic modulus produce effects in flow that tend to reduce throughout. This phenomenon seems to be due to the generation of surface waves and a corresponding fluid zone into which these waves are also partially propagated. Experiments are summarized that are consistent with this point of view. The implications for arterial and other blood flow are discussed.

Arteries↗
PubMed1976

The effect of a strongly-interacting macromolecular probe on the swelling and exclusion properties of loose connective tissue.

Poly(L-lysine), a cationic polypeptide known to undergo specific interactions with acid mucopolysaccharides, is used as a macromolecular probe in an investigation into the structure of loose connective tissue. The polypeptide apparently binds, via an electrostatic mechanism, to the mucopolysaccharide component of the tissue, leading to a reduction in the swelling of the tissue. The polypeptide does not, however, have a deswelling effect on the tissue; the ultimate reduction in swelling is influenced by the absolute amount of polybase which enters the tissue during the swelling process. Dextran 2000 is found to have a dwelling effect on the tissue which is independent of the action of the polypeptide; this is suggestive of a large degree of independence between the collagen network and the mucopolysaccharide-containing matrix. The polypeptide, moreover, causes a reduction in the excluded volume of the tissue.

Arginine↗
PubMed1975

Behavioral contrast in the pigeon: a study of the duration of key pecking maintained on multiple schedules of reinforcement.

Pecks on an operant key were reinforced on either multiple variable-interval variable-interval or multiple variable-interval extinction schedules of reinforcement. The stimuli that signalled the multiple-schedule components were located on a second key (signal key), and a changeover delay prevented reinforcement of signal key-peck-operant key-peck sequences. No behavioral contrast was observed on the operant key, and appreciable responding to the signal key occurred during the variable-interval component of the multiple variable-interval extinction procedure. Peck durations on the signal key were markedly shorter than peck durations on the operant key. Moreover, most responses on the signal key occurred just after the multiple-schedule components changed. These data support an account of behavioral contrast in terms of the summation of pecks that are separately controlled by stimulus-reinforcer and response-reinforcer dependencies, and suggest that the stimulus-reinforcer dependency is responsible primarily for local contrast. In addition, the data suggest that pecks that are controlled by these two dependencies may belong to topographically different classes.

Journal Article↗
PubMed1975

Stray animals: their impact on a community.

The statistical import of the study not-withstanding, we found the most serious problem to be the lack of understanding of the pet population crisis and compassion toward animals on the part of pet owners, as evident in the pet columns of the classified ads. Our study leads us to believe that pet owners are allowing the reproduction of kittens and puppies in such numbers that they often have no cash value and, in fact, the owners will spend money, in the form of advertising, to facilitate their disposal. The street observations indicated that relatively few animals (lessthan 1%) actually are allowed to run free. Dog bites occur at a ratio of 1:20 for the dog population. In the area under study, free roaming dogs and cats present a mild to moderate problem, originating from a small percentage of pet owners. Only a small amount of pet animal suffering occurs by death from environmental hazards (ie, automobiles), and there is just a moderate amount of intentional killing of nondersirable pet animals. We fell the method used in this study and the results obtained from it have importance elsewhere. It should be coupled with a broader based survey questionnaire to better establish the ratio of pet ownership to the general population and the reasons and benefits of pet ownership. We could then have the "facts" about the pet overpopulation problem, as well as better understand the community values toward pet animals. A complete report with additional accompanying tables is available from the senior author at Rural Route One, Urbana, Illinois 61801.

Adolescent↗
PubMed1974

Modulation of the copulatory sequence of the male rat by a schedule of reinforcement.

Copulating male rats were permitted a maximum of seven intromissions in which to ejaculate. This experimental constraint of the male rat's sexual behavior produced an increase in the number of sessions in which the male ejaculated before the seventh intromrission. This species-specific behavior pattern is therefore susceptible to environmental conditioning.

Animals↗
PubMed1974

Choice behavior on discrete trials: a demonstration of the occurrence of a response strategy.

