The formation and execution of sequential plans in pigeons (Columba livia)

The ability to formulate and execute plans is a hallmark of human behaviour. Here we present evidence of planning in pigeons. Subjects were trained to respond to three geometric shapes in a prescribed order. Probe trials were then introduced in which, following a response to the first item, the on screen positions of the second and third item were exchanged. If subjects were planning a sequence of responses at the outset of a trial, we would expect reaction time to the second item to increase, reflecting the updating of a predetermined response plan. This is exactly what was found. Subjects also responded correctly on trials in which, following a response to the first item, stimuli were covered by opaque white squares. Together these results suggest pigeons are able to plan one step ahead on the simultaneous chaining paradigm.     

Some characteristics of spatial associative memory in the pigeon, Columba livia

Willson and Wilkie (1993) developed a novel procedure to assess pigeons' memory for the spatial location of food. Only one of four locations provided food each daily session. Each location consisted of an illuminated pecking key and grain feeder. Over different days different locations, randomly selected, provided food during a 16-min session. The pigeons tended to revisit the location at which food was found on the previous day thereby demonstrating memory for food-spatial location associations over 24 h. Three experiments were conducted to further investigate this phenomenon. In Experiment 1 the session duration was varied between 4 and 32 min. Longer sessions had no detectable effect on their ability to remember the rewarded location 24 h later, a result that suggests that only brief encounters with food at a particular location are necessary for recall. In Experiment 2 the necessity of an active search for the day's rewarded location was removed; a 5-min period in which only the rewarded key was lit preceded the regular 16-min session. Pecks to the lit key in this 5-min period produced grain on the standard schedule. This manipulation facilitated the pigeons' discovery of food but did not affect their ability to remember the rewarded location, suggesting that the process of search and discovery is not essential to the associative memory process. In Experiment 3, food was available during the complete session (non-depleting condition) or was available only during the first half of the session (depleting condition). No detectable differences in the birds' memory of yesterday's profitable location were found. This suggests that non-depletion of food is not a necessary condition for day-to-day recall of food location. Taken together these findings enlarge our understanding of the spatial associative memory process.     

Learning strategies in matching to sample: if-then and configural learning by pigeons

Pigeons learned a matching-to-sample task with a split training-set design in which half of the stimulus displays were untrained and tested following acquisition. Transfer to the untrained displays along with no novel-stimulus transfer indicated that these pigeons learned the task (partially) via if-then rules. Comparisons to other performance measures indicated that they also partially learned the task via configural learning (learning the gestalt of the whole stimulus display). Differences in the FR-sample requirement (1 vs. 20) had no systematic effect on the type of learning or level of learning obtained. Differences from a previous study [Wright, A.A., 1997. Concept learning and learning strategies. Psychol. Sci. 8, 119-123] are discussed, including the effect of displaying the stimuli vertically (traditional display orientation) or horizontally from the floor.     

Pigeons’ (Columba livia) hierarchical organization of local and global cues in touch screen tasks

Redundant encoding of local and global spatial cues is a common occurrence in many species. However, preferential use of the each type of cue seems to vary across species and tasks. In the current study, pigeons (Columba livia) were trained in three experiments on a touch screen task which included redundant local positional cues and global spatial cues. Specifically, pigeons were required to choose the middle out of three choice squares, such that the position within the array provided local information and the location on the screen provided global information. In Experiment 1, pigeons were trained and tested on vertically aligned arrays. In Experiment 2, pigeons were trained and tested on horizontally aligned arrays, and in Experiment 3, pigeons were trained and tested with vertical, horizontal and diagonally aligned arrays. The results indicate that preference for cue type depends upon the type of spatial information being encoded. Specifically, on vertical and diagonally aligned arrays, pigeons preferred global cues, whereas on horizontally aligned arrays, pigeons preferred local cues.     

The peeping response of pigeons (Columba livia) to isolation from conspecifics and exposure to a novel environment

The present study examined the acute behavioral responses of pigeons to separation from conspecifics and exposure to an unfamiliar environment (UE). The effects of (1) repeated exposure to the UE; (2) visual isolation from surroundings, or saline injections; and (3) diazepam treatment (i.p., 0.25, 0.75, 2.5 or 7.5 mg/kg) before the trial were also examined. UE exposure evoked intense ballistic head movements (peeping), gradually replaced with angular head movements (AHM), both associated with immobility of the trunk and legs. These behaviors failed to habituate after three trials (7-day intertrial intervals). Visual isolation from the surroundings and saline injection prior to exposure to the UE increased the AHM and reduced peeping. Doses of diazepam (0.25 and 0.75 mg/kg) that have demonstrated anti-conflict effects in other tests did not affect the behavioral responses to the UE. Diazepam at 2.5 and 7.5 mg/kg doses consistently increased time spent in immobility. These data suggest that peeping, although expressed in potentially threatening or harmful situations appears not to be a fear-motivated behavior or, alternatively, this specific behavioral response is not diazepam sensitive.     

