Comprehensive Visual Attention and Neural Mechanisms in Cognitive Neuroscience

Covert Attention

Focusing the mind's attention on a location or stimulus without moving the eyes.

Event-Related Potential (ERP)

The measured brainwave response that is the direct result of a specific sensory, cognitive, or motor event, extracted from EEG by averaging.

Effect of Spatial Attention on Early Sensory ERPs (e.g., P1)

Attended stimuli elicit ERPs (like the P1 wave from occipital cortex) with greater amplitude than unattended stimuli, showing attention modulates early sensory processing.

V4 Neuron Receptive Field

The specific region of the visual field that a single V4 neuron responds to. V4 neurons have larger receptive fields than V1 neurons.

Experiment: Attention Modulates V4 Neuron Activity (Fig 7.18)

Showed that when two stimuli (one preferred, one non-preferred) are in a V4 neuron's receptive field, the neuron fires strongly if attention is on the preferred stimulus and weakly if attention is on the non-preferred one, even though visual input is identical.

Experiment: Attention Modulates V1 Neuron Activity (Fig 7.19)

Demonstrated that attention amplifies the response (both excitatory and inhibitory components) of V1 neurons (the first stage of cortical visual processing) to stimuli within their receptive field.

Contralateral Processing in Attention (Fig 7.20)

Attending to the left visual field activates the right visual cortex (V1-V4), and attending to the right visual field activates the left visual cortex.

Retinotopic Maps

Maps in the visual cortex (V1, V2, etc.) where the spatial layout of the visual field is preserved.

Experiment: Attention Moves Across Retinotopic Maps (Fig 7.21)

Showed that directing attention to a specific location (e.g., lower-left) causes increased fMRI activity in the precise area of the brain's visual map representing that location.

Reason for Larger Attention Effects with Competing Stimuli

Attention's primary role is to resolve competition. It not only enhances the target but actively suppresses distractors within the same receptive field, creating a larger contrast.

Effect of Simultaneous vs. Sequential Stimuli (Without Attention)

Simultaneously presented stimuli evoke weaker brain responses (esp. in V4) than sequentially presented ones due to mutual suppression/competition.

Sequential Stimuli

Directed attention overcomes the suppression caused by simultaneous stimuli, making the brain's response strong regardless of presentation type.

Top-Down Attention

Voluntary, goal-directed attention driven by internal intentions, tasks, or instructions.

Bottom-Up Attention

Involuntary, automatic attention captured by salient (conspicuous) external stimuli.

Determining Focus in a Cluttered Scene

A competition between top-down (goal relevance) and bottom-up (stimulus salience) factors. Top-down usually wins if the goal is strong.

Relationship Between Attention Stage and Spatial Scale

Attention operates at different stages depending on scale. Small/distant objects can be selected in earlier areas (e.g., V4); large/close objects require selection in later areas with larger receptive fields (e.g., IT).

Experiment: Attention Shifts Based on Spatial Scale (Fig 7.24 / N2pc)

Searching for small-scale targets activated earlier (posterior) visual areas, while searching for large-scale targets activated later (anterior) areas, shown by the N2pc attention signal.

Lateral Geniculate Nucleus (LGN)

The primary relay station in the thalamus for visual information traveling from the retina to V1.

Thalamic Reticular Nucleus (TRN) / Perigeniculate Nucleus

A layer of inhibitory neurons surrounding thalamic nuclei (like LGN). Receives cortical feedback and modulates thalamic output.

Attention Effect in LGN (fMRI)

fMRI shows increased activity in the LGN contralateral to the attended location, proving attention modulates this subcortical relay.

Disinhibition Mechanism in LGN/TRN (Fig 7.27)

Attention increases LGN firing by decreasing the firing of inhibitory TRN neurons that synapse onto it. Attention 'releases the brake'.

Reflexive (Exogenous) Cuing

The automatic, involuntary capture of attention by a sudden, task-irrelevant stimulus (like a flash).

