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-right 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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The vector sum model of pigeon landmark use.

Two experiments further tested a model of how pigeons use landmarks to find a location. The vector sum model (K. Cheng, 1988) predicts that when a landmark is shifted in one direction from its usual position, the bird's peak place of search may shift in that direction, but not in the orthogonal direction. The weight placed on a particular landmark is estimated by the extent to which the bird shifts its searching in the direction of the landmark shift. In the experiments, birds were trained to find a goal with one near landmark and one far landmark on either side of it. On occasional tests, one or both landmarks were shifted. Results showed that on the whole, the birds weighted the nearer landmark more than the farther landmark. In conformity with the predictions of the vector sum model, no bird shifted its peak place of search in the direction orthogonal to the direction of landmark shift. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multiple-landmark piloting in pigeons (Columba livia): Landmark configuration as a discriminative cue.

Using the landmark-transformation technique, researchers have shown that pigeons (Columba livia) tend to encode a goal location relative to 1 landmark, even when multiple landmarks are in the vicinity of the goal. The current experiments examined pigeons' ability to use configural information from a set of landmarks by making the arrangement of 4 landmarks a discriminative cue to the location of buried seeds. Results showed that pigeons used information from the 3 consistently placed landmarks to search accurately when 1 landmark was displaced. Findings indicate that pigeons are able to search for a goal using information from multiple landmarks instead of just 1 and that landmark use by these birds may be more flexible than previously theorized. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Homing in pigeons: the role of the hippocampal formation in the representation of landmarks used for navigation

When given repeated training from a location, homing pigeons acquire the ability to use familiar landmarks to navigate home. Both control and hippocampal-lesioned pigeons succeed in learning to use familiar landmarks for homing. However, the landmark representations that guide navigation are strikingly different. Control and hippocampal-lesioned pigeons were initially given repeated training flights from two locations. On subsequent test days from the two training locations, all pigeons were rendered anosmic to eliminate use of their navigational map and were phase- or clock-shifted to examine the extent to which their learned landmark representations were dependent on the use of the sun as a compass. We show that control pigeons acquire a landmark representation that allows them to directly use landmarks without reference to the sun to guide their flight home, called "pilotage". Hippocampal-lesioned birds only learn to use familiar landmarks at the training location to recall the compass direction home, based on the sun, flown during training, called "site-specific compass orientation." The results demonstrate that for navigation of 20 km or more in a natural field setting, the hippocampal formation is necessary if homing pigeons are to learn a spatial representation based on numerous independent landmark elements that can be used to directly guide their return home.     

Searching by rules: Pigeons' (Columba livia) landmark-based search according to constant bearing or constant distance.

Pigeons (Columba livia) searched for a goal location defined by a constant relative spatial relationship to 2 landmarks. For one group, landmark-to-goal bearings remained constant while distance varied. For another group, landmark-to-goal distances remained constant while direction varied. Birds were trained with 4 interlandmark distances and then tested with 5 novel interlandmark distances. Overall error magnitude was similar across groups and was larger than previously reported for Clark's nutcrackers (Nucifraga columbiana). During training, error magnitude increased with interlandmark distance for constant-bearing but not constant-distance birds. Both groups searched less accurately along the axis parallel to landmarks than along the perpendicular axis. Error magnitude increased with novel extrapolated interlandmark distances but not with novel interpolated distances. Results suggest modest geometric rule learning by pigeons. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A comparative study of geometric rule learning by nutcrackers (Nucifraga columbiana), pigeons (Columba livia) and jackdaws (Corvus monedula).

