Pulmonary hypertension (PH) is an end result of a diverse array of complex clinical conditions that invoke hemodynamic and pathophysiological changes in the pulmonary vasculature. Many patients' symptoms begin with dyspnea on exertion for which screening tests such as chest roentgenograms and more definitive noninvasive tests such as CT scans are ordered initially. It is imperative that clinicians are cognizant of subtle clues on these imaging modalities that alert them to the possibility of PH. These clues may serve as a stepping stone towards more advanced noninvasive (echocardiogram) and invasive (right heart catheterization) testing. On the CT scan, the signs are classified into mediastinal and lung parenchymal abnormalities. In addition to suspecting the diagnosis of PH, this paper provides a pictorial essay to guide health care professionals in identifying the etiology of PH. This paper also provides concrete definitions, wherever possible, of what constitutes abnormalities in PH, such as dilated pulmonary arteries, pruning of vessels, and increased thickness of free wall of the right ventricle. The sensitivities and specificities of each sign are enumerated. The common radiographic and clinical features of many different etiologies of PH are tabulated for the convenience of the readers. Some newer imaging modalities such as dual-energy CT of the chest that hold promise for the future are also described.

Honeybees foraged from six locations, each of which was baited with sugar solution prior to each experimental trial. Under a variety of conditions, bees exhibited a small but reliable tendency to avoid revisits to locations that they had visited earlier during the experimental trial. These results replicate those of Brown and Demas (1994),who concluded that bees use working memory to discriminate previously visited locations from those not yet visited. The present experiments included procedures that allowed alternatives to this explanation to be more completely ruled out. The extent of spatial working memory performance exhibited by honeybees in these experiments appears to be limited by a process other than working memory capacity, perhaps the ability of bees to discriminate among several locations in close proximity to one another.A distinction fundamental to our understanding of human and animal memory systems is that between reference memory and working memory (see, e.g., Baddeley, 1986;Honig, 1978). Information that remains more or less stable over time is thought to be stored in a largecapacity, long-duration reference memory system, whereas a relatively small-capacity and often short-duration system is used to store information that changes in content often or is only temporarily useful. In humans, working memory is generally considered to be the cognitive structure in which information is stored while active cognitive processes operate on that information (Baddeley, 1986).

Experiment 3 was conducted in partial fulfillment of the requirements for J.A.M.'s master's degree under the supervision of M.F.B.

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