Load Theory of Selective Attention and Cognitive Control

Core Hypothesis: Selective attention is determined by the level and type of load involved in processing task-relevant information. This theory resolves the "early selection" versus "late selection" debate.
Perceptual Load: Perception has a limited capacity but processes stimuli automatically until that capacity is exhausted.
Cognitive Control: Executive functions, such as working memory, are required to actively maintain task goals and prioritize targets over distractors when perceptual load is low.

High Perceptual Load: When a task is perceptually demanding (e.g., searching for a target among many similar items), all available capacity is consumed by relevant stimuli. This lead to "early selection," where distractors are not perceived.
Low Perceptual Load: When a task is simple, spare capacity involuntarily "spills over" to process task-irrelevant distractors, leading to "late selection" effects.
Behavioral Evidence: Distractor interference in response-competition paradigms is typically eliminated under high perceptual load but present under low load.
Distinction from Difficulty: General task difficulty or sensory degradation (reducing target contrast) does not reduce distractor interference unless it specifically increases the perceptual load on attention.

Opposite Effect: Unlike perceptual load, increasing the load on working memory (e.g., memorizing a string of digits while performing a task) increases distractor interference.
Function of Frontal Control: High working memory load depletes the cognitive resources needed to distinguish between targets and distractors, allowing potent distractors to capture attention and influence behavior.

Neuroimaging (fMRI): High perceptual load reduces or eliminates neural activity related to irrelevant stimuli in the visual cortex, including areas $V1$ , $V2$ , $V3$ , and $V4$ , as well as motion-selective area $MT$ .
Early Gating: Load effects can be seen as early as the Lateral Geniculate Nucleus ( $LGN$ ), the gateway for sensory entry into the visual cortex.
Electrophysiology: Event-related potentials ( $ERPs$ ) show that the amplitude of the occipital $P1$ potential at $80-130\,ms$ is significantly reduced under high perceptual load.

Exceptions for Social Significance: Famous faces can cause interference and priming even under high perceptual load, though explicit long-term recognition memory of these faces still depends on load levels.
Age-Related Changes: Children and the elderly have reduced information-processing capacity. Consequently, lower levels of task load are sufficient to eliminate distractor interference in these groups compared to mature adults.
Neuropsychological Patients: Patients with parietal lesions (spatial neglect) or frontal lobe damage show improved distractor rejection with small increases in perceptual load, as their limited capacity is easily exhausted.
Video Game Players: Expert players exhibit enhanced visual capacity, meaning they continue to process distractors at load levels that would eliminate interference in non-players.
Crossmodal Effects: Research is mixed on whether load in one modality (e.g., auditory) consistently reduces distractor processing in another (e.g., visual), with some studies suggesting capacity may be modality-specific or dependent on temporal overlap.