The distribution of mallophaga on the domestic pigeon (Columba livia)

The distribution of Hohorstiella lata, Colpocephalum turbinatum, Campanulotes bidentatus compar, and Comlumbicola columbae on domestic pigeons were determined. Each species laid its eggs on a different part of the body but all fed on the fluffy part of the body feathers. H. lata also fed on blood, and C. turbinatum on its own eggs and nymphs. Reduction of the efficiency of preening led to an increase in the number of lice and more widespread distribution of nymphs and adults but not to a rapid change in the distribution of eggs. It is suggested that preening has played a major selective role, and that the morphological and behavioural adaptions of the lice are to ensure that they and their eggs survive this type of predation.     

Attention to uninformative features expressed by pigeons in a duration matching-to-sample task

Pigeons were trained on a matching-to-sample task in which they had to respond to a different choice stimulus following the same durations (2 or 10 s) of two different signals. The duration signals consisted of a white light presented from the ceiling and a red light presented from the front wall. Subsequent test performance indicated that matching accuracy declined (1) when the set of choice stimuli following a duration signal differed from the set presented during training, and (2) when the color or location of the duration signal was changed from values used during training. These results are discussed in terms of attention to uninformative features of a visual stimulus.     

Manipulating pre-feed, density of reinforcement, and extinction produces disruption in the Location variation of a temporal discrimination task in pigeons

When pharmacological and non-pharmacological agents are used to disrupt temporal discrimination, two major findings have emerged in the literature. One result reveals lateral shifts of the psychophysical curve for time due to disruptors, while the other is a decrease in accuracy for classifying short and long intervals and a flattening of the psychophysical curve. These results represent a discrepancy within the timing literature that requires clarification. The current study determined the effects of pre-feed, increased density of reinforcement during session, and extinction on the Location variation of a temporal discrimination procedure. The results showed that extinction and pre-feed (at higher levels), when presented in an acute fashion, led to right-ward shifts in the psychophysical curve. Our results, when compared to similar studies in the literature, suggest that lateral shifts are more likely to be found due to disruptors when the Location variation is being used and when procedures are less complicated.     

Changes in stimulus control during guided skill learning in rats

We examined the changes in stimulus control occurring during guided skill learning in rats. Twenty rats were trained to complete a left-right sequence of lever presses guided by the onset and offset of panel lights over their respective levers. Once sequence accuracy was high and stable, the rats were divided into two groups. For the No-Lights group, the lights were eliminated without changing the response requirements. Sequence accuracy decreased in all subjects, but accuracy was higher than that predicted by random chance. More practice produced greater autonomy and reduced dependence on the guiding lights. For the Reversed-Lights group, the lights were presented in reversed order without changing the response requirements. Sequence accuracy immediately plummeted and did not recover, violating expectations of automatization. The guiding lights appeared to overshadow other sources of stimulus control.     

Absolute and relational control of a sequential auditory discrimination by pigeons (Columba livia)

Recent evidence indicates that pigeons can readily learn visual discriminations based on both absolute and relational stimulus factors. To examine how these two types of control function in their non-dominant auditory modality, we tested four pigeons in a go/no-go sequential auditory discrimination in which both absolute and relational cues were redundantly available. In this task, sequences of different sounds created from one set of pitches were reinforced, while different sequences created from another set of pitches and any same sequences made from either set of pitches were not. Across three experiments, we independently varied the relative discriminability of the absolute and relational components. The pigeons were consistently and primarily controlled by the absolute fundamental pitch of our notes in all of the experiments, although this was influenced by the range and arrangement of the pitches used in each set. A majority of the pigeons also demonstrated relational control when this component was made more salient. The more robust control exhibited by absolute factors is consistent with the comparative hypothesis that birds in general may have a well-developed aptitude for processing absolute pitch in many auditory settings. The relational control is consistent with our recent evidence of same/different auditory learning by pigeons.     

Rats (Rattus norvegicus) and pigeons (Columbia livia) are sensitive to the distance to food,but only rats request more food when distance increases

Three experiments investigated foraging by rats and pigeons. In Experiment 1, each response on a manipulandum delivered food to a cup, with the distance between the manipulandum and the cup varying across conditions. The number of responses made before traveling to collect and eat the food increased with distance for rats, but not for pigeons. In Experiment 2, two manipulanda were placed at different distances from a fixed food source; both pigeons and rats preferentially used the manipulandum closest to the food source. Experiment 3 was a systematic replication of Experiment 1 with pigeons. In different conditions, each peck on the left key increased the upcoming hopper duration by 0.5, 1.5 or 2.5 s. Completing a ratio requirement on the right key of 1, 4, 8, 16 or 32 pecks, depending on the condition, then produced the food hopper for a duration that depended on the number of prior left pecks. As the ratio requirement increased on the right key, pigeons responded more on the left key and earned more food. Overall, the results replicate previous research, underlining similarities and differences between these species. The results are discussed in terms of optimal foraging, reinforcer sensitivity and delay discounting.     

