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Biomedical subjects

A Silberberg

Publications and source records attributed to A Silberberg.

At least 37 records · Page 2Linked to original sources
PubMed1990

Income maximizing on concurrent ratio-interval schedules of reinforcement.

Three experiments examined the effect of food availability on pigeons' choice behavior under concurrent schedules of reinforcement. In Experiment 1, 3 pigeons earned their daily food ration by choosing, in 30-min sessions, between concurrent variable-ratio 30 variable-interval 40-s schedules. Food presentations during both schedules lasted 2 or 12 s, depending upon the condition. Relative variable-ratio response rate was inversely related to hopper duration. In Experiment 2, 4 pigeons received their daily feeding by responding on the same schedule pair as in Experiment 1 (with 4-s food presentations) in sessions that varied in length from 10 to 30 min, depending on the condition. The length of a vertical slit projected on a response key increased with time so that "passage of time" might be more easily discriminable. As session duration decreased, relative variable-ratio response rate increased. In Experiment 3, 4 pigeons chose between two variable-interval 40-s schedules. One schedule operated without regard to the schedule selected, whereas the other operated only when the subject responded in its presence (dependent). Although these schedules had the same feedback function, preference for the dependent variable interval increased as session duration decreased from 30 to 10 min. The preference changes in these studies reveal the operation of an income-maximizing process in choice.

Journal Article↗
PubMed1990

On mucociliary transport.

The periodically changing flow pattern in the mucus layer which lies between the ciliary tips and the transported load is discussed and analyzed. The resulting energy dissipation per cilium is estimated, as is the energy dissipated per cilium in the periciliary fluid. The rate of supply of energy to each cilium by far exceeds these two loss rates. It is shown why the elastic character of mucus is important for good momentum transfer from cilium to load and for good load carrying properties. Fast flow requirements upon secretion of mucus, on the other hand, make it desirable that elasticity and viscosity be low as possible. A compromise is needed and the rheological character of mucus is matched to satisfy these opposing demands.

Cilia↗
PubMed1989

Income maximizing in concurrent interval-ratio schedules.

Three mice chose between concurrent variable-ratio variable-interval schedules to produce a warm air stream while they were housed in a cold chamber. Across conditions, the duration of the warm air stream was varied between 10 and 80 s and was equal for both schedules. Preference for the VI schedule covaried with reinforcer duration as predicted by maximizing accounts of choice.

Journal Article↗
PubMed1989

Transport through deformable matrices.

In order to induce and maintain a pressure gradient in a fluid mixture in steady state, the fluid has to pass through a solid-like matrix capable of generating and carrying an extra stress gradient. Frictional interactions between fluid components and the matrix then produce separations. Matrix deformation occurs and the implication of this is discussed. A general solution for multicomponent systems is given and then specialised to the case of three components--a deformable gel matrix component, a solvent and a macromolecular solute. A method is given for solving the system of equations and is applied in the steady state. Applications involving transendothelial flow and self-regulated selectivity are stressed in particular. The calculations are based on the Flory-Huggins equation, on the Flory gel deformation model and on ad hoc, very crude approximations to the concentration dependence of the three, pairwise defined friction coefficients between the three components involved.

Biological Transport↗
PubMed1989

Mucus glycoprotein, its biophysical and gel-forming properties.

