(i) Subject data files are normally given the filename extension ".DAT".
(ii) Conceptually, DAT files are divided into blocks of 512 bytes (=256 words) of disk storage. A DAT file always consists of an integral number of such blocks.
(iii) All numerical values are stored as integers. All integers occupy one word (two bytes) except where otherwise noted.
(iv) The first blocks in a DAT file contain descriptive comments, experimental parameters and item and subject means. Later blocks contain raw subject data.
There are two different formats for DAT files. If the number of items (second word of the first block) is positive, the file is in Format 1. If the number of items is negative, the file is in Format 2.
Format 1
block 1 - comments and parameters;
block 2 - assignment of items to conditions;
blocks 3 & 4 - means for each item;
blocks 5 to 8 - means for each condition for each subject;
blocks 9 on - raw subject data, one block per subject.
Format 2
block 1 - comments and parameters;
blocks 2 & 3 - assignment of items to conditions;
blocks 4 to 7 - means for each item;
blocks 8 to 11 - means for each condition for each subject;
blocks 12 on - raw subject data, two blocks per subject.
word 1 the number of subjects whose results have been incorporated into the subject and item means;
word 2 the total number of items in all conditions (multiplied by -1 in Format 2 files);
word 3 the number of conditions in the experiment;
words 4-28 the number of items in each condition;
word 29 the absolute lower cutoff for reaction times;
word 30 the standard deviation cutoff multiplied by 100;
words 31-254 the title and comments in ASCII format;
word 255 the absolute upper cutoff multiplied by -1;
word 256 the scaling factor for item means (usually = 1).
(block 2 in Format 1 DAT files; blocks 2 and 3 in Format 2)
Contains the item numbers of items in condition 1 in the order they were entered to DATMAK, followed by the item numbers for conditions 2, 3 etc.
Items are in the same order as in the assignment of items to conditions. Two words correspond to each item:
odd numbered words -
odd byte - number of errors on that item
even byte - number of correct responses on that item
even numbered words -
mean RT for that item multiplied by the scaling factor in
word 256 of block 1 (usually equal to 1).
Mean RT and errors for all conditions for subject 1, followed by mean RT and errors for all conditions for subjects 2, 3, etc. Two words correspond to each subject-condition:
odd numbered words -
odd byte - number of errors in that condition
even byte - subject number
even numbered words -
mean RT for that condition for that subject.
One block (Format 1) or two blocks (Format 2) of reaction time data for subject 1, followed by 1 or 2 blocks for subject 2, etc.
Words 1 to 255 (Format 1) or 1 to 511 (Format 2) contain reaction times in item number order, ie. RT for item number 1 is in word 1, etc. The RT stored is positive for correct responses, negative for incorrect responses, and zero for items that were not presented.
Word 256 (Format 1) or word 512 (Format 2) contains the subject number, which is positive for subject data which has been analysed and incorporated into subject and item means, negative for subject data which has been analysed and not incorporated, and zero for subject data which has not been analysed.
The DMASTR display program collects subject reaction time data and outputs it in DTP (Data TemPorary) files. A DTP file consists of either 1 block per subject (Format 1) or two blocks per subject (Format 2). Format 1 DTP files should only be UPDATEd into Format 1 DAT files. Format 2 DTP files should only be UPDATEd into Format 2 DAT files.
Within each set of subject data, words 1 to 255 (Format 1) or 1 to 511 (Format 2) contain reaction times in item number order, ie. RT for item number 1 is in word 1, etc. The RT stored is positive for correct responses, negative for incorrect responses, and zero for items that were not presented.
In a Format 1 DTP file, word 256 of every block (i.e. the last word for every subject) will contain the value 0. In a Format 2 DTP file, word 256 of every even-numbered block (i.e. the last word for every subject) will contain the value 1.