When using the Magnetic Lasso tool, the following shortcuts can help to quickly change tool options.
[ or ] decreases/increases the lasso width
[ or ] + Shift goes to the minimum/maximum lasso width
‘,’ (comma) or ‘.’ (period) decreases/increases the edge contrast
‘,’ (comma) or ‘.’ (period) + Shift goes to the minimum/maximum edge contrast
‘;’ (semicolon) or ‘’’ (apostrophe) decreases/increases the frequency
‘;’ (semicolon) or ‘’’ (apostrophe) + Shift goes to the minimum/maximum frequency