Marcia L. Spetch

PIGEONS' (COLUMBA LIVIA) ENCODING OF GEOMETRIC AND FEATURAL PROPERTIES OF A SPATIAL ENVIRONMENT

Pigeons (Columba livia) searched for hidden food in a rectangular environment constructed to eliminate external orientation cues. A feature group was initially trained with distinct features in each corner. A geometric group was initially trained with no featural information. Tests revealed that both groups encoded the geometry of the apparatus. The geometric group was then retrained with features, and a series of tests was administered to both groups. Transformation tests revealed that the groups differed in reliance on features versus geometry. Pigeons in the feature group followed the positive feature even when it was placed in a geometrically incorrect corner, whereas pigeons in the geometric group showed shared control by features and geometry. Both groups were able to use features in corners distant to the goal to orient themselves, and both groups relied more on the color than on the shape of the features. Survival within an environment frequently requires efficient processing of spatial information. Spatial abilities underlie activities that are critical for the individual (e.g., establishment of lodging, avoidance of predation, and attainment of nourishment) and for a species (e.g., migratory behavior or reproduction); these activities may involve a

Backward Conditioning: A Reevaluation of the Empirical Evidence

There is an apparent discrepancy between the widespread view that backward conditioning does not occur and the experimental evidence which suggests that it does. Backward pairing of conditioned and unconditioned stimuli frequently has resulted in effects similar to those produced by forward pairing, and the results of several recent experiments have established that such effects cannot be attributed to factors other than stimulus pairing per se. Surprisingly, even some of the earlier experiments that provided the basis for the current skepticism concerning backward conditioning provide evidence of its existence. The failure to recognize backward conditioning as a legitimate phenomenon seems to reflect theoretical biases rather than a paucity of empirical evidence. Thus backward conditioning and its properties merit renewed interest and rcexamination.

Use of Landmark Configuration in Pigeons and Humans: II. Generality Across Search Tasks

Pigeons and humans searched for a goal that was hidden in varied locations within a search space. The goal location was fixed relative to an array of identical landmarks. Pigeons searched on the laboratory floor, and humans searched on a table top or an outdoor field. In Experiment 1, the goal was centered in a square array of 4 landmarks. When the spacing between landmarks was increased, humans searched in the middle of the expanded array, whereas pigeons searched in locations that preserved distance and direction to an individual landmark. In Experiment 2, the goal was centered between and a perpendicular distance away from 2 landmarks aligned in the left-fight dimension. When landmark spacing was increased, humans, but not pigeons, shifted their searching away from the landmarks along the perpendicular axis. These results parallel those obtained in touch-screen tasks. Thus, pigeons and humans differ in how they use landmark configuration.

Overshadowing in landmark learning: touch-screen studies with pigeons and humans.

Overshadowing in landmark learning was studied in pigeons and undergraduates using a touch-screen spatial search task. Ss searched for an unmarked goal presented in varied locations on a computer screen. Graphic stimuli served as landmarks. The effect of the presence of other landmarks on the control acquired by a given landmark was assessed using a design in which each S was trained with 2 sets of landmarks. Both pigeons (Experiment 1) and humans (Experiments 2-4) showed evidence of learning more about a landmark that was the closest landmark of its set to the goal than about a landmark that was of equal distance to the goal but was not the closest landmark of its set. That is, control by a landmark was overshadowed when it occurred together with a landmark that was closer to the goal. Landmark effectiveness appears to depend not only on the absolute properties of a landmark but on relative factors. The relevance of basic principles of associative learning to spatial landmark learning is discussed.

Learning the Configuration of a Landmark Array: I. Touch-Screen Studies With Pigeons and Humans

Pigeons and humans searched on a touch-screen monitor for an unmarked goal located relative to an array of landmarks presented in varied screen locations. After training with the goal centered in various square arrays of 4 landmarks, humans, but not pigeons, transferred accurately to arrays with novel elements. Humans searched in the middle of expanded arrays, whereas pigeons preserved the distance and direction to a single landmark. When trained with the goal centered below 2 identical horizontally aligned landmarks, humans responded to horizontal expansions or contractions of the array by shifting their search vertically, preserving angles from landmarks to goal. Pigeons did not adjust their search vertically. Humans trained with a single landmark adjusted search distance when landmark size was changed. Both pigeons and humans use the configuration of a landmark array, but the underlying processes seem to differ.

Spatial encoding in mountain chickadees: features overshadow geometry

Encoding the global geometric shape of an enclosed environment is a principal means of orientation in human and non-human animals. Animals spontaneously encode the geometry of an enclosure even when featural information is available. Although features can be used, they typically do not overshadow geometry. However, all previously tested organisms have been reared in human-made environments with salient geometrical cues. Here, we show that wild-caught mountain chickadees (Poecile gambeli) do not spontaneously encode the geometry of an enclosure when salient features are present near the goal. However, chickadees trained without salient features encode geometric information, but this encoding is overshadowed by features.

