Pain tolerance selectively increased by a sweet-smelling odor

The mechanism underlying reported analgesic effects of odors in humans is unclear, although odor hedonics has been implicated. We tested whether odors that are sweet smelling through prior association with tasted sweetness might influence pain by activating the same analgesic mechanisms as sweet tastes. Inhalation of a sweet-smelling odor during a cold-pressor test increased tolerance for pain compared with inhalation of pleasant and unpleasant low-sweetness odors and no odor. There were no significant differences in pain ratings among the odor conditions. These results suggest that smelled sweetness can produce a naturally occurring conditioned increase in pain tolerance.     

Characteristics of memories for traumatic and nontraumatic birth

Evidence for memory characteristic differences between trauma and other memories in non‐clinical samples is inconsistent. However, trauma is frequently confounded with the event recalled. This study compares trauma and nontrauma memories for the same event, childbirth, in a non‐clinical sample of 285 women 4–6 weeks after birth. None of the women met diagnostic criteria for post‐traumatic stress disorder. Traumatic birth, defined by the DSM‐5 event criterion, was reported by 100 women. The ratings of some memory characteristics did not differ between memories for traumatic and nontraumatic birth: All were rated highly coherent and central to women's lives, with moderate sensory memory. However, women who experienced traumatic births reported more involuntary recall, reliving, and negative/mixed emotions. Thus, trauma memories differed from nontrauma memories. In this non‐clinical sample, this is likely to be due to encoding during trauma rather than the distinctive memory profile for memories retrieved by those experiencing trauma symptoms.     

The role of gaze and road edge information during high-speed locomotion

Robust control of skilled actions requires the flexible combination of multiple sources of information. Here we examined the role of gaze during high-speed locomotor steering and in particular the role of feedback from the visible road edges. Participants were required to maintain one of three lateral positions on the road when one or both edges were degraded (either by fading or removing them). Steering became increasingly impaired as road edge information was degraded, with gaze being predominantly directed toward the required road position. When either of the road edges were removed, we observed systematic shifts in steering and gaze direction dependent upon both the required road position and the visible edge. A second experiment required fixation on the road center or beyond the road edges. The results showed that the direction of gaze led to predictable steering biases, which increased as road edge information became degraded. A new steering model demonstrates that the direction of gaze and both road edges influence steering in a manner consistent with the flexible weighted combination of near road feedback information and prospective gaze information.     

Pigeons' spatial memory: III. Effect of distractors on delayed matching of key location.

The effect of distractors on pigeons' delayed matching of key location was investigated. Baseline trials began with a "ready" stimulus (brief operation of the grain feeder). Then one (randomly chosen) key from a three-by-three matrix was lit briefly as the sample. After a short delay (retention interval) the sample key was lit again along with one of the other eight keys. A peck at the key that had served as the sample (correct comparison) produced grain reinforcement, whereas a peck to the other key (incorrect comparison) produced only the intertrial interval. In Experiment 1, a houselight distractor, presented during either the sample, retention interval, or choice phases of the trial, had little if any effect on accuracy of matching key location. In Experiment 2, one of three types of spatial stimuli was interpolated during the retention interval, or the interval was blank as during baseline trials. The three stimuli were: the sample (correct comparison) location for that trial, the incorrect comparison location for that trial, or one of the seven unused locations for that trial. Relative to blank trials, accuracy improved slightly on sample-interpolated trials, decreased slightly on unused location-interpolated trials, and decreased considerably on incorrect comparison-interpolated trials. In Experiment 3, retention intervals were blank or had one of six types of interpolation: the sample, the incorrect comparison, two presentations of the sample, two presentations of the incorrect comparison, the sample followed by the incorrect comparison, or the incorrect comparison followed by the sample.(ABSTRACT TRUNCATED AT 250 WORDS)     

Discrimination training facilitates pigeons' performance on one-trial-per-day delayed matching of key location

