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Younger and older men (18-25 vs. 65-76 years of age) were given extended practice (44 hr) with a memory scanning procedure in which lists of visual and auditory items were presented singly (single-task condition) or together with a second visual or auditory list (dual-task condition). For both age groups, identification of test items was slower with the(More)
Young men pulled a plunger on mixed and multiple schedules in which periods of variable-interval monetary reinforcement alternated irregularly with periods of extinction (Experiment 1), or in which reinforcement was contingent on different degrees of effort in the two alternating components (Experiment 2). In the baseline conditions, the pair of stimuli(More)
Five younger (18 to 23 yrs) and five older (65 to 73 yrs) men were exposed to a series of immediate and delayed (0 to 15 seconds) matching-to-sample problems. Presentation of the pairs of delayed comparison stimuli was either signaled or unsignaled, and the sample contained either 1, 2, or 3 elements, one of which appeared as the positive stimulus. During(More)
Influences of extended training and temporal contingencies on reaction time were studied in relation to developmental differences. Older and younger men were trained on a chained schedule in which completion of a variable interval produced a terminal link in which reaction time was measured. The reaction-time procedure involved a conditional discrimination(More)
SUMMARY Cloudy juices from six apple cultivars from PolandJudor') were produced and chemically characterised. The analyses encompassed 23 chemical parameters and phenolics profiles. The most important parameter, differentiating cloudy juice from clear juice, was turbidity. Cloudy juices were characterised by having an average total turbidity of 1,210(More)
Four rats were studied with variants of a progressive-ratio schedule with a step size of 6 in which different terminal components followed completion of the 20th ratio: (a) a reversal of the progression, (b) a fixed-ratio 6 schedule, or (c) extinction. Responding in the progressive-ratio components of these schedules was compared to performances under(More)
Rats responded under progressive-ratio schedules for sweetened milk reinforcers; each session ended when responding ceased for 10 min. Experiment 1 varied the concentration of milk and the duration of postreinforcement timeouts. Postreinforcement pausing increased as a positively accelerated function of the size of the ratio, and the rate of increase was(More)
Seven rats responding under fixed-ratio or variable-ratio schedules of food reinforcement had continuous access to a drinking tube inserted into the operant chamber. Under different conditions they could drink either tap water or one of two saccharin solutions. In a baseline condition, the drinking bottle was empty. Preratio pausing was observed with both(More)
Critics have questioned the value of human operant conditioning experiments in the study of fundamental processes of reinforcement. Contradictory results from human and animal experiments have been attributed to the complex social and verbal history of the human subject. On these grounds, it has been contended that procedures that mimic those conventionally(More)