Basic Descriptions of Attention

• "What-is-it?" reaction: survival value

• Orienting response - behavioral - central

• Components of orienting response
  • Sensory organ threshold reduction
  • Pupil dilates
  • Behavioral orienting
  • Muscle tone increases
  • EEG desynchrony
  • GSR
  • Vasoconstriction in limbs
  • Respiration
  • Heart rate changes

• Function -- to prepare animal to deal with novel stimulus

Physiological Mechanisms

Need some labile, fast-acting system to modify activity of brain areas

Several components

• Generalized desynchrony (Reticular Formation and Limbic System)
• Localized desynchrony (thalamus)
• Adaptive and defensive reactions (Limbic system)
• Orienting for more information (cortex)
• Interpreting (cortex)

• Collateral's to Reticular Formation (weighted); certain highly-weighted stimuli may activate
• Synapse in thalamic nuclei (control from cortex and thalamic nuclei)
• Relay to cortex
  • Sensory input to cortex alone will not produce activation
  • Interpreted -- initial stimulus lost but subject ready for subsequent stimuli

Role of the Cortex in Attention

After analysis, cortex initiates excitation or inhibition of orienting response

Threshold reduction (novel stimulus)

• Increased cortical excitation
• EEG arousal - desynchrony related to efficiency
• Receptors more excitable

• Broadbent -- filter mechanism -- select stimulus and then allow to enter analyzing mechanism
• Sokolov (1960) arousal to different meanings
• Lower centers may take over with conditioning
• Message reaches all levels - attending or not
• General arousal necessary for interpretation
• Even in stupor, brain responds to selective stimuli
• Meaning may be as important as stimulus intensity

Role of Activation in Attention

Generalized activation and reduced threshold

• Via reticular formation and limbic system to thalamus and cortex
• Prepares cortex to maximize all sensory input
• Limbic system activity (emotion) provides push to get additional information
• Also prepares to avoid or fight (limbic system activation)
• Shows up as threshold reduction

• Cortex terminates signals from reticular formation, thalamus, limbic system
• Thalamus selectively activates cortex
• Thalamus has ability to inhibit or excite cortex

• Motor cortex and sensory projection area
• Habituation - reduction in amplitude with repeated presentation
• Dishabituation -- return to original amplitude
• Frequency, pattern, and modality-specific

Orienting Reflex

Attention (orienting reflex)

• Hernandez-Peon et al. (1956); decreased auditory EP with visual stimulus (filtering)
• Horn (1960): light flash response; also decrease in same modality
• Novel stimulus causes marked & significant depression in all modalities

Is ARAS important?

• Important as one general activation route
• Thalamus -- major since this system can operate from limbic system in absence of reticular formation
• Habituation -- thalamus filtering
  • Shift to subcortical interpretation (hippocampus)
  • If signal incongruous, cortex again activated

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