Biomedical subjects

M Davison

Publications and source records attributed to M Davison.

At least 91 records · Page 5Linked to original sources

PubMed1985

Sensitivity of time allocation to concurrent-schedule reinforcement.

Four pigeons were trained on concurrent variable-interval schedules programmed on a center response key, with access to those schedules controlled by responses on left or right side keys. Two procedures were used. In one, the pigeon was given limited access, in that each side-key response produced 3-s access to a center-key schedule, and in the other procedure, access was unlimited. Data were analyzed using the generalized matching law. Comparison of sensitivities to reinforcement of interchangeover time for both procedures showed them to be of similar magnitude. Response sensitivities were also similar in magnitude for both procedures. From the limited-access procedure a second time measure that was available, switched-in time, was relatively uncontaminated by time spent emitting behavior other than key pecking. Sensitivities to reinforcement for the switched-in time measure were always smaller than interchangeover-time sensitivities for either procedure, and were approximately equal to response sensitivities for the limited-access procedure. Two other access times (5 and 7.5 s) were studied to validate the choice of 3 s as the main access time. These results indicate that when time spent emitting other behavior is excluded from interchangeover time, time and response sensitivities will be approximately equal.

Journal Article↗

PubMed1984

The structure of mammalian rod opsins.

Ovine rhodopsin is organised in disc membranes as a monomer. The determination of its amino acid sequence has permitted the utilisation of structure prediction programmes which indicate the probable disposition of the polypeptide chain in the bilayer. This putative model is consistent with labelling data using the chemical probes, [14C]succinic anhydride, [125I]diazodiido sulphanilic acid and [125I]iodophenyl azide, and with the cleavage points for several proteases. More surprisingly the predicted structure points to the occurrence of breaks/distortions in the transmembrane helical segments. These distorted regions may be of primary functional importance to the protein and at least one is associated with the attachment point of the chromophore. This particular part of the structure is also identified as a "mutational hot spot", for bovine, equine, ovine and porcine opsins exhibit different sequences (but conserved molecular volumes) in the four residues following the retinyllysine. In an otherwise highly conserved protein with no obvious functional differences between the four species, the high substitution rate in this region is unexplained.

Amino Acid Sequence↗

PubMed1984

A microprocessor-based system for readout of x-ray penetrameter films.

A microprocessor-based instrument has been constructed which allows rapid analysis of a standard penetrameter film using a handheld probe. Compensation for non-uniformity of the X-ray viewing box used as a light source is automatic and there is a paper record of procedures and results. Calibration data for the penetrameter can be easily modified. The instrument can also be used for spot readouts of optical density.

Humans↗

PubMed1984

Concurrent variable-interval schedule performance: Fixed versus mixed reinforcer durations.

Six pigeons were trained on concurrent variable-interval schedules. Two different reinforcer durations were arranged on the left key, and which of these was delivered was determined probabilistically. A single reinforcer duration was arranged on the right key. In Parts 1 and 3 of the experiment, the probability of the left-key reinforcer durations (1 and 7 seconds in Part 1; 3 and 10 seconds in Part 3) was varied from 0 to 1, keeping the schedules constant and the right-key reinforcer at 3 seconds. Response allocation to the left key fell as the probability of the shorter left-key reinforcer duration was increased. In Part 2, one left-key reinforcer duration was 3 seconds and the other was varied from 0 to 10 seconds, while again the schedules and right-key reinforcer duration (3 seconds) were kept constant. Left-key response allocation increased as the varied reinforcer duration on the left key increased. An extension of the generalized matching law failed to provide a good description of response allocation in these procedures. In Part 4, the left- and right-key reinforcer durations were 3 seconds and the variable-interval schedules were varied. Response allocation was well described by the generalized matching law. Part 5 arranged equal variable-interval schedules on the left and right keys, 3-second reinforcers on the right key, and the left-key reinforcer durations were varied from 1 to 10 seconds. The relationship between the log response and reinforcer-duration ratios was nonlinear. The effects of varying reinforcer durations in concurrent schedules cannot be described using the generalized matching law with constant parameters. It is suggested more generally that this quantitative relation may not describe performance either when reinforcing situations differ in duration (e.g., with delayed reinforcers) or when response requirements differ in duration.

Journal Article↗

PubMed1984

Delayed signal detection, differential reinforcement, and short-term memory in the pigeon.

