In procedures used to study timing behavior, the availability of reinforcement changes according to time since an event. Manipulation of this reinforcer differential often produces violations of scalar timing, but it is unclear whether such effects arise because of a response bias or a change in temporal discrimination. The present experiment investigated the effects of the overall and relative probability of obtaining a reinforcer on performance in the free-operant psychophysical procedure. We arranged short and long trials with unequal reinforcer ratios, at high or low overall reinforcer rates. Changes in the overall reinforcer rate produced only small changes in timing behavior. Changes in relative reinforcer probability, which caused differences in the likely availability of reinforcers across time within a trial, produced a change in both bias and discrimination. We suggest reinforcers affect timing, and that discrimination in timing tasks depends on the distribution of reinforcers in time, as well as on the interval to be timed.

The aim of this study was to compare the demand by possums for foods under different arrangements of concurrent progressive-ratio and fixed-ratio schedules of reinforcement. In Experiment 1, every possible food pair made up of berries, chicken, egg, foliage, insects, and mushroom was presented (30 pairs in total). The requirement on the progressive-ratio schedule increased within a session and the fixed-ratio was kept constant at 30. In Experiment 2, a subset of the foods from Experiment 1 were used (chicken, mushroom, egg, and berries) and in separate conditions the fixed-ratio was either 30 or 10 responses. In Experiment 3, the foods were the same as used in Experiment 2 and the progressive-ratio schedule increased every five sessions and the fixed-ratio was kept constant at 30. Exponential models of demand were applied to consumption rates to compare the parameters of initial demand, essential value and Pmax, and break point and cross point across foods. The models described the data well and consumption rates were similar when the incrementing schedules increased within- and across sessions. Demand was highest for berries, egg, and locust in Experiment 1 and egg and chicken in Experiments 2 and 3. This finding has practical implications for understanding possum food preferences in the wild as a function of other available food sources and for informing pest control strategies of potential lures.

Food and sounds were used to condition 32 chicks to one side of a 2-compartment apparatus. This process was repeated in the alternate compartment with no food or sound present. Post-conditioning test sessions showed a conditioned place preference towards the area associated with food and away from the area associated with white noise but no significant effects were found for a food call or the sounds of other chicks. Overall, these results showed it was possible to use the conditioned place preference procedure to assess the effects of sounds and that the procedure has potential use for assessing other environmental stimuli.

Manipulation of unconditioned Motivating Operations (MOs) such as pain, food and water deprivation and the lowering of body weight can be potentially harmful and distressing to animals. Past research that has manipulated such MOs in order to motivate animals to respond for reinforcers is reviewed and directions for future research are discussed. The focus is on the extent that potentially distressing MO's need to be altered in order to change motivation for reinforcers in animals. In addition research directions for investigating alternative MOs that can motivate animals to respond for reinforcers are discussed.

This Special Issue is titled 'Quantitative Analysis of Behavior'. The 37th Annual Meeting of the Society for the Quantitative Analyses of Behavior (SQAB) took place at the McCormick Place Convention Center (Chicago, IL) May 22-May 24, 2014. Presentations from that conference are reported in this special issue as reviews, theoretical papers or reports of original research. Quantitative models of behavior can to some look like an impenetrable forest of equations, assumptions, and parameters. To others those trees provide the wood to build frameworks for assisting our understanding of forces that control behaviour. In this special issue, quantitative models of behaviour are examined from philosophical, theoretical, experimental and applied perspectives. The variety and breadth of approaches and areas of study covered by contributors highlight the continued importance and value of quantitative analyses to our understanding of behavior.

Motivating Operations (MOs) are frequently manipulated (by altering access to commodities and manipulating other variables such as body weight) in order to change responding. This study had two aims, firstly to investigate the effect of altering body weight on concurrent schedule performance of hens, secondly to investigate the effect of altering body weight on the time duration of each component of hens' pecks under these schedules when analysed from high speed videos filmed at 240 fps. Six hens (at 85% 5%) were shaped (three via the method of successive approximations and three via autoshaping) to respond for food reinforcers on an infra-red screen. Hens then responded under a range of concurrent VI VI schedules, with body weight held at 85% 5%, 95 5% and 100 5% over conditions. It was found that applying the Generalised Matching Law to the data did not result in any consistent differences in responding with the three body weights. However, response rates, inter-response times and video analysis of the individual components of the hens pecking responses did show consistent differences between responding at the three weights.

The common brushtail possum ('Trichosurus vulpecula') has been reported to eat vegetation, fruit, invertebrates, and occasionally fungi, eggs and meat. The relative preference between food types found in the wild, however, has not been investigated systematically in a controlled laboratory study. This research investigated captive possums' food choice using two different methods of preference assessment. The first experiment involved a single stimulus assessment of possums' (n = 20) consumption of individually presented food items. More than 75% of possums consumed berries, locusts and mushrooms but fewer than 50% of possums consumed fivefinger, raw chicken and eggs. The second experiment that used a paired stimulus assessment to establish relative preference for those foods revealed that no single food was preferred by all possums. Overall locusts were the most preferred food, followed in order of preference by berries, egg, mushrooms, chicken and foliage. The single stimulus preference assessment confirmed the palatability of foods. The paired stimulus assessment provided a rank order of food preferences.

The demand for six different foods was assessed using a concurrent available Fixed and Progressive Ratios for the Common Brushtail Possum. Responses to the left lever were reinforced with timed access to one food type on a FR 30, and responses to the right lever were reinforced according a geometric PR schedule with timed access to another food type. The food pairs were based on the results of single and paired stimulus preference assessments combinging pairs of mushroom, egg, foliage, blackberry, raw chicken, egg and locust. Cross-point demand functions showed the shift from the PR schedule to the constant FR 30 schedule occurred at about 30 responses for most food pairs. Cross-points that occurred before the equivalence point suggested a preference for food available on the FR schedule as the possum responded more for this food over responding on the PR schedule which initially required fewer responses. There was no significant difference in overall elasticity between the foods. This means that as the response requirement increased, responding decreased. Pooled consumption data from within each pair of foods showed inelastic demand for several preferred foods when paired with non-preferred foods. These data show that the context for assessing demand affects the conclusions of food preference.

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 Brushtail possum ('Trichosurus vulpecula') is reported to eat vegetation, fruit, flowers, fungi and meat in the form of birds (e.g., starlings, blackbirds) and their eggs. However, this omnivorous behaviour and ability to adapt to a varying diet has not been investigated systematically. The first experiment involved a single stimulus preference assessment of possum's consumption of individually presented food items that included: meat, eggs, native foliage, fruit and invertebrates. The second and third experiments used paired stimulus assessment and concurrent schedule procedures to establish ranked preference and demand curves for these different food types. Results suggest that captive possums display similar opportunistic feeding behaviour observed in wild possums. Further studies will examine the development and influence of food choices by other possums on the transmission of taste preferences between possums. These studies may provide information relevant to maintaining captive populations of possums for behavioural research by contributing to the knowledge of methodologies compatible with possums and provide strategies and practices for the management of the pest problem in New Zealand.