Oculomotor behavior and perceptual strategies in complex tasks.

While we know a great deal about the dynamics and characteristics of eye movements in relatively simple tasks performed under reduced laboratory conditions, we know less about oculomotor behavior in complex, multi-step tasks. Complex tasks are not necessarily difficult. Part of the transition from 'hard' to 'easy' in completing complex tasks is the gradual reduction in conscious effort required to complete the sub-tasks. We are interested in learning whether high-level perceptual strategies can aid that transition. In the past, subjects performed relatively simple tasks or the eye movements themselves were the instructed task. But outside the laboratory vision is a tool, not the task. To study the oculomotor system in its native mode, we developed a wearable eyetracker that allows natural eye, head and whole-body movements. Using the over-learned, common task of hand-washing, we measured the global characteristics of fixation duration, saccade amplitude, and the spatial distribution of fixation positions. An important observation was the emergence of higher-order perceptual strategies in the complex task: while most fixations were related to the immediate action, a small number of fixations were made to objects relevant only to future actions. Based on a control task that differed only in the high-level goal, we conclude that the look-ahead fixations represent a task-dependent strategy, not a general behavior elicited by the salience or conspicuity of objects in the environment. We propose that the strategy of looking ahead to objects of future relevance supports the conscious percept of an environment seamless in time as well as in space.

Effect of methotrexate in the biology of free vascularized bone grafts. A comparative experimental study in the dog.

To evaluate the effects of methotrexate (MTX) on the biology of a vascularized bone graft (VBG), a study of adult dogs was performed. Different protocols of treatment using MTX, with or without the administration of citrovorum rescue factor (CRF), were studied. A controlled experiment involving 18 dogs was performed to evaluate the biology of a free vascularized rib graft used to reconstruct a 7-cm segmental defect in the femoral shaft. The grafts were examined at five, eight, and 14 weeks after surgery. Bone union, remodeling, and vasculature were found to be normal, despite a high rate of cortical necrosis in the early follow-up periods (30-40%). In a similar group of VBG, MTX was administered at a dose of 1500 mg/m2 body surface (intravenous) from the 14th postoperative day, every three weeks, until the animals were killed. Citrovorum rescue factor was administered to avoid the toxic side effects of the MTX. The results of this group did not differ from those of the control group as far as bone union, remodeling, vasculature, and viability of the graft were concerned. Methotrexate did not, for the most part, affect the biology of a free vascularized bone graft.

The caudal gluteal vessels: a suitable recipient bundle for free bone grafting in the canine femur.

The caudal gluteal vascular bundle was analyzed in the dog to determine its suitability as a recipient area for free vascularized bone grafts in the femur. The anatomy of the caudal gluteal artery and vein, as well as the arterial blood flow, were studied. This bundle was also used to revascularize 50 free vascularized rib grafts for proximal and femoral shaft reconstruction. The pedicle was constant, long (6.12 +/- 1.85 cm), and easily accessible via a lateral approach. It was large enough (artery: 1.74 +/- 0.46 mm, vein: 2.27 +/- 0.69 mm) and had an adequate blood flow (99 +/- 8 ml/mn) for microvascular techniques. Due to the existence of three anastomotic vascular rings with both the superficial and deep femoral bundles, these vessels had a bidirectional blood flow. In all the free vascularized rib grafts the caudal gluteal vessels were distally based (reversed blood flow) and provided a sufficient blood supply to the grafted bone. These results suggest that the caudal gluteal vessels are excellent recipient vessels for research in the field of free vascularized bone grafts using the canine femur.

Vascular medullary patency in free vascularized bone grafts: CT scan experimental study.

In an experimental study using 13 mongrel adult dogs, 6 cm of the anterior part of the left ninth rib were harvested, including the posterior intercostal vessels. The grafts were transferred, based on the periosteal circulation alone, to a previously induced femoral head ischemic necrosis. Microsurgical anastomoses were performed between the posterior intercostal vascular bundle and the caudal gluteal vessels at the recipient thigh zone. Using a high resolution CT scan and morphologic evaluation, it was demonstrated that the medullary circulation network filled on contrast medium. The entire cortex and medullary cavity were supplied from endosteal vessels coming from a reversed periosteal blood flow.