The amygdala was more responsive to fearful (larger) eye whites than to happy (smaller) eye whites presented in a masking paradigm that mitigated subjects' awareness of their presence and aberrant nature. These data demonstrate that the amygdala is responsive to elements of.

List memory of pigeons, monkeys, and humans was tested with lists of four visual items (travel slides for animals and kaleidoscope patterns for humans). Retention interval increases for list-item memory revealed a consistent modification of the serial-position function shape: a monotonically increasing function at the shortest interval, a U-shaped function at intermediate intervals, and a monotonically decreasing function at the longest interval. The time course of these changes was fastest for pigeons, intermediate for monkeys, and slowest for humans.

Pigeons were trained to match-to-sample with several new methodologies: a large number of stimuli, computer-drawn color picture stimuli, responses monitored by a computer touch screen, stimuli presented horizontally from the floor, and grain reinforcement delivered onto the picture stimuli. Following acquisition, matching-to-sample concept learning was assessed by transfer to novel stimuli on the first exposure to pairs of novel stimuli. One group (trial-unique), trained with 152 different pictures presented once daily, showed excellent transfer (80% correct). Transfer and baseline performances were equivalent, indicating that the matching-to-sample concept had been learned. A second group (2-stimulus), trained with only two different pictures, showed no evidence of transfer. These results are discussed in terms of the effect of numbers of exemplars on previous failures to find concept learning in pigeons, and the implications of the positive finding from this experiment on abstract concept learning and evolutionary cognitive development.Human cognitive behavior is characterized, in part, by our ability to abstract rules and form abstract concepts (Medin & Schaffer, 1978). Indeed, even our ability to effectively communicate with others depends upon this ability (Premack, 1978). One question that logically follows from discussions of human cognitive capabilities is: To what degree can animals form and learn concepts? Whether they can or not, bears upon one measure of how unique humans really are in the evolutionary hierarchy of cognitive abilities.The concepts, which are the focus of this article, are relational ones; they depend upon relations between pairs of items, for example, in situations in which subjects judge whether or not two items are identical (same) or nonidentical (different)-a same/different task-or ones in which they choose a comparison item to match a previously presented sample item-matching-to-sample. It is possible to learn a rule-based concept in these situations, so that any pair of items can be correctly judged. These relational concepts are to be contrasted to

Although learning and memory theories hypothesize that memories are encoded by specific circuits, it has proven difficult to localize learning within a cortical area. Neural network theories predict that activation of a small fraction of the neurons in a circuit can activate that circuit. Consequently, altering the physiology of a small group of neurons might potentiate a specific circuit and enhance learning, thereby localizing learning to that circuit. In this study, we activated protein kinase C (PKC) pathways in small groups of neurons in rat postrhinal (POR) cortex. We microinjected helper virus-free herpes simplex virus vectors that expressed a constitutively active PKC into POR cortex. This PKC was expressed predominantly in glutamatergic and GABAergic neurons in POR cortex. This intervention increased phosphorylation of five PKC substrates that play critical roles in neurotransmitter release (GAP-43 and dynamin) or glutamatergic neurotransmission (specific subunits of AMPA or NMDA receptors and myristoylated alanine-rich C kinase substrate). Additionally, activation of PKC pathways in cultured cortical neurons supported activation-dependent increases in release of glutamate and GABA. This intervention enhanced the learning rate and accuracy of visual object discriminations. In individual rats, the numbers of transfected neurons positively correlated with this learning. During learning, neuronal activity was increased in neurons proximal to the transfected neurons. These results demonstrate that potentiating small groups of glutamatergic and GABAergic neurons in POR cortex enhances visual object learning. More generally, these results suggest that learning can be mediated by specific cortical circuits.

Four experiments investigated the content of the memory used by rats in mediating retention intervals interpolated during performance in a 12-arm radial maze. The delay occurred following either the 2nd, 4th, 6th, 8th, or 10th choice. A 15-min delay had the greatest disruptive effect when interpolated in the middle of the choice sequence and less of an effect when it occurred either earlier or later. This pattern of results was obtained when either a free- or forced-choice procedure was used prior to the delay and regardless of whether postdelay testing consisted of completion of the maze or two-alternative forced-choice tests. Assuming that the disruptive effect of a delay is a function of memory load, this implies that the rats used information about previously visited arms (retrospective memory) following an earlier interpolated delay but information about anticipated choices (prospective memory) following a delay interpolated late in the choice sequence. There appeared to be a recency effect only in the early and middle delay conditions. This provides converging evidence for the dual-code hypothesis. No evidence for prospective memory was obtained following a 60-min delay.