Three avian species, a seed-caching corvid (Clark's nutcrackers; Nucifraga columbiana), a non-seed-caching corvid (jackdaws; Corvus monedula), and a non-seed-caching columbid (pigeons; Columba livia), were tested for ability to learn to find a goal halfway between 2 landmarks when distance between the landmarks varied during training. All 3 species learned, but jackdaws took much longer than either pigeons or nutcrackers. The nutcrackers searched more accurately than either pigeons or jackdaws. Both nutcrackers and pigeons showed good transfer to novel landmark arrays in which interlandmark distances were novel, but inconclusive results were obtained from jackdaws. Species differences in this spatial task appear quantitative rather than qualitative and are associated with differences in natural history rather than phylogeny. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning of absolute and relative distance and direction from discrete visual landmarks by pigeons (Columba livia).

In an open-field search task, pigeons (Columba livia) were trained to search for a goal located at the midpoint of the hypothetical line connecting two discrete visual landmarks positioned 60 cm apart. In Experiment 1, global orienting cues were absent. After reaching training criteria, pigeons were tested with novel interlandmark distances. Search location and error on test trials suggested pigeons learned relative distance. In Experiment 2, a global orienting cue was present. After reaching training criteria, pigeons were again tested with novel interlandmark distances. Results suggested pigeons learned relative and absolute distances. In Experiment 3, pigeons searched at the midpoint of rotated arrays in both the presence and absence of an orienting cue indicating learning of relative direction. In Experiment 4, pigeons searched in the appropriate goal direction when presented with a single landmark in the presence of the orienting cue but not in its absence indicating learning of absolute direction. Results implicate a stable frame of reference as critical to spatial coding strategies and suggest pigeons are able to code location based on absolute and relative distance and direction from discrete visual landmarks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Geometric rule learning by Clark's nutcrackers (Nucifraga columbiana).

Clark's nutcrackers (Nucifraga columbiana) were trained to search in a location defined by its geometric relationship to 2 landmarks. Two groups were trained to search at different points along the line connecting the landmarks, and 2 groups were trained to find the 3rd point of a triangle, on the basis of either direction or distance from the landmarks. All groups learned and transferred to new interlandmark distances. However, the constant-distance group learned more slowly, searched less accurately, and showed less transfer than the other 3 groups. When tested with new orientations of the landmarks, the birds tended to follow small but not large rotations. When tested with a single landmark, birds in the half quarter, and constant-bearing groups searched in the appropriate direction from the landmark, but birds in the distance group did not. These results demonstrate that nutcrackers can learn a variety of geometric principles, that directional information may be weighted more heavily than distance information, and that the birds can use both absolute and relative information about spatial relationships. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Internal sense of direction and landmark use in pigeons (Columba livia).

The relative importance of an internal sense of direction based on inertial cues and landmark piloting for small-scale navigation by White King pigeons (Columba livia) was investigated in an arena search task. Two groups of pigeons differed in whether they had access to visual cues outside the arena. In Experiment 1, pigeons were given experience with 2 different entrances and all pigeons transferred accurate searching to novel entrances. Explicit disorientation before entering did not affect accuracy. In Experiments 2-4, landmarks and inertial cues were put in conflict or tested 1 at a time. Pigeons tended to follow the landmarks in a conflict situation but could use an internal sense of direction to search when landmarks were unavailable. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Flexible learning and use of multiple-landmark information by pigeons (Columba livia) in a touch screen-based goal searching task.

Three touch screen-based experiments were conducted to investigate whether pigeons would learn to use configural information about a goal's location in relation to a multiple-landmark array. In Experiment 1, 4 pigeons (Columba livia) were trained to peck a computer monitor at a location that constituted the third vertex of a hypothetical triangle defined by 2 different landmarks. The landmarks appeared in 3 orientations during the training, and the pigeons' goal-searching ability easily transferred to the landmarks presented in 3 novel orientations. Each landmark was asymmetric, so we next examined whether the pigeons used (a) the small-scale, local orientation information that could be inferred from each landmark individually, or (b) the large-scale, configural information that could be inferred from the spatial arrangement of multiple landmarks taken as a whole. Even when each single landmark appeared by itself, the pigeons were able to locate the goal accurately, suggesting that the large-scale, configural information was not essential. However, when 1 landmark locally pointed to a location that was consistent with the triangular configuration and the other landmark locally pointed to a different location, the pigeons predominantly pecked at the configurally array-consistent location. These results suggest that the pigeons redundantly learned both the large-scale, configural strategy and the local, single-landmark strategy, but they mainly used the latter information, and used the former information solely to disambiguate conflicts when the 2 landmarks pointed toward different targets. Such flexible learning and use of redundant information may reflect the pigeons' adaptation to unstable wild environments during their evolutionary history. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Control of pigeons' spatial search by graphic landmarks in a touch-screen task.