Initial Effect of Reflexive Cue

Faster reaction times and enhanced ERPs (e.g., P1) for targets appearing briefly (50-200ms) after the cue at the same location.

Inhibition of Return (IOR)

Slower reaction times and reduced ERPs (e.g., P1) for targets appearing >300ms after a reflexive cue at the same location. Discourages re-attending.

Neural Similarity of Reflexive vs. Voluntary Attention

Both types initially enhance early visual processing (e.g., boost the P1 wave), though triggered by different control networks.

Pop-Out Search (Feature Search)

Fast, effortless search where the target differs from distractors by a single basic feature (e.g., color).

Reaction time

Independent of set size.

Conjunction Search

Slow, effortful search where the target is defined by a combination (conjunction) of features shared with distractors (e.g., red O among red Xs and green Os). Reaction time increases with set size.

Feature Integration Theory (Treisman)

Basic features (color, shape) are processed preattentively and in parallel. Focused spatial attention is needed to 'bind' these features together into objects (solving the binding problem), required for conjunction search.

Spatial Attention vs. Feature Attention

Spatial attention focuses on a location; feature attention focuses on a characteristic (e.g., color, motion) across the visual field.

Experiment: Feature Attention Effects (Carrasco)

Cuing attention to a feature (e.g., motion direction) improves accuracy in detecting targets with that feature, similar to spatial cuing effects.

Timing Differences: Spatial vs. Feature Attention (ERPs)

Spatial attention modulates very early ERPs (P1, ~100ms). Feature attention effects appear later (~200ms), suggesting they act at different processing stages.

Neural Basis of Feature Attention (fMRI/MEG)

Attending to a feature (e.g., motion) selectively boosts activity in the cortical area specialized for that feature (e.g., MT/V5) within ~100ms.

Object-Based Attention

Attention that selects entire objects, not just spatial locations or features.

Experiment: Attention Spreads Within Objects (Wrench Study / Fig 7.36)

Participants responded faster, and visual cortex (V1-V4) showed more activity, for targets appearing on the same object as a cue, even at an uncued location, compared to equidistant targets on a different object.

Experiment: Selective Attention to Object Categories (Face/House Study)

Attending to superimposed faces selectively boosted FFA activity; attending to houses boosted PPA activity; attending to motion boosted MT/MST activity, despite identical spatial location.

Neural Synchrony (Coherence)

When neurons or brain areas fire together in a coordinated rhythm.

Communication Through Coherence Hypothesis

Attention enhances communication between brain areas (e.g., V1 and V4) by increasing the synchrony (coherence) of their neural oscillations, especially in the gamma band.

Experiment: Attention Increases V1-V4 Synchrony (Fig 7.38)

Showed that coherence between V1 neurons processing an attended stimulus and a downstream V4 neuron increased, while coherence for ignored V1 neurons decreased.

Dorsal Attention Network (DAN)

A cortical network (including FEF and IPS/SPL) responsible for top-down, voluntary control of spatial attention.

Attentional Priming

Increased baseline activity in sensory cortex before a target appears, specific to the attended location/feature, triggered by top-down signals from the DAN.

Frontal Eye Fields (FEF)

A region in the frontal cortex (part of DAN) involved in planning eye movements (saccades) and directing spatial attention.

Experiment: FEF Stimulation Enhances Attention

Subthreshold electrical stimulation of monkey FEF (too weak to cause eye movement) improved performance on a spatial attention task specifically at the location encoded by the stimulated neurons.

Experiment: FEF Sends Task-Specific Signals (TMS)

TMS over human FEF selectively enhanced activity in MT/V5 when attending motion, and in FFA when attending faces, proving FEF sends goal-specific signals.

Role of FEF in Cortical Synchrony

FEF appears to initiate/drive the increased gamma-band synchrony between itself and V4 during spatial attention.

Inferior Frontal Junction (IFJ)

A region in the PFC implicated as the source of top-down control for feature/object attention, using gamma synchrony to connect with relevant sensory areas (FFA/PPA).