The mucus glycoprotein molecules of mildly solubilised mucus have been called 'the first units into solution'. These are strand-like, randomly coiling macromolecules 0.5 to 50M. Dalton in molecular weight. Light scattering shows them to be Kuhn coils of a approximately 1000 A long, thin, linearly repeated segment built on a protein chain of about 1000 amino acids, the presumable gene product synthesized by the cell. Mucus, from all sources, involves this glycosylated (approximately 80% sugar) structural subunit, composed of two parts: a bare peptide part, B, and a heavily glycosylated peptide part, T, containing all the sugar in some 200 O-glycosidically linked side chains. The network required for the rheological functioning of mucus, the mucus gel, is built up of these units. A large number of cysteines occur in the bare protein region B. As the crosslink, therefore, either a direct intermolecular disulfide bond (B to B), or a disulfide bond stabilized lectin protein-to-sugar bond (B to T), is presumed to be involved. There may be two levels of crosslinking. Bonds entered into in nascent mucus may be labile, and a freshly secreted mucus blob swells easily. Later on the links seem to become more stable, no longer exchange with ease and there is little swelling. The gel network in mucus may not be infinite, but only an effectively entangled system of very large molecules. On normally functioning respiratory epithelia, indeed, the network may only be transient. Anything which destroys the bare peptide region, e.g. proteolysis, dissolves the network and yields T-domains. There is at most a side-to-side association of the individual glycoprotein subunits in the network strands and rather few branches. The lectin hypothesis for the crosslink would give the cell very easy control over the structural and rheological properties of the secreted product. In the context of the lectin hypothesis it is proposed that the so-called 'link' protein of intestinal mucus is a degraded part of the B+T subunit, the B part plus some of the adjacent T domain. The 'link' protein would thus contain the lectin and would stay bound until released by thiol reduction.

Animals↗
PubMed1988

Maximizing present value: A model to explain why moderate response rates obtain on variable-interval schedules.

In Phases 1 and 3, two Japanese monkeys responded on a multiple variable-ratio 80 variable-interval X schedule, where the value of X was adjusted to ensure equal between-schedule reinforcement rates. Components strictly alternated following the delivery of a food pellet, and each session ended following 50 components. Phase 2 differed from the others only in that the 50 pellets previously earned during the session were delivered together at session's end. Variable-ratio response rates did not decrease across phases, but variable-interval response rates decreased substantially during the Phase 2 procedure. This rate decrease was attributed to the food-at-session's-end manipulation removing the greater immediacy of reinforcement provided by short interresponse times relative to long interresponse times. Without this time preference for short interresponse times, the variable-interval interresponse-time reinforcement feedback function largely controlled response emission, dictating a response-rate reduction. This result was explained in terms of the economic notion of "maximizing present value."

Journal Article↗
PubMed1988

Choice in the repeated-gambles experiment.

Humans chose 10 times between two roulette wheels projected on a monitor. During the first trial, the left wheel provided a hypothetical $100 with p = .94, and the right wheel provided $250 with p = .39. A titration procedure adjusted the probability of a $250 win across trials to permit estimation of an indifference point between alternatives. In Experiment 1, intertrial-interval duration (25 vs. 90 s) and whether sessions began with an intertrial interval or a trial were varied in a 2 x 2 design in this risky-choice procedure. Risk aversion (preference for the $100 wheel) increased with intertrial interval but was unaffected by whether sessions began with a trial or an intertrial interval. In Experiment 2, all sessions began with a trial, and subjects were informed that the experiment ended after 10 trials. Intertrial-interval duration had no effect on choice. In Experiment 3, intertrial-interval duration and whether subjects were given $10 or $10,000 before beginning were varied among four groups in a 2 x 2 design. In all other ways, the procedure was unchanged from Experiment 2. Intertrial interval had no effect on choice, but the $10,000 groups showed less risk aversion than the $10 groups. These results can be explained more readily in terms of Kahneman and Tversky's (1984) notion of "framing of the prospect" than in terms of Rachlin, Logue, Gibbon, and Frankel's (1986) behavioral account of risky choice.

Journal Article↗
PubMed1988

Structure of the interendothelial cell cleft.

Since the work of Bundgaard it is known that the interendothelial cell cleft is a narrow, but open, sometimes highly convoluted gap linking the blood vessel lumen with the subendothelial space. A remarkable feature of this cleft is its constant width. It is here suggested that electrostatic repulsions, and the presence of a system of posts between the walls act to maintain cleft width. Contrary to intuition the presence of posts would not constitute an intolerable increase in hydrodynamic resistance, since no massive posts are necessary. Links between the walls involving only a single macromolecular chain each, which would be very difficult to detect ultrastructurally, would, nevertheless, particularly when charged, act as extremely stiff springs of essentially fixed length. A detailed calculation is presented to show how this idea could work and it is proposed that similar such posts support the subendothelial layers. Recent ultrastructural evidence in support of single chain links is quoted.