Three pairs of pigeons were trained to peck at two keys presented simultaneoulsy in discrete trials with intertrial intervals of 1, 22, or 120 sec. Left-key responses incremented the probability of reinforcement for the first right-key response and, conversely, right-key responses incremented the probability of reinforcement for the first left-key response. In terms of relative response rates, it was found that all birds' choices were described by a momentary maximizing strategy, but this fact was not reflected in the detailed sequential statistics for birds with the longer (22 or 120 sec) intertrial intervals. It was hypothesized that choice behavior, in general, may be accurately described by a momentary maximizing sequence, but that prior failures to demonstrate this were due to "errors" in executing the momentary maximizing sequence. These misappropriated responses, which are hypothesized to be randomly distributed among the responses defining the momentary maximizing sequence, caused successive choices to appear to be statistically independent when, in fact, they were not.

Journal Article↗
PubMed1974

A yoked-chamber comparison of concurrent and multiple schedules: the relationship between component duration and responding.

Two experimental chambers were electrically connected so that the component selected by a pigeon confronting concurrent variable-interval schedules in one chamber could be successively presented as a multiple schedule to a second pigeon in the other chamber. Component duration was regulated by the use of a changeover delay, the value of which was systematically varied between 0 and 30 sec. It was found that the relative local response rates on the preferred key (absolute response rate to that component divided by the sum of the absolute response rates during both components) tended to increase with increasing component durations for the birds in the concurrent chamber, but decreased for the birds in the multiple chamber. These data support the interpretation that there are fundamental differences in the mode of responding to multiple and concurrent schedules. Based on these findings, it was concluded that previous demonstrations of matching on multiple schedules do not establish that response allocation is controlled by a process equivalent to that found on choice paradigms. It now appears that matching on multiple (but not concurrent) schedules is a consequence of selecting short component durations. The implications of these data for Herrnstein's (1970) and Rachlin's (1973) formulations of the relationship between multiple and concurrent schedules are examined.

Journal Article↗
PubMed1974

Lever-contact responses in rats: automaintenance with and without a negative response-reinforcer dependency.

Pairing the presentations of one lever (cueing lever) with food led to the acquisition and persistence of lever contacts by rats. This behavior did not occur with a second lever, which was presented randomly with regard to food delivery. This finding obtained whether food delivery was independent of cueing-lever contacts (positive automaintenance) or dependent on the absence of cueing-lever contacts (negative automaintenance). The general findings were: (1) cueing-lever contacts on the positive automaintenance procedure occurred on a higher proportion of trials and at higher rates when contacts occurred than on the negative automaintenance procedure; (2) instances of the cueing lever's failure to support responding were more frequent on the negative than the positive automaintenance procedure; and (3) the topography and median contact duration of positively automaintained responding differed from negatively automaintained responding. These findings agree substantially with the automaintenance literature on pigeons, suggesting that similar processes may characterize automaintained responding in both pigeons and rats.

Journal Article↗
PubMed1970

Choice, rate of reinforcement, and the changeover delay.

Pigeons distribute their responses on concurrently available variable-interval schedules in the same proportion as reinforcements are distributed on the two schedules only when a changeover delay is used. The present study shows that this equality between proportions of responses and proportions of reinforcements ("matching") is obtained when the value of the changeover delay is varied. When responses are partitioned into the set of rapid response bursts occurring during the delay interval and the set of responses occurring subsequently, the proportion of neither set of responses matches the proportion of reinforcements. Instead, each set deviates from matching but in opposite directions. Matching on the gross level results from the interaction of two patterns evident in the local response rates: (I) the lengthening of the changeover delay response burst is accompanied by a commensurate decrease in the number of changeovers; (2) the changeover delay response burst is longer than the scheduled delay duration. When delay responses are eliminated by introducing a blackout during the delay interval, response matching is eliminated; the pigeon, however, continues to match the proportion of time spent responding on a key to the proportion of reinforcements obtained on that key.

Journal Article↗