Middle Frontal Gyrus (MFG) and Distraction

Higher activity in MFG predicts better ability to resist attentional capture by salient distractors.

Experiment: tDCS over MFG Reduces Distraction (Fig 7.44)

Excitatory transcranial direct current stimulation (tDCS) over MFG temporarily reduced the slowing effect of distractors in a visual search task.

Parietal Cortex (IPS/SPL) Role in Attention

Part of the DAN. Neurons here increase firing when a stimulus is the target of attention or action (saccade/reach), signaling behavioral relevance.

Lateral Intraparietal Area (LIP)

Subregion of IPS involved in saccades and spatial attention.

Experiment: LIP Activity Predicts Attentional Focus (Fig 7.47)

LIP neuron activity tracked the 'winner' of the attentional battle between a goal and a distractor, predicting the monkey's performance moment-by-moment.

Ventral Attention Network (VAN)

A largely right-hemisphere network (including TPJ and VFC) responsible for detecting salient, unexpected stimuli and triggering reorienting of attention (bottom-up control). Acts like a 'circuit breaker'.

Temporoparietal Junction (TPJ)

A key node in the VAN. Damage here is linked to neglect. Activated by unexpected stimuli requiring reorienting.

DAN vs. VAN Function

DAN maintains voluntary, goal-directed focus (top-down). VAN detects salient/unexpected events and interrupts focus for reorienting (bottom-up).

Superior Colliculus (SC)

Midbrain structure involved in controlling eye movements (overt attention) and now known to be involved in covert spatial attention and IOR.

Experiment: SC Stimulation Enhances Covert Attention

Subthreshold electrical stimulation of monkey SC (too weak to cause eye movement) improved detection performance at the corresponding spatial location.

Progressive Supranuclear Palsy (PSP)

Disease involving SC degeneration. Patients have difficulty engaging attention (shifting to a cued location).

Pulvinar

Large thalamic nucleus with subregions forming loops with cortex. Involved in attention, filtering, and potentially synchronizing cortical areas.

Pulvinar's Role in Attention Engagement

Neurons fire more for attended stimuli. Deactivating the dorsomedial pulvinar impairs covert orienting to contralesional targets.

Ventrolateral Pulvinar (VLP) and Cortical Synchrony

Forms loops with V4/TEO. Attention increases VLP activity and synchrony between V4 and TEO.

Parkinson's Disease Cause

Death of dopamine-producing cells in the Substantia Nigra pars compacta (SNc).

MPTP

A neurotoxin discovered accidentally that selectively kills dopamine neurons, creating an animal model for Parkinson's disease.

Motor Hierarchy

Conceptual organization of motor control: Highest (Goals - Association Cortex) -> Mid (Planning/Sequencing - Motor Cortex/BG/Cerebellum) -> Lowest (Execution - Spinal Cord/Muscles).

Effector

A part of the body that can move (arm, leg, eye, etc.).

Antagonist Muscle Pair

Muscles arranged in opposition (e.g., biceps flexes, triceps extends) to allow movement around a joint.

Alpha Motor Neuron

Originates in spinal cord, innervates muscle fibers, releases acetylcholine to cause contraction. Final common pathway for movement.

Muscle Spindle

Sensory receptor within a muscle that detects changes in muscle length (stretch).

Stretch Reflex

Automatic contraction of a muscle in response to an unexpected stretch, mediated by the spinal cord (e.g., knee-jerk reflex). Maintains stability.

Extrapyramidal Tracts

Motor pathways originating in the brainstem (outside the main pyramidal/corticospinal tract). Modulate posture, muscle tone, and movement speed.

Basal Ganglia Nuclei

Striatum (Caudate + Putamen), Globus Pallidus (GPi + GPe), Subthalamic Nucleus (STN), Substantia Nigra (SNc + SNr).

Basal Ganglia Function

Action selection, initiation, and gating. Modulates cortical activity via thalamic loops.

Cerebellum Function

Coordination, balance, timing, motor learning, comparing intended vs. actual movement (error correction).

