Stimulus change as a factor in response maintenance with free food available

Value-modulated attentional capture is augmented by win-related sensory cues

Attentional prioritisation of stimuli in the environment plays an important role in overt choice. Previous research shows that prioritisation is influenced by the magnitude of paired rewards, in that stimuli signalling high-value rewards are more likely to capture attention than stimuli signalling low-value rewards; and this attentional bias has been proposed to play a role in addictive and compulsive behaviours. A separate line of research has shown that win-related sensory cues can bias overt choices. However, the role that these cues play in attentional selection is yet to be investigated. Participants in this study completed a visual search task in which they responded to a target shape in order to earn reward. The colour of a distractor signalled the magnitude of reward and type of feedback on each trial. Participants were slower to respond to the target when the distractor signalled high reward compared to when the distractor signalled low reward, suggesting that the high-reward distractors had increased attentional priority. Critically, the magnitude of this reward-related attentional bias was further increased for a high-reward distractor with post-trial feedback accompanied by win-related sensory cues. Participants also demonstrated an overt choice preference for the distractor that was associated with win-related sensory cues. These findings demonstrate that stimuli paired with win-related sensory cues are prioritised by the attention system over stimuli with equivalent physical salience and learned value. This attentional prioritisation may have downstream implications for overt choices, especially in gambling contexts where win-related sensory cues are common.

Response-independent outcomes impact response rates and judgments of control differentially depending on rate of response-dependent outcomes

Two experiments examined the impact of response-independent outcome delivery on human rates of response and judgments of control in an instrumental conditioning task. In Experiment 1, when participants responded on a schedule with a relatively high probability of a response producing an outcome, a random ratio (RR-5), judgments of control declined as rates of response-independent outcomes increased. However, when response-dependent outcomes were delivered with a relatively low probability (RR-15), increasing the rate of response-independent outcomes increased rates of response and judgments of control. Experiment 2 replicated this effect, but also noted a differential effect of response-independent outcome and response-independent sensory presentations on response rate and judgments of causal effectiveness. Ratings of the context in which the conditioning occurred suggested these were correlated with total outcome presentation, and that the role of context on response rate and judgments of control may be important to consider.

Automaintenance without stimulus-change reinforcement: Temporal control of key pecks

Yoked pairs of experimentally naive pigeons were exposed to a modified autoshaping procedure in which key pecking by the leader birds postponed both keylight termination and access to grain for the leader and the follower bird. Key pecking developed and was maintained in all birds and continued through two reversals of roles in the yoked procedure. Although temporal control developed more slowly in follower birds, asymptotic temporal distributions of key pecking were similar for all birds in both leader and follower roles; maximum responding occurred soon after keylight onset and decreased to a minimum prior to reinforcement. Response distributions for both leader and follower birds were described by Killeen's (1975) mathematical model of temporal control. Follower birds received response-independent reinforcement, and the development by these birds of temporal distributions which are minimal immediately prior to reinforcement is without precedent in Pavlovian appetitive conditioning. However, maintenance of key pecking by the leader birds, whose responses postponed both stimulus-change and food reinforcement, supports an interpretation of autoshaped and automaintained key pecking as responding elicited by signaled grain presentation.

Free food or earned food? A review and fuzzy model of contrafreeloading

Animals will work (e.g. lever press) for 'earned' food even though identical 'free' food can easily be obtained from a nearby dish. This phenomenon, called contrafreeloading, appears to contradict a basic tenet of most learning, motivation and optimal foraging theories; namely that animals strive to maximize the ratio of reward, or benefit, to effort, or cost. This paper reviews the factors that have been found to affect the level of contrafreeloading, to try to explain the behaviour. In experiments involving intensive training, contrafreeloading may be explained on the basis of secondary reinforcement and/or differential exposure to the alternative food sources. However, contrafreeloading also occurs without prior training. Contrafreeloading declines with increasing hunger and with increases in the effort required to obtain the earned food: it also has an inverted-U relationship with the degree of stimulus change associated with the earned food. A fuzzy logic model is developed to predict the outcome of interactions between these factors. The model successfully simulates previous empirical findings and provides novel, testable predictions. It is argued that contrafreeloading does not contradict reinforcement theory, provided that the sensory reinforcement obtained from stimuli associated with the earned food is also taken into account. A functional explanation of why such stimuli are reinforcing, and of contrafreeloading itself, is based upon the advantage of gathering information for animals living in changing environments (i.e. an information primacy model). Animals work for earned food in order to update their estimate of a currently sub-optimal food source because, in the longer term, it may unpredictably become the optimal place to feed. Contrafreeloading is therefore a behaviour that, under natural conditions, is adaptive.