In two discrete-trial delayed-detection experiments, six pigeons were trained on dependent concurrent variable-interval schedules. Pecking a red side key was reinforced when the brighter of two white lights (S1) had been presented on the center key, and pecking a green side key was reinforced when the duller of two white lights (S2) had been presented on the center key. Incorrect responses were red side-key pecks following S2 presentations and green side-key pecks following S1 presentations; these resulted in three-second blackouts. In Experiment 1, the time between presentation of S1 or S2 on the center key and the onset of the red and green side keys was varied nonsystematically from 0.06 seconds to 19.69 seconds across experimental conditions. Stimulus discriminability decreased as the stimulus-choice delay increased. A rectangular-hyperbolic function better described this decrease in discriminability over time than did a negative-exponential function. In Experiment 2, at each of three stimulus-choice delays (0.06, 3.85, and 10.36 seconds), relative reinforcer frequency for correct responses to the red and green side keys was varied by changing the values of the dependent concurrent variable-interval schedules. The sensitivity of choice to relative reinforcer frequency was independent of the decrease in stimulus discriminability with increasing stimulus-choice delay.

Animals↗

PubMed1984

Isobias and alloiobias functions in animal psycophysics.

An analogue of the human yes-no detection task was used to train six pigeons to discriminate luminance differences under two different reinforcer-scheduling procedures. When a controlled reinforce-ratio procedure was used, relative stimulus frequency was constant at .5, and relative reinforcer frequency for correct detections was held constant at three different values for each of five luminance differences. When an uncontrolled reinforcer-ratio procedure (the typical detection paradigm) was used, relative reinforcer frequency for correct detections was allowed to covary with changes in relative stimulus frequency for each of five luminance differences. Two measures of bias, response bias (Davison & Tustin, 1978) and the detection-theory likelihood-ratio measure (beta obt), were compared. The controlled reinforcer-ratio procedure generated equal- or iso-response-bias functions, and the uncontrolled reinforcer-ratio procedure gave changing or alloio-response-bias functions. The Davison-Tustin model accounted for 88% and 93% of the data variance in the controlled and uncontrolled reinforcer-ratio procedures, respectively. The best-fitting equal-beta functions accounted for an average of 53% and 69%, respectively, in the two procedures. In addition, neither procedure gave constant measures of beta obt for constant bias manipulations across different discriminability measures.

Animals↗

PubMed1983

Measurement of daylight UVA in Glasgow.

Measurements of daylight UVA have been carried out in Glasgow using a UVA-band detector and a spectroradiometer, both with the aperture window horizontal. Daily energy densities, defined as the total UVA energy each day per unit area, were obtained for the period November 1980 to May 1982. Levels rose from a mean December daily energy density of 4 J cm-2 to an average of 69 J cm-2 in June, with considerable fluctuations from day to day and with up to seven-fold changes observed on consecutive days. The UVA level sometimes varied rapidly during the day, with differences of up to a factor of six in successive 10 min periods. The daily temporal distribution of UVA for summer and winter, and the measured daylight spectra are presented. The spectroradiometer contained a double-grating monochromator used at a band-width of 1 nm. Measurements made by the spectroradiometer were compared with earlier published findings o solar UVA doses received by 56 patients who were photosensitized by 8-MOP in the course of PUVA therapy. It is shown that the median dose represented only 12 min daylight exposure and this indicates that the majority of patients to take care to avoid unnecessary exposure. However, the maximum dose was equivalent to some 84 min exposure to daylight UV and so there is clearly scope for a considerable reduction in exposure in some cases.

PUVA Therapy↗

PubMed1983

Sensitivity to reinforcement in concurrent arithmetic and exponential schedules.

The generalized matching law states that the logarithm of the ratio of responses emitted or time spent responding in concurrent variable-interval schedules is a linear function of the logarithm of the ratio of reinforcements obtained. The slope of this relation, sensitivity to reinforcement, varies about 1.0 but has been shown to be different when obtained in different laboratories. The present paper analyzed the results from 18 experiments on concurrent variable-interval schedule performance and showed that response-allocation sensitivity to reinforcement was significantly smaller when arithmetic, rather than exponential, progressions were used to produce variable-interval schedules. There were no differences in time-allocation sensitivity between the two methods of constructing variable-interval schedules. Since the two laboratories have consistently used different methods for constructing variable-interval schedules, the differences in obtained sensitivities to reinforcement are explained. The reanalysis suggests that animals may be sensitive to differences in the distribution of reinforcements in time.

