Accessing measurement properties

The Neuroimaging.jl library uses functions to access underlying properties of the data structures. This is to enable a consistent API to users, while allowing flexibility in the underlying design.

To minimise the risk of making errors when specifying values, passing arguments, and scaling values, the Neuroimaging.jl library uses units wherever possible. The Unitful.jl package provides a convenient interface for handling unitful data.

Handling of units

Many of the underlying components of this package store values with units. For example, coordinates are stored internally in the unit of meters, and sampling rates are stored in hertz. This minimises errors in two ways. First, if you pass arguments in the wrong order to a function it may be caught. Second, if you accidentally pass kHz as a sample rate this will be correctly converted to Hz for you internally.

Retrieving information from data

To access information about your neuroimaging data you must query it using the provided functions. A list of functions is provided for each type in the documentation. And common functions available across all types are described in the types documentation. So for example, if you wanted to query the samplerate of a measurement:

using Neuroimaging, DataDeps, Unitful
data_path = joinpath(
    datadep"ExampleSSR",
    "Neuroimaging.jl-example-data-master",
    "neuroimaingSSR.bdf",
)
s = read_EEG(data_path)
samplingrate(s)

8192.0 Hz

However, sometime you do not want the data with its units. Let us say you want the sample rate in kHz. In this case you can pipe the data manually...

samplingrate(s) |> u"kHz" |> ustrip

8.192

Or you may wish to know the sample rate in mHz and require that the value is an integer, then you could run...

samplingrate(s) |> u"mHz" |> ustrip |> Int

8192000

Or you could simply specify the return type of the function...

samplingrate(Float64, s)

8192.0

You should access all properties of the data in this fashion. For example the functions data, modulationrate, channel_names should all be used to query this properties.

Displaying data properties

The underlying data is stored with units wherever possible and in SI units. This makes it easy to keep track of everything when programming. However, when we report data these units may not be appropriate. For example, fNIRS data is usually reported in micro Mol, it would be inconvenient to report and plot values with six leading zeros. Similarly locations of neuroimaging coordinates are often reported in millimeters. So the show functions will report the data in the typical scale for the area of research.

show(sensors(s)[2])

Sensor: TP7 Electrode - (-85.54294425259022 mm, -45.29458746142005 mm, -3.140954703225086 mm) (Talairach)