http://www.princeton.edu/~ashenhav/Publications_Presentations_files/Neuron%202013%20Shenhav.pdf

The Expected Value of Control: An Integrative Theory of Anterior Cingulate Cortex Function

How Does the Brain Solve Visual Object Recognition

Cognitive functions rely on the coordinated activity of neurons in many brain regions, but the interactions between cortical areas are not yet well understood. Here we investigated whether low-frequency (α) and high-frequency (γ) oscillations characterize different directions of information flow in monkey visual cortex. We recorded from all layers of the primary visual cortex (V1) and found that γ-waves are initiated in input layer 4 and propagate to the deep and superficial layers of cortex, whereas α-waves propagate in the opposite direction. Simultaneous recordings from V1 and downstream area V4 confirmed that γ- and α-waves propagate in the feedforward and feedback direction, respectively. Microstimulation in V1 elicited γ-oscillations in V4, whereas microstimulation in V4 elicited α-oscillations in V1, thus providing causal evidence for the opposite propagation of these rhythms. Furthermore, blocking NMDA receptors, thought to be involved in feedback processing, suppressed α while boosting γ. These results provide new insights into the relation between brain rhythms and cognition.

/pdf/alpha-and-gamma-oscillations-characterize-feedback-and-ucp72uxr89.pdf

Alpha and gamma oscillations characterize feedback and feedforward processing in monkey visual cortex.

https://www.cell.com/trends/cognitive-sciences/pdf/S1364-6613(15)00102-3.pdf

‘Activity-silent’ working memory in prefrontal cortex: a dynamic coding framework

https://www.cell.com/trends/cognitive-sciences/pdf/S1364-6613(11)00085-4.pdf

Different states in visual working memory: when it guides attention and when it does not

Paying attention to an object facilitates its storage in working memory. The authors investigate whether the opposite is also true: whether items in working memory influence the deployment of attention. Participants performed a search for a prespecified target while they held another item in working memory. In some trials this memory item was present in the search display as a distractor. Such a distractor has no effect on search time if the search target is in the display. In that case, the item in working memory is unlikely to be selected as a target for an eye movement, and if the eyes do land on it, fixation duration is short. In the absence of the target, however, there is a small but significant effect of the memory item on search time. The authors conclude that the target for visual search has a special status in working memory that allows it to guide attention. Guidance of attention by other items in working memory is much weaker and can be observed only if the search target is not present in the display.

The effect of items in working memory on the deployment of attention and the eyes during visual search

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.

/pdf/incremental-grouping-of-image-elements-in-vision-21goserlnu.pdf

Incremental grouping of image elements in vision.

When we perform a visual search we know what we are looking for and determine where it is. A representation of the object in our working memory, the 'search-template', is compared to the items in the scene until a match is found. So far it is unknown whether observers can search for multiple items at the same time. Here we compare the performance of subjects between a task in which they search for one of two target-items in a stream of visual objects and a task with only a single target. We find that search is effectively limited to one item at a time. This limitation occurs for simple and complex objects and even if the subjects have to look for two features from different domains. We conclude that matching has a fundamental capacity-limitation as the visual input can be matched to only one search-template at a time.

/pdf/matching-of-visual-input-to-only-one-item-at-any-one-time-1w1yss3qfc.pdf

Matching of visual input to only one item at any one time

The visual system has to segregate objects that are relevant to behavior from other objects and the background, if they are embedded in a visual scene. This segregation process can be time consuming, especially if the relevant object is spatially extended and overlaps with other image components, but the cause of the delays is presently not well understood. In the present study, we used a curve-tracing task to investigate processing delays during the grouping of contour segments into elongated curves. Our results indicate that contour segments that need to be grouped together are labeled with visual attention. Attention gradually spreads from contour segments that were labeled previously to other contours that are colinear and connected to them. The contour-grouping task is completed as soon as attention is directed to the entire curve. We conclude that processing delays during contour grouping are caused by a time-consuming spread of visual attention.

https://link.springer.com/content/pdf/10.3758/BF03194840.pdf

Roos Houtkamp

Papers

Different states in visual working memory: when it guides attention and when it does not

The effect of items in working memory on the deployment of attention and the eyes during visual search

Incremental grouping of image elements in vision.

Matching of visual input to only one item at any one time

A gradual spread of attention during mental curve tracing.