# Introduction¶

## Goals of the workshop¶

- Learn the basics of Multivariate Pattern Analysis
- Get your hands dirty with data manipulation and algorithm implementation
- Build a your own data analysis toolkit

**Why study brain imaging?**

Organization of Human Brain Mapping (OHBM) throws great parties.

**What is MVPA?**

When applied to **fMRI** data it is multi-*voxel* pattern analysis.

But multi-*variate* analysis is general, and widely used set of techniques. Variables or *features* can be from all sorts of neuroscience data:

- EEG
- MEG
- Multi-unit recording
- Electrocorticography (ECoG)

… or almost anything else you can think of:

- Geological data
BIGdata culled from internet users- etc.

- What is a
*pattern*?**fMRI**: Pattern is a vector of voxels (time points, averages of conditions, stats, etc.)- In
**general**: It is a vector of*features*or*variables* - In
**practice**, i.e., in**MATLAB**: A pattern is a row vector.

A dataset is a set of patterns over the same features that are vertically stacked on one another into a 2-D N x M matrix with N patterns and M features. Patterns are sometimes called “observations” or “samples”. In this tutorial we will call them samples.

In a simplistic and generic sense, MVPA includes any analysis where the outcome is dependent on the variablility of measurements across a a samples by features matrix.

**MATLAB** is an ideal environment for dealing with this sort of data with
hundreds of function for do MVPA analysis on rectangular matrices, some of which
you may be familiar with:

corrcoef: compute the pair-wise correlations for a set of column vectorscmdscale: classic multidimensional scalingsvmclassify / svmtrain: support vector machineprocrustes: Procrustes transformation (used in hyper-alignment, )- and many many others …

## MVPA Dataset¶

Given this general formulation, our workshop will aim to build a foundation and
a working MATLAB toolbox for MVP analysis around the **dataset** as a common
starting point. For this we have adopted the terminology and many of the
semantics of the PyMVPA Python library which you are
encouraged to learn more about especially if you interesting in learning to
program in Python.

Other useful resources:

- NeuroDebian : One stop shopping for all Neuroscience related computing needs
- Numpy for MATLAB users

## Code for the workshop¶

## Sample Dataset¶

We have preprocessed data for 8 subjects from [CGG+12]. A slow event-related design with six different types of animals.

The six categories included 2 primates: monkeys and lemurs; 2 birds: mallard ducks and yellow-throated warblers; and 2 bugs: ladybugs and luna moths.

We also have model similarity structures, which you can see here:

## Plan for the day¶

Learn how to manipulate data as a “

**cosmo_fmri_dataset**”- Do several exercises with pattern classification
- Split-half correlations
- Write your own Nearest-neighbor classifier
- Write a wrapper for MATLAB’s support vector machine functions to work with dataset
- Implement a N-Fold data partitioner for cross-validation
- Write an abstraction of cross-validation as a “dataset measure”

- Representational Similarity Analysis
- Viewing dissimilarity matrices
- Comparign dissimilarity matrices
- Write an abstraction “RSA dataset measure”

- Searchlight analysis
- Implement a function to calculate sphere offsets for searchlight
- Implement searchlight with cross-validation
- Implement RSA searchlight
- View searchlight results

In the end we will keep the cosmo_mvpa toolbox in a public repository on git-hub. Here: https://github.com/andycon/cosmo_mvpa You (or any one else) may “clone” the repository using git and contribute your own code to the project.