fLoc

Functional localizer experiment used to define category-selective cortical regions (published in Stigliani et al., 2015)

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Notes:

The code in this package uses functions from Psychtoolbox-3 and is compatible with MATLAB R2016b and later versions. The repetition time (TR) of fMRI data for the localizer experiment must be a factor of its block duration (6 s by default).

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Contents:

1. Experimental Design

   1. Stimulus Conditions
   2. Image Sets
   3. Task

2. Instructions

   1. Setup
   2. Execution
   3. Debugging

3. Code

   1. Using the runme fucntion
   2. Customizing the experiment

4. Analysis

   1. Analysis with vistasoft
   2. General Linear Model
   3. Regions of Interest

5. Citation

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Experimental design

This repository contains stimuli and presentation code for a functional localizer experiment used to define category-selective cortical regions that respond preferentially to faces (e.g., fusiform face area), places (e.g., parahippocampal place area), bodies (e.g., extrastriate body area), or printed characters (e.g., visual word form area).

The localizer uses a mini-block design in which 12 stimuli of the same category are presented in each 6 second block (500 ms/image). For each 4 minute run, a novel stimulus sequence is generated that randomizes the order of five stimulus conditions (faces, places, bodies, characters, and objects) and a blank baseline condition. We recommend collecting at least 4 runs of data per subject (16 minutes total) to have sufficient power to define regions of interest.

Stimulus conditions

Each of the five stimulus conditions in the localizer is associated with two related image subcategories with 144 images per subcategory (see ~/fLoc/stimuli/ for entire database):

• Bodies
  • body — whole bodies with cropped heads
  • limb — isolated arms, legs, hands, and feet
• Characters
  • word — pronounceable pseudowords (adapted from Glezer et al., 2009)
  • number — uncommon strings of digits
• Faces
  • adult — portraits of adult faces
  • child — portraits of child faces
• Objects
  • car — four-wheel motor vehicles
  • instrument — musical string instruments
• Places
  • house — outdoor views of buildings
  • corridor — indoor views of hallways

The specific image categories packaged with the localizer were selected to contain common sets of parts, such that all images from a given category are different configurations of the same basic components. This is intended to minimize differences in within-category similarity across image sets.

To normalize the low-level properties of stimuli from different categories, we placed each exemplar on a phase-scrambled version of another randomly selected image from the database. We also matched the mean luminance and histograms of grayscale values of each image using the SHINE toolbox (see Stigliani et al. (2015) for more details).

Image sets

The localizer code will prompt you to select which stimulus set to use when executing the experiment. You can further customize which image categories to include by editing the fLocSequence class file (see below for more details). Three options are provided by default:

Option 1:

| Default categories | | | | | | | | ------------------------------- |:-----------:|:-----------:|:-----------:|:-----------:|:-----------:| :----------:| | Bodies: body | | | | | | | | Characters: word | | | | | | | | Faces: adult | | | | | | | | Objects: car | | | | ![ca4][ca4] | ![ca5][ca5] | ![ca6][ca6] | | Places: house | ![ho1][ho1] | ![ho2][ho2] | ![ho3][ho3] | ![ho4][ho4] | ![ho5][ho5] | ![ho6][ho6] |

Option 2:

| Alternate categories | | | | | | | | ------------------------------- |:-----------:|:-----------:|:-----------:|:-----------:|:-----------:| :----------:| | Bodies: limb | | | | | | | | Characters: number | | | | | | | | Faces: child | | | | | | | | Objects: instrument | ![in1][in1] | ![in2][in2] | ![in3][in3] | ![in4][in4] | ![in5][in5] | ![in6][in6] | | Places: corridor | ![co1][co1] | ![co2][co2] | ![co3][co3] | ![co4][co4] | ![co5][co5] | ![co6][co6] |

Option 3:

| Both categories | | | | | | | | ------------------------------- |:-----------:|:-----------:|:-----------:|:-----------:|:-----------:| :----------:| | Bodies: body limb | | | | | | | | Characters: word number | | | | | | | | Faces: adult child | | | | | | | | Objects: car instrument | | ![in1][in1] | | ![in2][in2] | | ![in3][in3] | | Places: house corridor | ![ho1][ho1] | ![co1][co1] | ![ho2][ho2] | ![co2][co2] | ![ho3][ho3] | ![co3][co3] |