New class of antihypertensive agents

Three pigeons were trained to peck at a horizontally oriented rubber srtip 10 in. long. The spatial distribution of responding along this strip is found to be nonrandom when every peck is reinforced with food. The degree of nonrandomness increases markedly when the pecking is intermittently reinforced     

Errorless discrimination, autoshaping, and conditioned inhibition

Pigeons were exposed to a discriminated autoshaping procedure in which brief presentation of a green light on a key was always followed by food whereas presentation of a vertical white line on the key was never followed by food. Pigeons acquired an errorless discrimination by pecking reliably in the presence of the green light but never in the presence of the line. The line inhibited pecking in later tests: when the white line was paired with food, key peck acquisition was retarded; and when the white line was superimposed on the green background, responding was suppressed.     

Classical conditioning of a complex skeletal response

The pigeon's so-called "arbitrary" response of pecking an illuminated disk can be established and maintained by procedures resembling those of classical conditioning. This phenomenon was shown to be independent of the specific signaling relationships between illumination of the pecking disk and presentation of food; it will appear as long as the key is differentially associated with food. When a nondifferential condition is introduced, pecking "extinguishes" even if it has previously been established and even when the new condition involves as much reinforcement as the old one. Reinstating differential conditions reestablishes pecking. The initial conditions determine the speed and apparently the asymptote of pecking rates in the differential condition; initial exposure to a nondifferential procedure retards subsequent acquisition, possibly quite permanently. These findings are discussed in the context of mechanisms of adaptive learning, not involving reward and punishment, which lead to selection of effective behaviors on a nonarbitrary basis.     

Signals for food: reinforcers or informants?

Ring doves pecked one of two keys for food. Pecks at the chosen key then stopped being reinforced, and the signals that normally preceded food were either present or absent. In the presence of signals for food, the dove switched to the second key more quickly. When only one key was used, the same signals acted, as expected, to keep the bird pecking the extinguished key.     

Stimulus control in pigeons based on proprioceptive stimuli from floor inclination

Two groups of pigeons trained to peck a dimly illuminated disc in an otherwise dark experimental chamber with the floor horizontal (0 degrees tilt) or inclined 30 degrees to the left, respectively, show decremental generalization gradients of response rate when the floor inclination is varied from its training position. Discrimination training in which food reinforcement is available under one floor tilt condition but not under another steepens the slope of such gradients. In a secondv experiment, pigeons reinforced for pecking when the floor was tilted 10 degrees or 20 degrees and not reinforced under the alternative condition showed steep gradients with maximal responding displaced from the reinforced stimulus.     

Avoidance sessions as aversive events

Rats living continuously in conditioning chambers were permitted to work for food before and after their daily avoidance sessions. The avoidance procedure disrupted this responding reinforced by food, a result that indicates conditioned suppression on a time scale much greater than that previously studied in nonhuman animals.     

Control of vocal responding in chickens

Schedules of reinforcement were shown to control the rate of chirping bychickens in the same way as other motor responses in subhumans. Under a discrimination procedure, chickens responded selectively to the visual stimulus associated with food reinforcement for chirping. Control experiments demonstrated that food influenced the rate of responding because it was presented dependent on the chick's vocalizing and not because it had an innate eliciting or "emotionalizing" power.     

Conditioned reinforcement in the goldfish

Goldfish were trained to press a lever on a 10:1 fixed-ratio schedule of reinforcement. They were extinguished under three conditions. Responding was followed by (i) solenoid noise and water delivery formerly associated with food reinforcement, (ii) solenoid noise only, or (iii) nothing. The number of extinction responses was largest in condition 1, less in condition 2, and smallest in condition 3, thus providing evidence for conditioned reinforcement in goldfish.     

Operant conditioning of cortical unit activity

The activity of single neurons in precentral cortex of unanesthetized monkeys (Macaca mulatta) was conditioned by reinforcing high rates of neuronal discharge with delivery of a food pellet. Auditory or visual feedback of unit firing rates was usually provided in addition to food reinforcement. After several training sessions, monkeys could increase the activity of newly isolated cells by 50 to 500 percent above rates before reinforcement.     

Natural occurrence of malaria in rhesus monkeys

A tone ending in unavoidable electric shock was periodically presented to pigeons while they pecked a key for food. When pecking was completely disrupted by tone, shock was disconnected, and the training tone and tones having new frequencies were presented. Initially the gradient of generalization was broad; as testing proceeded, however, the gradient narrowed severely.     

Learning: classical and avoidance conditioning the mollusk Pleurobranchaea

Naive specimens of the marine gastropod Pleurobranchaea withdraw from tactile stimulation of the oral veil and show feeding responses to food chemicals. Experimental subjects, trained by pairing touch (conditioned stimullus) with food chemicals (unconditioned stimulus), soon acquired a classically conditioned feeding response to touch alone. Control subjects that received touch alone or unpaired touch and food chemicals showed significantly fewer feeding responses to touch than did experimentals. Classically conditioned specimens were used for avoidance conditioning. Subjects that received aversive electrical stimulation when they did not withdraw from touch rapidly learned to withdraw rather than to feed in response to touch alone. Controls that received touch alone or unpaired touch and shock continued to exhibit the feeding response to touch alone. The learned responses persisted for up to 2 weeks without reinforcement before extinction, and could be demonstrated in the isolated nervous system.     

