What is attention?
Given limited capacity to process competing options, attentional mechanisms select, modulate, and sustain focus on information most relevant for behavior
Attention sources
- Exogenous: in the environment, reflexive, automatic, “bottom-up”
- Endogenous: in the mind, voluntary, intentional, “top-down”
Attention targets
- External: sensory info, in the environment
- A sensory modality, spatial location, feature, or object
- Internal: mental representations, in the mind
- A memory, imagery, or plan
Attention types
- Overt and covert
- Transient and sustained
- Selective and divided
Overt vs. Covert
- Overt: Involves actual movement of the sensory surface, e.g.: moving
the eyes, directing the ear - Covert: Does not involve actual movement, e.g.: “looking out the corner
of your eye”, “eavesdropping on a conversation at the next table”
transient vs. sustained
- Transient: Momentary focus on something
- Sustained: Prolonged focus on something
Selective vs. divided
- Selective: Focus on one thing to the exclusion of others
- Divided: Try to focus on multiple things simultaneously
Dichotic listening
-Source: endogenous
● “Attend to the left ear”
- Target: external
● Sounds entering ear
- Covert
- Sustained
- Selective
Dichotic listening: Cherry (1953)
- Could report existence of
message - Could report gender of
speaker - Could NOT report content
Dichotic listening: Moray (1959)
- Could report change in
gender of speaker - Could report change in
pitch of a tone - Could NOT report a word
repeated 35 times! - Could report hearing own
name
Dichotic listening: Gray & Weddeburn (1960)
- Told to shadow left ear
- Left ear hears: “Dear 7 Jane”
- Right ear hears: “9 Aunt 6”
- Participant reports: “Dear Aunt Jane”
- Meaning of unattended words
being taken into account
Dichotic listening: McKay (1973)
- Meaning of biasing word
(“river” or “money”) in
unattended ear affected
participants’ choice - However, participants were
unaware of presentation of
biasing words
Attentional selection models
- Early all-or-none filtering (Broadbent) occurs between low-level perceptual and high-level semantic analysis
- Early attenuation (Treisman) occurs between low-level perceptual and high-level semantic analysis
- Late selection model (McKay) occurs between high-level semantic analysis and decision-making/memory storage
- Strategic control of attention:
● Early versus late selection can
be chosen based on situation and approach
● Attention is applied by top-
down modulation
Electroencephalography (EEG)
- Non-invasive technique
- Measures surface electric fields generated by post- synaptic potentials in
dendrites of neurons - High temporal resolution: signal sampled >1000/sec
- Low spatial resolution: up to 256 electrodes
Event-related potentials (ERPs)
- Average of EEG signals
- Time-locked to event of interest
- Typically plotted with negative up
Attentional stream paradigm
- Random sequence of auditory “pips”
- Occasional deviant targets (different volume or pitch)
- Instructed to attend to one ear
- No effect of attention on brainstem evoked potentials
- Effect of attention on midlatency potentials (primary auditory) and late waves (secondary/tertiary auditory)
Posner’s orienting task
- Maintain central fixation
- Spatially cued trials
● 80% valid
● 20% invalid - Neutral trials
● No spatial cue - Source: endogenous
- Target: external
- Covert
- Transient
- Selective?
(McAdams and Maunsell, 1999)
- Orientation tuning curve: Attention causes gain (multiplicativescaling), but no change in feature selectivity
Visual attention and V4 neurons
Attention enhances signal-to-noise ratio:
- No contrast:
● Small response
● Small change
- Subthreshold/Medium:
● Medium response
● Big change
- High contrast
● Big response
● Small change
Synchronization in V1 and V4 (Bosman et al. 2005)
- Recording local field potentials (LFPs) in V1 & V4
- Attention to a stimulus increases synchronization between brain areas representing that stimulus
The effects of attention
- Attention affects reaction time, accuracy, and awareness of sensory stimuli
- Attention can have effects less than 100 ms after stimulus onset
- Attention modulates neural activity in brain areas for locations and objects
- Attention enhances neural response to attended stimuli (e.g. enhanced signal-to-noise ratio)
- Attention increases neural synchronization between brain areas
Unilateral (hemispatial) neglect
- A defict of attention
- A deficit in perceiving & responding to stimulation contralateral to damaged hemisphere
- Cannot be explained by primary sensory or motor disturbance
Reference frames of of neglect
- Spatial
● e.g. neglect of left side of space
● Location-based attention - Object-based
● e.g. neglect of left side of objects
● Object-based attention
Attentional control network
Regions involved in endogenous and exogenous shifts of attention
