Task 3: what brain areas are involved in attention?
Attention
Selective attention
Overt attention
Covert attention
Exogeneous attention
Endogenous attention
Reflexive attention
Voluntary attention
Vigilance
Sustained attention
Divided attention
Posner's model: Three networks
Corbetta's model: both processes described are about orienting
Differences Posner and Corbetta: Corbetta focuses on the aspect of orienting (divides into two systems), while Posner describes 3 independent networks
Basic concepts attention system
Attention system is anatomically separate from processing systems, emphasize on sources of attentional influences
Attention utilizes a network of anatomical areas
Anatomical areas carry out different functions that can be specified in cognitive terms
Brain lesions
(1) Alerting = producing and maintaining optimal vigilance and performance during tasks
(3) Executive: resolving conflict among responses. Studied by task that involve conflict, such as Stroop.
(2) Orienting: selection of information from sensory input
Acetylcholine
Norepinephrine: active after a warning signal
Posner´s Task: the task assesses an individual’s ability to perform an attentional shift. It has been used and modified to assess disorders, focal brain injury, and the effects of both on spatial attention.
Brain stem reticular system, frontal cortex, parietal areas
Frontal as well as posterior areas. Parietal areas implicated in related forms of processing, not restricted to orienting to sensory stimuli, but also other related processes
Course of the day (circadian rhythm) has influence: RT longer in early morning
midline frontal areas (anterior cingulate) and the lateral prefrontal cortex. Common activation in tasks involving conflict and other forms of mental effort.
Alerting = no cue - double cue (when a target will occur)
Full attention Network Task (ANT) -objective: development of such a measure that makes possible to determine if the three-network function independently or if the activity of one network interacts or is correlated with the other networks. This task is the combination of the cued reaction time (RT) and the flanker task
Studying alerting: use a warning signal prior to a target event to produce a phasic change in alertness. Warning signal leads to replacing resting state with a new state that involves preparation in detecting and responding an expected signal
The ANT requires participants to determine whether a central arrow points left or right. The arrow appears above or below fixation and may or may not be accompanied by flankers.
Efficiency of the three networks if assessed by measuring how response times are influenced by alerting cues, spatial cue, and flankers.
Four cue conditions
Center Cue (alerting cue) / control (no orienting effect, because you're already oriented)
Double Cue (When)
No cue
Spatial cue (location cue)
Target could be: neutral (lines), congruent (same direction) and incongruent (opposite direction)
Trail -five events
warning cue
short fixation period after the warning cue and then the target and flankers appeared simultaneously
Fixation period
after the response, target and flankers disapeared
Posttarget fixation period for a variable duration (interval) and the next target began
Results of the tasks
Executive = incongruent - congruent cue
The orienting effect: was calculated by substracting the mean RT of the spatial cue conditions from the mean RT of the center cue (center cue- spatial cue) #
The conflict (executive control) effect: calculated by substracting the mean RT of all congruent flanking conditions, summed across cue types, from the mean RT of incongruent flanking conditions. Incongruent minus congruent/ congruent (interference effect, because the flankers interfere with the task) -neutral (facilitations) #
Alerting effect: calculated by substracting the mean RT of the double-cue conditions from the mean RT of the no clue-condition (double cue- no cue) #
Orienting = center cue (alerting cue) - spatial cue (location cue)
Results demonstrate (1) no correlation between any combination of alerting, orienting, and conflict resolution, suggesting that these are functionally orthogonal constructs. (2) Under all cuein conditions, the presence of incongruent flankers increased RT, however, this effect was enhanced when subjects were given alerting cues (center or double cues) that contained no spatial information (interaction between alerting and orienting => executive functioning) =>it appears that there are some interactions between the network suggesting that they may not prove to be independent in all behavioural studies even though they use different anatomy and chemical modulators
gives specific measure of warning influence
Unilateral spatial neglect
Patients with neglect tend to ignore stimuli towards the side of space opposite to their lesion (involves right TBJ). After a lesion to the right side of the brain, they ignore people on their left side, miss food on the left side of the plate, and fail to dress/shave the left side of the body/face. They have problems in directing actions (eye/arm movements) towards the contralateral side of space. Finally, they have low vigilance, which exacerbates deficits in spatial processing.
The strong right-hemisphere dominance of the ventral frontoparietal network has important clinical
implications for the pathophysiology of unilateral spatial neglect, a common neuropsychological syndrome that occurs after injury to the right hemisphere.
