Attention: Characteristics and Mechanisms

Overview of Attention

• Presented on February 11, 2025, for NEUROSCI 217 / PSY 217.
• The lecture will cover key characteristics, drivers, modes, and stages of attentional selection.

Midterm I

• Without the bonus question, the median score was 90%.
• With the bonus question, the median score increased to 93%.

Defining Attention

• William James described attention (1890) as the mind's clear and vivid focus on one object or train of thought among several possibilities.
• Attention involves mechanisms that prioritize resources to preferentially process relevant information, given limited brain processing capacity.

Key Characteristics of Attention

• Attention exhibits selectivity.
• Its capacity is limited.
• It enables the selection of different information, based on various features like voice or content.
• Attention can be internally driven or externally "captured".
• It can be allocated covertly.

Selective and Capacity-Limited Attention

• Attended information is processed faster and more accurately than unattended information; attention provides a "signal gain" and enhances the attended information.
• Metaphors include attention as a 'spotlight', a 'filter', or as biasing the competition between stimuli for processing resources.
• Effective attention is limited to a specific amount of information.
• Selectivity and capacity limitations are two aspects of the same attentional processes.

Attentional Blink

• Capacity limitations become apparent in the temporal one.
• During the rapid serial visual presentation paradigm (RSVP) if a target stimulus ('T1') is detected in a fast stream of stimuli (e.g., 10Hz), the detection of targets right after (‘T2') is limited if they follow T1 in short time.
• The 'attentional blink' describes detecting one target in a series impairs detection of subsequent targets soon after.
• The amplitude of the P3 ERP component, which indexes the detection of a target, diminishes during the 'attentional blink'.

Internal vs. External & Overt vs. Covert Attention

• Attention can focus on external or internal information, across different sensory modalities.
• External visual attention is typically associated with eye movements but can be separated as 'covert' attention.
• Stimuli at locations where one is covertly attending can still be reported.

Attention vs. Arousal

• Attention is selective, while arousal is global.
• Attentiveness varies with arousal in an 'inverted U-shape' fashion.

Top-Down vs. Bottom-Up Attentional Selection

• Attention can be guided endogenously ('top-down', from internal goals) or exogenously ('bottom-up', from salient stimulus features).
• The Posner task demonstrates endogenous cuing; detection times are fastest after valid cues and slowest after invalid cues, while focus is on a red dot.

Exogenous Cuing Study

• Salient task-irrelevant stimuli can capture attention ('attentional capture').
• Capture effect appears rapidly and is short-lived.
• If a distracter precedes more than ~300 ms before the target there is an 'inhibition of return.

Top-Down & Bottom-Up: Contingent Capture

• Top-down and bottom-up attention influences can interact, as seen in "contingent capture."
• If one looks at a color "singleton’ stimulus attention may likely be captured “bottom-up”, but only if it is a color cue

Modes of Attentional Selection

• Attention can be allocated to spatial locations (spatial attention).
• It can be allocated to stimulus features (feature-based attention).
• To whole objects can get allocated attention (object-based attention).

Combining Modes of Selection

• Spatial and feature-based attention often cooperate.
• One often uses known target features to search.
• This search involves the collaboration of top-down feature-based attention and spatial attention.

Modes of Selection: Bottom-Up & Top-Down Influence

• Jeremy Wolfe's "Guided Search Model" describes visual accomplished by bottom-up input channels that produce bottom-up feature maps to identify visual features.
• Feature maps interact with top-down attentional biasing, to produce an integrated “activation map"which guides spatial attention and eye movement.

Visual Search Tasks: Pop-out & Conjunction Search

• In the lab, visual search tasks often probe attention.
• One can manipulate features of the distractor stimuli in a search array, and measure decision time.
• The data resulting represents a "search slope".

Object-Based Attention

• Research suggests objects are the the mode of attentional selection ('object-based' attention).
• Attending to part of the object one automatically gives it increased attention, spreading to fill the space.

Supramodal Attention

• Attention can also spread over features to other sensory ones.
• Attending with visuals allows for better processing with auditory senses.

Early vs. Late Selection

• The stage at "filtering" that occurs has been historically debated.

Early vs. Late Selection Cognitive Psychology Pioneers

• Donald Broadbent (1958) and Anne Treisman (1969).
• These figures espoused the 'early selection' view.
• They argued that one only examines for rudimentary physical features largely inaccessible

Early vs. Late Selection; Semantic content in Stroop Task

• The semantic content has an affect on preformance.
• One sees that even information that the subject is told to ignore affects performance

Early vs Late Selection Researchers

• A 'late selection' view of attention has arisen.
• Attentional selection happens at the point that someone says so (e.g., Deutsch & Deutsch, 1963; Norman, 1968).

Early vs Late Selection In Context

• In Today's day and age most would agree to a strongly context-dependent level of selection.

Load Theory

• One theorizes that stage selection changes to adapt.
• Says that some will allocate, when the task is low.

Early vs Late Selection Network

• Recent imaging techniques have worked to describe the neural sources or attention.

Summary

• "everyone knows what attention is…” – yet it's hard to describe clearly.
• Overt vs. covert attention has it's own affect
• There is a difference in the selection process depending on whether or not it happens early or late
• The Load is perceptually limited.
• It is also different depending on if there is exogenous vs. endogenous factors or something that causes contingent capture