Categorization is essential for survival, and it is a widely studied cognitive adaptation in humans and animals. An influential neuroscience perspective differentiates in humans an explicit, rule-based categorization system from an implicit system that slowly associates response outputs to different regions of perceptual space. This perspective is being extended to study categorization in other vertebrate species, using category tasks that have a one-dimensional, rule-based solution or a two-dimensional, information-integration solution. Humans, macaques, and capuchin monkeys strongly dimensionalize perceptual stimuli and learn rule-based tasks more quickly. In sharp contrast, pigeons learn these two tasks equally quickly. Pigeons represent a cognitive system in which the commitment to dimensional analysis and category rules was not strongly made. Their results may reveal the character of the ancestral vertebrate categorization system from which that of primates emerged. The primate results establish continuity with human cognition, suggesting that nonhuman primates share aspects of humans' capacity for explicit cognition. The emergence of dimensional analysis and rule learning could have been an important step in primates' cognitive evolution.

An evaluation of computational models is carried out for flight dynamics simulations on low-speed aircraft with very-flexible high-aspect ratio wings. Structural dynamic models include displacement-based, strain-based, and intrinsic (first-order) geometrically-nonlinear composite beams, while thin-strip and vortex lattice methods are considered for the unsteady aerodynamics. It is first shown that all different beam finite element models (previously derived in the literature from different assumptions) can be consistently obtained from a single set of equations. This approach has been used to expand existing strain-based models to include shear effects. Comparisons are made in terms of numerical efficiency and simplicity of integration in flexible aircraft flight dynamics studies. On the structural modeling, it was found that intrinsic solutions can be several times faster than conventional ones for aircraft-type geometries. For the aerodynamic modeling, thin-strip models based on indicial airfoil response are found to perform well in situations dominated by small amplitude dynamics around large quasi-static wing deflections, while large-amplitude wing dynamics require three-dimensional descriptions (e.g. vortex lattice)

Previous research has shown that birds and primates have a rich repertoire of behavioral and cognitive skills, but the mechanisms underlying these abilities are not well understood. A common hypothesis is that these adaptations are mediated by an efficient long-term memory, allowing animals to remember specific external events and associate appropriate behaviors to these events. Because earlier studies have not sufficiently challenged memory capacity in animals, our comparative research examined with equivalent procedures the size and mechanisms of long-term memory in baboons and pigeons. Findings revealed very large, but different, capacities in both species to learn and remember pictureresponse associations. Pigeons could maximally memorize between 800 and 1,200 picture-response associations before reaching the limit of their performance. In contrast, baboons minimally memorized 3,500 -5,000 items and had not reached their limit after more than 3 years of testing. No differences were detected in how these associations were retained or otherwise processed by these species. These results demonstrate that pigeons and monkeys have sufficient memory resources to develop memory-based exemplar or feature learning strategies in many test situations. They further suggest that the evolution of cognition and behavior importantly may have involved the gradual enlargement of the long-term memory capacities of the brain.intelligence ͉ primate ͉ bird ͉ categorization ͉ picture processing B irds and primates have demonstrated a wide variety of cognitive capacities in different settings and are especially adept at learning visual discriminations (1-3). There has been a long and active debate on how such discriminations are learned. One prominent view has been an exemplar approach in which learning is mediated by the memorization of large number of stimulus-specific exemplars (4-7). Previous examinations of the size and durability of associative memory capacity in animals provide some credence for this possibility. Clark's Nutcrackers can remember 18-25 caches in a room containing 69 cache sites for as long as 180-285 days (8) and have been indirectly estimated to retrieve food from 3,000 to 6,000 stored caches over the winter, likely by using memory. In an earlier operantdiscrimination task, pigeons were able to memorize up to 320 randomly assigned pictorial stimuli (9). Comparable capacity studies have not been conducted in monkeys, but experimental evidence has demonstrated that objects viewed three to four times continue to be categorized as familiar by macaques 6 months later (10). In addition, macaques could reliably recognize pictures 6 months after an initial brief exposure of 30 sec (11). Despite these remarkable accomplishments of birds and monkeys, we postulated that earlier animal studies did not sufficiently challenge memory capacity over extended periods of time (12) and therefore had underestimated memory size in these different animals. These studies also were limited by their use of different procedures, making...