Systematic errors in pigeons’ memory for event duration: Interaction between training and test delay

Pigeons trained to choose different stimuli following short- and long-duration signals make disproportionately more “short” choices (i.e., “choose-short errors”) following an increase in the retention interval and more “choose-long errors” following a decrease in this delay. The present experiment provided a systematic investigation of how these selective errors depend on the relationship between the training delay and the test delay. Pigeons were first trained with a 0-sec delay between the signal (2- or 8-sec food presentations) and the choice stimuli (red- and blue-lit keys). On subsequent test trials with 5- and 10-sec delays, choose-short errors predominated. Next, the birds were trained with a constant 10-sec delay and then tested with shorter or longer delays on some trials. The birds now responded accurately and without selective errors at the 10-sec training delay, but made choose-long errors at shorter delays and choose-short errors at longer delays. Finally, the birds were trained with a constant 20-sec delay and then tested with shorter and longer delays. Choose-long errors again appeared at shorter test delays, choose-short errors at longer test delays, and no differential errors at the 20-sec training delay. The selectivity of these errors generally increased with the absolute difference between the training and test delay. Theoretical implications of these results are discussed.

Growing in Circles Rearing Environment Alters Spatial Navigation in Fish

Animals of many species use the geometric shape of an enclosed rectangular environment to reorient, even in the presence of a more informative featural cue. Manipulating the rearing environment affects performance on spatial tasks, but its effect on the use of geometric versus featural navigational cues is unknown. Our study varied the geometric information available in the rearing environment (circular vs. rectangular rearing tanks) of convict cichlids (Archocentrus nigrofasciatus) and tested their use of navigational cues. All the fish used geometric information to navigate when no features were present. When features were present, the fish used geometric and featural information separately. If cues were in conflict, fish raised in a circular tank showed significantly less use of geometric information than fish raised in a rectangular tank. Thus, the ability to use geometry to navigate does not require exposure to angular geometric cues during rearing, though rearing environment affects the dominance of featural and geometric cues.

Pigeons Memory for Event Duration - Intertrial Interval and Delay Effects

The effects of within-session variations in the intertriai interval (ITI) and delay on pigeons’ memory for event duration were studied in delayed symbolic matching-to-sample tasks. Pigeons were trained to peck one color following a long (8 sec) sample and another color following a short (2 sec) sample. In the first three experiments, the baseline conditions included a 10-sec delay (retention interval) and a 45-sec ITI. During testing, the delay was varied from 0 to 20 sec, and the ITI that preceded the trial was varied from 5 to 90 sec. When the ITI and delay were manipulated separately (Experiments 1 and 2), the pigeons displayed a choose-short tendency when the delay was longer than 10 sec or when the ITI was longer than 45 sec, and a choose-long tendency when either the delay or the ITI was shorter than these baseline values. These effects occurred whether the sample was food access or light. When the ITI and delay were manipulated together, the pigeons showed a large choose-long error tendency when the short delay was tested together with a short ITI, and no systematic error tendency when the short delay was tested together with a longer ITI. A very large choose-short error tendency emerged on trials with a long delay and a long ITI; a reduced choose-short tendency was present when the long delay was presented together with a short ITI. In Experiment 4, the baseline conditions were a 0-sec delay and a 45-sec ITI. In this case variations in the ITI had a smaller and unidirectional effect: the pigeons showed a choose-long error tendency when the ITI was decreased, but no effect of ITI increases. Two hypotheses were proposed and discussed: (1) that pigeons judge sample durations relative to a background time composed of the ITI and delay, and (2) that the delay and ITI effects might arise from a combination of subjective shortening and proactive effects of samples from previous trials.

Pigeons' memory for event duration: Differences between choice and successive matching tasks☆

Abstract Two experiments examined memory for event duration in pigeons using choice and successive matching tasks. In the choice task, two stimuli were presented following the sample, and the correct choice depended upon the duration of the preceding sample. In the successive task, only one of two stimuli was presented following the sample, and whether responding was or was not reinforced depended upon the duration of the preceding sample. In the first experiment, a successive matching task was employed and accuracy decreased at an equivalent rate as a function of delay on short-sample and long-sample trials, regardless of whether the events which differed in duration were samples of houselight or food. The second experiment, which employed as samples different durations of houselight, replicated this result both in naive subjects and in subjects previously trained in a choice matching task. In addition, it was found that naive subjects which were trained and tested in a choice matching task demonstrated a more rapid decrease in accuracy on long-sample trials than on short-sample trials as a function of delay; a result which has been obtained in several previous studies and has been referred to as the “choose-short” effect. It was also found, however, that the choose-short effect did not occur in the choice matching task if subjects had been trained and tested previously in the successive matching task. It was concluded that pigeons employ different coding strategies in matching to sample duration in the choice and successive tasks.