Journal Article↗

PubMed1983

Choice: Some quantitative relations.

Six pigeons responded in fifty-six conditions on a concurrent-chains procedure. Conditions included several with equal initial links and unequal terminal links, several with unequal initial links and equal terminal links, and several with both unequal initial and terminal links. Although the delay-reduction hypothesis accounted well for choice when the initial links were equal (mean deviation of .04), it fit the data poorly when the initial links were unequal (mean deviation of .18). A modification of the delay-reduction hypothesis, replacing the rates of reinforcement with the square roots of these rates, fit the data better than either the unmodified delay-reduction equation or Killeen's (1982) model. The modified delay-reduction equation was also consistent with data from prior studies using concurrent chains. The absolute rates of responding in each terminal link were well described by the same hyperbola (Herrnstein, 1970) that describes response rates on simple interval schedules.

Journal Article↗

PubMed1983

Bias and sensitivity to reinforcement in a concurrent-chain schedule.

Six pigeons were trained on concurrent-chain schedules in which the initial links were either dependent (Experiment 1) or independent (Experiment 2) concurrent variable-interval schedules and the terminal links were fixed-duration delays to reinforcement in blackout. A changeover delay of three seconds operated in the initial links. Both the initial- and terminal-link schedule values were varied over 61 experimental conditions. An analysis of the data using the generalized matching law showed that the sensitivity of initial-link response allocation to the frequency of terminal-link production was independent of both the duration of the terminal-link delays and, though less clearly, of the duration of the initial-link schedules. Sensitivity of initial-link response allocation to terminal-link reinforcer-rate ratios was a joint function of the terminal-link durations and the smaller average initial-link duration. The results showed that the generalized matching law is useful in analyzing concurrent-chain schedule performance and that a changeover delay in the initial links eliminates some terminal- to initial-link interactions that have made quantitative predictions for concurrent-chain performances difficult.

Journal Article↗

PubMed1983

On the effects of food deprivation and component reinforcer rates on multiple-schedule performance.

Six pigeons were used to investigate the effects of varying body weight and component reinforcer rates in two-component multiple variable-interval variable-interval schedules. In Parts 1 and 3 of the experiment, unequal component reinforcer rates were arranged, and body weights were respectively increased and decreased. At 80% ad lib weight, response-rate ratios were closer to unity than reinforcer-rate ratios, but at 100% or more of ad lib weight, response-rate ratios generally equaled reinforcer-rate ratios. In Part 2, component reinforcer-rate ratios were varied over five conditions with the subjects maintained at 100% or more of their ad lib weights, and response-rate ratios matched reinforcer-rate ratios. The data thus support the empirical finding that response allocation in multiple schedules is a function of deprivation. Although this qualitative result is predicted by three models of multiple-schedule performance, only a model that assumes no direct component interaction adequately describes the data.

Journal Article↗

PubMed1982

Partial purification of a low molecular weight inhibitor of epidermal DNA synthesis.

An attempt has been made to purify factors present in aqueous extracts of pig epidermis which inhibit epidermal cell proliferation. A lipophilic factor of low molecular weight (less than 10,000), has been shown to inhibit DNA synthesis as measured by the uptake of tritiated thymidine in mouse ear epidermis. Purification by alcohol precipitation, ethyl acetate extraction and silicic acid column chromatography produced a fifteen-fold increase in the specific activity of the inhibitory action. It seems likely that aggregation or absorption of this low molecular weight factor may explain the high molecular weight of epidermal cell proliferation inhibitors previously studied, as well as the difficulty in their characterization.

Animals↗

PubMed1982

Independence of response force and reinforcement rate on concurrent variable-interval schedule performance.

Five pigeons were trained over 43 experimental conditions on a variety of concurrent variable-interval schedules on which the forces required on the response keys were varied. The results were well described by the generalized matching law with log reinforcement ratios and log force ratios exerting independent (noninteractive) effects on preference. A further analysis using the Akaike criterion, an information-theoretic measure of the efficiency of a model, showed that overall reinforcement rate and overall force requirement did not affect preference. Unlike reinforcement rate changes, force requirement increases did not change the response rate on the alternate key, and an extension of Herrnstein's absolute response rate function for force variation on a single variable-interval schedule is suggested.

