Description of stimulus 'objects' for mrVista 2.0.
started by ras, 10/2005.

Stimulus 'objects' are matlab structs intended to contain
information specifiying the design of an experiment. This
includes the onset times of different event types, both in 
seconds from the onset of a scan and in MR frames, numbers
indicating the stimulus type, names, and colors associated with
each.

Fields in a stim struct include:

stimFiles: cell-of-strings specifying full path to each stimulus (.par)
file loaded.

stimFileNames: cell-of-strings specifying stimulus file names only.

conds: vector of integers, specifying the condition (event type) 
number for each event. Conds less than or equal to 0 are considered
as null conditions. Non-zero conds should be continuous integers
(e.g., [1 2 3 4], but not [1 2 4 5]).

onsetSecs: onset times in seconds of each event. Vector of same size as
conds.

onsetFrames: onset times in MR frames of each event.

framePeriod: duration of each MR frame, in seconds. (Like TR, but b/c
of fancy scanner things like multi-shot recordings, where each frame
technically consists of multiple TRs, we use framePeriod).

nConds: number of non-null conditions specified.

condNames: 1xnConds cell-of-strings specifying the name of each condition
 
condColors: 1xnConds cell-of-strings specifying colors associated with
each condition. Can be [R G B] color designations, or single characters,
as allowed by the PLOT command.

labels: 1xnTrials cell-of-strings containing the label specified in 
the stimulus (.par) files.

images: 1xnTrials cell array containing images, or paths to image files,
associated with each event.

user1 and user2: each is a 1xnTrials cell array containing user-defined
values (like response times or comments).