The effect of stimulus discriminability on strategies for learning multiple temporal discriminations

The goal was to identify training conditions under which temporal intervals that are signaled by different stimuli are memorized (i.e., the temporal behavior is readily shown to be under stimulus control). Undergraduate students were trained on three signaled temporal discriminations using a peak procedure. The intervals were trained in either blocks of trials or with trials intermixed within the session, and then they were given a transfer test with intermixed trials. There were two levels of stimulus discriminability, defined by the similarity of the stimuli. Most participants memorized the intervals when the discriminations were intermixed within the session, or were easy, but not when the discriminations occurred in blocks and were difficult. In the transfer tests, those participants trained in the difficult discrimination that occurred in blocks of trials typically continued to perform as they did during the last-trained interval, regardless of the stimulus presented. These results are better explained by a memory retrieval than a memory storage account.     

Inter-modal learning task in bottlenosed dolphins (Tursiops truncatus): a preliminary study showed that social factors might influence learning strategies

We studied the dolphins capacity to perform a cognitive task when information arrives through two different sensory modalities (visual and auditory). Three female bottlenosed dolphins (Tursiops truncatus) were submitted to a two-, three-, or four-choice visually combined with auditory discrimination problem without any food reward. Since they were not isolated, we examined the significance of the role of identified social constraints on the learning process. The results tended to show an ability to associate simple visual forms and auditory information using an underwater touchscreen. This task was learnt in various ways according to identified social constraints. For each subject, we examined and discussed the number of successful answers, their ability to focus attention on the test and to acquire, or not, the specific task, while noting influences of the social interactions and the social hierarchy on the whole acquisition process.     

Response sequence difficulty in an incremental repeated acquisition (learning) procedure

Incremental repeated acquisition (IRA) procedures require subjects to learn a different sequence of behavioral responses during each experimental session with required response sequences increasing incrementally in length as subjects demonstrate mastery of shorter response chains. The purpose of this study was to investigate whether some response sequences are more or less difficult to acquire than others. If true, then sequence difficulty must be considered as a potential confound when attempting to assess the effects of drugs and other experimental manipulations on learning. Accuracy for each response sequence was assessed using control data from two large rodent studies, and each sequence was classified as easy, moderate or hard. Sequences that required responses on adjacent levers were easier (characterized by higher accuracies) to acquire than those that required responses on non-adjacent levers. In addition, sequences that required responses on only two of three response levers were easier to acquire than those that required responses on all three levers. These results provide strong evidence for differing levels of response sequence difficulty in IRA procedures with sequence difficulty seeming to be dependent on whether or not responses are required on adjacent levers.     

Ultrastructural reconstruction of Taenia ovis oncospheres from serial sections

The cellular organisation of Taenia ovis oncospheres is interpreted from ultrathin serial sections and transmission electron microscopy following high pressure freezing and freeze-substitution. The surface of a hatched, non-activated T. ovis oncosphere is covered by an oncospheral membrane below which is the tegument bearing microvilli. The basal lamina of the tegument is underlain by broad bands of peripheral somatic musculature. Three pairs of hooks and associated muscles are present in the somatophoric third of the oncosphere. Approximately 19 cells of seven different types were identified which include: (i) a quadri-nucleated syncytium of penetration gland type 1 containing two lateral pairs of cell bodies interconnected by narrow cytoplasmic bridges (PG1); (ii) a quadri-nucleated syncytium of penetration gland type 2 (PG2); (iii) a single-nucleated median mesophoric gland cell; (iv) 10 somatic cells; (v) two germinative cells; (vi) two nerve cells; and (vii) a pair of median somatophoric cells. This study provides a clear understanding of the morphology of T. ovis oncospheres and forms the basis for further investigations into the biology of taeniid oncospheres.     

Scrounger numbers and the inhibition of social learning in pigeons

Social foraging can inhibit the learning and performance of food-finding behaviours. Confusion, overshadowing and frequency-dependent payoffs may all contribute to the inhibition, but standard experimental procedures make the separation of these effects difficult. In this study, we combine characteristics of cage and aviary experiments and present either a single naive pigeon or groups of three naive pigeons with a pre-trained producer opening an apparatus in an aviary. All naive birds scrounged on the 3456 openings they witnessed. In a post-test given in the absence of other birds, all single scroungers opened the apparatus, but only one of the group-scrounging pigeons did. Scrounger numbers appear to play an important role in the inhibition of food-finding behaviour, suggesting that confusion is a major component of learning in a social context.     

Stimulus comparison in perceptual learning: roles of sensory preconditioning and latent inhibition

Rats were given exposure to a compound flavour (AX) and to one element of that compound (X). Two drinking tubes were made available to the rat on each exposure trial. For group concurrent (CNC) one tube contained AX and the other X. For groups alternating (ALT) and blocked (BLK), however, both tubes contained the same flavour (AX or X). Group ALT received AX and X on alternate trials; group BLK received AX in the first block of trials and X on the second, or vice versa. After an aversion had been established to X the groups were tested with AX. It was found that group ALT showed less generalization from X to AX than did group BLK. This difference was not accompanied by a parallel difference in the level of conditioning to X. However, group CNC showed both stronger conditioning to X and greater generalization from X to AX than groups ALT and BLK. Implications for the role of stimulus comparison in the perceptual learning effect are discussed.