Six pigeons were tested on a one-trial-per-day variant of delayed matching of key location. In one condition, a trial began with the illumination of a pair of quasi-randomly selected pecking keys in a large 10-key test box. Pigeons' pecks to one key (the sample) were reinforced with 8-second access to grain on a variable-interval 30-second schedule, whereas pecks to the other key (the distractor) had no scheduled consequences. In the second condition, the nonreinforced distractor was not presented. In both conditions, subjects were removed from the apparatus after 15 minutes and placed in a holding cage. Subjects were subsequently replaced in the box after a delay (retention interval) of 30 seconds and were reexposed to the illuminated sample and distractor keys for 1 minute. If a pigeon made more pecks to the sample during this interval, the distractor was extinguished and subsequent pecks to the sample were reinforced on the previous schedule for an additional 15 minutes. If, however, a pigeon made more pecks to the distractor, both keys were extinguished and the subject was returned to its home cage. For all subjects, matching-to-sample accuracy was higher in the first condition. In a second experiment, the retention interval was increased to 5, 15, and 30 minutes, and then to 1, 2, 4, 8, 12, and 24 hours. Most subjects remembered the correct key location for up to 4 hours, and in one case, up to 24 hours, demonstrating a spatial-memory proficiency far better than previously reported in this species on delayed matching tasks. The results are discussed in terms of the commonly held distinction between working and reference memory.     

Variable-time reinforcement in multiple and concurrent schedules

Experiment I examined the role of a reduced rate of responding in the occurrence of behavioral contrast. Four rats and a pigeon were exposed to a two-component multiple schedule in which one component was always a variable-interval schedule. The second component was, at different times, either a variable-time schedule in which food was delivered independently of responding, or extinction. Both extinction and the variable-time schedule reduced the rate of responding in the second component. Behavioral contrast was observed, however, only when extinction was scheduled in the second component. Experiment II examined preference, as measured by time allocation in concurrent schedules for a variable-interval schedule relative to a variable-time schedule. Two rats displayed a lack of preference between the two schedules. The results of these experiments support a preference interpretation of behavioral contrast, which holds that behavioral contrast is the result of the introduction of a less-preferred condition in one component of a multiple schedule.     

Stimulus control of defensive burying in the rat

Rats shocked once through a wire-wrapped stationary prod mounted on the wall of a test chamber incorporated the bedding material covering the chamber floor into a defensive reaction. When tested 1 min later, they approached the prod and buried it. Evidence was provided by three separate studies of this burying response that rats had learned about the association of both the position and brightness of the prod with shock after this single conditioning trial. In Experiment 1, the amount of burying decreased if either the position or brightness of the prod had been changed prior to the test. In Experiments 2 and 3, rats were shocked through one of two prods (white or black) mounted on opposite walls of the test chamber. When the positions of the prods were unchanged for the test, almost every subject buried the prod through which it had been shocked, even when the conditioning-test interval was 24 hr; whereas, each rat directed substantial amounts of bedding material at both prods when the positions of the two prods were reversed. Thus, discriminated “avoidance” learning can be rapid, reliable, and enduring when shock is administered “by” a clearly defined stimulus object, i.e., when cue and consequence are spatially contiguous.     

A computer simulation model of rats’ place navigation in the Morris water maze

Rats rapidly learn to swim from a variety of starting locations, including novel ones, to a small invisible platform submerged in a pool of cool opaque liquid. A computer simulation based on a simple perceptual memory-matching model successfully mimics this ability. The model assumes that the rat, when it successfully reaches the platform, notes the distance to prominent extramaze landmarks and stores this perceptual information in memory. When placed in the pool on subsequent trials, the simulated rat attempts to match perceived distance between itself and the landmarks to the remembered distances from the platform to the landmark. The model accounts for many of the known facts about rats’ behavior in the swimming pool and makes some interesting predictions that could be easily tested experimentally. The model has the advantage, relative to other cognitive map models, of specifying how spatial information is represented in memory and how this information guides behavior.