Hursh and Silberberg (2008) proposed an exponential function to describe the curvilinear demand functions obtained in much animal research. An advantage of this was that it gave a single measure of the value of the reinforcer, alpha, which they called essential value. This measure has scalar invariance and should not be affected by dose size, amount, or duration of the reinforcer. This paper examines the essential value measure obtained from studies with hens. In each study fixed-ratio schedules were used to generate demand functions. The properties of the reinforcer differed both within and across studies. Foster et al. (2009) and Lim (2010) varied food quality using 40-min sessions. Both found that the essential value was larger for the less preferred reinforcer when consumption was measured by number of reinforcers. Jackson (2011), using sessions terminated after 40 reinforcers and with body weight strictly controlled, found essential value (based on reinforcer rate) was the same for these same two foods. Lim (2010) found the preferred food had the greater essential value when the consumption was measured as weight of food consumed. Grant's (2005) data showed longer reinforcer durations were associated with lower essential values when consumption was measured as numbers of reinforcers. For these data the weight of food consumed generally resulted in the longest durations having the highest essential value. Harris (2011) varied delay to the reinforcer and found longer delays normally gave lower essential values. Stuart (2013) compared delays to the reinforcer and inter-trial-intervals (ITIs). She found essential was lower with the longer intervals for all hens with ITI and, for some hens, with delay and was lower with delays than with ITIs. Thus the measure of essential value has been found to vary in circumstances where this would not be predicted, to be the reverse of what might be expected in some cases, and to be affected by the procedure used. The present data show that essential value does not provide an easily interpretable measure.

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 performance of hens under multiple fixed-ratio fixed-ratio schedules was examined when the consequences were two different durations of reinforcement. The components of the multiple schedule were arranged so that the four possible transitions between reinforcer durations occurred (short to long, long to short, short to short and long to long). The response requirement in effect was the same in both components and varied over conditions. The between-ratio pauses increased with response requirement increases for all transitions. The pauses were consistently longest when the previous reinforcer duration was long and the upcoming duration was short. The next longest between-ratio pauses occurred when both the previous and the upcoming reinforcer durations were short. The between-ratio pauses were short when the upcoming reinforcer duration was long, tending to be shortest when the previous duration was short rather than when it was long. These data showed that the upcoming reinforcer had the greatest affect, although the previous reinforcer also had some effect on pause length. Longer between-ratio pauses were not the result of having just received access to a longer reinforcer. When the discriminative stimuli were removed and the response requirement was varied, between-ratio pauses again increased with FR increases. They were now similar and longer when the previous reinforcer duration was long and similar and shorter when the previous duration was short, regardless of the upcoming reinforcer duration. Thus pauses following a longer reinforcer were longer than those following a shorter reinforcer, as is seen with the magnitude of reinforcer effect. The range of pause lengths was reduced when compared to that with the multiple schedule, with the shorter pauses being longer and longer pauses being shorter.

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.

In separate experiments the timing abilities of brushtail possums and domestic hens on the peak procedure was investigated. This procedure involved animals responding on two trial types within an experimental session. On some trials responding was reinforced according to a Fixed Interval (FI) schedule, and on other trials, Peak Interval (PI) trials responding was not reinforced with food. Possums lever pressed and hens key pecked for food reinforcers on different FI schedules, and the duration of the PI was varied across a range. For 20% of trials, responding was not reinforced longer than the FI schedule that was in effect on the other 80% of trials when responding was reinforced. Response rates typically increased to a maximum at about the time the responses were normally reinforced and then decreased after the time that food would normally be reinforced, before increasing again towards the end of the PI regardless of the duration of the PI trial. When relative response rates were plotted as a function of relative time the function typically superposed for the ascending, but not descending portions of the function. The results are discussed in terms of Weber's law, and various quantitative models timing.

Food and sounds (white noise, a food call and the sound of other chicks) were used in an attempt to establish conditioned place preferences with domestic hen chicks. Thirty-two chicks were randomly allocated to one of the 4 groups, and exposed to a 3-compartment apparatus to establish a baseline of their movements across 4 15-min sessions. They were then confined to one compartment and provided with free access to food or exposed to one sound for 15 min and then they were confined to the alternate compartment with no food or sound for 15 min. This process was repeated 3 times. Post-conditioning test sessions showed a conditioned place preference towards the area associated with food and away from the area associated with white noise. After conditioning, chicks showed no preference for spending time in the side associated with the food call or the sounds of other chicks; however, they entered a compartment first more often when it was associated with the food call and less often when it was associated with chick-sounds. Overall, these results showed that 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.