Ataxia

Difficulty with balance and coordinated movement, resulting from damage to the cerebellum.

Corticospinal Tract (CST) / Pyramidal Tract

Direct pathway from motor cortex to spinal cord. Essential for voluntary movement. Mostly crosses to control the opposite side of the body.

Primary Motor Cortex (M1)

Located in precentral gyrus. Main origin of CST. Executes voluntary movements. Contains a rough motor map.

Hemiplegia / Hemiparesis

Paralysis (plegia) or weakness (paresis) on one side of the body, contralateral to a lesion in M1 or the CST.

Corticomotoneurons (CM Neurons)

Neurons in M1 (caudal part) that synapse directly onto alpha motor neurons.

Dexterity

Crucial for fine, independent finger control in primates.

Premotor Cortex (PMC)

Lateral part of Area 6. Involved in planning movements guided by external sensory cues.

Supplementary Motor Area (SMA)

Medial part of Area 6. Involved in planning movements based on internal goals, sequences from memory, and bimanual coordination.

Apraxia

A disorder of skilled action/motor planning, often due to left parietal lesions. Muscle strength is normal, but the knowledge of how to perform complex actions or use tools is lost.

Central Pattern Generators (CPGs)

Neural circuits within the spinal cord that can produce rhythmic patterns of activity (like walking) without input from the brain or sensory feedback.

Endpoint Control (Location Coding)

Motor commands specify the desired final position of a limb, rather than the specific trajectory to get there. Supported by Bizzi's deafferented monkey experiment.

Hierarchical Representation of Action Sequences

Complex actions are organized as nested goals and subgoals, from abstract concepts down to specific muscle commands. Involves chunking.

Center-Out Task

Experimental task where an animal moves a limb from a central point to one of several peripheral targets. Used to study neural coding of movement.

Directional Tuning

Property of many motor neurons that fire most strongly for movements in a specific 'preferred' direction.

Population Vector

A representation of movement direction calculated by summing the 'votes' (vectors representing preferred direction weighted by firing rate) of many individual neurons.

Planning vs. Execution Activity

The population vector predicts movement direction before movement onset (during a delay period), showing neurons are involved in planning. However, tuning can change between planning and execution.

Brain-Machine Interface (BMI)

Systems that use neural signals (e.g., from motor cortex) decoded by algorithms to directly control external devices (cursors, prosthetic limbs).

Affordance Competition Hypothesis (Cisek)

Proposes that action selection and specification happen in parallel. The brain prepares multiple potential actions simultaneously, which compete based on goals, rewards, costs, etc.

Evidence for Parallel Planning (Premotor Cortex)

During a delay before choosing between two targets, monkey premotor cortex shows activity related to both potential movements until a cue resolves the competition.

Bimanual Interference

Difficulty performing two different actions with two hands simultaneously.

Alien Hand Syndrome

Condition often after SMA lesions where one limb performs complex actions without the person's conscious intent.

Parietal vs. Premotor Reference Frames

Parietal cortex tends to represent locations in an eye-centered frame; premotor cortex uses a more hand-centered frame. Requires transformation.

Parietal Cortex and Intention

Stimulation here can evoke the conscious intention or desire to move, even without actual movement. Linked more to goals/outcomes.

Premotor Cortex and Execution

Stimulation here can trigger complex movements without conscious awareness or intention. Linked more to movement kinematics.

Mirror Neuron

A neuron (found in premotor, parietal, temporal areas) that fires both when an individual performs an action and when they observe the same action performed by another.

Mirror Neuron Network Function

Hypothesized to link action perception and production, supporting understanding/comprehending others' actions, imitation, and empathy by simulating observed actions internally.

Constraint-Induced Movement Therapy (CIMT)

Rehabilitation technique where the unaffected limb is restrained, forcing use of the paretic limb after stroke/injury.

Role of GABA Post-Stroke

Increased GABAergic inhibition in the peri-infarct cortex (area around the stroke) may hinder recovery. Reducing GABA pharmacologically improved recovery in mice.