Case series: Lymphoid neoplasia in three elasmobranch species.

Elasmobranchs (sharks and rays) are charismatic cartilaginous fish, popular in public aquaria. Almost 200 shark and ray species are listed as threatened by the International Union for Conservation of Nature (IUCN), demonstrating the importance of captive breeding and research programmes. Limited studies investigate diseases of elasmobranchs in captive and free-living environments, and among available literature neoplasia is rarely reported, with even fewer cases of lymphoid neoplasia documented. This article outlines the first reports of lymphoid neoplasia in three elasmobranch species in which haematopoietic neoplasms have not been reported to date. It summarizes signalment, history and histopathologic findings in an undulate ray, Raja undulata (Lacepede), a common smooth-hound, Mustelus mustelus (Linnaeus) and a bat ray, Myliobatis californica (Gill). Lesions were confirmed in a wide range of tissues and evidence of lymphoid leukaemia was seen in two cases. This small-scale review demonstrates that lymphoid neoplasia should be considered as a differential diagnosis in elasmobranchs presenting with lethargy and anorexia and highlights the challenges of immunohistochemical work up.

A space of goals: the cognitive geometry of informationally bounded agents.

Traditionally, Euclidean geometry is treated by scientists as a priori and objective. However, when we take the position of an agent, the problem of selecting a best route should also factor in the abilities of the agent, its embodiment and particularly its cognitive effort. In this paper, we consider geometry in terms of travel between states within a world by incorporating information processing costs with the appropriate spatial distances. This induces a geometry that increasingly differs from the original geometry of the given world as information costs become increasingly important. We visualize this 'cognitive geometry' by projecting it onto two- and three-dimensional spaces showing distinct distortions reflecting the emergence of epistemic and information-saving strategies as well as pivot states. The analogies between traditional cost-based geometries and those induced by additional informational costs invite a generalization of the notion of geodesics as cheapest routes towards the notion of infodesics. In this perspective, the concept of infodesics is inspired by the property of geodesics that, travelling from a given start location to a given goal location along a geodesic, not only the goal, but all points along the way are visited at optimal cost from the start.

The effect of Gaussian noise on the threshold, dynamic range, and loudness of analogue cochlear implant stimuli.

The deliberate addition of Gaussian noise to cochlear implant signals has previously been proposed to enhance the time coding of signals by the cochlear nerve. Potentially, the addition of an inaudible level of noise could also have secondary benefits: it could lower the threshold to the information-bearing signal, and by desynchronization of nerve discharges, it could increase the level at which the information-bearing signal becomes uncomfortable. Both these effects would lead to an increased dynamic range, which might be expected to enhance speech comprehension and make the choice of cochlear implant compression parameters less critical (as with a wider dynamic range, small changes in the parameters would have less effect on loudness). The hypothesized secondary effects were investigated with eight users of the Clarion cochlear implant; the stimulation was analogue and monopolar. For presentations in noise, noise at 95% of the threshold level was applied simultaneously and independently to all the electrodes. The noise was found in two-alternative forced-choice (2AFC) experiments to decrease the threshold to sinusoidal stimuli (100 Hz, 1 kHz, 5 kHz) by about 2.0 dB and increase the dynamic range by 0.7 dB. Furthermore, in 2AFC loudness balance experiments, noise was found to decrease the loudness of moderate to intense stimuli. This suggests that loudness is partially coded by the degree of phase-locking of cochlear nerve fibers. The overall gain in dynamic range was modest, and more complex noise strategies, for example, using inhibition between the noise sources, may be required to get a clinically useful benefit.