A handful of studies have examined the relationship between schedules of reinforcement and behavioural variability, with mixed results. The present study compares a greater range of schedules, examining the effects on location variability. Hens worked in an operant chamber containing five, horizontally arranged and active response keys. Experiment 1 compared eight schedules: FR 40, FR 10, FI (yoked FR 40), FI (yoked FR 10), VR 40, VR 10, VI (yoked VR 40) and VI (yoked VI 10). Experiment 2 compared a series of DRL schedules: 0.5 s to DRL 19.2 s, incrementing in step sizes of 20%. Location variability was measured as the percentage of switching across keys from within trials, between trials (switching from the reinforced response location to the first response location of the following trial), and the number of keys used. Results from Experiment 1 suggested no relation between schedules and location variability. However a relation between response rate and location variability was found; faster response rates resulted in less variability. Experiment 2, in attempt to control for response rate, found no relation between response rate and location variability. Switches within trials occurred more frequently in Experiment 2 than in Experiment 1, an aspect that needs further examination.

Many diverse species have demonstrated interval timing, the ability to respond appropriately to time in the range of seconds to minutes, suggesting that an ability to time is adaptive. The peak procedure is a common method of studying interval time perception. In the peak procedure, animals experience a mix of fixed-interval (FI) and extinction (EXT) trials. On EXT trials, responding typically increases to a peak at the time the FI schedule would normally deliver reinforcers before decreasing. Responding on different FI schedules within the peak procedure has been found to conform to Weber's law, whereby response variability is proportional to the length of the fixed interval. We conducted possibly the first investigation of the timing abilities of a marsupial common to Australia and New Zealand, the brushtail possum ('Trichosurus vulpecula'), using FI 15-, 30-, and 60-s schedules of reinforcement in the peak procedure. Response rates on EXT trials peaked at the time of usual reinforcer delivery, decreasing at longer time intervals, and were well fit by 3-parameter Gaussian curves, demonstrating the ability of possums to respond to time-based stimuli. Coefficients of variation suggested that the ability of possums to time was less accurate than that of mammals, but similar to that of birds, invertebrates, and reptiles. Coefficients of variation did not differ consistently over increasing FI intervals, showing that timing responses of possums likely conforms to the scalar property of timing also shown by other species.

The independence of dimensions of operant responses by humans was investigated in two experiments using a computerized rectangle drawing task from Ross and Neuringer (2002). Variability on the dimensions of area, shape and location was required for reinforcement for one group (VAR); and variability was not required for the other (YOKE). For all three dimensions, U-values, a measure of variability, were higher for the VAR group than for YOKE group; and the number of trials that met the criteria for reinforcement was higher for the VAR group than for the YOKE group. In Experiment 2, reinforcement was contingent on variability on two dimensions regardless of variability on the third. Participants were divided into three groups; each group had one dimension that was not required to vary. U-values were higher for dimensions when reinforcement was contingent on varying shape and location, or area and location. However, U-values did not differ significantly across dimensions when reinforcement was contingent on varying just area and shape. The results of Experiment 1 and 2 are broadly consistent with those of Ross and Neuringer (2002). The importance of orthogonality of dimensions on this task will be discussed.

The added reinforcement of variable responding will facilitate the learning of a difficult target sequence in rats, however, the added requirement of variability has been shown to impede difficult sequence learning in humans. The present study aimed to explore the notion of sequence difficulty in humans by manipulating sequence length (6-12 items). Eighty participants were randomly allocated to one of two groups: Control and Variable. In the control conditions sequences were only reinforced if they were the target sequence, in the variability conditions sequences were concurrently reinforced on a Variable Interval 60-s schedule if the just entered sequence met a variability criterion. For the six-item sequence (122121) the Control group were most likely to produce the target sequence, while for the twelve digit sequence (221112211121) there was no difference between the two groups. The Variable group were most likely to produce the target sequence for the intermediate nine-digit sequence (112212121).The use of sequence length as a definition of sequence difficulty in both the current and previous studies are discussed.

Effective dog training depends on timely delivery of rewards. Critical to an understanding of "timely" for dogs is an understanding of the psychophysical performance of dogs when temporal durations are used as stimuli. Fifteen dogs were tested, food was used as reinforcers, and owners were asked not to feed their dogs before testing. The dogs were shown a white light for either a short or long duration, on the centre of the display. They were trained to nuzzle the lever above the screen whose colour is associated with the duration shown, for example touch the red screen lever when it was a 1 sec duration and the green screen lever when it was 4 sec. The location of the comparison stimuli was randomised across the left and right sides. Across the pairs of delays, difference in delays was one to four. If dogs made the correct response a piece of food is delivered. Once the dog responded with above 80% accuracy the testing phase began. During testing the two original signal durations were presented on 25% of trials on the remaining trials intermediate duration e.g. 6 sec are presented. Psychometric functions from stimulus-generalization sessions, when novel test durations were introduced, are presented.