function data = optostim_traces(date_string, indexes, channel, color)
if nargin < 3
    disp('usage:   optostim_traces(date_string, indexes, channel, color');
    disp('example: optostim_traces(''03-Mar-2005'', 2:11, 0, ''i'' )');
    disp('omit ''color'' argument to simply load the data without plot');
else
    for index = indexes
        if index < 10 
            index_string = ['00' num2str(index)];
        elseif index < 100
            index_string = ['0' num2str(index)];
        else
            index_string = num2str(index);
        end
        filename = [date_string '_' index_string '_trace'];
        disp(filename)
        trace = load(filename);
        if channel == 0
            pick = trace.ch0;
        else
            pick = trace.ch1;
        end
        if index == indexes(1)
            data.time = trace.time_values;
            data.values = pick;
        else
            data.values = [data.values pick];
        end
    end
    if nargin > 3
        % only plot if 'color' argument is provided
        if strcmp(color,'i')
            plot(data.time, data.values);
        else
            plot(data.time, data.values, color);
        end
    end 
end