Difference between revisions of "Web-based perception experiments"

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Finally, in (4) above you may have noticed there was reference to a file: process.php. Here is that file.
 
Finally, in (4) above you may have noticed there was reference to a file: process.php. Here is that file.
⚫
*It constructs a filename from the parameters that you pass to it, and then stores the data from a single key press response as a line in the data file.
 
⚫
** for example, "process.php?p=id&n=1" translates into the filename "id_data1.csv"
  
⚫
*The <input..> elements of "dataform" (# 4 above) are now saved as columns in the data file.
  
⚫
*The data file must already exist on the server
  
⚫
** This script adds lines, but does not create a new file
  
⚫
** The data file must be writable, for example: chmod a+w id_data1.csv
  
   
   
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}
  
}
 
?>
  
?>
  +
  ⚫
*This script constructs a filename from the parameters that you pass to it, and then stores the data from a single key press response as a line in the data file.
  ⚫
** for example, "process.php?p=id&n=1" translates into the filename "id_data1.csv"
  ⚫
*The <input..> elements of "dataform" (# 4 above) are now saved as columns in the data file.
  ⚫
*The data file must already exist on the server
  ⚫
** This script adds lines, but does not create a new file
  ⚫
** The data file must be writable, for example: chmod a+w id_data1.csv
   
   

Revision as of 10:38, 9 February 2018

Experiments can be hosted on the Department of Linguistics server, and then distributed to listeners by email link, or via Amazon Mechanical Turk.

An example is here: example experiment

A Javascript library audexp.js makes it realatively easy to implement the following four typical kinds of experiments:

  • Identification (id) - a single audio file is played, and a two-alternative forced choice (2AFC) is given.
  • Discrimination (ax) - two audio files are played, and a 2AFC is given.
  • Rating (r) - a single audio file is played, and a rating number (from 1 to 7) is given.
  • Contrast Rating (cr) - two audio files are played, and a rating number is given.


Your html code must have four features:

1) after loading audexp.js, load a javascript file that defines:

  • an array (or two arrays) of filenames that will be presented.
  • a variable called 'block'
    • here's an example of such a file
    • this .js file was created with a small perl script from a .csv spreadsheet.
    • the html header contains the following two lines to get the audexp.js library and the experiment-specific list of sound files.
 <script src="js/audexp.js"></script>
 <script src="js/blocktest_list.js"></script>

2) a call to load the experiment when the page is loaded

  • this call specifies the type of experiment (in the script below this is 'id')
  • whether to randomize the order of presentation of the list of sound files
  • the interstimulus interval for 'ax' and 'cr' types
  • and the intertrial interval for all experiments.


 <body onload="load('id',false,500,2000);">

3) Three or four span elements that will be used to give feedback to listeners.

  • Show warnings to the listener
<span id="wr"></span>
  • indicate that an audio file is playing
<span id="f1">sound 1</span>
  • indicate that a second audio file is playing (for ax, and cr type experiments)
<span id="f2">sound 2</span>
  • give feedback to the lister, showing which key they pressed.
<span id="key">#</span>

4) A <form ...> element named "dataform"

  • the order of the input items determines the column order in the output file.
<form method="POST" id="dataform" action="process.php?p=id&n=1">
     <input type="hidden" name="subject" value=<?php echo $subj; ?> />
     <input type="hidden" name="trial" />
     <input type="hidden" name="list" />
     <input type="hidden" name="file1" />
     <input type="hidden" name="filedur" />
     <input type="hidden" name="mystatus" />
     <input type="hidden" name="loadtime" />
     <input type="hidden" name="response" />
     <input type="hidden" name="rt" />
</form>

Saving data to a server file

Finally, in (4) above you may have noticed there was reference to a file: process.php. Here is that file. 


<?php
$prefix = $_GET["p"];
$n = $_GET["n"];
$datafile = $prefix . "_data" . $n . ".csv";
if ($_SERVER["REQUEST_METHOD"] == "POST") {
  $data = "empty";
  foreach($_POST as $key=>$value) {      // we don't have to know the keys
      if ($data == "empty") { $data = $value; }
      else {$data = $data . "," . $value;}
  }
  $data = $data . "\n";
  $ret = file_put_contents($datafile,$data,FILE_APPEND| LOCK_EX);
  if ($ret) {
     echo "saved data";
  } else {
     echo "there was a problem writing the data";
  } 
} else {
 http_response_code(403);
 echo "invalid submission";
}
?>
  • This script constructs a filename from the parameters that you pass to it, and then stores the data from a single key press response as a line in the data file.
    • for example, "process.php?p=id&n=1" translates into the filename "id_data1.csv"
  • The <input..> elements of "dataform" (# 4 above) are now saved as columns in the data file.
  • The data file must already exist on the server
    • This script adds lines, but does not create a new file
    • The data file must be writable, for example: chmod a+w id_data1.csv


  • You can read the data file directly into R from your server address:
data <- read.csv("http://linguistics.berkeley.edu/~kjohnson/talkers/id_data.csv",header=TRUE);
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