David R. Painter

Neural Responses to Target Features outside a Search Array Are Enhanced during Conjunction but Not Unique-Feature Search

The visual world is typically too complex to permit full apprehension of its content from a single fixation. Humans therefore use visual search to direct attention and eye movements to locations or objects of interest in cluttered scenes. Psychophysical investigations have revealed that observers can select target elements from within an array of distractors on the basis of their spatial location or simple features, such as color. It remains unclear, however, how stimuli that lie outside the current search array are represented in the visual system. To investigate this, we recorded continuous neural activity using EEG while participants searched a foveal array of colored targets and distractors, and ignored irrelevant objects in the periphery. Search targets were defined either by a unique feature within the array or by a conjunction of features. Objects outside the array could match the target or distractor color within the array, or otherwise possessed a baseline (neutral) color present only in the periphery. The search array and irrelevant peripheral objects flickered at unique rates and thus evoked distinct frequency-tagged neural oscillations. During conjunction but not unique-feature search, target-colored objects outside the array evoked enhanced activity relative to distractor-colored and neutral objects. The results suggest that feature-based selection applies to stimuli at ignored peripheral locations, but only when central targets compete with distractors within the array. Distractor-colored and neutral objects evoked equivalent oscillatory responses, suggesting that feature-based selection at ignored locations during visual search arises exclusively from enhancement rather than suppression of neural activity.

Mountain high, valley low: direction-specific effects of articulation on reaching.

Representations underpinning action and language overlap and interact very closely. There are bidirectional interactions between word and action comprehension, semantic processing of language, and response selection. This study extends our understanding of the influence of speech on concurrent motor execution. Participants reached-to-grasp the top or bottom of a vertically oriented bar in response to the location of a word on a computer screen (top/bottom). Words were synonyms for “up” or “down”, and participants were required to articulate the word during movement. We were particularly interested in the influence of articulated word semantics on the transport component of the reach. Using motion capture to analyse action kinematics, we show that irrespective of reach direction, saying “up” synonyms led to greater height of the hand, while saying “down” synonyms was associated with reduced height. This direction-specific influence of articulation on the spatial parameters of the hand supports the idea that linguistic systems are tightly integrated and influence each other.

Value learning modulates goal-directed actions

With experience, particular objects can predict good or bad outcomes. This alters our perceptual response to them: Reliable predictors of salient outcomes are recognized faster and better than unreliable predictors, regardless of the value (gain, loss) of the outcome they predict. When attentional resources are constrained, learned value associations matter, causing recognition of gain-associated objects to be spared. Here, we ask how learned predictiveness and value change the way we interact with potentially rewarding objects. After associating virtual objects (drinking flutes) with monetary gains or losses, reaching for and grasping corresponding real objects depended on the objects learned value. Action was faster when directed at objects that previously predicted outcomes more rather than less consistently, regardless of value. Conversely, reaches were more direct for gain- than for loss-associated objects, regardless of their predictiveness. Action monitoring thus reveals how value learning components become accessible during action.

Event coding and motor priming: how attentional modulation may influence binding across action properties

When we perceive an action it is internally transformed into a motor representation akin to the execution of that same action. Motor priming studies show that action observation facilitates the execution of physically similar actions, but interferes with the performance of dissimilar actions. Some evidence suggests, however, that once a specific motor plan is formed, perceiving an action with partially overlapping features (e.g. a congruent grip-type but and incongruent end-goal) can result in interference. In two experiments we investigate how modulating attention towards observed actions influences the binding that occurs between action features, and therefore the amount of partial-overlap interference to participants’ performance. In the first study we directed attention towards a salient action feature (the grip-type). We found that perceiving partially overlapping (i.e. partially congruent) actions slowed participants’ responses compared with observation of completely congruent or incongruent actions. In the second experiment attentional resources were taxed through the use of a secondary task. This resulted in the elimination of the partial-overlap interference effect. We discuss results in relation to feature binding and event codes.

