Rich-lean transitions produced by stimuli associated with accurate and inaccurate responding by pigeons.

Discriminable transitions from relatively favorable schedules of reinforcement to unfavorable schedules (rich-lean transitions) can produce disruptions in operant behavior. A prior evaluation in our laboratory (Toegel et al., 2021) found that placing a border around a key displayed on a resistive touchscreen increased pigeons' response accuracy relative to conditions without the border. We sought to evaluate (a) whether effects of the key border on accuracy could be replicated in a within-session comparison and (b) whether transitions from a response alternative associated with accurate responding to one associated with inaccurate responding functioned as rich-lean transitions. Pigeons' key pecks were reinforced according to a two-component multiple schedule with identical fixed-ratio (FR) requirements and reinforcer magnitudes. The components differed based on whether the virtual key was displayed behind a border or with no border. In line with prior research, within-session comparisons yielded higher response accuracy in components with the key border than in components without the border. Furthermore, transitions from the border component to the no border component functioned as rich-lean transitions for pigeons whose obtained FRs in no border components were substantially larger than the FR programmed in that component.

Repeat Closed-Head Injury in Male Rats Impairs Attention but Causes Heterogeneous Outcomes in Multiple Measures of Impulsivity and Glial Pathology.

Repetitive mild traumatic brain injury, or concussion, can lead to the development of long-term psychiatric impairments. However, modeling these deficits is challenging in animal models and necessitates sophisticated behavioral approaches. The current set of studies were designed to evaluate whether a rubberized versus metal impact tip would cause functional deficits, the number of injuries required to generate such deficits, and whether different psychiatric domains would be affected. Across two studies, male rats were trained in either the 5-choice serial reaction time task (5CSRT; Experiment 1) to assess attention and motor impulsivity or concurrently on the 5CSRT and the delay discounting task (Experiment 2) to also assess choice impulsivity. After behavior was stable, brain injuries were delivered with the Closed-head Injury Model of Engineered Rotational Acceleration (CHIMERA) either once per week or twice per week (Experiment 1) or just once per week (Experiment 2). Astrocyte and microglia pathology was also assayed in relevant regions of interest. CHIMERA injury caused attentional deficits across both experiments, but only increased motor impulsivity in Experiment 1. Surprisingly, choice impulsivity was actually reduced on the Delay Discounting Task after repeat injuries. However, subsequent analyses suggested potential visual issues which could alter interpretation of these and attentional data. Subtle changes in glial pathology immediately after the injury (Experiment 1) were attenuated after 4 weeks recovery (Experiment 2). Given the heterogenous findings between experiments, additional research is needed to determine the root causes of psychiatric disturbances which may arise as a results of repeated brain injuries.

The aversiveness of timeout from response-dependent and response-independent food deliveries as a function of delivery rate.

Seven experiments with rats assessed the aversiveness of timeout using punishment and avoidance procedures. Experiments 1 and 2 considered the contributions of stimulus change, suspending the response-reinforcer contingency, response prevention, the general disruption in the reinforcement schedule during time-in, and overall decreases in reinforcement. Results support the conclusion that response-contingent timeouts punish behavior because they are signaled periods during which an ongoing schedule of positive reinforcement is suspended. Experiments 3, 4, and 5 assessed effects of the reinforcement rate during time-in on the punitive efficacy of timeout and, for comparison, electric shock. Evidence for a direct relation between reinforcement rate and punitive efficacy was equivocal. In Experiments 6 and 7, responding avoided timeout from response-independent food deliveries. Responding was acquired rapidly when it avoided timeouts from free deliveries of pellets or a sucrose solution, but not when it avoided free deliveries of water. At steady-state, avoidance rates and proficiency were directly related to the rate of pellet or sucrose deliveries. The relation between the nature of the time-in environment and the aversiveness of timeout was clear in our avoidance experiments, but not in our punishment experiments. We discuss interpretive problems in evaluating the aversiveness of timeout in the punishment paradigm.

Design and evaluation of a touchscreen apparatus for operant research with pigeons.

We developed a touchscreen apparatus for pigeons and conducted a series of experiments that assessed its utility for free-operant procedures. The apparatus incorporated an on-board Windows computer, an electromechanical interface, an amplified speaker, and the touchscreen. We found that merely projecting a virtual key on the screen was insufficient; too many pecks missed the key. Adding a visual target in the center of the key and providing visual feedback for on-key pecks both failed to improve response accuracy. Accuracy was improved by imposing a timeout after off-key pecks or providing a physical boundary around the key. With the physical boundary, response accuracy was comparable to that obtained with conventional plastic keys, and response acquisition via autoshaping also was comparable. Mixing the color elements of the screen's pixels produced color stimuli, but the colors did not function as pure wavelengths of light in tests of stimulus generalization. Both colors and geometric shapes functioned as discriminative stimuli in multiple schedules with variable-interval and extinction components or rich and lean fixed-ratio components. In general, our touchscreen apparatus is a viable alternative to conventional pigeon chambers and increases the experimenter's options for visual stimuli, auditory stimuli, and the number and location of response keys.