Fast Coding of Orientation in Primary Visual Cortex

Understanding how populations of neurons encode sensory information is a major goal of systems neuroscience. Attempts to answer this question have focused on responses measured over several hundred milliseconds, a duration much longer than that frequently used by animals to make decisions about the environment. How reliably sensory information is encoded on briefer time scales, and how best to extract this information, is unknown. Although it has been proposed that neuronal response latency provides a major cue for fast decisions in the visual system, this hypothesis has not been tested systematically and in a quantitative manner. Here we use a simple ‘race to threshold’ readout mechanism to quantify the information content of spike time latency of primary visual (V1) cortical cells to stimulus orientation. We find that many V1 cells show pronounced tuning of their spike latency to stimulus orientation and that almost as much information can be extracted from spike latencies as from firing rates measured over much longer durations. To extract this information, stimulus onset must be estimated accurately. We show that the responses of cells with weak tuning of spike latency can provide a reliable onset detector. We find that spike latency information can be pooled from a large neuronal population, provided that the decision threshold is scaled linearly with the population size, yielding a processing time of the order of a few tens of milliseconds. Our results provide a novel mechanism for extracting information from neuronal populations over the very brief time scales in which behavioral judgments must sometimes be made

Incremental grouping of image elements in vision

One important task for the visual system is to group image elements that belong to an object and to segregate them from other objects and the background. We here present an incremental grouping theory (IGT) that addresses the role of object-based attention in perceptual grouping at a psychological level and, at the same time, outlines the mechanisms for grouping at the neurophysiological level. The IGT proposes that there are two processes for perceptual grouping. The first process is base grouping and relies on neurons that are tuned to feature conjunctions. Base grouping is fast and occurs in parallel across the visual scene, but not all possible feature conjunctions can be coded as base groupings. If there are no neurons tuned to the relevant feature conjunctions, a second process called incremental grouping comes into play. Incremental grouping is a time-consuming and capacity-limited process that requires the gradual spread of enhanced neuronal activity across the representation of an object in the visual cortex. The spread of enhanced neuronal activity corresponds to the labeling of image elements with object-based attention

Surgical Management of the Labyrinthine Fistula Complicating Chronic Otitis Media with or without Cholesteatoma

Objectives: To present our most recent experience on the diagnosis and treatment of the labyrinthine fistula. The relative data are compared with those of our past experiences adopting the same modality of presenting the results. Methods: The clinical and surgical records of 334 patients affected with chronic otitis media with or without cholesteatoma were analyzed to evaluate the frequency, site, and size of the labyrinthine fistulae. In this study, a more agressive strategy was adopted that comprised immediate total removal of the cholesteatoma matrix and the surrounding inflammatory tissues even when they involved the membranous labyrinth. Results: Sixteen labyrinthine fistulae were found, only one of which was in a patient with chronic otitis media without cholesteatoma. Only one patient suffered from postoperative hearing deterioration of the bone conduction above 10 dB. The fistulae were smaller in size than in the previous survey, although the total incidence was slightly higher. Conclusions: Imaging techniques have demonstrated a favourable clinical impact on the diagnosis regarding the size and involvement of one or more anatomic structures of the otic capsule, not on the frequency percentage of fistulae. Total removal of the cholesteatoma matrix in one step, also combined with partial labyrinthectomy, yields satisfactory hearing results. To obtain successful outcomes, it is essential to respect certain fundamental precautions

Partial labyrinthectomy in the treatment of labyrinthine fistula: how we do it

[No abstract available