User manual

110 Data Files

4.10 Processing ASC Files

An ASC file is a simple text file, and thus can be accessed by almost any

programming language. The usual way to process the file is to read each line

into a text buffer (at least 250 characters in size), and to scan the line as a

series of tokens (non-space character groups).

The first token in each line identifies what the line is:

First character in first token Line type

<no token> Blank line--skip

# or ; or / Comment line--skip

* Preamble line--skip

Digit (0..9) Sample line

Letter (A..Z) Event or Specification line

Once the line is identified, it may be processed. Some lines may simply be

skipped, and the next line read immediately. For sample lines, the tokens in the

line can be read and converted into numerical values. The token "." represents a

missing value, and may require special processing. For lines where the first

token begins with a letter, processing depends on what the first token is. The

tokens after the first are read and desired data from the line are extracted from

them. Lines with unrecognized first tokens or with unwanted information can

simply be skipped.

Processing of events and samples will depend on what type of analysis is to be

performed. For many cognitive eye movement analyses, MSG line text specifying

experimental conditions, EFIX event data, and BUTTON event times from each

block are used to create data files for statistical analysis. For neurological

research, samples between SFIX and EFIX events can be processed to

determine smooth-pursuit accuracy and gain. In some cases, an entire block of

samples may need to be read and stored in data arrays for more complex

processing. For all of these, the organization and contents of the ASC files have

been designed to simplify the programmer's task.