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Biomedical subjects

P Killeen

Publications and source records attributed to P Killeen.

11 recordsLinked to original sources
PubMed1987

A portable silicon photodiode luminometer.

A simple, inexpensive, battery-powered, portable luminometer which is based on a silicon photodiode is described. The instrument is intended to measure the light produced by chemiluminescent and bioluminescent reactions. The device shows a good detection limit and, in a bioluminescent reaction for adenosine 5'-triphosphate (ATP), detected 0.5 pmol in 1 ml of aqueous solution. The instrument measures irradiance from 10(-13) to 10(-11) W cm-2 at the sensor, within the range 300 to 900 nm.

Adenosine Triphosphate↗
PubMed1977

The effects of scopolamine on the temporal control of behavior.

Pigeons were provided access to food once every 75 sec independently of their behavior. The effects of scopolamine hydrobromide on the temporal distribution of locomotor activity during the interfood interval were evaluated on the basis of a recently developed model. Drug-induced changes in activity, as evaluated by the model, showed that scopolamine (a) decreased the effect of postfood inhibition, (b) decreased the effect of terminal behaviors that occur late in the interfood interval and compete or interfere with general activity, (c) decreased the total amount of activity engendered by the appetitive schedule of reinforcement, (d) and appeared to produce an underestimation of time intervals. These effects were systematically related to drug dosage.

Animals↗
PubMed1975

The effect of timeout on performance on a variable-interval schedule of electric-shock presentation.

Responding was maintained in squirrel monkeys under variable-interval schedules of electric shock presentation when a period of timeout followed each response-dependent shock. Response rate decreased when timeout duration was decreased, and responding ceased when timeout was eliminated. These results indicate that under certain conditions, a shock-free period following each response-produced shock is necessary to maintain responding.

Journal Article↗
PubMed1972

The matching law.

The matching law may be viewed either as an empirical generalization, and therby subject to disproof, or as part of a system of equations used to define the utility ("value") of a reinforcer. In the latter case it is tautologous, and not subject to disproof within the defining context. A failure to obtain matching will most often be a signal that the independent variables have not been properly scaled. If, however, the proper transformations have been made on the independent variables, and matching is not obtained, the experimental paradigm may be outside the purview of the matching law. At that point, reinterpretations or revisions of the law are called for. The theoretical matching law is but one of many possible ways to define utility, and it may eventually be rejected in favor of a more useful definition.

Journal Article↗
PubMed1972

A yoked-chamber comparison of concurrent and multiple schedules.

Pigeons were exposed to alternative pairs of variable-interval schedules correlated with red and green lights on one key (the food key). In one experimental chamber, responses on a white key (the changeover key) changed the color of the food key and initiated a 2-sec changeover delay. Pigeons in a second chamber obtained food by pecking on a colored key whenever the pigeons in the first (concurrent) chamber had obtained food for a peck on that key color. There was no changeover key in the second (multiple) chamber: changeover responses in the first chamber alternated the schedules and colors in both chambers. The pigeons in both chambers emitted the same proportion of responses on each of the variable-interval schedules, and mastered discrimination reversals at the same rate. The pigeons differed only in their absolute response rates, which were greater under the concurrent schedules. In a second experiment, changes in key color occurred automatically, with different proportions of time allocated to the two variable-interval schedules. Matching of relative response frequency to relative reinforcement frequency was affected by the relative amounts of time in each component, by rate of changeovers, and by manipulations of the variable-interval scheduling.

Journal Article↗
PubMed1970

Preference for fixed-interval schedules of reinforcement.

Pigeons were trained on a two-link concurrent chain schedule in which responding on either of two keys in the initial link occasionally produced a terminal link, signaled by a change in the color of that key and a darkening of the other. Further responding on the lighted key was reinforced with food according to a fixed-interval schedule. For one of the keys, this fixed interval was always 20 sec, while for the other it was held at values of 5, 14, 30, or 60 sec for several weeks. In the initial link, all pigeons responded relatively more often on the key with the shorter fixed interval than was predicted by the matching hypothesis. Responding in the initial link showed a large negative recency effect: pigeons responded less frequently on the key that provided their last reinforcement than predicted from the overall response rates.

Journal Article↗
PubMed1969

Reinforcement frequency and contingency as factors in fixed-ratio behavior.

Two variables often confounded in fixed-ratio schedules are reinforcement frequency and response requirement. These variables were isolated by a technique that yoked the distributions of reinforcements in time for one group of pigeons to those of pigeons responding on various fixed-ratio schedules. The contingencies for the yoked birds were then manipulated by adding various tandem fixed-ratio requirements to their schedules. Post-reinforcement pause was approximately equal for the yoked and ratio pigeons, and was relatively insensitive to changes in the tandem requirement. Terminal response rate increased with increases in the tandem requirement, even though reinforcement rate was invariant. This increase was attributed to the progressive interference of the tandem requirement with the differential reinforcement of long interresponse times.

Journal Article↗
PubMed1968

On the measurement of reinforcement frequency in the study of preference.

In a two-link, concurrent-chain schedule, pigeons' pecks on each key during the initial link occasionally produced a terminal link, during which only that key was operative. Responses in the terminal link were reinforced with food on either fixed-interval or variable-interval schedules. In one experiment, relative amount of responding in the initial link equaled the relative harmonic rate of reinforcement in the terminal links. In a second experiment, the selection of interreinforcement intervals in variable-interval schedules in the terminal links was such that rates of reinforcement based on the harmonic or on the arithmetic means of the interreinforcement intervals predicted opposite preferences in the initial links. The observed preference was consistent with that predicted by the harmonic rather than by the arithmetic rates of reinforcement.

Animals↗