A Multi-Stage Model for Fundamental Functional Properties in Primary Visual Cortex

Many neurons in mammalian primary visual cortex have properties such as sharp tuning for contour orientation, strong selectivity for motion direction, and insensitivity to stimulus polarity, that are not shared with their sub-cortical counterparts. Successful models have been developed for a number of these properties but in one case, direction selectivity, there is no consensus about underlying mechanisms. We here define a model that accounts for many of the empirical observations concerning direction selectivity. The model describes a single column of cat primary visual cortex and comprises a series of processing stages. Each neuron in the first cortical stage receives input from a small number of on-centre and off-centre relay cells in the lateral geniculate nucleus. Consistent with recent physiological evidence, the off-centre inputs to cortex precede the on-centre inputs by a small (∼4 ms) interval, and it is this difference that confers direction selectivity on model neurons. We show that the resulting model successfully matches the following empirical data: the proportion of cells that are direction selective; tilted spatiotemporal receptive fields; phase advance in the response to a stationary contrast-reversing grating stepped across the receptive field. The model also accounts for several other fundamental properties. Receptive fields have elongated subregions, orientation selectivity is strong, and the distribution of orientation tuning bandwidth across neurons is similar to that seen in the laboratory. Finally, neurons in the first stage have properties corresponding to simple cells, and more complex-like cells emerge in later stages. The results therefore show that a simple feed-forward model can account for a number of the fundamental properties of primary visual cortex

Context Modulation of Facial Emotion Perception Differed by Individual Difference

Background: Certain facial configurations are believed to be associated with distinct affective meanings (i.e. basic facial expressions), and such associations are common across cultures (i.e. universality of facial expressions). However, recently, many studies suggest that various types of contextual information, rather than facial configuration itself, are important factor for facial emotion perception. Methodology/Principal Findings: To examine systematically how contextual information influences individuals ’ facial emotion perception, the present study estimated direct observers ’ perceptual thresholds for detecting negative facial expressions via a forced-choice psychophysical procedure using faces embedded in various emotional contexts. We additionally measured the individual differences in affective information-processing tendency (BIS/BAS) as a possible factor that may determine the extent to which contextual information on facial emotion perception is used. It was found that contextual information influenced observers ’ perceptual thresholds for facial emotion. Importantly, individuals ’ affectiveinformation tendencies modulated the extent to which they incorporated context information into their facial emotion perceptions. Conclusions/Significance: The findings of this study suggest that facial emotion perception not only depends on facial configuration, but the context in which the face appears as well. This contextual influence appeared differently wit

Contrast Adaptation Contributes to Contrast-Invariance of Orientation Tuning of Primate V1 Cells

BACKGROUND: Studies in rodents and carnivores have shown that orientation tuning width of single neurons does not change when stimulus contrast is modified. However, in these studies, stimuli were presented for a relatively long duration (e. g., 4 seconds), making it possible that contrast adaptation contributed to contrast-invariance of orientation tuning. Our first purpose was to determine, in marmoset area V1, whether orientation tuning is still contrast-invariant with the stimulation duration is comparable to that of a visual fixation. METHODOLOGY/PRINCIPAL FINDINGS: We performed extracellular recordings and examined orientation tuning of single-units using static sine-wave gratings that were flashed for 200 msec. Sixteen orientations and three contrast levels, representing low, medium and high values in the range of effective contrasts for each neuron, were randomly intermixed. Contrast adaptation being a slow phenomenon, cells did not have enough time to adapt to each contrast individually. With this stimulation protocol, we found that the tuning width obtained at intermediate contrast was reduced to 89% (median), and that at low contrast to 76%, of that obtained at high contrast. Therefore, when probed with briefly flashed stimuli, orientation tuning is not contrast-invariant in marmoset V1. Our second purpose was to determine whether contrast adaptation contributes to contrast-invariance of orientation tuning. Stationary gratings were presented, as previously, for 200 msec with randomly varying orientations, but the contrast was kept constant within stimulation blocks lasting >20 sec, allowing for adaptation to the single contrast in use. In these conditions, tuning widths obtained at low contrast were still significantly less than at high contrast (median 85%). However, tuning widths obtained with medium and high contrast stimuli no longer differed significantly. CONCLUSIONS/SIGNIFICANCE: Orientation tuning does not appear to be contrast-invariant when briefly flashed stimuli vary in both contrast and orientation, but contrast adaptation partially restores contrast-invariance of orientation tuning

