2 Attention What is attention? There is a limit to how much information the human brain can processThe process of choosing what information to further process is “attention.”
3 Attention How can we characterize attention? Alertness and arousal: general awareness of the world (decreases during sleep)Vigilance (“sustained attention”): the ability to maintain alertness continuously over time, important when a task must be performed in a nonstop matterSelective attention: the selection of information essential to a task, such as ignoring background noise during a conversation in a crowded restaurant
4 AttentionAre these “attention systems” distinct? Do they use the same resources?Evidence to the contrary: the brain’s processing capacity is larger when tasks draw from different resource pools (e.g. spatial, auditory) than from the same one
5 Attention What brain structures are involved in attention? Reticular activating systemSuperior colliculusThalamusParietal lobeAnterior cingulate cortexFrontal lobe
6 Reticular Activating System (RAS) The RAS is involved in alertness and arousal and is responsible for controlling sleep-wake cyclesCell bodies in the RAS have diffuse connections to most regions of the cortex, allowing them to modulate the arousal and alertness of the entire brainDamage to the RAS or its functioning results in coma
7 Superior colliculusResponsible for saccades (to quickly bring peripheral visual stimuli into foveal vision)Express saccades: fast (~120ms), triggered by novel visual stimulus in the periphery, disappear upon destruction of the superior colliculusRegular saccades: voluntary, take about ms
8 ThalamusSome nuclei (medial dorsal, intralaminar, reticular nuclei) in the thalamus modulate the level of arousal of the cortexSensory information is relayed to the brain through the thalamus, so it is in a logical position to have a role in selective attentionThe pulvinar seems to play an important role in selective attentionPET studies indicate that the thalamus is more engaged when filtering of sensory information is required, such as in a task where an item must be detected among eight other items as opposed to when it is shown aloneERP and MEG studies indicate that such filtering occurs very early after the receipt of the stimulus
9 Parietal LobeThe parietal lobe, important for visual and spatial aspects of attention, is thought to be involved in more fine-grained selection of sensory informationThe parietal lobe is also taught to be responsible for the overall allocation of attentional resources to a particular stimulus or task
10 Parietal Lobe Evidence: Single-cell recordings in monkeys show that the firing rate of some parietal neurons is enhanced any time attention is directed to a visual object (independently of motor actions). In particular, the lateral intraparietal region is important for the representation of attended or salient spatial locations, responding regardless of the modality of information about a location or whether there is a motor responseNeuroimaging in humans has provided converging evidence: increased activation in parietal regions across a variety of tasks that involve increased visual attention but not by highly demanding tasks in general
11 Parietal LobeThe parietal lobe is thought to play a role in binging together visual attributes with their position in spaceFeature integration theory: basic visual features such as color are detected relatively automatically, but we cannot know which features go together unless we direct our attention to a particular locationAttention is the “glue” that binds this informationClassic example:Finding a single red X in a table of green Xs happens at the same speed regardless of the number of green Xs (preattentive processing)Finding a single red X in a table of green Xs and red Os takes longer with larger tablesThis increase in time occurs because attention can be directed to only one point at a time; directing attention to a point in space precedes the identification of information, which means that directing attention to a particular spatial location allows the features at that location to be bound together so that an item can be identified
12 Parietal LobeBilateral damage to the parietal regions disrupts the ability to bind together featuresIndividuals with such deficits cannot detect conjunction of features, whereas their ability to detect a single attribute remains intact
13 Anterior Cingulate Cortex Once the brain has filtered sensory information, it must choose a response; the region responsible for that is the cingulate cortex, which can be thought of as an interface between subcortical and cortical regionsRecall from lecture 3 that the anterior cingulate cortex is involved in choosing a novel responseActivity in the anterior cingulate cortex during conflicting responses but not during noncongruent responses in the Stroop task supports that the cingulate is critically involved in response selectionCingulate activity is observed when there is a need to select between directly conflicting responses, and when selecting the correct response is demanding or complicated (such as wel there are multiple possible responses)Greater cingulate activity is also found when the determination of a response is complicated because it relies on multiple attributes of a stimulus (e.g. color, form speed) rather than a single one (e.g. color)Also, cingulate activity is thought to be correlated with task difficulty
14 Frontal LobeThe frontal lobe is involved in selection of information for more abstract characteristics, such as selecting words that have particular meanings or selecting information that must be held in working memoryDiscussion of the frontal lobe’s role in attention falls more in the realm of discussions of executive function
15 Attentional selection Early selection (early stage of processing, before items are identified) or late selection (after sensory processing is complete and items have been identified)?Classic example of an experiment designed to answer this question:Individuals are instructed to listen and count the number of target tones, such as long tones, interspersed within more frequent non-targets, such as short tonesThey are told to attend only to information in one earResponses are compared for targets when they are attended for as compared to when they are unattendedThe point in time as which the amplitude of the ERP to the attended stimulus begins to diverge from that of the unattended stimulus is notedThis happens approximately 80ms after stimulus presentation, suggesting that attention can happen earlyHowever, the P300 component (mentioned in lecture 2) occurs only in response to stimuli being attended toSo, attentional selection can happen early or late
16 Selection by featuresWhat aspect of the sensory world is used when selecting information?Space-based viewpoint of attentionObject-based viewpoint of attention
