Noise Correlations Have Little Influence on the Coding of Selective Attention in Area V1

Neurons in the visual primary cortex (area V1) do not only code simple features but also whether image elements are attended or not. These attentional signals are weaker than the feature-selective responses, and their reliability may therefore be limited by the noisiness of neuronal responses. Here we show that it is possible to decode the locus of attention on a single trial from the activity of a small population of neurons in area V1. Previous studies suggested that correlations between the activities of neurons that are part of a population limit the information gain, but here we report that the impact of these noise correlations depends on the relative position of the neurons' receptive fields. Correlations reduce the benefit of pooling neuronal responses evoked by the same object but actually enhance the advantage of pooling responses evoked by different objects. These opposing effects cancelled each other at the population level, so that the net effect of the noise correlations was negligible and attention could be decoded reliably. Our results suggest that noise correlations are caused by large-scale fluctuations in cortical excitability, which can be removed by a comparison of the response strengths evoked by different objects

The costs of switching attentional sets

People prioritize those aspects of the visual environment that match their attentional set. In the present study, we investigated whether switching from one attentional set to another is associated with a cost. We asked observers to sequentially saccade toward two color-defined targets, one on the left side of the display, the other on the right, each among a set of heterogeneously colored distractors. The targets were of the same color (no attentional set switch required) or of different colors (switch of attentional sets necessary), with each color consistently tied to a side, to allow observers to maximally prepare for the switch. We found that saccades were less accurate and slower in the switch condition than in the no-switch condition. Furthermore, whenever one of the distractors had the color associated with the other attentional set, a substantial proportion of saccades did not end on the target, but on this distractor. A time course analysis revealed that this distractor preference turned into a target preference after about 250–300 ms, suggesting that this is the time required to switch attentional sets

We can guide search by a set of colours, but are reluctant to do it.

For some real-world color searches, the target colours are not precisely known, and any item within a range of color values should be attended. This, a target representation that captures multiple similar colours would be advantageous. If such multicolour search is possible, then search for two targets (e..g Stroud, Menneer, Cave and Donnelly, 2012) might be guided by a target representation that included the target colours as well as the continuum of colours that fall between the targets within a contiguous region of color space. Results from Stroud et al (2012) suggest otherwise, however. The current set of experiments show that guidance for a set of colours that are from a single region of color space can be effective if targets are depicted as specific discrete colours. Specifically, Experiments 1-3 demonstrate that a search can be guided by four and even eight colours given the appropriate conditions. However, Experiment 5 gives evidence that guidance is sometimes sensitive to how informative the target preview is to search. Experiments 6 and 7 show that a stimulus showing a continuous range of target colours is not translated into a search target representation. Thus, search can be guided by multiple discrete colours that are from a single region in color space, but this approach was not adopted in a search for two targets with intervening distractor colours

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

Understanding similarities and differences in land use visions for Scotland

The successful transition towards a global society that can live within planetary boundaries is one of the greatest challenges for the twenty-first century. Sustainable land use and land management will be essential to ensure the continued delivery of the ecosystem goods and services needed to support a rapidly growing global population. To support the transition towards sustainable development, decision-makers need to better understand how land use change affects people and the environment. However, these insights are of limited use without societal agreement on future land uses. Understanding synergies and differences between land use visions forms a first step in assessing and comparing alternative pathways towards a sustainable future. This thesis uses a range of methods to understand visions of future land use amongst professional land use stakeholders, society at large, and young people in Scotland. Twenty semi-structured interviews were held with policy experts from the Scottish land use sectors. A nationwide statistically representative web-based survey provided insight into the visions of the Scottish population. And finally, a novel visual interview methodology was used to interview 26 pupils from two high schools in Perthshire. Inductive content analysis and descriptive statistics were used to analyse the results and understand and compare the land use visions of these different groups. As expected, different groups had different visions of future land use. There was, however, general agreement on certain themes, in particular the desire for a more sustainable lifestyle and the importance of a healthy environment. The sectoral stakeholders would like to see more partnerships, dialogue and collaboration; a society that is more engaged and aware about land use; resilient local economies; and short-, medium-, and long-term policies that help to achieve these goals. One of the key challenges for these groups will be how to translate abstract concepts such as ‘healthy ecosystem’ and ‘dialogue and partnerships’ into practice. This clearly requires a shared understanding of what a ‘healthy ecosystem’ means to different stakeholders, as well as appreciation of what true dialogue means and how this can be used to co-create solutions – potentially a radical change from the traditional top-down approaches. The research also identified divisions in Scottish society between those who want to continue a ‘status quo’ lifestyle, and those – in particular younger people (who spent time in the natural environment, through either school or home life) and those from a higher socio-economic background – who want a more sustainable lifestyle and to be more connected with the natural environment. These results are important, as policy makers need to be able to identify the factors that have successfully engaged certain groups and to promote these factors. Programmes that provide access to the natural environment (such as the Duke of Edinburgh’s Award) need to ensure equal opportunities by targeting disadvantaged groups. Simultaneously, it needs to be explored how to encourage those who would like to continue a ‘status quo’ lifestyle into a more sustainable one. Past research has shown how preferences can be influenced and how changes can be initiated by incentives and restrictions in order to promote desired behaviours. The power of the media should be leveraged: programmes such as BBC’s ‘Blue Planet’ highlight how our lifestyle choices impact on the natural environment and can provide the motivation for change. The current issues surrounding Brexit and Climate Change require a national conversation; using methods such as those presented in the thesis to elicit land use visions can help identify the commonalties and differences between stakeholders’ views. This can provide a starting point for dialogue and critical reflection on current instruments and objectives, and how they might be adapted to better reflect Scottish preferences and conditions