Attention

by

SALIENT CHARACTERISTICS OF ATTENTION

  • Sequential process involving many brain systems
  • Limited capacity- engagement of system in one task can interfere with second task
  • Varies between and within individuals under different conditions (depression, fatigue, injury can all impact attention)

NEUROANATOMICAL SUBSTRATES

  • Inferior Parietal Cortex– spatial selective attention; hemineglect
  • Frontal Cortex– response selection; control; sustained attention; switching; searching
  • Orbital Frontal Region– response initiation; inhibition
  • Medial Frontal Lobe (paralimbic cingulate cortex)- intent to respond; consistency of responding; focused attention
  • Dorsolateral Frontal Cortex– sequencing; persistence; switching; focus
  • Limbic System– establishes salience, whereby determining priority of incoming stimuli; limits of attention (hippocampus- memory encoding and retrieval constrain attention)
  • Subcortical System– relay of sensory input through thalamus; caudate nucleus selection of motor responses, selection and coordination of sensory info
  • Midbrain System– arousal and activation

MODELS OF ATTENTION

Pibram & McGuiness (1975)

Based on animal research- Three essential factors

  • Arousal- “the primordial attention system”
    • orienting response to sensory input
    • system from spinal cord through brainstem reticular formation, with forebrain control exerted by amygdala and portions of frontal cortex
  • Activation
    • basal ganglia
  • Effort

Lezak

“Mental activity variables”: Efficiency of mental processes involved in cognitive functions, but do not have unique behavioral end product

  • Attention
  • Activity rate- speed of mental operations and motor responses
  • Consciousness- awareness of self and surroundings; level of arousal

Link between arousal and attention: disorder of arousal always involves disorder of attention; disorder of attention does not always involve disorder of arousal

Mesulam (2000)

  • (critics think model is too narrow)
  • Discusses matrix (confusional state) vs. vector (where you are focusing your attention)
  • Attentional Matrix (general state)
    • Domain-specific attentional processes: attentional processes to certain stimuli; visual neurons mediate visual attention to visual stimuli
    • Domain-independent attentional processes: “bottom up” influence of ascending reticular activating system and “top down’ influence of cerebral cortex (frontal lobe)
  • Bottom-up modulation– Ascending reticular activating system (ARAS)
    • reticulothalamocortical pathway- cortical arousal by passing sensory information through thalamus towards cortex
    • transmitter-specific extrathalamic pathways from brainstem and basal forebrain to cortex
    • Global influence on attention without selectivity for sensory modality or cognitive domain
  • Top-down modulation– parietal, limbic, prefrontal cortex (right hemi preference)
    • context, motivation, significance, volition
    • research: activation of prefrontal cortex and posterior parietal cortex common to almost all attentional tasks, regardless of modality or domain
    • frontal important in processing novel information
    • limbic important for mood and motivational factors
  • Top-down Modulation and Bottom-up Modulation impact Modality- and Domain-Specific Attentional Modulations (for sounds, tactile stim, colors, motion, words, spat targets, faces, objects, memories, etc.)

Posner & Peterson (1990)

Three major functions:

  • orienting to sensory events- involuntary process
  • detecting signals for focal processing- voluntary
  • maintaining vigilant or alert state

Two attentional systems:

  • Posterior attention system: orienting, awareness of environment; dorsal visual pathway; primary cortical connections to parietal lobe
  • Anterior attention system: signal detection; anterior cingulate gyrus, supplementary motor cortex

Disengage – posterior parietal region

  • Shift – superior colliculus
  • Engage – pulvinar of the thalamus

Mirsky (1996)

Factor analyzed neuropsych data for 5 factor solution

  1. Focus/execute
  • capacity to concentrate attentional resources and screen out distracting stimuli
  • tests require ability to identify salient task elements and perform motor responses under conditions of distraction (digit symbol, stroop, trails, letter cancellation)
  • focus- superior temporal and inferior parietal cortices; corpus striatum
  • execute- inferior parietal and corpus striatum
  1. Sustain
  • ability to stay on task in vigilant manner
  • tests require person to maintain attention over time (CPT)
  • rostral midbrain
  1. Shift
  • ability to change attentional focus from one aspect of stimulus to another in flexible, efficient manner
  • selective- maintain cognitive set in presence of distracting stimuli
  • divided- processing more than one set of information at a time
  • prefrontal, frontal association areas
  1. Encode
  • ability to hold info briefly in mind while performing mental operation on it
  • hippocampus, amygdala
  1. Stabilize
  • reliability of attentional effort
  • measures by Mirsky using variability in reaction time on CPT and commission errors
  • midline thalamic and brainstem structures

Problems

  • Critics think Mirsky’s model is too broad; overlap between attention and exec fx (encode vs working memory)
  • Also, he used factor analysis, so model highly dependent on tests used
  • Problem of shared method variance- uses same or highly related tests to measure functions

Cohen, Malloy, & Jenkins (1998)

Four components:

  1. Sensory selective attention
  • process by which sensory input is chosen for additional processing and focus
  • depends on filtering (selection of what is attended to occurs on basis of sensitivity; may attend to something novel; early stage of processing), focusing and selecting, and disengagement (attention remains on stimulus until another stimulus or internal event shifts attention)
  1. Attentional capacity and focus
  • focused attention- intensity and attentional resources devoted to task
  • influenced by “energetic factors”- arousal, motivation, effort
  • influenced by “structural factors”- memory, processing speed, cognitive ability
  1. Sustained attention
  • helps to maintain optimal performance over time
  • even “normal” people can have variations in attention (this distinguishes attention from other cognitive processes- visual-spatial skills always same)
  • highly dependent on task duration
  • also dependent on vigilance requirement (high demand for readiness for low-probability target); dependent on reinforcement and target:distracter ratio
  1. Response selection and control
  • facilitates action
  • controlled and effortful
  • exec fx strongly associated: intention, initiation, generative capacity, persistence, inhibition, switching

METHODOLICAL ISSUES IN ASSESSMENT OF ATTENTION

  • No pure test of attention
  • Attention primarily serves to facilitate other cognitive functions (memory, EF). Therefore, many tests load not only on attention, but also other domains.
  • Attention not a unitary process; can’t be assessed with only one test; use a multifactorial approach
  • Attentional performance usually derived from comparing performance across tasks that load on different cognitive functions.
  • Absolute performance provides less info than looking at performance inconsistencies.