Corbetta propose that the areas damaged in neglect better match the ventral network
Arguments for
Arguments against
Neglect is more frequent after damage to the right than to the left hemisphere
Patients with neglect have deficits primarily in stimulus detection rather than in top-down goal-directed orienting
Lesions that cause neglect are located more ventrally in the brain that the core regions of the IPs-FEF network, and most frequently involve the TPJ
Two brain systems related to orienting (Corbetta)
Dorsal attention system: top-down visuospatial ==> Some parietal regions, Frontal Eye Fields (FEF) and intraparietal sulcus/superior parietal lobe (IPS/SPL)
Detection deficits in neglect show a gradient across the visual field
− The TPJ is not well activated by motor preparation/execution, whereas neglect patients
clearly show a deficit in initiating arm movements contra to the lesion.
Ventral attention system: bottom-up reorienting ==> Temporoparietal junction (TPJ) and ventral frontal cortex (VFC)
When target miscued: you have to break your focus of attention on the cued location and switch to the target location. TPJ and VFC have to do with this switch
Two theories:
Cognitive view: ACC has role in monitoring conflict and in relation to lateral frontal areas in resolving conflict
Dual network view: there are two different top-down control networks: 1) Cingulo-opercular control system: shows maintenance across trials and acts as a stable background maintenance for task performance as a whole (sustained) ==> overlaps with original executive network 2) Frontoparietal system: shows start-cue signals, is thought to relate to task switching and initation and to adjustment within trials in real time (transient) ==> distinct from first orienting network of Posner
Observers are seated in front of a computer screen situated at eye level. They are instructed to fixate at a central point on the screen, marked by a dot or cross. To the left and the right of the point are two boxes. For a brief period, a cue is presented on the screen. Following a brief interval after the cue is removed, a target stimulus, usually a shape, appears in either the left or right box. The observer must respond to the target immediately after detecting it
Cues:two major cue types are used to analyze attention based on the type of visual input
endogenous: cue is presented in the center of the screen, usually at the same location as the center of focus. It is an arrow or other directional cue pointing to the left or right box on the screen. This cue relies on input from the central visual field.
exogenous: cue is presented outside of the center of focus, usually highlighting the left or right box presented on the screen. An exogenous cue can also be an object or image in the periphery, a number of degrees away from the centre, but still within the visual angle. This cue relies on visual input from the peripheral visual field
Support: 1) lateral frontal and parietal regions that showed start-cue activity correlated well 2) midline and anterior insular regions that showed additional sustained activity correlated well
Valid and invalid trials
In invalid trials, the stimulus is presented on the side opposite to that indicated by the cue. In this case, the arrow pointed to the right (directing attention to the right), but the stimulus in fact appeared in the box on the left. Posner used a ratio of 80% valid trials and 20% invalid trials in his original studies. The observer learns that usually the cue is valid, reinforcing the tendency to direct attention to the cued side
In valid trials, the stimulus is presented in the area as indicated by the cue. For example, if the cue was an arrow pointing to the right, the subsequent stimulus indeed did appear in the box on the right.
Top-down processing (dorsal frontoparietal network): The flow of information from ‘higher’ to ‘lower’ centers, conveying knowledge derived from previous experience rather than sensory stimulation.
Function:preparing and applying goal-directed selection for stimuli and responses. It is modulated by
the detection of stimuli.
Condition that is specially active: Cue makes you voluntary orient -interval between one target and the other target. Cue tells you when the target will appear.
Areas involved: intraparietal cortex and superior frontal cortex
Bottom-up processing (ventral frontoparietal network): Information processing that proceeds in a single direction from sensory input, through perceptual analysis, towards motor output, without involving feedback information flowing backwards from ‘higher’ centers to ‘lower’ centers.
Function: the detection of behaviorally relevant stimuli, particularly when they are salient or unexpected. It works as a ‘circuit breaker’ for the dorsal system, directing attention to salient events.
Areas involved: temporoparietal cortex and inferior frontal cortex. It is largely lateralized to the right.
The two systems might interact (Corbetta)
One possibility is that the ventral network serves as an alerting system that detects
behaviorally relevant stimuli in the environment, but is not equipped with high-resolution
spatial sensors. Once a relevant stimulus is detected, its precise localization depends on the
dorsal IPs–FEF system
A related hypothesis is that the TPJ–VFC system acts as a circuit breaker of ongoing
cognitive activity when a behaviorally relevant stimulus is detected. When subjects detect a
low-frequency or unexpected event, they must break the current attentional set and adopt a
new one on the basis of the incoming stimulus.