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 variety of mechanisms. Navigation, for example, may be achieved through inertial guidance, orientation to a beacon, piloting by use of landmarks, or developing a spatial representation of the environment (Gallistel, 1990). Questions concerning which aspects of an environment are encoded and used in navigation have been addressed in recent research (for reviews, see Cheng & Spetch, 1998; Gallistel, 1990; and Poucet, 1993). Many studies have shown that animals can encode and use multiple sources of information to locate a goal (e.g., Spetch & Edwards, 1988) and that the primacy of control by different sources of information may differ according to context (e.g., Strasser & Bingman, 1996) or species (e.g., Brodbeck, 1994). One particularly interesting set of results has emerged from studies that have controlled and manipulated the information available for encoding by restricting access to navigational cues in an enclosed environment and by disrupting other positional cues through disorientation techniques (Cheng,

Pigeons' choice between reliable (100%) and unreliable (50%) reinforcement was studied using a concurrent-chains procedure. Initial links were fixed-ratio 1 schedules, and terminal links were equal fixed-time schedules. The duration of the terminal links was varied across conditions. The terminal link on the reliable side always ended in food; the terminal link on the unreliable side ended with food 50% of the time and otherwise with blackout. Different stimuli present during the 50% terminal links signaled food or blackout outcomes under signaled conditions but were uncorrelated with outcomes under unsignaled conditions. In signaled conditions, most pigeons displayed a nearly exclusive preference for the 100% alternative when terminal links were short (5 or 10 s), but with terminal links of 30 s or longer, preference for the 100% alternative was sharply reduced (often to below .5). In unsignaled conditions, most pigeons showed extreme preference for the 100% alternative with either short (5 s) or longer (30 s) terminal links. Thus, pigeons' choice between reliable and unreliable reinforcement is influenced by both the signal conditions on the unreliable alternative and the duration of the terminal-link delay. With a long delay and signaled outcomes, many pigeons display a suboptimal tendency to choose the unreliable side.

When making decisions on the basis of past experiences, people must rely on their memories. Human memory has many well-known biases, including the tendency to better remember highly salient events. We propose an extreme-outcome rule, whereby this memory bias leads people to overweight the largest gains and largest losses, leading to more risk seeking for relative gains than for relative losses. To test this rule, in two experiments, people repeatedly chose between fixed and risky options, where the risky option led equiprobably to more or less than did the fixed option. As was predicted, people were more risk seeking for relative gains than for relative losses. In subsequent memory tests, people tended to recall the extreme outcome first and also judged the extreme outcome as having occurred more frequently. Across individuals, risk preferences in the risky-choice task correlated with these memory biases. This extreme-outcome rule presents a novel mechanism through which memory influences decision making.

Pigeons' memory for event duration was investigated using a delayed matchingto-sample procedure. When a retention interval of variable length intervened between sample and comparison stimuli, pigeons responded as though long samples had been short after retention intervals of 10 sec or more. This "chooseshort" effect occurred in each subject, whether the subject was naive or experienced, whether sample durations were represented by food access or light, or whether a two-or three-choice procedure was used. A subjective-shortening model was proposed in which it was assumed that working memory of the sample duration "shortens" over the retention interval. Comparison of this memory with a stable reference memory produces the tendency to respond as though a long sample were short. Three predictions derived from the model were confirmed. First, after a long-retention interval, psychophysical functions relating probability of choosing "long" to sample duration were shifted toward longer durations. Second, stepwise increases in the retention interval produced a temporary chooseshort effect, whereas stepwise decreases produced a temporary choose-long effect. Third, with extended training at a given retention interval, the choose-short and choose-long effects diminished. Only the subjective-shortening model appears to account for all of these results.

Whether buying stocks or playing the slots, people making real-world risky decisions often rely on their experiences with the risks and rewards. These decisions, however, do not occur in isolation but are embedded in a rich context of other decisions, outcomes, and experiences. In this paper, we systematically evaluate how the local context of other rewarding outcomes alters risk preferences. Through a series of four experiments on decisions from experience, we provide evidence for an extreme-outcome rule, whereby people overweight the most extreme outcomes (highest and lowest) in a given context. As a result, people should be more risk seeking for gains than losses, even with equally likely outcomes. Across the experiments, the decision context was varied so that the same outcomes served as the high extreme, low extreme, or neither. As predicted, people were more risk seeking for relative gains, but only when the risky option potentially led to the high-extreme outcome. Similarly, people were more risk averse for relative losses, but only when the risky option potentially led to the low-extreme outcome. We conclude that in risky decisions from experience, the biggest wins and the biggest losses seem to matter more than they should.

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. Many creatures remember places to return to by the use of visual landmarks. In this spatial search strategy, some kinds of spatial relationships between the goal and its surrounding landmarks are encoded and are later used to find the goal again (for reviews, see Collett, 1992; GaUistel, 1990). In many studies of landmark-based spatial memory, the landmarks defining the goal are shifted about from one trial to the next, thus forcing the subject to use the experimentally specified landmarks to locate the target. This method has demonstrated the use of landmarks in studies with insects (e.g.,

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 airay 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.Experimental work has demonstrated that many animal species can encode the location of an important place in terms of nearby visual landmarks (see Gallistel, 1990, and Collett, 1992, for reviews). In several investigations of landmark use, a goal was located near an array of two or more local landmarks, with a directionally stable frame of reference provided by other cues (e.g.,

Pigeons responded on concurrent chains with equal initial- and terminal-link durations. In all conditions, the terminal links of one chain ended reliably in reinforcement; the terminal links on the alternative chain ended in either food or blackout. In Experiment 1, the terminal-link stimuli were correlated with (signaled) the outcome, and the durations of the initial and terminal links were varied across conditions. Preference did not vary systematically across conditions. In Experiment 2, terminal-link durations were varied under different stimulus conditions. The initial links were variable-interval 80-s schedules. Preference for the reliable alternative was generally higher in unsignaled than in signaled conditions. Preference increased with terminal-link durations only in the unsignaled conditions. There were no consistent differences between conditions with and without a common signal for reinforcement on the two chains. In the first series of conditions in Experiment 3, a single response was required in the initial links, and the stimulus conditions during 50-s terminal links were varied. Preference for the reliable outcome approached 1.0 in unsignaled conditions and was considerably lower (below .50 for 3 of 5 subjects) in signaled conditions. In a final series of signaled conditions with relatively long terminal links, preference varied with duration of the initial links. The results extend previous findings and are discussed in terms of the delay reduction signaled by terminal-link stimuli.