Disinhibition of inhibitory conditioned responses following selective brain lesions in dogs

Discrete lesion of the genual portion of the anterior cingulate gyrus in three dogs produced temporary disinhibition of preoperatively trained inhibitory food conditioned responses. This disinhibition was accompanied by increase in general behavior motivated by food reinforcement. Lesion of the posterior cingulate gyrus in three other dogs did not produce such impairment.     

Conditioned Approach and Contact Behavior toward Signals for Food or Brain-Stimulation Reinforcement

When presentation of a retractable lever always preceded food delivery, rats licked or gnawed the lever. They also approached but seldom orally contacted a lever signaling brain-stimulation reinforcement; instead, subjects sniffed, pawed, or "explored" the lever. Therefore, a Pavlovian conditioned stimulus evoked directed skeletal responses whose specific form depended on the forthcoming unconditioned stimulus.     

Rats' preference for earned in comparison with free food

Rats were trained to eat free food from a dish, then trained to press a lever for similar food. The free food was then presented while subjects were pressing on several reinforcement schedules. Subjects continued to press for reinforcement when one or two presses were required for reinforcement, and ate little free food. When ten presses were required for reinforcement, rats preferred free food and pressed little or not at all. It was concluded that, when work demands are not too high, rats prefer earned food to free food.     

Training and maintenance of keypecking in the pigeon by negative reinforcement

Pigeons were trained to peck a key to escape a pulsing shock of linearly increasing intensity. As the rate of increase was varied from 0.0374 milliamperes per minute to 37.4 milliamperes per minute, the intensity at which most pecking occurred varied from 2.2 to 5.0 milliamperes.     

Stimulus generalization of a positive conditioned reinforcer

Stimulus generalization has been observed for discriminative, eliciting, and emotional functions of stimuli. In our study, in order to investigate the generalization of the reinforcing function of stimuli, pigeons were trained in a Skinner box to peck at an unlighted key to obtain aperiodic, brief exposures of light at a wavelength of 550 mmicro, the positive conditioned reinforcer, which was immediately followed by food reward. Testing in extinction, we obtained generalization gradients for the number of responses and the time the pigeons expended to produce exposures on the unlighted key of 550 mmicro, 530 mmicro) 510 mmicro, or no light. This finding suggests that stimulus generalization occurs with all functions of stimuli.     

The resilience of long and short food chains: a case study of flooding in Queensland,Australia

This paper provides new insights into the food security performance of long and short food chains, through an analysis of the resilience of such chains during the severe weather events that occurred in the Australian State of Queensland in early 2011. Widespread flooding cut roads and highways, isolated towns, and resulted in the deaths of people and animals. Farmlands were inundated and there were food shortages in many towns. We found clear evidence that the supermarket-based (long) food chain delivery system experienced significant difficulties in supplying food to flood-affected towns. In contrast, more localized (short) food supply chains—which relied upon supply from growers in peri-urban areas and community-based food initiatives—remained largely intact, and provided food at a time when the supermarkets were limited in their ability to respond to consumer demand. However, on closer examination of food distribution during flooding in the regional city of Rockhampton and in the State capital, Brisbane, the demarcation of success between “long” and “short” food chains became blurred. Both types of food supply chains shared some key resilience characteristics in responding to crisis but diverged in other important ways. We argue that conceptualizing food chains in terms of key elements of resilience—scale, diversity, flexibility and cohesion—may be more fruitful than the short-long dichotomy alone. This approach is particularly useful when prioritizing food security as the basis for evaluating food system sustainability in a context of predicted increases in extreme weather events and future climate change.     

Morphine: conditioned increases in self-administration in rhesus monkeys

Operant responding in three monkeys was maintained by intravenous presentations of morphine. Nalorphine produced reliable increases in morphine-reinforced responding. With successive daily nalorphine injections there was a decreased latency of self-administration responding for morphine, and substituted saline injections produced conditioned increases in morphine-reinforced responding.     

Hippocampal unit activity during classical aversive and appetitive conditioning

Rats were trained with a tone being followed by either food or electric shock, on alternate days. Unit activity during application of the conditioned stimulus was recorded from the dorsal hippocampus. The results indicate differentiation of the hippocampal system. Dentate units respond by augmentation to a conditioned stimulus which leads to food and by inhibition to the same stimulus when it precedes electric shock. The hippocampus proper responds by augmentation in both situations. The intensity of the hippocampal response to the conditioned stimulus on the first day of training is higher if the unconditioned stimulus is food than if it is electric shock. These data cast light on the functions of the dorsal dentate-hippocampal connections and the hippocampus proper during aversive and appetitive conditioning.     

Relationship between feeding and satiation centers of the hypothalamus

Electrodes were implanted in the hypothalamus of five goats in which an alimentary instrumental conditioned reflex had been previously established. Electrical stimulation of the ventromedial hypothalamus inhibited the conditioned movements and food intake in hungry goats. This also occurred in those satiated goats in which eating and conditioned movements were elicited by stimulation of the lateral hypothalamic area. Withdrawal of the stimulation of the medial hypothalamus evoked a short aftereffect in the form of a recovery or increase in the trained movements and food intake.