Understanding amica#

amica is a native Python implementation of Adaptive Mixture Independent Component Analysis (AMICA), an ICA algorithm originally developed at the University of California, San Diego (UCSD) for blind source separation of EEG and other multichannel signals.

Unlike many ICA algorithms that assume a single statistical model for all sources, AMICA models each source using a mixture of generalized Gaussian distributions and can optionally fit multiple ICA models to account for non-stationary recordings.

Independent Component Analysis#

Independent Component Analysis (ICA) seeks to recover statistically independent latent sources from observed mixtures.

Given an observed signal

X = AS

where

  • X is the observed data,

  • A is an unknown mixing matrix,

  • S contains the latent independent sources,

ICA estimates an unmixing matrix

W ≈ A⁻¹

such that

S = WX.

In EEG, ICA is commonly used to separate brain activity from artifacts such as eye blinks, muscle activity, and cardiac signals.

What makes AMICA different?#

Most ICA algorithms assume that each source follows a fixed probability distribution.

AMICA instead models each source as a mixture of generalized Gaussian distributions, allowing it to adapt to a much wider range of source characteristics.

Key features include:

  • adaptive source density estimation

  • natural-gradient optimization

  • optional Newton optimization for faster convergence

  • optional outlier rejection

  • support for multiple ICA models

These capabilities have made AMICA one of the strongest-performing ICA methods for EEG source separation.

amica#

amica brings AMICA into the modern scientific Python ecosystem.

It provides:

  • a fully native Python implementation

  • optional JAX acceleration for CPU and GPU execution

  • integration with MNE-Python

  • reproducible APIs for research workflows

  • compatibility with the broader Scientific Python ecosystem

The goal is not only to reproduce the original algorithm but also to make it easier to understand, extend, and integrate into modern neuroimaging pipelines.

Choosing an interface#

amica provides two primary interfaces.

MNE-Python interface#

For EEG analysis with MNE, use:

from amica import fit_ica

This returns a standard mne.preprocessing.ICA object that integrates directly with existing MNE workflows.

Native amica interface#

For NumPy arrays or custom pipelines, use:

from amica import Amica, AmicaConfig

This provides direct access to the AMICA algorithm and all configuration options.

Numerical validation#

amica has been validated against the original MATLAB AMICA implementation across a range of configurations.

The documentation includes validation experiments, reproducibility analyses, and performance benchmarks demonstrating numerical agreement between the two implementations.

References#

  • Palmer JA, Kreutz-Delgado K, Makeig S. AMICA: An Adaptive Mixture of Independent Component Analyzers with Shared Components. 2011.

  • Palmer JA, Makeig S, Kreutz-Delgado K, Rao BD. Newton Method for the ICA Mixture Model. ICASSP, 2008.

  • Delorme A, et al. Independent EEG Sources Are Dipolar. PLOS ONE, 2012.