Age differences in encoding-related alpha power reflect sentence comprehension difficulties

When sentence processing taxes verbal working memory, comprehension difficulties arise. This is specifically the case when processing resources decline with advancing adult age. Such decline likely affects the encoding of sentences into working memory, which constitutes the basis for successful comprehension. To assess age differences in encoding-related electrophysiological activity, we recorded the electroencephalogram from three age groups (24, 43, and 65 years). Using an auditory sentence comprehension task, age differences in encoding-related oscillatory power were examined with respect to the accuracy of the given response. That is, the difference in oscillatory power between correctly and incorrectly encoded sentences, yielding subsequent memory effects (SME), was compared across age groups. Across age groups, we observed an age-related SME inversion in the alpha band from a power decrease in younger adults to a power increase in older adults. We suggest that this SME inversion underlies age-related comprehension difficulties. With alpha being commonly linked to inhibitory processes, this shift may reflect a change in the cortical inhibition–disinhibition balance. A cortical disinhibition may imply enriched sentence encoding in younger adults. In contrast, resource limitations in older adults may necessitate an increase in cortical inhibition during sentence encoding to avoid an information overload. Overall, our findings tentatively suggest that age-related comprehension difficulties are associated with alterations to the electrophysiological dynamics subserving general higher cognitive functions

Consciousness and the prefrontal parietal network: insights from attention, working memory, and chunking

Consciousness has of late become a “hot topic” in neuroscience. Empirical work has centered on identifying potential neural correlates of consciousness (NCCs), with a converging view that the prefrontal parietal network (PPN) is closely associated with this process. Theoretical work has primarily sought to explain how informational properties of this cortical network could account for phenomenal properties of consciousness. However, both empirical and theoretical research has given less focus to the psychological features that may account for the NCCs. The PPN has also been heavily linked with cognitive processes, such as attention. We describe how this literature is under-appreciated in consciousness science, in part due to the increasingly entrenched assumption of a strong dissociation between attention and consciousness. We argue instead that there is more common ground between attention and consciousness than is usually emphasized: although objects can under certain circumstances be attended to in the absence of conscious access, attention as a content selection and boosting mechanism is an important and necessary aspect of consciousness. Like attention, working memory and executive control involve the interlinking of multiple mental objects and have also been closely associated with the PPN. We propose that this set of cognitive functions, in concert with attention, make up the core psychological components of consciousness. One related process, chunking, exploits logical or mnemonic redundancies in a dataset so that it can be recoded and a given task optimized. Chunking has been shown to activate PPN particularly robustly, even compared with other cognitively demanding tasks, such as working memory or mental arithmetic. It is therefore possible that chunking, as a tool to detect useful patterns within an integrated set of intensely processed (attended) information, has a central role to play in consciousness. Following on from this, we suggest that a key evolutionary purpose of consciousness may be to provide innovative solutions to complex or novel problems

Getting the gist of it: An investigation of gist processing and the learning of novel gist categories

Gist extraction rapidly processes global structural regularities to provide access to the general meaning and global categorizations of our visual environment – the gist. Medical experts can also extract gist information from mammograms to categorize them as normal or abnormal. However, the visual properties influencing the gist of medical abnormality are largely unknown. It is also not known how medical experts, or any observer for that matter, learned to recognise the gist of new categories. This thesis investigated the processing and acquisition of the gist of abnormality. Chapter 2 observed no significant differences in performance between 500 ms and unlimited viewing time, suggesting that the gist of abnormality is fully accessible after 500 ms and remains available during further visual processing. Next, chapter 3 demonstrated that certain high-pass filters enhanced gist signals in mammograms at risk of future cancer, without affecting overall performance. These filters could be used to enhance mammograms for gist risk-factor scoring. Chapter 4’s multi-session training showed that perceptual exposure with global feedback is sufficient to induce learning of a new gist categorisation. However, learning was affected by individual differences and was not significantly retained after 7-10 days, suggesting that prolonged perceptual exposure might be needed for consolidation. Chapter 5 observed evidence for the neural signature of gist extraction in medical experts across a network of regions, where neural activity patterns showed clear individual differences. Overall, the findings of this thesis confirm the gist extraction of medical abnormality as a rapid, global process that is sensitive to spatial structural regularities. Additionally, it was shown that a gist category can be learned via global feedback, but this learning is hard to retain and is affected by individual differences. Similarly, individual differences were observed in the neural signature of gist extraction by medical experts

What are the neuronal correlates and dynamics of gist processing, and what is its role in the interplay of two modes of visual attention?

The ability for humans to extract information from their environment with no more than brief glimpse is well-establish in vision science. This is known as ‘gist extraction’, and is the product of the first feed-forward sweep of information from the eye, through the visual cortex, and into higher-order cognitive control areas in the frontal lobes. This process results in ‘sparse’ attention, which contains multiple elements including gist. The first aim of this thesis was to more clearly define gist in terms of its neuronal locations and time signatures, including observing the effects of multiple gists destructively colliding (in which the presence of more than one relevant image causes participants to be unable to identify the presence of a cued target). The second aim of the thesis was to explore the relationship between sparse attention and focused attention. As established by the data, sparse attention represents a broad ‘vision at a glance’ understanding of the visual environment. Focused attention represents a narrow mode of attention. The following novel findings were identified in this thesis: 1. Processing of target category gist can be observed neuronally using fMRI techniques in category-selective cortex; these selective areas show different % BOLD signal responses to their preferred targets. Place-selective areas show a greater % BOLD signal change in a perceptually-driven manner, and face- selective regions show a greater BOLD change in a manner requiring both the actual presence and the subjective perception of the target. 2. Destructive interference is a decisional, not a perceptual process; it is associated with the N300 and D220 ERPs, which are indicative of greater resources being allocated to a difficult task, conflict resolution, and decision-making. 3. Sparse and focused attention operate in a serial manner, with the first feed- forward sweep (including gist) producing the conscious percept of the world

Effects of scene properties and emotional valence on brain activations : a fixation-related fMRI study

Temporal and spatial characteristics of fixations are affected by image properties, including high-level scene characteristics, such as object-background composition, and low-level physical characteristics, such as image clarity. The influence of these factors is modulated by the emotional content of an image. Here, we aimed to establish whether brain correlates of fixations reflect these modulatory effects. To this end, we simultaneously scanned participants and measured their eye movements, while presenting negative and neutral images in various image clarity conditions, with controlled object-background composition. The fMRI data were analyzed using a novel fixation-based event-related (FIBER) method, which allows the tracking of brain activity linked to individual fixations. The results revealed that fixating an emotional object was linked to greater deactivation in the right lingual gyrus than fixating the background of an emotional image, while no difference between object and background was found for neutral images. We suggest that deactivation in the lingual gyrus might be linked to inhibition of saccade execution. This was supported by fixation duration results, which showed that in the negative condition, fixations falling on the object were longer than those falling on the background. Furthermore, increase in the image clarity was correlated with fixation-related activity within the lateral occipital complex, the structure linked to object recognition. This correlation was significantly stronger for negative images, presumably due to greater deployment of attention towards emotional objects. Our eye-tracking results are in line with these observations, showing that the chance of fixating an object rose faster for negative images over neutral ones as the level of noise decreased. Overall, our study demonstrated that emotional value of an image changes the way that low and high-level scene properties affect the characteristics of fixations. The fixation-related brain activity is affected by the low-level scene properties and this impact differs between negative and neutral images. The high-level scene properties also affect brain correlates of fixations, but only in the case of the negative images