You have
annotation(['textbox',[0.42 0.864 0.1 0.1],'String','L. St. Lawrence - INCREASE IN ISI (n=',num2str(q),')','EdgeColor','none','FontSize',12,'Color','black','FontWeight','bold'])
This includes a [] expression that must be evaluated first, and the result of the [] expression will be passed as a parameter to annotation()
The [] expression is
['textbox',[0.42 0.864 0.1 0.1],'String','L. St. Lawrence - INCREASE IN ISI (n=',num2str(q),')','EdgeColor','none','FontSize',12,'Color','black','FontWeight','bold']
which asks to [] together characters and numeric values.
When you [] together characters and numeric values, the numeric values are converted using char() . Note that char() of a numeric value is not the printable representation of the numeric value. If you char(65) for example you do not get '65' (the character for the digit 6 followed by the character for the digit 5). Instead, char() does a uint16() of the provided value (except it rounds down) and then treats the resulting integer as a Unicode Code Point. char(65) requests the 66'th Unicode Code Point (they start at 0) which happens to be the character 'A'
So ['textbox',[0.42 0.864 0.1 0.1]] would be the same as [['textbox',char([0.42 0.864 0.1 0.1])] which would be the same as ['textbox',char(uint16(floor([0.42 0.864 0.1 0.1])))] which would be ['textbox', char(uint16([0 0 0 0]))] which would be ['textbox', char(0), char(0), char(0), char(0)] so would be a character vector that started with 'textbox' and was then 4 binary characters.
This is clearly no what you want.
What you might have wanted might have been
annotation('textbox',[0.42 0.864 0.1 0.1],'String',['L. St. Lawrence - INCREASE IN ISI (n=',num2str(q),')'],'EdgeColor','none','FontSize',12,'Color','black','FontWeight','bold'])
which leaves 'textbox' and the double precision numbers as separate parameters, and constructs a character vector from the 'L. St. Lawrence' and so on through to the ')' and passes that as the parameter after 'String'
So your [] were out of place.
These days I would probably suggest
annotation('textbox',[0.42 0.864 0.1 0.1],'String',"L. St. Lawrence - INCREASE IN ISI (n="+q+")",'EdgeColor','none','FontSize',12,'Color','black','FontWeight','bold'])
when you use "" objects those are string() objects whereas '' objects are character vectors. string() objects define a + operation that converts numeric values to representable text and append that to the end of the string object.
