now and then or here and there
e.g. he was arrogant and occasionally callous
e.g. open areas are only occasionally interrupted by clumps of trees
e.g. they visit New York on occasion
e.g. now and again she would take her favorite book from the shelf and read to us
e.g. as we drove along, the beautiful scenery now and then attracted his attention
Synonym: on occasion once in a while now and then now and again at times from time to time