Pigeons learned to peck an unmarked 2-cm–2 target area, defined by 4 visually distinct graphic landmarks, on a color monitor with an attached touch frame. The configuration of landmarks and target area was constant during training, but their location on the screen varied across trials. The presence, relative location, and features of the landmarks were manipulated on probe trials. Most birds showed control by only 1 or 2 of the landmarks, and some birds displayed surprisingly accurate search with a single landmark. For individual birds, landmark-removal tests were very consistent with landmark-shift tests in indicating which landmark or landmarks controlled search. However, the dominant landmark varied across birds. Manipulation of landmark color and shape revealed that control was based exclusively on color. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pigeons encode absolute distance but relational direction from landmarks and walls.

In recent studies, researchers have examined animals' use of absolute or relational distances in finding a hidden goal. When trained with an array of landmarks, most animals use the default strategy of searching at an absolute distance from 1 or more landmarks. In contrast, when trained in enclosures, animals often use the relationship among walls. In the present study, pigeons were trained to find the center of an array of landmarks or a set of short walls that did not block external cues. Expansion tests showed that both groups of pigeons primarily used an absolute distance strategy. However, on rotational tests, pigeons continued to search in the center of the array, suggesting that direction was learned in relation to array. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Searching in the Center: Pigeons (Columba livid) Encode Relative Distance From Walls of an Enclosure.

Pigeons (Columba livia) searched for food hidden in the center of a square enclosure. On occasional tests without food, the enclosure was (a) unchanged from training (control tests), (b) moved to different corners of the testing room (corner tests), or (c) doubled in size (expansion tests). The birds showed localized search in the center of the enclosure on control and corner tests. On expansion tests, some birds searched near the center of the enclosure, suggesting relative-distance encoding. Other birds searched at locations that maintained the training distance from walls, suggesting absolute-distance encoding. These results are consistent with previous studies on chicks (Gallus gallus) in similar enclosures and contrast with previous results on pigeons' responses to expansions of discrete landmark arrays. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Clark's Nutcrackers (Nucifraga columbiana) and the Effects of Goal--Landmark Distance on Overshadowing.

Three groups of Clark's nutcrackers (Nucifraga columbiana) were trained to find a goal location defined by an array of 4 landmarks that varied in goal--landmark distance. The arrays for each group differed in the distance of the closest landmark and contained goal--landmark distances that were common across groups, allowing for the examination of the effects of both relative and absolute goal--landmark distance on encoding of a landmark array. All 3 groups readily learned the task and were subsequently tested in probe tests with only single landmarks from the array available. Search error in tests with single landmarks was compared both within and across groups. Results demonstrated that both relative and absolute goal-landmark distances are important in spatial search. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The relative importance of global and local landmarks in navigation by Columbian ground squirrels (Spermophilus columbianus).

In order to survive, small burrowing mammals need to remember the locations of escape burrows. Therefore, it is important to know what types of landmarks are used to aid navigation in the wild. The author tested the ability of free-ranging Columbian ground squirrels (Spermophilus columbianus) to locate escape burrows when local (e.g., vegetation pattern, local relief), global (e.g., forest edge, mountain outline), or both types of landmarks were obstructed. Results suggest that squirrels need both local and global landmarks of the environment for successful navigation, and that the upper portion of the horizon is especially important for orientation. Moreover, the lack of information from one type of landmark (local or global) cannot be completely compensated by the other type. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sun compass and landmark orientation by black-capped chickadees (Parus atricapillus).