Animals↗
PubMed1987

Income and choice between different goods.

In Experiment 1, 3 rats chose between two simultaneously operating variable-interval schedules, one of which provided saccharin water and the other, food. In five conditions, the absolute (and equal) reinforcement rates provided by the pair of equal-valued schedules were manipulated in the range of 36 to 240 per hour. Experiment 2 was identical to Experiment 1 except that these schedules operated successively, arranged by requiring the rat to stand on the side of the chamber correlated with each schedule. Food/saccharin choice ratios were inversely related to reinforcement rate in both experiments, although this effect was stronger in Experiment 2. When delivery rates were high, preference for food over saccharin often reversed as the session progressed. The results were interpretable in terms of economic accounts of choice (e.g., the minimum-needs hypothesis), as well as in terms of traditional psychological accounts (e.g., matching theory).

Journal Article↗
PubMed1987

A model for mucus glycoprotein structure.

An approximately 500,000Da subunit characterizes the structural glycoprotein of mucus. This unit is composed of a rod-like very heavily glycosylated protein chain with an unglycosylated cysteine rich region at its end. It is proposed that the 'bare' peptide portion of the subunit forms itself into a lectin by undergoing a disulfide bond stabilised conformational fold. The lectin binding site, R, is assumed to be selective for a rare sugar sequence, which, when present, creates a binding site R. The site R has to be relatively rare. The average number less than s greater than of sidechains which contain R per subunit will only be of order 1. When less than s greater than less than or equal to 1 reasonably long, chain-like aggregates are formed which behave like coiling polymer chains with the subunit the Kuhn statistical element. When less than s greater than much greater than 1 the entire system forms one structure. Data obtained from the literature are analysed. They favor finite size, separate chains. The Kuhn statistical element length, derived from the data, is shown to agree well with the lectin model hypothesis.

Animals↗
PubMed1985

Experimental artifacts in the study of mucociliary transport.

Mucociliary transport was studied on frog palate epithelium preparations. Three preparations were used: the detached palate preparation (prepared by detaching the upper part of the head from the frog), the live frog preparation (prepared by exposing the palate of a sedated live frog), and the thin preparation (prepared by excising a 1-mm thin section). Because the transport behavior in each of the 3 preparations is different, extirpation or sedation or excision, or all 3, introduce artifacts into the system.

Animals↗
PubMed1985

Reanalysis of the equation for simple action.

De Villiers and Herrnstein (1976) have shown that the equation for simple action, derived from the matching law, predicts change in behavioral output for some 40 experiments in which the value of a single source of reinforcement has been varied. Using only the positive-reinforcement studies they cite that used five or more different reinforcement values, we found the high percentage of variance they report accommodated by this equation (94%) is predicated on instances of averaging rates of behavioral output before making a least-squares fit of the equation. In our reanalysis, which minimizes rate averaging, only 78% of the data variance is accommodated. This diminished data-variance accommodation can be improved by adding parameters that permit the equation's scaling constant to change as a function of reinforcement. Although these parameters permit acceptable levels of accommodation of data variance, they correspond to no obvious psychological processes. These findings support the view that the equation for simple action is an inadequate model for behavioral output.

Journal Article↗
PubMed1985

Molecular maximizing characterizes choice on Vaughan's (1981) procedure.