Journal Article↗

PubMed1982

Stimulus discriminability in free-operant and discrete-trial detection procedures.

Six pigeons were trained to discriminate different light intensities in four experimental procedures. Experiment 1 compared stimulus discriminability in a yes-no signal-detection task with discriminability measures obtained from two free-operant procedures. Discriminability estimates were significantly lower in the detection procedure. Experiment 2 showed this lowered discriminability to be a function of the delay between stimulus presentation and the availability of the choice-response keys in the standard detection task. In addition, reinforcement sensitivity was lowest when correct choice responses were intermittently, rather than continuously, reinforced.

Animals↗

PubMed1982

Independence of stimulus discriminability from absolute rate of reinforcement in a signal-detection procedure.

Three experiments are reported in which two pigeons were trained to detect differences in stimulus duration under varying levels of absolute rate of reinforcement. Two red stimuli, differing in duration, were arranged probabilistically on the center key of a three-key chamber. On completion of the center-key duration, the center keylight was extinguished and the two side keys were illuminated white. Correct responses were left-key pecks following the shorter duration and right-key pecks following the longer duration. In Experiment 1, relative rate of reinforcement for correct responses was held constant and absolute rate of reinforcement was varied in seven conditions from continuous reinforcement to a variable-interval 90-second schedule. In Experiment 2, relative rate of reinforcement was manipulated across three different absolute rates of reinforcement (continuous reinforcement, variable-interval 15-second, and variable-interval 45-second). Stimulus discriminability was unaffected by changes in absolute or relative rates of reinforcement. Experiment 3 showed that discriminability was also unaffected by arranging the same consequences (three-second blackout) for unreinforced correct responses and errors.

Animals↗

PubMed1982

On the effects of component durations and component reinforcement rates in multiple schedules.

Four experiments, each using the same six pigeons, investigated the effects of varying component durations and component reinforcement rates in multiple variable-interval schedules. Experiment 1 used unequal component durations in which one component was five times the duration of the other, and the shorter component was varied over conditions from 120 seconds to 5 seconds. The schedules were varied over five values for each pair of component durations. Sensitivity to reinforcement rate changes was the same at all component durations. In Experiment 2, both component durations were 5 seconds, and the schedules were again varied using both one and two response keys. Sensitivity to reinforcement was not different from the values found in Experiment 1. In Experiment 3, various manipulations, including body-weight changes, reinforcer duration changes, blackouts, hopper lights correlated with keylights, and overall reinforcement rate changes were carried out. No reliable increase in reinforcement sensitivity resulted from any manipulation. Finally, in Experiment 4, reinforcement rates in the two components were kept constant and unequal, and the component durations were varied. Shorter components produced significantly increased response rates normally in the higher reinforcement rate component, but schedule reversals at short component durations eliminated the response rate increases. The effects of component duration on multiple schedule performance cannot be interpreted as changing sensitivity to reinforcement nor to changing bias.

Journal Article↗

PubMed1982

Preference in concurrent variable-interval fixed-ratio schedules.

Five pigeons were trained on concurrent variable-interval fixed-ratio schedules in three experiments. Experiment 1 used two variable-interval schedules and one fixed-ratio schedule, and the ratio requirement was varied. Using the generalized matching law, sensitivity to reinforcement was close to 1.0, but performance was biased toward the variable-interval schedule with the lower reinforcement rate. In Experiment 2, which used one variable-interval and one fixed-ratio schedule, the interval schedule was varied. All birds showed sensitivities to reinforcement of less than 1.0 and of less than the values obtained in Experiment 1. The performance was also biased toward the fixed-ratio schedule. Because the generalized matching law could not account for the differences in the data from Experiments 1 and 2, an extension of this law was suggested and successfully tested in Experiment 3. The proposed dual-sensitivity model was also shown to clarify some previously reported results.

Journal Article↗

PubMed1981

Exposure of physiotherapists to microwave radiation during microwave diathermy treatment.

Power density was measured during several microwave diathermy treatment sessions in order to determine levels to which the physiotherapist might be exposed during normal practice. Measurements were made at a distance of 30 cm from the patient. In half the cases investigated readings were less than 10 mW cm-2, the maximum permissible level for continuous exposure during an 8-hour working day. In the other cases levels exceeded 10 mW cm-2 at some sites. The results indicate that physiotherapists are unlikely to be exposed to radiation levels which would be considered harmful, provided reasonable care is taken.

Diathermy↗