Factors to consider in assessment

Test factors

  • spatial characteristics
  • temporal demands
  • memory demands
  • EF demands
  • processing speed
  • complexity
  • task salience, relevance, reward value

Patient factors

  • arousal
  • motivation
  • effort
  • anxiety
  • depression
  • fatigue
  • general cognitive ability

Type of attention

  • goal-directed activity: anterior
  • awareness of environment: posterior

Tests of Attention

Selective attention- cancellation tasks; spatial search tasks (computerized presentation of visual stimuli, evaluates time taken to scan visual array); spatial cue paradigms (neutral cue is presented at some spatial location prior to onset of target, on some trials, cue correctly signals future position of target, other times it doesn’t)

Response selection and control- go/ no-go and CPT (inhibit responses); Trail Making (response alternating and switching); CPT; Sorting tasks (failure to maintain response set; switching); Fluency measures (quantity of response output, initiation, persistence); Stroop (ability to inhibit a response)

Attentional capacity and focus- Digit Span; Arithmetic; PASAT; Symbol Digit Modalities; Digit Symbol; Corsi Blocks; Stroop; Sentence Repetition

Sustained attention and vigilance- CPT; cancellation tasks; symbol coding tasks (earlier vs later performance)

ATTENTIONAL IMPAIRMENT

  • Most common of all cognitive impairment
  • Inability to allocate resources to task at hand
  • Failure to perform at optimal level, despite intact cognitive ability
  • Inconsistency in performance

Mirksy’s Nosology of Disorders of Attention (presented at INS 2000)

  1. Familial/ Genetic
  • deficits in sustained attention among first degree relatives of schizophrenics
  • relatives of children with juvenile myoclonic epilepsy have similar deficits in visual and auditory attention
  • “epilepsy gene”- human lymphocytic antigens (HLA) region of chromosome 6p. Present in kids with JME and their relatives. This gene also implicated in schizo and ADHD. A form of inherited deafness also found on this gene, and Mirsky found that auditory CPTs more sensitive than visual versions among schizo, absence epilepsy, and JME. Tentatively suggests that all disorders share common genetic fault expressed as an impairment in sustained attention.
  1. Metabolic disorders
  • affect biochemistry and neurochemistry of body, can result in changes in brain structure and EEG
  • Uremia from end-stage kidney failure: deficits in sustained attention; EEG pattern similar to absence epilepsy; toxins associated with kidney failure “attack” centrecephalic brainstem structures implicated in absence epilepsy
  • Early-treated PKU: problems with attention, impulse control, distractibility, persistence; many receive ADHD dx
  1. Environmental factors
  • Poverty: associated malnutrition and infection
  • Maternal alcohol use and FAS
  • Pregnancy and birth complications
  • Lead exposure
  • Lack of intellectual stimulation
  1. Other factors
  • Cerebral insults: head injury, tumor, infection
  • Sleep and breathing disorders

DISORDERS OF ATTENTION

Acute Confusional State

Abrupt change in mental state, usually caused by toxic or metabolic disorder, environmental stressor, or multifocal brain disease (meningitis, encephalitis, TBI in acute phase)

Three primary features:

  • disturbance of vigilance; distractibility; impaired working memory
  • inability to maintain stream of thought
  • inability to carry out goal-directed movement

Clinical features

  • inattention with poor mental control
  • poor concentration and vigilance
  • distractibility
  • disorientation
  • other cog problems: arousal problems, memory loss, hallucinations
  • interferes with performance on tests of other cognitive abilities.

Neglect Syndrome

  • Disorder of spatial attention.
  • Right posterior parietal lesion
  • Spatial attention- two components
    • sensory-motor: translate visual-spatial info into body movements
    • cognitive: mental representation, planning strategies, volitionally shifting from a target
  • Behave as though left half of universe ceases to exist
  • “Probability of attracting attention, entering awareness, influencing cognitive processes or becoming target for action decreases in proportion to relative leftness of stimuli”
  • Can be multi-modal- rightward bias of auditory, somatosensory, and olfactory targets

ADHD

  • Disorder of sustained attention, behavioral inhibition, and executive function (Barkley)
  • Behavioral diagnosis
  • Barkley study looking at validity of measures in assessing ADHD symptoms- able to discriminate ADHD from normal children, but less consistent in discriminating ADHD from other clinical groups

TBI

  • Result from impact injury or shearing injury (damage subcortical white matter, result in arousal and activation deficits)
  • Changes in attention throughout recovery process
    • initial diminished alertness; later decreased response inhibition, slower reaction time
  • Common ongoing complaint even after recovery of most other functions
  • More pronounced deficits when younger age at injury
  • Compounded by EF deficits and slow processing speed

Sleep Apnea and Snoring

  • Apnea- deficits in attention and concentration; hyperactivity in kids; seem to be related to daytime sleepiness secondary to frequent nighttime arousals (other cognitive problems related to hypoxemia)
  • Snoring- also see attention problems due to daytime sleepiness