Pigeons keypecked on a two-key procedure in which their choice ratios during one time period determined the reinforcement rates assigned to each key during the next period (Vaughan, 1981). During each of four phases, which differed in the reinforcement rates they provided for different choice ratios, the duration of these periods was four minutes, duplicating one condition from Vaughan's study. During the other four phases, these periods lasted six seconds. When these periods were long, the results were similar to Vaughan's and appeared compatible with melioration theory. But when these periods were short, the data were consistent with molecular maximizing (see Silberberg & Ziriax, 1982) and were incompatible with melioration, molar maximizing, and matching. In a simulation, stat birds following a molecular-maximizing algorithm responded on the short- and long-period conditions of this experiment. When the time periods lasted four minutes, the results were similar to Vaughan's and to the results of the four-minute conditions of this study; when the time periods lasted six seconds, the choice data were similar to the data from real subjects for the six-second conditions. Thus, a molecular-maximizing response rule generated choice data comparable to those from the short- and long-period conditions of this experiment. These data show that, among extant accounts, choice on the Vaughan procedure is most compatible with molecular maximizing.

Journal Article↗
PubMed1984

Stimulation of mucus secretion, ciliary activity, and transport in frog palate epithelium.

Particle transport velocity and ciliary beat frequency, at the level of a single cell of the epithelium, were measured simultaneously. The preparation used keeps the mucociliated epithelium of the frog palate functionally intact but is thin enough for light to be transmitted. The observations confirm that there exists a resting, or unstimulated, state of the epithelium in which the cilia do not beat. It is shown that tactile stimulation (contact with a small 50- to 75-microns foreign particle or with a fine wire probe) restarts ciliary beat. If the epithelium has not been depleted of its mucus, normal ciliary beat frequency is restored, and there is particle transport at the normal velocity. Only the cilia surrounding the moving particle in a patch about 10 times larger are beating at one time. Beat frequency is highest in the center of the patch, near the particle, and tapers to zero toward the edge. Mucus has to be present for particle transport to occur. Particles impacted on a depleted epithelium are not moved. The placement of previously collected endogenous mucus onto a depleted epithelium produces full ciliary activity and normal particle transport. The moving patch of beating cilia corresponds to a plaque of mucus surrounding the particle being transported. This plaque was produced upon first impact of the particle, presumably by mucus secretion, from the epithelial region which then surrounds it. Stimulation of a quiescent nondepleted epithelium with a wire probe induces a normal ciliary beat frequency that gradually decreases to zero. Stimulation by a wire probe of a mucus-depleted epithelium produces a level of initial beat frequency much below normal. Depletion of the epithelial preparation is by an episode of "creeping" over a glass surface. Depletion of the epithelium could be demonstrated histochemically. Analysis of the data of particle velocity and beat frequency is consistent with a wave-length of 45 microns for the metachronous wave.

Animals↗
PubMed1984

Concurrent variable-interval variable-ratio schedules can provide only weak evidence for matching.

Herrnstein and Heyman (1979) showed that when pigeons' pecking is reinforced on concurrent variable-interval variable-ratio schedules, (1) their behavior ratios match the ratio of the schedules' reinforcer frequencies, and (2) there is more responding on the variable interval. Since maximizing the reinforcement rate would require responding more on the variable ratio, these results were presented as establishing the primacy of matching over maximizing. In the present report, different ratios of behavior were simulated on a computer to see how they would affect reinforcement rates on these concurrent schedules. Over a wide range of experimenter-specified choice ratios, matching obtained - a result suggesting that changes in choice allocation produced changes in reinforcer frequencies that correspond to the matching outcome. Matching also occurred at arbitrarily selected choice ratios when reinforcement rates were algebraically determined by each schedule's reinforcement-feedback function. Additionally, three birds were exposed to concurrent variable-interval variable-ratio schedules contingent on key pecking in which hopper durations were varied in some conditions to produce experimenter-specified choice ratios. Matching generally obtained between choice ratios and reinforcer-frequency ratios at these different choice ratios. By suggesting that reinforcer frequencies track choice on this procedure, instead of vice versa, this outcome questions whether matching-as-outcome was due to matching-as-process in the Herrnstein and Heyman study.

Journal Article↗