17 Space-based viewpoint of attention Neuroimaging studies have provided evidence that regions of both visual and parietal cortex mediate space-based attentional deficitsThe mapping of the visual world in early visual processing areas (V1-V4) is retinotopicAttending to information in one visual field increases activation over V2-V4 regions of the opposite hemisphereERP and MRI studies show that this space-based attentional modulation occurs early in processing, ~100ms after stimulus presentation, in the secondary visual cortex
18 Object-based viewpoint of attention In a task where attention is directed to a spacially constant attribute associated with faces, increased activation was observed in the fusiform face area (which recognizes faces); in contrast, when attention was directed to an attribute associated with houses, increased activation was observed in the parahippocampal place area (which recognizes scenes)This modulation of attention appeared to occur relatively early on in processing, when visual features are first recognized as forming a particular object
19 AttentionThe conclusion of all the evidence mentioned in this lecture is that attention manifests as increased activation of the areas of the brain involved in processing the type of information being attended toThere is also some evidence that task-irrelevant information undergoes decreased processing
20 HemineglectHemineglect (sometimes referred to as hemi-inattention) is a syndrome in which an individual ifnotes, or does not pat attention to, the side of space contralteral to a lesionThe side of space is usually defined with reference to the body midline but may occur with regard to other spatial reference ftames as wellThis inattention is seen regardless of the modality in which information is presentedDepending on the severity, an individual might fail to eat food on the left side of a plate, draw the left side of objects, read the left side of words, or use the left side of the bodyIn severe cases, an individual may even deny that the left side of this body belongs to him
21 Hemineglect One severr case: Another: A patient with hemineglect complained to a nurse that a staff member had played a cruel practical joke on him by placing a severed leg in his bed.The patient then attempted to throw the leg out of his bed, hurling himself onto the floor.Another:A woman had a stroke and fell in her bathroom.While being examined, she insisted that her left arm was not hers but the examiner’s. When the examiner brought the patient’s left arm into view and asked whose it was, she answered, “It’s not mine. I found it in the bathroom, when I fell. It’s not mine because it’s too heavy; it should be yours. It can move and do everything; when I feel it too heavy, I put it on my stomach. It doesn’t hurt me, it’s kind.”When she was asked where her own arm was, she replied, “behind the door.”Denying ownership of a limb and claiming it belongs to someone else without any other deficit in reasoning is called somatoparaphrenia.
22 HemineglectNeglect is usually observed after vascular damage to the parietal regions extending into subcortical regions.Neglect is observed more commonly and is more severe after right then left hemisphere lesions, and so neglect is observed more often for the left side of space.Neglect can also occur after damage to fronta regions, the basal ganglia, and the thalamusUsually, neglect is severe at first (all items on one side of space are ignored), but, with weeks to months, some information on the neglected side is processed. However, it rarely, if ever, disappears completely.
23 HemineglectHemineglect does not occur from low-level sensory processing deficits; patients with hemineglect can still perform motor acts such as showering, dressing, and eating with both sides of the body (though one side may be preferred).Lack of information from one half of the visual field cannot account for neglect because re-orienting the head would bring that side of space into view, but patients with hemineglect ignore it.Sensory processing deficits cannot account for hemineglect because information from the contralateral side of space is generally ignored regardless of modality, but ipsilateral and contralateral projections in the auditory system, for example, make that unlikely.
25 HemineglectBringing attention to the left side of the line in the line bisection task can improve performanceIf information on the neglected side is critical for understanding or compregension, it tends to receive attention“antiballistic” might be read as “ballistic” though only the letters “llistic” are past the midline of the wordPerformance on a task can improve if a greater reward is promisedHemineglect seems to be associated with attention“The patient with hemineglect treats one side of space the way you normally treat the space behind your head.”
26 HemineglectPerhaps hemineglect is the result of the lack of an internal mental representation of the neglected side of spaceBisiach and Luzzatti, 1978:Two patients with hemineglect for the left side of space were asked to imagine standing at one end of the Piazza del Duomo of Milan and to describe what they saw. They described landmarks on the right.The patients were then asked to imagine standing at the opposite end of the plaza, facing the opposite direction, and to describe what they saw. The described landmarks on the remaining half of the plazaThis rules out the theory of lack of a full mental map
27 HemineglectOne theory says that hemineglect is due to preference for stimuli on one side of space, which can be interpreted as an uneven competition between hemispheres for controlling the direction of attentionOliveri et al. 1999:Using TMS to disrupt the processing of the intact hemisphere briefly eliminated hemineglect
28 HemineglectActively or passively moving the limb on the neglected side of space to make the neglected side of space more salientCaloric stimulation:Water at least 7 degrees Celsius cooler than body temperatere is poured into the ear canal, inducing motion in the semicircular canals of the vestibular systemCan result in vertigoNeck-proprioceptic stimulation (vibration in the left neck muscles)No permanent treatment
29 Attentional BiasEach hemisphere appears to have an attentional bias for the contralateral side of space.Damage to the right hemisphere appears to slow response times to simple stimuli more than damage to the left hemisphere, suggesting that the right hemisphere had a larger role in alerting and arousal.PET studies indication that the right hemisphere is important in sustaining overall attention, such as in vigilant tasks.
31 Attentional BiasMost right-handed individuals perceive the face on the left as happier.It is suggested that the left half-face is perceived as more expressive because the right hemisphere is more adept at processing emotional and facial information.