Process and impact evaluation of the Greater Christchurch Urban Development Strategy Health Impact Assessment

<p>Abstract</p> <p>Background</p> <p>despite health impact assessment (HIA) being increasingly widely used internationally, fundamental questions about its impact on decision-making, implementation and practices remain. In 2005 a collaboration between public health and local government authorities performed an HIA on the Christchurch Urban Development Strategy Options paper in New Zealand. The findings of this were incorporated into the Greater Christchurch Urban Development Strategy;</p> <p>Methods</p> <p>using multiple qualitative methodologies including key informant interviews, focus groups and questionnaires, this study performs process and impact evaluations of the Christchurch HIA including evaluation of costs and resource use;</p> <p>Results</p> <p>the evaluation found that the HIA had demonstrable direct impacts on planning and implementation of the final Urban Development Strategy as well as indirect impacts on understandings and ways of working within and between organisations. It also points out future directions and ways of working in this successful collaboration between public health and local government authorities. It summarises the modest resource use and discusses the important role HIA can play in urban planning with intersectoral collaboration and enhanced relationships as both catalysts and outcomes of the HIA process;</p> <p>Conclusion</p> <p>as one of the few evaluations of HIA that have been published to date, this paper makes a substantial contribution to the literature on the impact, utility and effectiveness of HIA.</p

Bifurcation study of a neural field competition model with an application to perceptual switching in motion integration.

Perceptual multistability is a phenomenon in which alternate interpretations of a fixed stimulus are perceived intermittently. Although correlates between activity in specific cortical areas and perception have been found, the complex patterns of activity and the underlying mechanisms that gate multistable perception are little understood. Here, we present a neural field competition model in which competing states are represented in a continuous feature space. Bifurcation analysis is used to describe the different types of complex spatio-temporal dynamics produced by the model in terms of several parameters and for different inputs. The dynamics of the model was then compared to human perception investigated psychophysically during long presentations of an ambiguous, multistable motion pattern known as the barberpole illusion. In order to do this, the model is operated in a parameter range where known physiological response properties are reproduced whilst also working close to bifurcation. The model accounts for characteristic behaviour from the psychophysical experiments in terms of the type of switching observed and changes in the rate of switching with respect to contrast. In this way, the modelling study sheds light on the underlying mechanisms that drive perceptual switching in different contrast regimes. The general approach presented is applicable to a broad range of perceptual competition problems in which spatial interactions play a role

Understanding the Differences Between Vendor Types in Local Governance

It is commonly posited that for-profit, nonprofit, and other government vendors have fundamental differences, which make one or the other the superior choice depending on the circumstances of service delivery. Past research, focusing on service and market characteristics, finds support for this proposition. In this article, we investigate not only the typical theoretical expectations regarding vendor traits, service characteristics, and market conditions associated with the sectors, but also the presumed trustworthiness and management practices that are argued to differentiate them in an effort to better understand the roles played by each in local government contracting. Our findings indicate that as expected, nonprofits are most commonly employed when dealing with hard to define, “soft” services with weak markets. However, contrary to expectations, nonprofits are not generally considered more trustworthy than for-profits and are not managed more “loosely” (i.e., more ambiguous contracts, more discretion exercised in sanctioning) than their for-profit peers. Rather, public vendors seem to be the most trusted and are managed less rigidly than contractors from the other sectors.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline