# Virtual Keypad

Spawn and communicate with a virtual keypad, eg for use in online psychology 
experiments. 

This client-side module creates a QR Code linking to the appropriately 
specified keypad, handle's a user-defined callback on the incoming data,
and allows for real-time changes to the keypad content.

## How
**tl;dr** instantiate a `Receiver`, eg from within a PsychoJS experiment,
and scan the generated QR Code from your mobile device. By default the user 
is taken to a publically-hosted webpage wrapper around `Keypad`. 
Use the `keypadURL` parameter of `Receiver` to instead direct
the user to a keypad hosted elsewhere.

### Receiver
Most users, eg experimenters, should only need to use the `Receiver` class.
This class handles configuring the content of the keypad (ie what symbols to
show, and in what font face), creates a link -- in the form of a QR code -- to
a keypad for the user to use.

## What
A simple (optionally self-hosted) keypad webapp, with user-specified callback behavior.
Built using [PeerJS](https://www.npmjs.com/package/peerjs) and [QRCode](https://www.npmjs.com/package/qrcode).

## Why
In [Denis Pelli's NYU psychology lab](https://denispelli.com), 
we carry out a lot of psychophysical experiments. For example,
we may want to 
[measure a participant's crowding](https://www.biorxiv.org/content/10.1101/2021.04.12.439570v1), 
so we can investigate the possibility of a 
[link between crowding performance and the size of the participants hV4](https://jov.arvojournals.org/article.aspx?articleid=2749904) region of the visual cortex.
These experiments often involve the participant responding to stimuli
with a keypress. If the task requires a long viewing distance, a
wireless keyboard is provided to the participant, so they can respond
when positioned further than an arm's length away from the experiment computer.

Increasingly so, these types of experiments are being run remotely, 
in participants' homes, by participants recruited on platforms such as
[MTurk](https://en.wikipedia.org/wiki/Criticism_of_Amazon) 
or [Prolific](https://www.prolific.co). 
Under the presumption that smartphones are more
generally available than wireless, Bluetooth keyboards, this utlility
emulates a wireless keyboard on any internet-connected smartphone.