What does contralateral delay activity mean?: A guide to cognitive neuroscience

October 1, 2025 •

3 min read

Visual working memory, the brain's limited workspace for temporarily holding visual information, is a foundational aspect of cognition. Contralateral delay activity (CDA) is a key electrophysiological marker used in neuroscience to measure the neural processes involved in this capacity. It provides a direct and reliable way to study how the brain actively stores information over short delays.

Quick Summary

The contralateral delay activity (CDA) is a sustained, negative electrical brain wave measured during visual working memory tasks, indicating the neural resources allocated to holding visual information in mind. Its amplitude increases with the number of items being remembered, up to a person’s memory capacity, and is measured over the hemisphere opposite the side of the attended visual stimuli.

Key Points

CDA is a Neural Measure: The Contralateral Delay Activity (CDA) is a specific electrical brainwave recorded using EEG, primarily used to study visual working memory (VWM).
Reflects VWM Capacity: The amplitude of the CDA increases with the number of visual items a person holds in memory, plateauing at their individual storage limit.
Measured via Subtraction: It is calculated by subtracting the ipsilateral (same side) EEG activity from the contralateral (opposite side) activity, isolating the signal related to VWM storage.
Indicates Filtering Efficiency: CDA helps distinguish between high- and low-capacity individuals by showing how effectively they filter out irrelevant visual information.
Applied in Clinical Research: This measure is used to investigate VWM deficits in various clinical populations, including those with Parkinson's disease, schizophrenia, and anxiety.
Subject of Ongoing Research: While largely accepted as a VWM marker, there is still some debate about the extent to which CDA also reflects sustained spatial attention.
Reveals Real-Time Cognitive Processes: Due to the nature of EEG, CDA provides insight into the dynamic, online processes of visual working memory, not just static capacity.

The Foundational Concept of Contralateral Delay Activity

The contralateral delay activity (CDA), also known as Sustained Posterior Contralateral Negativity (SPCN), is a type of Event-Related Potential (ERP) measured using electroencephalography (EEG). It is used in cognitive neuroscience to understand visual working memory (VWM). The term "contralateral" refers to the brain hemisphere opposite the visual stimulus, and "delay activity" signifies sustained neural activity while information is held in memory.

How is CDA Measured?

CDA is calculated as a difference wave from EEG recordings. Participants in studies are shown visual objects and directed to remember items in one visual field. EEG activity is recorded from posterior electrodes. The CDA is derived by subtracting the activity from ipsilateral (same side) electrodes from the activity of contralateral (opposite side) electrodes during the delay. This process isolates the brain activity related to holding attended visual information in memory.

The Relationship Between CDA and Working Memory Capacity

A significant finding is the direct link between CDA amplitude and visual working memory capacity. The amplitude of the CDA increases as more items are remembered, up to a person's memory limit, typically around three to four items for young adults. This makes CDA valuable for researchers, with larger amplitudes indicating more neural resources used for memory maintenance. High-capacity individuals efficiently filter irrelevant information, while low-capacity individuals may store distractors, which is reflected in their CDA amplitude.

Interpreting the Significance of the CDA

The CDA provides insights into visual attention and memory. It helps researchers understand filtering efficiency. In tasks with distractors, high-capacity individuals' CDA reflects only relevant items, showing successful distractor filtering. Low-capacity individuals may show a larger CDA, suggesting they store distractors. Neuroimaging studies point to the posterior parietal cortex as a primary source of VWM activity related to CDA. EEG's timing ability allows CDA to track real-time cognitive processes, like losing track of an object or transferring information to long-term memory.

CDA in Various Research and Clinical Contexts

CDA is useful in various populations, both healthy and clinical.

Developmental Psychology: Used to study VWM development in children and adolescents.
Aging: Helps identify early signs of cognitive decline or filtering differences in older adults.
Neurological Disorders: Characterizes VWM deficits in conditions like Parkinson's disease, schizophrenia, and ALS. Impaired filtering in Parkinson's patients is reflected in CDA.
Psychiatric Conditions: Research suggests filtering efficiency, shown by CDA, may be impaired in individuals with anxiety and depression.

The Difference Between Ipsilateral and Contralateral Activity


Feature	Contralateral Activity	Ipsilateral Activity
Definition	Neural activity in the brain hemisphere opposite the stimulus.	Neural activity in the brain hemisphere on the same side as the stimulus.
Role in CDA	Reflects general processing and specific VWM storage.	Reflects general sensory processing.
Measurement	Used to derive the CDA difference wave.	Used as a baseline for subtraction.
Example	Activity in the right hemisphere when attending to a left visual stimulus.	Activity in the left hemisphere when attending to a left visual stimulus.
Interpretation	Larger negative wave indicates more items in VWM.	Subtracted to isolate memory signal.

Recent Controversies and Developments

While often seen as a VWM storage measure, some studies suggest CDA might also reflect sustained spatial attention, especially with dynamic stimuli. This impacts interpreting neural processes in different tasks. However, evidence generally supports CDA's primary sensitivity to VWM storage load. Ongoing research continues to explore the relationship between memory, attention, and neural signals.

For more in-depth information, consult authoritative sources such as peer-reviewed journal articles, like the review published in Trends in Cognitive Sciences. The contralateral delay activity as a neural measure of visual working memory - PMC

Conclusion

Contralateral delay activity is a vital neurophysiological measure in cognitive science for understanding visual working memory. By analyzing this brainwave, researchers can measure memory capacity, filtering ability, and cognitive deficits in various disorders. It provides a reliable metric for the processing of visual information and remains a crucial tool for studying human cognition.

Frequently Asked Questions

Contralateral activity occurs in the brain hemisphere opposite to the body side or visual field being stimulated, while ipsilateral activity occurs on the same side. In the context of CDA, contralateral activity reflects both general processing and specific visual memory storage, whereas ipsilateral activity mainly reflects general sensory processing and serves as a baseline for comparison.

The CDA is calculated during an EEG experiment. Electrodes are placed on the scalp over posterior brain regions. After subjects attend to a stimulus in one visual field, the electrical activity recorded over the contralateral (opposite) hemisphere is subtracted from the activity over the ipsilateral (same) hemisphere. This difference wave is the CDA.

A larger, or more negative, CDA amplitude generally signifies that more visual items are being held in an individual's visual working memory. The amplitude increases with the number of items to remember, up to the person's memory capacity limit.

While the CDA is most recognized as a measure of visual working memory (VWM) capacity, some research suggests it may also reflect sustained spatial attention. However, the consensus is that it primarily tracks the storage demands of VWM.

Yes, the CDA is a valuable tool for studying cognitive deficits in various clinical populations. It has been used to investigate visual working memory impairments and filtering issues in conditions like Parkinson's disease, schizophrenia, and anxiety disorders.

The CDA amplitude reaches an asymptote when the number of items to be remembered exceeds an individual's visual working memory capacity. At this point, the amplitude stops increasing, indicating that the memory system can no longer store additional items.

Filtering efficiency, or the ability to ignore irrelevant information, is closely linked to VWM capacity and is reflected in the CDA. Individuals with better filtering efficiency show a CDA that reflects only the relevant items, while those with poorer filtering may show a larger CDA, indicating they are storing irrelevant distractors.