Domestic dogs (Canis familiaris) perform above chance on invisible displacement tasks despite showing few other signs of possessing the necessary representational abilities. Four experiments investigated how dogs find an object that has been hidden in 1 of 3 opaque boxes. Dogs passed the task under a variety of control conditions, but only if the device used to displace the object ended up adjacent to the target box after the displacement. These results suggest that the search behavior of dogs was guided by simple associative rules rather than mental representation of the object's past trajectory. In contrast, Experiment 5 found that on the same task, 18-and 24-month-old children showed no disparity between trials in which the displacement device was adjacent or nonadjacent to the target box.The invisible displacement task was originally conceived by Piaget (1937Piaget ( /1954) as a measure of toddlers' transition to Stage 6 in his theory of object permanence. In the classic task, the subject sees the experimenter hide a desired object under a displacement device, typically a small opaque container. The experimenter slides the displacement device under one of several hiding boxes, surreptitiously deposits the object beneath this box, and shows the subject that the displacement device is now empty. To find the object, the subject cannot rely on perceptual information alone but rather must infer the object's location by mentally representing its past trajectory (e.g., Call, 2001). The task is thus thought to provide evidence of representational thought: the ability to entertain representations of objects or events that cannot be directly perceived.As such, Piaget's invisible displacement task continues to feature strongly in both developmental and comparative research and theory. In Perner's (1991) theory of representational development, for example, passing the invisible displacement task is one of several markers of the emergence of a capacity for secondary representation. Perner suggests that prior to the middle of their 2nd year, infants have access only to primary representations; that is, they maintain a direct model of reality that is continually updated with incoming perceptual information. Passing the invisible displacement task indicates that the child can go beyond a single updating model to entertain multiple models of the world. That is, the child is able to hold in mind a model of the current world (primary representation: displacement device empty) as well as a model of the past world (secondary representation: displacement device with object under large box). By collating these two models the child can infer the likely location of the surreptitiously displaced object. Children typically begin passing the invisible displacement task at approximately 18 -24 months of age (e.g., Kramer, Hill, & Cohen, 1975;Piaget, 1937Piaget, /1954. Perner (1991) argues that several other abilities emerging in the 2nd year, such as mirror self-recognition and pretend play, also involve secondary representations. At le...

Previous research suggests that chimpanzees understand single invisible displacement. However, this Piagetian task may be solvable through the use of simple search strategies rather than through mentally representing the past trajectory of an object. Four control conditions were thus administered to two chimpanzees in order to separate associative search strategies from performance based on mental representation. Strategies involving experimenter cue-use, search at the last or first box visited by the displacement device, and search at boxes adjacent to the displacement device were systematically controlled for. Chimpanzees showed no indications of utilizing these simple strategies, suggesting that their capacity to mentally represent single invisible displacements is comparable to that of 18-24-month-old children.

Proximal fractures of the fifth metatarsal are most common in young male athletes. These fractures are devastating to athletes because they are slow to heal and have a high potential for delayed union, nonunion, and refracture. 4,9,[14][15][16][17][18][19]26,28 These fractures can be acute, stress, or combined acute/stress fractures of the proximal portion of the fifth metatarsal. The Jones fracture 4,8 was first described by Jones in 1902 13 and involves the proximal third of the fifth metatarsal, distal to the insertion of the fibularis (peroneus) brevis tendon, 1.5 cm from the tuberosity of the fifth metatarsal (figure 1). 5,7,8,16,23 Jones described the mechanism of injury in vivid terms: "so powerful are the ligaments that dislocation is rare. It is obviously easier to break the bone than to dislocate it." 13 The fifth metatarsal is subjected to 3-point bending (figure 1) when the foot lands in a relatively inverted position. Forces are imposed at the proximal end of the fifth metatarsal by the ground reaction force and soft tissues such as the fibularis brevis, lateral bands of the plantar fascia, and ligamentous/capsular tissue between the cuboid and the base of the fifth metatarsal. Force is also imposed by the ground reaction force at the distal end of the metatarsal as a result of the foot being in a relatively inverted position. Finally, the base of the fourth metatarsal applies a force in response to the previously described forces, completing the 3-point bending stress that may produce a stress fracture in response to cumulative fatigue, an acute fracture following sufficiently high-magnitude loading, or a combination of the two. Weight bearing that occurs with the foot in an inverted position, therefore, tends to promote the t studY design: Preintervention and postintervention, repeated-measures experimental design.t oBJectives: The objective was to investigate the effects of foot orthoses with medial arch support on ankle inversion angle and plantar forces and pressures on the fifth metatarsal during landing for a basketball lay-up and during the stance phase of a shuttle run.t Background: Proximal fractures of the fifth metatarsal, specifically the Jones fracture, are common in sports. Wearing foot orthoses with medial arch support could increase the ankle inversion angle and the plantar forces and pressure on the fifth metatarsal that may increase the risk for fifth metatarsal fracture.t MetHods and Measures: Three-dimensional (3-D) videographic, force plate, and in-shoe plantar force and pressure data were collected during landing after a basketball lay-up and during the stance phase of a shuttle run with and without foot orthoses with medial arch support for 14 male subjects. Two-way ANOVAs with repeated measures were performed to compare ankle inversion angle, maximum forces, and pressure on the fifth metatarsal head and base between conditions and between tasks.t results: The maximum ankle inversion angle and maximum plantar force and pressure on the base of the fifth metatarsal during both ...

This study investigated the ability of a captive chimpanzee (Pan troglodytes) to recognise when he is being imitated. In the experimental condition of test 1a, an experimenter imitated the postures and behaviours of the chimpanzee as they were being displayed. In three control conditions the same experimenter exhibited (1) actions that were contingent on, but different from, the actions of the chimpanzee, (2) actions that were not contingent on, and different from, the actions of the chimpanzee, or (3) no action at all. The chimpanzee showed more "testing" sequences (i.e., systematically varying his actions while oriented to the imitating experimenter) and more repetitive behaviour when he was being imitated, than when he was not. This finding was replicated 4 months later in test 1b. When the experimenter repeated the same actions she displayed in the experimental condition of test 1a back to the chimpanzee in test 2, these actions now did not elicit those same testing sequences or repetitive behaviours. However, a live imitation condition did. Together these results provide the first evidence of imitation recognition in a nonhuman animal.

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