The oddball paradigm: a clasical neuropsychology experiment

Tested on MEDUSA© Platform v2022 & v2023

General information

The oddball paradigm is an experimental design widely used in neuropsychology research. It involves presenting a sequence of repetitive stimuli to participants, which are occasionally interrupted by a deviant stimulus known as "oddball." 

Generally, the test aims to investigate attentional processes, perceptual sensitivity, and cognitive resource allocation in response to this stimulation paradigm.  The test can be used to:

• Assess the ability to detect and respond to rare or unexpected events.
• Examine attention allocation and discrimination processes.
• Investigate memory encoding and retrieval mechanisms.
• Explore response inhibition and cognitive control processes.

The outcomes of the oddball paradigm include behavioural responses and neurophysiological biomarkers.

Behavioural outcomes

In the oddball paradigm task, several behavioral metrics can be derived to assess participants' performance and cognitive processes. The most used are:

• Reaction Time: The time taken by participants to respond to the target stimuli.
• Accuracy: The proportion of correct responses to the target stimuli.
• False Alarm rate: False alarms occur when participants respond to stimuli that are not targets. It indicates the participant's tendency to incorrectly identify non-target stimuli as targets, reflecting their response bias or impulsivity.
• Misse rate: Misses refer to instances when participants fail to respond to a target stimulus. It indicates the participant's inattention or inability to detect the deviant stimuli within the sequence of standard stimuli.

Neurophysiological outcomes

Event-Related Potentials (ERPs) are the neurophysiological response to the different events of the oddball paradigm obtained from EEG recordings. ERPs provide valuable insights into the timing and dynamics of cognitive processes underlying perception, attention, memory, and decision-making. Several metrics and analyses can be derived from ERPs to investigate various aspects of neural processing. Here are some common metrics and analysis techniques used in ERP research:

• The peak amplitude represents the maximum positive or negative deflection in the ERP waveform. It reflects the magnitude of neural activity associated with a specific component of interest. Peaks are typically labeled with letters (e.g., P1, N2) and can provide information about sensory processing, attention, or cognitive functions.
• Latency: Latency refers to the time between the onset of a stimulus/event and the occurrence of a specific ERP component or peak. It indicates the speed at which neural processes are occurring and can provide insights into the temporal dynamics of cognitive processing.
• Component Analysis: ERP waveforms consist of several distinct components that reflect different stages of cognitive processing. Component analysis involves identifying and quantifying these components based on their timing and topography. Commonly studied components include the P1, N1, P2, N2, and P3, each associated with specific cognitive processes.
• Difference Waveform: Difference waveforms are created by subtracting the ERP waveforms elicited by two different conditions or stimuli. This analysis helps to isolate specific cognitive or perceptual processes by highlighting the differences in brain activity between conditions.
• Scalp Distribution/Topography: ERPs exhibit specific scalp distributions, which refer to the spatial pattern of electrical activity across the scalp. Analyzing the topography allows researchers to examine how neural processes are distributed across different brain regions and assess the involvement of specific cortical areas.
• Source Localization: Source localization techniques aim to estimate the underlying brain regions that generate the observed ERP components. By combining EEG data with anatomical models or additional neuroimaging methods (e.g., fMRI), researchers can infer the neural generators responsible for the observed scalp-recorded ERPs.
• Statistical Analyses: Various statistical techniques can be applied to ERP data to assess the significance of differences between conditions or groups. These include analysis of variance (ANOVA), t-tests, clustering-based permutation tests, and multivariate pattern analyses. Statistical analyses help determine if observed ERP differences are reliable and provide insights into the underlying cognitive processes.

Implementation

Our implementation of the oddball paradigm incldues both visual and auditory modes and utilizes three types of stimuli: repetitive background stimuli, distractors, and targets:

1. Repetitive Background Stimuli: These stimuli serve as the standard or frequent events presented throughout the task. In the visual mode, they may consist of simple geometric patterns on a screen. In the auditory mode, they can be repetitive tones of a specific pitch and duration.

2. Distractors: These stimuli are the deviant events that occur less frequently within the sequence of background stimuli. They differ from the background stimuli in some aspect, such as color, shape, or intensity. In the visual mode, they may be different colored or shaped patterns or letters. In the auditory mode, they can be tones of a different pitch or duration than the background stimuli.

3. Targets: These stimuli are the specific deviant events that participants are instructed to respond to. They are presented even less frequently than the distractors and are designed to require a specific response from the participant. In the visual mode, they may be a unique pattern or letter that stands out from the background stimuli and distractors. In the auditory mode, they can be a distinct tone that differs from both the background stimuli and distractors.

The responses to target stimuli can be given using the mouse (let and right clicks) and keyboard (space key) of the computer. All the main parameters can be configured for different experimental settings (e.g., stimulus duration, shape and colors of the visual stimuli, frequency of auditory stmuli, etc)

References

[1] García-Larrea, L., Lukaszewicz, A. C., & Mauguiére, F. (1992). Revisiting the oddball paradigm. Non-target vs neutral stimuli and the evaluation of ERP attentional effects. Neuropsychologia, 30(8), 723-741.