The evolution of visual processing and the construction of seeing systems

This paper is concerned with the evolution of visual mechanisms and the possibility of copying their principles at different levels of sophistication. It is an old question how the complex interaction between eye and brain evolved when each needs the other as a test-bed for successive improvements. I propose that the primitive mechanism for the separation of stationary objects relies on their relative movement against a background, normally caused by the animal's own movement. Apparently insects and many lower animals use little more than this for negotiating through a three-dimensional world, making adequate responses to individual objects which they 'see' without a cortical system or even without a large brain. In the development of higher animals such as birds or man, additional circuits store memories of the forms of objects that have been frequently inspected from all angles or handled. Simple visual systems, however, are tuned to a feature of the world by which objects separate themselves by movement relative to the eye. In making simple artificial visual systems which 'see', as distinct from merely projecting the image, it is more hopeful to copy the 'ambient' vision of lower animals than the cortical systems of birds or mammals.     

The ommatidium of the termite mastotermes darwiniensis

An electron microscope study of the compound eye of the termite Mastotermes darwiniensis shows that the ommatidia have both primitive and specialized features. The ommatidia are of the apposition type with eight similar retinular cells, a fused rhabdom, irregularly orientated rhabdomere tubules and no tracheae. The retinula cells contain lipid. The cone cells have unusual processes, which thicken towards the basement membrane and contain rough endoplasmic reticulum, granules and dense bodies. These processes may act as a primitive transport system for nutrients.     

Statocysts of medusae and evolution of stereocilia

Ectodermal sensory cells of the statolith each bear one nonmotile kinocilium, and in some hydromedusae bear stereocilia which are defined as distinct from microvilli by having fibrillar rootlets. The progressive elaboration of stereocilia can be traced. A hypothesis in which jellyfish statocysts evolve from vibration receptors avoids the difficulty of the uselessness of incipient gravity organs. Comparative study suggests that the kinocilium or its basal body is the transducer.     

Visual discrimination of radial cues by the honeybee (Apis mellifera)

This is a systematic study of the discrimination of black radially symmetrical patterns presented on a white vertical background and subtending 45 degrees or 50 degrees at the point of choice in a Y-maze apparatus. Before discrimination can occur, the ability to fixate is promoted by any radial pattern irrespective of the number of symmetry axes. A ring of spots can also stabilize the eye before the positions of the spots are discriminated.Cues for discrimination are of two main types. First, with fixed patterns of sectors or spots, the cue is the location of an area of black relative to the fixation point, and the particular number of axes is less important than the size of the individual areas. Secondly, evidence is presented for a family of filters with large fields and coarse tuning that detect patterns of radially symmetrical edges. These filters become more evident when the patterns are made of thin black radial bars or when they are rotated at random during the training. An angular shift of one radial pattern relative to the other, or a difference between numbers of bars, is best discriminated when one of the patterns but not the other has angles of 30 degrees, 60 degrees, or 120 degrees between radial edges, and least when the angles are 90 degrees. Baffles in the apparatus make the bees pause and fixate so that discrimination is improved. When targets are rotated during the learning process, radial cues for discriminations must be presented as edges, not as spots or areas. Besides detecting and fixating flowers, this system could be useful to estimate the perfection of their symmetry.     

Spatial coincidence of cues in visual learning by the honeybee (Apis mellifera)

The discrimination of patterns was studied in a Y-choice chamber fitted with a transparent baffle in each arm, through which the bees had a choice of two targets via openings 5cm wide. The bees see the positive (rewarded) and the negative (unrewarded) targets from a fixed distance. The patterns were bars (subtending 22 degrees x5.4 degrees at the point of choice) presented in one-quarter of each target. The bars were moved to a different quarter of the target every 5min, to make the location of black useless as a cue. A coincident presentation is when the bar on the left target is on the same side of the target as the bar on the right target. The bees learn the orientation cue when the presentation is coincident but otherwise cannot learn it. This experiment shows that bees do not centre their attention on the individual bars, otherwise they would always discriminate the orientation. Centring the target as a whole precedes learning. Having learned with the bar on one side of the targets, bees do not recognize the same cue presented on the other side. A separate orientation cue can be learned on each side. A radial/tangential cue is preferred to a conflicting orientation cue.     

The development of an innervated epithelial barrier model using a human corneal cell line and ND7/23 sensory neurons

The corneal epithelium is a highly innervated tissue and hence in vitro models that mimic the effects of chemicals or radiation (e.g. ultra violet) on this important barrier should include consideration of the potential role of innervation. A sensory neural cell line, ND7/23, was incorporated into a 2D and 3D model of a corneal epithelium, using a human corneal cell line, and effects on barrier integrity were neither adverse nor stimulatory. In the 3D model the nerve cell bodies were separated from the corneal epithelium, via a porous polycarbonate insert membrane. The ND7/23 cells were induced to form neurites and cease division when cultured in the keratinocyte medium employed for the corneal cells. In the absence of calcium, the epithelial barrier function was lost, shown by enhanced fluorescein leakage and relocation of ZO-1 and E-cadherin from the cell membrane. At 60 microM calcium, and above, the corneal cells formed tight junctions, with peripheral membrane location of ZO-1 and E-cadherin. The presence of the ND7/23 cells did not compromise or enhance the time taken to form these junctions, when monitored at 24-h intervals over 72 h. Both male- and female-derived human corneal cell lines showed a similar tight junction functional response to different medium calcium concentrations in the presence or absence of the ND7/23 cells. Once differentiated in keratinocyte medium, patch-clamped ND7/23 cells were capable of producing a whole-cell current when exposed to low pH (5.4), indicative of the presence of active pH-gated ion channels.     

Populous: a tool for building OWL ontologies from templates

BACKGROUND: Ontologies are being developed for the life sciences to standardise the way we describe and interpret the wealth of data currently being generated. As more ontology based applications begin to emerge, tools are required that enable domain experts to contribute their knowledge to the growing pool of ontologies. There are many barriers that prevent domain experts engaging in the ontology development process and novel tools are needed to break down these barriers to engage a wider community of scientists. RESULTS: We present Populous, a tool for gathering content with which to construct an ontology. Domain experts need to add content, that is often repetitive in its form, but without having to tackle the underlying ontological representation. Populous presents users with a table based form in which columns are constrained to take values from particular ontologies. Populated tables are mapped to patterns that can then be used to automatically generate the ontology's content. These forms can be exported as spreadsheets, providing an interface that is much more familiar to many biologists. CONCLUSIONS: Populous's contribution is in the knowledge gathering stage of ontology development; it separates knowledge gathering from the conceptualisation and axiomatisation, as well as separating the user from the standard ontology authoring environments. Populous is by no means a replacement for standard ontology editing tools, but instead provides a useful platform for engaging a wider community of scientists in the mass production of ontology content.