Causal involvement of visual area MT in global feature-based enhancement but not contingent attentional capture

When visual attention is set for a particular target feature, such as color or shape, neural responses to that feature are enhanced across the visual field. This global feature-based enhancement is hypothesized to underlie the contingent attentional capture effect, in which task-irrelevant items with the target feature capture spatial attention. In humans, however, different cortical regions have been implicated in global feature-based enhancement and contingent capture. Here, we applied intermittent theta-burst stimulation (iTBS) to assess the causal roles of two regions of extrastriate cortex - right area MT and the right temporoparietal junction (TPJ) - in both global feature-based enhancement and contingent capture. We recorded cortical activity using EEG while participants monitored centrally for targets defined by color and ignored peripheral checkerboards that matched the distractor or target color. In central vision, targets were preceded by colored cues designed to capture attention. Stimuli flickered at unique frequencies, evoking distinct cortical oscillations. Analyses of these oscillations and behavioral performance revealed contingent capture in central vision and global feature-based enhancement in the periphery. Stimulation of right area MT selectively increased global feature-based enhancement, but did not influence contingent attentional capture. By contrast, stimulation of the right TPJ left both processes unaffected. Our results reveal a causal role for the right area MT in feature-based attention, and suggest that global feature-based enhancement does not underlie the contingent capture effect.

Stimulus-Driven Cortical Hyperexcitability in Individuals with Charles Bonnet Hallucinations

Throughout the lifespan, the cerebral cortex adapts its structure and function in response to changing sensory input [1, 2]. Whilst such changes are typically adaptive, they can be maladaptive when they follow damage to the peripheral nervous system, including phantom limb pain and tinnitus [3, 4]. An intriguing example occurs in individuals with acquired ocular pathologies-most commonly age-related macular degeneration (MD) [5]-who lose their foveal vision but retain intact acuity in the peripheral visual field. Up to 40% of ocular pathology patients develop long-term hallucinations involving flashes of light, shapes, or geometric patterns and/or complex hallucinations, including faces, animals, or entire scenes, a condition known as Charles Bonnet Syndrome (CBS) [6, 7, 8]. Though CBS was first described over 250 years ago [9, 10], the neural basis for the hallucinations remains unclear, with no satisfactory explanation as to why some individuals develop hallucinations, while many do not. An influential but untested hypothesis for the visual hallucinations in CBS is that retinal deafferentation causes hyperexcitability in early visual cortex. To assess this, we investigated electrophysiological responses to peripheral visual field stimulation in MD patients with and without hallucinations and in matched controls without ocular pathology. Participants performed a concurrent attention task within intact portions of their peripheral visual field, while ignoring flickering checkerboards that drove periodic electrophysiological responses. CBS individuals showed strikingly elevated visual cortical responses to peripheral field stimulation compared with patients without hallucinations and controls, providing direct support for the hypothesis of visual cortical hyperexcitability in CBS.

Differential Deployment of Visual Attention During Interactive Approach and Avoidance Behavior

The ability to coordinate approach and avoidance actions in dynamic environments represents the boundary between extinction and the continued survival of many animal species. It is therefore crucial that sensory systems allocate limited attentional resources to the most relevant information to facilitate planning and execution of appropriate actions. Prominent theories of how attention regulates visual processing focus on the distinction between behaviorally relevant and irrelevant visual inputs. To date, however, no study has directly compared the deployment of attention to visual inputs relevant for approach and avoidance behaviors, which naturally occur in dynamic, interactive environments. In two experiments, we combined electroencephalography, frequency tagging, and eye gaze measures to investigate whether the deployment of visual selective attention differs for items relevant for approach and avoidance actions. Participants maneuvered a cursor to approach and avoid contact with moving items in a continuous interactive task. The results indicated that while the approach and avoidance tasks recruited equivalent attentional resources overall, attentional biases were directed toward task-relevant items during approach, and away from task-relevant items during avoidance. We conclude that the deployment of visual attention is guided not only by relevance to a behavioral goal, but also by the nature of that goal.