Black-capped chickadees (Parus atricapillus), nutcrackers, and jays use a variety of visual cues to relocate and retrieve hidden food caches. Results with scrub jays (Aphelocoma coerulescens) show that sun compass orientation may play an important role in cache retrieval. In a series of experiments, black-capped chickadees were trained to find food along 1 side of an octagonal cage and then subjected to a photoperiodic phase shift to test for the use of sun compass orientation. In some experimental conditions, search was influenced by sun compass information, even when this produced search in conflict with local landmarks. In other conditions, however, there was no indication that birds used the sun compass for orientation. Sun compass orientation by chickadees may depend on the nature and availability of familiar landmarks. Directional information provided by the sun compass is probably integrated with local landmark information, and may require local landmark information, to produce oriented spatial search by chickadees. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reorienting strategies in a rectangular array of landmarks by domestic chicks (gallus gallus).

Spatial reorientation in a rectangular array of four landmarks located in the center of a circular enclosure was investigated in domestic chicks (Gallus gallus). One of the landmark possessed unique visual features, indicating the location of a food reward. After training, chicks were tested (a) with the same array as during the training; (b) with four identical landmarks of the type previously nonrewarded, of the type previously rewarded, or of a new type; (c) after having transformed one of the landmarks located at the geometric incorrect location into the type of landmark previously rewarded; or (d) with a fifth landmark of the rewarded type at a new location. Chicks encoded information provided by local featural cues but not the geometric information provided by the shape of the array. Moreover, when trained in a rectangular array of identical landmarks chicks failed to reorient. In a second series of experiments, the array was located in correspondence to the corners of a rectangular enclosure. This time chicks successfully learned to locate the reward using geometric information. However, when the rectangular array was located in the center of a larger rectangular enclosure, chicks failed to reorient, indicating that the geometric information given by the macroscopic layout of arena surfaces was not used to specify different locations. These results suggest that chicks reorient on the basis of a local representation of single landmarks and that encoding of the global aspects of geometry only occurs with respect to the large, extended surfaces of an enclosure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Searching for the center: Spatial cognition in the domestic chick (Gallus gallus).

Chicks learned to find food hidden under sawdust by ground-scratching in the central position of the floor of a closed arena. When tested in an arena of identical shape but a larger area, chicks searched at 2 different locations, one corresponding to the correct distance (i.e., center) in the smaller (training) arena and the other to the actual center of the test arena. When tested in an arena of the same shape but a smaller area, chicks searched in the center of it. These results suggest that chicks are able to encode information on the absolute and relative distance of the food from the walls of the arena. After training in the presence of a landmark located at the center of the arena, animals searched at the center even after the removal of the landmark. Marked changes in the height of the walls of the arena produced some displacement in searching behavior, suggesting that chicks used the angular size of the walls to estimate distances. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Absolute pitch: Frequency-range discriminations in pigeons (Columba livia)--comparisons with zebra finches (Taeniopygia guttata) and humans (Homo sapiens).

Absolute pitch (AP) is the ability to classify individual pitches without an external referent. The authors compared results from pigeons (Columba livia, a nonsongbird species) with results (R. Weisman, M. Njegovan, C. Sturdy, L. Phillmore, J. Coyle, & D. Mewhort, 1998) from zebra finches (Taeniopygia guttata, a songbird species) and humans (Homo sapiens) in AP tests that required classification of contiguous tones into 3 or 8 frequency ranges on the basis of correlations between the tones in each frequency range and reward. Pigeons' 3-range discriminations were similar in accuracy to those of zebra finches and humans. In the more challenging 8-range task, pigeons, like zebra finches, discriminated shifts from reward to nonreward from range to range across all 8 ranges, whereas humans discriminated only the 1st and last ranges. Taken together with previous research, the present experiments suggest that birds may have more accurate AP than mammals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)